DOCUMENT RESUME
ED 090 391 CE 001 242 TITLE Aviation Structural Mechanic S 3 & 2. NAVTRA-10308-C. Rate Training Manual. INSTITUTION Bureau of Naval Personnel, Washington, D.C.; Naval Training Publications Detachment, Washington, D.C. REPORT NO NAVTRA-10308-C PUB DATE 74 NOTE 392p.
EDRS PRICE MF-$0.75 HC-$18.60 PLUS POSTAGE DESCRIPTORS Armed Forces; *Aviation Mechanics; Aviation Technology; Equipment Maintenance; *Manuals; *Military Personnel; *Military Training; Repair; *Technical Education IDENTIFIERS Navy
ABSTRACT This document is one of a series of rate training manuals designed to provide enlisted personnel of the Navy or Naval Reserve with the background information that will be useful in preparing for advancement in Aviation Structural Mechanics S(AMS) rating and to present necessary information for the proper performance of duties in that rating. The manual outlines the areas of Aviation Structural Mechanic S rating; aeronautic publications; aircraft materials; airframe construction; sheet-metal working machines, tools, and procedures; aircraft hardware; aircraft damage repair; airframe maintenance; landing wheels, tires and tubes; tubing, flexible hose, and clamps; corrosion control; and. line operations and maintenance. Numerous illustrations, diagrams, photographs, and data tables are included. (KP) 4 .
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04 xa ;I:itfV 1,14
U 5 OEPARTMENT OF HEALTH EOUCATION & WELFARE NATIONAL INSTITUTE OF EOUCATION THIS DOCUMENT HAS BEEN REPRO DUCED EXACTLY AS RECEIVED FROM THE PERSON OR ORGANIZATION ORIGIN ATING IT POINTS OF VIEW OR OPINIONS STATED DO NOT NECESSARILY REPRE SENT OFFICIAL NATIONAL INSTITUTE OF EDUC..TiON POSITION OR POLICY
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I I : PREFACE This Rate Training Manual is one of a series of training manuals prepared for enlisted personnel of the Navy and Naval Reserve who are studying for advancement inthe Aviation Structural Mechanic S (AMS) rating. As indicated by the title, the manual is based on the professional qualifications for the rates AMS3 and AMS2, as set forth in the Manual of Qualifications for Advancement. NavPers 18068 (Series). A reading list, which includes USAFI texts recommended as study material for AMS personnel. is provided in the front of the manual. Combined with the nfxessary practical experience, the completion of this manualwillgreatlyassistthe AMSAN and AMS3 inpreparing for advancement. This training manual should also be valuable as a review source for the more senior rates. This training manual was prepared by the Navy Training Publications
Center, NAS Memphis, Millington, Tennessee,for . the Chief of Naval Training. Technical review of the manuscript was provided by personnel of the AMS(A) School. NAS Memphis, Millington. Tennessee; the Naval Examining Center. Great Lakes, Illinois; and the Naval Aviation Integrated Logistic Support Center, Patuxent River, Maryland. Technical assistance was also provided by the Naval Air Systems Command. THE UNITED STATES NAVY
GUARDIAN OF OUR COUNTRY The United States Navy is responsible for maintaining control of the sea and is a ready force on watch at home and overseas, capable of strong action to preserve the peace or of instant offensive action to win in war. It is upon the maintenance of this control that our country's glorious future depends: the United States Navy exists to make it so.
WE SERVE WITH HONOR Tradition, valor, and victory are the Navy's heritage from the past. To these may be added dedication, discipline, and vigilance as the watchwords of the present and the future.
At home or on distant stations we serve with pride, confident in the respect of our country, our shipmates, and our families. Our responsibilities sober us: our adversities strengthen us. Service to God and Country is our special privilege. We serve with honor.
THE FUTURE OF THE NAVY The Navy will always employ new weapons, new techniques, and greater power to protect and defend the United States on the sea, under the sea, and in the air. Now and in the future, control of the sea gives the United States her greatest advantage for the maintenance of peace and for victory in war. Mobility, surprise, dispersal, and offensive power are the keynotes of the new Navy. The roots of the Navy lie in a strong belief in the future, in continued dedication to our tasks, and in reflection on our heritage from the past. Never have our opportunities and our responsibilities been greater. iMMI.=
ii CONTENTS Chapter Page
1. Aviation Structural Mechanic S rating 2. Aeronautic publications 12 3. Aircraft materials 4. Airframe construction 57 5. Sheet-metal working machines, tools, and procedures 85 6. Aircraft hardware 119 7. Aircraft damage repair 155 S. Airframe maintenance 210 9. Landing wheels, tires, and tubes 235 10. Tubing, flexible hose, and clamps 258 11. Corrosion control 284 12. Line operations and maintenance 333
Index 381
iii READING LIST USAFI TEXTS United States Armed Forces Institute (USAFI) courses for additional reading and study are available through your Educational Services Officer.* The following courses are recommended:
C'151 General Mathematics I C 152 Genertil Mathematics II D 700 General Aeronautics E 275 General Science I F 290 Physics I
* Members of the United States Armed Forces Reserve components, when on active duty, are eligibleto enrollfor USAFI courses, services, and materials it' the orders calling them to active duty specify a period of 120 days or more, or it' they have been on active duty for a period of 120 days or more.
iv CHAPTER 1
AVIATION STRUCTURAL MECHANIC S RATING
This training manualisdesigned as a self - not.Both Regular Navy and Naval Reserve study text for use by those personnel or the personnel may hold general ratings. Navy and Naval Reserve who are preparing to Serviceratingsidentifysubdivisionsor meet the professional (technical) qualifications specialties within a general rating which require for advancement to petty officer third class and related patterns of aptitudes and qualifications, pettyofficer second classintherating of and which provide paths of advancement for AviationStructuralMechanic S (Structures). career development. The general rating provides Mini mumprofessionalqualificationsfor the primary means of identifying billet require- advancement are listed in the Manual of Quali- ments and personnel qualifications; itis estab- ficationsforAdvancement,NavPers18068 lished or disestablished by the Secretary of the (Series). Inpreparingforthe advancement Navy: anditisprovided adistinctive rating examination, this manual should be studied in badge. The term"rate"identifies personnel conjunctionwithMilitaryRequirements for occupationally by pay grade. "Rating" refers to Petty Officer 3 & 2, NavPers 10056 (Series), The the occupational field. Service ratings can exist latter covers the military requirements for all at any petty officer level, but they are most third and second class petty officers, as well as common atthe P03 and P02 levels. Both detailedinformation on the NavalAviation Regular Navy and Naval Reserve personnel may Maintenance Program (NAMP). hold service ratings. The intent of this chapteristoprovide information on the enlisted rating structure, the AMS ratting, requirements and pr6cedures for AVIATION STRUCTURAL MECHANIC advancement, and references that will help you (AM) RATING in performing your duties as an Aviation Struc- tural Mechanic S. This chapter also includes The AM rating is divided into three service information on how to make the best use of ratings at paygrades E-4 through E-7. The service Rate Training Manuals. Itis therefore strongly ratingsare AME (Safety Equipment), AMS recommended that you study this chapter care- (Structures), and AMH (Hydraulics). fully before beginning intensive study of the At paygrade E-8 the generalrating, AM, remainder of the manual. applies. Therefore, upon advancement to E-8, paygrade E-7 personnel kAMEC's, AMSC's and AMHC's)arecombinedtobecome Senior ENLISTED RATING STRUCTURE Aviation Structural Mechanics (AMCS'). At paygrade E-9 the AM. rating losesits The present enlisted rating structure consists identity and personnel in the rating advance, of general ratings and service ratings. along with ADCS', to MEster Chief Aircraft General ratings identify broad occupational Maintenancemen (AFCM's). fields of related duties and functions. Some Figure 1-1 illustrates all paths of advancement general ratings include service ratings; others do for an Airman Recruit to Master Chief Aircraft AVIATION STRUCTURAL MECHANIC S 3 & 2
LDD AV. MAINT.
WARRANT OFFICER CWO ZIA CWO CWO W-1 W -2 V W -3 W- 4 \\A AFCM E-9 \ N4M\
ADCS AMCS E-8 \ ADJc ADRC E-7 AMHC AMEC I. ADJI ADM AMHI AMEI\ E-6
AOR2 ADJ2 AmH2 E-5 AME2
ADJ3 ADR3 AmE3 E-4 112
AWE "A" AIRMAN AMEAN E-3 SCHOOL
AIRMAN APPRENTICE E-2
LBO INPUT ZONE
AIRMAN * SUCCESSFUL COMPLETION RECRUIT OF CLASS A SCHOOL IS A WARRANT OFFICER INPUT ZONE MANDATORY REQUIREMENT E-I FOR ADVANCEMENT TO AWE 3.
AM.1 Figure 1-1.-Paths of advancement.
2 Chapter IAVIATION STRUCTURAL MECHANIC4.1 S RATING Maintenanceman. Warrant Officer (W-4), or to LEADERSHIP Limited Duty Officer. Shaded areas indicate careerstages where qualifiedpersonnel may One does not have to be a member of the advance to Warrant Officer (W-1) and selected Armed Forces very long before he realizes that Warrant Officers may advance to Limited Duty more leadership is required of the higher rates. Officer. Personnel in enlisted rates and warrant Advancement not only entails the acquisition of ranks not in a shaded area may advance only as superior knowledge. but also the demonstrated indicated by the lincs. ability to handle people. This ability increases in TheANISmaintainsthefuselage,wings. importance as one advances through the petty stabilizers. movable surfaces, landing wheels and officer rates. tires, and the flight control systems. In perform- In General Order No. 21, the Secretary of the inrthese duties the AMS fabricates and as- Navy outlined some of the most important sembles various types()I'metallic and non- aspects of naval leadership. By naval leadership metallicparts, makes minor skin repairs and is meant the art of accomplishing the Navy's structural repairs. replaces rivets and other types mission through people. Itis the sum of those of metalfasteners.performstire and wheel qualities of intellect, of human understanding, buildup, and paints aircraft. In performing these and of moral character that enable a man to duties the ANIS performs operational checks, inspire andtomanageagroup of people locatestroubles.removes andreplaces mal- successfully.Effectiveleadershipthereforeis functioning components, and performs daily. based on personal example, good management preflight.postflight, and periodic inspections practices, and moral responsibility. The term under the assigned AMS scope. leadership includes all three of these elements. Duty assignments available to the AMS3 and The current NavyLeadership Programis ANIS: arclimitedonly bythelocation of designed to keep the spirit of General Order No. operating aircraft. Billets exist on most carriers 21 ever before Navy personnel. It' the threefold from the smallest to the largest. AMS personnel objectiveiscarried out effectivelyinevery assigned aboard carriers may be attached either command, the program will make better leaders to the ship or to one of the embarked squad- of men in their present and future assignments. rons.Regardless of how assigned,the AMS As one advances up the leadership ladder, more will he working with other maintenance person- and more of his worth to the Navy will be nel assisting in keeping the aircraft flying. judged on the basis of the amount of efficient AMS personnel play an equally important role work obtained from his subordinates rather than in patrol squadrons. which constitute a portion how much of the actual work is performed by of the nation's antisubmarine warfare protec- himself. tion. By hard work and initiative, the AMS may For further information onthepractical become qualified as an aircrewman in patrol application of leadership and supervision, the type aircraft. latest edition of Military Requirements for Petty Many interesting overseas shore billets exist Officer 3 & 2, NavPers 10056 -C, should be for AMS's. If married, some third class and all studied. The principles and problems ot' naval second class petty officers may qualify to bring leadership covered in NavPers 15924 (Series) their dependents to these overseas locations at and the Leadership Checklist for Petty Officers, government expense. Shorter duty tours usually NavPers 2932-3, will be useful tools in develop- prevailatthefewoverseasstationswhere ing sound leadership traits. dependents are not allowed or choose not to go. Between sea tours, the AMS Third of Second Class may be assigned to one of the many naval ADVANCEMENT air stations along the Gulf, East Coast, and West Coast. In addition, the Naval Training Command Some of the rewards of advancement are easy has a few naval air stations-located inland, from to see. You get more pay. Your job assignments which aircraft are operated and AMS's may be become more interesting and more challenging. assigned. You are regarded with greater respect by officers
3 AVIATION STRUCTURAL MECHANIC S 3 & 2
;ind enlisted personnel. You enjoy the satisfac- 1-2 gives a more detailed view of the require- tionof gettinga headin your chosen Navy ments for advancement of active duty personnel; career, Figure1-3 givesthis information for inactive The advantages of advancement are not yours duty personnel, alone. The Navy alsoprofits.Highly trained Remember that the requirements for advance- personnel are essential to the functioning of the ment can change. Check with your educational Navy. 1.3,' advancement, you increase your value services office to be sure that you know the to the Navy in two ways: First, you become most recent requirements. more valuable as a technical specialist in your Advancement isnot automatic. Ale!: you own rating: and second, you become more have met all the requirements, you are eligible valuable as a person who can train others and for advancement. You will actually be advanced thus make Far-reaching contributionstothe only it' you meet all the requirements (including entire Navy. making ahigh enough score on the written examination) and if quotas permit.
HOW TO QUALIFY FOR ADVANCEMENT HOW TO PREPARE FOR ADVANCEMENT What must you do to qualify for advance- ment? The requirements may change from time What must you do to prepare for advance- to time, but usually you must: ment'? You must study the qualifications for advancement, work on the personal qualification I. Have a certain amount of time in your standardand practical factors,study the present grade. required Rate Training Manuals, and study other 2. Complete therequired RateTraining material thatis required. You will need to be Manuals by either demonstrating a knowledge of familiar with the following: the material in the manual by passing a locally prepared and administered test, or by passing I. Manualof Qualificationsfor Advance- the Enlisted Correspondence Course based on ment, NavPers 18068 (Series). the Rate Training Manual and the appropriate 2. Personnel Qualification Standard for the military requirements manual. equipment/system and rating assigned. 3.Utilizing an appropriate Personnel 3, RecordofPracticalFactors,NavPers
Qualification Standard (when applicable) as a 1414/ I. guideline, become qualified and demonstrate 4. BibliographyforAdvancementStudy, your ability to perform all the practical require- NavTra 10052 (Series). mentsfor advancement bycompletingthe 5, ApplicableRateTraining Manuals and Record of Practical Factors, NavPers 14 14/1. their companion EnlistedCorrespondence 4. Be recommended by your commanding Courses. officer,afterthepetty officers and officers 6. Examinations for advancement. supervising your work have indicated that they consider you capable of performing the duties of Collectively, these documents make up an the next higher rate. integrated training package tied together by the 5.Successfully complete the applicable qualifications. The following paragraphs describe military/leadershipexamination which is these materials and give some information on required prior to participating in the advance- how each one is related to the others. ment (professional) examination, "Quals" Manual Some of these general requirements may be modified in certain ways. One of these ways is The Manual of Qualifications for Advance- through the accelerated advancement program ment, NavPers 18068 (Series), gives the (BuPers Note 1430 of 22 Sept. 1970). Figure minimum requirements for advancement. This
4 Chapter 1 AVIATION STRUCTURAL MECHANIC S RATING
#1 E3 #E4 t 1.5 t E6 t El t E8 REQUIREMENTS E1 to E2E2 to E3 to Fe to E5 to E6 to El to E8 to E9 4 mos. 36 mos. service as El. Or 0 mos. 6 mos.12 mos.24 mos.8 years SERVICE comple- total 36 mos 24 mos. tion of as E-2. as E-3 as (4 as E-5. enlisted as (.as (8. service.8 of 11 10 of 13 years years Recruit Class A total total for PR3, Trainin Class B service service (c.o. 013,1,13, may ad- AME 3, for AGCmust bemust be SCHOOL vance up' NM 3, MUC, enlisted.enlisted, to 10% PN 3, MNC. t t of grad- FIB 3, uating class.) MT 3,
Locally PRACTICAL prepared Record of Practical Factors, Hailers 1414/1, must be FACTORS check- completed for I3 and all PO advancements. offs.
Specified ratings must complete PERFORMANCE applicable performance tests be- TEST fore taking examinations.
As used by CO ENLISTED Counts toward performance factor credit in ad- when approving PERFORMANCE vancement EVALUATION advancement.
Locally See Navywide examinations required Navywide, EXAMINATIONS prepared below. selection board. tests. for all PO advancements.
Required for El and all PO advancements Correspondence RATE TRAINING unless waived because of school comple- courses and MANUAL (INCLUD- tion, but need not be repeated if identical recommended ING MILITARY reading. See course has already been completed. See REQUIREMENTS1 NayPers 10052 liarPers 10052 (current edition'. (current edition'.
Commanding AUTHORIZATION. Naval ExaminingCenter Officer * All advancements require commanding oflicer's recommendation. t 1 year obligated service required for E-5 and (6; 2 years for El, E-8 and E9. # Military leadership exam required for E-4 and E-5. ** For E-2 to E-3, NAVEXAMCEN exams or locally prepared tests may be used. tt Waived for qualified E00 personnel.
Figure 1-2.Active duty advancement requirements.
5 AVIATION STRUCTURAL MLC1IANIC S 3 & 2
1
I REQUIREMENTS J.,TE1 to E2 to E3 to 1 E4 to E5 to E6 to ra
E2 E3 E4 1 E5 E6 El 1 ES
36 mos.36 mos.;24 mos. with with with TON T4TIME :
4 mos.6 mos.6 mos.12 mos. 14 mos. total total ; total I GRADE 8 yrs 11 yrs 13 yrs serviceservice ; service
1 TOTAL TRAINING 114 DUTY INGRADE t days '14 days14 days,14 days28 days42 days42 days 28 days
I
PERFORMANCE Specified ratings must complete applicable TESTS pertormance tests before taking 'examination.
DRILL Satisfactory participation as a member of a drill unit PARTICIPATION in accordance witn BUPERSINST 5400.42 series.
PRACTICAL FACTORS Record of Practical Factors. NavPers 1414/1, must be completed [INCLUDING MILITARY for all advancements. REQUIREMENTS)
RATE TRAINING MANUAL (INCLUDING Completion of applicable course or courses must be entered MILITARY REQUIRE in service record. MENTS)
Standard Exam required for all PO Advanaments. Standard Exam, EXAMINATION Standard Exam Also pass Selection Board. Military Leaoership Exam for E-4 and E-5.
I Commanding AUTHORIZATION Naval ExaMining Center Officer
* Recommendation by commanding officerrequired for all advancements. I Active duty periods may be substituted for training duty.
Figure 1.3. Inactive duty advancement requirements.
6 Chapter I AVIATION STRUCTURAL MECHANIC S RATING manualis usually calledthe "Qua's" Manual, Personnel Qualification Standards andthequalificationsthemselvesareoften called "qua's". The qualifications are of two Personnel Qualification Standards(PQS) general types: military requirements. and profes- (Op Nav Instruction 3500.34) are presently being sional (or technical ) qualifications. utilized to provide guidelines in preparing for Militaryrequirements apply toallratings advancement and qualificationtooperate rather than to any one particular rating. Military specificequipmentandsystems.Theyare requirements for advancement to third class and designed to support the advancement require- second class petty officer rates deal with mili- ments as,stated in the "Qua Is" Manual. tary conduct. naval organization,military TheQuals" and Record of Practical Factors justice,security, watchstanding, and other are stated in broad terms. Each PQS is much subjects which are required of petty officers in morespecificinits questionsthatleadto all other ratings. qualification. It provides an analysis of specific Professionalqualifications aretechnical or equipment and duties. assignments. or respon- professional requirements thataredirectly sibilities which an individual or group of individ- related to the work of each rating. uals (withinin the same rating) may be called Boththemilitaryrequirements andthe upon to carry out. In other words. each PQS professional qualifications are dividedinto provides an analysis of the complete knowledge subject matter groups: then, within each subject andskillsrequiredof that rating tiedto a matter group. they are divided into practical specific weapon system (aircraft and/or individ- factors and knowledge factors. Practical factors ual systems or components). are things you must be able to DO. Knowledge Each qualification standard has four main factors are things you ,must KNOW in order to subdivisions in addition to an introduction and a perform the duties of your rate. glossary of PQS terms. They are as follows: The qualificationsfor advancement and a bibliography of study materials are available in 100 Series Theory your educational services office. Study these 200 Series Systems qualificationsand themilitaryrequirements 300 Series Watchsta dons (duties, assign- carefully. The written examination for advance- ments, or responsibilities). mentwillcontain questions relatingtothe 400 Series Qualifications cards knowledge factors and the knowledge aspects of the practical factors of both the military require- The introduction explains the complete use of ments and the professional qualifications. If you the qualification standard in terms of what it are working for advancement to second class, will mean to the user as well as how to use it. remember that you may be examined on third The Theory (100 Series) section specifies the class qualifications as well as on second class theory background required as a prerequisite to qualifications. the commencement of study in the specific It is essential that the "quals" reflect current equipment or system for which the PQS was requirements of fleet and shore operations, and written. These fundamentals are normally taught that new fleetwide technical. operational, and intheformalschools(Preparatory, Funda- procedural developments be included. For these mentals, and Class A) phase of an individual's reasons, the qualifications are continually under training. However, if the individual has not been evaluation.Although thereisan established to school, the requirements are outlined and schedule for revisions to the "quals" for each referenced to provide guidelines for a self-study rating, urgent changes to the " quals" may be program. made at any time. These revisions are issued in The Systems (200 Series) section breaks down the form of changes to the " Quals" Manual. the equipment or systems being studied into Therefore, never trust any set of "quals" until functional sections. PQS items are essentially you have checked the change number against an questions askedinclear,concise statement up-to-date copy of the "Quals" Manual. Be sure (question) form and arranrdina standard you have the latest revision. format. The answers to the questions must be AVIATION STRUCTURAL MECHANIC S 3 & 2
extracted from the various maintenance manuals divisionofficer, and maintenance officeras covering the equipment or systems for which the requiredtocertify proper qualification. The PQS was written. This section asks the user to completion of part or all of the PQS provides a explain the function of the system, to draw a basis for the supervising petty officer and officer simplified version of the system from memory, to certify completion of Practical Factors for andtousethisdrawnschematicorthe Advancement. Feheina t ie provided in the maintenance manual whilestudyingthesystemorequipment. Emphasis is given to such areas as maintenance Record of Practical Factors managementprocedures,components, component parts, principles of operation, sys- Before you can take the Navy-wide examina- tem interrelations, numerical values considered tion for advancement, there must be an entry in necessaryto operation and maintenance, and your servicerecordto show that you have safety precautions. qualifiedinthe practical factors of both the The Watchstation (300 series) section includes military requirements and the professional quali- questions regarding the procedures the individ- fications. A special form known as the Record ual must know to operate and maintain the of Practical Factors, NavPers 1414/1 (plus the equipment or system. A study of the items in abbreviation of the appropraite rating), is used the 200 series section provides the individual tokeeparecordof your practicalfactor with the required information concerning what qualifications.Theformlistsallpractical the system or equipment does, how it does it, factors, both military and professional. As you and other pertinent aspects of operation. In the demonstrateyourabilitytoperform each 300 series section, the questions advance the practical factor. appropriate entries are made in qualific ition process by requiring answers or the DATE and INITIALS columns. demonstrations of ability to put this knowledge Changes are made periodically to the Manual to use or to cope with maintenance of tit: of Qualifications for Advancement and revised system or equipment. Areas covered include forms of NavPers 1414/1are provided when normaloperation;abnormaloremergency necessary. Extra space is allowed on the Record operation; emergency procedures which could ofPracticalFactorsforentering additional limit damage and/or casualties associated with a practicalfactorsastheyarepublishedin particular operation; operations that occur too changes. The Record of Practical factors also infrequentlytobeconsideredmandatory providesspaceforrecordingdemonstrated performanceitems; andmaintenanceproce- proficiency in skills which are within the general dures/instructions such as checks, tests, repair, scope of the rate but which are not identified as replacement, etc. minimum qualifications for advancement. The 400 series section consists or the quali- If you are transferred before you qualify in fication cards. These cards are the accounting all practical factors, NavPers 1414/1 should be documents utilizedto record the individual's forwarded with your service record to your next satisfactory completion of items necessary for duty station. You can save yourself a lot of becoming qualified in duties assigned. Where the trouble by making sure that this form is actually individual starts in completing a standard will inserted in your service record before you are depend on his assignment within an activity. The transferred. If the form is not in your service complete PQS is given to the individual being record, you will be required to start all over qualifiedsothat he canutilizeitat every again and requalify in the practical factors which opportunity to become fully qualifiedinall have already been checked off. areas of his rating and the equipment or system A second copy of the Record of Practical for which the PQS was written. Upon transfer to Factors should be made available to each man in a differentactivity, each individual must re- pay grades E-2 through E-8 for his personal qualify. The answers to the questions asked in record and guidance. the qualification standards may be given orally The importance of NavPers 1414/1 cannot be or in writing to the supervisor, the branch or overemphasized. It serves as a record to indicate
8 Chapter I AVIATION STRUCTURAL MECHANIC S RATING to the petty officers and officers supervising the material that is listed for third class. It' you yourworkthatyou havedemonstrated are working for advancement to second class, proficiency in the performance of the indicated study the material that is listed for second class. practicalfactors andispart of the criteria Remember that you are also responsible for the utilized by your commanding officer when he references listed at the third class level. considers recommending you for advancement. In using Nav Tra 10052, you will notice that In addition, the proficient demonstration of the some Rate Training Manuals are marked with an applicable practical factors listed on this form asterisk (*). Any manual marked in this way is can aid you in preparing for the examination for MANDATORYthat is, it must be completed at advancement. Remember that the knowledge the indicated rate level before you are eligible to aspects of the practical factors are covered in the take the Navy-wide examination for advance- examinations for advancement. Certain knowl- ment. Eachmandatorymanualmay be edge is required to demonstrate these practical completed by passing the appropriate enlisted factorsandadditionalknowledgecanbe correspondence coursethatisbased on the acquired during the demonstration. Knowledge mandatorytrainingmanual:passinglocally factorspertaintothat knowledge whichis prepared tests based on the information given in requiredtoperform acertain job. In other the training manual, or in some cases, success- words. the knowledge factors required for a fully completing an appropriate Class A School. certain rating depend upon the jobs (practical Do not overlook the section of Nav Tra 10052 factors) that must be performed by personnel of which lists the required and recommended refer- that rating. Therefore. the knowledge required encesrelatingtothemilitarystandards/ toproficientlydemonstratethesepractical requirements for advancement. For example, all factors will definitely aid you in preparing for personnel must complete theRate Training the examination for advancement. Manual, Military Requirements for Petty Officer 3 & 2, NavPers 10056 (Series),for the ap- NavTra 10052 propriate rate level before they can be eligible to advance. Bibliography for Advancement Study, NavTra The references in NavTra 10052 which are 10052 (Series), is a very important publication recommended, but not mandatory, should also for anyone preparing for advancement. This be studiedcarefully. All references listedin lists required and recommended Nav Tra 10052 may be used as source material bibliography for the written examinations at the appropriate RateTraining Manuals and other reference material to be used by personnel working for rate levels. advancement. Nav Tra10052isrevised and issued once each year by the Naval Training Rate Training Manuals Command. Each revised edition is identified by aletter following the NavTra number. When There are two general types of Rate Training using this publication, be sure that you have the Manuals. Rating manuals (such as this one) are most recent edition. prepared t'or most enlisted rates, giving informa- If extensive changes in qualifications occur tion that is directly related to the professional between the annual revisions of NavTra 10052, a qualifications. Basic manuals give information supplementary list of study material may be that applies to more than one rate and rating. issued in the form of a Notice. When you are Basic Electricity, NavPers 10086 (Series), is an preparingforadvancement,checktosee example of a basic manual, because many ratings whether changes have been made in the quali- use it for reference. fications. If changes have been made, see if a Rate Training Manuals are produced by field BuPers Notice has been issued to supplement activities under the management control of the NavTra 10052. Naval Training Command. Manuals are revised The required and recommended references are from time to time to keep them up to date listed by rate level in NavTra 10052. If you are technically. ;he numbering systemisbeing working for advancement to third class, study changed from NavPers to NavTra. The revision
9 AVIATION STRUCTURAL MECHANIC S 3 & 2 of a Rate Training Manualisidentified by a in the details by .intensive study. In each study letter following the Navl'ers or NavTra number. period, try to cover a complete unitit may be a You can tell whether any particular copy of a chapter. a section of a chapter. or a subsection. Rate Training Manual isthe latest edition by If you know the subject well, or it' the material checking the number in the most recent edition is easy, you can cover quite a lot at one time. of List of Training Manuals and Correspondence Difficult or unfamiliar material will require more Courses, Nav Tra 10061 (Series), NavTra 10061 study time. is actually a catalog that lists training manuals and correspondence courses: you will find this 6. In studying any one unitchapter. section, catalog useful in planning your study program. or subsectionwrite down the questions that Rate Training Manuals are designed to help occur to you. Many people find it helpful to you prepare for advancement. The following make a written outline of the unit as they study, suggestions may help you to make the best use or at least to write down the most important of this manual and other Navy training publica- ideas. tions when you are preparing for advancement. 7. As you study. relate the information in the training manual to the knowledge you already hare. When you read about a process, a skill. or 1. Study the military requirements and the a situation, try to see how this information tic§ professional qualifications for your rate before in with your own past experience. you study the training manual. and refer to. the 8. When you have finished studying a unit, "quals" frequently as you study. Remember. take time out to see what you have learned. you are studying the training manual in order to Look back over your notes and questions. meet these "quals." Maybe some of your -questionshave been 2. Set up a regular study plan. If possible. answered, but perhaps you still have some that schedule your studying for a time of day when arenot answered. Without referringtothe you will not have too many interruptions or training manual, write down the main ideas that distractions. you have learned from studying this unit. Do 3. Before you begin to study any part of the not quote the manual. If you cannot give these training manual intensively, become familiar ideas in your own words. the chances are that with the entire manual. Read the preface and you have not really mastered the information. the table of contents. Check through the index. 9. UseEnlistedCorrespondenceCourses Look at the appendixes. Thumb through the whenever you can. The correspondence courses manual without any particular plan, looking at are based on Rate Training Manuals or on other the illustrations and reading bits here and there appropriate texts. As mentioned before, as you see things that interest you. completionof a mandatory Rate Training 4. Lookatthetraining manualin more Manual can be accomplished by passing an detail, to see how it is organized. Look at the Enlisted Correspondence Course based on the table of contentsagain.Then, chapter by Rate Training Manual. You will probably find it chapter, read the introduction, the headings. and helpful to take other correspondence courses, as the subheadings. Thiswillgive you a clear wellasthose based on mandatory training picture of the scope and content of the manual. manuals. Taking a correspondence course helps As you look. through the manual in this way, ask you to master the information given inthe yourself some questions: What doIneed to training manual, and also helps you see how learn about this? What do I already know about much you have learned. this? How isthis information relatedto in- 10. Think of your future as you study Rate formation given in other chapters? How is this Training Manuals. You are working for advance- informationrelatedtothe qualifications for ment to third class 01 second class right now, advanCement? but someday you will be working toward higher 5, When you have a general idea of what is in rates. Anything extra that you can learn now the training manual and how it is organized, fill will help you.
10 Chapter IAVIATION STRUCTURAL MECHANIC S RATING
SOURCES OF INFORMATION handtool operationsthatare performed by enlisted men or ali ratings in their day-to-day One of the most useful things you can learn work. The manual is plentifully supplied with about a subject is how to rind out more about it. illustrations showing, as well as telling, how to No singlepublication can give youallthe perform specific operations. Many of the jobs information you need to perform the duties of performed by the AMS are included, making it a your rating. You should learn where to look for valuable reference not only in performing your accurate, authoritative, up-to-date information daily duties but also in studying for advance- on all subjects related to the military require- ment. ments for advancement and the professional Itisessential that AMS's have a thorough qualifications of your rating. understandingofbaskmachines. Basic Some of the publications described inthis Machines, NavPers 10624, contains an excellent chapter are subject to change or revision from presentation on basic machines. Beginning with time to timesome at regular intervals, others as the simplest of machines- the lever the manual the need arises. When using any publication that proceeds withthediscussion of block,- and is subject to change or revision, be sure that you tackle, wheel and axle, inclined plane, screw, have the latest edition. When using any publica- and gears. It explains the concepts or work and tion that is kept current by means of changes, be power, and differentiates between the terms sure you haveacopyin which allofficial "force" and "pressure." The fundamentals of changes have been made. Studying canceled or hydrostatic and hydraulic mechanisms arc dis- obsolete information will not help you to do cussedindetail. Thefinal chapter includes your work or to advance in rating: it is likely to several examples of the combination of simple be a waste of time, and may even be seriously mechanisms to make complex machines. misleading. A thorough understanding of the material Several publications that you will need to presented in Basic Machineswillgreatly study or refer to as you prepare for advance- facilitate an understanding of the machines with ment have already been discussed earlier in this which the AMS works, many of which are a chapter. In addition, you may find it useful to combination of a number of simple machines. consult some of theRate Training Manuals Additional publications that you may find prepared for other Group IX (Aviation) ratings. useful are as follows: Reference to these training manuals will add to your knowledge of the duties of other men in thefield of aviation.Also, you may findit BlueprintReading and Sketching, NavPers usefultoconsulttheBasicRate Training 10077 (Series). Manuals described in the following paragraphs. BasicElectricity,NavPers10086(Series) Tools and Their Uses, NavPers 10085 (Series), (chapters 1,3). contains descriptions of a number of basic Fluid Power, NavPers 16193 (Series).
11 CHAPTER 2
AERONAUTIC PUBLICATIONS
Aeronautic publications areissued by au- specific purpose. They are identified as follows: thority of the Commander of the Naval Air AirborneWeapons/Stores,Conventional/ Systems Command. These publications are the Nuclear,Checklists/StoresReliabilityCards/ sources of information for guiding naval person- Manual, NavAir 01-700. This part of the publica- nel inthe operation and maintenance of all tions index is not used by AMS personnel and aircraft and related equipment within the Naval therefore is given no further coverage in this Establishment. By proper use of these publica- cha pter. tions,allaircraft and other aeronautic equip- Navy Stock List of Forms and Publications, ment can be operated and maintained efficiently NavSup Publication 2002; Section VIII, Parts C and uniformly throughout the Navy. and D, Numerical Sequence List (,,Iso referred to Aeronautic publications may IN: grouped into as Numerical Index). two major classes or groups- -those issued in the EquipmentApplicabilityList (Volumes I form of MANUALS, and those issued in the through 7), NavAir 00-500A. form of LETTER MATERIAL. Aircraft Application List, NavAir 00-500B. When a new aircraft, engine, accessory, or Directives Application List, NavAir 00-500C. other item of equipmentis accepted by the Letter Type Technical Directives Equipment Navy, manuals necessaryto insure its proper and Subject Application List, NavAir 00-500D. operation and upkeep are prepared and issued to A description of these lists and their uses is all activities using and/or maintaining the equip- presented in the following paragraphs. ment.Supplementalinformationand other directive type publications that must be issued NUMERICAL SEQUENCE LIST from time to time are issued in the form of letter material. Both manual and letter publica- Nav Sup Publication 2002isa I 3-section tions may, on occasion, be properly referred to index of allthe forms and publications used as directives. Broadly speaking, any communica- throughout the Navy and stocked by the Naval tion which initiates or governs action, conduct, Supply Systems Command. Section VIII of this or procedure is a directive. Stock List contains Naval Air Systems Com- All aeronautic publications, both manual and mand (NavAirSysCom) publications. This sec- letter type, are assigned a title and code number. tion is made up of four partsA, B, C, and D. When they are available for issue, all publica- Parts A and B pertain to ordnanc:. publica- tions, except Instructions and Notices, are listed tions. Part C is the numerical listing of manual in the Naval Aeronautic Publications Index. type aeronautic technical publications, and Part D is the numerical listing of letter type publica- tions. These two, Parts C and D, are referred to NAVAL AERONAUTIC PUBLICATIONS as the Numerical Sequence List or Numerical INDEX Index of the Naval Aeronautic Publications Index. The Naval Aeronautic Publications Index is Part C (manual publications) contains its table made up of six parts, each of which serves a of contents, as well as the instructions for using
12 Chapter 2AERONAUTIC PUBLICATIONS both Parts C and D of Nav Sup Publication 2002. restrictions concerning the requisitioning of the 'Included in these instructions are the method publication. In addition, the date of the latest for procuring aeronautic publications, the forms issue or revision of the publication is listed. This and procedures required for ordering publica- providesameans whereby theissue and/or tions, and explanations of certain codes used in revision dates of the publications on hand in an the Index. Also a listing of canceled publications activity can be checked against the dates listed for Part C is contained in the last pages of Part in the current issue and supplement (discussed C. later) of the Numerical Index, thus assuring that Part C is divided into subject matter groups, the publications are current. and allpublications within a group are then listedinnumericalorder.For example, all EQUIPMENT APPLICABILITY LIST manuals in the 00 series are listedfirst, then followed by the 01, 02, 03, etc., through the 51 Basically, the Equipment Applicability List, series. The listing includes the publication code NavAir 00-500A,isacross-referenceindex number, stock number, title, date of latest issue listing of Naval Air Systems Command (NavAir- or revision, security classification, requisition SysCom) publications of aircraft components restriction code, and basic or change code. A listing of the general subject groups is shown in Table 2-I.General subject classification table 2 -I. numbers for manual type publications. Part D (letter type directives) contains a table a generalalphabeticalcross- ofcontents, 00 reference listing, and a listing of Air Force-Navy General 01 code cross-references. Aircraft Powerplants 02 Part D isdivided into a number of sub- (02A Reciprocating engines, 02B Jet en- sections. Included among those of interest to the aircraft,accessories, gines, 02F Rocket engines) AMS aregeneral, and 03 support equipment. Listed in the general section Accessories Hardware and Rubber Material 04 areAircrew SystemBulletinsand Changes, Instruments 05 AviationClothingandSurvivalEquipment Fuels, Lubricants, and Gases 06 Bulletins and Changes, Technical Orders, and 07 Technical Notes. In the aircraft section are listed Dopes and Paints Electronics 08 & 16 allAircraft Changes and Bulletins.. The acces- sories section contains a listing of all Accessories InstructionalEquipment and Training Changes and Bulletins. The support equipment Aids 09 & 28 section contains a listing of all Support Equip- Photography 10 ment Changes and Bulletins. Aviation Armament Il Fuel and Oil Handling Equipment 12 TheNumericalIndexmustbeusedto completely identify and, therefore, to order Parachute and Personal Survival Equipment 13 required publications. However, the other parts HangarS and Flying Field Equipment .. .. 14 of the Index (discussed in the following para- Standard Preservation and Packaging Instruc- graphs) must be used to determine what publica- tions 15 tions are available for a .specific item of equip- Machinery, Tools, and Test Equipment 17 & 18 ment and to check the applicability of publica- Ground Servicing and Automotive Equip tions to specific equipment. ment 19 When an applicable publication number is Descriptive Data Sheets for Aviation Sup- found in one of the other parts of the Naval port Equipment 20 Aeronautic Publications Index, it can be easily (Being superseded by Ground Support located in the Numerical Index, Here, it can be Equipment Illustrations (GSEI)) Chemical Equipment 24 & 39 more completely identifiedastotitle and nomenclature, stock number (for manual type Meteorology 50 Ship Installations 51 publicationS),securityclassification, and any
13 AVIATION STRUCTURAL MECHANIC S 3 & 2 and related equipment according to model, type, DIRECTIVES APPLICATION LIST or part number. BY AIRCRAFT CONFIGURATION Sincethis index contains several thousand entries, one volume would be very cumbersome The Directives Application List by Aircraft to use. For this reason, this index is divided into Configuration, Nav Air 00-500C, contains a list- several volumes. At the time of this writing, ing of the active Naval Air Systems Command there are seven volumes. letter type technical directives with respect to With the exception of several small sections in their applicability to aircraft. The lists in this thefirstpart of Volume1,the Equipment volume arearrangedfirstby aircraftseries, ApplicabilityListis one continuous index of second by aircraft configuration, and third by model, type, or part numbers in alphanumerical Airframe /AircraftBulletinand/orChange sequence. numbers.NOTE:Configurationrefersto InadditiontoanIntroduction,which modifications made to a basic aircraft model. explains the headings at the top of each page. For instance, A-4A, A-4B, TA-4F, etc., are all the other sections in the first part of Volume 1 differentconfigurations oftheA-4 aircraft pertainprimarilytomanualsforaircraft, model. weapons systems, and aircraft engines. There- fore, the publication numbers are listed accord- EQUIPMENT AND SUBJECT ing to aircraft, aircraft engine, and weapons APPLICABILITY LIST system designation. The Equipment Applicability List should be The Equipment and Subject Applicability usedwhen attemptingtodeterminewhat List,NavAir 00-500D.isa relativelyrecent publications are available on a particular item or addition to the Naval Aeronautic Publications equipment, andthemanufacturer and part Index. It contains a cross-reference index listing number of the item are known. of Naval Air Systems Command letter type technical directives. It serves the same purpose AIRCRAFT APPLICATION LIST for letter type technical directives as the Equip- ment Applicability List, NavAir 00-500A, does TheAircraftApplicationList,Nav Air fortechnicalmanuals.However,sincethe 00-500B,containsalistingofallmanuals NavAir 00-500D lists only those model /type grouped according totheir application to an part numbers for which technical directives have aircraft. This part of the index does not contain been issued, it is much smaller than the NavAir listings of any letter type publications, and all 00-500A. The complete List is contained in one manuals are listed by publication code number volume but is divided into two parts. Part A is only. the Equipment Index and Part B is the Subject Alistofbasicnumbering categoriesis Index. provided in the front of the book. This list may Part A contains alisting of allNaval Air be usedin determining the general type of Systems Commandlettertypetechnical equipment covered in a publication. For deter- directives on aircraft components and related mining the specific item of equipment covered equipment by model/type part number. Each by a publication and the title of the publication. numberislistedinalphanumerical sequence reference should be made to Part C of Section withinits cognizant equipment series. At the VIII in Nav Sup POblication 2001. present time, Part A is divided into nine series. The Aircraft Application Listisespecially The Accessories, Aircrew Systems, and Clothing handy for determining what manuals are avail- andSurvival Equipment Series are of most able for a particular model of aircraft. Included interest to AM personnel. under each modelisa completelisting of Part B of NavAir 00-500D contains a listing of applicablemanuals.Thislisting includesall active Naval Air Systems Command letter type allowance lists, aircraft manuals, engine manuals, directives bysubject. This part of theList accessoriesmanuals, etc.,pertaining to that pertains primarilyto Airframe Bulletins and particular model of aircraft. Changes.
14 Chapter2--AERONAUTIC PUBLICATIONS
UPDATING THE INDEX and filed. A knowledge of the numbering sys- tems used will enable the AMS to locate any Each Listin the Naval Aeronautic Publica- desired information with a minimum of effort.. tions Index is updated at regular intervals by the A brief explanation of the coding of manuals issuance of a new list. In addition, some of these listedinthe indexis given in the following Lists arc kept current by the periodic issuance of sections.Coding forlettertype materialis supplements between issues of the Basic List. covered later in this chapter. The dates and intervals of the issuance of new Code numbers assigned to manuals consist of Lists and supplements have changed from time a prefix and a series of three parts. The prefix to time in the past. consists of letters which identify the originator At the time of this writing, the Numerical of the publication. Index (Parts C and D of Nav Sup Publication NavAir isthe prefix assigned totechnical 2002)isissued annuallyin September. Sup- publications originated by the Naval Air Systems plements are issued bimonthly between each Command. In the stock list, itis shortened to basic issue. The Equipment Applicability List. NA. NavAir00-500A. is issued annually in The three parts which make up the remaining November. This Listiskept current by the portions of the number indicate the following: issuance of quarterly supplements between each basicissue.TheAircraftApplicationList, Part Iis a two-digit number that indicates the Nav Air00-500B, is issuedinMarchand general subject classification of the equipment September. and the Directives Appli-ation List covered by the publication. Table 2-1lists the by Aircraft Configuration, Nav Air 00-500C, is general subject categories and the appropriate issued in January and July of each year. Sup- two-digit numbers. plements are not issued for these Lists. PartIIof the publications code number The Equipment and Subject Application List, consists of numbers and/or numbers and letters Nav Air 00-500D, is issued in May and November and indicates the specific class, group, type, or of each year. and as of this writing, supplements model and manufacturer of the equipment. The will be issued as the information is developed. subject breakdowns are listed at the beginning of Supplements listall aeronautic publications each separate major division within the distributed during the previous period, and those Numerical Index. superseded, publicationsthat have been PartIIIconsists of a number or numbers canceled, or revised. Supplements are cumula- which designate a specific manual. For aircraft tive, thatis.allmaterial from the preceding and powerplants,thisnumber designates a supplementis incorporated in the latest sup- specific type of manual. For other types of plement: therefore, at any given time, not more equipment, this partis assigned in numerical than one supplement is in effect for any List. sequence and has no reference to the type of Naturally, the reissue of a basic List cancels the manual. outstanding supplement. Supplements for the Numerical Index (Parts C Figure 2 -Iillustrates the identification and and D of Section VIII of NavSup Publications decoding of a complete manual publication 2002) are identified by the word "supplement" number. printed near the upper right-hand corner of the cover.Supplements tothe NavAir 00-500A SECURITY OF CLASSIFIED Series publications are identified by the word PUBLICATIONS "supplement" printed in the middle of the cover page. The Department of the Navy Supplement to the DOD Information Security Program Regula- PUBLICATIONS NUMBERING SYSTEM tions (OpNav Instruction.55 10.1 Series), issued by the Chief of Naval Operations, is the basic Code numbers are assigned to all publications security directiverelating tosafeguarding in order that they may be identified, indexed, classified information. Its provisions apply to all
15 AVIATION STRUCTURAL MECHANIC S 3 & 2
Prolix Part I Part IIPart III
-L- _L NA Oi 85 ADA A NavAlaysCom originated publication pertaining to an aircraft built by Grumman Aircraft Engineering Corporation The particular model is the A CA, the publication in a Maintenance Instructions Manual, and this entire code number identifies a particular volume of the Maintenance Instructions Manual. AIVI.224 Figure 2-1.Identification and decoding of manual publication code number. military and civilian personnel and to all activi- delivery of urgently required technical informa- ties of the Naval Establishment. tion. Under this system, information affecting The manual contains detailed instructions for flight safety, hazards to personnel, or grounding classifying, marking, and handling classified in- of aircraft is disseminated via naval message and formation, and for access to and authorized immediatelyincorporatedintotheaffected disclosure of the information. manual. A manual change page followup is then The AMS, from time to time, has occasion to required within 15 days of the release of the use classified publications relating to the per- message. Information of a less urgent nature is formance of his work. Before he accepts such disseminated by RAC change pages that must be publications he must be clearedto the ap- printed within 30 days after problem resolution propriate degree to handle this classified matter. and is generally limited to 12 pages or less. It is then mandatory that he have knowledge of The RAC System for manw:.1 changes replaces and abide by the instructions inthe Security the previous Interim Manual Change System but Manual pertaining to handling classified mate- does not affect the normal manual change and rial. revision requirements. It merely supplements the Publications listedin the Numerical Index existing Normal Change System to provide for (Parts C and D of Section VIII of Nav Sup rapidissue of urgently required data which Publication 2002) are unclassified unless other- previously was not available to the user for long wise marked "1" (confidential) or "4" (secret) periods of time due to system red tape, such as inthe column headed PS (physical security). routing and printing delays. The Index is not classification authority. The As shown in table 2-1, manuals are published supplements to the Index contain information in a number of different general subject cate- of classification action on a "when-occurring" gories. Those of special interest to the AMS3 basis: and AMS2 are the General Manuals (00 series), Aircraft Manuals (01 series), and the Accessories Manuals (03 series). Certain manuals in other MANUAL TYPE PUBLICATIONS series may be used occasionally, but those listed here are of special importance to the Aviation To attain a satisfactory state of readiness, Structural Mechanic. technical manuals are developed, published, and distributed concurrently with the weapon sys- GENERAL MANUALS (00 SERIES) tem or equipment that they cover. Periodic changes and revisions are issued as necessary to As indicatedby thetitle,thisseries of insure that manuals continually reflect equip- manuals includes information of interest to all mentchanges and currentoperational and naval aviation personnel. included are four parts support concepts and procedures. of theNaval Aeronautic Publications Index TheRapid Action Change (RAC) System (00-500A. 00-500B, 00-500C, and 00-500D, providesa quick response capabilityfor the already described). NavAir Outfitting Lists and
16 Chapter 2AERONAUTIC PUBLICATIONS
Allowance Lists, and Aviation Training Litera- Training Literature (00-80 Series) ture. This series of publications is issued by au- thority of the Deputy Chief of Naval Operations Allowance Lists and Outfitting (Air). Included are various Air Safety Pamphlets Lists (00-35Q Series) and General Aviation Training Publications. All such publications listed in the current issue of Allowance Lists and Outfitting Lists consist the Numerical Index are available at the various of listings of the equipment and material neces- NavAir Publications Supply Points. All requests sary to place and maintain various activities in a for 50 or more copies of a publication must be material readiness condition. These allowances submitted to the Chief of Naval Operations, are based on known or estimated requirements Flight Training Branch, Washington, D. C., with or on available usage data. a statement of justification. Allowance Lists are identified by SECTIONS. Certain sections such as A, 1-1, and K are issued as individual publications. Others such as B and AIRCRAFT MANUALS (01 SERIES) R appear as a series of publications, each of whichisapplicabletoaspecific model of The following types of manuals are prepared equipment,model ofaircraft,ortypeof and issued for each model of aircraft used by the activity. Navy: The AMS shouldbefamiliarwiththe following sections: NATOPS Flight Manual. Maintenance Instructions Manual. Section A, Standard Aeronautical and Navy Structural Repair Manual. Stock Account Material. Periodic Maintenance Requirements Manual Section B, Airframe and Engine Maintenance or Periodic Maintenance Information Cards. Parts. This section contains the initial outfitting Illustrated Parts Breakdown. list for each model of aircraft in current use. Technical Manual of Weight and Balance Data Section G, General Support Equipment. This (certain aircraft only). sectionlistsallconsumable general support equipment for all classes, types, and models of NATOPS Flight Manual aircraft. Section H, Flight Operational Material for The NATOPS (NavalAirTrainingand Aircraft Squadrons. This section lists aviator's Operating Procedures) Flight Manual contains flight clothing as well as the protective clothing complete operating instructions for the aircraft available for use when handling liquid oxygen. anditsoperationalequipment. Emergency Section K, Allowance List for Naval Aero- operatinginstructionsaswellasnormal nautic Publications and Forms. operating instructions are provided. Although AllowanceListsarereissuedperiodically. NATOPS Flight Manuals are issued primarily for When new issues or reissues are published, they the use of pilots and aircrewmen, all main- arelisted in the next issue of the Numerical tenance personnel should become familiar with Index. All lists not appearing in the current issue the contents of the Flight Manual for their of the Numerical Index or latest supplement respective aircraft. have been canceled. NATOPS Flight Manuals are kept up to date All Allowance List and Outfitting List code by two types of revisionsregular revisions and numbersare NA 00 -35Q plus thesection interim revisions. Regular revisions cover routine identificationletterand a dash number to changes and instructions and are generally issued identify a particular section in a series. For every 90 days. Interim revisions cover vital example, the Section B Allowance List for the operating instructions and are used when im- S-2D aircraft is NA 00-35QB-177. This publica- mediate action isnecessary. Interim revisions tion contains the initial outfitting list for the may be issued in letter form to the individual S-2D aircraft. activities and by naval message to commands,
17 AVIATION STRUCTURAL MECFIANIC S 3 & 2 and are later incorporated as regular revisions. Flight Control Systems. Corrosion Control,- Cleaning, Painting, and Maintenance Instructions Manuals Dc contamination. TheMaintenanceInstructionsManuals NOTE: The different aircraft manufacturers (MIM's) containallthe essential information may group the material in the various volumes required by aircraft maintenance personnel for of the Maintenance Instructions Manuals under service and maintenance of the complete air- different titles. For example, the Survival and craft.MlM's includethe data necessary for Environmental Systems volume for the RA-5C troubleshooting andmaintainingthe power- covers the ejection seat, canopy, liquid oxygen, plant, accessories, and all other systems and heating, air-conditioning, ventilation, and anti-g components of_the aircraft. systems. Two volumes, titled Personnel Environ- Maintenance Instructions Manuals are divided mental Systems and Canopy and Survival Sys- into three types. Type 1manuals contain all tems, are prepared to cover the same subjects for essential information required for performing the A-4 aircraft. Organizational level maintenance,suchas TheGeneralInformationandServicing descriptionandoperationof systemsand volumeisdesigned primarily forthe plane components, maintenance considerations, and captain: however, this volume also contains a appropriate diagrams and schematics. great deal of information important to all AMS Type II manuals contain Intermediate level personnel.Thisvolumecontains ageneral maintenance instructions required for the main- description of the aircraft, all necessary informa- tenance of components, systems, groups of tion which is not contained in other specialized systems, or equipment when separate coverage is manuals,andallinformation pertainingto not provided in othel. manuals. Included are servicing the aircraft. proceduresforcheckout,troubleshooting, Each of the specialized system volumes of the repair, replacement, adjustment, calibration, and MaintenanceInstructionsManualisfurther preinstallation,and/orshippinginformation divided into four sections, as described in the (methodofpackaging). Coverageon following paragraphs. componentsorequipment may includea Section Iis the same in all volumes of a description of component operation if it is not particularaircraftMaintenanceInstructions covered in the Type I manual. Manual. This section provides an introduction to Type 111 manuals contain Depot level over- the manual and usually supplies a list of the haul and repair instructions for components, Changes applicableto theparticular volume accessories, and any other equipment necessary concerned. for unit operation. .Section II describes thesystemand Inmany cases,aconsolidationof any components as well as their operation. combination of Types I,II, or III manuals is SectionIII provides suchmaintenance providedin one manual. Thisisthe type coverage as removal and installation procedures discussed in the following paragraphs and most and troubleshooting chartsfor Organizational common to the AMS. level of maintenance. The Maintenance Instructions Manual for all Section IV provides component repair proce- currentproductionaircraftismade upin dures for the Intermediate level of maintenance. volumes, each volume being individually bound Figure 2-2is an example of apage from and issued separately. This permits each shop in sectionIIIof a MaintenanceInstructions an activity to have its own applicablevolume, or Manual. This page shows the basic layout of the volumes, at hand for ready reference. Volumes maintenance-coverage sections of the specialized of most interest to the AMS are as follows: type manuals. Each component maintenance procedure is identified by a boldface heading General Information and Servicing. (item A,fig.2-2)for easeinlocating the Landing Gear and Arresting Gear Systems. material on the page. All removal and installa- Airframe and Related Systems. tion procedures provide a recommended man-
18 Chapter 2 AERONAUTIC PUBLICATIONS
Section RI 'LWOW Ot*,0,110AA*1401 Potwar-00r 0.414 bs 34 311 , Ittatiovel Proaduta sg, &OA' lateclOtt Strtlenite WhigN461344 screws end PANMOrtiin washers, ha the two umtand Remove! taaretitta Oak; o PitaittAik 3040. two Iowa WO. tJtt NokS60-3-4 isnews end Ar40011t0 tt, Ramer& three strews bons each bracket atimettl washers in. the two middle ha m. and mouse damps; h inspect attachmentof brackets to structure. Damper E a. Remove b0h11, nuts and. washers which to40 tOlt- must rotate freely and there must be a minimum of 0.12 Mang tad asteinlAta Os 40430 emu. inch clearance to structure. J. Unitive nut* washer Ind Arad 1401t top i.Rainatati a evateitt et to 00110 bottom locations end remove bockats, laving dempet Quality Assurance Summary assembly. a.Inspect installation of upper and lower brackets to Noe damper assembly to check nut and cotter pin installation The Owns damper assembly must he Awed Inspect installation of upper and lower rod assem- if storW with the top side b. with the top aide blies for lightness of attachments and lock-wiring ofF upside doom for more than four hoots, it it loner bolt head. pool:lir OW ale 00V. big .entrapped in the fluid Damper between the disc end the IMUSI nioldniVrektutinit c. Inspect attachment of brackets to structure, damping ram, This copdhlon an be catrected must rotate freely and there must be a minimum of 0.12 by storing the dampen in its normal pcoirion inch clearance to structure. ..:::...-...:.%:,,,:::,:,:,:.:.:.,..,..,::::::,,,.:;::..:::;:;,;:::::55::,:::!;::::::::..,:7:::;,,:;:::,,,,,,,:::::::: at room teMpecature. appeasittnattly 21.1 °C . .. . (70 °F) for one week. 3-330. ELEVATOR MAINTENANCE A PROCEDURES. *.928,: PARTS. REptitcuottsrr. 3414- 41444OVAL (W. -7. and Depsit Pam Data ,, - Tools and Equipment List forward to:neitc:btatter 013ktte01001r levet . Truck, Fork Lift TC-200 C Hoist HSKS-153113 IElevator Slinu Assembly 551241.1 Materials List Cotter Pin (2) NIS24665-100 Manpower Requirements 8 Spacer (top) 9230i3-1 Two men are required. 923013.3 Spacer (bottom) Demoval Procedure' .. 14C ttlower Itetpotettieut st,;Placard oontrttl column., 00e mast is melted, b. Open ale aft isolontet latches and null *Mom beds Cf4t Quality Assurance Iteapairetnent c. ,Suffiattthe elevator with elevator tiling assembly. An inspection is required when seeps appear in hoar.. UGC V$12414 or KVIVIPOlt and molt she eletttor td the up paathott. Installation Procedure 1. fletrove she lockAvire and twasboles Atittbiltig the. inboard esti of the eitionor to the and &dm taf the ale- a, Install tippet btatkes using bee 9-2'03-.1 spew, *MO Wipe tube.' Abl1-20-1 nut and hlSzot46S40a cotter pin. /stove the AMOK* et:asthma tool remove- b. Install lower bracket _using one 0303343 sport nne bolt attaching the elevator tti the toBits nut 04 l'0446.31* tOtfet141: f. Open the hot binged bolt smee e loaatsta c. Inspect installation of upper andlower bearing ems& the underside sat the hmktimeal E brackets to check nut and toner Inn installation...... mkt and pot tilt 00 nisi treating edge of the d, Install upper toll assembly 016a aft 1.4A./1 t044/ Ittnitentalaamedtehltatit bolt and NotS6'79A.417 mat with an ltd washes biionove the- two .44st.04 diottrt pilits utuier the boil heed and under the rtes. 00 head is op. toattai KIkatfuntid stabilizers station 43:114. e, Insult lower 1.94 *ounkly oins 111) ishil7410t lb. Disconnect. WI; tapeand stow eltwator.ttina tab bolt and.NASh7944W:norwitb,att,ANSictiVOCINaeher* Abler (ear tom .* -with -44 tliwatot, Zakabstrictemfor under the bolt heiet# ?::tint under the nut. Bois bead titt tiShg titvw.ttitit tab etc dkattested in that fuse dawn. Leawire is ;ls a sad m lower lever. tags tall eol*. me* "rum buckdOt iot ;heti* altinttop E 1.Inspect installation of upper and lower rod assem- tab are toconnetted aripicatts acmes tIstongb ateett pail on the Waiting *Igo of &e browlett ltafe. Eblies for tightness of attachments and lock-wiring of lower bolt head. vomit subillut
AM.225 Figure 2-2.Typical page of a Maintenance Instructions Manual.
19 AVIATION STRUCTURAL MECHANIC S 3 & 2 power requirement (item 13) for the shop chief's and contains information for use at Intermediate use in assigning personnel to perform the job. and Depot level facilities. Alltools and equipment other than standard The Structural Repair Manual is identified by tools are noted (item C) ahead of the main- a "-3" in the manual publications code (fig. 2-1). tenance procedure, so that these items may he The two volumes are further identified by an drawn from the toolroom prior to starting the additional dash number. An example of the code operation. for a Structural Repair Manual in current use is When consumable materials such as i,ibri- NA 01-75PAA-3-I. This is the code for Volume cants, lock wire, and cotter pins are required I of the Structural Repair Manual for the P-3A during an installation procedure, alisting of aircraft. theseitems (item D) is made ahead of tho Each volume of the Structural Repair Manual proceduralsteps.Miscellaneoussmallparts isdividedinto sections.Section 1 contains (other than standard AN and MS hardware), information of a general nature. Each of the which are necessary for removal and installation, other sections contains information of a more also appear in the materials list. specific nature. These sections cover portions of As an aid to Quality Assurance Representa- the aircraft such as wings, tail, fuselage, alighting tives, those steps in a procedure which require gear,andengines. Thereisalsoa section an inspection are set in in italics (items marked covering typical repairs. E). (NOTE: In some MIM's the steps ina BeforeattemptingtousetheStructural procedure which require a Quality Assurance Repair Manual, the .mechanic should read the inspection are underlined. ) These italicized steps introductionto VolumeI.Included inthe are a very important feature and are summarized introduction is information concerning the use (item F) at the end of each procedure. of the manual. NOTE: Since the format of the Classifiedmaintenanceinformation isnot various Structural Repair Manuals may differ, included in the regular volumes of the Main- the instructions in the introduction may differ tenance Instructions Manual. Essential classified slightly. information is contained in separate volumes or TheStructuralRepairManual is sup- supplements of the Maintenance Instructions plemented by the NA 01-1A Series general Manual, which areclassified"confidential." manuals. Classified volumes of the Maintenance Instruc- tions Manual are bound in red in order that they Periodic Maintenance may be readily identified. These volumes must Requirements Manual be handled in accordance with the Department of the Navy Security Manual for Classified This manual contains the complete require- Information (OpNav Instruction 5510.1 Series). mentsforinspectionoftheaircraft,its components, and accessories. The inspection Structural Repair Manual requirements are stated in such a manner as to establish what equipment isto be inspected, The Structural Repair Manual is used as a when it is to be inspected, and what conditions guide in making structural repairs to the air- are to be sought. It does not contain instructions frame. It contains general information such as forrepair,adjustment,or other means of airframesealing, control surface rebalancing, correctingdefectiveconditions, nor doesit general shop practices, damage evaluation and contain instructions for troubleshooting to find support of structure, and a description of the causes for malfunctioning. structure through the medium of indexed il- lustrations and repair drawings. Periodic Maintenance The Structural Repair Manual for most new Requirements Data aircraft is published in two volumes. This is not due to its size but is to suit its usage by different ThePeriodicMaintenanceRequirements facilities. Volume Iis for use at all levels of Manuals are being replaced by periodic main- maintenance. Volume II supplements Volume 1 /enance requirements data contained in three
20 Chapter 2AERONAUTIC PUBLICATIONS types of publicationsPeriodic Maintenance In- ment, and special support equipment subject to formation Cards (PMIC), Maintenance Require- separate maintenance. ments Cards (MRC), and Sequence Control Charts (SCC). The latest type 1PB has a separate volume for The PMIC's have a listing of items having an theNumerical Index. The Numerical Index approved mandatory replacement interval and contains an alphanumeric listing of all the parts thoseitemsrequiringscheduledremoval in the IPB or volume. In addition to the part component cards as defined in Op Nav Instruc- numbers, the Numerical Index contains such tion 4790.2. information as federal stock number data figure They also contain a maintenance reference and index numbers, source code data, and table that lists those publications which have recoverability information. been incorporated in the maintenance require- The number of IPB manuals for some aircraft ments since the last revision. are numerous and for this reason some of the The Maintenance Requirements Cardsand the aircraft manufacturer's have published a Master Sequence Control Chart are discussed in Military Locator Index in conjunction with their 1PB. Requirements for Petty Officer 3 & 2, NavPers This Master Locator Index is used to locate the 10056-C, Chapter 14. IPB manual in which the part number is shown when only the part number is known. Most Master Locator Index pages are divided into 4 Illustrated Parts Breakdown columns, each containing a part number and a manual number column. The number shown in the "Manual Number" column is the last dash The purpose of the Illustrated Parts Break- number of the NavAir IPB manual in which the down (IPB) is to assist supply, maintenance, and partwillbefound.Example:PartNo. overhaul personnel in the identification, requisi- 128B10855, for an A-6A Aircraft, listed in the tioning, storing, and issuing of parts for the Master Locator Index, shows a "3" in the applicable aircraft. "Manual Number" column. This means that The IPB for older aircraft, like the Main- complete information on the part will be found tenance Instructions Manual, may be found in in A-6A IPB, NavAir 01-85ADA-4-3. Once one volume. The IPB prepared forcurrent directed to a specific volume of the 1PB the part productionaircraft contains several volumes, can be further traced through the use of that which usually correspond to the volumes in the volume's numerical index. Maintenance Instructions Manual. The IPB, like the Maintenance Instructions Prior to using any volume of the IPB, all of Manual, has a code number. A "-4" in part Hi of the information in Section I should be read. The the publications code (fig. 2-1) identifies the information contained in this section will aid the IPB. The individual volumes of the IPB are AMS in locating the necessary part or parts identified by an additional dash and number. An quickly and easily. example of the code number for an IPB in current useis NA 01-60ABC-4-3. This is the code numberfortheMechanical Controls Technical Manual of volume of the RA-5C 1PB. Weight and Balance Data Each volume of the IPB is divided into at least two sections and sometimes threeSection I, This manual provides a standard system for Introduction, Sectici II, Group Assembly Parts fieldweight and balance control of certain List, and Section ILwhen used,- Numerical aircraft. The forms, charts, and records in this Index. The Introduction (Section I) contains manual are prepared by the manufacturer prior detailed instructions for the use of the IPB. to delivery of the aircraft to the Navy and Section II includes illustrations of all pare of provide the means of maintaining a continuous the applicable aircraft and its systems, equip- and current record of the basic weight and
21 AVIATION STRUCTURAL MECHANIC S 3 & 2 balanceand loading information duringthe provide adequate instructions for operating the aircraft's service life. item and maintaining it throughout its service Procedures and instructions for maintaining life.AccessoriesManualsthereforecontain the weight and balance records are contained in descriptive data; detail instructions for installa- the manual. These records must be maintained tion, operation, inspection, maintenance, and by operating and overhaul activities and must be overhaul; and an illustrated parts list. All Acces- brought up to date 'prior to transfer of the sories Manuals available for issue are listed in aircraft. The manual must be retained in the numerical order (by publication number) in the aircraft at all times. Accessories Section of Part C, Section VIII of NavSup Publication 2002. They are also listed in 00-500A, but in alphanumeric order according General Aircraft Manuals (01 Series) topartnumber.In00-500B,Accessories Manuals are listed under the aircraft in which the accessory is installed. To avoidconfusion between the General Accessories Manuals are used to supplement Manuals (00 series) and general Aircraft Manuals information found in the aircraft Maintenance (01series), an explanation isin order at this Instructions Manual. For example, when the point.Thischapter is concernedwith Maintenance Instructions Manual does not give AERONAUTIC publications. There are many instructionsforrepairingaparticular item, generalaeronauticpublications that do not referenceshould be made to the applicable directly concern aircraft; these are in the 00 Accessories Manual. series. There are other manuals that are ap- plicabletoaircraft in general without being If an accessory is relatively simple, all the identifiedwithaspecific model; theseare necessary instructions may be contained in a general AIRCRAFT manuals. Some general air- single manual. An example is NA 03-25BA-19, craft manuals with which the AMS works are as OverhaulInstructionswithIllustratedParts follows: Breakdown for a landing gear wheel manufac- tured by the B. F. Goodrich Company. NA 01-1A-1, General Manual for Structural More complex accessories may require two or Repair. more, manuals. For example, one manual may NA Ol-1 A-8, AircraftStructural Hardware cover operation, service, and overhaul instruc- for Aircraft Repair. tions, while the parts breakdown is contained in NA 0l -1A -509, Aircraft Cleaning and Cor- a separate manual. rosion ControlforOrganizational and Inter- To determine what manuals are available for a mediate Maintenance Levels. particular accessory, proceed as follows: If the name of the manufacturer and the model/part number of the item are known, turn ACCESSORIES MANUALS (03 SERIES) tothe alphanumeric part number listingin NavAir 00-500A andlocatetheitem.All The 03series manuals cover all types of manuals applicable to that particular item of accessories. An accessory is defined as any item equipment will be listed by code number along of equipment which is required for operation of with the item nomenclature. the aircraft and which cannot be considered an integral part of the airframe or engine. Examples of accessories for which the AMS is responsible SUPPORT EQUIPMENT MANUALS are aircraft wheels and helicopter rotor com- (17, 18, AND 19 SERIES) ponents. The manufacturer of each item of support The manufacturer of each item of equipment equipmentisrequiredtofurnishadequate (wheels, valves, cylinders, etc.)is required to instructions for operating the equipment and
22 Chapter 2AERONAUTIC PUBLICATIONS
maintaining it throughout its service life. Like personneltoinjury or propertytoloss or aircraft Maintenance Instructions Manuals and damage., Accessories Manuals, these publications prepared Safetyprecautionsshallbepostedina by the manufactuier are issued under the au- conspicuous place on or near any equipment, thority of the Naval Air Systems Command and component, or material which presents a hazard are then official Navy publications. to the security of the activity or to the safety of personnel.Forexample,thoseprecautions The 17 and 18 series of aeronautic manuals necessary for the safe handling, stowage, and provide information and instructions for most securityofdangerousmaterialssuchas tools, machinery, and test equipment used in explosives or flammables shall be posted at or support of aircraft and components. Each item near the storage spaces designated for those iscovered by a manual which contains the materials. purpose, procedures for preparing the item for Each individual is responsible for knowing, use, operation, inspection, maintenance, lubrica- understanding, and observingallsafetypre- tion, troubleshooting, and other pertinent data. cautions applicable to his work and work area. The 19 series manuals contain information on All chapters of the Safety Precautions Manual groundservicingand automotive equipment are extremely important; and the AMS should related to performing aircraft maintenance. be especially concerned with the chapter titled Aviation.Thischaptercoversgeneralpre- SupportEquipment Manuals are stocked, cautions applicable to the maintenance, repair, cataloged,listed,andlocatedinthesame and overhaul of aircraft. manner as Accessories Manuals. NOTE: Groundsupportequipmentdata formerly provided as Descriptive Data Sheets TECHNICAL INFORMATION FILE (20 Series publications) are now identified as OF GROUND SUPPORT EQUIPMENT GroundSup portEquipmentIllustrations (GSEI). This information is coordinated with (MI L-HDBK-300B) other branches of the service and is published and identified as MIL-HDBK-300. This publicationis intended to provide, in concise and convenient form, factual pictorial and descriptive data to familiarize designers, SAFETY PRECAUTIONS MANUAL engineering, maintenance and training personnel (NAVMAT P-5100 SERIES) and Government contractors with the charac- teristics, performance capability and physical makeup ofthe ground support equipment The safetyprecautionscontainedinthis presentlyintheinventory of themilitary manual are applicable toall Navy personnel, services and under development for use with military and civilian, and-to all naval commands aircraft and missile systems. In the case of and activities. They are of necessity basic and Government contractors, the data sheets are general in nature and are not inclusive of all intended to provide sufficient information for conceivable operations and functions involved in determining that an item of equipmentis the great variety of Navy activities. In many suitable or unsuitable for a contemplated ap- instances references are made to other publica- plication. This will insure the following: tions for detailed safety precautions applicable to specific conditions. A lack of documented 1. Maximum usage of in-service assets. hazards and pertinent precautions is not to be 2. Elimination of duplicate design or develop- construed as an indication of their nonexistence ment of ground support equipment for different orunimportance; therefore,thecontinuous weapon systems. cooperation and vigilance of all peisonnel, is needed to see that all operating procedures and Thishandbookcontainsinformationon work methods do not unnecessarilye-(pose ground support equipment foraircraft and 23 AVIATION STRUCTURAL MECHANIC S 3 & 2 missile weapon systems. Ground support equip- cannot be satisfactorily disseminated by revi- ment is construed to include ground operation, sions or changes totechnical manuals. This handling,andservicingequipment. Ground informationisdisseminated inthe form of support equipmentisfurther definedas all Changes, or in the case of special circumstances, equipment required on the ground to make a by Interim Changes or Bulletins. weapon system operationalinitsintended A formal TD isa document issued asa environment. Change, orasan Amendment or Revision Data sheets for the Technical Information thereto, and promulgated byletter. Formal File (T1F) will normally be selected or sub- technical directives are used to direct the ac- mitted only for ground support equipment items complishment and recording of modifications to that have a unit cost of $1,000 and over or a weapons, weapons systems, support equipment, potential or actual procurement total dollar trainers,andrelatedequipmentandare value in excess of $100,000, regardless of unit comprised of Changes and Amendments and/or cost. Revisions thereto. Data sheets will not normally be acquired or An interim TD isa document issued as a submitted for common tools or power tools Bulletin or a Change, or as an Amendment or normally found ina standard machine shop; Revision thereto, and promulgated by message component parts or sub-assemblies of end items; to insure speedy dissemination. The interim TD kits, sets of tools, fixtures for manufacturing in isreservedfor those instances requiring im- depotuse;sling,,,iapters,smallcontainers, mediate correction of an operational or safety cabinets; or obsolete items of supply. condition which embodies risks calculated to be This handbook supersedes individual descrip- intolerable within the lead time of a formal tivedata sheets which were previously issued directive or maintenance publication change. separately for each item of support equipment Interim Changes are superseded by a Formal not covered by an individual technical manual. Change directive which will have the same number a's the interim directive. Interim Bulletin directives are not superseded by formal Bulletins as was previously the case. The Nav Sup Publica- LETTER TYPE PUBLICATIONS tion 2002, Section VIII, Part D, will still have many formalBulletinslisteduntiltheyare TECHNICAL DIRECTIVES eventually phased out. A Change is a document containing instruc- The Technical Directive (TD) System has tions and information which directs the ac- been established for control and issue of all complishmentandrecordingof a material technical directives. This system standardizes the change, a repositioning, a modification, or an method of issuance for such directives and is the alteration in the characteristics of the equipment authorized means for directing the accomplish- to which it applies. A Change is issued to direct mentandrecordingofmodifications and that parts be added, removed, or changed from one-time inspections to equipment procured by theexistingconfiguration orthat parts or and for the NavAirSysCom. The TD system is an material be altered, relocated, or repositioned. important element in the programs designed to A Change may be issued inparts to ac- maintain equipment in a configuration which complish distinct parts of a total directed action providesthe optimum conditions of safety, or to accomplish action on different configura- operational, and material readiness. The system tions of affected equipment. A Change may also encompasses two types of technical directives be issued for record purposes. A Record Purpose differentiated by their method of dissemination. Change is a TD issued to provide documentation These two types are Formal (letter type) and of a modification which has been completely Interim (message type). In general terms, they incorporatedbythecontractor or inhouse are both consideredasletter type technical activity in all accepted equipment and which directives. Such directives contain instructions does not require retrofit or the modification of or information of atechnical nature which iepairables in the Navy's possession.
24 Chapter 2AERONAUTIC PUBLICATIONS
An Amendment is a document comprised of Photographic. information which clarifies, corrects, adds to, Support Equipment. deletes from, makes minor changes in require- Airborne Weapon. mentsto,or cancels anexistingtechnical Clothing and Survival Equipment. directive. It '; only a supplement to the existing Target Control System. directive and not a complete directive in itself. A Meteorological Equipment. maximum of three Amendments may be applied to any TD, each remaining ineffect until If the technical directive involves safety of rescindedor superseded by aRevision. A flight, the word "SAFETY" will appear im- requirementforfurtheramendment action mediately following the title and number. necessitates the issuance of a Revision. Technical directives are numbered by two A Revision is a completely new edition of an differentmethods.Somearenumbered existing technical directive.It supersedes the consecutively from the beginning of the calendar originaldirective or revision and all existing year with the last two digits indicating the year Amendments. of issue. Thus, a Change or Bulletin designated A Bulletin is an interim document comprised 47-54 would be the 47th change or bulletin of of instructions and information which directs an that type issued in 1954. This type of number- initial inspection to determine whether a given ing system is no longer being used for identify- condition exists. It specifies what action is to be ing new directives. However, those which have taken if a given condition is found or not found. been numbered in this manner and are still in Interim Bulletin directives are self-rescinding effect are cataloged under this system. withrescissiondatesof 30 Juneor31 The present numbering system isa conse- December, whichever is appropriate for the case cutive numerical application regardless of the at hand. Rescission is the process by which the year of issue. For example, F-4 Airframe Change filesafter all TD's are removed from active 204 would be the 204th Airframe Change that is requirementshave been incorporated.Final applicable to the F-4 aircraft. This numbering rescission action is directed in the TD Index, system has been in effect for some time and Nav Sup Publication 2002, Section VIII, Part D. most technical directives are cataloged under Allactivitiesmaintainingactivetechnical libraries must maintain the TD's on file until this system. assignedtoChangesand they are deleted from the TD Index. Thenumbers Cancellation of a technical directive is the Bulletinsareprovidedby theTechnical process whereby the TD is removed froin the Directives Control Center, which is located at TechnicalServicesFacility active files when it is determined that a previous- theNavalAir ly issued TD is not to be incorporated. Cancella- (NATSF), Philadelphia. Changes or Bulletins tion is directed by the issuance of an Amend- that have been amended will have their basic ment to the TD. The cancellation explicitly number followed by the words "Amendment states the required configuration of each article I," "Amendment 2," etc. A revised directive initially specified for modification; for example, will have the basic directive number followed whether installed modifications are to remain with the words "Rev. A," "Rev. B," etc., as installed or are to be removed, etc. appropriate to denote the first, second, etc., The title subject of a Change or Bulletin will revisions to that basic directive. be one of the following, as appropriate: The Changes and Bulletins are automatically distributed to all concerned activities through Airframe. inclusion on the Mailing List Request for Aero- Powerplant. nautic Publications, Nav Air Form 5605/3., All Avionics. TD's are issued by Nav Air or NavAirTechSerFac Accessory. except in cases where the time delay in obtain- Aviation Armament. ing approval is unacceptable. In such cases the Aircrew System. controlling custodians are authorized to issue Propeller. interim TD's to preclude unacceptable risks to
25 AVIATION STRUCTURAL MECHANIC S 3 & 2
personnel or equipment. The Changesor Bulle- scheduled basis, not later than 18 months after tins are generally based on Contractor Service the date of issuance. Bulletins, other letters of recommendation,or Routine Action directives are issued where proposed modifications from field service activ- there arereliability,capability,or maintain- ities. ability deficiencies which could, if uncorrected, become a hazard through prolonged usageor Directive Categories have an adverse effect on the operational lifeor general service utilization of equipment. The Technical directives are assigned a "category" conditions embody a degree of risk or require- in accordance with the importance and urgency ment determined to be tolerable within a broad of accomplishing the work involved. A category time limit. The compliance requirement specifies of Immediate, Urgent,Routine, orRecord the incorporation of the instructions not later Purposes is assigned each technical directive. than the next regularly scheduled overhaulor The category "Immediate Action" is assigned rework, or for equipment not reworkedor to directives which are issued to correct safety overhauled on a scheduled basis, not later than conditions, the uncorrected existence of which 16 months after issuance of the directive. If would probably result in fatal or serious injury accomplishment of the work requires Depot to personnel, extensive damage, or destruction levelmaintenance capability, the compliance of property. Immediate Action directives involve may be deferred if it will seriously interfere with the discontinued use of the aircraft, engines, or operationalcommitmentsorschedules. equipment in the operational employment under Routeine Action directives are identified by the which the adverse safety condition exists, until words "ROUTINE ACTION" printed in black the directive has been complied with. If the use capital letters at the top center of thecover of the aircraft, engines, or equipment will not page. involve the use of the affected component or The category "Record Purposes" is used ona system in either normal or emergency situations, technical directive when a modification has been compliance may be deferred, but should be completely incorporated by the contractor or accomplished no later than the next periodic in-house activity in all accepted equipment and inspection for the aircraft and no later than 120 when retrofit is not required on repairables in days from the date of issue for the equipment. the Navy's possession. They are identified by the The Immediate Action directive is identified by words "RECORD PURPOSES" printed in black a border of red X's broken at the top center of capital letters at the top center of the cover thepage IJ y thewords"IMMEDIATE page. This type of TD merely documents the ACTION," also printed in red. action for configuration management purposes; The category "Urgent Action" is assigned to therefore, compliance informationis not ap- directives which are used to correct safety plicable and is indicated as such. conditions which, if uncorrected, could result in personnelinjuryor property damage. Such conditions compromise safety and embody risks INSTRUCTIONS AND NOTICES calculated to be tolerable within narrow time limits and may or may not necessitate the InstructionsandNoticesaredirectives impositionof operatingrestrictions.Urgent containinginformationandinstructions Action directives are identified by the words concerning policy, administration, and air opera- "URGENT ACTION" minted in red ink at the tions. They are issued by all bureaus, systems top of thefirstpage and a border of red commands,ships,stations,andoperating diagonals around the cover page. activities. Those issued by the Naval Air Systems The compliance requirement specifies that the Command are known as NavAir Instructions and incorporation of the instructions must be ac- Notices. complished not later than the next regularly Instructions aredirectives of a continuing scheduled rework or overhaul or for equipment nature and are effective until canceled or super- notreworked or overhauled on aregularly seded by a later directive. 26 Chapter 2--AERONAUTIC PUBLICATIONS
Notices are directives of a one-time nature or by the U. S. Naval Aviation Safety Center and is directives which are applicable for a brief period distributed to all naval aeronautic organizations of time. Each Notice contains a provision for its on the basis of I copy for every 10 persons. It own cancellation. presents the most accurate information current- Instructionsarenumberedinconsecutive ly available on the subject of aviation accident order according to the subject covered in the prevention. Instruction. Notices are numbered according to A large number of aviation accidents are the subject covered and serialized by the date of maintenence-induced; that is, they occur during issue. They may be addressed to "All Ships, preparation for, performance of, and securing Stations, and Units concerned with Naval Air- from maintenance or as a result of sloppy or craft," or to certain activities only. Each activity impropermaintenance.Forinstance,one maintains a file of all pertinent Instructions and fatality was reported which occurred when a Notices still in effect. nuintenance man unintentionally ejected him- self while arming an ejection seat. Additionally, a recent statistic reported in Approach revealed MISCELLANEOUS AVIATION that in 9 accidents during a recent 15-month PUBLICATIONS period 9 aircraft were lost-9 million dollars lost due to the omission of 9 cents worth of cotter Several otherunofficialpublicationsof pins. general interest to aviation personnel are avail- The Approach magazine reports the results of able in most operating activities. These should accident investigations; and for those accidents be read regularly by all maintenance personnel. that are maintenance-induqed, describes what was done wrong and how it should have been NAVAL AVIATION NEWS done; suggests corrective measures to prevent future accidents resulting from these causes; and The Naval Aviation News, Nav Air 00-75R-3, when appropriate,cites aeronautic technical publications ispublished monthly by the Chief of Naval whichprovideauthorityfor Operations and the Naval Air Systems Com- changes in techniques or material to improve the mand. Its purpose isto disseminate data on maintenance product. aircrafttraining and operations, space tech- In short, the maintenance man who reads and nology,missile,rocket, and otheraviation heeds the messages in Approach is the man who ordnance developments, aeronautical safety, air- benefits from other mechanics' experiences. Put craft design, powerplants, aircraft recognition, Approach on your required reading list and look technical maintenance, and overhaul procedures. for it every month. As its name implies, this publication is es- sentially a news magazine. It enables readers to keep abreast of the latest unclassified develop- ments in every facet of naval aviation. In ad- MECH dition, the coverage of fleet operations and the human interest articles on the noteworthy feats MECH ispublished quarterly by the U.S. and accomplishments of individuals, both officer Naval Safety Center and is distributed to naval and enlisted, make the Naval Avis ion News an aeronautic organizations on the basis of 1 copy entertainingas wellasaninformational per 10 persons. It prese.:ts the most accurate periodical. informationavailable on maintenance-caused mishap prevention and general aviation ground APPROACH safety. Contents are informational and should not be considered as regulations, orders, or Approach, Nav Air00-75-510,The Naval directives.Reference to commercial products Aviation Safety Review, is published monthly does not imply Navy endorsement.
27 CHAPTER 3
AIRCRAFT MATERIALS
In this chapter we will discuss the properties, aircraft maintenance and repair, even a slight characteristics, and uses of various materials deviation from designspecifications orthe used in the construction of aircraft, primarily substitution of inferior materials may result in metals and plastics. An AMS should have a the loss of both lives and equipment. The use of knowledge and understanding of these proper- unsuitable materials can readily erase the finest ties, characteristics, and uses in order to inspect, craftsmanship. The selectionof the specific maintain, andrepairthe airframe properly. materialforaspecificrepair job demands An AMS is required to inspect metals for flaws familiarity with the most common properties of anddefects.Therefore, information on the various metals. general procedure for the inspection of metals using the dye penetrant method isalso dis- PROPERTIES OF METALS cussed. This section is devoted primarily to the terms used in describing various properties and charac- AIRCRAFT METALS teristics of metals in general. Of primary concern in aircraft maintenance are such general proper- Metallurgists have been working for more ties of metals and their alloys as hardness, than a half century improving metals for aircraft malleability,ductility,elasticity,toughness, construction. Each metal has certain properties density,brittleness,fusibility,conductivity, and characteristics which make it desirable for a contraction and expansion, etc. The AMS must particular application, but it may have other know the definition of the terms included here qualitiesthatare undesirable. For example, as they form the basis for fufiller discussion of some metals are hard, others comparatively soft; aircraft metals. some arebrittle, some tough; some can be formed and shaped without fracture; and some are so heavy that weight alone makes them Hardness unsuitable for aircraft use. The metallurgist's objectives are to improve the desirable qualities Hardness refers to the ability of a metal to and tone down or eliminate the undesirable resist abrasion, penetration, cutting action, or ones. This is done by alloying (combining) of permanent distortion.Hardness may be in- metals and by various heat-treating processes. creased by working the metal and, in the case of One does not need to be a metallurgist to be a steel and certain titanium and aluminum alloys, good AMS, but he should possess a knowledge by heat treatment and cold-working (discussed and understanding of the uses, strengths, limita- later). Structural parts are often formed from tions,andothercharacteristicsofaircraft metals in their soft state and then heat treated structural metals. Such knowledge and under- to harden them so that the finished shape will be standingisvitaltoproperly construct and retained.Hardness and strength are closely maintain any equipment, especially airframes. In associated properties of all metals.
28 Chapter 3AIRCRAFT MATERIALS
Brittleness members and parts are so designed that the maximum loads to which they are subjected will Brittleness is the property of a metal which never stress them beyond their elasticlimit. allows little bending or deformation without (NOTE: STRESS is the internal resistance of shattering. In other words, a brittle metal is apt any metal to distortion.) This desirable property to break or crack without change of shape. (elasticity) is present in.metals used for making Because structural metals are often subjected to springs. shock loads, brittleness is not a very desirable property. Cast iron, cast aluminum, and very Toughness hard steel are brittle metals. A material which possesses toughness will Malleability withstandtearing or shearing and may be stretched or otherwise deformed without break- A metal which can be hammered, rolled, or ing. Toughness is a desirable property in aircraft pressed into various shapes without cracking or metals. breaking, or other detrimental effects, is said to be malleable. This property is necessary in sheet Density metal which is to be worked into curved shapes Density is the weight of a unit volume of a such as cowlings, fai-h,gs, and wingtips. Copper material. In aircraft work, the actual weight of a is one example of malleable metal. material per cubic inch is preferred since this figure can be used in determining the weight of a Ductility part before actual manufacture. Density is an important consideration when choosing a mate- Ductility is the property of a metal which rial to be used in the design of a part and still permits it to be permanently drawn, bent, Or maintain the proper weight and balance of the twisted into various shapes without breaking. aircraft. This propertyis essential for metals used in making wire and tubing. Ductile metals are Fusibility greatly preferred for aircraft use because of their ease of forming and resistance to failure under Fusibility is defined as the ability of a metal shock loads. For this reason, aluminum alloys to become liquid by the application of heat. are used for cowl rings, fuselage and wing skin, Metals are fused in welding. Steels fuse around and formed or extruded parts, such as ribs, 2,500° Fahrenheit (F) and aluminum alloys at spare, and bulkheads. Chrome-molybdenum steel approximately 1,110°F. isalsoeasilyformedintodesiredshapes. Ductility is similar to malleability. Conductivity
Elasticity Conductivity is the property which enables a metal to carry heat or electricity. The heat Elasticityisthat property which enables a conductivity of a metal is especially important metal to return to its original shape when the in welding, because it governs the amount of force which causes the change of shapeis heat that will be required for proper fusion. removed. This property is extremely valuable, Conductivity of the metal, to a certain extent, because it would be highly undesirable to have a determines the type of jig to be used to control part permanently distorted after an applied load expansion and contraction. In aircraft, electrical was removed. Each metal has a point known as conductivity must also be considered in conjunc- the ELASTIC LIMIT beyond which it cannot be tion with bonding, to eliminate radio interfer- loaded without causing permanent distortion. ence. Metals vary in their capacity to conduct When metal is loaded beyond its elastic limit and heat. Copper, for instance, has a relatively high permanent distortion does result, itis said to rate of heat conductivity and is a good electrical have been STRAINED. In aircraft construction, conduct or,
29 AVIATION STRUCTURAL MECHANIC S 3 & 2
Contraction and Expansion apart. Tensile strength is measured in pounds per square inch (psi) and is calculated by dividing Contractionandexpansionarereactions the load, in pounds required to pull the material produced in metals as the result of heating or apart,byitscross-sectionalarea,insquare cooling. A high degree of heat applied to a metal inches. Metal being pulled is under tension. will cause it to expand or become larger. Cooling COMPRESSION.Compression is the hot metal will shrink or contract it. Contraction opposite of tension. The compressive strength of and expansion affect the design of welding jigs, a material isits resistance to a crushing force, castings, and tolerances necessary for hot-rolled whichistheoppositeoftensilestrength. ma terial. Compressive strength is also measured in psi. SHEAR.Shear is the tendency on the part of QUALITIES OF METALS parallel members to slide in opposite directions. Itis like placing a cord or thread between the The selection of proper materials is a primary blades of a pair of scissors. In fact, that is how consideration in the development of an airframe shears got their name. When a piece of metal is and in the proper maintenance and repair of being cut with shears, the material is subject (as aircraft. Keeping in mind the general properties it comes in contact with the cutting edges) to of :netals,itis now possible to consider the shear. The shear strength is the shear force in specific requirements which metals must meet to pounds per square inch at which a material fails. be suitable for aircraft purposes. It is the load divided by the shear area. Strength, weight, and reliability--these three BENDING.Bending may be described as the factors determine the requirements to be met by deflection or curving of a member due to forces any material used in airframe construction and acting upon it. The bending strength of material repair. Airframes must be strong and also as light is the resistance it offers to deflecting forces. in weight as possible. There are very clef -:'c TORSION.Torsion is a twisting force. Such limits to which increases in strength can be action would occur in a member fixed at one accompanied by increase in weight. An aircraft end and twisted at the other. The torsional so heavy that it could not support more than a strength of material is its resistance to twisting. few hundred pounds of additional weight would be of little use in this age. All metals, in addition Weight to having a good strength/weight ratio, must be thoroughly reliable,thus minimizing the pos- The relationship between the strength of a sibility of dangerous and unexpected failures. In material and its weight per cubic inch, expressed addition to these general properties, the material asaratio,is known asthe STRENGTH/ selected for definite application must possess WEIGHT RATIO. This ratio forms the basis of specific qualities suitable for the purpose. comparing the desirability of various materials In determining the most suitable material for foruseinairframe construction and repair. a particular aircraft construction or. repair job, Neither strength nor weight alone can be used as the following qualities must be considered. a means of true comparison. In some applica- tions, such as the skin of monocoque structures Strength (ch.4),thicknessismore importantthan strength; and in this instance, the material with Thematerialmustpossessthestrength the lightest weight for a given thickness or gage required by the demands of dimensions, weight, is best. Thickness or bulk is necessary to prevent and use. There arefive basic stresses which buckling or damage caused by careless handling. metals may be required to withstand. These are tension,compression,shear,bending,and Corrosive Properties torsion. Each isexamined separately in the following paragraphs. Corrosion is the eating away or pitting of the TENSION.The tensile strength of a material surfaceor the internal structure of metals. is its resistance to a force which tends to pull it Because of the thin sections and the safety
30 Chapter 3AIRCRAFT MATERIALS factors used in aircraft design and construction, failure. Resistance to this condition is known as itwould be dangerous toselecta material shock and fatigue resistance. It is essential that subject to severe corrosion if it were not possible materials used for critical parts be resistant to to reduce or eliminate the hazard. Corrosion can these stresses. be reduced or prevented by using better grades The preceding discussion of the properties of base metals; coating the surfaces with a thin and qualities of metals is intended to show why coating of paint, tin, chromium, or cadmium; or the AMS must know which traits in metals are by an electrochemical process, called anodizing. desirable and which are undesirable to do certain Corrosion and its control is discussed at length jobs. The more one knows about a given in chapter I I. material, thebetter able heisto handleit intelligently in airframe repair. Working Properties METAL WORKING PROCESSES Another significant factor to consider in the selection of metals for aircraft maintenance and When metal is not cast in a desired manner, it repair is the ability of material to be formed, isformed into special shapes by mechanical bent,or machined to required shapes. The working processes.Severalfactors must be hardening of metals by cold-working or forming considered when determining whether a desired is termed WORK HARDENING. If a piece of shape is to be cast or formed by mechanical metal is formed (shaped or bent) while cold, it is working.Iftheshapeisvery complicated, said to be cold-worked. Practically all the work casting willbe necessary in order to avoid an AMS does on metal is cold-work. While this is expensive machining of mechanically formed convenient, it causes the metal to become harder parts. On the other hand, if strength and quality and more brittle. of material are the prime factors in a given part, If the metal is cold-worked too much (that is, a casting will be unsatisfactory. For this reason, if it is bent back and forth or hammered at the steel castings are seldom used in aircraft work. same place too often), it will crack or break. There are three basic methods of metalwork- Usually, the more malleable and ductile a metal ing; namely, hot-working, cold-working, and is, the_more cold-working it can withstand. extruding. The process chosen for a particular application depends upon the metal involved Joining Properties and the part required, although in some in- stances one might employ both hot- and cold- Joiningmetalsstructurallybywelding, working methods in making a single part. brazing, or soldering, or by such mechanical means as riveting or bolting, is a tremendous Hot-Working help in design and fabrication. When all other properties are equal, material that can be welded Almost all steel is hot-worked from the ingot has the advantage. into some form from which it is either hot- or cold-worked to the finished shaped. When an Shock and Fatigue Properties ingot is stripped from its mold, its surface is solid, but the interior is still molten. The ingot is Aircraft metals are subject to both shock and then placed in a soaking pit which retards loss fatigue (vibrational) stresses. Fatigue occurs in of heat, and themolten interior gradually materialswhichareexposedtofrequent solidifies.After soaking, the temperature is reversals of loading or repeatedly applied loads, equalized throughout the ingot, which is then ifthefatiguelimitis reached or exceeded. reduced to intermediate size by rolling, making Repeated vibration or bending will ultimately it more readily handled. cause a minute crack to occur at the weakest The rolled shape is called a bloom when its point. As vibration or bending continues, the sectional dimensions are 6 x 6 inches or larger, crack lengthens until complete failure of the and approximately square. The section is called part results. This is termed shock and fatigue a billet when it is approximately square and less
31 AVIATION STRUCTURAL MECHANIC S 3 & 2 than 6 x 6 inches. Rectangular sections which Cold-Working have width greater than twice the thickness are called slabs. The slab is the intermediate shape Cold-working applies to mechanical working from which sheets are rolled. performed at temperatures below the critical HOT ROLLING. Blooms,billets,or slabs range and results in a strain hardening of the are heated above the critical range and rolled metal. In fact,it becomes so hard thatitis into a variety of shapes of uniform cross section. difficult to continue the forming process with- The more common of these rolled shapes are out softening the metal by annealing. sheet, bar, channels, angles, I- beams, and the Sincetheerrors attendingshrinkageare like. In aircraft work, sheet, bar, and rods are eliminatedincoldworking,amuch more the most commonly used items that are rolled compact and better metalisobtained. The from steel. As discussed later in this chapter, strength and hardness, as well as the elastic limit, hot-rolled materials are frequently finished by are increased, but the ductility decreases. Since cold-rolling or drawing to obtain accurate finish this makes the metal more brittle, it must be dimensions and a bright, smooth surface. heated from time to time during certain opera- FORGING.Complicated sections which can- tions to remove the undesirable effects of the not be rolled, or sections of which only a small working. quantity is required, are usually forged. Forging While t he r e areseveralcold-working of steelis a mechanical working of the metal processes,the two with which the AMS is above the critical range to shape the metal as principally concerned are cold-rolling and cold- desired. Forging is done either by pressing or drawing.Theseprocessesgivethemetals hammering the heated steel until the desired desirable qualities which cannot be obtained by shape is obtained. hot-working. Pressing is used when the parts to be forged COLD-ROLLING.Cold-rolling usually refers arelarge and heavy, and this process also to the working of metal at room temperature. In replaces hammering where high-grade steel is this operation, the materials that have been required. Since a press is slow acting, its force is hot-rolled to approximate sizes are pickled to uniformly transmitted to the center of the removed any scale, after which they are passed section, thus affecting the interior grain struc- throughchilledfinishedrolls.This givesa ture as well as the exterior to give the best smooth surface and also brings the pieces to possible structure throughout. accurate dimensions. The principal forms of Hammering can be used only on relatively cold-rolled stocks are sheets, bars, and rods. small pieces. Since hammering transmits its force COLDDRAWING.Cold-drawing is used in almost instantly, its effect is limited to a small making seamless tubing, wire, streamlined tie depth. Thus, it is necessary to use a very heavy rods, and other forms of stock. Wire is made hammer or to subject the part to repeated blows from hot-rolled rods of various diameters. These to insure complete working of the section. If the rods are pickled n acid to remove scale, dipped force applied is too weak to reach the center, in lime water, and then dried in a steam room the finished forging surface will be concave. If where they remain until ready for drawing. The the center is properly worked, the surface will lime coating adhering to the metal serves as a be convex or bulged. The advantage of hammer- lubricant during the drawing operation. Figure ingis that the operator has control over the 3-1illustrates the drawing of rod, tubing, and amount of pressure applied and the finishing wire. temperature, and is able to produce parts of the The size of the rod used for drawing depends highest grade. upon the diameter wanted in the finished wire. This type of forging is usually referred to as To reduce the rod to the desired wire size, it is smith forging and is used extensively where only drawn cold through a die. One end of the rod is a small number of parts are needed. Consider- filedor hammered toa point and slipped able machining and material are saved when a through the die opening, where it is gripped by partissmithforgedto approximately the the jaws of the draw, then pulled through the finished shape. die.This series of operations is done by a
32 Chapter 3- AIRCRAFT MATERIALS mechanism known as the drawbench, as shown and more resistant to impact. Heat treating can in figure 3-1. also make a metal softer and more ductile. No In order to reduce the rod gradually to the one heat-treating operation can produce all of desired size,itis necessary to draw the wire these characteristics. In fact, some properties are through successively smaller dies. Because each often improved at the expense of others. For of these drawings reduces the ductility of the example,inbeing hardened,ametal may wire, it must be annealed from time to time become brittle. before further drawings can be accomplished. All of the heat-treating processes are similar in Although cold-working reduces the ductility, it that they involve three stepsheating the metal increasesthetensilestrengthofthe wire to a specific temperature, holding or soaking at enormously. the specified temperature for a definite period, In making seamless steel aircraft tubing, the andcooling. They differ,however,inthe tubing is cold-drawn through a ring-shaped die temperatures to which the metal is heated, the with a mandrel or metal bar inside the tubing to time at temperature, the rate at which itis supportitwhile the drawing operations are cooled, and, of course, in the final result. being performed. This forces the metal to flow The most common forms of heat treatment between the die and the mandrel and affords a for ferrous metalS (metals containing an iron means of controlling the wall thickness and the base)are hardening, tempering, normalizing, inside and outside diameters. annealing, and casehardening. Most nonferrous metals (aluminum, magnesium, titanium, copper Extruding etc.) can be annealed and many of them can be hardened by heat treatment. An AMS should The extrusion process involves the forcing of have a general understanding of the following metal through an opening in a die, thus causing heat-treating terms, definitions, and processes. the metal to take the shape of the die opening. ANNEALING is a heat-treating operation in Some metals such as lead, tin, and aluminum which a metal is heated to a temperature above may be extruded cold; but generally, metals are its recrystallization point and is then cooled heated before the operation is begun. slowly. Its purpose may be to induce softness, The principaladvantage of the extrusion alter ductility, or refine the grain size of the process is, in its flexibility. Aluminum, because metal. During annealing, the metal is usually of its workability and other favorable properties, cooled in a furnace, or is packed in insulating can be economically extruded to more intricate material to retard cooling. shapes and larger sizes than is practicable with CASEHARDENING is a heat-treating opera- manyothermetals.Extrudedshapesare tion in which the surface of the metal is made produced in very simple as well as extremely hard and wearresistantwhile theinterior complex sections. remains relatively soft and tough. In this opera- A cylinder of aluminum, for instance,is tion,the surface of the metal isaltered in heated to 750' to 850°F and is then forced composition by adding carbon, nitrogen, or a through the opening of a die by a hydraulic ram. combination of both. Many structural parts, such as stringers, are CRITICAL TEMPERATURE RANGE is the formed by the extrusion process. temperature at which a ferrous metal undergoes a change in internal structure while being heated HEAT TREATMENT or cooled (also called transformation range.) NORMALIZING is a heat-treating operation Heat treatmentisaseries of operations involving the heating of a ferrous metal above its involving the controlled heating and cooling of a critical temperature range and cooling it in still metal in its solid state. Heat treating is for the air for the purpose of removing stresses. purpose of obtaining or restoring certain desired PRECIPITATION HEAT TREATMENT is an characteristics or conditions so that the metal aging treatment for nonferrous alloys, usually will be more suitable for a specific use. By heat performed at room or slightly elevated tempera- treating, a metal may be made harder, stronger, tures. Certain aluminum alloys are given this
33 AVIATION STRUCTURAL MECHANIC S 3 & 2
HOT ROLLED DRAWING JAW ROD DRAWN ROD
Li> 25% TO 45% REDUCTION STEEL DIE FOR EACH DRAW
MANDREL ROD DIE TUBING DRAW HEAD
SHORT MANDREL
DIE WIRE \DIE HEAD JAWS
DRAW HEAD
ROD
AM.227 Figure 3-1.Cold-drawing operations for rod, tubing, and wire.
34 Chapter 3AIRCRAFT MATERIALS
treatment following the solution heat treatment. but by adding small amounts of other elements QUENCHING.. is the cooling.of.a metal. from a such as copper, manganese, magnesium, zinc, relatively high temperature by immersing it in a and the like, its strength can be increased many cooling medium. The cooling medium may be times. A luminumcontainingsuchother water, oil, or air. elements purposely added during manufacture is RECRYSTALIZATION POINTis the called an aluminum alloy. , temperature at which the grains in a metal In addition to increasing the strength, alloying recrystalize or re-form into very small crystals. may change the heat resistant qualities of a SOAKING refers to holding .4 metal at a metal, itscorrosionresistance,electrical required temperature for a specified time to conductivity, or magnetic properties. It may obtain an even temperature throughoutthe cause an increase or decrease in the degree to section. whichhardeningoccursaftercold- working. SOLUTION HEAT TREATMENT is a heat Alloying may also make possible an increase or treatment for nonferrous alloys in which the decrease strength and hardness by heat ahoy is heated to a specified temperature (below treatment. Alloys are, therefore, of great impor- the inching point), is held at this temperature tancetotheaircraftindustryinproviding for the required length of time, and is then materials with properties that pure metals alone quenched. The purpose of this treatment is to do not possess. cause as much of the alloying constituents as possible to go into solid solution and to retain FERROUS AIRCRAFT METALS this condition by quenching. TEMPER DESIGNATION isa term which A wide variety of materials is required in the refersspecificallytononferrousalloys.It repair of aircraft. This is a result of the varying consists of letters or letters and numbers which needswithrespecttostrength,weight, show the condition of the alloy and the heat durability, and resistanceto deterioration of treatment it has had. The temper designation is specificstructures or parts. In addition, the usually printed on the surface of the metal. particular shape or form of the material plays an TEMPERING is a heat-treating operation in important role. In selecting materials for aircraft which hardened steel is partially annealed and repair,thesefactorsplus many othersare the desired mechanical properties induced by considered in relation to their mechanical and reheating the metal to a temperature below its physical properties. Among the common mate- critical point. rials used are ferrous metals. The term FER- ROUS applies to the group of metals having iron ALLOYING OF METALS as their principal constituent.
A substance that possesses metallic properties Identification andis composed of two or more chemical elements, of which at least one is a metal, is If carbon is added to iron, in percentages called an ALLOY. The metal present in the alloy ranging up to approximately 1.00 percent, the in the largest proportion is called the BASE product will be vastly superior to iron alone and METAL. All other metals and/or elements added is classified as carbon steel. Carbon steel forms to the alloy are called ALLOYING ELEMENTS. the base of those alloysteels produced by The metals are dissolved in each other while combining carbon with other elements known to molten, and they do not separate into layers improve the properties of steel. A base metal when the solution solidifies. Practically all the (such as iron) to which small quantities of other metals used in aircraft are made up of a number metals have been added is called an ALLOY. of alloying elements. The addition of other metals is to change or Alloying elements, either in small or in large improve the chemical or physical properties of amounts, may result in a marked change in the the base metal. properties of the base metal. For example, pure SAE NUMERICAL INDEX.Thesteel aluminum isa relatively soft and weak metal, classification of the Society of Automotive
35 AVIATION STRUCTURAL MECHANIC S 3 & 2
Engineers (SAE) is used in specifications for all this test the piece of iron or steel is held against highgrade steels used in automotive and aircraft a revolving stone and the metal is identified by construction. Anumericalindexsystem the sparks thrown off. Each ferrous metal has its identifies the composition of SAE steels. own peculiar spark characteristics. The spark Each SAE number consists of a group of streams vary from a few tiny shafts to a shower digits, the first of which represents the type of of sparks several feet in length. Few nonferrous steel; the second, the percentage of the principal metals give off sparks when touched toa alloying element; and usually the last two or grinding stone. Therefore, these metals cannot three digits the percentage, in hundredths of 1 be successfully identified by the spark test. percent, of carbon in the alloy. For example, the Wrought iron produces long shafts that are SAE number 4150 indicates a molybdenum steel dull red colored as they leave the stone and end containing 1 percent molybdenum and 50 up a white color. Cast iron sparks are red as they hundredths of 1 percent of carbon. Refer to the leavethe stone and turn to a straw color. SAE numerical index shown in table 3-1 to see Low-carbon steels give off long straight shafts how the various types of steel are classified into having a few white sprigs. As the carbon content four-digit classilicaticn numbers. of the steel increases, the number of sprigs along each shaft increases and the stream becomes Table 3-1.-SAE numerical index. whiter in color. Nickel steel causes the spark stream to contain small white blocks of light within the main burst.
Type of steel Classification Types, Characteristics, and Carbon Uses of Alloyed Steels Nickel Nickel-chromium While steel of the plain carbon type remains Molybdenum the principal product of the steel mills, so-called Chromium alloy or special steels are being turned out in Chromium-vanadium ever increasing tonnage. Let us now consider Tungsten those alloyed steels and their uses in aircrcft. Silicon - manganese CARBON STEELS.Steel containing carbon in percentages ranging from 0.10 to 0.30 percent areclassedas LOWCARBON STEEL. The equivalent SAE numbers range from 1010 to 1030. Steels of this grade are used for making such items as safety wire, certain nuts, cable HARDNESS TESTING METHODS. - bushings, and threaded rod ends. Low-carbon Hardness testing is a factor in the determination steelinsheet formisusedfor secondary of the results of heat treatment as well as the structural parts and clamps, and in tubular form condition of the metal before heat treatment. for moderately stressed structural parts. There are two commonly used methods of Steelscontainingcarboninpercentages hardness testing, the BRINELL and the ROCK- ranging from 0.30 to 0.50 percent are classed as WELL tests.These tests require the use of MEDIUM-CARBON STEEL.Thissteelis specific machines and are not covered in this especially adaptable for machining or forging training manual. (A knowledge of hardness and where surface hardness is desirable. Certain testing procedures is a requirement for E-6.) An rod ends and light forgings are made from SAE additional somewhat indirect method (SPARK 1035 steel. TESTING) is used in identifying ferrous metals, Steel containing carbon in percentages ranging thisidentification,inturn,givingsome from 0.50 to 1.05 percent are classed as HIGH- indication of the hardness of the metal. CARBON STEEL.Theadditionof other Spark testing is a common means of identify- elements invarying quantities adds to the ing ferrous metals which have become mixed. In hardness of this steel. In the fully heat-treated 36 Chapter 3AIRCRAFT MATERIALS condition it is very hard and will withstand high and about 1.00 percent chromium. When heat shear and wear and have little deformation. It treated,they havestrength, toughness, and has limited use in aircraft. SAE 1095 in sheet resistance to wear and fatigue. A special grade form is used for making flat springs, and in wire of this steel in sheet form can be cold-formed form for making coil springs. intointricate shapes.Itcan be folded and NICKEL STEELS.The various nickel steels flattened without signs of breaking or failure. are produced by combining nickel with carbon SAE 6150 is usedfor making springs; and steel. Steels containing from 3 to 3.75 percent chrome-vanadium withhigh-carboncontent, nickel are commonly used. Nickel increases the SAE 6195, is used for ball and roller bearings. hardness, tensile strength, and elastic limit of CHROMEMOLYBDENUM STEELS. steelwithoutappreciablydecreasingtht Molybdenum in small percentages is used in ductility. It also intensifies the hardening effect combination with chromium to form chrome- of heat-treatment. SAE 2330 steelisused molybdenum steel which has various uses in extensivelyfor aircraftparts such as bolts, aircraft. Molybdenum is a strong alloying ele- terminals, keys, devises, and pins. ment, only 0.15 to 0.25 percent being used in CHROMIUM STEELS.Chromium steels are the chrome-molybdenum steels; the chromium highinhardness,strength,andcorrosion- contentvaries from 0.80to1.10 percent. resistant properties. SAE 51335 is particularly Molybdenum raises the ultimate strength of steel adaptable for heat-treated forgings which require without affecting ductility or workability. Moly- greater toughness and strength than may be bdenum steels are tough, wear-resistant, and obtained in plain carbon steel. It is used for such harden throughout from heat treatment. They articles as the balls and rollers of antifriction are especially adaptable for welding, and for this bearings. reason are used principally for welded structural CH ROME-NICKLE OR STAINLESS parts and assemblies. SAE 4130 is used for parts STEELS.These are corrosion-resisting metals. such as engine mounts, nuts, bolts, gear struc- The anticorrosive degree is determined by the tures, support brackets for accessories and other surface condition of the metal as well as by the structural parts. composition, temperature, and concentration of The progress of jet propulsion in the field of the corrosive agent. naval aviation has been aided by the continuous Theprincipalpartofstainlesssteelis research in high - temperature metallurgy. This chromium, to which nickel may or may not be research has brought forth alloys to withstand added. The corrosion-resisting steel most often the high temperatures and velocities encount- used in aircraft construction is known as 18-8 ered in jet power units. These alloys are chemic- steelbecause of its content of .18 percent ally similar to the previously mentioned steels, chromium and 8 percent nickel. One of the but may also contain cobalt,copper, and distinctivefeatures of 18-8 steelis that its columbium in varied amounts as alloying ele- strength may be increased by cold-working. ments. Stainless steel may be rolled, drawn, bent, or formed to any shape.Because thesesteels NONFERROUS AIRCRAFT METALS expand about 50 percent more than mild steel and conduct heat only about 40 percent as The term NONFERROUS refers to all metals rapidly, they are more difficult to weld. Stain- which have elements other than iron as their lesssteel,with but aslight variation inits principal constituent. This group includes alumi-. chemical composition, can be used for almost num, titanium, copper, and magnesium and their any part of an aircraft. Some of its more alloys; and in addition, such alloy metals as common applications are in the fabrication of monel and babbitt. exhaust collectors, stacks and manifolds, struc- tural and machined parts, springs, castings, and Aluminum and Aluminum Alloys tie rods and cables. CHROME - VANADIUM STEELS.These are Commercially pure aluminumisawhite, made of approximately 0.18 percent vanadium lustrous metal, light in weight and corrosion
37 AVIATION STRUCTURAL MECHANIC S 3 & 2
resistant. Aluminum combined with various per- The varioustypes of aluminum may be centages of other metals (generallycopper, divided into two classesCASTING ALLOYS manganese, magnesium, and chromium) form (those suitable for casting in sand, permanent the alloys which are used in aircraft construc- mold, and die castings) and the WROUGHT tion. Aluminum alloys in which the principal ALLOYS (those which may be shaped by alloying ingredients are either manganese, mag- rolling, drawing, or forging). Of the two, the nesium, or chromium, or magnesium and silicon wrought alloys are the most widely used in show little attack in corrosive environments. On aircraft construction, being used for stringers, the other hand, those alloys in which substantial bulkheads, skin, rivets, and extruded sections. percentages of copper are used are more sus- Casting alloys are not so extensively used in ceptible to corrosive action. The total percent- aircraft. age of alloying elements is seldom more than 6 WROUGHT ALLOYS.Wrought alloys are or 7 percent in the wrought aluminum alloys. divided into two classesnonheat treatable and TYPES, CHARACTERISTICS, AND USES. heat treatable. In the nonheat-treatable class, Alu minum is one of the most widely used metals strain hardening (cold-working)isthe only in modern aircraft construction. It is vital to the means of increasing the tensile strength. Heat- aviation industry because of its high strength/ treatable alloys may be hardened by heat treat- weight ratio, its corrosion-resisting qualities, and ment, by cold-working, or by the application of its comparative ease of fabrication. The out- 'both processes. standing characteristic of aluminum is its light Aluminum productsareidentifiedby a weight.Incolor, aluminum resembles silver universally used designation system. Under this althoughitspossesses acharacteristic bluish arrangement, wrought aluminum and wrought tinge of its own. Commercially pure aluminum aluminum alloys are designated by a four-digit melts at the comparatively low temperature of index system. The first digit of the designation indicates the 1,220°F. It is nonmagnetic and is an excellent major alloying element or alloy group, as shown conductor of electricity. in table 3-2. Thus lxxx indicates aluminum of Commercially pure aluminum has a tensile 99.00 percent or greater, 2xxx indicates an strength of about 13,000 psi, but by rolling or aluminum alloy in which copper is the major other cold-working processes its strength may be alloying element, 3xxx indicates an aluminum approximately doubled. By alloying with other alloy with manganese as the major alloying metals, together with the use of heat-treating element, etc. Although most aluminum alloys processes, the tensile strength may be raised to as high as 96,000 psi, or to well within the strength range of structural steel. Table 3-2.Designations for aluminum Aluminum alloy material, although strong, is alloy groups. easily worked, for itis very malleable and ductile. It may be rolled into sheets as thin as 0.0017 inch or drawn into wire 0.004 inch in diameter. Most aluminum alloy sheet stock used in aircraft construction ranges from 0.016 to Aluminum-99.00 percent minimum 0.096 inch in thickness; however, some of the and greater larger aircraft use sheet stock which may be as Aluminum alloys, grouped by major thick as 0.356 inch. alloying element: Copper ..2xxx One disadvantage of aluminum alloy is the Manganese 3xxx difficulty of making reliable soldered joints. Silicon toot Oxidation of the surface of the heated metal Magnesium. 5xxx preventssoftsolder from adheringtothe Magnesium and silicon...... 62ciac material; therefore, to produce good joints of Zinc 7xxx aluminum alloy, a riveting process is used. Some Other elements 8xxx aluminum alloys are also successfully welded.
38 Chapter 3AIRCRAFT MATERIALS containseveralalloying elements, only one structural purposes in aircraft in preference to group (6xxx) designates more than one alloying thenonheat-treatablealloys.Heat-treatable element. alloys commonly used in aircraft construction In the lxxx group the second digit in the (in order of increasing strength) are 6061, 6062, designation indicates modifications in impurity 6063, 2017;'2024, 2014, 7075, and 7178. limits. If the second digitis zero, it indicates Alloys 6061, 6062, and 6053 are sometimes, that there is no special control on individual used for oxygen and hydraulic lines and in some impurities. The lasttwo of the four digits applications as extrusions and sheet metal'. indicate the minimum aluminum percentage. Alloy 2017 is used for rivets, stressed-skin Thus,alloy1030indicatbs99.30percent covering, and other structural members. aluminum without special control on impurities. Alloy 2024 is used for airfoil covering and Alloys 1130, 1230, 1330, etc., indicate the same fittings.Itmay be used wherever 2017 is aluminum purity with special control on one or specified, since it is stronger. more impurities. Likewise,. 1075, 1175, 1275, Alloy 2014 is used for extruded shapes and etc., indicate 99.75 percent aluminum. forgings. This alloy is similar to 2017 and 2024 In the 2xxx through 8xxx groups, the second in that it contains a 'high percentage of copper. digit indicates alloy modifications. If the second It is used where more strength is required than digit in the designation is zero, it indicates the that obtainable from 2017 or 2024. originalalloy,while numbers 1 through 9, assigned consecutively, indicate alloy modifica- Alloy 7178 is used where highest strength is tions. The last two of the four digits have no necessary. Alloy 7178 contains a small amount special significance, but serve only to identify of chromium as a stabilizing agent as does alloy the different alloys in the group. 7075. The temper designation follows the alloy Nonheat-treatablealloysusedinaircraft designation and shows the actual condition of construction are 1100, 3003, and 5052. These the metal. It is always separated from the alloy alloys do not respond to any heat treatment designation by a dash, as shown in Table 3-3. other than a softening, annealing effect. They The letter F following the alloy designation may be hardened only by cold-working. indicates the "as fabricated" condition, in which Alloy 1100 is used where strength is not an no effort has been made to control the mechani- important factor but where weight, economy, cal properties of the metal. and corrosion resistance are desirable. This alloy The letter 0 indicates dead soft, or annealed, is used for fuel tanks, fairings, oil tanks, and for condition. the repair of wingtips and tanks. The letter W indicates solution heat treated. Alloy 3003 is similar to 1100 and is generally Solution heat treatment consists of heating the used for the same purposes. it contains a small metal to a high temperature followed by a rapid percentage of manganese and is stronger and quench incoldwater. Thisisan unstable harder than1100, but retains enough work temper, applicable only to those alloys which ability that it is usually preferred over 1100 in spontaneously age at room temperature. Alloy most applications. 7075 may be ordered in the W condition. Alloy 5052 is used for fuel lines, hydraulic The letter H indicates strain hardened; that is, lines,fueltanks, and wingtips. Substantially cold-worked, hand-drawn, or rolled. Additional higher strengths without too much sacrifice of digits are added to the H to indicate the degree workability can be obtained in5052.Itis of strain hardening. (See table 3-3.) Alloys in therefore preferred over 1100 and 3003 in many this group cannot be strengthened by heat applications.Table3-4 shows the nominal treatment, hence the term nonheat treatable. chemical compositions for the wrought alloys. The letter T indicates fully heat treated. Alcladisthenamegiventostandard Digits are added to the T to indicate certain aluminum alloys which have been coated on variations in treatment. both sides with a thin layer of pure aluminum. Greater strength is obtainable in the heat- Alclad has very good corrosion-resisting qualities treatable alloys. Therefore, they are used for and is used exclusively for exterior surfaces of
39 AVIATION STRUCTURAL MECHANIC S 3 & 2 Table 3.3. Temper designations for aluminum alloys.
Designation Condition indicated Example
- -F As fabricated ' 3003-F
-0 . Fully annealed 6061-0 -W Unstable following solution heat treatment. 7075-W -H Strain hardened (cold worked) -31, Strain hardened only 3003-H12 plus one or more digits.
-112, Strain hardened and then partially annealed. 3003-H24 plus one or more digits. -H3, Strain hardened and then stabilized 5052-H36 plus one or more digits. -T Heat treated -T3 Solution heat treated and then cold worked. 2024-T3 -T4 Solution heat treated 2024-T4
-T5 Artificially aged only 6063 -T5 -T6 Solution heat treated and then artificially 7075-T6 aged. -T7 Solution heat treated and then stabilized to 7075-T7 control growth and distortion. -T8 Solution heat treated, cold worked, and then 2024-T86 artificially aged. -T9 Solution heat treated, artificially aged, and 6061 -T91 then cold worked. -T14 Artificially aged and then cold worked. 2014-T10
NOTE: The -T designations above may have one or more digits added to denote certain variations of the basic heat treatments described.
40 Chapter 3- AIRCRAFT MATERIALS
Table 3-4.-Chemical composition of aluminum alloys.
Alloy Alloying elements in percent. Aluminum and normal impurities constitute remainder.
Silicon Copper Manganese Magnesium Chromium Zinc
3003 0.6 0.2 1.2 0.1 2014 0.8 4.5 0.8 0.4 0.1 0.25 2017 0.8 4.0 0.5 0.5 0.1 0.25 2117 2.5 0.3 2024 0.5 4.5 0.6 1.5 0.1 0.25 5052 0.45 0.1 0.1 2.5 0.25 0.1 5056 0.1 5.2 0.1 6061 0.6 0.25 0.15 1.0 0.25 0.25 6062 0.6 0.25 0.15 1.0 0.06 0.25 6063 0.4 0.1 0.1 0.7 0.1 0.25 7075 0.5 1.6 0.3 2.5 0.3 5.6 7178 2.0 0.3 2.7 0.3 6.8 aircraft. Alc lad sheet is available in all tempers Aluminum alloy castings are produced by one of 2014, 2017, 7075, and 7178. of three basic methods-sand mold, permanent CASTING ALLOYS.-.Aluminumcasting mold, and die cast. In casting aluminum, it must alloys, like wrought alloys, are divided into two be remembered that in most cases different groups. In one, the physical properties of the types of alloys must be used for different types alloys are determined by the elements added and of castings.Sandcastings anddie castings cannot be changed after the metal is cast. In the requiredifferenttypes thanthose used in other, the elements added make it possible to permanent molds. heattreatthecastingtoproduce desired SHOP CHARACTERISTICS OF ALUMINUM physical properties. ALLOYS.-Aluminum is one of the most readily The casting alloys are identified by a letter workable of all the common commercial metals. preceding the alloy number. This is exactly It can be fabricated readily into a variety of opposite from the case of wrought alloys in shapes by any conventional method; however, which the letters follow the number. When a formability varies a great deal with the alloy and letter precedes a number, it indicates a slight temper. variation in the composition of the original In general, the aircraft manufacturers form alloy. This variation in composition is made the heat-treatable alloys in the -0 or -T4 condi- simply to impart some desirable quality. In tion before they have reached their full strength. casting alloy 214, for example, the addition of They are subsequently heat treated or aged to zinc,toincreaseitspouringqualitiesis the maximum strength (-T6) condition before designated by theletter A in front of the installation in aircraft. By this combination of number, thus creating the designation A214. processes, the advantage of forming in a soft When castings have been heat treated, the conditionis obtained without sacrificing the heat treatment and the composition of the maximum obtainable strength/weight ratio. casting are indicated by the letter T and an Aluminum is one of the most readily weldable alloying number. An example of this is the, sand of all metals. The nonheat-treatable alloys can casting alloy 355 which has several different be welded by all methods, and the heat-treatable compositions and tempers and is designated by alloys can be successfully spot welded. The 355-T6, 355-T51, and A355-T51. melting point for pure aluminum is 1,220°F,
41 AVIATION STRUCTURAL MECHANIC S 3 & 2 while various aluminum alloys melt at slightly of glass, moistened titanium will leave a dark lower temperatures. Aluminum products do not line similar in appearance to a pencil mark. show any color changes on being heated, even up to the melting point. Riveting is the most Copper and Copper Alloys reliable method of joining stress-carrying parts of heat-treated aluminum alloy structures. Most commercial copper is refined to a purity of 99.9 percent minimum copper plus silver. It is the only reddish colored metal and is second Titanium and Titanium Alloys only to silver in electrical conductivity. Its use as a structural material is limited because of its Titanium and titanium alloys are used chiefly great weight. However, some of ita outstanding for parts which require good corrosion resist- characteristics, such as its high electrical and ance, moderate strength up to 600°F, and light heat conductivity, in many cases overbalance the weight. weight factor. TYPES, CHARACTERISTICS, AND USES. Becauseitisvery malleable and ductile, Titanium alloys are being used in quantity for copper isideal for making wire.In aircraft, jetenginecompressorwheels,compressor copper is used primarily for the electrical system blades, spacer rings, housing compartments, and and for instrument tubing and bonding. Itis airframe parts such as engine pads, ducting, wing corroded by salt water but is not affected by surfaces, firewalls, fuselage skin adjacent to the fresh water. The ultimate tensile streivth of engine outlet, and armor plate. copper variesgreatly. For castcopper, the In view of titanium's high melting tempera- tensile strength is about 25,000 psi; and when ture,approximately3,300°F,itshigh- cold-rolled or cold-drawn, itstensile strength' temperature properties are disappointing. The increases, ranging from 40,000 to 67,000 psi. ultimate and yield strengths of titanium drop BRASS.Brass is a copper alloy containing fast above 800°F. In applications where the zinc and small amounts of aluminum, iron, lead, declines might be tolerated, the absorption of manganese, magnesium, nickel, phosphorous, oxygen and nitrogen from the air at temperature and tin. Brass with a zinc content of 30 to 35 above 1,000°F, makes the metal so brittle on percent is very ductile while that containing 45 long exposure that it soon becomes worthless. percent has relatively high strength. MUNTZ Titaniumhassomemeritforshort-time METAL isa brass composed of 60 percent exposure up to 2,000°F where strength is not copper and 40 percent zinc. It has excellent important, as in aircraft firewalls. corrosion-resistantqualities when in contact Sharp tools are essential in machining tech- with salt water. Its strength can be increased by niques as titanium has a tendency to resist or heattreatment. As cast,this metal has an back away from the cutting edge of tools. It is ultimate tensile strength of 50,000 psi and 'can readily welded, but the tendency of the metal to be elongated 18 percent. It is used in making absorb oxygen, nitrogen, and hydrogen must bolts and nuts, as well as parts that come in never be ignored. Machine welding with an inert contact with salt water. RED BRASS, some- gas atmosphere has proven most successful. times termed bronze because of its tin content, Both commercially pure and alloy titanium is used in fuel and oil line fittings. This metal has can absorb large amounts of cold-work without goodcastingandfinishingpropertiesand cracking. Practically anything that can be deep machines freely. drawn in low-carbon steel can be duplicated in BRONZES.Bronzesarecopperalloys commerciallypuretitanium,althoughthe containing tin. The true bronzes have up to 25 titanium may require more intermediate anneals. percent tin, but those below 11 percent are most IDENTIFICATION OF TITANIUM. useful, especially for such items as tube fittings Titaniummetal, pure oralloyed,iseasily in aircraft. identified. When touched with a grinding wheel, Among the copper alloys are the copper itmakes whitesparktraces which endin aluminumalloys,ofwhichthealuminum brilliant white bursts. When rubbed with a piece bronzes rank very high in aircraft usage. They
42 Chapter 3AIRCRAFT MATERIALS
would find greater usefulness in structures it'it tensile strength rising from 70,000 psiin the were notfortheir strength/weightratioas annealed state to 200,000 psi in the heat-treated compared with alloy steels. Wrought aluminum state. The resistance of beryllium copper to bronzes are almost as strong and ductile as fatigue and wear makesitsuitable for dia- medium-carbon steel and possess a high degree phrams, precision bearings and bushings, ball of resistance to corrosion by air, salt water, and cages, spring washers, and nonsparking tools. chemicals, They arereadilyforged, hot- or cold-rolled, and many react to heat treatment. Monel These copper-base alloys contain up to 16 percent of aluminum (usually 5 to 11 percent) Monet, the leading high-nickel alloy, combines to which other metals such as iron, nickel, or the properties of high strength and excellent manganese may be added. Aluminum bronzes corrosion resistance. This metal consists of 67 have good tearing qualities, great strength, hard- percent nickel, 30 percent copper, 1.4 percent ness, and resistance to both shock and fatigue. iron, 1 percent manganese, and 0.15 percent Because of these properties, they are used for carbon. It cannot be hardened by heat treat- diaphragms and gears,air pumps, condenser mentresponding only to cold-working. bolts, and slide liners. Aluminum bronzes are Monet, adaptable to castings and hot- or cold- available in rods, bars, plates, sheets, strips, and working, can be successfully welded and has forgings. working properties similar to those of steel. It Cast aluminum bronzes, using about 89 per- has a tensile strength of 65,000 psi which, by cent copper, 9 percent aluminum, and 2 percent means of cold-working, may be increased to of other elements, have high strength combined 160,000psi,thusentitlingthismetalto with ductility, and are resistant to corrosion, classification among the tough alloys. Monet has shock, and fatigue. Because of these properties, been successfully used for gears and chains, for cast aluminum bronzeis used in gun mounts, operatingretractablelandinggears, andfor bearings, and pump parts. These alloys are useful structural parts subject to corrosion. In aircraft, in areas exposed tosalt water and corrosive monel has long been used for parts demanding gases. both strength and high resistance to corrosion, Manganese bronze is an exceptionally high- such as exhaust manifolds and carburetor needle strength, tough, corrosion-resistant copper zinc valves and sleeves. alloycontaining aluminum, manganese, iron, and occasionally nickel or tin. This metal can be K-Monel formed,extruded, drawn, or rolledto any desired shape. In rod form, itis generally used K-monelisanonferrousalloy containing for machined parts.Otherwiseitis used in mainlynickel, copper, and aluminum.Itis catapults, landing gears, and brackets, producedbyaddinga smallamountof Siliconbronzeiscomposed of about 95 aluminum to the monel formula. .It is corrosion percent copper, 3 percent silicon, and 2 percent resistantand capable of hardening by heat manganese,zinc,iron,tin,and aluminum. treatment. K-monel has been successfully used Although not a bronze in the true sense of the for gears, chains, and structural members in word because of its small tin content, silicon aircraft which are subjected to corrosive attacks. bronze has high strength and great corrosion This alloy is nonmagnetic at all temperatures. resistance and is used variably. K-monel can be successfully welded. BERYLLIUM COPPER.Beryllium copper is one of the most successful of all the copper-base alloys. It is a recently developed alloy containing Magnesium and Magnesium Alloys about 97 percent copper, 2 percent beryllium, and sufficient nickel to increase the percentage Magnesium, the world'slighteststructural of elongation. The most valuable feature of this metal, is a silvery-white material weighing only metalisthat the physical properties can be two-thirds as much as aluminum. Magnesium greatlysteppedup by heattreatmentthe does not possess sufficient strength in its pure
43 AVIATION STRUCTURAL MECHANIC S 3 & 2
state for structural uses; but when alloyed with Magnesium alloys possess good casting charac- zinc, aluminim, and manganese, it produces an teristics.Their properties compare favorably alloy having the highest strength/weight ratio. with those of cast aluminum. In forging, hy- TYPES, CHARACTERISTICS, AND USES. draulicpresses arc ordinarily used; although, Magnesium is probably more widely distributed under certainconditions, forging can be ac- in nature than any other metal.It can be complished in mechanical presses or with drop obtainedfromsuchoresasdolomite and hammers. magnesite, from underground brines, from waste Magnesium embodies fire ,hazards of an un- liquors of potash, and from sea water. With predictable nature. When in large sections, its
about 10 million pounds of magnesium in 1 high thermal conductivity makes it difficult to cubic mile of sea water, there is no danger of a ignite, and prevents its burning. It will not burn dwindling supply. untilthe melting pointis reached, whichis Magnesium isused extensivelyin the approximately1,200°F. However, magnesium manufacture of helicopters. Its low resistance to dust andfine chips are ignitedeasily.Pre- corrosion has been a factor in reducing its use in cautions must be taken to avoid this if possible, conventional aircraft. andtoextingushthemimmediately.An The machining characteristics of magnesium extinguishing powder, such as powdered soap- alloysareexcellent.Usuallythe maximum stone, clean, dry, unrusted cast iron chips, or speeds of machine tools can be used with heavy graphite powder, should be used. cuts and high feed rates. Power requirements for magnesium alloys are about one-sixth of those for mild steel. An excellent surface finish can be CAUTION: Water or any standard liquid or produced, and in most cases grinding is not foam extinguisher causes magnesium to burn essential. Standard machine operations can be more rapidly and may cause small explosions. performedtotolerancesofa fewten- thousandths of an inch. There is no tendency of the metal to tear or drag. Magnesium alloy sheets can be worked in much the same manner as other sheet metal with one exceptionthe metal must be worked while hot. The structure of magnesium is such that the HYDRAULIC RAM alloys work-harden rapidly at room tempera- tures. The work is usually done at temperatures ranging from 450° to 650°F, which is a dis- advantage. However, compensations are offered by the fact that in the ranges used, magnesium is more easily formed than other materials. Sheets can be sheared in much the same way as other metals, except that a rough flaky fracture is produced on sheets thicker than about 0.064 inch. A better edge will result on a sheet over 0.064 inch thick if it is sheared hot. Annealed sheet can be heated to 600°F, but hard rolled sheet should not be heated above 275°F. A straight bend with short radius can be made by the GUERIN PROCESS, as shown in MALE DIE STATIONARY BED figure 3-2, or by press or leaf brakes. The Guerin processisthe most widely used method for forming and shallow drawing, employinga rubber pad as the femal die, which bends the AM.228 work to the shape of the male die. Figure 3-2.Guerin process.
44 Chapter 3 AIRCRAFT MATERIALS
SUBSTITUTION AND maintenance and repair involving substitution INTERCHANGEABILITY andinterchangeabilityofaircraftstructural OF AIRCRAFT METALS metals. BE SURE YOU HAVE THE AERO- NAUTIC TECHNICAL PUBLICATION OF THE Inselectinginterchangeableorsubstitute MOST RECENT ISSUE. materials for the repair and maintenance of naval aircraft, it is of the utmost importance to checktheappropriateaeronautictechnical publications when specified materials are not in stock nor obtainable from another source. It is INSPECTION OF METALS impossible to determine that another material is as strong as th?, original by mere observation. When a metallic part is suspected of having a There are four requirements that must be kept tiny crack or other invisible defect, it is general- clearly in mind in this selection. The first and ly inspected by one of the following methods: most important of theseismaintaining the the penetrant method, the magnetic particle original strength of the structure. The other inspection method, the radiographic (X-ray) three are maintaining contour or aerodynamic method, the eddy current method, orthe smoothness,maintainingoriginalweightif ultrasonic method. possible or keeping added weight to a minimum, The various types and methods of penetrant and maintaining the original corrosive-resistance inspections are suitable for locating almost any properties of the metal. type of defect open to the surface on a variety The importance of checkingthespecific of nonabsorbent materials such as ferrous and technical publication can be appreciated by nonferrousmetals,ceramics,hardrubber, understandingthatdifferentmanufacturers plastic, and glass. Metals that can be magnetized design structural members to meet various load (ferrous metals) are usually inspected by the requirementsforspecificaircraft.Structural magnetic particle method. The X-ray method repair of these members, apparently similar in may be used for inspecting any of the foregoing construction, will thus vary in their load carry- metals. All of these methods are nondestructive ing design with different aircraft. tests, which means they are performed on the Structural repair instructions, including tables actual part without damage to the part. ofinterchangeabilityandsubstitutionfor To advance to E-4, all AMS strikers must be ferrousandnonferrousmetalsandtheir able to perform dye penetrant inspections, and specifications for all types of aircraft used by to advance from E-4 to E-5, the AMS must be the Navy, are normally prepared by-the contrac- able to interpret the results obtained by using tor. Such instructions are usually promulgated in thepenetrantmethod.Coverageonother the -3 manual covering structural repair instruc- methods of inspecting metals mentioned above tionsfor specific model of aircraft. Similar is not included in this chapter, as proficiency in information is also contained in Nav Air 01-1A-1, these methods is not a requirement at this level. General Manual for Structural Repair. Thefollowing sectionwill providebasic Nav Air 01-IA-1, section III, table IV, presents coverage on the types and methods of penetrant the substitution and conversion information for inspection, general inspection procedures, and aluminum alloy sheet metal. In section IV, table interpretation of results. Complete and detailed IV, steel specifications are given; table V, in coverage necessary for a thorough understanding section IV, covers aluminum specifications. of the penetrant methods of inspectionis NavAir 01-IA-9, Aerospace MetalsGeneral provided in NavAir 01-1A-16, Nondestructive Data and Usage Factors, provides precise data on Inspection Methods, Technical Manual. Tests on specific metals to assist in selection, usage, and critical aircraft components require a thorough processing for fabrication and repair. knowledge ofallmaterial included inthat Always consult these publications and the -3 section of the manual for the specific test being aircraftmanual for the specific-type aircraft conducted to insure proper testing and inter- when confronted with a problem concerning pretation.
45 AVIATION STRUCTURAL MECHANIC S 3 & 2
PENETRANT INSPECTIONS the defects. If the part has been in contact with water it may be possible to heat the part slightly Penetrant inspection is a nondestructive test to evaporate the water. for defects open to the surface in parts made of Penetrant is then applied to all surfaces. This any nonporous material. Penetrantinspection may be done by dipping, flow-on, brushing, or depends for its success upon a penetrating liquid spraying. It is important that all suspect areas be entering the surface opening and remaining in wet with penetrant. The penetrant must be that opening, making it clearly visible for the allowed to remain on the part for a period of operator. It calls for visual examination of the time called the penetration (dwell) time. This part by the operator after it has been processed, allows the penetrant to seek and till surface but the visibility of the defect is increased so openings. The length of the penetration time thatitcan be detected.Visibilityof the varies with the process and techniques used, the penetrating material is increased by the addition material of which the part is made, and the of dye which may be either one of two types of defects present. typesvisible or fluorescent. The excess surface penetrant is removed from The main disadvantage of penetrant inspec- the part by means of a forceful water spray. This tionis that the defect must be open to the operation does not remove the penetrant from surface in order to let the penetrant into the deep defects but does remove the penetrant on defect. For this reason, if the part in question is the surface. made ofmaterialwhichismagnetic,the A developer is then applied to the part before magnetic particle inspection or X-ray is generally inspection. The function of the developer is to recommended. It is also essential that there be blot back to the surface the penetrant that is no contaminant within thedefect which might entrapped in fissures or defects in the part. The either prevent the penetrant from entering or developer should be allowed to remain on the which may reduce its visibility. part for a time before inspection for defects. The materialsusedinthevisibledye This elapsed time is to allow the developer to penetrant inspection are available in aviation bring back to the surface and magnify the traces supply stock in the form of a complete inspec- of penetrant. Some types of defects in some tion kit. Included in the kit are the following parts may be detectable without the use of a items:twospraycansofpenetrant,dye developer,butforconsistentandpositive remover-emulsifier,anddeveloper.For results, current instructions recommend that a replenishment purposes, these materials are also developer always be used. A drying operation is available as individual items. The chemicals are necessary which increases the effectiveness of available in ordinary containers for use when the method and, depending upon the type of dipping or brushing is desired. developer used, either dries the wet developer or The fluorescentinspectionmaterials and prepares the part for the application of the dry equipment are also furnished in kit form. The developer. complete equipment is contained in a metallic After the proper developing time has elapsed, carrying case. Included are the following items: the part is ready for inspection. If thb penetrant penetrant,penetrantcleaner,penetrant used has a fluorescent dye in it, the inspection developer (both powder and suspension types), must be performed in a darkened area and under dauber for applying powder, and a black light black light. If the penetrant used has a visible (ultra violet) assembly complete with power die, then inspection can be performed under transformer. The chemicals may be replenished ordinary lighting conditions. individually from aviation supply stock. All traces of the developer should be removed from the part before it is returned to service. General Inspection Procedure First of all, the part to be inspected must be Types of Processes clean. This includes the removal of surface dirt, scale, paint, and oil, as well as removing any There are two types of penetrant inspection materials or compounds that might fill or cover processes. Type I employs the use of fluorescent 46 Chapter 3AIRCRAFT MATERIALS penetrants, and Type IIprocesses employ the lists the types and methods of penetrant inspec- use of visible dye penetrants. Within each type tion and their related group of materials. there are three methods, which are referred to as Group Ithrough group IIIpenetrants are methods A, B, and C. Each method within a visible dye penetrants containing dyes that make type uses a specific group of materials. Table 3-5 them readily visible when exposed to natural or
Table 3-5.Penetrant inspection types, methods, and material groups
MIL-I-25135 Penetrant Material Family of Items Type Method Used Group Used In Group
I A Water-washable Group IV Consists of a water-washable fluorescent dye fluorescent penetrant and a dry, wet, or nonaqueous wet developer.
B Post-emulsifiable Group V Consists of a post-emulsifiable fluorescent dye. fluorescent penetrant, an emul- sifier, and a dry, wet, or non- aqueous wet developer.
. Group VI Consists of a high-sensitivity post-emulsifiable fluorescent penetrant, an emulsifier, and a dry, wet, or nonaqueous wet developer.
I C Solvent-removableGroup VII Consists of a solvent-remov- . fluorescent dye. able fluorescent penetrant, a penetrant remover (solvent) and a nonaqueous wet developer.
II A Water-washable Group HI Consists of a water-washable visible dye. visible dye penetrant and a dry, wet, or nonaqueous wet developer.
II B Post-emulsified Group II Consists of a post-emulsifi- visible dye. able visible dye penetrant, an emulsifier, and a dry, wet, or nonaqueous wet developer.
II C Solvent-removableGroup I Consists of a solvent-remov- visible dye. able visible dye penetrant, a penetrant remover (solvent), and a dry, wet, or nonaqueous wet developer.
47 AVIATION STRUCTURAL MECHANIC S 3 & 2 artificial white light. Penetrants in group I are Sulfonates in the emulsifying agents will not removed by wiping with a, cloth dampened by a affect nickel bearing steels. specially prepared compatible solvent supplied NOTE: This method is not recommended for with the portable penetrant kit. Penetrants in detecting extremely fine intergranular corrosion group II are water washable (for removal) after or stress corrosion defects. applicationof anemulsifier.Thistwo-step The water-washable flourescent dye penetrant process makes group II penetrants more suitable used in this type/method insures good visibility for detecting wide, shallow defects. Group II of flaw patterns and can be easily washed off penetrants are referred to as post-emulsifiable with water. Since itis considered a one-step penetrants. GroupIllpenetrants contain an process, it is fast and economical in time and is emulsifier which makes them water washable as relatively inexpensive to perform. This process is furnished. not reliable in finding scratches and shallow Group IV through VII penetrants contain discontinuities as the penetrant is susceptible to dyes which will fluoresce (glow) when exposed overwashing.Itisnot reliable on anodized to black light. Group IV penetrants contain an surfaces, and the penetrant can be affected by emulsifier which makes it water washable as acids and chromates, furnished. Groups V and VI are water washable Following precleaning and drying, the water- after application of an emulsifier the same as washable fluorescent penetrant is applied to the group II. Group VII penetrants are removed by surface being inspected by dipping, flow-on, wiping with a solvent-dampened cloth the same spraying, or brushing methods. After the pre- as group I. determined dwell time, it is flushed from the surface with a low-pressure (20-30 psi) spray of Selection of Inspection Process cold water. The developer is then applied and will cause the penetrant to bleed from any The selection of the best type of penetrant discontinuities or defects, and these flaw indica- inspectionsuitable for the job at hand will tions will become visible when exposed to black depend on several factors as follows: light. TYPE1, METHOD B,INSPECTION 1.Previouslyestablishedrequirements P R OC E SS.This methodisusedwhen specified on documents requiring the inspection. inspecting large volumes of parts which may 2. Penetrant sensitivity required. have defects that are contaminated with in- 3. Surface condition of the part. service soils or that may be contaminated with 4. Configuration of the part. acids or other chemicals that will harm water- 5. Number of parts to be tested. washable penetrants.Itisthe type/method 6. Facilities and equipment available. recommended for use when: 7. Effect of the penetrant chemicals on the material being tested. A higher sensitivity than that offered by Type 1, Method A, is required. TYPEI,METHOD A,INSPECTION Discontinuities are wider than their depth. PROCESS.This method lends itself to inspect- Inspectingpartsforstresscracks,inter- ing large volumes of parts, large areas, rough granular corrosion, or grinding cracks. surfaces, and threads and keyways. Itis the Variable, controlled sensitivities are necessary recommended type/method to be used when: so that nondetrimental discontinuities can be Discontinuitiesarenot wider thantheir disregarded while harmful or detrimental ones depth. can be detected. The lowest flourescent penetrant sensitivity is The group V penetrant used with this type/ sufficient to detect the defects inherent to the method is more sensitive than the group IV part. penetrant of Type 1, Method A; however, the Removal of excess penetrant may be difficult group VI penetrant used with Type I, Method B, due to rough surfaces on the part. is more sensitive than group V.
48 Chapter 3AIRCRAFT MATERIALS
NOTE: Only group VI materials are used for spraying, or brushing methods. After the pre- inspectingforstresscracks or intergranular determined dwell time, it is then removed with corrosion. thesolvent remover. The part is thoroughly The fluorescent penetrant used in this process dried and developer is applied. Penetrant will is more brilliant than other processes and affords bleed from any discontinuities or defects and greater visibility when exposed to black light. the flaw indicationswill be apparent when For field use where light exclusion is not always exposed to black light. possible,itprovides the greatest degree of TYPEII, METHOD A,INSPECTION brilliance. PROCESS.This process is utilized for inspect- The Type I, Method B, process is highly ing surfaces when the circumstances described sensitive to fine defects and is also good on for Type I, Method A, exist and a fluorescent wide, shallowdefects. The penetrant washes dye penetrant is not necessary. A black light is easily after emulsification and the penetrant is not needed; therefore, the work area need not not as susceptible to overwashing. Since itis bedarkened.Theprocessisrelativelyin- considered a two-step process, because of the expensive, highly portable, excellent for spot emulsifier, itis slower than Type I, Method A. checking, and can be used on anodized parts. The process is liot as good on rough surfaces, The penetrant is easily washed off with fresh keyways, or threads; and because of the extra water. materials used in the inspection, itis slightly Following precleaning and drying, the water- more expensive. washable visible dye penetrant is applied by Following precleaning and drying, the post- dipping, flow-on, spraying, or brushing methods. emulsifiable fluorescent penetrant is applied to After the predetermined dwell time, it is flushed the surface being inspected. After being allowed from the surface with a low-pressure spray of todwellforthe predeterminedtime,the water and the surface is dried. The application emulsifier is applied. The emulsifier combines of developer then draws out penetrant left in with the penetrant and is water washable. The any discontinuities or defects, end these flaw excess penetrant is then removed using a low- indications should appear clearly against the pressure (30 to 40 psi) spray of cold water. The white developer background. The indications part is then thoroughly dried and the developer can be easily seen in natural or artificial light. applied. The penetrant is then drawn to the TYPEII,METHODB, INSPECTION surface and any flaw indications will become PROCESS.This method is used when a higher apparent as abrilliant greenish-yellow color sensitivitythan thatafforded by TypeII, when exposed to black light. The sensitivity of Method A, is required. It is used when inspecting this process can be controlled by. the type of large volumes of parts,parts that are con7 penetrant used, dwell time, emulsifying time, taminated with acid or other chemicals that will rinsing technique, and drying temperature and harm water-washable penetrant., parts which time. may have defects that are contaminated with TYPE I, METHOD C, INSPECTION inservice soils, and for inspecting finished sur- PROCESS.This method is used for spot inspec- faces and other general purpose applications. tion on large or small parts where the water The materials in this process are the most rinsing method is not fensible because of part sensitive of the visible dye penetrant inspection size, weight, surface conditions, and lack of methods; however, itis not recommended for water, or there is no heatfor,drying or field use. detecting extremely fine intergranular corrosion The use of solvent required to remove the or stress corrosion defects. penetrant prohibits this process in inspecting Following precleaning and drying, the post- large areas. Its sensitivity can also be reduced by emulsifiable visible dye penetrant is applied to theapplicationofexcessiveamountsof the surface being inspected by dipping, flow-on, penetrant remover. spraying, or brushing methods. After this group Following precleaning and drying, the solvent II penetrant is allowed to dwell for a predeter- removable fluorescent penetrant is applied to mined time, the emulsifierisapplied. The the surface being inspected by dipping, flow-on, emulsifier combines with the penetrant, which AVIATION STRUCTURAL MECHANIC S 3 & 2 becomes water washable. The excess penetrant is to the flaw openings wetted by the penetrant then washed off using a low-pressure (30-40 psi) liquid and provides sharp flaw delineations. It is spray of cold water. Application of the desired applied by dipping, dusting, or flow-on method. developer will then draw out and absorb the Aqueouswetdeveloperconsistsofan intense red penetrant from the discontinuity to absorbent powder supplied in dry form which is providea clear indicationagainst the white mixed and suspended in water for application to developer background. the part being penetrant inspected. The suspen- TYPEII,METHOD C,INSPECTION sion of the wet developer must be agitated to PROCESS.This method isused when spot insurethorough suspension of the absorbent inspection is required and where water rinsing is powder in the water. Excess penetrant is re- not feasible. The use of solvent in removing the moved from the part and the wet developer is penetrant prohibits inspection of large areas and applied to the part while it is still wet. The wet the processisnot adaptablefor detecting developer, on drying, provides an absorbent extremely fine defects. white background for maximum color contrast Following precleaning and drying, the solvent and causes the penetrant to bleed from the flaw removable visible dye penetrant is applied as cavity, obtaining increased inspection accuracy. with previous methods. After the predetermined Wet developers cause greater bleeding and are dwell time, it is removed from the surface with more sensitive when applied as a spray. They are solvent remover and thepartis thoroughly applied by dipping or flow-on method. dried. The application of the developer draws Nonaqueous wet developer consists of an out the bright red indication as with the other absorbent powder suspended in a volatile liquid. two visible penetrant types and methods. Thisdeveloperoffersthehighestrelative EMULSIFIERS.Theemulsifiersdiscussed sensitivity and is used primarily for spot inspec- underthevarioustypesand methods are tion where the surface being inspected has not liquid additives which, when applied to post- been heated during the process. The sensitivity emulsifiablepenetrants,combine withthe of the developer can be increased by vibrating excesssurface penetrant to lenderitwater the spray gun during application. The preferred removable. These emulsifiers have low pene- method of application is spraying. It may also be trating properties, a necessary feature to avoid applied by brushing, but thisis not generally having the emulsifier remove the penetrant from preferred. the discontinuity. They are of a contrasting NOTE: Nonaqueous developers should not be color to the post-emulsifiable penetrant so that applied to a hot part until the part has been it can be determined easily if all the emulsifier cooled enough to be hand held. Some of the has been removed during the water rinsing. nonaqueous developers have aflash point of Properrinsingof fluorescentemulsifiersis 50°F. checked using the black light. Emulsifier dwell Developer dwell time will depend on the type time is that time which it takes for the emul- of penetrant developer and the type of defect. sifier to mix with the surface penetrant in order Allow sufficient time for an indication to form, for it to rinse properly. but do not allow penetrant to bleed into the DEVELOPERS.Aspreviouslymentioned developer in such quantities to cause a loss of under the types and methods (table 3-5), there defined indications. are three types of developersthy, aqueous wet, The developer dwell time will vary from a few and nonaqueous wet. minutes to an hour or more. A good rule of Dry developer isa highly absorptive fluffy thumb is as follows: development time for a white powder. It is applied to the part after it given material or type of defect is about one-half has been thoroughly driedand providesa of the time considered proper for penetration contrasting background to flaw indications and dwell time. absorbs the penetrant at the defect. The dry Interpreting Results type developerscauselessbleeding of the penetrantindication and thus provide better With penetrant inspections there are no false resolution. Tliz dry developer adheres primarily indications in the sense that such things occur in
50 Chapter 3AIRCRAFT MATERIALS
the magnetic particle inspection. However, there sectioning and viewing under black light will are two conditions which may create accumula- rapidly build up experience and knowledge of tions of penetrant that sometimes are confused the character of defects lying below various with true surface cracks. types of indications. For best results, inspection The first condition is a result of poor washing. should be done in a darkened area. The darker If all the surface penetrant is not removed in the the area of inspection, the more brilliant the washingorrinseoperationfollowingthe indications will show. This is extremely impor- penetration time, the unremoved penetrant will tant when looking for very fine indications. The be visible.This conditionisusually easy to inspection table should be kept free of random identify since the penetrant will be in broad fluorescentmaterials.If penetrant has been areas rather than in the sharp patterns found spilled in the inspection area, on the table, or with true indications. When accumulations of the operator's hands, it will fluoresce brilliantly unwashed penetrant are found on a part, the and may confuse the operator. part should be completely reprocessed. Degreas- Visible dye penetrant indications appear as ing is recommended for removal of all traces of red lines. As the developer dries to a smooth the penetrant. white coating, red indications will appear at the Another condition which may create false location of defects. If no red indications appear, indications is where parts are press-fit to each there are no surface flaws present. No special other. For example, if a wheel is press-fit onto a lighting is required for the visible dye penetrant shaft, the penetrant will show an indication at inspection. the fitline. This is perfectly normal since the Itispossibleto examine an indication of two parts are not meant to be welded together. discontinuity and to determine its cause as well Indications of this type are easy to identify since as its extent. Such an appraisal can be made if they are so regular in form and shape. something is known about the manufacturing The success and reliability of the penetration processes to which the part has been subjected. inspection depend upon the thoroughness with The extent of the indication, or accumulation of which the operator prepares the part from the penetrant, will show the extent of the dis- precleaning all the way through to the actual continuity, and the brilliance will be a measure search for indications.Itis not a method by ofitsdepth.Deep crackswillhold more which a part is thrown into a machine which penetrant and therefore will be broader and separates the good parts from the bad. The more brilliant. Very fine openings can hold only operator must carefully process the part, search small .amounts of penetrant and therefore will out indications, and then decide the seriousness appear as fine lines. of defects found in order to determine the The most effective training tool for identify- disposition of parts with indications. Penetrant ing and recognizing defects is a collection of inspectionsareimportanttoolsforfinding parts with typical defects which can be referred defects before those defects grow into failures. tofrequently. Parts that have been rejected As an operator, it is up to you to get the most because of defects should be clearly marked or out of the method used. partially damaged sothat theywill not be Fluorescent indications, when viewed under confused with acceptableparts.Unlessthe black light, fluoresce brilliantly and the extent defects are extremely large the indications will of the indication marks the extent of the defect. remain on the parts for several months or longer. Pores, shrinkage, lack of bond and leaks will It is not advisable to reinspect any part using show as glowing spots, while cracks, laps, forging a different type process than the one originally bursts or cold shuts will show as fluorescent used. Fluorescent penetrants and visible dye lines.Where alargedefecthastrappeda penetrants are not very compatible; therefore, if quantity of penetrant the indications will spread atallpossible,ifreinspection of apartis on the surface. Experience in the use of the required,theoriginalprocessshouldbe method allows interpretations to be drawn from employed. the extent of the spread as to the relative size of Documentation of penetrant inspections can the defects. Grinding into certain defects, or be done on Support Action Forms (SAF's),
51 AVIATION STRUCTURAL MECHANIC S 3 & 2
Maintenance Action Forms (MAF's), or Tech- their shatter resistance, which is much higher nicalDirective Compliance Forms (TDCF's), than that of the airstretched solid plastics. dependinguponthecircumstanceswhich Stretched acrylic is a thermoplastic conform- warrant or require the inspection. Figure 3-3 ing to Military Specification MIL-P-25690. This illustrates the use of a MAF for penetrant specification covers transparent, solid, modified inspection during acalendar inspection, and acrylicsheetmaterial having superior crack figure3-4illustratesthe TDCF being used propagation resistance (shatter resistance, craze because of an Aircraft Bulletin. When the MAF resistance,fatigueresistance)as aresult of is used, the worker in most cases initiates and proper hot stretching. completes the form, while the TDCF is usually Stretched acrylic is prepared from modified initiated by Maintenance/Production Control, acrylic sheets, using a processing technique in and the worker complies with it and completes which the sheet is heated to its forming tempera- the form. ture and then mechanically stretched so as to Detailed information on MAF's and TDCF's increase its area approximately 3 or 4 times with and their uses is covered in Military Require- a resultant decrease in its thickness. Most of the ments for Petty Officer 3 & 2, NavPers 10056-C, Navy's high-speed aircraft are equipped with and OpNav 4790.2 (Series) Instruction. canopies made from stretched acrylic plastic. Identification Most transparent plastic sheet used in naval NONMETALLIC MATERIALS aircraftis manufactured in accordance with various MIL specifications, some of which are TRANSPARENT PLASTICS listed in table 3-6. Individual sheets are covered with a heavy masking paper on which the Transparent plastic materials used in aircraft specification number appears. In addition to canopies,windshields, and other transparent serving as a means of identification, the masking enclosures may be divided into two major paper helps to prevent accidental scratching of classes, or groups, depending on their reaction to the plastic during storage and handling. heat. They are the THERMOPLASTIC materials and the THERMOSETTING materials. Table 3.6. Transparent plastics. Thermoplastic materialswillsoften when heated and harden when cooled. These materials can be heated until soft, formed into the desired shape, and when cooled will retain this shape. The same piece of plastic can be reheated and Tvrtp Specification No. reshaped any number of times without changing the chemical composition of the material. Solid Thermoplastic Thermosetting plastics harden upon heating, Thermoplastic Heat-resistant MIL-P-5425 and reheating has no softening effect. They acrylic cannot be reshaped after once being fully cured Modified acrylic MIL-P-8184 by the application of heat. These materials are Stretched modified MIL-P-25690 rapidly being phased out in favor of stretched acrylic (8184) acrylic, a thermoplastic material. Thermosetting Transparent plastics are manufactured in two Polyester craze MIL-P-8257 formsofmaterialsolid(monolithic)and resistant laminated. Laminated plastic consists of two sheets of solid plastic bonded to a rubbery Laminated - inner-layermaterial similar to the sandwich Laminated modified MIL- P- 25374 material used in plate glass. acrylic (8184) Laminated transparent plastics are well suited to pressurized applications in aircraft because of
52 Chapter 3-:-AIRCRAFT MATERIALS
MAINTENANCE ACTION FOAM OPMAY FORM 4790/40 (10 -69) SIN.0107.770.4400
I. JOBCONTROL NUMBER 2. TYPE [QUIP. 3. 60/SER NO, 4. ACTION S. WORN -6. MAINT. LEVEL 7. ACTION DATE ORO. CENTER ORG. OATE SER SUF pri-o n / PH6ao2o400 AREA /57 5" 77 PH5 El 04. I4T m3 p v4 6. *ORR UNIT CODE 9. MIEN DISCO 10. TYPE MAINT. II. ACTION I2. MM. II. ITEMS14. MAN. 16.EMT 16. TAXER PROC. HOURS /k-/ 030 0 P o 00o 0 Ill' 2O. REmOVEC TEM 2IINSTALLED ITEM
.1 USSR .2 SERIAL NUMBER .1 MEGA .2 SERIAL NO.
3 PART NUMDER . I E/CYCLES .3 FARTNUMBER TIME/CYCLES
D. I C. CORRECTIVE ACTION
CoMPLTs. CARD5 /33A-193A.1 0,e-... GomPLEre0 CART'S 139A-193;1.1i LooK PHASE CAI-en/04R IN5PecrioN ANDayePe'NETIMNr iNsPecrioni PPR CALENDAR IN5Ptcnom.
D. ENTRIES REQUIRED SIGNATURE E. CORRECTEO BY F. INSPECTED BY G. SUPERVISOR CON, IGLmAl IOM DYES ORO LOG 0 YES 0p ACCESS RECORD 0 'ICS II NO 11/ 0414/tr, 4 ilif3 X #1:4,414kAlf41c.0°i."17fAl $ 4 30. '3o-. % r- REPAIR CYCLE DATA FAILED MATERIAL
.1 ACT'2 .3 .4 .5 DATE DATE MAL OTY MAW PART NUMBER/REF..SYMBOL TAN
I. REMOVED 5. TO AMP
2 RECEIVED 'MAIL. CONTROL 6. OFF AMP
3. m3RA STARTEO 7. TO AwP
4. COMPLETED 6. OFF AAP
RFI O B CORD O R/S O 9.
O.
H. PCN PRIORITY DATE DUE
IN OUT
J. ACCUMULATED HOURS R. REQUIRED MATERIAL DATE/TIME NAME/SHIFT OATE MAN.HOUBS DAT REQ. NO. MFGR PART NUMBER OTT PRI ORD NEE
TOTAL . II
AM.5 Figure 3-3.- MAF used for penetrant inspection during calendar inspection.
53 AVIATION STRUCTURAL MECHANIC S 3 & 2
1 TECHNICAL DIRECTIVE COMPLIANCE FORM OPBAV PORN 4790/41 (10401. 0107710.4400
I. J05 CONTROL NUMBER 2. TOE 3 lei/SEA NO. 4. ACTION 5. WORK B. MAINTENANCE LEVEL 7. ACTION EQUIP. DAG CENTER 1 DATE PH5 2020 126 AAEA 156994 P115 120 LOROII]INT 11111 DEP
8.SYSTEM 9. STATUS III. ITEMS11.LIANNRSIT EMT 13. INTERIM 14. TECHNIC L DIRECTIVE IDENTIFICATION 15, CORR PRCC '21 II .1 11111CND..1UV. .4 AND .1 4411 .4KIT g 11 ,,E e / A 5"3. .5 74 80 I I 00 c46. OLD1 IBM 47 N W ITEM
.1 ATOP 2 SERIAL NUMBER .1 MFGR I.1 SERIAL PLOWER
3 PART NUMBER 3 PART WADER
A. PRI 8. TM Ay C. ASSISTANT RA CENTERS U BY DATEE. EST M/H F. CREW G. KIT REOG H. SE POD RITCENTERA SITE YESEa NOII YES NO 3 120 none 2024 4.0 1 Ej I. RE1 YWW
Perform dyepenetrantinspection as per A/C Bulletin Nn. 80
A. MATERIAL /KITSTOCIINUMBER B. DATE ORDERED C. SvUe NO. D. DATE F. ISSUED BY ItZEIVED
C. REMARKS G. OBLIVERBO BY
H. DATE
A. STATUS C.,..REMA KS G-STATUS CODES t 4 lat +A,tradti..)LYZsre)6.,;yx A-ASSISTING WORK CENTER . SAMT/CAMI C-COMPLIED TH IS NO. N B240.4.%p?10e.itaclo--.ze..e.fre0,17,,,,1 0-00ES NOT APPLY 1D. AGLOW% iS.HECT B 1 E.INS ECTE. BY F. SUPERV I SO P. PRE V I OUSLY COMTN. I ED I TM _21 Z. WiatAe14-Ams.1rx,,,hifilet.. -Ald5eW.WORK IN PROGRESS A. COmLIANCE RECORDED ON HISTORICAL RECORDS BOATS SIGNATURE 1LiEr- . ACCESSORY CARD 20Z(oba,42, ...C. CONFIGURATION PG DATE SIGNATURE IEl YES23NO g 0 2.6M, :7,y-42... A-21
AM.7 Figure 3-4.TDCF documentation for penetrant inspection. Identification of unmasked sheets of plastic is Storage and Handling often difficult; however, the following informa- tion mayserveasanaid.MIL-P-8184, a Transparent plastic sheets are available in a modified acrylic plastic, has a slight yellowish number of thicknesses and sizes which can be tint when viewed from the edge; MIL -P -8257, a cut and formed to required size and shape. thermosetting polyester plastic, has a bluish or These plastics will soften and/or deform when blue-green tint; and MIL-P-5425, heat-resistant heatedsufficiently;therefore,storage areas acrylic, is practically clear. In addition, stretched having hightemperatures must be avoided. acrylicsheets andfabricated assemblies are Plastic sheets should be kept away from heating permanently marked to insure positive iden- coils,radiators, hot water, and steam lines. tification. Storage should be in a cool, dry location away Plastic enclosures on aircraft may be distin- from solvent fumes, such as may exist near paint guished from plate...glass enclosures by tapping spray and paint storage areas. Paper masked lightly with a blunt instrument. Plastic will transparent plastic sheets should be kept indoors resound with a dull thud or soft sound, whereas as direct rays of the sun will accelerate deteriora- plate glass will resound with a metallic sound or tion of the masking paper adhesive, causing it to ring. cling to the plastic so that removal is difficult.
54 Chapter 3AIRCRAFT MATERIALS
Plasticsheetsshouldbe stored with the removed permanently; therefore, prevention of masking paper in place, in bins which are tilted crazing is a necessity.) at approximately 10 degrees from the vertical to When it is necessary to remove masking paper prevent buckling.Ifitisnecessary to store from the plastic sheet during fabrication, the sheets horizontally, care should be taken to surface should be remasked as soon as possible. avoid chips and dirt getting between the sheets. Either replace the original paper on relatively Stacks should not be over 18 inches high, and flat parts or apply a protective coating on curved small sheets should be stacked on the larger ones parts. toavoid unsupported overhang.Storage of transparent plastic sheets presents no special fire REINFORCED PLASTICS hazard, as they are slow burning. Masking paper should be left on the plastic Glass fiber reinforced plastic and honeycomb sheetas longaspossible.Careshould be areusedintheconstruction of radomes, exercised to avoid scratches and gouges which wingtips, stabilizer tips, antenna covers, fairings, may be caused by sliding sheets against one access covers, etc.It has excellent dielectric another or across rough or dirty tables. characteristics,makingitidealforusein Formed sections should be stored so that they radomes. Its high strength/weight ratio, resist- are amply supported and there is no tendency ance to mildew and rot, and ease of fabrication for them to lose their shape. Vertical nesting make it equally suited for other parts of the should be avoided. Protect formed parts from aircraft. Themanufactureofreinforcedplastic temperatures higher than120°F. Protection laminates involves the use of liquid resins re- from scratches may be provided by applying a inforced with a filler material. The resin, when protective coating. properly treated with certain agents known as If maskingpaperadhesivedeteriorates catalysts, or hardeners, changes to an infusible through long or improper storage, making re- solid. moval of paper difficult, moisten the paper with The reinforcement materials are impregnated aliphaticnaphtha,whichwillloosenthe with the resin while the latter is still in the liquid adhesive. Sheets so treated should be washed (uncured) state. Layers or plies of cloth are immediately with clear water. stacked up and heated under pressure in a mold CAUTION:Aliphaticnaphtha ishighly to produce the finished, cured shape. Another volatile and flammable. Extreme care should be technique, called "filament winding," consists of exercised when using this solvent. winding a continuous glass filament or tape, Do notusegasoline,alcohol,kerosene, impregnated with uncured resin, over a rotating xylene,ketones,lacquerthinners,aromatic male form. Cure is accomplished in a manner hydrocarbons, ethers, glass cleaning compounds, similar to the woven cloth reinforced laminates. or other unapproved solvents on transparent Glass fiber reinforced honeycomb consists of a acrylicplastics to remove masking paper or relatively thick, central layer called the core and otherforeignmaterial, as thesewill soften two outer laminates called facings. (See figure and/or craze the plastic surface. (NOTE: Just as 3-5.) woods split and metals crack in areas of high, The core material commonly used in radome localized stress, plastic materials develop, under construction consists of a honeycomb structure similar conditions, small surface fissures called made of glass cloth impregnated either with a CRAZING. These tiny cracks are approximately polyester or epoxy, or a combination of nylon perpendicular to the surface, very narrow in and phenolic resin. The material is normally width, and usually not over 0.01 inch in depth. fabricatedin blocks that are later cut on a These tinyfissures are not only an optical bandsaw to slices of the exact thickness desired, defect, but also a mechanical defect, inasmuch or it may be originally fabricated to the proper asthereisa separation or parting of the thickness. material. Once a part has been crazed, neither The facings are made up of several layers of theopticalnormechanical defect can be glass cloth, impregnated and bonded together
55 AVIATION STRUCTURAL MECHANIC S 3 & 2
balsa wood. This material is found in a variety of places such as wing surfaces, decks, bulkheads, HONEYCOM B stabilizersurfaces,ailerons, trim tabs, access CORE doors, and bomb bay doors. Figure 3-6il- lustrates one type of sandwich construction using a honeycomb-like aluminum alloy core, sandwiched between aluminum alloy sheets, called facings. The facings are bonded to the lightweightaluminum core withasuitable adhesive so as to develop a strength far greater than that of the components themselves when used alone. Another type structural sandwich construc- tion consists of a low-density balsa wood core FA CINGS combined with high-strength aluminum alloy (MULTIPLE LAYERS OF GLASS CLOTH) facings bonded to each side of the core. The grain in the balsa core runs perpendicular to the AM.230 aluminum alloy facings, and the core and alumi- Figure 3-5.Reinforced plastic. num facings are firmly bonded together under controlled temperatures and pressures. with resin. Each layer of clothis placed in The facings in this type construction carry the position andimpregnated with resin before major bending loads, and the cores serve to another layerisadded. Thickercloths are support the facings and carry the shear loads. normally used for the body of the facings, with The outstandingcharacteristicsof sandwich one or more layers of a finer weave cloth on the construction are strength, rigidity, lightness, and surface. surface smoothness. The resins are thick, sirupy liquids of the so-called contact-pressure type (requiring little or no pressure during cure), some times referred to as contact resins. They are usually thermoset- tingpolyester or epoxy resins. Cure can be UPPER FACING effected by adding a catalyst and heating, or (SKIN) they can be cured at different temperatures by adjusting the amount and type of catalysts. CORE - ALUMINUM Inspection and repair procedures for reinforced HONEYCOMB plastic are covered in chapter 7 of this manual. ADHESIVE TAPE
SANDWICH CONSTRUCTION LOWER FACING From the standpoint of function, sandwich (SKIN) parts in naval aircraft can be divided into two broad classes: (1) radomes and (2) structural. The first class, radomes, is a reinforced plastic sandwich construction designed primarilyto permit accurate and dependable functioning of the radar equipment. This type construction was discussed in the preceding section under rein- forced plastics. The second class, referred to as structural sandwich, normally has either metal or rein- AM.231 forced plastic facings on cores of aluminum or Figure 3.6.Sandwich construction.
56 CHAPTER 4
AIRFRAME CONSTRUCTION
Familiarity with the various terms used in outline and general design. They vary mainly in reference to airframe construction is one of the size and arrangement of the different compart- firstrequirements of the Aviation Structural ments. Detail design varies with the manufac- Mechanic.Maintenanceoftheairframeis turer and the requirements of the type of service primarily the responsibility of the AMS; there- which theyareintended to perform. For fore, he should be familiar with the principal instance, the U-16 (widely used in Search and units which make up the airframe and know the Rescue) may have to operate as an amphibious purpose, location, and construction features of aircraft.Whenoperatingfromwaterthe each. fuselage, being watertight, keeps the aircraft The airframe of afixed-wing (sometimes afloat. In fact, the fuselage so nearly performs referredtoas "conventional" when distin- the function of a boat thatitiscalled the guishing from helicopters) aircraft is generally HULL. considered to consist of five principal unitsthe Two general types of fuselage construction fuselage, wings, stabilizers, flight control sur- arethe WELDED STEEL TRUSS and the faces, and landing gear. Helicopter airframes MONOCOQUE designs. The welded steel truss is consist of the fuselage (or hull), main rotor and usedin many of the smaller,civilian type related gearbox, tail rotor (on helicopters with a aircraft and was formerly used in many Navy single main rotor), and the landing gear. A aircraft. It is still being used in some helicopters. further breakdown of these principal units into An example of truss type construction is shown major componentsis made inthis chapter, in figure 4-1. describing the purpose, location, and construc- tion features of each.
FIXED-WING AIRCRAFT
FUSELAGE
The fuselage is the main structure or body of the airframe. It provides space for personnel, cargo, controls, and most of the accessories and other equipment. In single-engine aircraft, it also houses the powerplant. In multiengine aircraft the engines may either be in the fuselage, or attached to or suspended frbm the wing struc- ture. Fuselages of the various types of naval aircraft A1111.232 have much M common from the standpoint of Figure 44.Truss type fuselage construction.
57 AVIATION STRUCTURAL MECHANIC S 3 & 2
The monocoque design relies largely on the which usually extend across several points of strength of the skin or covering to carry the support. The longerons are supplemented by various loads (discussedin chapter3). This other longitudinal members, called STRING- designmay bedividedintothreeclasses: ERS. Stringers are more numerous and lighter MONOCOQUE, SEM1MONOCOQUE, and RE- inweightthanarelongerons. The vertical INFORCED SHELL. The monocoque has as its structural members are referred to as BULK- only reinforcement vertical rings, station webs. HEADS, FRAMES,andFORMERS.The formers, and bulkheads. The semimonocoque heaviest of these vertical members are located at has, in addition to these vertical reinforcements, intervalstocarry concentrated loads and at the skin reinforced by longitudinal members. points where fittings are used to attach other The reinforced shell has the skin reinforced by a units,suchasthewings, powerplant, and complete framework of structural members. stabilizers. Figure 4-2 shows a modified form of Different portions of the same fuselage may thr, monocoque design now used in all combat- belong to any one of these three classes, but type aircraft, most Navy !Aircraftare considered to be of The metal skin, or covering, is riveted to the semimonocoque type construction. longerons,bulkheads,andotherstructural The semimonocoque fuselage is constructed members andcarries part of the load. Skin primarilyofthealloysof aluminum and thickness varies with the loads carried and the magnesium, althoughsteel and titanium are stresses sustained. found in areas of high temperatures. Primary There are a number of advantages in the use bending loads are taken by the LONGERONS, of the semimonocoque fuselage. The bulkheads,
AM.233 Figure 4-2.Semimonocoque fuselage construction.
58 Chapter 4AIRFRAME CONSTRUCTION frames, stringers, and longerons facilitate the Various points on the fuselage are located by designandconstructionofa streamlined stationnumber. Station 0 (zero)isusually fuselage, and add to the strength and rigidity of located at or near the nose of the aircraft, and the structure. The main advantage; however, lies other stations are located at measured distances in the fact thatit does not depend on a few (in inches) aft of station zero. members for strength and rigidity. This means A typical station diagram is shown in figure that a semimonocoque fuselage, because of its 4-3. On thisparticular aircraft, station 0 is stressed-skinconstruction,maywithstand located16 inches forward of the nose. The considerable damage and still be strong enough fuselage break (for engine removal) is located at to hold together. station 277.5. Fuselages are generally constructed in two or Quick access to the accessories and other more sections. On fighters and other small types equipment carried in the fuselage is provided for of aircraft, they are generally made in two or by numerous access doors, inspection plates, three sections, while larger aircraft may be made landingwheelwells,andotheropenings. up of as many as six sections. Servicing diagrams showing the arrangement of
Le, hn o .0o A tly, M 041 N /NJ CV trt rca wi en Is to 0 0 :1 N esi
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AM. 234 Figure 43.Typical station diagram. equipment and location of access doors are particular design for any given aircraft depends suppliedby the manufacturer inthe Main- upon a number of factors; for example, size, tenance Instructions Manual and Maintenance weight, and use of the aircraft,itsdesired Requirements Cards for each aircraft. 7.3ure 44 landing speed and desired rate of climb. The shows the servicing diagram for a typical air- wings are designated as left and right, cor- craft. responding to the left and right sides of the pilot when seated in the aircraft. The wings of Navy aircraft are usually of WINGS all-metal construction with cantilever design; that is no external bracing. Both aluminum alloy The wings are airfoils designed to develop the and magnesium alloy are used extensively in major portion of the lift of the aircraft. The wing construction. The internal structureis
59 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.235 Pneumatic system servicing. 1. Forward refueling and defueling receptacle. 10. Compressor oil reservoir. 2. Aft refueling and defueling receptacle. 11. Pneumatic system chemical dryer. 3.Oil filling and draining. 12. Pneumatic system depressurizing and draining. 4. Liquid oxygen filling and draining. 13. Electronic pressurizing desiccator. 5. Emergency oxygen servicing. 14. Pitot-static system draining. 6. Hydraulic reservoir servicing panel. 15. 7. Hydraulic systems servicing. 16. Landing gear strut servicing. Arresting gear snubber. 8. Hydraulic reservoirair dump valves and sight 17. Arresting gear hook bumper. gages. 18. 9.Accumulator servicing. 19. A-c external power. Figure 4-4.Typical servicing diagram.
60 Chapter 4AIRFRAME CONSTRUCTION made up of SPARS and STRINGERS running theribs to the spars. The spars support all spanwise, and RIBS and FORMERS running distributedloadsaswellasconcentrated chordwise (leading edge to trailing edge). The weights, such as fuselage, landing gear, and (on spars are the principal structural members of the multiengine aircraft) nacelles. Corrugated sheet wing and are often referred to as BEAMS. aluminum alloy is sometimes used as a subcovey One of the numerous methods of wing ing for wing structures, especially on very constructionis shown in figure 4-5. In this aircraft. The C-I 21wing has thistype of illustration two main spars are used with ribs construction. placed at intervals to space them and develop The wing, like the fuselage, is constructed in wingcontour.ThisiscalledTWO-SPAR sections. One commonly used type is made up construction. Other variations of wing construc- of a CENTER SECTION with OUTER PANELS tion include MONOSPAR (one spar), MULTI- and WINGTIPS. Another arrangement may have SPAR (three or more spars), and BOX BEAM in WINGSTUBS as integral parts of the fuselage in which stringers and spar-like sections are joined place of the center section, although from the together in a box shaped beam about which the outside they are very much like the wing center remainder of the wing is constructed. section in appearance. The skin is riveted, or in some cases attached Inspection openings and access doors are with screws, to all these internal members and provided, usually on the lower surfaces of the carries part of the wing stresses. During flight, wing, and drain holes are placed in the lower. applied loads which are imposed on the wing surfaces. On some aircraft, built-in walkways are structure act primarily on the skin. From the provided on the areas where it is intended that skin they are transmitted to the ribs and from personnel will walk or step. On others there are
TRAILING EDGE
NOSE FAIRING
RIBS
SPARS
AM.236 Figure 4-5. Two -spar wing construction.
61 AVIATION STRUCTURAL MECHANIC S 3 & 2
LEFT AND RIGHT WINO JACK POINT FITTINGS
N MAIN STRUT JACK POINT R/H AND L/H
FUSELAGE JACK POINT FITTING
/7- I) )53111
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TAIL JACK POINT FITTING
AM.237 Figure 46.Typicat jacking diagram. no built-in walkways, but removable mats or STABILIZERS covers are used to protect the wing surface when servicing the aircraft. The stabilizing surfaces of an aircraft consist of vertical and horizontal airfoils, called the Jacking points are providedon the underside VERTICAL STABILIZER (orfin) and the of each wing in the form of recessed openings HORIZONTAL STABILIZER.Thesetwo for quick installation of jackpads. A typical airfoils, together with the rudder and elevators, jacking diagram is shown in figure 4-6. Onsome form the tail section. For inspection and main- aircraft the jackpads may be used as tiedown tenance purposes theentiretailsectionis fittings for tiedown of the aircraft; other aircraft considered a single unit of the airframe called make use of removable jackpads andmore the EMPENNAGE. convenienttiedownfittings.Jackingand The primary purpose of the stabilizers is to tiedownproceduresaredescribedfullyin stabilize the aircraft in flight, that is, to keep the chapter 12. craft in straight and level flight. The vertical stabilizer maintains the stability of the aircraft Various points on the wingare located by aboutitsverticalaxis.Thisis known as station number. Wing station 0 (zero) is located DIRECTIONAL STABILITY.Thevertical at the centerline of the fuselage, and all wing stabilizer usually serves as the base to which the stations are measured outboard from that point, rudderisattached. The horizontal stabilizer in inches. provides stability of the aircraft about the lateral 62 Chapter 4AIRFRAME CONSTRUCTION axis. This is LONGITUDINAL STABILITY. It movement is about the lateral axis. The rudder, usually serves as the base to which the elevators attached to the vertical stabilizer, determines the are attached. horizontal direction of flight (turning or yawing Onallhigh-performanceaircraftthe motion) of the aircraft. This is DIRECTIONAL horizontal stabilizer isa movable airfoil, con- CONTROL and it occurs about the vertical axis trollable from the cockpit, commonly referred of the aircraft. to as the "flying tail." At extremely high (at or The ailerons and elevators are operated from about the speed of sound) speeds, the elevators the cockpit by a control stick on fighter type have a tendency tolosetheir effectiveness. aircraft and by a wheel and yoke assembly on Forces acting upon the control stick become largeaircraftsuch as transports and patrol veryhigh, andlongitudinalcontrol of the planes. The rudder is operated by rudder pedals aircraft becomes difficult. By changing the angle on all types of aircraft. of attack of the stabilizer, adequate longitudinal The ailerons are operated by a lateral (side to control is maintained. This is accomplished by side) movement of the control stick, or a turning raising or lowering the leading edge of the motion of the wheel on the yoke, and are stabilizer. interconnected inthe control system so that Construction features of the stabilizers are in they work simultaneously in opposite directions many respects identical with those of the wings. to one another. As one aileron moves downward They are usually of all-metal construction and of to increase lift on its side of the fuselage, the cantileverdesign.Monospar andtwospar aileron on the opposite side of the fuselage construction are both commonly used. Ribs moves upward to decrease lift on its side. This develop the cross-sectional shape. Fairing is used opposingactionresultsinmoreliftbeing to round out the angles formed between these produced by the wing on one sideof the surfaces and the fuselage. fuselage than on the other side, the result being a controlled movement or roll due to unequal forces on the wings. FLIGHT CONTROL SURFACES The elevators are operated by a fore-and-aft movement of the control stick or yoke, as the The flightcontrol surfaces arehinged or case may be. Raising the elevators causes the movable airfoils designed to change the attitude aircraft to climb; lowering the elevators causes it of the aircraft during flight. The basic controls to dive or descend. The elevators are raised by aretheAILERONS, ELEVATORS,and pulling back on the stick or yoke, and they are RUDDER. A miscellaneous grouping of the lowered by pushing the stick or yoke forward. remainder of the flight controls would include The rudder is operated by the rudder pedals theTRIM TABS, SPRING TABS, WING SPEED BRAKES, SLATS,and andis used to move the aircraft about the FLAPS, vertical axis. Moving the rudder to the right SPOILERS. turns the aircraft to the right; moving it to the Basic Controls left turns the aircraft to the left. The rudder is moved to the 'jell by pushing the right rudder The basic controlsailerons, elevators, and pedal, and is moved to the left by pushing the rudderare used to move the aircraft about its left pedal. Practicallyallhigh-speed aircraft have hy- three axes.(Seefig.4-7.) The aileronsare attached to the trailing edge of the wings and draulic actuators incorporated within the flight control the rolling (or banking) motion of the control systems to aid the pilot in movement of aircraft.Thisis known as LONGITUDINAL the control surfaces at accelerated airspeeds. CONTROL since the rollis about the longi- Another method of decreasing the amount of tudinalaxis. The elevators, attachedto the force required to operate the controls is by the horizontalstabilizers,controltheclimbor use of spring tabs, which are described later. descent (pitching motion of the aircraft). This is The construction of control surfaces is similar known as LATERAL CONTROL sincethe to that of the wing and stabilizers. They are
63 AVIATION STRUCTURAL MECHANIC S 3 & 2
VERTICAL AXIS
LATERAL AXIS
LONGITUDINAL AXIS
AM.238 Figure 4-7.Axes and fundamental movements of the aircraft. usually built around a single spar or torque tube. controls not designated as basic controls. These Ribs are fitted to the spar near the leading edge, controls supplement the basic controls by aiding and at the trailing edge are joined together with the pilot in controlling his aircraft. There are a suitable metal strip or extrusion. The control various types used on naval aircraft, but only the surfaces of some aircraft are fabric-covered, but most common are discussed here. alljetaircrafthaveall-metalsurfacesfor TRIM TABS.Trim tabs are small airfoils additional strength. Some basic control surfaces recessed into the trailing edge of a basic control have lead counterweights inside the leading edge. surface. Their purpose is to enable the pilot to This balances the surface, makilig it easier to trim out any unbalanced condition which might move the surface in flight. Counterweights also exist during flight, without exerting any pressure prevent the surface from fluttering during flight. on the control stick or rudder pedals. Each trim For greater strength, especially inthinner tab is hinged to its parent control surface, but is airfoil sections typical of trailing edges, a honey- operated independently by a separate control. comb type of construction is utilized. (This type Trimming is accomplished by setting the tab of material is described in detail in chapter 3.) in the opposite direction to that in which it is desiredfor thebasic control surface to be Miscellaneous Flight Controls moved. The airflow striking the trim tab causes the larger surface to move to a position that will Miscellaneousflightcontrols include those correct the unbalanced condition of the aircraft. 64 Chapter 4AIRFRAME CONSTRUCTION
For example, to trim out a hose-heavy condi- tion, the pilot sets the elevator trim tab in the DOWN position. This causes the elevator to be moved and held in the UP 'position, which in 111=1111P----- turn causes the tail of the aircraft to be lowered. PLAIN FLAP Without the use of the trim tab, the pilot would 111'ilii\) have to hold the elevator in the UP position by exerting constant pressure on the control stick or wheel. Internal construction of trim tabs is similar to that of the other control surfaces, although increasing use is being made of plastic materials to fill the tab completely, thus improving its stiffness. They may also be honeycomb filled. loom(--411111111111 Tabs are covered with either metal or reinforced LEADING EDGE plastic. Trim tabs are actuated either electrically FLAP or manually on all aircraft. SPRING TABS.Spring tabs are similar in appearance to trim tabs, but serve an entirely different purpose. Spring tabs are used for the same purpose as hydraulic actuators, that is, to FOWLER FLAP aid the pilot in moving a larger control surface. On the P-2 aircraft, a spring tab is hinged to the trailing edge of each aileron alongside the AM.239 trimtab.The spring tabis actuated by a Figure 4-8.Types of flaps. spring-loaded, push-pull rod assembly which is also linked to the aileron control linkage. The linkage is connected in such a way that move- ment of the aileron in one direction causes the use of flaps during takeoff serves to reduce the spring tab to be deflectedinthe opposite length of the takeoff run. direction. This provides a balanced condition, Most flaps are hinged to the lower trailing thus reducing the amount of force required by edges of the wings inboard of the ailerons; the pilot to move the ailerons. The deflection of however, leading edge flaps are in use on at least the spring tab is directly proportional to the one model Navy aircraft, the F-4, Phantom II. aerodynamic load imposed upon the aileron. Four types of flaps are shown in figure 4-8. The Therefore, at low speeds the spring tab remains PLAIN type flap forms the trailing edge of the in a neutral position with respect to the aileron airfoil when the flap is in the up position. In the (faired) and the aileron is then entirely manually SPLIT flap, the trailing edge of the airfoil is split controlled. At high speeds, however, where the and the lower half is so hinged that it can be aerodynamic load is great, the tab functions as lowered to form the flap. The FLOWER flap an aid to the-pilot in moving the primary control operates on rollers and tracks, causing the lower surface. Spring tabs are referred to by some surface of the wing to roll out and then extend manufacturers as balance tabs, other may call downward. The LEADING EDGE flap operates them servo tabs. similar to the plain flap, that is, it is hinged on WING FLAPS.Wing flaps are used to give the bottom side and, when actuated, the leading the aircraft extra lift. Their purpose is to reduce edge of the wing actually extends in a downward the landing speed, thereby shortening the length direction to increase the camber of the wing. of the landing rollout, and to facilitate landing Leading flaps are used in conjunction with other in small or obstructed areas by permitting the type flaps. gliding angle to be increased without greatly SPOILERS.Spoilers, in general, are for the increasing the approach speed. In addition, the purpose of decreasing wing lift; however, their
65 AVIATION STRUCTURAL MECHANIC S 3 & 2 specificdesign,function, and use vary with Lateral control of the A-5 is exercised entirely different type aircraft. through a system of spoilers and deflectors. In The spoilers on theP-2 aircraft are long thisinstallation.an automatic ratio changer narrow surfaces, hinged at their leading edge to provides reduced throw of thespoilers and the upper wing skin.(Seefig.4-9.) In the deflectors for the same amount of stick move- retracted position, the spoiler is flush with the ment when above a given speed. This reduces wing skin. The action of the spoilersis to the rate of roll and keeps it within controllable destroy the smooth flow of air over the wing so limits. that burbling takes place. The lift is consequent- SPEED BRAKES.Speed brakes are hinged ly greatly reduced and considerable dragis movable control surfaces used for reducing the added to the wing. Spoilers are effective for speed of aircraft. Some manufacturers refer to 'ateralcontrol of the P-2 at high angles of them as DIVE BRAKES, others call them DIVE attack. In the extended position, the spoiler is FLAPS.On some aircraft they are hinged to the pivotedup and forward approximately 60 sides or bottom of the fuselage, on others they degrees above the hinge point. are attached to the wings. Regardless of their Another type of spoiler in common use is a location, speed brakes serve the same purpose on long, slender, curved and perforated baffle that allaircraft on which they are used. Their israisededgewise throughthe wing upper primary purposeisto keep the speed from surface forward of the aileron. It also disrupts building up too high in dives. They are also used the orderly flow of air over theairfoil and inslowing down the speed of the aircraft destroys lift. This type of spoiler is used on S-2 preparatorytolanding.Speedbrakesare aircraft and is also illustrated in figure 4-9. operated hydraulically or electrically. The S-2 spoilers are actuated through the SLATS.Slats are movable control surfaces same linkage that actuates the ailerons. This attached to the leading edge of the wing. When arrangement makes movement of the spoiler the slat is retracted, it forms the leading edge of dependent upon movement of the aileron. The thewing. When theslatis open (extended linkageto the aileronis devised so that the forward), a slot is created between the slat and spoileris extended only when the aileron is the wing leading edge. Thus, high-energy air is raised. In other words, when the aileron moves introduced into the boundary layer over the top downward, no deflection of the spoiler takes of the wing. At low airspeeds this improves the place. lateral control handling characteristics, allowing the aircraft to be controlled at airspeeds below the otherwise normal landing speed. This is known as "boundary layer control." Boundary layer control is intended primarily for use during operations from carriers; that is, for catapult takeoffs and arrested landings. Boundarylayercontrolcanalso be ac- complished by directing high-pressure engine FLAP TYPE bleed air through a narrow orifice located just forward of the wing flap leading edge. This latter method is used on the T-1 aircraft. (Review NavPers 10307-C, Airman.)
LANDING GEAR Thelandinggearoffixed-wingaircraft RETRACTABLE TYPE consists of main and auxiliary units. For land- based aircraft and amphibians, two main wheels AM.240 are placed side by side under the wings or under Figure 4-9.Types of spoilers. the fuselage, and an auxiliary wheel is located
66 Chapter 4AIRFRAME CONSTRUCTION either under the nose or tail. If the aircraft is with hydraulic fluid and compressed air or designed for carrier operations, an arresting gear nitrogen.Figure4-11 showstheinternal (hook) is also provided. When amphibians are construction of a shock strut. operatingfromwater,thehullprovides The telescoping cylinders, known as cylinder buoyancy, but because of the large wingspan, and piston, when assembled, form an upper and wingtip floats are needed to provide stability at lower chamber for movement of the fluid. The low speeds. lower chamber (piston) is always filled with The landing gearof theearliest aircraft fluid,whiletheupper chamber(cylinder) consisted merely of protective skids attached to contains compressed air or nitrogen. An orifice the lower surfaces of the wing and fuselage. As isplaced between the two chambers through aircraftdeveloped, skids became impractical, whichfluid passes intothe upper chamber and were replaced by a pair of wheels placed during compression and returns during extension side by side ahead of the center of gravity with a of the strut. The size of the orifice is controlled tailskidsupporting the aftsection of the by the movement of a tapered metering pin up aircraft. The tail skid was later replaced by a and down through the orifice. swivelingtailwheel.Thisarrangementwas Whenever a load comes on the strut due to standard on all land-based aircraft for so many landing or taxiing and compression of the two years that it became known as the conventional strut halves starts, the piston (to which wheel type landing gear. As the speed of aricraft and axle are attached) forces fluid through the increased,theeliminationofdrag became orifice into the cylinder, where the rising fluid increasingly important. This led to the develop- level compresses the air or nitrogen above it. ment of retractable landing gear. When the strut has made sufficient stroke to Just before World War II, new aircraft were absorb the energy of the impact, the air or designed with the main landing gear located nitrogen at the top expands and forces the fluid behind the center of gravity and an auxiliary back. The slow metering of the fluid acts as a gear under the nose of the fuselage. This became snubber, preventing rebounds. Instructions for known as the tricycle type landing gear, and in servicing shock struts with hydraulic fluid and many ways, itis a keig improvement over the compressed air or nitrogen are contained on an conventional type. The tricycle gear is more instruction plate attached to the strut, as well as stable in motion on the ground, maintains the in the Maintenance Instructions Manual for the fuselage in a level position which increases the typeaircraft involved. The shock absorbing pilot's visibility and control, and also makes qualities of a shock strut are heavily dependent landing easier, especially in cross winds. Nearly on maintenance of properairornitrogen all present-day Navy aircraft including amphi- pressure and fluid level. (Shock strut servicing is bians are equipped with this type landing gear. covered in chapter 12.) RETRACTING MECHANISMS.Some air- Main Landing Gear craft have electrically actuated landing gear but most are hydraulically actuated. In figure 4-10, A main landing gear assembly is shown in theretractingmechanism ishydraulically figure4-10.The major components of the actuated and consists of an actuating cylinder, assembly are shock strut,tire,tube, wheel, UP position and DOWN position locks, a safety retracting and extending mechanism, and side switch, two position-indicating switches, and struts and supports. Tires, tubes, and wheels are sidestruts andsupports. The landing gear discussed in chapter 9. A description of the control handle in the cockpit allows the landing major components follows. gear to be retracted or extended by directing The shock strutabsorbs theshock that hydraulic fluid under pressure to the actuating otherwise would be sustained by the airframe cylinder. The locks hold the gear in the desired structure during takeoff, taxiing, and landing. position and the safety switch prevents ac- The AIR-OIL type shock strut is used on all cidental retracting of the gear when the aircraft Navy aircraft.This type strutis composed is resting on its wheels. essentially of two telescoping cylinders filled A position indicator on the instrument panel 67 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.241 1. Side strut bearing support 9. Shock strut 2. Truss member. 10. Safety switch. 3. Fulcrum bearing support 11. Torque arms. 4. Springloaded cartridge. 12. Towing eye. 5. Hydraulic actuating cylinder. 13. Brake assembly. 6. Down lock assembly. 14. Lower side strut member. 7. Air valve. 15. Upper side strut member. 8. Piston rod attachment fitting. Figure 4-10.Main landing gear assembly.
68 Chapter 4AIRFRAME CONSTRUCTION
Nose Gear A typical nose gear assembly is shown in All VALUE figure 4-12. Major components of the assembly includeshockstrut,dragstruts,retracting mechanism,wheel,tire,tube, and shimmy damper.
OUTER The nose gear shock strut, drag struts, and CYLINIER retracting mechanism are all similar to those already described for the main landing gear. The shimmy damper is a self-contained hy- NETERINO PIN draulic unit which resists sudden twisting loads applied to the nosewheel during ground opera- RIFICE PLATE tion but does permit slow turning of the wheel. (See fig. 4-12.) The primary purpose of the shimmy damper isto prevent the nosewheel fromshimmying(extremelyfastleft-right oscillations) during takeoff and landing. This is IONE ORIFICE AIMS accomplished by the metering of hydraulic fluid through a small orifice between two cylinders or chambers. Some aircraft are equipped with steerable INNER nosewheels and do not require a separate self- CYLINIER contained shimmy damper. In such cases, the (PISTON) steering mechanism is hydraulically controlled WHEEL AXLE and incorporates two spring-loaded hydraulic 1411%,, TOYING EYE steering cylinders which, in addition to serving asa steering mechanism, also automatically subdue shimmy and center the nosewheel.
Tail Gear The tail gear assembly consists of a shock strut, retracting mechanism, wheel, tire, yoke, centering mechanism, and locking mechanism. AM.242 The shock strut and retracting mechanism are Figure 4-11.Shock strut, showing internal construction. similar to those described for the main landing gear. The wheel is usually equipped with a solid rubbertire;however, someaircraftusea indicates the position of the landing gear to the pneumatic tire on thetail wheel. The yoke pilot. The position indicator is operated by the usuallyconsists of a fork or single arm of position-indicating switches mounted on the UP aluminum or steel, which link the wheel axle and DOWN locks of each landing gear. with the shock strut. The centering mechanism EMERGENCY EXTENTION.Methods of causes the tailwheel to caster to the trailing extending the landing gear inthe event of position during ground handling of the aircraft. normal system failure vary with different models It consists of a spring assembly which forces a of aircraft. Most aircraft utilize an emergency roller against a cam mounted on top of the hydraulic system.Allothers are pneumatic shock strut inner cylinder. (compressedairornitrogen),mechanical, The locking mechanism is independent of the gravity, or a combination of these systems. centering mechanism andis operated by a
69 AVIATION STRUCTURAL MECHANIC S 3 & 2
2
to
GEAR UP
GEAR DOWN
AM.243
1. Hydraulic actuating cylinder. 8. Cam. 2. Downlock switch. 9. Lower drag strut member. 3. Up lock cylinder. 10. Up lock engagement fitting. 4. Uplock switch. 11. Piston-axle. 5. Up lock. 12. Torque arms. 6. Upper drag strut 13. Shock strut cylinder. 7. Down lock. 14. Shimmy damper. Figure 4-12.Nose gear assembly. control cable system connected to the tailwheel is used only during takeoff and landing. When lock control lever in the cockpit. When the the control lever is placed in UNLOCK, the tail- control lever is in LOCK position, the tailwheel wheel is free to swivel. This position must be is locked in the trailing position. LOCK position used for taxiing and all other ground handling
70 Chapter 4AIRFRAME CONSTRUCTION
PRIMARY RELEASE DASHPOT CABLE BOTTLES
ARRESTING HOOK BUMPER
ARRESTING HOOK ASSEMBLY
EMERGENCY RELEASE CABLE
AM.244 Figure 4-13.Arresting gear installation. operations. FAILURE TO OBSERVE THIS hook, and conduct specifiedinspection and CAN RESULT IN SERIOUS STRUCTURAL regular replacement of hook points. Removed DAMAGE. hooks are forwarded to the nearest naval air stationthatprovidesDepotmaintenance Arresting Gear support for inspection, test, and overhaul. Thearresting gear shown infigure 4-13 consists of an arresting hook and its control Tail Skag mechanism. The hook generally consists of a steel shank and detachable steelpoint. The Most aircraft having a tricycle type landing control mechanism is hydraulically operated. It gear are equipped with a tail skag to protect the is similar to the retracting mechanism for the aft fuselage section from damage while landing, landing gear, but is operated independently of taxiing, or while being serviced. the landing gear by a separate control in the The tail skag consists of a steel shoe or solid cockpit. On some aircraft the arresting gear is wheel, a conventional air-oil shock strut, retract- electrically operated. ing mechanism, and attachment fittings. The The aircraft arresting gear is a critical part of retracting mechanism operates simultaneously the aircraft equipment. In keeping with this with the landing gear mechanism so that when importance, operating activities are required to the landing gearis lowered the tail skag is maintain the appropriatelogs, including the lowered, and when the landing gear is retracted number of arrested landings on every arresting thetailskagis retracted. Some aircraft are
71 AVIATION STRUCTURAL MECHANIC S 3 & 2 equipped with a stationary bumper in place of a the ground (hover). No runway is required for a retractable tail skag. helicopter to takeoff or land. The roof of an office building is an adequate landing area. The helicopter is considered a safe aircraft because ROTARY-WING AIRCRAFT the takeoff and landing speed is practically zero. As willbe noticed during studyof the Thehistoryof rotary-wingdevelopment following section concerning the construction of embraces 500-year oldefforts to produce a helicopters, they are in many ways similar to workable direct-lift-type flying machine. Man's fixed-wing aircraft. The chapter concludes with early experiments in the helicopter field were a brief study of helicopter theory of flight. fruitless. It is only within the last 30 years that encourgaging progress has been made, and it is FUSELAGE within the past 20 years that production line helicoptershavebecomeareality.Today, Likethefuselageinfixed-wingaircraft, helicopters are found throughout the world, helicopter fuselages may be welded truss or performing countless tasks especially suited to some form of monocoque construction. The theuniquecapabilitiesof themodern-day welded truss fuselages predominate in the very version of the dream envisioned centuries ago by small one and two-place "choppers." Larger Leonardo da Vinci. helicopters, characteristic of those designed for Da Vinci, who is recognized as the "Father of the military, run to the monocoque design. the Helicopter," made a series of drawings, with A typical Navy helicopter, the H-3 aircraft proper notations, which introduced the direct- builtfor the Navy by Sikorsky Aircraft,is lift principle of flight. The da Vinci Helix (as he illustrated in figure 4-14. A flying boat type hull termed his craft) was a spiral wing on a vertical provides this helicopter with water-operational shaft. It embodied the basic principles of the capabilities for emergencies only. The fuselage present-day helicopters. Da Vinci claimed that consists of the entire airframe from the forward air had substance (we call it density), and that a fuselage to the tail pylon. A cabin area occupies spiral wing device, if turned at a sufficiently high most of the forward fuselage not used for the speed, would bore up into the air much in the flight deck (pilot and copilot compartment). same fashion as an auger bores into wood. The fuselage areas are sometimes known as the Earlyinthedevelopment of rotary-wing body group as is the case in the H-3. aircraft,a needarosefora new word to The bodygroupisofallmetalsemi- designatethis direct-liftflying device, and a monocoqueconstruction,consistingof resourceful Frenchman seized upon the two aluminum alloy and titanium skin panels cover- words, "He lis" which means screw or spiral, and ing a reinforced aluminum alloy framework or "Pteron" which means wing. Combining these skeleton. The skeleton of the lower fuselage two words he fashioned the word "helicopter," consists of bulkheads, frames, and formers sup- which should be pronounced "hell-i-cop-ter." ported longitudinally (fore and aft) by a keel A helicopter employs one or more power- beam, chine angles, longerons, and stringers. The driven horizontalair screws or rotors from skeleton of the remainder of the body group which it derives lift and propulsion. If a single consists of bulkheads and frames, which form rotor is used, it is necessary to employ a means the crosssectional shape, and longerons, inter- to counteract torque. If more than one rotor is costals (between rib stiffeners), and stringers used, torque can be "washed out" effectively by which form the longitudinal contour. turning a combination of rotors in opposite directions. LANDING GEAR GROUP The fundamental advantage the helicopters has over conventional aircraft is that lift and The landing gear group includes all the equip- control are relatively independent of forward ment necessary to support the helicopter when speed. A helicopter can fly forward, backward, not in flightconventional landing gear consist- or sideways, or remain in stationary flight above ing of a right- and left-hand main landing gear 72 Chapter 4AIRFRAME CONSTRUCTION
V
AM.245 Figure 4-14.H-3 helicopter. and a nonretractable tail landing gear plus right- Retractable alighting gear is not a feature and left-hand sponsons which house the main common to all helicopters, nor even a majority landing gear during flight and aid in stabilizing of them. The H-3 is discussed here because it is the aircraft during emergency operation from one of the Navy's latest helicopter designs and it water when the aircraft is floating. has the emergency water operational capability. The H-3 is illustrated in figure 4-14. Note the Main Landing Gear boat-shaped hull and the sponsons with landing gear extended from them. Most other heli- Each main landing gear is composed of a copters have fixed tricycle alighting gear or a shock strut assembly, dual wheels, a retracting dual sled-like skid arrangement which eliminates cylinder, an uplock cylinder, and upper and the necessity for a nose or tail support. lower drag braces. The wheels retract into a well recessed into the underside of the sp,...nsons. The dual wheels, equipped with tubeless tires and Tail Landing Gear hydraulic brakes, are mounted on axles which are part of the lower end of the shock strut The H-3 tail landing gear is nonretractable and piston. full swiveling and serves as an aft touch-down Normally, the main landing gear is extended point for land-based operations only. An air-oil hydraulically. However, in the case of hydraulic type shock absorber unit, hinged to the yoke failure, an emergency system of compressed air andshaft, cushions thelanding shock. All may be used to lower the gear. Should the air components, with the exception of the axle and system fail, a valve, actuated by the pilot, allows the shock absorber, are made from 7075-T6 the gear to fall of its own weight. aluminum alloy forgings.
73 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.246 1. Cuff. 7. Tip pocket 2. Plate. 8. Tip cap. 3. Spar. 9. Abrasion strip. 4. Root pocket cap. 10. Abrasion strip. 5. Root pocket 11. Ice guard. 6. Pocket (typical). 12. Bracket Figure 4-15.Typical rotary wing blade.
MAIN ROTOR ASSEMBLY blade is attached to the hub. The main support- ing member of the blade is a hollow, aluminum The main rotor (rotary wing) and the rotor alloy extruded spar which forms the leading head are discussed in this section under the one edge. The steel cuff is bolted to the root end of heading because their functions are so closely the spar. related.Neither has a function without the Twenty-threeindividualpockets,each other. constructed of aluminum ribs, an aluminum channel, andaluminumskincovering,are Rotary Wing bonded to the aft edge of the spar. The tip end of the blade contains a readily removable tip The main rotor or rotary wing of the H-3 is cap, fastened to the spar and tip pocket rib by comprised of five identical wing blades. Other means of screws. The root pocket of the blade is types of helicopter rotors may have two, three, sealed at its inboard end by an aluminum alloy or four blades. A typical wing blade is illustrated root cap, cemented and riveted to the pocket. in figure 4-15. A stainless steel abrasion strip is bonded to The rotary wing blade illustrated in figure the leading edge of the spar from blade pocket 4-15 is fabricated of aluminum alloy, with the No. 8 and extends along the entire leading edge, exception of the forged steel cuff by which the including the tip cap. Also, the blade illustrated
74 Chapter 4AIRFRAME CONSTRUCTION isfitted with a deicing guard. The guardis composed of fine wire braid heating elements, interwoven in bands and embedded in a rubber strap to which is bonded a stainless steel strap. The guard is bonded to the leading edge of the spar and is molded to the contour of the blade.
Rotor Head 5
The rotary wing headissplinedto, and supported by, the rotary wing shaft of the main gearbox. The head supports the rotary wing blades,isrotated by torque from the main gearbox, and transmits movements of the flight controls to the blades. The principal components of the head are the hub and swashplate. The hub consists of a hub plate and lower plate; hinges, between each arm of the plates; sleeve-spindles which are attached AM.247 to the hinges; and a damper-positioner for each 1. Pitch link. wing blade. The swashplate consists of a rotating 2. Rotary rudder blade. 3. Spindle. swashplate andstationary swashplate.Ot21.;,. LI. Pitch control beam. components of the rotary wing head are anti- Rotary rudder hub. flapping restrainers, droop restrainers, adjustable 3. Pylon. pitch control rods and rotating and stationary Figure 4-16.Tail rotor group. scissors. The swashplate and adjustable pitch control rods permit movement of the flight controls to aircraftwithdirectionalcontrol. These are be transmitted to the rotary wing blades. The pylon, rotary rudder blades, and rotary rudder hinges allow limited movement to the blades in head. The rotary rudder head includes such relationtothehub.These movements are items as the hub, spindle, and pitch control known as LEAD, LAG, and FLAP. LEAD beams. occurs during slowing of the drive mechanism when the blades have a tendency to remain in Pylon motion. LAG isthe opposite of LEAD and occurs during acceleration when the blade has The pylon illustrated infigure 4-16 is of been at rest and tends to remain at rest. FLAP is aluminum semimonocoque construction, and is the tendency of the blade to rise with high lift composedofbeams,bulkheads,stringers, demands as it tries to screw itself upward into formers, and channels. Various gages of alumi- the air. The damper-positioners restrict lead and num skin located on the left- and right-hand lag motion and position the blades in prepara- sides of the box structure are part of the tion for folding. Sleeve-spindles allow each blade primary pylon structure. Reinforced plastic fair- to be rotated on its spanwise axis to change the ings in the leading and aft surfaces forming the blade pitch. The anti-flapping restrainers and airfoil contour of the pylon are considered to be droop restrainers restrict flapping motion when secondary structure. the rotary wing head is slowing or stopped. The pylon houses an intermediate gearbox and the tail gearbox. The pylon is attached on TAIL ROTOR GROUP the right side of the aircraft to the main fuselage by hinge ,fittings. These hinge fittings also serve The tail rotor group (fig. 4-16) is comprised as the pivot point for the pylon to fold alongside of those helicopter components that provide the the right side of the rear fuselage. Folding of the
75 AVIATION STRUCTURAL MECHANIC S 3 & 2 pylon reduces the overall length ofthe11-3 principles involved in the aerodynamics of flight. helicopter by 7 1/2 feet. thereby greatly facili- Instead,thereisbutbrief mention of the tating its handling, particularly aboard ship. principles themselves, with the major emphasis on their application to the helicopter. Rotary Rudder Head Although in many respectsthehelicopter differs radically from the conventional aircraft, The rudder head, usually located on the left rotary-wingaerodynamicsisnotsomething side of the pylon, produces anti-torque forces entirelynew anddifferent from fixed-wing which may be varied by the pilot to control aerodynamics. The same basic principles apply flight heading. The rotary rudder head is driven ,to both aircraft. During flight, the two types of by the tail gearbox. Change in blade pitch is aircraft are subjected to many of the same forces accomplished through the pitch change shaft and affected by many of the same reactions. In that moves through the horizontal shaft of the short,theprinciples involvedin rotary-wing tail gearbox. As the shaft moves inward toward aerodynamics are those basic principles with the tail gearbox, pitch of the blade is decreased. which the Aviation Structural Mechanic S Third Astheshaft moves outward fromthetail ClassorStriker has alreadylearnedwhile gearbox, pitch of the blade is increased. The preparing himself for advancement to Airman. pitch control beam is connected by links to the In flight, both conventional aircraft and the forked brackets on the blade sleeves. helicopter are acted upon by four basic forces A flapping spindle foreach blade permits WEIGHT, LIFT, THRUST, and DRAG. In ad- flapping of the blade to a maximum of10 dition, both types of aircraft are affected by degrees in each direction. torque reaction. LIFT.Weight and lift are closely related in Rotary Rudder Blades thatweighttendstopullthe aircraftor helicopterdown, and lift holds itup. Right The blades arc on the rotary rudder head. here is where the basic similarity between the Each blade consists of an aluminum spar, an helicopter and the airplane begins; both aircraft aluminum pocket with honeycomb core, an are heavier than air and both are supported by aluminum tip cap, an aluminum trailing edge the reactions of airfoils to air passing over them. cap, and an abrasion strip. In addition, those This reaction, or lift,isa result of pressure bladesthathave de-icing provisions have a differential. The pressure on the upper surface neoprene anti-icing guard, embedded with elec- of the supporting airfoil is less than atmospheric, trical heatingelements. The root end of the while the pressure on the lower surface is equal blade permits attaching to the rotary rudder to, or greater than, atmospheric. head spindles.. The abrasion strip protects the The conventional aircraft'sairfoils are, of leading edge of the blade, or the de-icing guard, course, the wings. The helicopter's airfoils 'are from sand, dust, and adverse weather conditions. the rotor blades. One aircraft has fixed wings The skin is wrapped completely around the spar, and the other rotary wings, but the same basic and the trailing edge cap is installed over the principles of lift apply to both. edges of the skin at the trailing edge of the The length, width, and shape of an airfoil all blade. The tip cap is riveted to the outboard end affect its lifting capacity. However, for any one of the blade. airfoil there are but two primary factors affect- ing the amount of lift the airfoil will develop. THEORY OF FLIGHT The relation between these two factorsvelocity of airflow and angle of attackand their effect At this point itis assumed that the AMSAN on lift can be expressed as follows: or AMS3 who is studying for advancement in For a given angle of attack, the greater the rating isfamiliar with theory of flight and its speed, the greater the lift. application to fixed-wing aircraft. (Review Nav- For a given speed, the greater the angle of Pers 10307-C, Airman.) Therefore, this chapter attack (up to the stalling angle), the greater the contains no extended discussion of the basic lift.
76 Chapter 4AIRFRAME CONSTRUCTION
Thus, lift can be varied by varying either one of these two factors. Furthermore, increasing either speed or angle of attack, or both, (up to certain limits) increases lift. Velocity of Airflow.Not only is velocity of airflow a primary factor affecting lift, but a certain minimum velocityis required in order that the airfoils may develop sufficient lift to get either an airplane or a helicopter into the air and keep it there. This means that for either the airplane or the helicopter, the airfoils must be moved through the air at a relatively high speed. In the conventional aircraft the required flow of air over the airfoils can be obtained only by moving the entire aircraft forward. If the wings must move through the air at 100 miles per hour to produce sufficient lift to support the aircraft AM.248 in flight, then the fuselage and all other parts of Figure 4-17.Chord planes of airfoils. the aircraft must move forward at that same speed. This means that the aircraft must takeoff, fly, and land at relatively high speeds. Further- With the conventional aircraft, the angle of more, it means that the aircraft is limited to attack can be varied only by changing the forwardflight;itcannotfly backwards or attitude of the entire aircraft (F-8 excepted). sideways. When, for example, the pilot wishes to climb, he Thehelicopter's airfoils must also move pulls back on the control stick or column so that through the air at comparatively high speed to theaircraftwilltake anose-high attitude, produce sufficient lift to raise the aircraft off thereby increasing both angle of attack and lift. the ground or keep it in the air. But here, the When he reaches the desired altitude, he levels required speedisobtained by rotating the off to decrease the angle of attack. When he airfoils. Furthermore, the rotor can turn at the wishes to descend, he pushes forward on the required takeoff speed while the fuselage speed stick or column, causing the aircraft to take a remains at zero. nose-low attitude. Thus, the speed of the airfoils (rotor blades), The pilot can increase or decrease the heli- and the resultant velocity of airflow- over them, copter's angle of attack without changing the is independent of fuselage speed. As a result, the attitude of thefuselage. He does this by helicopter does not require high forward speeds changing the pitch of the rotor blades by means of the entireaircraft for takeoff, flight, and of a .cockpit control provided for this purpose. landing. Nor is it limited to forward flight. It can In fact, under certain flight conditions, the angle rise vertically. It can fly forward, backward, or of attack continually changes as the rotor blade sideways as the pilot desires. It can even remain turns 360 degrees. This occurs whenever the stationary in the air while the rotating airfoils rotor plane of rotation s tilted, as it is during develop sufficient lift to support the aircraft. In forward, backward, andl sideways flight. This fact, all of these kinds of flight are normal for tilting of the plane of rotation of the main rotor the helicopter. and the aerodynamics of the various kinds of Angle of Attack.Velocity of airflow around flight are discussed later. (Plane or rotation is an airfoil is but one of the factors affecting lift. also known as the tip path plane and includes The other factor is angle of attack. For either an that area swept by the rotating blades.) airplane wing or a helicopter rotor blade, the Angle of Incidence.For the airplane, the angle of attack is the angle formed by the chord final val %le of the angle of attack depends on the plane of the airfoil and the relative wind, as attitude of the airplane and one other 'actor shown in figure 4-17. the angle of incidence. The angle of incidence,
77 AVIATION STRUCTURAL MECHANIC S 3 & 2
FIXED ANGLE - -LONGITUDINALAXIS-t-
#
LONGITUDINAL AXIS
VARIABLE ANGLE VARIABLE ANGLE
AM.249 Figure 4-18.Angles of incidence. for either an airplane or helicopter, is the angle An unsymmetrical airfoil may be efficient for formed by the chord of the airfoil and the an airplane wing, but it has one disadvantage longitudinal axis of the aircraft. The longitudinal that makes it unsatisfactory for use as a rotor axis of a helicopter is a line at right angles to the blade. The center of pressure "walks" forward main rotor drive shaft. The conventional aircraft's angle of incidence is determined by the designer and is built into the aircraft. The angle of incidence cannot be changed by the pilot. UNSYMMETRICAL AIRFOIL The helicopter's angle of incidence can be changed at will by the pilotby changing the pitch of the rotor blades. Like the angle of WIND attack,theangleofincidencecontinually CENTER OF changes as therotor revolves whenever the PRESSURE TRAVEL control stick is moved from the neutral position SYMMETRICAL AIRFOIL and the rotor plane of rotation is tilted. Note the comparative angles of incidence, as sketched in figure 4-18. AIRFOIL! SECTION.Airfoil sections used CENTER OF for airplane wings vary considerablyeach being PRESSURE FIXED selectedto meet specific requirements. The airfoil may be symmt rical or unsymmetrical, AM.250 like the ones shown in figure 4-19. Figure 4-19.Center of pressure.
78 Chapter 4AIRFRAME CONSTRUCTION and rearward as the angle of attack changes. The within the rotor system. center of pressure is an imaginary point on the During vertical ascent, thrust acts vertically airfoil where all of the aerodynamic forces are upward while drag acts vertically downward. considered as being concentrated.Onan un- Here the drag opposing the upward motion of symmetrical airfoilthe center of pressureis the helicopter is increased by the down-wash of toward the rear of the wing at small angles of air from the main rotor. Thrust must be suf- attack and moves forward as the angle of attack ficient to overcome both of these forces which is increased. This forward movement continues make up the total drag. In the illustration (fig. until the angle of attack is approximately the 4-20), note that thrust acts in the same direction same as the angle of maximum lift coefficient. and in line with lift. Furthermore, the main (The angle of maximum lift coefficient is that rotor is responsible for both thrust and lift. angle at which I square foot of airfoil travelling Therefore, the force representing the total re-' at I mile per hour will produce the greatest action of the airfoils to the air may be con- possible lift.) sidered as being divided into two components. The center of pressure cannot be permitted to One component, lift,is the force required to walk back and forth on a helicopter rotor blade, support the weight of the helicopter. The other since shifting of the center of pressure would component, thrust,isthe force required to introduce pitch-changing forces. This would be overcome the drag on the fuselage. But drag is a undesirableanddangerous.Therefore,the separate force from weight, as is indicated in center-of-pressure travel is controlled by airfoil figure 4-20. design and is usually at a point 25 percent back Now let us examine the thrust and drag forces from the leading edge of the rotor blade. A acting on the fuselage during forward flight. symmetrical airfoilhas the desirable charac- In any kind of flightvertical, forward, back- teristic of limiting center-of-pressure travel. ward, sideways, or hoveringthe resultant lift THRUST AND DRAG.Like weight and lift, thrust and drag are closely related. Thrust moves the aircraft in the desired direction; drag tends to hold it back. THRUST The .conventionalaircraft'sthrustis,in general, forward, and drag to the rear. These t forces always act in opposite directions and are LIFT usually horizontal, or only slightly inclined from the horizontal. Seldom, if ever, do these forces approach the vertical. Furthermore, the con- ventional aircraft's thrust can be separated and considered apart from lift. The propeller (or jet) is responsible for thrust; the wings are respon- sible for lift. The helicopter gets both its lift and thrust from the main rotor. In vertical ascent, thrust acts upward in a vertical direction, while drag, the opposing force, acts vertically downward. In forward flight, thrust is forward and drag to the DRAG rear. In rearward flight, the two are reversed. In short, thrust acts in the direction of flight and 1 drag acts in the opposite direction. MIGHT The thrust and drag forcers and two of these conditionsvertical flight and forward flight are discussed in the following paragraphs. These AM.251 discussions deal with the thrust and drag forces Figure 4-20.Alignment of forces during acting on thefuselage, not with the forces vertical ascent.
79 AVIATION STRUCTURAL MECHANIC S 3 & 2
RESULTANT LIFT LIFT RESULTANT 44011LIFT t THRUST
ORAG
WEIGHT
AM.252 Figure 421.Transition from vertical to forward flight. forces of a rotor system are perpendicular to the one direction, the fuselage tends to rotate in the tip path plane (plane of rotation). Remember, oppositedirection. This torque effectisin thetippathplaneisthe imaginary plane accord with Newton's third law of motion which described by the tips of the blades in making a states that, "To every action there is an opposite cycle of rotation. During vertical ascent or and equal reaction." In the helicopter, the hovering, the tip path plane is horizontal and reaction is in a direction opposite to that in this resultant force acts vertically upward, as which the rotor is driven by the engine and is shown in figure 4-21. To accomplish forward proportional in magnitude to the power being flight, the pilot tilts the tip path plane forward. delivered by the engine. The resultant force tilts forward with the rotor Torque is of real concern to both the designer as shown in the illustration. The total force, now and pilot. There must be provisions for counter- beinginclined fromthevertical, acts both acting torque and for positive control over its upwardandforward; therefore,itcan be effect during flight. On dual-rotor and coaxial- resolved into two components as shown in the rotor helicopters, the rotors turn in opposite illustration. One component islift, which is directions, thus "washing out" torque reaction. equaltoandoppositeweight.The other In jet helicopters with engines mounted on the component, thrust, acts in the direction of flight main rotor blade tips, the power is initiated at to move the helicopter forward. therotorblade;therefore,thereactionis Although thisdiscussion covers only two between the blade and. the air, with no torque flight conditions, it should point the way to a reaction between the rotor and the fuselage. basic understanding of thrust and drag forces Therefore, it is in helicopters of the single main acting on the helicopter fuselage during flight. In rotorconfigurationthattorquepresentsa rearward flight, the thrust and drag forces are problem to the pilot during flight. similartothose in forward flight, butare The usual way of counteracting torque in a reversed. The tip path plane is tilted to the rear, single main rotor helicopter is by means of an the thrust component acts to the rear, and drag antitorque rotor. This axuiliary rotor is mounted opposes the rearward motion of the aircraft. In vertically on the outer portion of the tail boom. sideways flight, the pilot tilts the tip path plane Turning at a constant rpm, usuallyslightly in the desired direction of flight, thrust is to the higher than one-half engine speed, the tail rotor right or left in the direction of flight, and drag produces thrust in a horizontal plane, opposite acts in the opposite direction. in direction to the torque reaction developed by TORQUE.As the helicopter rotor turns in the main rotor. Figure 4-22 shows the direction
80 Chapter 4AIRFRAME CONSTRUCTION
means of heading the helicopter in the desired direction offlight.Therefore, thetail rotor control pedals serve as rudder pedals. The effect of the tail rotor controls is shown in figure 4-23. Applying left rudder causes the nose of the helicopter to turn to the left; applying right rudder causes the nose to swing to the right. When the pilot wishes to maintain a constant heading, he keeps just enough pitch in the tail rotor to neutralize torque effect. Although the tail rotor is the primary means of counteracting and controlling torque, the tail rotor alone does not quite do the job. This is ROTOR BLADE ROTATION true because torque cannot be compensated for by a single force. The tail rotor alone would prevent rotation of the fuselage, but would cause TRANSLATION (movement in a lateral direction) of the helicopter, during hovering, in the direction of tail rotor thrust. Complete compensation for torque requires a COUPLEa pair of equal forces acting in op- DIRECTION TAIL ROTOR THRUST TO COMPENSATE posite directions. Tail rotor thrust constitutes OF TORQUE FOR TORQUE oneoftheforces.The secondforceis introduced by rigging the helicopter with the tip path plane tilted from 1 to 2 1/2 degrees to the AM.253 left, depending upon the helicopter. Figure 4-24 Figure 4-22.Torque reaction and compensation. shows the balance of forces on a helicopter employing a single right-to-left main rotor. Note that the slight tilt of the tip path plane to the left results in a thrust force to the left. This of the torque reaction and the direction of tail force andtail rotor thrust form the couple rotor thrust for a helicopter in which the main required to completely compensate for torque. rotor turns from the pilot's right, to his front, to his left, and then to his rear. Most single rotor Hovering systems turn in this direction. Since the torque effect on the fuselage is a Hovering isthe maintaining of ,a position result of the engine power supplied to the main above a fixed spot on the ground, usually at an rotor, any change in engine power brings about a altitude of about 8 feet. Helicopters normally corresponding change inthetorqueeffect. hover on takeoffs and landings. Furthermore, power requirements vary with For the helicopter to hover, its main rotor flight conditions. Therefore, the torque effect is must supply lift equal to the helicopter's weight. not constant but varies during flight. This means Lift is controlled by controlling the pitch of the that there must be some provision for varying rotor blades. As the blades rotate, air flows tail rotor thrust. Usually, a variablepitch tail across the leading edge of each blade in the rotor is employed and rudder pedals are linked direction indicated in figure 4-25. The airflow by cables with the pitch change mechanism in crosses the leading edge of each blade through- the tail rotor head. This permits the pilot to outthecomplete rotationalcycleof 360 increase or decrease tail rotor thrust, as required, degrees. At the same time the blades have a to neutralize the torque effect. tendency to screw upward into the air, and air The tail rotor and its controls serve as both a flows down through the rotor system from means of counteracting torque effect and 'a above as shown in figure 4-26.
81 AVIATION STRUCTURAL MECHANIC S 3 & 2
-.4 I" TO 2.1/2" TILT
NOSE
LEFT RUOOER TAIL ROTOR THRUST
MAIN ROTOR ROTOR BLADE TORQUE REACTION ROTATION
AM.255 Figure 424.Balance of forces on a helicopter.
MAIN ROTOR TAIL ROTOR THRUST TORQUE REACTION INCREASING
NOSE
RIGHT RUOOER
ROTOR BLAOE ROTATION
AM.256 Figure 4-25.Airflow across blades. MAIN ROTOR TAIL ROTOR THRUST TORQUE REACTION OECREASING The pitch and rpm of the rotor blade are controlled by the COLLECTIVE PITCH stick. Control by this stick affectsallthe blades AM. 254 collectively. The normal location of this control is shown in figure 4-27. By raising or lowering Figure 4-23.Effect of tail rotor pitch the collective pitch stick one can change the changes on heading. collective pitchthe pitch on all of the main
82 Chapter 4AIRFRAME CONSTRUCTION
from the bottom of the collective pitch stick to the carburetor by a series of push-pull rods. As the blade pitch is increased, calling for more engine power to maintain a constant rotor rpm, the synchronization unit opens the throttle. The oppositeis also true, of course. If the blade pitch is decreased, less engine power is required for the same rotor rpm, so the synchronization unit acts to reduce engine power. On the upper end of the collective pitch stick is a motorcyclegrip type throttle, with which the throttle can be "rolled on" or "rolled off" if the synchronization unit does not maintain exact engine rpm. This hand throttle permits over- riding of the synchronization unit in making the final adjustments to obtain the specified engine rpm.
AM.257 Directional Flight Figure 426.Airflow through blades. Directional flight of a helicopter demands pilotcoordinationtoproperlyexecutethe desired flightpath. The helicopter can fly either vertically, horizontally, or a combination of the two directions. Both vertical and horizontal flight are discussed in the following paragraphs. VERTICAL FLIGHT.Vertical flight is con- CYCLIC CONTROL STICK trolled exactly the same way as hovering, since hovering is an element of vertical flight. To climb, the collective pitch stick is raised, using the throttle on the pitch stick to make any rpm
COLLECTIVE PITCH adjustments not made automatically. At the STICK was MOTORCYCLE GRIP TYPE THROTTLE same time, the cyclic control (discussed under "Horizontal Flight") is held in a vertical posi- fion, so that lift will be vertical. The flow of air is still over the leading edge of each blade, but the helicopter is now moving upward as shown in figure 4-28. When the helicopter is climbing vertically the main rotor supplies not only the lift necessary to 7. / AM.258 support the helicopter's weight, but also the Fiure 4-27.Main rotor-pitch controls. thrust necessary to cause the helicopter to rise vertically. To descend, the collective ,pitch stick is lowered to decrease main rotor pitch and the rotor blades the same amount. Raising the stick resultant lift. increases the pitch; lowering it decreases the HORIZONTAL FLIGHtHorizontal flight is pitch. If the rotor rpm remains constant, in- controlled by tilting the tip path plane in the creasing or decreasing the blade pitch causes the direction of desired flightforward, backward, helicopter to climb or descend. to the left, or to the right. As detailed in figure To maintain constant rotor rpm during pitch 4-28, the helicopter moves in the direction the change, a built-in synchronization unit is linked tip path plane is tilted.
83 AVIATION STRUCTURAL MECHANIC S 3 & 2
HIGH FLAP LOW PITCH RESULT APPLIED
LOW FLAP HIGH PITCH RESULT APPLIED
VERTICAL FLIGHT
AM.260 Figure 4-29.Pitch changes for forward flight.
The pilot tilts the tip path plane by means of the cyclic pitch control. This control provides a mechanical means of changing the pitch of the main rotor blades inany direction of tilt BACKWARD FLIGHT throughout their full 360 degrees of rotation. Cy- clic pitch change is equal and opposite, as shown in figure 4-29. If the blade pitch is increased 3 degrees on one side of the rotor center, at a point 180 degrees around the cycle of rotation, the blade pitch is decreased 3 degrees. For every pitch change there is a resulting flapping action of the individual blades, as they constantly change pitch during rotation. As is shown, maximumflappingtakesplace90 SIDEWARD FLIGHT degrees around the cycle of rotation from the place where the pitch change was applied. The equal and opposite pitch change and the result- ing flapping of the individual blades causes the tip path plane to tilt in the same direction as the pilot moves the cyclic control stick. Thus, to fly forward, backward, sideways, or in fact, any di- rection horizontally, all that is required is to tilt the cyclic control stick in the desired direction. To climb or descend while moving forward, FORWARD FLIGHT backward, or to either side, is merely a matter of coordinating the movements of the collective pitch control, which governs vertical flight; and AM.259 the cycle control, which governs horizontal Figure 4-28.Directional flight attitudes. flight.
84 CHAPTER 5
SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
TOOLS Readiness List (IMRL). NavAir 00-35QG-016 includes all of theac- The AMS3 and AMS2 must have a thorough countableand consumablegeneralsupport knowledge of the tools of his trade to enable equipment which isrequired for the main- him to increase his performance and the quality tenance and operation of all types of aircraft at of hisproducts.Usingthis knowledge and the Intermediate and Organizational levels of applying itin the right direction will aid in maintenance. Most of the tools listed in Nav Air increasing the squadron's efficiency and opera- 00-35QG-016, appropriate for use by the AMS, tional availability. One of the most important are found in the toolbox he is issued. factors that a mechanic can have is the ability to TheIndividualMaterialReadinessList use the tools which are required to complete any (IMRL), which applies to an activity by name, given task in a skilled and technical manner. specifies items and quantities of aircraft ground A mechanic is known by the tools he keeps. supportequipmentrequiredformaterial The use of tools may vary; but safety, good care, readiness of the aircraft maintained by the and the proper stowage of tools never vary. In activity. this chapter, some of the various tools that the Whenever the number of tools in the activity AMS uses in the course of his duties are briefly fallsbelow a certain minimum, the central described. The Rate Training Manuals, Tools and toolroom supervisor reorders to replenish his Their Uses, NavPers 10085 (Series), and Airman, stock. The quantity status of tools on hand is NavPers 10307 (Series), also contain a descrip= determined by regular inventories. tion of most of the tools used by the AMS, together with detailed instructions for using them. The material given in this chapter is CUSTODY intended to supplement, rather than repeat, the When it becomes necessary or desirable for an information given in Tools and Their Uses and AMS to have a toolbox 'assigned to him on a the Airman manuals. custody basis, the shop supervisor will notify the toolroom personnel to issue an AMS toolbox to PROCUREMENT the designated person. Normally, the central Some activities have a centrally located tool- toolroom will have a locally prepared toolbox room which procures tools for the activity as a inventory form. This form will be applicable to whole. This allows for better usage and ac- the particular aircraft, equipment, and main- countability of the equipment. An activity's tenance level to be supported. They will issue alloted amount of handtools is in accordance the toolbox' in accordance with this inventory with an allowance which isestablished by form, making two copiesone (master copy) to Nav Air00-35QG-016,ConsumableGeneral be held by the central toolroom, and one to be Support Equipment for All Types, Classes, and placed inthe toolbox ina grease-resistant Models of Aircraft, and the Individual Material envelope. The AMS should use this copy to
85 AVIATION STRUCTURAL MECHANIC S 3 & 2 inventory his toolbox after completion of each the Illustrated Parts Breakdown; for example, assigned task to insure that all of his tools have Nav Air 01 -75PAA-4-I3, P-3A Special Support been placed back in his toolbox. Equipment, and NavAir 01-24FDA-4-6, F-4A NOTE: Reinventory of tools taken to the Special Support Equipment. When determining jobs is a MUST to eliminate the possibility of special support equipment allowances for any damage to the aircraft due to foreign objects left activity,refertotheIndividualMaterial adrift within or around the aircraft. Readiness List.
INVENTORY HANDTOOLS The AMS who has custody of a toolbox must prevent the loss of tools through neglect or Before discussing the tools individually, a few misuse. Although handtools are normally classed comments on the care and handling of handtools as consumable items, they are very expensive in general might be appropriate. The condition and must be paid for when lost or carelessly in which an AMS maintains his assigned tools damaged. One method of preventing loss of determines his efficiency as well as affecting the tools isa thorough inventory after each job judgment that his superiors pass upon him in his assignment. Usually, the activity will have a local day-to-day work. A mechanic is always judged instruction concerning the inventory interval heavily by the manner in which he handles his and method of reporting lost or damaged tools. tools. NOTE: Broken or damaged tools can damage Each mechanic should keep all his assigned aircraft hardware and parts. They can also cause tools in his toolbox when he is not actually personal injury to the worker or others. using them. He should have a place for every At the periodic inventory, which is normally tool, and every tool should be kept in its place. performed by central toolroom personnel, all All tools should be cleaned after every use and broken or missing tools should be replaced. before being placed in the toolbox. If they are Nonproductive time between job assignments not to be used again the same day, they should provides ample time for further inspection and be oiled with a light preservative oil to prevent upkeep of toolboxes. Someone has said "show rusting. Tools that are being used at a work- me a mechanic with a poor toolbox and I will bench or at a machine should be kept in easy show you a poor mechanic." reach of the mechanic, but should be kept where In addition to the tools normally issued with they will not fall or be knocked to the deck. the toolbox, there are many special tools an Tools should not be placed on finished parts of AMS3 or AMS2 will come in contact with and machines. use. Later in this chapter we will discuss just a few of these tools. Special tools are normally RIVETING TOOLS kept in the central toolroom and signed out on an as-needed basis. These tools are returned to Rotary Rivet Cutters the toolroom as soon as the AMS has completed his work assignment. (Tools should be returned Incaseone cannot obtain rivets of the no later than the same day as checked out.) required length, rotary rivet cutters (fig. 5-1) are Each activity has an allowance of special tools used to cut longer rivets to the desired length. which they may have on custody. Often the When using the rotary rivet cutter, insert the allowance for an item is only one, which means rivet part way into the correct diameter hole, positive control must be exercised. The special place the required number of shims (shown as tools allowance list for a particular aircraft on staggered, notched strips in theillustration) which the AMS might be working is contained in under the head, and squeeze the handles. The the activity's Individual Material Readiness List compound action from the handles rotates the (IMRL) publications. two discs in opposite directions. Rotation of Some of the newer aircraft manuals list the discs shears therivet smoothly togive the special tools and equipmert in one section of correct length (as determined by the number of
86 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
eliminate any opening between them before the rivet is bucked. Each draw set has a hole 1/32 inch larger than the diameter of the rivet shank for which it was made. Sometimes, especially in hand working tools, the draw set and the rivet header areincorporated into one tool. The header partconsistsof aholesufficiently shallow for the set to expand the driven rivet "bucktail" and form a head on it when the set is struck by a hammer. Figure 5-2 illustrates a rectangular-shaped hand set which combines the draw and header sets and a flush set used with a pneumatic hammer. Sets used with pneumatic hammers (rivet guns) are provided in many sizes and shapes to fit the type and location of the rivet. These sets are the same as the hand rivet sets except that AM.290 Figure 5-1.Rotary rivet cutter. the shank is shaped to fit into the rivet gun. The sets are made of high-grade carbon tool steel and areheattreatedtoprovidethenecessary shims inserted under the head). When using the strength and wear resistance. The tip or head of larger cutter holes, place one of the tool handles the rivet set should be kept smooth and highly in a vise, insert the rivet in the hole, and shear it polished at all times to prevent marring of rivet by pulling the free handle. If this tool is not heads. available, diagonal cutting pliers can be used as an emergency cutter although the sheared edges Bucking Bars will not be as smooth and even as when cut with the rotary rivet cutter. Bucking bars are tools used to form bucktails (the head formed during riveting operations) on Rivet Set rivets. They come in many different shapes and sizes, as illustrated in figure 5-3. Bucking bars A rivet set is a tool equipped. with a die for are normally made from an alloy steel similar to driving a particular type of rivet. Rivet sets are usedinboth hand and pneumatic hammer riveting methods. Rivet sets are available to fit every size and shape of rivet head. The ordinary hand set is made of 1/2-inch-diameter carbon steel about 6 inches long and isknurled to prevent slipping in the hand. Only the face of the set is hardened and polished. Sets for the oval head rivets (universal, round, and brazier) are recessed (or cupped) to fit the rivet head. In selecting the correct set, be sure that itwill ',NNW., provide the proper clearance between the set and the sides of the rivet head and between the surfaces of the metal and the set. Flush or flat sets are used for countersunk and flathead rivets. In order to set flush rivets properly, the flush sets should be at least 1 inch in diameter. Special sets, called "draw" sets, are used to AM.291 "draw up" the sheets being riveted in order to Figure 5-2Rivet sets.
87 AVIATION STRUCTURAL MECHANIC S 3 & 2
the ability of the AMS using it. If possible, hold the bucking bar in such a manner that will allow the longest portion of the bar to be in line with the rivet. The AMS should hold the bucking bar lightly but firmly against the end of the rivet shank so as not to unseat the rivet head. The inertia of this tool provides the force that bucks (upsets)therivet,forming aflat,head-like bucktail.
Hole Finder
ANGLE SPECIAL STRINGER A holefinderisatoolused to transfer BUCKING FLANGE existing holes in aircraft structures or skin to replacement skin or patches. The tool has two leaves parallel to each other and fastened to- gether at one end. The bottom leaf of the hole GP finder has a teat installed near the end of the leaf which is aligned with a bushing on the top TORPEDO DIAMOND SPECIAL leaf, as illustrated in figure 5-4. The desired hole POINT TUBE to be transferred is located by fitting the teat on the bottom leaf of the hole finder into the existing rivet hole. The hole in the new part is made by drilling through the bushing on the top leaf. If the hole finder is properly made, holes drilled in this manner will be perfectly aligned. SPECIAL DUCKBILL A separate duplicator must be provided for each NUT PLATE OFFSET diameter of rivet to be used.
AM.292
Figure 5-'.Bucking bars. toolstet..the particular shapeto be used depends upon the location and accessibility of the rivet to be driven. The size and weight of the bar depend on the size and type of the rivet to be driven. Under certain circumstances, and for specificrivetinstallations,specially designed bucking bars are manufactured locally. These AM.293 bars are normally made from tool steel. The Figure 5-4.Hole finder. portion of the bar designed to come in contact with the rivet has a polished finish. This helps to Skin Fasteners prevent marring of formed bucktails. Bucking bar faces must be kept smooth and perfectly flat There are several types of skin fasteners used and the edges and corners rounded at all times. totemporarily secure partsinpositionfor NOTE: Never hold a bucking bar in a vise drilling and riveting and to prevent slipping and unless the vise jaws are equipped with protective creeping of the parts. C-clamps, machine screws, covers. This will prevent marring of the bucking and Cleco fasteners are frequently used in the bar. Navy. (See figure 5-5.) Of the three, the Cleco is Asatisfactoryrivetinstallationdepends the most popular. Cleco fasteners come in sizes largely on the condition of the bucking bar and ranging from 1/16 to 3/8 inch. The sizeis
88 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES normally stamped on the fastener, but may also spring compressed, the pin of the Cleco is be recognized by the following color code: inserted in the drilled hole. The compressed I /16 inchblack spring is then released, allowing spring tension 3/32 inchcadmium on the pin of the Cleco to draw the materials 1/8 inchcopper together. Clecos should be stored on a U channel 5/32 inchblack plate to protect the pins of the Cleco. Clecos 3/16 inchbrass stores at random among heavy tools will become 1/4 inchgreen useless due to bent pins. 3/8 inchred The Cleco fastener is installed by compressing STRIKING TOOLS the spring with Cleco pliers (forceps). With the Generally speaking, this group is composed of various types of hammers, all of which are used to apply a striking force where the force of the hand alone is insufficient. Each of these ham- mers is composed of a head and a handle, even though these parts differ greatly from hammer to hammer. The mallet and the ball-peen hammer (fig. 5-6) are of the most concern to the AMS and adequate coverage on their selection, use, care, and safety is contained in Tools and Their Uses, NavFers 10085 (Series), and Airman, NavPers 10307 (Series), and is therefore not repeated here.
BALL PEEN HAMMER
PLASTIC HAMMER
PLASTIC FACE
AM.294 AM.23 Figure 5-5.Skin fasteners. Figure 5-6.Striking tools.
89 AVIATION STRUCTURAL MECHANIC S 3 & 2
CUTTING TOOLS This lug fits into one of the notches of the nut. The spanner may be made for just one particular Included in this group of tools are diagonal size notched nut, or it may have a hinged arm to cutting pliers, files, hacksaws, twist drills, count- adjust it to a range of sizes. ersinks, chisels, and the various types of snips Pin spanners have a pin in place of a hook, used by the AMS to trim or cut material by and the pin fits into a hole in the outer part of hand. (See fig. 5-7.) the nut. Face pin spanners are designed so that Adequate coverage on the selection, care, and the pins fit into holes in the face of the nut. use of cutting tools is contained in Tools and The AMS uses several differenttypes of Their Uses, NavPers 10085 (Series), and Airman, spanner wrenches which are manufactured for a NavPers 10307 (Series), and is therefore not spe 1:ic job. Figure 5-11 shows a special spanner repeated here. being used on a wheel nut of a main landing wheel. MISCELLANEOUS TOOLS TENSIOMETER Miscellaneous tools are tools that do not fall into the category of striking or cutting tools. The tensiometeris an instrument used in Some of the miscellaneous tools that are of checking cable tension. The amount of tension concern to the AMS are the flashlight, mechani- applied in a cable linkage system is controlled by cal fingers, inspection mirrors, and steel scales. turnbuckles in the system. NOTE: Tension is (See fig. 5-8.) the amount of pulling force applied to the cable. The Rate Training Manuals, Tool;; and Their A tensiometer is a useful instrument, but is Uses, NavPers 10085(Series), and Airman, not precision-built. Itisinaccurate for cable NavPers 10307 (Series), adequately cover the tension under 30 pounds. All tensiometers in use use and care of these tools and is therefore not must be checked for accuracy at least once a repeated here. month. One type of tensiometer is shown in figure 5-12. This instrument works or. the principle of measuring the amount of force required to SPECIAL TOOLS deflect a cable a certain distance at right angles to its axis. The cable to be tested is placed under TORQUE WRENCHES the two blocks on the instrument, and the lever assembly on the side of the instrument is pulled There are times when, for engineering reasons, down. Movement of this lever pushes up on the a definite pressure must be applied to a nut. In center block, called a riser. The riser pushes the such cases a torque wrench must be used. The cable at right angles to the two clamping points. three most commonly used torque wrenches are The force required to do this is indicated by a the Deflecting Beam, Dial Indicating, and Micro- pointer on the dial. Different risers are used with meter Setting types. (See fig. 5-9.) different size cables. Each riser carries an identi- Adequate coverage on the selection, care, and fying number and iseasily insertedinthe use of torque wrenches is contained in Tools and instrument. Their Uses, NavPers 10085 (Series), and Airman, Each tensiometer is supplied with a calibra- NavPers 10307 (Series), and is therefore not tiontabletoconvert the dial readings into repeated here. pounds. One of these calibration tables is illu- strated in figure 5-12. For example, in using a SPANNER WRENCHES No. 2 riser with a 3/16 inch-diameter cable, if the pointer on the dial indicates 48, the actual Many special nuts are made with notches cut tension on the cable is 100 pounds. It will be into their outer edge. For these nuts, a hook noted that in the case of this particular instru- spanner (fig. 5-10) is required. This is a wrench ment, the No. 1riser is used with 1/16-, 3/32-, that has a curved area with a lug on the end. and 1/8-inch-diameter cables.
90 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
POINTS
STRAIGHT SNIPS
THROAT
DIAGONAL CUTTING PLIERS
AVIATION SNIPS
HACKSAWS
TYPICAL BIT TYPE COUNTERSINK
COLD CHISEL
P / / /74 V7/7 %, CAPE CHISEL SINGLE-CUT
COARSE BASTARD SECOND-CUT SMOOTH W../ /Mgr /,Ntia,\V 01 DIAMOND POINT DOUBLE-CUT TYPES OF POINTS ON METAL FILE NOMENCLATURE AND GRADES OF FILE TEFTH CUTTING CHISELS AM.1123 Figure 5-7.Types of cutting tools.
91 AVIATION STRUCTURAL MECHANIC S 3 & 2
MECHANICAL FINGERS
RIGID TYPE
32 NDS.
11 2 3
EXTENDED POSITION RETRACTED POSITION it iiiIi110111111111116111141116011111illiiiiiiiiillhililli1111111illdlillililligilliiiilli ( A ) ( B 1 64 THS.
1111111 1111!11 STEEL SCALE
41=.'it rte"'+31f1 4
INSPECTION MIRROR r-----/
AM.1126 Figure 5-8. Miscellaneous tools.
92 Chapter 5 -- SHEET -METAL WORKING MACHINES, TOOLS, AND PROCEDURES
DIAL INDICATING
MICROMETER SETTINO T
DEFLECTING BEAM
AM.30 r igure 5-9.Torque wrenches.
CAUTION: The calibration table applies to top of the instrument is moved to the closed the particular instrument only and cannot be position which locks the pointer in place. Then, used with anyother. For this reason, the the lever assembly is released and the instrument calibration table is secured inside the cover of removed from the cable with the pointer locked the box- in which the instrument is kept. The in position. After the reading has been taken, chart is serialized with the same serial number as the brake lever rodis moved to the open the instrument. position, and the pointer will return to zero. During the adjustment of turnbuckles, the The tensiometer, like any other measuring calibration table must be used to obtain the instrument, is a delicate piece of equipment and desired tension in a cable. For example, if it is shouldbehandledcarefully.+Tensiometers desired to obtain a tension of 110 pounds in a should never be stored in a toolbox. 3/1 6-inch-diametercable, the No. 2riseris Temperature changes must be considered in inserted in the instrument and the figure oppo- cable type systems since this will affect cable site 110 pounds is read from the calibration tensions. When a temperature is encountered table.Inthiscase,thefigureis52. The that is lower than that at which the aircraft was turnbuckle is then adjusted until the pointer rigged, thecables become slack because the indicates 52 on the dial. (NOTE: Tensiometer aircraft structure contracts more than the cables. readings should not be taken within 6 inches of When temperatures higher than that at which any turnbuckle, end fitting, or quick discon- theaircraft was rigged are encountered, the nect.) aircraft structure expands more than the cables In some cases, the position of the tensiometer and the cable tension is increased. on the cable may be such that the face of the The cables in any cable linkage system are dial cannot be seen by the operator. In such rigged in "accordance with a temperature chart cases, after the lever has been set and the pointer which is contained in the applicable Mainte- moved on the dial, the brake lever rod on the nance Instructions Manual. This chart will give
93 AVIATION STRUCTURAL MECHANIC S 3 & 2 the proper tensions for the various temperature on the model shown in figure 5-13. On some changes above and below the temperature at models the depth of cut adjustment can be made which the system was rigged. in increments of 0.0008 inch. The operator can change cutters and adjust their depth without RIVET HEAD SHAVER the use of special tools. Once the depth is set, the positive action of the serrated adjustment The rivet head haver shown in figure 5-13 is locking collar prevents accidental loss of setting. used by the AMS to smooth countersunk rivet The AMS should position the cutters directly heads that protrude slightly but are still within over the rivet head, holding the tool at an angle specified limits. The rivet head shaver is also of 90 degrees to the surface being smoothed. called a Micro Miller. The depth of cut adjust- With the tool turning maximum rpm, it is then ment can be made in increments of 0.0005 inch pressed in towards the surface, maintaining the 90-degree angle. The pressure feet will then be compressed until they bottom out. At this time, assumingtherivetheadshaverisadjusted correctly prior to the shaving operation, the rivetheadwillbeshaved aerodynamically smooth.
HOOK SPANNER WRENCH
SAk
ADJUSTABLEHOOK SPANNER WRENCH
SPANNER WRENCH
PIN SPANNER WRENCH
AM.304 Figure 5-11.Using a special spanner wrench on a wheel nut of a main landing wheel.
PNEUMATIC RIVETERS
FACE PIN SPANNER WRENCH Rivet guns vary in size and shape and have a variety of handles and grips, ranging from the offset type to the pistol grip type. Nearly all riveting is done with pneumatic riveters. The AM.31 pneumatic riveting guns operate on compressed Figure 5-10.General-purpose spanner wrenches. air supplied from a compressor or storage tank.
94 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
LEFT SECTOR RIGHT NO. 2 P.ISER BRAM LEVER ROD.
3/16!' DIAMETER CABLE
LEVER ASSEMBLY
No. 1 Riser No. 2 No. 3 DIA1/16 3/32 1/8 Tension 5/32 3/16 7/32 1/4 Lbs.
14 15 21 30 14 20 18 22 27 40 18 25 23 27 33 50 22 29 27 32 39 60 26 33 31 37 44 70 29 37 35 41 49 80 32 41 39 45 54 90 35 45 43 49 59 1001 38 gill 46 53 63 110 41 52 49 57 67 120 44 55 53 61 71 130 47 58 56 65 75 140 49 61 59 68 79 150 51 64 62 71 82 160 54 67 65 74 86 170 56 70 68 77 90 180 58 72 73 80 93 190 60 74 72 83 96 200 62 76 Typed figures are instru- 220 66 81 ment scale reading cor- 240 70 85 respondinp, to tension 260 74 89 280 78 93 Instrument No. 6659 97 Model 401-1C-2 300 80
AM.33 Figure 5-12.Cable tensiometer and chart.
Normally, rivet guns are equipped with an air trigger, and into the cylinder in which the piston regulator on the handle to control the amount moves. Air pressure forces the piston down of air entering the gun. Regulated air entering against the rivet set and exhausts itself through the gun (Fig. 5-14) passes through the handle sideports. The rivetsetrecoils, forcing the and throttle valve, which is controlled by the piston back, and the cycle is repeated: Each time
95 AVIATION STRUCTURAL MECHANIC S 3 & 2
Slow-Hitting Gun The slow-hitting gun has a speed of 2,500 ADJUSTMENT LOCKING SLEEVE bpm (blows per minute). As long as the trigger is held down, the rivet set continues to strike the SKIRT rivet.This guniswidely usedfor driving medium-sized rivets. It is easier to control than the one-shot gun.
CUTTER Fast-Hitting Gun The fast-hitting gun heads the rivet with a number of relatively lightweight blows. It strikes ADJUSTMENT LOCKING COLLAR between 2,500 and 5,000 bpm and is generally used with the softer rivets. Like the slow-hitting STABILIZER ASSEMBLY gun, it continues to strike the rivet head as long as the trigger is depressed. This gun is sometimes PRESSURE FOOT referred to as a vibrator.
Corner Riveter
The corner riveter is so named because it can AM.305 be used in corners and in close quarters where Figure 5-13.Rivet head shaver. space is restricted. The main difference between this riveter and the other types described lies in the fact that in this type the set is very short and the pistonstrikes the rivetset, the forceis can be used in confined spaces as can be seen in transmitted to therivet.Rivet sets come in figure 5-15. various sizes and shapes to fit the various shaped rivet heads. Squeeze Riveter Several types of pneumatic riveters are in general use.Included arethe one-shot gun, The squeeze riveter differs from the other slow-hitting gun, fast-hitting gun, corner riveter, riveters in that it forms the rivet head by means and the squeeze riveter. (See fig. 5-15.) The type of squeezing or compressing instead of by of gun used depends on the particular job at distinct blows. Once it is adjusted for a particular hand, each type having its advantages for certain type of work, it will form rivet heads of greater types of work. Small parts can be riveted by one uniformity than the riveting guns. It is made man if the part is accessible for both bucking both as a portable unit and as a stationary anddriving, provided the work isproperly riveting machine. As a portable unit, it is larger secured. The greaterpartof riveted work, than the riveting guns and can be used only for however, requires two men. certain types of work that can be accommo- dated between the jaws. The stationary, or fixed One-Shot Gun jaw, contains the set and is placed against the rivet head in driving. The rivet squeezer illu- The one-shot gun is designed to drive the rivet strated in figure 5-15 is the pneumatic type. with just one blow. It is larger and heavier than other types and isgenerally used for heavy Rivet Gun Selection riveting. Each time the trigger is depressed the gun strikes one blow. It is rather difficult to The size and the type of gun used for a control on light-gagemetals. Under suitable particular job depend upon the size of rivets conditions it is the fastest method of riveting. being driven and the accessibility of the rivet.
96 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
BANK RIVET SET SLIDING VALVE PISTON SET SLEEVE
7 \ illimillpoop111011411'1.111111111411111111111111111111111 :1111;1"101111111111011111111iiiii VIMIM arA ' "... "AinilFF...... SET RETAINER EXHAUST DEFLECTOR CYLINDER THROTTLE
THROTTLE LEVER MOVEMENT OF AIR DURING 0 FORWARD STROKE THROTTLEVALVE --4.- MOVEMENT OF AIR DURING THROTTLE TUBE REARWARD STROKE
BUSHING
REGULATOR ADJUSTMENT SCREW
;./ AIR PATH
AM.306 Figure 5 -14. Rivet gun internal airflow.
For driving medium-sized, heat-treated rivets Table 5-1.Approximate air pressures for rivet guns. which are in accessible places, the slow-hitting gun is preferred. For small, soft alloy rivets, the fast-hitting gun ispreferable. There will be places where a conventional type gun cannot be Rivet size Air pressure psi used. For this type of work, a corner gun is employed. 3/32 35 1/8 40 The larger therivet, the greater the air 5/32 60 pressure that is required. Air pressure reaches 3/16 90 the gun through a long, flexible hose. Approxi- mate air pressures for four of the mast common rivet sizes are given in table 5-1. Conditions may vary slightly with different alloys.
97 AVIATION STRUCTURAL MECHANIC S 3 &. 2
TAPS AND DIES Taps and dies are used to cut threads in metal, ONE SHOT plastic, or hard rubber. The taps are used for cutting internal threads, and the dies are used to cut external threads. Taps and dies usually come in complete sets, containing tap wrenches, die stocks, guides, and the necessary screw-drivers and wrenches to loosen and tighten adjusting PISTOL GRIP screws and bolts. Taps and dies should be kept clean and well oiled when not in ti§e. Store them so that they SLOW HITTING do not contact each other or other tools. Tools and Their Uses, NavPers 10085 (Series), de- scribes and illustrates the principles involved in the selection of the proper taps and/or dies for OFFSET different types of work. HANDLE SCREW AND BOLT EXTRACTORS Screw and bolt extractors are used to remove broken screws and bolts without damaging the COMPRESSION (SQUEEZE) RIVETER surrounding materials or the threaded hole. The straight flute type extractors are available in sizes to remove broken or damaged screws having 1/4 to 1/2 inch outside diameter. Spiral tapered extractors are sized to remove screws and bolts from 3/16 inch to 2 1/8 inches outsidc diameter. Most sets of extractors include twist drills and CORNER adrill guide. Tools and Their Uses, NavPers 10085 (Series), illustrates and outlines the pro- cedures to use in removing screws and bolts that have been damaged or broken.
STRAP WRENCH The strap wrench is used during assembly and disassembly of cylinder type components. The strap wrench (fig. 5-16) has a metal body with a FAST HITTING webbed strap attached. To use this wrench, the webbed strap is placed around the cylinder and passed through the slot in the metal body. As STRAIGHT the mechanic turns the, wrench in the desired direction, the webbed strap tightens around the cylinder. This gripping action of the strap causes the cylinder to turn. With the end cap held stationary, the cylinder will be tightened or loosened, depending upon thedirection the mechanic turns the wrench. The main advantage AM.307 of this type of wrench, if used properly, is that Figure 5-15.Various types of rivet guns. it will not mar or damage the cylinder.
98 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
RIG PINS Rig pins are used by the AMS in rigging control systems. Figure 5-17 shows a rigging pin kit used on one of the Navy's aircraft. As can be seen by this kit, rig pins may come in various sizes and shapes and may be designed for one or many installations. The AMS should refer to the specific Maintenance Instructions Manual for use and selection of rig pins. Rigging of controls and use of rig pins are discussed in chapter 8 of this manual.
THROW BOARDS
Throw boards are special equipment used on specific aircraftfor accurate measurement of AM.308 Figure 5-16.Strap wrench. control surfacetravel.(Seefig. 5-18.) Each
REMOVE BEFORE FLIGHT
AM.309 Figure 5-17.Rigging pin kit.
99 AVIATION STRUCTURAL MECHANIC S 3 & 2
PROTRACTOR
NAMEPLATE
INSPECTION PLATE
AM.310 Figure 5-18.Typical throw board used for rigging rudder and rudder tab controls. throw board has a protractol type scale which out on the metal, the next step is to cut it out. indicates a range of travelin degrees. Zero The type of cutting equipment to be used degree normally indicates the neutral position of depends primarily upon the type and thickness the control surface. When the throw board is of the material. Another consideration is the size mounted in place and the control column/stick and number of pieces to be cut. A few fairly is in neutral, the trailing edge of the control thin pieces of comparatively soft metal may be surface should be aligned on zero. As the control more readilyturned out by hand-trimming column/stick is moved to its extreme limits, the methods. But for harder metals, faster output, AMS reads the corresponding degree indication andgenerallymoreworkmanshipresults, on the throw board. If the travel of the control machines designed for metal cutting purposes surface is out of limits, the AMS should adjust are used. cables, push-pull rods, control limit stops, etc., asnecessary,to obtain the correct control surface travel. When inspecting and rigging con- trol surfaces, the specific Maintenance InStruc- CUTTING EQUIPMENT tions Manual should be consulted. The use of throw boards is discussed further in chapter 8. Machines used in cutting sheet metal may be divided into two groupsmanually operated and power operated. Each type of cutting machine CUTTING SHEET METAL has a definite cutting capacity which should never be exceeded. A few of the more common Cutting of sheet metal is a common occur- types that are available to the AMS are described rence for the AMS. Once a project has been laid in this section.
100 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
Squaring Shears on the bed--the beginning and ending marks on the cutting edge of the bed, and the cut made. 'Squaring shears (fig. 5-19) are used for cutting A holddown mechanism positioned by hold- and squaring sheet metal. They may be foot down handles (fig. 5-19) is incorporated in front operated or power operated. Squaring shears of the movable cutting edge in the crosshead. Its consist of a stationary blade attached to a bed, purpose is to clamp the work firmly in place and a movable blade attached to a crosshead. To whilethe cutisbeing made. The clamp is
. make a cut, the work is placed in the desired quickly and easily madethe operator merely position on the bed of the machine and the rotatesthe handle toward himself and the blade is moved through its downward stroke. holddown lowers into place. A firm downward The stroke of the cutter blade is always identical pressure on the handle at this time should rotate in its relation to the bed. Foot-powered squaring the mechanism over center on its eccentric cam shears are equipped with a spring which raises and lock the holddown in place. Reverse the the blade when foot pressure is taken off the action to release the work. treadle. A scale graduated in fractions of an inch Three distinctly different operationscutting is scribed on the bed. Two side guides, consisting to a line, squaring, and multiple cutting to a of thick steel bars, are fixed to the bed, one on specific sizemay be accomplished on the squar- the left and one on the right. Each is placed so ing shears. When cutting to a line, proceed as that its inboard edge creates a right angle with aboveplace the beginning and ending marks on the cutting edge of the bed. These bars are used the cutting edge and make the cut. Squaring toalignthemetal when absolutely square requires a sequence of several steps. First, square corners are desired. When cuts other than right one end of the sheet with one side. Then square angles are to be made across the width of a piece the remaining edges, holding one squared end of of metal, the beginning and ending points of the the sheet against the side guide and making the cut must be determined and marked in advance. cut, one edge at a time, until all edges have been Then the work is carefully placed into position squared. When several pieces are to be cut to the same dimensions, make use of the adjustable gage stop with which most squaring shears are equipped. HOLD-DOWN SAFETY GUARD This stop is located behind the bed cutting edge, ACK GAGE and its purpose is to limit the amount of metal BEVEL GAGE 3LHE' in trla4 SIDE GAGE that ran be slipped between the cutting edges of _Itri020 the blade and bed. The supporting rods for the stop gage are graduated in inches and fractions of an inch, and the gage bar is rigged so that it may be set and fixed at any point on the rods. FRONT With the gage set at the desired distance from GAGE the cutting blade, push each piece to be cut against the stop. Itis then possible to cut all pieces to the same dimensions without measur- ing and marking each one separately. (NOTE: FOOT TREADLE Physically measure the first piece in such a series
HOUSING to make sure that the stop is accurately set.)
Throatless Shears
GRADUATIONS ON BED (ENLARGED) Throatless shears (fig. 5-20) are constructed so that sheets of any length may be cut and the metal turned in any direction during the cutting AM.261 operation. Thus, irregular lines can be followed, Figure 5-19.Squaring shears. or notches made without distorting the metal.
101 AVIATION STRUCTURAL MECHANIC S 3 & 2
This type of throatless shears is essentially an Unishear adaptation of heavy handshears or snips in which the handles are removed, one blade secured to a Unishearisatrade name fora type of base, and a long lever attached to the tip of the portable power shears, used for cutting curves movable blade. The heavy duty throatless shears and notches as well as straight-line cutting. are capable of cutting stainless steel up to 0.083 This tool might be called a power-operated, inch in thickness. cGmbination snips. It has two short blades. The lower bladeisheldina fixed positionThe Hand Bench Shears upper blademoves up and down in short strokes at a high rate of speed. Its chewing motion is the The hand bench shears are similar in opera- basis for the widely used nickname of this power tion to a papereutter. They have one fixed blade tool"nibblers," The tool will cut metal up to and a movable blade, hinged at the back, similar its rated capacity which should never be ex- to the throatless shears except that the blades ceeded. Figure 5-21illustrates an 18-gage uni- are straight and, therefore, used only for straight shear. . cutting. Some bench shears have a punching The cutting blades are easily removed for attachment on the end of the frame opposite the sharpening and replacement. The machine will shearing blades. This attachment is for punching cut as fast as it can be fed up to 15 feet per holes in metal sheets. minute. This is a ruggedly constructed machine; and for satisfactory performance, the best of care is necessary. It should be kept cleaned and oiled at all times.
LEVER Hand-Operated Turret Punch
A hand-operated turret punch is shown in STOP figure 5-22. Twelve mated punches and dies are mounted in a rotating turret. Each die block has KNIFE the size of hole it will punch, as well as the thickness of the material itwill accommodate, stamped on the front. These capacities are for PLATE mild steel, and this must be kept in mind when punching stainless steel or otheralloys. The operation of the turret punch is simple: release the locking handle on the side of the punch frame, rotate the turret until the desired punch set is lined up with the actuating mechan- ism (ram), then lock the turret into position. Punch thehole by pulling the operating lever toward the operator, which actuatesthe ram and AM.262 punch. Figure 5-20.Throatless shears.
MACHINE FORMING OF SHEET METAL For cutting stock that is narrower in width than the length of the blades, the lever of the SLIP-ROLL FORMING MACHINE shears can be pulled all the way down. When cuttinglarger pieces, a continuous series of short Sheet metal can be formed into curved shapes bites should be made, since complete closing of over apipeor amandrel, but the slip-roll the blade tends to tear the sheet at the end of forming machine (fig. 5-23) is much easier to use each cut. andproduces more accurate bends. Rolling
102 Chapter SSHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
AM.263 Figure 5-21.-18-gage unishear. machines areavailablein various sizes and capacities; some are hand operated, like the one shown in figure 5-23, and others are power operated. The machine shown in the illustration has two rollers in the front and one roller at the rear. 44.,144.4 Adjusting screws on each end of the machine control the distance between the front rolls. By varying the adjustments, the machine can be used to form cylinders, cones, and other curved shapes. The front rolls grip the metal and pull it into the machine; therefore, the adjustment of distance between the two front rolls is made on the basis of the thickness of the sheet being worked. To form a cylinder in the machine (fig. 5-24), follow this procedure: I. Adjust the front rolls so that they will grip the sheet properly. 2. Adjust the rear roll to height that is less AM.264 than enough to form the desired radius, of the Figure 5-22.Handoperated turret punch. cylinder. 103 MECHANIC S 3 & 2 AVIATIONSTRUCTURAL
OPERATING HANDLE ROOVES HOUSING
UPPER FRONT 11*(11111*. LOWER FRONT ROLL ROLE.
HAti\
ICI11111i7NRCRINSSIONS11
GROOVES SCREWS BASE KNURLED ADJ STING KNURLED ADJUSTING SCREWS AM.265
Figure 5-23.Slip-rollforming machine.
.SECTIONAL VIEW OF ROLLS
AM.266
Figure 5.24.Forming acylinder.
104 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
3. Check to be sure that all three rolls are rolls in such a manner that the element lines parallel. (Same space exists between any two (A-A', B-B', etc., in the illustration) pass over rollers at each end of the rollers.) the rear roll in a line parallel to the roll. This 4. Start the sheet into the space between the involves slipping the large end of the cone two front rolls. As soon as the front rolls have through the rolls at a slightly faster rate than the gripped the sheet, raise the free end of the sheet small end is being rolled through. slightly. The grooves at the end of the rolls can be 5. Pass the entire sheet through the rolls. This used to form circles of wire or rod; they can also forms part of the curve required for the cylin- be used to roll wired edges, as shown in figure der. 5-26. 6. Set the rear roll higher to form a shorter radius. 7. Turn the partially formed sheet end over end and again pass it through the rolls. 8. Continue turning the sheet end over end and passingitthrough the rolls, each time adjusting the rear roll for a new radius, until a truly cylindrical shape has been formed. 9. Remove the cylinder from the machine. The top front roll has a quick-releasing device by which one can release one end of the roll. This allows the released end of the roll to be raised and the newly formed cylinder slipped off just as one would slip a ring from his finger. Conical shapes can be formed by setting the back roll at an angle before running the sheet through it, or they can be made with the rolls parallel. (See fig. 5-25.) To make a cone with the AM.268 rolls parallel, the sheet must be fed through the Figure 5-26.Rolling a wired edge.
ROTARY MACHINE The rotary machine shown in figure 5-27 is used on cylindrical and flat sheet metal to shape the edge or to form a bead along the edge. Various shaped rolls (some illustrated in fig. 5-28) can be installed on the rotary machine to perform the following operations; beading, turn- ing. wiring, crimping, and burring. These opera- tions are described in the following paragraphs.
Beading Rolls
Beadingrollsare used for turning beads (grooves) on such items as tubing, cans, and buckets; and for stiffening and gripping. Beads may also be placed on sheet stock that is tobe welded. There are several different types of AM.267 beading rolls. Those shown in figure 5-28 are the Figure 5-25.Rolling a conical shape. single bead rolls. Whenever beading, the groove
105 AVIATION STRUCTURAL MECHANIC S 3 & 2 should not be made too deeply ina single Wiring Rolls rotation as this tends to weaken the metal. Wiring rolls are used to finish the wired edges prepared in the turning rolls. To use the wiring rolls, adjust the top roll so that it is directly CRANK SCREW above the point on the lower roll where the beveled and flat surfaces meet, as shown in (A)
UPPER ROLL of figure 5-29. Adjust the guide to the position LOCK NUT-- shown in (B), then bring the top roll down so that it will turn the edge of the metal as shown ADJUST ING SCREW LOWER ROLL in (C). Remove the stock from the machine by OPERATION H NDLE raising the top roll.
Crimping Rolls Crimping rolls are used to make one end of a pipe smaller than the other so that two sections AM. 269 may be slipped together, one end into the other. Figure 5.27. Rotary machine. A bead is placed on a pipe first, then itis crimped. The bead forms a shoulder to keep the Turning Rolls pipe from slipping too far into the adjoining section. Turning rolls are used for turning an edge to receive a stiffening wire. When turning an edge, Burring Rolls rest the cylinder to be.wired on the lower wheel and press against the gage. The gage is adjusted Burring is perhaps the most difficult opera- according to the size of wire to be used. With tion performed on a rotary machine. Before the work set in place, bring down the upper roll placing the work in the machine, make sure that until it grips the metal. Turn the crank slowly, the cylinder or circular disc to be burred is cut holding the metal so that it will feed into the or formed as perfectly round as possible. Then rolls while continuing to press against the guide. adjust the gage on the machine so that the space After the first revolution, gradually raise the between the inside of the upper roll and the gage metal until it touches the outer face of the top is set to the width of the burr. Next, place the roll. Remove the stock by raising the top roll. object between the rolls and against the gage,
SINGLE BURRING ROLLS STRAIGHT TURNING ROLLS WIRING ROLLS BEAD ROLLS CRIMPING ROLLS
AM.270 Figure 5-28.Roll dies used an rotary machine.
106 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES and lower the upper rolluntilitscores the They must not be used as backing when chisel- materialslightly. Now turn the crank slowly, ing holes or notches in sheet metal, or when allowing the metal to slide between the thumb pefforming any other job which might damage and fingers. Apply a slight upward pressure as the faces of the stakes. the metal passes between the tolls. After the first revolution, lower the top roll and again pass BENDING IN A VISE the metal between the rolls. Repeat this process, raising the edge slightly with each complete Straight-line bends of comparatively short revolution of the material until the edge has sections can be made by hand with the aid of been burred to the proper angle. wooden or metal bending blocks. After the part has been laid out and cut to size, clamp it rigidly along the bend line between two forming blocks held in a vise. The forming blocks usually have one edge rounded to give the desired bend UPPER radius. (See fig. 5-31.) By tapping lightly with a ROLL rubber, plastic, or rawhide mallet, bend the metal protruding beyond the bending block to the desired angle.
CaLOWER Start tapping at one end, and work back and ROLL forth along the edge, making the bend gradually (A) (B) (C) and evenly. Continue this process until the protruding metal is bent to the desired angle. If a large amount of metal extends beyond the bending blocks, maintain enough hand pressure AM.271 against the protruding sheet to prevent the metal Figure 5-29.-Wiring operation. from bouncing. Remove any irregularity' in ,the flange by holding a straight block of hardwood edgewise against the bend and striking it with BENDING SHEET METAL heavy blows of a hammer or mallet. If the amount of metal protruding beyond the bending Straight-line bends and folds in sheet metal blocks is small, make the entire bend by using are ordinarily made on the cornice brake and bar the hardwood block and hammer. folder; however, c considerable amount of bend- Curved flanged parts have mold lines that are ing is also carried out by hand-forming methods. either concave or convex. The concave flange is Hand forming may be accomplished by using formed by stretching, while the convex flange is stakes, blocks of wood, angle iron, a vise, or the formed by shrinking. Such parts are shaped with edge of a bench. theaid of hardwood or metal form blocks. These blocks are made in pairs and specifically BENDING OVER STAKES for the shape of the part being formed. Each pair fits exactly and conforms to the actual Stakes are used to back up sheet metal for the dimension and contour of the finished article. forming of many different curves, angles, and Cut thematerialto be formed tosize, seams in sheet metal. Stakes are available in a allowing about one-quarter inch of excess ma- wide variety of shapes, some of which are shown terial for trim. File and smooth the edges of the in figure 5-30. The stakes are held securely in a material to removeallnicks caused by the stake holder or stake plate (also illustrated) cutting tools. This reduces the possibility of the which is anchored in a workbench. The stake material cracking at the edges during the form- holder contains a variety of holes to fita ing operation. Place the material between the number of different types of shanks. form blocks and clamp tightly in a vise so that Although stakes are by no means delicate, the material will not move or shift. Clamp the they must be handled with reasonable care. work as closely as possible to the particular area
107 AVIATION STRUCTURAL MECHANIC S 3 & 2
COPPERSMITH APRON SQUARE CREASING STAKE 11 STAKE BEAKHORN STAKE WITH HORN BLOWHORN STAKE
COMMON SQUARE STAKE HATCHET BEVEL EDGE STAKE BOTTOM STAKE SQUARE STAKE
HORN SOLID CANDLEMOLD STAKE CONDUCTOR STAKE NEEDLECASE STAKE MANDREL STAKE
HOLLOW MANDREL STAKE DOUBLE-SEAMING STAKE
AM.272 Figure 5-30.Stakes and stake plate. being formed to prevent strain on the form extreme ends of the part, and continue toward block and to keep the material from slipping. the center of the bend. This procedure permits Concave surfaces are formed by stretching the some of the material at the ends of the part to material over a form block. (See fig. 5-32.) Using be worked into the center of the curve where it aplasticor rawhide mallet with a smooth, will be needed. Continue hammering until the slightly rounded face, start hammering at the metal is gradually worked down over the entire
108 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES flange and flush with the form block. After the BENDING ON A BRAKE flange is formed, trim off the excess material and check the part for accuracy. The easiest and most accurate method of making straight-line bends on a piece of sheet metal is by the use of a box and pan brake or a cornicebrake. The use of these brakesis MATERIAL TO BE FORMED relatively simple; however, if they are not used
FORM BLOCKS correctly, the time and the work involved in 7° (TYP) BEVEL TO ALLOW FOR MATERIAL SPRING BACK computing and laying out of bend allowance, as well as the metal, are wasted. Before bending any work demanding an accurate bend radius and definite leg length, the settings of the brake should be checked with a piece of scrap metal. When making an ordinary bend on a brake, place the sheet to be bent on the bed so that the bend line is directly under the upper jaw or clamping bar, then pull down the clamping bar handle. This brings the clamping bar down to hold the AM.273 sheet firmly in place. Set the stop for the proper Figure 5-31.Preparation for straight bend by hand. angle or amount of bend, and make the bend by raising the bending leaf until it strikes the stop. If more than one bend is to be made, bring the next bend line under the clamping bar and Convex surfaces are formed by shrinking the repeat the bending procedure. material over a form block. (See fig. 5-33.) Using a wooden orplastic shrinking mallet and a Cornice Brake backup or wedge block, start at the center of the curve and work toward both ends. Hammer the The cornice brake (fig. 5-34) is designed for flange down over the form, striking the metal bending large sheets of metal. It is adjustable for with glancing blows at an angle of approxi- mately 45 degrees, and with a motion that will tend to pull the part away from the radius of the form block. While working the metal down over SMOOTH, SLIGHTLY ROUNDED the form block, the wedge block is used to keep PLASTIC OR RAWHIDE MALLET the edge of the flange as nearly perpendicular to the form block as possible. The wedge block also lessens the possibility of buckles and of splitting or cracking the metal. MATERIAL BEING Another method of hand forming convex FORMED flanges is by using a lead bar or strap. The material, while secured in the form block, is struck by the lead strap which takes the shape of FORM the part being formed and forces it down against BLOCKS the form block. One advantage in using this method is that the metal is formed without marring or wrinkling and is not thinned out as much as it would be by other methods of hand forming. This method is also illustrated in figure 5-33.After the flangeis formed by either method, trim off the excess material and check AM.274 the part for accuracy. Figure 5-32.Forming concave hand bend.
109 AVIATION STRUCTURAL MECHANIC S 3 & 2
BACKUP BLOCK SHRINKING UNFORMED MATERIAL MALLET
SHRINKING MALLET
1 BACY.UP MATERIAL BLOCK V FORM BEING BLOCKS FORMED
FORM BLOCKS
LEAD BAR
FORM BLOCK
MATERIAL BEING FORMED
AM.275 Figure 5-33.Forming convex hand bends. clamping a wide variety of metal thicknesses and limited. This is a useful feature when it is desired for bending this metal to a variety of radii. to make a number of pieces with the same angle The brake isequipped with a stop gage, of bend. consisting of a rod, a yoke, and a setscrew, by The standard cornice brakeis extremely means of which the travel of the bending leaf is useful for making single hems, double hems,
110 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES lock seams, and various other shapes, some of The finger brake is particularly useful in the which require the use of molds. The molds are forming of boxes, pans, and other similar shapes. fastened to the bending leaf of the brake by If these shapes were formed on a cornice brake, means of friction clamps, in such a position that one would have to straighten part of the bend the work can be formed over them. Figure 5-35 on one side of the box in order to make the last shows sheet that is ready to be formed over a bend. In the finger brake, simply remove the mold attached to a cornice brake. fingers that in the way and use only the fingers required to make the bend. Box and Pan Brake The fingers are secured to the upper leaf by thumbscrews,as shown infigure5-37.All The box and pan brake (fig. 5-36) is often fingers which are not removed for any operation called the finger brake since it does not have one must be securely seated and firmly tightened solid upper jaw as does the cornice brake, but before the brake is used. instead is equipped with a series of steel fingers To keep brakes in good condition, keep the of varying widths. The finger brake can be used working parts well oiled and be sure that the to do everything that the cornice brake can do jaws are free of rust and dirt. In operating the and several things that the cornice brake cannot brakes, take care to avoid doing anything that do. would spring theparts, force them out of
CIAMPING SAS HANDLIS COUNTIR-WI IGHT (TYMCAL TWO KAU'S] (TYPICAL TWO PLACI
JAW OI CLAMPING PAR
DIUSTAMI STOP
SINGING
MINDING LIM HANDLE (TYMCAL TWO MACS
JAW OS CIA/APING IAA JAW O CLAMPING JAR
IGOLPAITO MING LAGI MIMI° MATERIAL
MATITUAL TOMIFORMS
MINDING LIA
STATIONARY SIG UNPIN° LIAT STATIONARY KO
BENDING OPERATION
AM.276 Figure 5-34.Cornice brake and operation.
1 1 I AVIATION STRUCTURAL MECHANIC S 3 & 2 alignment, or otherwise damage them. Never use brakes for bending metal that is beyond their capacity as to thickness, shape, or type. Never try to bend rod, wire, strap iron, or spring steel sheets in a brake. If it is necessary to hammer the work, take it out of the brake first.
UPPER JAW STOCK
MOL AM.278 LOWER JAW Figure 5-36.Box and pan brake being used to form box. LEAF
OP' tidoelf
.i.E...,[111111111111141
AM.277 Figure 5-35.Cornice brake with mold and stock.
BENDING ON BAR FOLDER AM.279 Figure 5-37.Finger secured in box and pan brake. The bar folder may be used to bend and fold metalina number of different shapes, as illustrated in figure 5-38. This machine has two SHEET METAL EDGES AND SEAMS adjustments, one for regulating the width of the fold and the other to provide sharp or rounded REINFORCED EDGES bends. To operate the bar folder, adjust the thumbscrew to the specified width of the fold, There are several methods used to reinforce or then turn the adjusting knob on the back of the stiffen the edges of sheet metal. One method is machine for the desired sharpness of the bend. to form either a single or double hem; another is Insert the metal under the folding blade until it to reinforce the edge with a wire or rod. rests against the stops. Hold the metal firmly in A single hem is formed by simply turning the place with one hand, grasp the handle with the metal back on itself once, as shown in figure other, and pull forward until the desired fold is 5-40. A double hem, also shown in the illustra- made. The necessary steps in making a single tion, is formed in the same manner, except that hem are illustrated in figure 5-39. the metal is folded twice instead of once.
112 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
( A ) ( B ) START* THE MAKING THE FOLD FOLD
(C) FLATTENING THE HEM
AM.281 Figure 5-39.Bar folding a single hem.
SINGLE HEM DOUBLE HEM
AM.282 Figure 5-40.Single and double hems.
SHEET METAL SEAMS
AM.280 The place where two sheets of metal are Figure 5-38.Types of bends made on a bar folder. joined together is called a seam. The three most common types of seams used in sheet metal work are the lap seam, grooved seam, and the A wire edge is made by wrapping the metal standing seam. around a piece of wire or rod, the metal being The lap seam is the least difficult to fabricate. bent by hand or on a bar folder. An allowance In making this seam, the pieces of stock are equal to two and one-half times the diameter of merely lapped one over the other and secured by the wire should be provided for the fold to riveting or soldering, or both, the method used receive the wire. Figure 541 shows a wire edge depending upon the degree of structural strength being formed by hand although a much more required and whether or not a watertight seam is workmanlike job is accomplished by using the required. rotary machine illustrated in figure- 5-27. The A grooved seam is used in the construction of final wrapping operation may be continued cylindrical objects, such as funnels, pipe sec- either with the peen of a hammer or with a tions, containers, marking buoys, and tanks. The wiring machine. steps in forming a grooved seam are shown in
113 AVIATION STRUCTURAL MECHANIC S 3 & 2
LLi L,
14--A
1 2 3 DISTRIBUTION OF SEAM ALLOWANCE
AM.285 Figure 5-43.Steps in forming a standing seam.
section, the remaining portion on the other. Sections A and B are equal, and C is one thickness of the metal less than A.
BEND ALLOWANCE
AM.283 When bending metal to exact dimensions, the Figure 5-41.Hand forming a wire edge. amount of material used in forming the bend must be known. The amount of material which figure 5-42. Step (C) is accomplished with either is actually used in making the bend is known as a hand or machine groover. BEND ALLOWANCE. The standing seam is frequently used when Bending compresses the metal on the inside of joining two sections or parts of an object, such the bend and stretches the metal on the outside as the splash ring to the body of a funnel. The of the bend. Approximately halfway between steps in making a standing seam are shown in these two extremes lies a space that neither figure 5-43. If the object has straight sides, the shrinks norstretches, but retainsthe same flanges may be turned in the bar folder; and if length. This is known as the neutral line or cylindrical, the flanges are turned on the burring neutral axis. Figure 5-44 illustrates the neutral machine. Notice the distribution of the allow- axis of a bend. It is along this neutral axis that , ancefor the seam. Two-thirds of it is on one bend allowance is computed.
BEND ALLOWANCE TERMS (A) (B) Familiarity with the following terms is neces- sary for an understanding of bend allowance and OPEN LOCKS LOCKS HOOKED its application to an actual bending job. Figure (C) 5-45 illustrates most of these terms. Leg. The longer part of a formed angle. Flange. The shorter part of a formed angle SEAM GROOVED the opposite of leg. If each side of the angle is the same length, then each is known as a leg. Mold Line (ML). The line formed by extend- ing the outside surfaces of the leg and flange. AM.284 (An imaginary point from which real base Figure 5-42.Forming a grooved seam. measurements are provided on drawings.)
114 Chapter 5SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
Radius (R). The radius of the bendalways to the inside of the metal being formed unless otherwisestated.(The minimumallowable radius for bending a given type and thickness of material should always be ascertained before proceeding with any bend allowance calcula- tions.) Setback (SB). The setback is the distance from the bend tangent line to the mold point. In a 90-degree bend SB = R + T (radius of the bend plus thickness of the metal). The setback dimen- sion must be determined prior to making the bend as it (setback) is used in determining the location of the beginning bend tangent line. NEUTRAL AXIS Bend Line (also called BRAKE or SIGHT line). The layout line on the metal being formed which is set even with the nose of the brake and serves as a guide in bending the work. (Before forming a bend, it must be decided which end of the material can be most conveniently inserted AM.286 in the brake. The bend line is then measured and Figure 5-44.Neutral axis. marked off with a soft-lead pencil from the bend tangent line closest to the end which is to be Bend Tangent Line (BL). The line at which placedunder thebrake.This measurement the metal starts to bend and the line at which should be equal to the radius of the bend. The the metal stops curving. All the space between metal is then inserted in the brake so that the the bend tangent lines is the bend allowance. nose of the brake will fall directly over the bend Bend Allowance (BA). The amount of ma- line, as shown in figure 5-46.). terial consumed in making a bend. Flat (short for flat portion). The flat portion or flat of a part is that portion not included in the bend. It is equal to the base measurement minus the setback.
BEND THICKNESS (t) TANGENT LINE (BL} BEND FLANGE LINE
LEG BEND ALLOWANCE
RADIUS (R)
BEND AL PIECE MOLD LINE (ML) TO BE BENT
MOLD POINT R+t 1-e SETBACK(904END) BENDING re--BASE MEASUREMENT LEAF
AM.287' AM.288 Figure 5-45.Bend allowance terms. Figure 5-46.Locating bend line in brake.
115 AVIATION STRUCTURAL MECHANIC S 3 & 2
Base Measurement., The base measurement is Table 5-3sho,..sthe bend allowance per the outside dimensions of a formed part. Base degree of bend for some commonly used thick- measurement will be given on the drawing or nesses, and bend radii used in aircraft constnie- blueprint, or may be obtained from the original tion,Thistableisbased on the foregoing part. formula. The blank spaces on the table are Closed Angle. An angle that is less than 90 spaces where values were omitted because the degrees when measured between legs, or more bends would betoo sharpfor satisfactory than 90 degrees when the amount of bend is production. measured, (See fig. 5-47.) Open Angle. An angle that is more than 90 degrees when measured between legs, or less than 90 degrees when the amount of bend is LAYOUT PRACTICES measured. K No. One of 179 numbers on the K chart In laying out metal prior to bending it to a corresponding to one of the angles between 0 desiredshape,there are certain precautions and 180 degrees to which metal can be bent. which should be observed. In the following (See table 5-2). Whenever metal is to be bent to paragraphs are some of the more important any angle other than 90 degrees (K No. of 1.0), precautions;forinformation on theuse of the corresponding K No. is selected from the layouttools refer to Tools and Their Uses, chart and is multiplied by the sum of the radius NavPers 10085-B. and the thickness of the metal. The product is Every precaution must be taken to avoid the amount of setback for the bend. marring aluminum-alloy sheet and even steel sheet should be carefully handled. To protect the under surface of the material from any possible damage, it is often advisable to place a piece of heavy paper, felt, or plywood between the material and the working surface. In working with a large sheet of material, it is important to avoid bending it; hence, it is a good idea to have a helper in placing it on the working surface. A layoutfluidshould be appliedto the surface of the metal so that the pattern will stand out clearly. Any one of several approved AM.289 Figure 5-47.Open and closed angles, fluids may be used. Zinc chromate and bluing fluid are two of the most commonly used. Since zinc chromate protects a metal surface against BEND ALLOWANCE FORMULA corrosion and also serves as a base for paint, it need not be removed after the layout is com- By experimentation with actual bends in pleted. Bluing fluid is merely a blue dye dis- metals, aircraft engineers have found that ac- solved in alcohol.It does not protect metal curate bending results could be obtained by against corrosion or serve as a paint binder, so it using the following formula for any degree of should be removed either with ordinary paint bend from 1 to 180. thinner or alcohol. To begin the layout, one edge of the metal (0.01743 x R + 0.0078 x T) x N = BA should be straight. Use the squaring shears if necessary, then test the job with a straightedge. where All measurements can then be based on the straight edge of the sheet. Lines at a known R equals the desired bend radius, angle or parallel to the straight edge can be made T equals thickness of the material, and by marking off points from a combination N equals number of degrees of bend. square held firmly against the straight edge.
116 Chapter 5-SHEET-METAL WORKING MACHINES, TOOLS, AND PROCEDURES
Table 5-2.-K chart.
A° KNo. A° KNo. A° KNo. A° KNo.
1 0.00873 46 0.42447 91 1.0176 136 2.4751 2 .01745 47 .43481 92 1.0355 137 2.5386 3 .02618 48 .44523 93 1.0538 138 2.6051 4 .03492 49 .45573 94 1.0724 139 2.6746 5 .04366 50 .46631 95 1.0913 140 2.7475 6 .05241 51 .47697 96 1.1106 141 2.8237 7 .06116 52 .48773 97 1.1303 142 2.9042 8 .06993 53 .49858 98 1.1504 143 2.9887 9 .07870 54 .50952 99 1.1708 144 3.0777 10 .08749 55 .52057 100 1.1917 145 3.1716 11 .09629 56 .53171 101 1.2131 146 3.2708 12 .10510 57 .54295 102 1.2349 147 3.3759 13 .11393 58 .55431 103 1.2572 148 3.4874 14 .12278 59 .56577 104 1.2799 149 3.6059 15 .13165 60 .57735 105 1.3023 150 3.7320 16 .14054 61 .58904 106 1.3270 151 3.8667 17 .14945 62 .60086 107 1.3514 152 4.0108 18 .15838 63 .61280 108 1.3764 153 4.1653 19 .16734 64 .62487 109 1.4019 154 4.3315 20 .17633 65 .63707 110 1.4281 155 4.5107 21 .18534 66 .64941 111 1.4550 156 4.7046 22 .19438 67 .66188 112 1.4826 157 4.9151 23 .20345 68 .67451 113 1.5108 158 5.1445 24 .21256 69 .68728 114 1.5399 159 5.3995 25 .22169 70 .70021 115 1.5697 160 5.6713 26 .23087 71 .71329 116 1.6003 161 5.9758 27 .24008 72 .72654 117 1.6318 162 6.3137 28 .24933 73 .73396 118 1.6643 163 6.6911 29 .25862 74 .75355 119 1.6977 164 7.1154 30 .26795 75 .76733 120 1.7320 165 7.5957 31 .27732 76 .78128 121 1.7675 166 8.1443 32 .28674 77 .79543 122 1.8040 167 8.7769 33 .29621 78 .80978 123 1.8418 168 9.5144 34 .30573 79 .82434 124 1.8807 169 10.385 35 .31530 80 .83910 125 1.9210 170 11.430 36 .32492 81 .85408 126 1.9626 171 12.706 37 .33459 82 .86929 127 2.0057 172 14.301 38 .34433 83 .88472 128 2.0503 173 16.350 39 .35412 84 .90040 129 2.0965 174 19.081 40 .36397 85 .91633 130 2.1445 175 22.904 41 .37388 86 .93251 131 2.1943 176 26.636 42 .38386 87 .94896 132 2.2460 177 38.188 43 .39391 88 .96569 133 2.2998 178 57.290 44 .40403 89 .98270 134 2.3558 179 114.590 45 .41421 90 1.00000 135 2.4142 180 Infinite
117 AVIATION STRUCTURAL MECHANIC S 3 & 2
Table 5-3.Bend allowance per degree of bend.
THICKNESS
RADIUS 0.020 0.025 0.032 0.040 0.050 0.063
1/32 0.00070 0.00074 0.00079 1/16 .00125 .00129 .00135 0.00140 0.00148 0.00158
3/32 . 00179 .00183 . 00188 . 0019 5 . 00202 .00212
1/8 . 00234 . 00238 . 00243 .00249 . 00257 .00267
5/32 . 00288 . 00292 . 00297 . 00304 . 00311 . 00321
3/16 .00342 .0034? . 00352 .00358 . 00366 . 00376
7/32 . 00397 . 00401 . 00406 .00412 . 00420 . 00430
1/4 .00451 .00455 . 00461 .00467 . 00475 .00485
If it is impossible to obtain a straight edge on A scriber must never be used for drawing lines a sheet to start a layout, or if the distance from on aluminum or magnesium except to indicate the edge is too great, a reference line may be where the metal is to be cut or drilled. All other used. The reference line may be made by lines must be drawn with a soft-lead pencil. connecting any two points with a straight line. Folding a piece of metal along a sharp line made Perpendiculars may be erected to the reference withascriberwill weaken the metal and line by using a compass or dividers, thus forming possibly cause it to crack along the bend. If it a cross. Once the cross is accurately laid out, it does not crack at the time of bending, it is very may be used as a basis for almost any type of susceptible to cracking in service, possibly at a fitting layout. time when failure of the part can be cata- strophic.
118 CHAPTER 6
AIRCRAFT HARDWARE
Aircraft hardware is a term used in reference SOLID RIVETS to a great many items used in aircraft construc- tion. Some hardware, such as electrical and Solid rivets are classified by their head shape, powerplant hardware, is not applicable to the by the material from which they are manu- AMS rating. The AMS is concerned with such factured, and by their size. Rivet head shapes hardware as rivets, turnlock fasteners, bolts, and their identifying code numbers are shown in screws, nuts, washers, wire and cables, and figure 6-1. The prefix MS identifies hardware related hardware. under the cognizance of the Department of Because of the small size of most hardware Defense and the item conforms to written items, their importanceis often overlooked; military standards. The prefix AN identifies however, the safe and efficient operation of any specifications which are developed and issued aircraft is greatly dependent upon correct selec- under joint authority of the Air Force -Navy. tion and use of aircraft structural hardware. This Countersunk-headrivets.Countersunk-head chapter discusses these various items, and pro- rivets, often referred to as FLUSH RIVETS, are vides information which will aid in the selection used whcre streamlining is important. On com- and correct use of aircraft structural hardware. bat aircraft, practically all external surfaces are flush riveted. Countersunk-head rivets are ob- tainable with heads having an included angle of RIVETS 78 and 100 degrees. The 100-degree is the most commonly used type. Every AMS should be a skilled riveter. The Universal-headrivets.Universal-headrivets fact that there are hundreds of thousands of offer only slight resistance to airflow and are, rivets in the airframe of some of our late model therefore, frequently used on external surfaces, tactical aircraftis an indication of how im- especially on helicopters, transports, and other portant riveting is in the work of the AMS. A low-speed aircraft where aerodynamic smooth- glance at any aircraft will disclose the thousands ness is not of prime importance. of rivets in the outer skin alone. In addition to the riveted skin, rivets are also used for joining Rivet Identification Code spar sections, for holding rib sections in place, for securing fittingsto various parts of the The rivet codes as shown in figure 6-1 are aircraft, and for fastening innumerable bracing sufficientto identify rivets only as to head members and other parts together. Rivets that shape. To be meaningful and precisely identify a are satisfactory for one part of the aircraft are rivet, certain other information is encoded and oftenunsatisfactoryfor another part.Itis added to the basic code. therefore important that the AMS know the A letter or letters following the head-shape strength and driving properties of the various code identify the material or alloy from which types of rivets and how to identify them as well the rivet was made. (Table 6-1 includes a listing as how to drive or otherwise install them. of the most common of these codes.) The alloy
119 AVIATION STRUCTURAL MECHANIC S 3 & 2 code is followed by two numbers separated by a are relatively soft and easy to drive. The cold dash. The first number is the numerator of a workresulting from drivingincreasestheir fraction which specifies the shank diameter in strength slightly. The 1100-F rivets are used thirty-seconds of an inch. The second number is onlyforrivetingnonstructural parts. These the numerator of a fraction in sixteenths of an rivets are identified by their plain head, (See inch and identifies the length of the rivet. The table 6-1.) rivet code is illustrated in figure 6-2. Alloy 2117 rivets. Like the 1100-F rivets, these rivets need no further treatment when Rivet Composition received from the manufacturer, and can be stored indefinitely. They are furnished in the Most of the rivets used in aircraft construc- solution-heat-treated(T4)temper,butwill tion are made of aluminum alloy. A few types, changetothesolution-heat-treated-and-cold- used for special purposes, are made of mild steel, worked (T3) temper after driving. The 21 17 -T4 Monet, titanium, and copper. Of the aluminum rivet is in general use throughout aircraft struc- alloy rivets, those made of 1100, 2117, 2017, tures and is by far the most widely used rivet, 2024, and 5056 are considered standard. (See especially in repair work. In most cases the table 3-4 in ch. 3 for composition of various 2117-T4 rivet may be substituted for 2017-T4 alloys.) and 2024-T4 rivets for repair work by using the Alloy1100rivets.Alloy :100 rivetsare next larger diameter of rivet. This is desirable supplied in the "as fabricated" (F) temper and since )oth the 2017-T4 and 2024-T4 rivets must are driven in this condition. No further treat- be heat treated prior to using, or kept in cold ment is required and the rivet properties do not storage. The 2117-T4 rivets are identified by a change with prolonged periods of storage. They dimple in the head. Alloy 2017 and 2024 rivets. As mentioned in the preceding paragraph, both these rivets are supplied in the T4 temper and must be heat treated. These rivets must be driven within 20 minutes after quenching or refrigerated at 32° F or lower which will delay the aging time 24 hours. If either time is exceeded, reheat treat- ment is required. These rivets may be reheated as many times as desirable provided the proper AN 470 AN 426 MS 20470 MS20426 solutionheat-treatmenttemperatureisnot UNIVERSAL COUNTERSUNK exceeded. The 2024-T4 rivets are stronger than the 2017-T4 and are therefore harder to drive. The 2017-T4 rivet is identified by the raised teat AM.311 on the head, while the 2024-T4 has two raised Fiaure 6-1.Rivet head shapes and code numbers. dashes on the head. Alloy 5056 rivets.These rivets are used primarily for joining magnesium alloy structures because of their corrosion resistant qualities MS 20 426 AD 5 - 8 T Length in sixteenths (8/16ths when used with magnesium. They are supplied of aninch). in the H32 temper (strain-hardened and then Diameter in thirty-seconds (5/32nds stabilized). These rivets are identified by a raised of aninch). cross on the head. 5056-H32 rivets may be Material or alloy (2117-T4). stored indefinitely with no change in driving Headshape(countersunk). characteristics. Specification (Military Standard). HI-SHEAR RIVETS AM.312 Hi-shear (pin) rivets are essentially threadless Figure 6-2.Rivet coding example. bolts. The pin is headed at one end and is 120 Chapter 6AIRCRAFT HARDWARE
Table 6-1.Rivet material identification.
Material or Code letters Head marking alloy on rivet
1100-P A Plain
2117-T4 AD Indented dimple WI= 2017-T4 Raised - -- teat 2024-T4 DD Raised double' dash 1/M. MI= 0110ENID 5056-H32 S Raised Cross grooved about the circumference at the other. A inch for the diameter and sixteenths of an inch metal collar is swaged ontc the grooved end, for the rivet grip length. Thus an NAS1055-5-7 effecting a firm tight fit. They are available in rivet would be a Hi-Shear rivet with a counter- two head styles, the flat protruding head and the sunk head, its diameter would be 5/32-inch, and flush 100-degree countersunk head. Hi-Shear its maximum grip length would be 7/16-inch. rivets are made in a variety of materials and are The collars are identified by a basic code used only in shear applications. Due to the shear number and a dash number which corresponds strength being greater than either the shear or to the, dash number for the diameter of the rivet. bearing strength of aluminum alloys, they are An A before the dash number indicates an used to greater advantage only in the thicker aluminum alloy collar. An NAS528-A5 collar gage sheets. They are never used where the grip would be used on a 5/32-inch diameter rivet ;pin. length is less than the shank diameter. Hi-Shear Repair procedures involving the installation or rivets are illustrated in figure 6-3. replacement of Hi-Sheer rivets generally specify the collar to be used. Rivet Identification BLIND RIVETS Hi-Shear rivets are identified by code numbers similar to the solid rivets. The size of the rivet is There are many places on an aircraft where measured in increments of thirty-seconds of an access to both sides of a riveted structural part is
GROOVE
EDGE
FLUSH HEAD FLAT HEAD COLLAR RIVET RIVET AM.295 Figure 6-3.Hi-Shear rivet installation.
121 AVIATION STRUCTURAL MECHANIC S 3 & 2 impossible, or where limited space does not same principle as the friction lock rivets, both permit the use of a bucking bar. Furthermore, in employing a mandrel stern and a hollow shank. the attachment of many non-structural parts, The main difference between the friction lock such as aircraft interior furnishings, flooring, and mechanical lock rivets is in the method of deicing boots, flotation equipment, and the like, pin retention; the friction lock relies on friction thefull strength of solid shank rivets is not alone for pin retention, while the mechanical necessary and their application would add extra lock rivet employs a mechanical lock between weightto theaircraftthereby reducing the the head of the rivet and the pull stem. Note in payload. view B that the collar, shown clearly in view A For useinsuch places,rivets have been attached to the head, has been driven into the designed which can be formed from the outside. head and has assumed a wedge or cone shape They are lighter than solid shank rivets, yet around the groove in the pin. This holds the amply strong. These rivets are manufactured by shank firmly in place from the head side. variouscorporations and havecharacteristic The self-plugging rivet is made of 5056 -H14 peculiarities, chief of which is the requirement aluminum alloy and includes the conical recess of special installation tools. Rivets in this cate- and locking collar in the rivet head. The stem is gory are commonly referred to as blind rivets made of 2024-T36 aluminum alloy. Pull grooves because of the self-heading feature. which fitinto the jaws of the rivet gun are Self-PluggingRivet. The self-plugging rivet provided on the stem end that protrudes above (friction lock) retains the stem in position by the rivet head. The blind end portion of the friction. The stem is drawn up into the rivet stem incorporates a head and a land with an shank and the mandrel portion of the stem extruding angle which expands the rivet shank. upsets the shank on the blind side, forming a Applied loads permissible for self-plugging plug in the hollow center of the rivet. The excess rivets are comparable to those for solid shank portion of the stem breaks off at a groove due to rivets of the same shear strength, regardless of the continued pulling action of the rivet gun or sheet thickness. The composite ultimate s:iear tool. The two styles or rivet heads are the strengthofthe5056-H14 shankandthe universal and the 100-degree countersunk. These 2024-T36 pin exceeds 38,000 psi on standard correspond to the MS20470 and MS20426 solid rivet hole diameter; their tensile strength is in rivets, respectively. Materials used are 2117-T4 excess of 28,000psi.Pin retentioncharac- and 5056-F aluminum alloys, and Mond for teristics are excellent in these rivets and the special application. The shank diameter and grip possibility of the pin working out is minimized lengths are designated by dash numbers after the by the lock formed in the rivet head. basic number. The first dash number indicates Rivnuts. The Rivnut is a hollow rivet made of the shank diameter in thirty-seconds of an inch 6063aluminumalloy,counterboredand and the second number indicates the grip length threadedontheinside.Installationisac- in sixteenths of an inch. The material code is the same as for solid rivets. Table 6-2.Rivet types with basic numbers. Pull-Through Rivets. Pull-through rivets are essentially the same as the self-plugging rivets, except that when the mandrel pulls on the stem, the stem forms the head on the rivet shank, then TYPE CONFIGURATION HEAD BASIC NUMBER pulls all the way through the shank, leaving a IDENTIFICATION 100 DEGREE cg2:0=0=4 MS20601 hole in the rivet. COUNTERSINK SELF PLUGGING The same installation tools are used for the UNIVERSAL 13:41=1=1 M520600 self-plugging (friction lock) and pull-through HEAD rivets. Table 6-2 shows the basic rivet types with 300 DEGREE MS20605 0:4=4 COUNTERSINK basic numbers. Figure 6-4 illustrates the installa- HOLLOW PULL THRU UNIVERSAL tion of both types of rivets. MS20604 HEAD Self-Plugging rivets (mechanical lock). Figure 6-5 illustrates a blind rivet that operates on the
122 Chapter 6AIRCRAFT HARDWARE
INSTALLATION TOOL ri SELF PLUGGING RIVET
RIVET STEM TRIMMED
II I N. As4. V 05r., .1/4 '4 MIN
SELF PLLI1101140
INSTALLATION HOLLOW PULL TOOL THRU MIT
RIVET INSTALLED
V ZS.N.N. '4 1 X,
PULL THIU AM.315 Figure 6-4.Self-plugging (friction lock) and pull-through rivet installation. complished with the aid of a special tool, which indicate the nominal diameter and the actual heads the rivet on the blind side of the work. number of threads per inch of the machine Rivnuts are primarily used as a nut plate, as in screw that fits into the Rivnut. Rivnuts are the attachment of deicer boots; however, they available with our without small projections, may be used as rivets in secondary structures, or called keys, attached to the underside of the for the attachment of accessories such as instru- head to keep Rivnut from turning. Keyed ments, brackets, and soundproofing materials. Rivnuts are used when the Rivnut serves as a nut After a suitable group of Rivnuts has been plate, while Rivnuts without keys are used for installed, accessories can be fastened in place straight blindriveting jobs where no torque with screws. loads are imposed. Rivnuts are manufactured in two head styles, Open-end Rivnuts are the most widely used flat and countersunk, and in two shank designs, and are recommended in preference to the open and closed ends, as shown in figure 6-6. closed-end type, except in sealed flotation or Each of these rivets is available in three sizes pressurized compartments, in which cases the Nos. 6-32, 8-32, and 10-32. These numbers closed-end Rivnut must be .sed.
123 AVIATION STRUCTURAL MECHANIC S 3 & 2
Blind Lockbolt. The blind lockbolt shown in figure 6-7 (B) is similar to the self-plugging rivet showninfigure6-5.Itfeatures a positive mechanical lock for pin retention.
LOCKING TURNLOCK FASTENERS COLLAR NOTE SHEET GAP Turnlock fasteners are used to secure inspec- LOCKING COLLAR tion plates, doors, and other removable panels aws; ; :or on aircraft. Turnlock fasteners are also referred Asfaik:**.e. to by such terms as quick-opening, quick-action, pvt, and stressed-panel fasteners. The most desirable feature of these fasteners is that they permit quick and easy removal of access panels for inspection and servicing purposes. Removal and (A) INSERTED (B) INSTALLED
LOCKBOLT PIN AM.316 Figure 6-5.Self-plugging rivet (mechanical lock).
LOCKBOLT FASTENERS
Lockbolt fasteners are designed to meet high- strength requirements. Used in many structural applications, their shear and tensile strengths equal or exceed the requirements of AN and NAS bolts. Lockbolt Pins (tension pull type). The lock- bolt shown in figure 6-7 (A) consists of a pin and collar. They are available in two head styles, protruding and countersunk. Pin retentionis accomplished by swaging the collar into the locking grooves on the pin.
COUNTERSUNK FLAT HEAD
OPEN END OPEN END COLLAR CLOSED END CLOSED END (A) (B)
AM.317 Figure 6-6.Sectional view of Rivnut showing head AM.297 and end designs. Figure 6-7.Lockbolts.
124 Chapter 6AIRCRAFT HARDWARE replacement of damaged turnlock fasteners is sembly. (See fig. 6-8.) The receptacle consists of one of the reFponsibilities of the AMS. analuminumalloyforging mountedina Turn lock fastenersaremanufactured and stamped sheet-metal base. The receptacle as- supplied by a number of manufacturers under semblyisriveted to the access door frame, various trade names. Some of the most common- which is attached to the structure of the aircraft. lyusedaretheDzus (pronounced zoo'-s), The grommet is a sheet-metal ring held in the Cam loc, and Airloc, all of which are discussed in access panel with the retaining ring. Grommets the following sections. are furnished in two types, the flush type and the protruding type. In addition to serving as a CAMLOC FASTENERS grommet for the hole in the access panel, it also holds the stud assembly. The stud assembly The 4002 series Cam loc fasteners consist of consists of a stud, a cross pin, spring, and a fourprincipalpartsthereceptacle,the spring cup. The assembly is so designed that it grommet, the retaining ring, and the stud as- can be quickly inserted into the grommet by OUTER MEMBER STUD ASSEMBLY
STUD ASSEMBLY GROMMET GROMMET RETAINING RING RIVET
FLUSH OR PROTRUDING GROMMET INNER MEMBER RECEPTACLE GROMMET STUD RETAINING RETAINING RING RING PROTRUDING TYPE INSTALLATION
STUD RETAINING OUTER MEMBER- RING (USED ON SOME FASTENERS) , STUDASSEMBLY GROMMET GROMMET RETAINING RECEPTACLE RING
RIVET
INNER MEMBER RECEPTACLE
FLUSH TYPE INSTALLATION
AM.38 Figure 6- 8. Camloc 4002 series fastener.
125 AVIATION STRUCTURAL MECHANIC S 3 & 2 compressing the spring. Once installed in the studs are held in the panel with flat or cone- grommet, the stud assembly cannot be removed shaped washers, the latter being used with flush unless the spring is again compressed. fasteners in dimpled holes. This fastener may be distinguished from screws by the deep No. 2 C.A_MLOC HIGH-STRESS Phillips recess in the stud head and by the PANEL FASTENERS bushing in which the stud is installed. A threaded insert in the receptacle provides The Camloc high-stress panel fastener shown an adjustable locking device. As the studis in figure 6-9 is a high-strength, quick release, inserted and turned counterclockwise 1/2 turn rotary type fastener and may be used on flat or or more, it screws out the insert sufficiently to curved, inside or outside panels. The fastener permit the stud key to engage the insert cam may have either a flush or protruding stud. The whenturnedclockwise.Rotating thestud
:Nt
AM.39 1. Tension spring. 6. Receptacle attaching rivets. 2. Stud assembly. 7. Outer skin. 3. Bushing. 8. Inner skin. 4. Retaining ring. 9. Insert. 5. Receptacle assembly. 10, Cover. Figure 6-9.Camloc highstress panel fastener.
126 Chapter 6AIRCRAFT HARDWARE clockwise1/4turnengages theinsert, and pin. The receptacle is riveted to the access panel continued rotation screws the insert in, tighten- frame. ing thefastener. Turning the stud 1/4 turn Two types of Air loc receptacles are available counterclockwise will release the stud, but will the fixed type (insert A) and the floating type not screw the insert out far enough to permit (insert B). The floating type makes for easier reengagement on installation. The stud should alignment of the stud in the receptacle. Several be turned at least 1/2 turn counterclockwise to types of studs are also available, but in each reset the insert. instance the stud and cross pin come as separate units so that the stud may be easily installed in AIRLOC FASTENERS the access panel. The Airloc receptacle is fastened to the inner Figure 6-10 illustrates the parts that make up surface of the access panel frame by two rivets. an Airloc fastener. As with the Camloc fastener, Rivet heads must be flush with the outer surface the Airloc fastener also consists of a receptacle, of the panel frame. When replacing receptacles, a stud, and a cross pin. The stud is attached to drill out the two old rivets and attach the new the access panel and is held in place by the cross receptacle by flush riveting. Be careful not to
FIXED TYPE. FLOATING TYPE (A) (B)
RECEPTACLE;
......
AM.40 Figure 6-10.Airloc fastener.
127 AVIATION STRUCTURAL MECHANIC S 3 & 2 mar the sheet. When inserting the stud and cross Figure 6-11 shows the parts making up a pin, insert the stud through the access panel and, light-dutyDzusfastener.Noticethatthey by use of a special handtool, insert the cross pin include a spring and a stud. The spring is made in the stud. Cross pins can be removed by means of cadmium-platedsteelmusic wire andis of special ejector pliers. usually riveted to an aircraft structural member. The stud comes in a number of designs (as DZUS FASTENERS shown in insets A, B, and C) and mounts in a dimpled hole in the cover assembly. Dzus fasteners are available in two types. One When the panel or plate is being positioned on is the light-duty type, used on box covers, access the aircraft preparatory to securing it in place, hole covers, and lighweight fairing. The second is the spring rivetedto the structural member the heavy-duty type, which is used on cowling enters the hollow center of the stud, which is and heavy fairing. The main difference between retained in the plate or panel. Then, when the the two types of Dzus fasteners is a grommet, stud is turned about 1/4 turn, the curved jaws of usedby heavy-dutybutnot by light-duty the stud slip over the spring and compress it. fasteners. Otherwise their construction features The resulting tension locks the stud in place are about the same. thereby securing the panel or plate.
B
STUD
SPRING
. IMO vA\ ieik 0000.10.0 11-vlt%\ iliffillig COVER \ DIMPLED ASSEMBLY HOLE
AM.319 Figure 6-11.Dzus fastener.
128 Chapter 6AIRCRAFT HARDWARE
THREADED FASTENERS in the case of flat-end bolts (fig.6-12) or in the case of chamfered (rounded) end bolts, at least BOLTS one full chamfer should extend through the nut. If the bolt is too short, it may not extend out of Many types of bolts are used on aircraft and the boltholefar enough for the nut to be each type is used to fasten something in place. securely fastened. If it is too long, it may extend However, before discussing some of these types, so far that it interferes with the movement of it might be helpful at this point to list and nearby aircraft parts. Unnecessarily long bolts, explain some commonly used bolt terms. The especially in numbers, can affect weight and AMS should know the names of bolt parts. He balanceandreducetheaircraftpayload should also be aware of the bolt dimensions that capacity. must be considered in selecting a bolt. Figure In addition, if a bolt is too long or too short, 6-12 illustrates both types of information. its grip will usually be the wrong length. As The three principal parts of a bolt are the shown infigure 6-13, grip length should be HEAD, THREAD, and GRIP. It is possible that approximately the same as the thickness of the two of these parts are well known but perhaps material to be fastened. If the grip is too short, the "grip" is an unfamiliar term. If so, notice the threads of the bolt will extend into the that the grip is the unthreaded part of the bolt bolthole and may act like a reamer when the shaft and that it extends from the threads to the materialisvibrating. To prevent this, make bolthead. The head is the larger diameter of the certain that no more than two threads extend bolt and may be one of many shapes or designs. into the bolthole. Also make certain that any The head retains the boltinplacein one threads that enter the bolthole extend only into direction and the nut used on the threads retains the thicker member that is being fastened. If the it in the other direction. grip is too long, the nut will run out of threads In order to choose the correct replacement before it can be tightened. In this event a bolt foranunserviceablebolt,severalbolt with a shorter grip should be used, or if the bolt dimensions must be considered, one being the grip extends only a short distance through the length of the bolt. As shown in figure 6-12, the hole, a washer may be used. bolt length is the distance from the tip of the A second bolt dimension that must be con- threaded end to the head of the bolt. Correct sidered is diameter. As shown in figure 6-12, the length selection is indicated when the chosen diameter of the bolt is the thickness of its shaft. bolt extends through the nut at least 1/32 inch If this thickness is 1/4 inch or more, the bolt diameter is usually give,, in such fractions of an inch as1/4, 5/16, 7/16, 1/2, and the like. However, if the bolt is less than 1/4 inch thick, the diameter is usually expressed as a whole number. For instance, a bolt that is 0.190 inch in diameter is called a No. 10 bolt, while a bolt that is 0.164 inch in diameter is called a No. 8. The results of using a wrong-diameter bolt should he obvious. If the bolt is too big, it cannot of course enter the bolthole. If the - THREADS' -- GRIP diameter is too small, the bolt has too much play in the bolthole, and the chances are that it is not as strong as the correct size of bolt. The third and fourth bolt dimensions that should be considered when choosing a bolt replacement are head thickness and width. If the head is too thin or too narrow, it may not be AM.320 strong enough to bear the load imposed on it. If Figure 6-12.Bolt terms and dimensions. the head is too thick or too wide, it may extend
129 AVIATION STRUCTURAL MECHANIC S 3 & 2 so far that it interfers with the movement of Boltheads adjacent aircraft parts. The most common type of head is the hex lead, shown in figure 6-12. This type of head may be thick for greater strength or relatively thin in order tofitin places having limited clearances.Inaddition,thehead may be common or drilled. A hex head bolt may have a single hole drilled through it between two of the sides of the hexagon and still be classed as a common. The drilled head hex bolt has three holes drilled in the head, connecting opposite sides of the hex.
BOLT GRIP LENGTH CORRECT (A) ..r.trr77777777===.17.7
EYE BOLT
(B)
CLOSE TOLERANCE BOLT BOLT GRIP LENGTH TOO SHORT
(C)
INTERNAL WRENCHING BOLT
(D) eEil=119
BOLTGRIP LENGTH TOO LONG CLEVIS BOLT
AM.321 AM.322 Figure 6-13.Correct and incorrect grip lengths. Figure 6-14.Boltheads.
130 Chapter 6AIRCRAFT HARDWARE
Four additional types of boltheadsare shown Bolt Material infigure 6-14. Notice that panel A in that illustration shows an eyebolt, often used in The type of metal used in an aircraft bolt flight control systems. Panel B showsa counter- 'helps to determine its strength and its resistance sunk head, close tolerance bolt. Panel C shows to corrosion. Therefore, make certain that mate- an internal wrenching bolt. Both the counter- rial is considered in the selection of replacement sunk head bolt and the internal wrenching bolts bolts.Likesolidshankrivets,boltshave have hexagonal recesses (six-sided holes) in their distinctive head markings that help to identify heads. They are tightened and loosened byuse the material from which they are manufactured. of appropriate size' Allen wrenches. Panel D Incertaincases,aircraft manufacturers are shows a clevis bolt with its characteristic round :ompelled to make bolts of different dimensions head. This head may be slotted,as shown, to )r greater strength than the standard types. Such receive a common screwdriveror recessed to bolts are made for a particular application and it receive a Reed and Prince or a Phillipsscrew- is of extreme importance that like boltsare used driver. in replacement. Such special boltsare usua:::, identified by the letter S stampedon the head. Bolt Threads Figure 6-15 shows the tops of several hex-bolt heads, each marked to indicate the type of bolt Another structural feature in which boltsmay material. differ is threads. These usually come inone of the two typescoarse or fine, and the twoare Bolt Identification not interchangeable. For any given size of bolt Unless current directives specify otherwise, there are a different number ofcoarse and fine every unserviceable bolt should be replaced with threads per inch. For instance, consider the a bolt of the same type. Of course, substitute 1/4-inch bolts. Some are called 1/4-28 bolts, andinterchangeableitemsaresometimes because they have 28 fine threadsper inch. available, but the ideal fixis a bolt-for-bolt Others have only 20 coarse threads per inch and replacement. The part number ofa needed bolt are called 1/4-20 bolts. To force one size of may be obtained by referring to the Illustrated threads into another size even though bothare Parts Breakdown (IPB) for the aircraftcon- 1/4 inch will strip the finer threadsor softer cerned. Exactly what this part numbermeans metal. The same thing is true concerning the depends upon whether the bolt is AN (Air other sizes of bolts; therefore, make certain that Force-Navy), NAS (National Aircraft Standard) bolts selected have the correct type of threads. or MS (Military Standard).
HEAD MARKINGS
STEEL ALUMINUM CORROSION STEEL STEEL CLOSE ALLOY RESISTANT (125,000 (160,000 TO TOLERANCE ( 62,000 STEEL P.S.I.) 180,000 (125,000 TO P. ) (125,000 PS.I. ) 145, 000 A.S.I) P.S.1.)
AM.41 Figure 6-15.Bolthead markings.
131 AVIATION STRUCTURAL MECHANIC S 3 & 2
case of a series number ending in 0, for instance
AIR FORCE BOLT SAFETYING AN30, the 0 stands for 10, and the bolt has a NAVY BOLT MATERIAL PROVISIONS diameter of 10/16 inch (5/8 inch). Refer again to figure 6-16 and notice that a dash follows the series number. When used in the part numbers for general-purpose AN bolts, 2017 clevis bolts, and eyebolts, this dash indicates AN 11114 that the bolt is made of carbon steel. With these types of bolts, the letter C, used in place of the dash, means corrosion-resistant steel; the letter D means 2017 aluminum alloy; and the letters SfiRIES LDASH NUMBER NUMBER (BOLT GRIP DD stand for 2024 aluminum alloy. For some (CLASS AND AND LENGTH) bolts of this type, a letter H is used with these DIAMETER) letters or with the dash. If it is so used, the H shows that the bolt has been drilled for safety- ing. AM.323 Next, notice the number 20 that follows the Figure 6-16.AN bolt part number breakdown. dash. This is called the dash number, and it represents the bolt's grip (as taken from special AN PART NUMBER.There areseveral tables). In this instance the number 20 stands classes of AN bolts, and in some instances their for a bolt that is 2 1/32 inches long. part numbers reveal slightly different types of The lastcharacterinthe AN number il- information.However,most AN numbers lustrated in figure 6-16 is the letter A. This contain the same type of information. signifies that the bolt is not drilled for cotter pin safetying. If no letter were used after the dash Figure 6-16 shows a breakdown of a typical number, the bolt shank would be drilled for AN boltpart number. Like the AN rivets safetying. discussed earlier,it starts with the letters AN. NAS PART NUMBER.Another series of Next, notice that a series number follows the boltsusedinaircraftconstruction isthe letters AN. This number usually consists of two NationalAircraft Standard (NAS). (Seefig. digits, and the first digit (or absence of it) shows 6-17.) In considering one of the NAS bolts, the class of the bolt. For instance, in figure 6-16 NASI44(specialinternalwrenchingtype), the series number has only one digit, and the notice that the bolt identification code starts absence of one digit shows that this part number with the letters NAS, which show, of course, representsageneral-purposehex-headbolt. that the code represents a National Aircraft However, the part numbers for some bolts of Standard piece of hardware. Next, notice that thisclass have two digits.In fact, general- purpose hex-head bolts include all part numbers beginning with AN3, AN4, and so on through AN20. Other series numbers and the classes of NAS 14 4 - 25 bolts that they represent are as follows: Dash number (bolt grip in sixteenths).
AN21 through AN36clevis bolts. Diameter in sixteenths. AN42 through AN49eyebolts. Series number.
The series number shows another type of National Aircraft Standard information besides bolt 'class.With a few bolt. exceptions, itindicates bolt diameter in six- teenths of an inch. For instance, in figure 6-16 the last digit of the series number is 4, so this AM.324 bolt is 4/16 inch (1/4 inch) in diameter. In the Figure 6-17.NAS bolt part number breakdown.
132 Chapter 6AIRCRAFT HARDWARE the series has a three-digit number, 144. The HI-LOK FASTENERS first two digits (14) show the class of the bolt. The next number (4) indicates the bolt diameter The Hi-Lok fastener shown in figure 6-19 in sixteenths of an inch. The dash number (25) combines the features of a rivet and a bolt, and indicates bolt grip in sixteenths. is used forhigh-strength, interference fit of MS PART NUMBER.Military Standard (MS) primary structures. The Hi-Lok fastener consists isanother seriesof bolts usedinaircraft of a threaded pin and threaded locking collar. construction. In considering the part number The pins are made of cadmium-plated alloy steel shown in figure 6-18, the MS indicates that the with protruding or100-degreeflush heads. boltisa Military Standard bolt. The series Collars for the pins are made of anodized number (20004) indicates the bolt class and 2024-T6 aluminumorstainlesssteel.The diameterinsixteenths of an inch (internal threaded end of the pin is recessed with a wrenching, 1/4-inch diameter). The letter H hexagon socket to allow installation from one before the dash number indicates that the bolt side. The major diameter of the threaded part of hasadrilled head for safetying. The dash the pin has been truncated (cut undersize) to number (9) indicates the bolt grip in sixteenths accomodate a 0.004-inch maximum interference of an inch. fit. One end of the collar is internally recessed with a 1/16-inch, built-in variation which auto- matically provides for variable material thickness 1S 20004 H 9 without the use of washers and without preload changes. The other end of the collar has a (Dash number (bolt grip in sixteenths). torque-off wrenching device which controls a. predeterminedresidualtensionofpreload Safetying provisicns. (±10%) in the fastener. Series ntmiber (class and diameter in sixteenths). Military Standard holt. HELL -COIL INSERTS Heli-Coil thread inserts are primarily designed AM.298 to be used in materials which are not suitable for Figure 6-18.MS bolt part number breakdown. threading because of their softness. They are
HI-LOK COLLAR
HI-LOK PIN HI-LOK PIN HI-LOK FASTENER PROTRUDING 100° FLUSH INSTALLATION HEAD TYPE HEAD TYPE
AM.325 Figure 6-19.Hi-Lok fastener.
133 AVIATION STRUCTURAL MECHANIC S 3 & 2
Tang Opposite. External Threads End
Internal Threads
Grip Coil PLAIN MID-GRIP HELl-COIL HELL -COIL CROSS SECTION APPLICATION
AM.326 Figure 6-20.Heli-Coil inserts. f made of a diamond cross-sectioned stainless steel a gripping effect on the engaging screw. For wire which is helically coiled and, in its finished quick identification, the self-locking mid-grip form, is similar to a small spring which has been inserts are dyed red. fully compressed. There are two types of He li- Coil inserts. (See fig. 6-20.) One is the plain insert, made with a tang that forms a portion of :0-BOLT FASTENERS the bottom coil offset, and is used to drive the insert.This tang isleft on the insert after The Jo-Bolt shown in figure 6-21 is a high- installation, except when its removal is necessary strength, blind, structural fastener that is used to provide clearance for the end of the bolt. The on difficult riveting jobs when access to one side tang is notched to provide for the breakoff from of the work is impossible. The Jo-Bolt consists the body of the insert, thereby providing full of three parts: an aluminum alloy or r..11oy steel penetration for the fastener. nut, a threaded alloy steel bolt, and a corrosion- The second type of insert used is the self- resistantsteelsleeve, which are factory pre- locking mid-grip insert which has a specially assembled. The head styles available for Jo-Bolts formed grip coil midway of the insert, producing are the1 00-degreeflushhead, hexagon
BOLT
NUT \% \ Affl COLLAR NMI
INSTALLED PROTUDING HEAD INSTALLED FLUSH HEAD
AM.327 Figure 6-21.Jo-Bolts.
134 Chapter 6AIRCRAFT HARDWARE protruding head, and the 100-degree flush milla- PLAIN HEX NUT.The plain hex nut is of ble head. rugged construction. This makes it suitable for carrying large tensional loads. However, since it AIRCRAFT NUTS requires an auxiliary safetying device, such as a checknut or lockwasher, itsuse on aircraft Aircraft. nuts differ in design and material just structures is somewhat limited. as bolts do, .that they are designed to do a LIGHT HEX NUT.The light hex nut is a specific job with the bolt. For instance, some of nuch lighter nut than the plain hex nut and must the nuts are made of cadmium-plated carbon be locked by an auxiliary device. It is used for steel, stainless steel, brass, or aluminum alloy. miscellaneous light-tension requirements. The type of metal used is not identified by CHECKNUTS.The checknut is employedas markings on the nuts themselves. Instead, the alocking deviceforplainnuts,setscrews, material must be recognized from the metallic threaded rod ends, and other devices. luster of the metal. WINGNUTS.Wingnutsareintendedfor Nuts also diftet greatly in size and shape. In placeswherethedesiredtightness can be spite of these many and varied differences they obtained by use of the fingers and where the allfall under one of two general groupsself assembly is frequently removed, such as battery locking and nonself-locking. Nuts are further terminal connections. In the illustration, note divided into types such as plain nuts, castle nuts, the hole in one of the wings, which is used for checknuts, plate nuts, channel nuts, barrel nuts, safetying the nut with wire. internal wrenching nuts,external wrenching nuts, shear nuts, sheet spring nuts, and wingnuts. Self-Locking Nuts Each of these groups is discussed in subsequent Self-locking nuts provide tight connections paragraphs and sections. which will not loosen under vibrations. Self- locking nuts approved for use on aircraft meet Nonself-Locking Nuts Nonselt'- locking nuts require the use of a separate locking device for security of installa- tion. There are several types of these locking devices which are mentioned in the following paragraphs in connection with the nuts on which they are used. Since no single locking device can be used with all types of nonself-locking nuts, the AMS must select one suitable for the type of nut being used. Figure 6-22 illustrates four CASTLE NUT PLAIN NUT nonself-locking nuts. CASTLE NUT.The castle nut is used in conjunction with drilled-shank bolts, hex-head bolts, clevis bolts, eyebolts, and drilled head studs. It is fairly rugged and can withstand large tensional loads. Slots (called castellations) in the nut are designed to accommodate a cotter pin or lock wire for safetying purposes. CASTELLATED SHEAR NUT.The castel- lated shear nut is designed for use with devices such as drilled clevis bolts and threaded taper pins which are normally subjected to shearing CASTELLATED stress only. Like the castle- nut, it is castellated SHEAR NUT WING NUT for safetying, but is not as deep nor as strong as AMA2 the castle nut. Figure 6-22.Nonself-locking nuts.
135 AVIATION STRUCTURAL MECHANIC S 3 & 2 critical specifications as to strength, corrosion ends must not be used. Bolts, studs, and screws resistance, and temperatures. The two general of 1/4 inch or less with cotter pin holes shall not types of self-locking nuts are the all-metal nuts be used with self-locking nuts. Bolts, studs, and and metal nuts with a nonmetallic insert to screws over 1/4 inch in diameter may be used provide the locking action. New self-locking nuts with self-locking nuts, provided the cotter pin must be used each time components are installed holes are free from burrs. in critical areas throughout the entire aircraft, Used self-locking nuts are generally suitable including allflight, engine, and fuel control for reuse in noncritical applications provided the linkage and attachments. The Boots and the threads have not been damaged and are in a Flexloc are examples of the all-metal type; the serviceable condition and if the locking material Elastic Stop is an example of the nonmetallic is not damaged or permanently distorted. insert type. Figure 6-23 shows several types of NOTE: If any doubt exists about the condi- self-locking nuts. tion of the nut, replace it with a new one. The Boots self-locking nutis of one-piece When anchoring lightweight parts the sheet all-metal construction, designed to hold tight in springnut(fig.6-24)isused. Applications spite of severe vibration. It has two sections include supporting line clamps, electrical equip- connected by a spring which is an Integral part ment, small access doors, etc. It is made of sheet of the nut. This load-carrying and locking nut is spring steel, cut so as to have two flaps. The so spaced that the two sets of threads are out of ends of these flaps are notched to form a hole phasethat is, so spaced that a bolt which has that is somewhat smaller in diameter than the been screwed through the load-carrying section screw used. The sheet spring nut has a definite must push the locking section outward against arch which tends to flatten out as the screw the force of the spring in order to engage the pulls theflapsin toward the threads. This threads of the locking section properly. Thus, flattening action forces the flaps of the nut the spring, through the medium of the locking tightly into the threads of the screw, and the section, exerts a constant locking force on the springiness ofthe sheetspring nut pushes boltin the same directionas a force that upward on the screw threads, binding them and tightens the nut. The nut can be removed and locking the screw in place. With the sheet spring used again without impairing its efficiency. nut, either a standard or a sheet-metal self- Other types of all-metal self-locking nuts are tapping screw is used. constructed with the threads in the load-carrying portion of the nut out of phase with the threads in the locking portion, or with a saw cut top portion with a pinched-in thread. The locking WASHERS actionofthesetypes depends uponthe resiliency of the metal when the locking section Washers used in aircraft structures may be and load-carrying section are forced into align- groupedintothreegeneralclassesPLAIN ment when engaged by the bolt or screw washers, LOCKWASHE RS,and SPECIAL threads. washers. Figure 6-25 shows some of the most The Elastic Stop nut is constructed with a commonly used types. nonmetallic (nylon) insert which is designed to Plain washers are widely used under nuts to lock the nut in place. The insert is unthreaded provide a smooth bearing surface, to act as a and has a smaller diameter than the nut proper. shim in obtaining the correct relationship be- When a screw orboltisinserted, contact tween the threads of the bolt and the nut, and between the bolt or screw threads and the insert to adjust the position of castellated nuts with produces the locking action. The Elastic Stop respect to drilled cotter pin holes in bolts. Plain nut is a low-temperature nut and must not be washers are also used under lockwashers to subjected to temperatures above 250° F. prevent damage to surfaces of soft materials. There are certain precautions which must be Lockwashers are used with plain nuts when observed with all self-locking nuts. Bolts, studs, self-locking or castellated type nuts are not and screws with damaged threads and rough applicable. Sufficient friction is provided by the
136 Chapter 6AIRCRAFT HARDWARE
- BOOTS AIRCRAFT NUT FLEXLOC NUT
NON-METALLIC ELASTIC ELASTIC TWO-LUG INSERT STOP NUT ANCHOR NUT LOCK NUT
BOOTS AIRCRAFT CHANNEL ASSEMBLY
ELASTIC STOP NUT CHANNEL ASSEMBLY
AM.44 Figure 6-23.Self-locking nuts.
137 AVIATION STRUCTURAL MECHANIC S 3 & 2
A B
00011=
TOP VIEW SIDE VIEW AA&
C INWARD D LOCK WASHERS THREAD LOCK ..:--- ..-- ...... ------,d/iZr"....: ....--...... s...--...... 1.--..,b____ \ "s',"...... ,... Nis, Ns,. Nt.r1:.+:'.,,zv\ NNII w ARCHED SPRING LOCK r I gal=t1fti AIM''I PLAIN GALL SOCKET TAPIA PIN DOUBLELOCKED STARTING POSITION POSITION SPECIAL WASHERS
AM.45 Figure 6-25.Various types of washers. AM.328 Figure 6-24.Sheet spring nut. are used in conjunction with NAS internal- wrenching bolts. The washer used under the spring action of the washer to prevent loosening head is countersunk to seat the bolthead/shank of the nut from vibration. Lockwashers are not radius. A plain washer is used under the nut. to be used on primary structures, secondary structures, or dwessories where failure might INSTALLATION OF result in damage or danger to aircraft or person- NUTS AND BOLTS nel. Special washers, such as ball-socket and seat Be certain that each bolt is of correct mate- washers, taper pin washers, and washers for rial.Examine the marking on the head to internal-wrenching nuts and bolts, are designed determine whether a bolt is steel or aluminum for special applications. alloy. Ball-socketandseat washers are usedin It is of extrerne importance to use like bolts applications where the bolt is installed at an.in replacement. In every case, referto the angle to the surface, or where perfect alignment applicable Maintenance Instructions Manual and with the surface is required at all times. These Illustrated Parts Breakdown. washers are used together. Be sure that washers are used under both the Taper pin washers are used in conjunction heads of bolts and nuts unless their omission is with threaded taper pins and are installed under specified. A washer guards against mechanical the nut to effect adjustment where a plain damagetothematerialbeing bolted and washer would distort. prevents corrosion of the structural members. Washers for internal-wrenching nuts and bolts An aluminum alloy washer should be used under
138 Chapter 6AIRCRAFT HARDWARE the head and nut of asteelbolt securing as bolts, but differ mainly in that they usually a'...rninum alloy or magnesium members. Steel have a lower material strength, a looser thread washers should be used when joining steel fit,and shanksthreaded alongtheir entire members with steel bolts. length.However, several types of structural Whenever possible the bolt should be placed screws are available which differ from structural with the head on top or in the forward position. bolts only in the type of head; the material is This position tends to prevent the bolt from equivalent and there is a difinite grip. Screws slipping out if the nut is accidentally lost. maybedividedintofourmaingroups- structural screws, machine screws, self-tapping SAFETYING OF NUTS screws, and setscrews.
It is very important that all nuts, except the Structural Screws self-locking type, be safetied after installation. This prevents nuts from loosening in flight due Structural screws are used for assembly of to vibration. Figure 6-26 illustrates the proper structural parts, as are structural bolts. They are way to secure a nut using a cotter pin. made of alloysteel and areproperly heat treated. Structural screws have a definite grip length (fig. 6-27) and the same shear and tensile strengths as the equivalent size bolt. They differ from structural bolts only in the type of head. Thesescrewsareavailableinround-head, countersunk-head, and brazier-head types, either slotted or recessed for the various types of screwdrivers.
Machine Screws OPTIONAL PREFERRED The commonly used machine screws are the round-head,flat-head, fillister-head, pan-head, AM.43 truss-head, and socket-head types. t-igure ti-Zli.Cotter pin installation. FLAT-HEAD MACHINE SCREWS. Flat -head machine screws are used in counter- APPLICATION OF TORQUE sunk holes where a flush finish is desired. These screws are available in 82 and 10) degrees of Torque:sthe amount oftwisting force head angle and have various types of recesses applied whe,n tightening a nut. If torque values and slots for driving. are specified in the appropriate manual, a torque ROUND-HEAD MACHINE SCREWS. wrench must be used. Regardless of whether Round -head machine screws are frequently used torque values are specified or not, it is improtant inassemblinghighlystressedaircraftcom- thatallnuts ina particular installationbe ponents. tightened a like amount. This permits each bolt FILLISTER-HEAD MACHINE SCREWS. in a group to carry its share of the load. It is a Fillister-head machine screws are used as general- good practice, therefore, to use a torque wrench purpose screws and also may be used as cap- in all nut and bolt applications. screws in light applications such as the attach- ment of cast aluminum gearbox cover plates. SCREWS SOCKET-HEAD MACHINE SCREWS. Socket -head machine screws are designed to be Screwsarethemost common typeof screwed into tapped holes by internal wrench- threaded fasteners used on aircraft. They are ing. They are used in applications which require similar to other types of threaded fasteners, such high strength precision products, compactness of
139 AVIATION STRUCTURAL MECHANIC S 3 & 2
internal threads as it is turned into the hole in which it is inserted. Self-tapping screws can be used only in comparatively soft metals and materials. Self-tapping screws may be further divided into two classes or groupsmachine self-tapping screws and sheet-metal self-tapping screws. Machine self-tapping screws are usually used for attaching removable parts, such as name- LENGTH plates, to castings. The threads of the screw cut mating threads in the casting after the hole has beenpredrilledundersize.Sheet-metalself- tapping screws are used for such purposes as temporarily attaching sheet metal in place for riveting and for permanent assembly of non- 119\1\OV structural assemblies, where itis necessary to insert screws in blind applications. CAUTION: Self-tapping screws should never be used to replace standard screws, nuts, or rivets in the original structure.
Setscrews Setscrews are used to position and hold in place components such as ge rs on a shaft. Setscrews are available with many different point styles. They are classified as hexagon- socket and fluted-socket headless setscrews.
MISCELLANEOUS FASTENERS GRIP Some fasteners cannot be classified as rivets, LLENGTH turnlocks, or threaded fasteners. Included in this category are taper and flathead pins.
TAPER PINS AM.329 Figure 6-27.Structural screws. Taper pins (fig. 6-28 (A) and (B)) are used in joints that carry shear loads and where the the assembled parts, or sinking of heads below absence of clearance is essential. The threaded surfaces into holes. taper pin is used with a taper-pin washer and a PAN-HEAD AND TRUSS-HEAD MACHINE shear nut if the taper pin is drilled or with a SCREWS.Pan-head and truss-head screws are self-locking nut if undrilled. When a shear nut is general-purpose screws used where head height is used with the threaded taper pin and washer, the unimportant. These screws are available with nut is secured with a cotter pin. cross-recessed heads only. FLATHEAD PINS Self-Tapping Screws The flathead pin is used with tie rod terminals A self-tapping screw is one that cuts its own or secondary controls, which do not operate
140 Chapter 6AIRCRAFT HARDWARE
SAFETYING MATERIAL
STATIONARY The AMS will come in contact with many MEMBER A different types of safetying materials. These 11111Iu materials are used to stop rotation and other -PPLAIN movement of fasteners, and securing of other TAPER equipment likely to come loose due to vibration PIN set tip in the aircraft during flight operations.
MOVABLE MEMBER COTTER PINS Cotter pins are used to secure bolts, screws, PLAIN TAPER PIN INSTALLED nuts, and pins. Some cotter pins are made of low-carbon steel, while others consist of stainless STATIONARY MEMBER B steel and thus are more resistant to corrosion. In COTTER PIN addition, stainless steel cotter pins may be used inlocations where nonmagnetic materialis required. Regardless of shape or material, all cotter pins areusedforthe same general THREADED CASTELLATED TAPINPER 1111111111111111111111 NUT purposesafetying.Figure 6-29 shows three types of cotter pins and how theirsizeis TAPER PIN determined. MOVABLE...r. WASHER MEMBER"- NOTE: Whenever uneven prong cotter pins are used, the length measurement is to the end THREADED TAPER PIN INSTALLED of the shortest prong.
FLATHEAD PIN lc-LENGTH
COTTER PIN DIAMETER
UNEVEN PRONGS OPTIONAL FLATHEAD PIN INSTALLED
AD.28 Figure 6-29.Types of cotter pins. AM.330 Figure 6-28.Types of aircraft pins. SAFETY WIRE Safety wire comes in many types and sizes. continuously.Theflatheadpinshouldbe One must first select the correct type and size of secured with a cotter pin. The pin is normally wire for the job. Annealed corrosion-resisting _installed with the head up (fig. 6-28 (C)). This wireisusedin high-temperature, electrical- precaution is taken to maintain the flathead pin equipment, and aircraft-instrument applications. in the installed position in case of cotter pin All nuts except the self-locking types must be failure. safetied; the method used depending upon the
141 AVIATION STRUCTURAL MECHANIC S 3 & 2
Annealed copper safety wireisusedfor sealing first aid kits, portable fire extinguishers, oxygen regulator emergency valves, and other valves and levers used for emergency operation of aircraft equipment. This wire can be broken BOLT HEADS by hand in case of an emergency.
CONNECTORS AND COUPLINGS
A variety of clamping devices are utilized in connecting ducting sections to each other or to Wheneverlines,com- CASTLE NUT variouscomponents. ponents, or ducting are disconnected or removed for any reason, install suitable plugs, caps, or coverings on the openings to prevent the entry SAFETY METHODS SHOWN ARE FOR of foreign materials. Tag the various parts to RICH i HAND THREADS. LEFT HAND OPPOSITE. insure correctreinstallation.Care should be exercised during handling and installation to insure that flanges are not scratched, distorted, or deformed. Flange surfaces should be free of dirt, grease, and corrosion. The protective flange caps should be left on the ends of the ducting until the installation progresses to the point where removal is necessary to continue with the SAFETY WIRE OVER HEAD installation. In most cases it is mandatory to discard and replace seals and gaskets. Insure that seals and gaskets are properly seated and that mating and alignment of flanges are fitted so that excessive torque is not required to close the joint and SAFETY WIRE AROUND HEAD impose structural loads on the clamping device. Adjacent support clamps and brackets should remain loose until installation of the coupling AM.331 has been completed. Figure 6-30.Safety wire installation. FLEXIBLE CONNECTORS/COUPLINGS particular installation. Figure 6-30 illustrates the correct methods of installing safety wire. The Some of the most commonly used plain band following general rules apply to safety wiring: couplings are illustrated in figure 6-31. When installing a hose between two duct sections, as 1. All safety wires must be tight after installa- illustrated in figure 6-31, the FT between the tion, but not under so much tension that normal duct ends should be 1/8 inch minimum to 3/4 handling or vibration will break the wire. inch maximum. When installing the clamps on 2. The wire must be applied so that all pull the connection, the clamp should be 1/4 inch exerted by the wire tends to tighten the nut. minimum from theend of the connector. 3. Twists should be tight and even and the Misalignment between the ducting ends should wire between nuts as taut as possible without not exceed 1/8 inch maximum. overtwisting.Wire betweennuts shouldbe Marman type clamps commonly usedin twisted with the hands. The use of pliers will ducting systems should be tightened to the damage the wire. Pliers may be used only for torque value indicated on the coupling. Tighten final end twist prior to cutting off excess wire. all couplings in the manner and to the torque
142 Chapter 6AIRCRAFT HARDWARE
MARMAN BAND CLAMPS TO MARMAN BAND CLAMP BE USED IN TIGHT AREAS
AN-77 BAND CLAMP FOR AN737 BAND CLAMP T A%0ARD INSTALLATIONS
I/B-INCH MAXIMUM MISALIGNMENT
.4-1/8 INCH MINIMUM 3/4 INCH MAXIMUM
LI/4 INCH MINIMUM AM.1135 Figure 6-31.-Flexible line connectors. valueas specified on the clamp or inthe 1. Fold back half of the sleeve seal and slip it applicable Maintenance Instructions Manual. onto the sleeve. 2. Slidethesleeve(with the sleeveseal When installing flexible couplings, such as the partially installed) onto the line. one illustrated in figure 6-32, the following steps 3. Position the splitsleeves over the line are recommended to assure proper security: beads.
143 AN/L-FLOM STRUCTURAL MECHANIC S 3 & 2
When installing rigid couplings, follow the SPLIT SLEEVE steps listed below and illustrated in figure 6-33. COUPLING SLEEVE SLEEVE SEAL 1. Slip the V-band coupling over the flanged tube. 2. Mace a gasket into one flange. One quick rotary motion assures positive seating of the gasket. 3. Hold the gasket in place with one hand LINE BEADS while the mating flanged tube is assembled into the gasket with a series of vertical and horizontal motions to assure the seating of the mating flange to the gasket. NOTE: View B of figure 6.33 illustrates the proper fitting and connecting of a rigid coupling, SPLIT utilizing a metal gasket between the ducting SLEEVE flanges. NSLEEVE SEAL ) SLEEVE FOLDED BACK 4. While holding the joint firmly with one hand, install the V-band coupling over the two flanges. 5. Pressthecouplingtightlyaround the flanges with one hand while engaging the latch. AM.91 6. Tighten the coupling firmly with a ratchet Figure 6-32.Installation of flexible line couplings. wrench. Tap the outer periphery of the coupling with a plastic mallet to assure proper alignment 4. Slide the sleeve over the split sleeves and of the flanges in the coupling. This will seat the fold over the sleeve seal so that it covers the scalingedges of theflanges inthe gasket. entire sleeve. Tighten again, making sure the recommended torque is not exceeded. 5. Install the coupling over the sleeve seal and 7. Check the torque of the coupling with a torque to correct value. torque wrench and tighten until the specified torque is obtained. NOTE: Torque values for the various sizes 8. Safety wire the V-band coupling as il- and types of couplings may be found by lustrated in figure 6-34 as an extra measure of referring to the applicable Maintenance Instruc- security in the event of T-bolt failure. If the nut tions Manual. Some couplings will have the on the T-bolt is drilled for safetying, extend the correct torque value marked on the outside of safety wire to the nut so that it will pull on the the band. nut in a clockwise (tightening) direction. Most V-band connectors willutilize a T-bolt with some type of self-locking nut.
RIGID COUPLINGS MECHANICAL CONTROLS The rigid line coupling illustrated in figure Included among the responsibilities of the 6-33 is referred to as a V-band coupling. When AMS are various mechanical control systems. A installing this coupling in restricted areas, some mechanical control system may be either a cable of the stiffness of the coupling can be overcome typesystem,push-pullrodsystem,ora by tightening the coupling over a spare set of combination of both. Push-pull rod systems are flanges and gasket to the recommended torque sometimes called "rigid" control systems, but value of the joint. Tap the coupling a few times this is not to imply that cable type systems are with a plastic mallet before removing it. to be called "flexible" control systems.
144 Chapter 6AIRCRAFT HARDWARE
11)
(A)
LATCH
HIGH-STRENGTH "T" BOLT
NUT
END VIEW COUPLING
FLANGE COPPER GASKET FLANGE (B)
AM.1136 Figure 6-33.Installation of rigid line couplings.
145 AVIATION STRUCTURAL MECHANIC S 3 & 2
present in system controls and no lost motion LQCKWIRE WITH exists between the actuating device and the unit. MS20995-NC40 Consequently, cable-controlledunits respond 2 STRANDS MIN 3 TURNS quickly and accurately to cockpit control move- IN THIS AREA ment. In some simple cable systems, only one cable is used and a spring provides the return action.
Control Cables A cable is a group of wires or a group of strands of wires twisted together into a strong wire rope. The wires or strands may be twisted in various ways. The relationship of the direc- tion of twist of each strand to each other and to the cable as a whole is called the lay. The lay of the cable is an important factor in its strength, for if the strands are twisted in a direction V SAND COUPLER opposite to the twist of the strands around the center strand or core, the cable will not stretch (or set) as much as one in which they are all twisted in the same direction. This direction of AM.1137 twist (in opposite direction's is most commonly Figure 6-34.Safetying a V-band coupling. adopted.Therefore,itiscalledregularor ordinary lay. Cables may have right regular lay CABLE CONTROL SYSTEMS or a left regular lay. If the strands are twisted in the direction of twist around the center strand Cables have many advantages. They will not or core, the lay is called a lang lay. There is a sever readily under sudden strains such as occur right and left lang lay. The only other twist during towing, as of aircraft, trucks, and the arrangement,thatis,twistingthestrands like. Cables are stronger than steel rods or tubing alternately right and left, then twisting them all of the same size. They flex without setting either to the right or to the left about the core is (permanent deformation) and can be led easily called a reverse lay. Most aircraft cable has a around obstacles by use of pulleys. Cables can right regular lay. be installed over long distances (such as in large When aircraft cables are manufactured, each aircraft) without a great degree of sagging (or strand is first formed to the spiral or helical bending), and vibration will not cause them to shape to fit the position it is to occupy in the harden, crystallize, and break, as may be the finished cable. The process of such forming is case with Push-pull control rods. Because of the called preforming, and cables made by such a great number of wires used in cables, cable process are said to be preformed. The process of failure is never abrupt, but is progressive over preforming is adopted to secure flexibility in the periods of extended use. When used for the fmished cable and to relieve bending and twist- manipulation of a unit in a control system, they ing stresses in the strands as they are woven into are usually worked in pairsone cable to move the cable. It also keeps the strands from spread- the unit in one direction, the other to move it in ing when the cable is cut. All aircraft cable is, the opposite direction. Yet, in spite of the internally lubricated during construction. second cable, weight is saved, because a push- Aircraft control cables are fabricated either pull rod needed to cause a similar movement in a from flexible, preformed, carbon-steel wire, or unit would have to be quite thick and heavy fromflexible,preformed, corrosion-resistant (comparatively speaking). Since cables are used steel wire. The smaller corrosion-resistant steel in pairs and are stretched taut, very little play is cables are made of steel containing not less than
146 Chapter 6AIRCRAFT HARDWARE
17 percent chromium and 8 percent nickel while Cable.Fittings the larger ones (those of the 5/16-, 3/8-, and 7/16-inch diameters) are made of steel which, in Cable ends may be equipped with several addition to the amounts of chromium and nickel different types of fittings such as terminals, just mentioned, also contain not less than 1.75 thimbles, bushings and shackles. Terminal fit- percent molybdenum. tings are generally of the swaged type. (NOTE: The swaging process is described in detail in Cables may be designated 7 x 7, 7 x 19, or 6 x chapter 8.) Terminal fittings are available with 19 according to their construction. A 7 x 7 cable threaded ends, fork ends, eye ends, single-shank consists of six strands of seven wires each, laid ball, and double-shank ball end. around a center strand of seven wires. A 7 x 19 Threaded ends,fork ends, and eye end cablec .insists of six strands of 19 wires, laid terminals are used to connect the cable to around a 19-wire central strand. A 6 x 19 IWRC turnbuckles, bellcranks, and other linkage in the cable consists of six strands of 19 wires each, system. The ball type terminals are used for laid around an independent wire rope center. attaching cable to quadrants and special con- nections where space is limited. The single-shank The size of cable is given in terms of diameter ball end is usually used on the ends of cables and measurement. If one speaks of a 1/8-inch cable the double-shank ball may be used at either the or a 5/16-inch cable, he means that the cable ends or in the center of a cable run. Figure 6-36 measures 1/8 inch or 5/16 inch in diameter, illustrates the various types of terminal fittings. measured as shown in figure 6-35. Note that the Thimble, bushing, and shackle fittings may be cable diameter isthat of the smallest circle used in place of some types of terminal fittings which would enclose the entire cross-section of when facilities and supplies are limited and thecable.Aircraftcontrolcables varyin immediate replacement of the cable is necessary. diameters ranging from 1/16 inch to 3/8 inch. Figure 6-37 illustrates these fittings.
5I32-7/32 DIAMETER 7X19 7 STRANDS-19 DIAMETER WIRES TO EACH STRAND
1/16- 3/32 DIAMETER 7X7 7 STRANDS-7 DIAMETER WIRES TO EACH
AM.332 Figure 6-35.-Cable cross sections.
147 AVIATION STRUCTURAL MECHANIC S 3 & 2
Turnbuckles minor adjustmentsincable length and for adjusting cable tension. One of the terminals has A turnbuckle is a mechanical screw device right-hand threads and the other has left -hand consisting of two threaded terminals and a threads. The barrel has matching right-and left- threaded barrel. Figure 6-38 illustrates a typical hand threads internally. The end of the barrel turnbuckle assembly. Turnbuckles are fitted in with left-hand threads inside can usually be the cable assembly for the purpose of making identified by either a groove or knurl around
DOUBLE SHANK BALL END TERMINAL (..-61)ozammi
SINGLE SHANK BALL END TERMINAL
WIRE CABLE THIMBLE
ROD END TERMINAL
THREADED CABLE TERMINAL CABLE BUSHING
FORK END CABLE TERMINAL -0
CABLE SHACKLE EYE END CABLE TERMINAL
AM.334 AM.333 Figure 6-37.Thimble, bushing, and shackle type Figure 6-36.Types of terminal fittings. fittings.
148 Chapter 6AIRCRAFT HARDWARE
SWAGING TERMINAL r GROOVE BARREL PIN EYE
AM.335 Figure 6-38.Typical turnbuckle assembly.
After a turnbuckle is properly adjusted, it must be safetied. There are several methods of safetyingturnbuckles.However,onlytwo methods have been adopted as standard proce- 1111110 111#1101\1\101% dures by the services. These methods are il- lustrated in figure 6-40. The preferred method is 1. -THREE THREADS theclip-locking method shown in(A). The I OUT wire-wrapping method shown in (B) is obsolete (MAX.) TURNBUCKLE and should be employed only where facilities BARREL will not permit the use of the clip locking Lu-FOUR THREADS IN method.
Adjustable Connector Links 01$14111110 An adjustable connector link consists of two \ or three metal strips with holes so arranged that TOTAL TOLERANCE 7 THREADS EACH they may be matched and secured with a clevis bolt to adjust the length of the connector. They are installed in cable assemblies for the purpose of making major adjustments in cable length and to compensate for cable stretch.Adjustable AM.336 connector links are used most often in very long Figure 6-39.Turnbuckle thread tolerance. cable assemblies. that end of the barrel. Barrels and terminals are available in both long and short lengths. Quick Disconnects When installing a turnbuckle in a control system,itis necessary to screw both of the Quick disconnects are used in cable systems terminals an equal number of turns into the that may require frequent disconnecting. One turnbuckle barrel.Itis also essential that all type of quick disconnect is made with steel balls turnbuckle terminals be screwed into the barrel swaged to the ends of the cable and which are at least until not more than three threads are slipped into a slotted bar and secured with exposed. On initial installation, the turnbuckle spring-loaded sleeves on each end of the bar. terminals should not be screwed inside the Figure 6-41 illustrates the procedure for discon- turnbuckle barrel more than four threads. Figure necting and connecting this type of quick- 6-39 illustrates turnbuckle thread tolerances. disconnect fitting.
149 AVIATION STRUCTURAL MECHANIC S 3 & 2
CTION Of PULL FOR INSPECTION
'1111181111.11111$11111'\1%01%, ,Sm's (A)
TURNSUCKLE FORK LOCK WIRE TURNBUCKLE 4 TURNS WRAP CARLE BARREL
_.d
TURNBUCKLE TURNS WRA.. THIMBLE EYE ANITO
(B)
AM.337 Figure 6-40.Safetying tumbuckles. (A) Preferred method; (B) wirewrapping method.
Cables Guides FAIRLEADS.Fairleads may be made of a solid piece of material to completely encircle Fairleads, rubstrips, grommets, pressure seals, cables when they pass through holes in bulk- and pulleys are all types of cable guides. They heads or other metal parts (See fig. 6-42.) This are used to protect control cables by preventing type also may be used to Jeduce cable whipping the cables from rubbing against nearby metal and vibration in long runs of cable. In the same parts. They are also used as supports to reduce figure is a rubstrip, which protects cable along cable vibration in long stretches (runs) of cable. one side from rubbing against metal edges. Figure 6-42 shows some typical cable guides. Split fairleads are made for easy installation
150 Chapter 6AIRCRAFTHARDWARE
NOTE HOW FITTING FITS IN CLIP- IN LINE WITH APPLY PRESSURE OUTER RECESS.
OUTER RECESS 3/16 CABLE
DISCONNECTED POSITION (FULL TENSION)
DISCONNECTING PROCEDURE
,,,CABLES DISCONNECTED AL (TENSION BROKEN)
CABLE END FITTING
SPRING SLEEVE FITTING
CABLE ENO FITTING VP! ED 3 CAB(LTESOBDELS/OLNEED)
_APPLY PRESSURE INNER RECESS
CONNECTING PROCEDURE
SET AS SHOWN
4 CONNECTING POSITION
5 CABLESCONNECTED (FULL TENSION)
AM.338
Figure 6-41.Quick-disconnectprocedure.
151 AVIATION STRUCTURAL MECHANIC S 3 & 2
SPLIT FAIRLEAD
ROUTE THE CABLE THROUGH THE BULKHEAD AND SPRING CLIP WITH THE CONCAVE SIDE OF THE CLIP TOWARD THE BULKHEAD.
A
C D
AM.339 Figure 6-42.Typical cable guides. around singlecables to protect them from to move with a minimum of friction. Most rubbing on the edges of holes. pulleys used on aircraft are made from layers of GROMMETS.Grommets are made of rubber cloth impregnated with phenolic resin and fused for use on small openings where single cables togetherunderelevatedtemperaturesand pass through the walls of unpressurized compart- pressures. Aircraft pulleys are extremely strong ments. and durable and cause a minimum of wear on PRESSURE SE AL S.Pressu re seals are used the cable passing over them. Pulleys are provided on cables or rods which must move through with grease-sealed bearings and usually do not pressurized bulkheads. They fit tightly enough require furtherlubrication. However, pulley to prevent air pressure loss but not so tightly as bearings may be pressedout,cleaned, and to hinder movement of the unit. relubricated with special equipment. Thisis usually accomplished only by Depot level main- Pulleys tenance activities. Pulley brackets (fig. 6-43), made of sheet or Pulleys (or sheaves) are grooved wheels used cast aluminum, are required with each pulley to change cable direction and to allow the cable installed in the aircraft. In addition to holding .152 Chapter 6AIRCRAFT HARDWARE
PULLEY FAIRLEAD BRACKET /INSTALLATION
CABLE rCABLE ATTACHMENT TTACHMENT POINT POINT
PUSH-PULL TUBE
PIVOT PIVOT POINT POINT
TYPICAL WALKING BEAM TYPICAL BELLCRANK
TYPICAL TYPICAL SECTOR QUADRANT
AM.340 Figure 6.43. Control system components. the pulley in the correct position and at the Sectors and Quadrants correct angle, the brakets provide a guard to prevent the cable from slipping out of the These units are generally constructed in the groove on the pulley wheel. form of an arc or in a complete circular form.
153 AVIATION STRUCTURAL MECHANIC S 3 & 2
They are grooved around the outer circum- structure do not permit a straight run. They are ference to receive the cable, as shown in figure often used in push-pull tube systems to decrease 6-43. The names sector and quadrant are used the length of the individual tubes and thus add interchangeably.Sectorsandquadrantsare rigidity to the system. similar to bellcranks and walking beams which A bellcrank has two arms which form an angle are used for the same purpose in rigid control of less than 180 degrees, with a pivot point systems. where the two arms meet. The walking beam is a straight beam with a pivot point in the center. Examples of a bellcrank and a walking beam are RIGID CONTROL SYSTEMS also shown in figure 6-43. The two are so similar in construction and use that the names bellcrank Rigid control systems transfer useful move- andwalkingbeamareoftenusedinter- ment through a system of push-pull rods, bell- changeably. cranks, walking beams, idler arms, and bungees. Bellcranks and walking beams are mounted in The simplest rigid control system may consist of the structure in much the same way as pulley push-pull rods and bellcranks only. assemblies. Brackets or the structure itself may be used as the point of attachment for the shaft Push-Pull Rods or bolt on which the unit is mounted.
Push-pull rods are rigid rods equipped with Idler Arms eye fittings at each end or with a clevis fitting at one end and an eye fitting at the other. The eyes Idler arms are levers with one end attached to containapressed-inbearing. The rods are the aircraft structure so it will pivot, and the generallyhollow, and they neck down to a other end is attached to the push-pull tubes. smaller diameter at each end where the fittings Idler arms are used to support push-pull tubes are attached. One or both of the fittings are and guide them through holes in structural screwed into the necked portion of the rod and members. are held in place by locknuts and are therefore adjustable. When only one stem is adjustable the Bungee stem of the other eye fitting is riveted into the neck at its end of the rod. A hole is drilled into Bungees are tension devices used in some rigid the threaded necks of the push-pull rods for systems that are subject to a degree of shock or inspection to insure that the stem has engaged a overloading. They are similar push-pull rods safe number of threads. The stem must be visible and performessentiallythe same function through the hole. Push-pull rods are generally except that one of the fittings is spring loaded in made in short lengths to prevent bending under one or both directions. That is.. a load may press compression loads and vibration. so hard in compression against the fittings that the bungee spring will yield and take up the Bellcranks and Walking Beams load, thus protecting the rest of the rigid system against damage. The internal spring may also be Bellcranks and walking beams are levers used mounted so as to resisttension rather than in rigidcontrol systems to gain mechanical compression. An internal double-spring arrange- advantage and to change the direction of motion ment will result in a bungee that protects against inthesystem n parts of the airframe both overtension and overcompression.
154 CHAPTER 7
AIRCRAFT DAMAGE REPAIR
DAMAGE REPAIR PROCEDURES CLASSIFICATION OF DAMAGES
In the modern age of high-speed aircraft, the TheStructuralRepairManualnormally AMS must be familiar with the principle of specifies the type of repair to be made to a streamlining and fairing; also, the behavior of damaged structure. Damages can normally be various metals in high-velocity air currents and classified under one of the following classifica- torsional stresses encountered during high-speed tions: negligible damage, damage repairable by flying and maneuvering. One of the most impor- patching, damage repairable by insertion, and tant jobs the AMS will encounter is the repair of damage necessitating replacement. (See fig. 7-1.) damaged skin. All repairs must be of the highest The AMS must decide, aftr.rcinspection of the quality and must conform to certain require- damaged area, on one of the four classifications. ments and specifications. Methods of repairingthestructure of a Negligible Damage damaged aircraftare given in the Structural Repair Manual for the specific aircraft. No one Negligible damage is damage or distortion that set of repair rules will apply to all aircraft. The can be permitted to exist or can be corrected by problem of repairinga damaged sectionis asimpleprocedure.Frequently,negligible usually solved by duplicating the original part in damage can be repaired by stop drilling cracks, strength, usingthe materials and procedures removingdents,andfabricatingtemporary specified intheaircraftStructuralRepair fabric patches without placing any restrictions Manual. on the aircraft.
PREINSPECTION OF DAMAGED AREAS Damage Repairable by Patching When any part of the airframe has been Damage which exceeds negligible damage damaged, the first step is to clean off all grease, limits should be investigated to determine the dirt, and paint in the vicinity of the damage so possibility of using a patch repair. A patch repair that the extent of the damage may be deter- is made by adding material around the damaged mined. The adjacent structure must be inspected area to enable the damaged structure to carry its to determine what secondary damage may have designed load. resulted from the transmission of the load or loadswhichcausedtheinitialdamage. Damage Repairable by Insertion Thoroughly inspect the adjacent structures for dents, scratches, abrasions, punctures, cracks, Thisrepairinvolvestheremoval of the loose seams, and distortions. Check all bolted damaged portion of a member and replacing this fittings which may have been damaged or portion with materials identical in shape and loosened by the load which caused the damage strength to the damaged member. A backup to the structure. plate (doubler) is used with this type of repair to
155 AVIATION STRUCTURAL MECHANIC S 3 & 2
NEGLIGIBLE DAMAGE
DAMAGE REPAIRABLE BY PATCHING
DAMAGE REPAIRABLE BY INSERTION
DAMAGE NECESSITATING REPLACEMENT
AM.341 Figure 7-1.Classification of damages.
156 Chapter 7AIRCRAFT DAMAGE REPAIR reinforce the damaged area and provide a surface from theillustration for the damaged com- to fasten the filler. This repair is used where a ponent. flat surface is required. 4. From the component diagram, find the index number/numbers for the damaged unit/ Damage Necessitating Replacement units. 5. Theindexnumber/numbersarethen Damage which cannot be repaired by any matched with the item number/numbers on the practical means is classified as damage neces- repair material chart. This chart will normally sitating replacement. give the parts description, drawing number, gage, type of materiai, and location of repair diagram. 6. The repair diagram is found by locating SELECTION OF REPAIR MATERIAL the required section of the manual and turning to the correct figure in that section. Access The major requirement in making a repair is provisions and negligible damage information are theduplication of strengthof theoriginal given on the repair diagrams. After the damage structure. The Structural Repair Manual for the has been cleaned up, determine whether or not aircraft concerned must be consulted for the the damage is negligible in accordance with the alloy thickness, and temper designation of the repair diagram. If the damage is within the limits repair material to be used. This manual will also of negligible damage,it may be disregarded designate the type and spacing of rivets or unlessitisnecessary to close the hole for fasteners to be used in the repair. aerodynamic smoothness or sealing purposes. If In some instances, substitution of materials the damage exceeds the limits of negligible are allowed. For example, the P-3 Structural damage, it must be repaired in accordance with Repair Manual specifies that 2024-T42 clad the repair diagram or replaced. material may be substituted for 2024-T3 clad materialsinfuselageareashaving sharp or double curvatures. When making a substitution LAYOUT FOR REPAIR of materials, and conflicting information be- tween manuals exists, the Structural Repair All repairs must be laid out to the given Manual for the aircraft being repaired should be dimensions or by using the damaged part as a used. pattern.Care should be exercised to avoid When using the Structural Repair Manual, the scratching the repair material, except where AMS normally has several steps- to take in cutting the material is desired. Scratches may finding the correct repair materials and proce- develop into cracks and cracks into structural dures. Figure 7-2 illustrates each of the steps, failures. All marks on repair materials, other and are listed in the procedures to follow. than cut lines, should be made with a pencil. NOTE: The P-3 Structural Repair Manual was selected as a typical manual. The procedures that follow are typical, but are not standard. Various manufacturers use different methods to SKIN REPAIRS indicate the types of materials used and special instructions for using their particular manual. Skin repair patches may be divided into two 1. The extent of the damage to the aircraft is general types, the LAP PATCH and the FLUSH determined by the preinspection of the damaged PATCH. A brief description of both types of area as previously explained. patches follows. 2. Using a master index diagram, identify the A lap patch is an external patch that has the damaged group of the aircraft. From the. table edges of the patch and the skin overlapping each shown on the diagram, determine the section of other. The overlapping portion of the patch is the manual where the component is found. riveted to the skin. On some aircraft, lap patches 3. After locating the correct group master are permitted in certain areas, but only where index diagram, obtain the correct item number aerodynamic smoothness is not important.
157 AVIATION STRUCTURAL MECHANIC S 3 & 2
1 FROM COMPONENT MASTER INDEX, LOCATE DETERMINE EXTENT OF DAMAGE STRUCTURE ILLUSTRATION
DO NOT USE DRAWING NUMBERS NUMBER FOLLOWING VIRGULE FOR OROERING PARTS- INDICATES OPPOSITE HAND ,' REFER TO NAVWEPS 01-75PAA-4 PART ."-71 1 =1,7=1M ML mr.,1 CI', =Iv=im [1. L.T=ICATIT_Ao INTSfAM
FROM MASTER INDEX DIAGRAM, LOCATE 5 FROM KEY TO STRUCTURE ILLUSTRATION, APPLICABLE GROUP MASTER INDEX LOCATE REPAIR ILLUSTRATION
MOW . _,.M 0114.111ON .41 ONO. Imam. 1.1. VA Meld *41 W.V. NNE .110/1. .111 MOM 1111
3 COMPARE CLEANED-UP DAMAGE WITH THE LIMITS OF NEGLIGIBLE FROM GROUP MASTER INDEX DAMAGE. IF DAMAGE EXCEEDS THESE LIMITS,REPAIR THE PART LOCATE COMPONENT MASTER INDEX 11(07187 IN ACCORDANCE WITH INSTRUCTIONS OR REPLACE PART,"0.0.,,,,
AM.342 Figure 7-2.How to use a Structural Repair Manual.
158 Chapter 7AIRCRAFT DAMAGE REPAIR
A flush patch consist of a filler patch which skin. This type of skin usually has a low margin is flush with the skin when inserted: It is backed of safety. up and riveted to a reinforcement plate which, in turn, is riveted to the inside of the skin. This Lap Patches reinforcement plate is usually referred to, on some repair diagrams, as the doubler, or backup Lap patches may be installed in areas where plate. On some high performance aircraft, only aerodynamic smoothness is not important. In the flush patch is permitted in making skin areas where it is permitted, the lap patch may be repairs. used in repairing cracks as well as small holes. In repairing cracks, always drill a small hole, (normally called stop drilling), in each end of OPEN AND CLOSED SKIN AREAS the crack before applying the patch. This is normally done by using a No. 30 or 40 drill bit. One of the factors which determine the exact This prever is the concentration of stresses at the procedure to be used in making skin repairs is apex of the crack and distributes the stresses the accessibility to the damaged area. Much of around the circumference of the hole. The patch the skin on an aircraft is inaccessible from the must be large enough to install the required inside for making repairs. The skin in such areas number of rivets as determined from the rivet is referred to as CLOSED SKIN. Skin that is schedule indicated for the gage material in the accessible from both sides is called OPEN SKIN. area which is damaged. (See fig.7-3.) The Repairs to open skin may usually be made in recommended patch may be cut circular, square, the conventional manner, using specified types rectangular, or diamond shaped. The edges are of standard rivets, but in repairing closed skin, normally chamfered (beveled) to an angle of 45 some type of special blind fasteners must be degrees, for approximately one-half its thick- used. The exact type of fastener used will ness. depend upon the type of repair made and the recommendations of the aircraft manufacturer. Another of the importantfactors to be considered when making a skin repair is the stress intensityof the damaged panel. For example, certain skin areas are classified as O 00000999 highly critical, other areas as semicritical, while O 000090 9 still other areas may be classified as noncritical. ci) Repairs to damages in highly critical areas must 0 0------provide100percentstrengthreplacement; 00 semicritical areas require 80 percent strength OQ000 0 0 0 0 replacement; and noncritical areas require 60 percent strength replacement. When-- a repair O 00000000 specifies it must provide 60 percent strength replacement, this indicates the amount of repair strength necessary to maintain a margin of safety in skin areas. The 60 percent stress AM.343 intensity repair is specified when production Figure 7.3. Lap patch for repairing a crack in methodsandstiffeningrequirementshave stressed skin. resulted in an overstrength skin with a high margin of safety. This repair provides strength andstiffnessequivalenttospecificdesign The rivet pattern is laid out on the patch, requirements rather than the original structure using the proper edge distance and spacing. The of the material. The 100 percent stress intensity installation position of each rivet is markidVith. repair makes the strength of the repaired skin a center punch. The impression in the material equal to, or greater than, the original undamaged made with the center punch helps to keep the
159 AVIATION STRUCTURAL MECHANIC S 3 & 2
damagedareaisremoved bycutting and trimmingtheholetoacircular,square, rectangular, or diamond shape. The corners of the hole should be rounded to a minimum of 1/4-inch radius. The lap patch is fabricated and installedin the same manner aspreviously explained for repairing cracks.
Flush Patches SURROUNDING MATERIAL DENTED Flush patches should be used where aero- dynamic smoothness is required. The type of flush patch used depends on the location of the damaged area. One type is clear of internal structures, and the other it is not. Like all types of repairs, the AMS must consult the applicable StructuralRepair Manualfor the necessary repair information. The repairs discussed next are typical of most repairs. AM.344 FLUSH PATCH CLEAR OF INTERNAL Figure 7-4.Drilling holes for rivets. STRUCTURES.In areas which are clear of internal structure, the repair is relatively simple drill from slipping away from the hole being to make. This is especially true where there is an drilled. (See fig.7-4). Drill only a minimum access door or plate through which the rivets can number of rivet holes in the patch, normally be bucked. In inaccessible areas, the flush patch four willsuffice at an angle of 90 degrees to may be made by substituting blind rivets for each other. Position the patch over the surface standard rivets, where permissible, and devising a being repaired, insuring that the correct edge means of inserting the doubler through the distances are being maintained. Drill four holes opening. in the surface being repaired, using the predrilled One method is shown in figure 7-5, in which holes in the patch as a pattern for alignment. As the doubler has been split. To insert the doubler, each hole is drilled, using the proper temporary slip the split edge under the skin and twist the fasteners, secure the patch in place. When the doubler until it slides in place under the skin. patch is temporarily secured, drill the remaining The screw in the center of the doubler is rivet holes through the patch and surface being temporarily installed to serve as a "handle" for repaired. Remove the patch and deburr all rivet inserting the doubler through the hole. This type holes, using a deburring tool or a large drill bit. of patch is normally recommended for holes up Prime therepair materials with the proper to 1 1/2 inches in diameter. It is generally more corrosionpreventivematerialpriortothe satisfactory to trim a hole -larger than 11/2 riveting operation. Secure the patch in position, inchestoa rectangular orelliptical shape, using temporary fasteners, to maintain align- rounding all corners to a generous radius. (See ment during riveting. Riveting procedures are fig. 7-6.) covered later in this chapter. On larger repair areas it is usually possible to Holes may be repaired in either stressed or buck the doubler rivets by inserting and holding nonstressed skin which are less than 3/16 inch in the bucking bar through the center of the diameter by filling with a rivet. Drill the hole doubler. The filler is then riveted in place using and install the proper size rivet to fill the hole. blind fasteners, if in a closed skin area. When For holes 3/16 inch and larger, the AMS should blind rivets are used as substitutes for solid consult the. applicable Structural Repair Manual rivets, the Structural Repair Manual normally forthenecessaryrepairinformation.The specifies the next larger size. The proper edge
160 Chapter 7AIRCRAFT DAMAGE REPAIR
ASSEMBLED REPAIR ASSEMBLED REPAIR
AM.345 AM.346 (1) Assumed damage. (2) Damage cut out to a smooth (1) Assumed damage. (2) Damage cut out to smooth round hole. 13) Doubler split for insertion through cut rectangular shape. (3) Doubler. (4) Filter. (5) Doubler out (4) Filler. (5) Doubler riveted in place. (6) Filler riveted in place. (6) Filler riveted in place. riveted in place. Figure 7.6. Flush rectangular patch. Figure 7.5. Repair of small holes in skin with a flush patch.
161 AVIATION STRUCTURAL MECHANIC S 3 & 2 distances for the substitute fasteners must be maintained. NOTE: Edge distance is discussed later. In all ASSUMED DAMAGE flush patches, the filler should be of the same gage and material as the original skin. The doubler, generally, should be of the same mate- rial, one gage heavier than the skin. Structural Repair Manuals will specify the allowable substi- tution of materials. This can be in the form of a note on the repair diagram. For example, the RA-3B Structural Repair Manual shows the following information in the form of a note: Curved sheet: When substituting 2024-T for 0.025 to 0.071 inch 7075-T, the 2024-T should be one gage heavier than called for in 7075-T; if the gage of the 7075-T is 0.080 or 0.090 inch the 2024-T should be two gages heavier than the 7075-T. Flatsheet:Substituteonegageheavier 2024-T for all 7075-T skin gages. When laying out the size of the doubler, the length should exceed the width. This enables the doubler to be slipped in through the skin, so it can bepositionedforinstallation.This eliminates the splitting and manipulation of the patch required in installing doublers of square and round flush patch repairs. The filler is fabricated slightly less than the dimensions of the hole being repaired. General- ly, the maximum clearance between the skin and the filler is 1/32 inch. The doubler is fabricated larger than the hole being repaired to allow for the specified number of rivets required to attach the doubler to the skin being repaired. The doubler, filler, and attaching skin rivet pattern may be laid out, drilled, and deburred in the identical manner as described previously for a lappatch.Aftertherequiredcorrosion preventive materials have been applied, the ASSEMBLED doubler is positioned in the structures interior REPAIR and secured with temporary fasteners. Inspect the rivet holes for proper alignment and rivet the doubler in place, using solid rivets. The filler can then be riveted in place using blind fasteners. AM.347. NOTE: If the flush repair is in an open skin (1) Assumed damage. .(2) Damaged skin cut out to a area, the filler may be riveted to the doubler smooth round hole and rib repaired. (3) Two half-round prior to installing the doubler. doublers. (4) Doublers riveted in place. (5) Filler. (6) FLUSH PATCH OVER INTERNAL Filler riveted in place. STRUCTURES.Fabricating a flush patch over Figure 7-7.Flush patch over internal structure.
162 Chapter 7AIRCRAFT DAMAGE REPAIR internal structure may tend to become difficult. stressed cover plate. The cover plate is normally In some instances, it may be done by simply fabricated from material identical to the skin. A using a split doubler and a filler, as shown in single row of nut plates is riveted to the doubler, figure7-7.Frequentlyasplit doubler, filler and the doubler is then riveted to the interior strips, and filler are used in the repair. The filler sideof theskin with two rows of rivets, stripis used as a spacer, if a structural com- staggered as shown in figure 7-8. The cover plate ponent under the skin has been damaged. In all is attached to the doubler with machine screws. cases, the existing structure rivet holes should be When an access door is permitted and installed used when the rivet pattern is laid out. The flush overinternalstructure,screwsshouldbe patch over internal structureis installed using installedthrough thecoverplateintothe the same methods as described for a flush patch internal structural member wherever possible. clear of internal structure, except for modifica- tion of the doubler. Skin Replacement
Flush Access Door Sometimes damage to the metal skin is so extensive that an entire panel must be replaced. A flush access door installation, as shown in Also, an excessive number of patches or minor figure 7-8, is sometimes permitted. It is installed repairs to a section or area may require the to facilitate repair to the internal structure and replacement of the entire panel. to repair damage to the skin in certain areas. The As in all other forms of repairs, the first step flush access door consists of a doubler and a is to inspect the damaged area thoroughly to
A.
t...) C-) C_) ) C_)iJ C-) C.) FLUSH ACCESS COVER PLATE (-)C.)
EXISTING SKIN
EXISTING RIB DOUBLER
rFLUSH ACCESS COVER PLATE EXISTING SKIN
SCREW DOUBLER EXISTINIRIB
EXISTING RIB NUT PLATE
SECTION A-A
AM.348 Figure 7-8.Flush access door installation.
163 AVIATION STRUCTURAL MECHANIC S 3 & 2 determine the extent of the damage. Inspect the the old sheet as a guide. The two sheets are then internal structure for damage or signs of strain. fastened together with sheet metal fasteners. Suchmembers, whenbent,fractured,or The use of sheet metal screws is not recom- wrinkled, must be replaced or repaired. They mended since they injure the edges of the rivet may be sheared considerably without visible holes. The drilling should proceed from the external evidence of such a condition. Drill out center to the outside of the sheet, inserting sheet rivets at various points in the damaged area and metal fasteners at frequent intervals. examine them for signs of shear failure. If impossible to use the old sheet as a During the inspection, notecarefullyall template, the holes in the new sheet should be unusualrivetingproblemsconditions which drilled from the inside of the structure. Use the render riveting difficult or which make replace- holes in the reinforcing members as guides, and ment impossible. Any fixtures which will hinder insert fasteners in the same manner as described riveting and prevent the use of straight bucking above. This is called back-drilling. Before placing bars will be apparent in a thorough inspection. the new sheet on the framework to drill the Therewillalso be places where flanges or holes,makecertainthatthereinforcing reinforcing members, or the intersection of members are aligned and flush at the points at stringers, longerons, formers, frames, or rings which they intersect, otherwise the holes in the make the bucking of rivets very difficult. This new sheets will not be accurately aligned. For problem can be solved by designing and making the same reason, the new sheet should have the bucking bars to suit these particular situations. same contour as the old before drilling the rivet Care must be taken to avoid mutilating the holes. damaged skin in the process of removal. In most I n duplicatingholesfromreinfording cases it can be used as a template for layout of memberstoskin,extremecaremust be and drilling holes in the new piece of skin. exercised or both frame and skin will be ruined. The rivet holes in stringers, longerons, bulk- Since most bulkheads, ribs, and stringers depend heads, formers, frames, rings, and other internal on the skin for some of their rigidity, they can members must be kept in as good condition as easily be forced out of alignment in the drilling possible. If any of these members are loosened process. The skin must be held firmly against the by the removal of rivets, their location should be framework, or the pressure from the drilling will marked so that they can be returned to their force it away from the frame and cause the holes original position as necessary, while the repair is to be out of alignment. This may be overcome being made. by placing a block of wood against the skin and Reference should be made to the applicable holding if firmly while the drilling progresses. repair material chart in the aircraft Structural Also, make sure that the drillis held at a Repair Manual for the gage and alloy of material 90-degree angle to the skin at all times, or the to be used for the replacement panel. The size holes will be elongated and out of alignment. and shape of the panel may be determined in When drilling through anchor nuts a smaller either of two ways. The dimensions can be pilot drill should be used first. Care must be measured during the inspection, or the old skin used so as not to damage the anchor nut threads. can be used as a template for the layout of the The pilot holes are then enlarged to the proper sheet and the location of the holes, the latter size. method being preferable and more accurate. It may be necessary to use an angle attach- Regardless of the procedure used, the new sheet ment or flexible shaft drill in places where it is must be large enough to replace the damaged impossible to inserta straightdrill. In cafe area, and may be cut with an allowance of 1 to 2 neither type can be inserted, the new section can inches of material outside the rivet holes. be marked carefully with a soft pencil through If the old sheet is not too badly damaged, it the holes in the old section. Another method of should be flattened out and used as a template. marking the location of the new holes is to use a The new sheet, having been cut approximately 1 transfer or prick punch as shown in figure 7-9. inch, larger than the old, should then be drilled Center the punch in the old hole, then tap the near the center of the sheet, using the holes in punch lightly with a hammer. The result should 164 Chapter 7AIRCRAFT DAMAGE REPAIR
At the free end of the botton section of the hole finder is a guide rivet which drops into the old holes in the sheet still in place. The free end TRANSFER of the top section of the hole finder has a hole PUNCH in a position which exactly matches the position of the guide rivet, and through this opening the new hole is drilled. Thus, as the hole finder is USE OLD SKIN AS moved along, the guide rivet drops into an old TEMPLATE hole and automatically determines the position of the new hole. After all the holes have been drilled, the 7C,74 04,17ASECCOVIS rxrrnyzisni TM ISSEPthill4 1 UM trAt: rWW,COUTILIN11,331.1.01.1211.0101,17,,,J . C . P . 7 1 7 3 t V C I I temporary fasteners are taken out and the sheet is removed from the framework. The burrs left NEW SKIN by drilling must be removed from both sides of all holes in the skin, the stringers, and the rib flanges. Burring may be accomplished with a few AM.349 light turns of a deburring tool or drill bit. In this Figure 7.9. Transferring rivet holes. way particles of metal left around the edges of the drilled holes are eliminated. If they were not removed, the joint would not be tight and rivets might expand, or flash, between the parts being riveted. REINFORCED PLASTIC AND ezzevizz,/,,, SANDWICH CONSTRUCTION REPAIR
01.0 SKIN This sectiondeals with the materials and ANGLE procedures to be used in repairing reinforced plastic and sandwich construction components. The procedures discussed are general in nature. When actually repairing reinforced plastic and/or sandwich construction components, refer to the applicable Structural Repair Manual.
REPAIR OF REINFORCED PLASTIC The repair of any damaged component made AM.350 of reinforced plastic requires the use of identical Figure 7-10.Using a hole finder. materials, whenever they are available, or of approved substitutes for rebuilding the damaged portion. Abrupt changes in cross-sectional areas be a mark which will serve to locate the hole in must be avoided by tapering joints, by making the new sheet. smallpatchesroundorovalinsteadof Still another way to locate the rivet holes rectangular, and by rounding the corners of all withouta template is to use a hole finder, large repairs. Uniformity of thickness of core similar to the one shown in figure 7-10. This and facingsisexceedingly important in the device makes it possible to drill holes in the new repair of radomes. Repairs of punctured facings section of skin in perfect alignment with the and fractured cores, therefore, necessitate re- holes in the old section. The hole finder is made moval of all the damaged material, followed by in two sectionsan upper part and a lower part replacement with the same type of material and which are fastened together at one end. in the same thickness as the original.
165 AVIATION STRUCTURAL MECHANIC S 3 & 2
All repairs to components housing radar or DAMAGE TO FACING radio gear must be made in accordance with the manufacturer's recommendations. This informa- tion may be found in the aircraft Structural Repair Manual or in drawings and specifications. (A) FACING Investigation of Damage DAMAGED MATERIAL REMOVED BY SANDING Before a thorough inspection of the damage can be made, the area should be cleaned with a clothsaturatedwithmethyl-ethyl-ketone (MEK). After drying, the paint should be re- moved by sanding lightly with No. 280 grit (B) sandpaper, then clean the sanded area with IMPREGNATED CLOTH MEK. The extent of damage can then be determined by tapping the suspected areas with a blunt instrument. The damaged areas will have a dull or dead sound, while the undamaged areas will have a clear metallic sound. Damages are divided into four general classes: (C) surfacedamage,facingandcoredamage, puncture damage (both facings and core), and damage requiring replacement.
Surface Damage REPLACED LAMINATIONS SANDED TO CONTOUR ( D1 The most common types of damage to the surfaceare abrasions, scratches, scars, dents, cuts, and pits. Minor surface damages may be repaired by applying one or more coats of room-temperaturecatalyzedresintothe damaged area. More severe damages may be AM.351 repaired by filling with a paste made from Figure 7-11.Ply repair (scarfed method). room-temperature resin and short glass fibers. Over this coated surface, apply a sheet of figure 7-11. This repair is made in the following cellophane, extending 2 or 3 inches beyond the manner: Sand out the damaged laminate plies as repaired area. After the cellophane is taped in shown in view (B). The area should be sanded to place, work out all the air bubbles and excessive a circular or oval shape, then the area should be resin with the hand or a rubber squeegee. Allow tapered uniformly down to the deepest penetra- the resin to cure at room temperature, or if tion of the damage. necessary, the cure can be hastened by the use The diameter of the scarfed (tapered) area of infrared lamps or hot sandbags. After the should be at least 100 times the depth of the resin has been cured, remove the cellophane and penetration. Care should be exercised when sand off theexcessresin; then the entire using a mechanical sander. Excess pressure on repaired area is lightly sanded preparatory to the sander can cause the sandpaper to grab, refinishing. resulting in the delamination of undamaged PLY DAMAGE (SANDWICH TYPE plies. LAMINATES).When the damage has pene- CAUTION: The sanding of glass cloth re- trated more than one ply of the cloth in the inforced laminates produces a fine dust that may sandwich type laminates, the repair may be cause skin irritation. In addition, breathing of an made using the scarfed method illustrated in excessive amount of this dust may be injurious; 166 Chapter 7AIRCRAFT DAMAGE REPAIR therefore, precautions as to skin and respiration used, the dimensions should be maintained as protection must be observed. illustrated. Brush coat the sanded area with one coat of In areas that have become delaminated, or room-temperature-setting resin and apply the contain voids or bubbles, clean the area with contoured pieces of resin-impregnated cloth, as MEK and determine the extent of the delamina- shown in (C) of figure 7-11. Tape a sheet of tion, then drill holes at each end, or on the cellophane over the built-up repair and work out opposite sides of the void using a No. 55 drill the excess resin and air bubbles. Cure the repair bit, extending through the delaminated plies. in accordance with the resin manufacturer's Figure 7-13 illustrates the procedure for repair instructions, then sand the surface down (if of delaminated plies. necessary) to the original surface of the facing. Additional holes may be needed if air entrap- PLY DAMAGE (SOLID LAMINATES).--Ply ment occurs when injecting the resin. Using a damage to solid laminates may be repaired using hypodermic needle or syringe, slowly inject the the scarfed method described for sandwich type appropriate amount of resin until the void is laminates, or the stepped method shown in filled and flows freely from the drilled holes. figure 7-12 (A) may be used. After the voids are completely filled, bring the When the wall isbeing prepared for the area down to proper thickness by working the stepped repair, a cutting tool with a controlled excess resin out through the holes, then cure and depth will facilitate the cutout and should be refinish. used to avoid possible damage to the layers underneath. If the layer of glass cloth under- Facing and Core Damage neath is scratched or cut, the strength of the a repair will be lessened. Care should be exercised HONEYCOMB CORE.Damages extending not to peel back or rupture the adhesion of the completely through one facing of the material laminate layers beyond the cutout perimeter. andintothecore requireremoval of the Remvval of the cutouts may be accomplished by damaged core and replacement of the damaged peeling from the center and working carefully to facings in such a manner that normal stresses can the desired perimeter of the cutout. Scrape each be carried over the area. The scarfed method .tep, wipe clean with cloths moistened with illustrated in figure 7-14 is the preferred method MEK, and allow to dry thoroughly. Cut the for accomplishing small repairs of this type. replacement glass fabric pieces to an exact fit Repairs of this type may be accomplished as with the weave directions of the replacement follows: plies runningin the same direction as the Carefully trim out the damaged portion to a existing plies. Failure to maintain the existing circular or oval shape and remove the core weave direction will result in a repair that is completely to the opposite facing. Be careful greatly under strength. Replace each piece of not to damage the opposite facing. The damaged fabric, being careful to butt the existing layers facing around the trimmed hole is then scarfed of fabric plies together, but do not overlap back carefully by sanding. The length of the them. The laminate layers should be kept to the scarf should be at least 100 times the facing proper matching thickness. thickness as shown in (B) of figure 7-14. This When the entire wall has been penetrated, as scarfing operation must be done vary accurately showninfigure 7-12(B),one-half of the to a uniform taper. damaged plies should be removed from one side Cut a piece of replacement core material (or a and the replacement buildup completed, then suitable substitute) to fit snugly in the trimmed repeat removal and buildup procedure on the hole.It should be equal in thickness to the oppositeside.If the damage occurs over a original core material. Brush coat the repair area relatively large or curved area, make up a plaster and the replacement honeycomb, exercising care mold conforming to the contour and extending to prevent an excessive amount of resin from 1 inch past the damage, and insertit in the entering the honeycomb cells. damaged area when repairing the first half of the Insert the honeycomb repair section and place plies. When the stepped method of repair is the resin-impregnated cloth over the repair area 167 AVIATION STRUCTURAL MECHANIC S 3 & 2
LAMINATED GLASS LAMINATED GLASS FABRIC DAMAGED FAMIC BROKEN IHRU ONE SIDE ONLY
CROSS SECTION DAMAGE CROSS SECTION DAMAGE
1
SECTION A-A SECTION B-B REPAIR CUTS REPAIR CUTS
REPAIR PLIES REPAIR PLIES . bOLVI.N. NI...N. %. c s. .: amee.....Nece:. commomoviamwoor...m..ve.... ve...voz...... N.vers .= NINIIIIMMA.
REPAIR INSTALLED REPAIR INSTALLED (A) (B)
AM.352 Figure 7-12.Repair of solid laminates (stepped methods.
168 Chapter 7AIRCRAFT DAMAGE REPAIR
Hypodermic needle filled resin. Laminated part Void or delaminated area.
0110Allk
Drill two holes at apposite ends of damaged area to depth that extends into void or delamination. Remove final-finish or rain-erosion coating approximately 2 inches beyond cutout in upper ply.
Plies of laminated part. Repair material: Resin injected into drilled hole.
SECTIONA-A
AM.353 Figure 7-13.Delaminated ply rapair.
DAMAGE TO CORE DAMAGED FACING SCARFED 14-100 T CORE FOR PATCH REMOVED
(Al (B) CORE REPLACED IMMEGNATED CLOTH j
AM.354 Figure 7-14.Honeycomb type core repair.
169 AVIATION STRUCTURAL MECHANIC S 3 & 2
as shown in (C) of figure 7-14. Cover the repair LAMINATED GLASS FORMED IN PLACE FILLER area with cellophane sheeting and cure the repair FABRIC SKIN BROKEN OR HONEYCOMB CORE in accordance with theresin manufacturer's DAMAGED instructions. After the repair has been cured, sand the surface to its original contour. The entire area should be lightly sanded before refinishing. FOAM TYPE CORE.The damaged core should be removed by cutting perpendicular to the surface of the face laminate opposite the damaged face. Scrape the inner facing surface DAMAGE clean, making sure there is no oil or grease film in the area, to insure good bondage of the foam to the laminate. Fill the area where the core has been removed with the filler material specified in the aircraft Structural Repair Manual. Figure 7-15 illustrates the replacement of a foam type core. NOTE: Do not use MEK to clean the damage as it may soften and weaken the foam.
Puncture Damage CUT AWAY DAMAGED CORE AREA AND FILL WITH HONEYCOMB CORE.Repairs to damages SPECIFIED FILLER completely through the sandwich structure may REMOVE LAYERS OF be accomplished either by the scarfed method LAMINATE AS SHOWN (similarto the repair describedfor damage extending into the core) or the stepped method. The scarfed method is normally used on small punctures up to 3 or 4 inches in maximum dimension and in facings made of thin cloths SECTION B-B (whicharedifficulttopeel),whereas the stepped method is usually employed on larger REPAIR CUTS repairs to facings composed of thick cloths. REAIR MATERIAL The scarfed method of repair for punctures is the same as that used for damage extending into the core, with the exception that the opposite side of the sandwich is provided with a tem- porary mold or block to hold the core in place during the first step. (See (C) fig. 7-16.) After the first facing repair is cured complete- ly, the mold and the shim (temporarily replacing the facing on the opposite side) are removed. REPAIR INSTALLED The repair is then completed by repeating the NOTE procedure used in the first step. When this facing D REPLACE DAMAGED CORE MATERIAL is cured, the surface should be sanded down to WITH SPECIFIED FILLER the original contour and the repair area lightly sanded in preparation for refinishing. AM.355 When using the stepped method of repair, the Figure 7.15. Foam type core repair. damaged area is first trimmed out to a round or
170 Chapter 7AIRCRAFT DAMAGE REPAIR
HOLETHROUGH RADOME HOLETHROUGH RADOME
(A)
(A ) HOLE TRIMMED, CORE REMOVED, HOLE TRIMMED, CORE REMOVED, AND FACING AND FACING "STEP-PEELED" SCARFED
(B)
(B) IMPREGNATED CLOTH WITH EXTRA THIN LAYER IMPREGNATED CLOTH 2
11111111111111111111111,
TEMPORARY BLOCK TEMPORARY SHIM OR MOLD TEMPORARY BLOCK TEMPORARY SHIM MOLD COMPLETE OPPOSITE FACING IN A SIMILAR (C1 OPERATION (C)
AM.356 Figure 7-16.Scarfed repair method. AM.357 Figure 7.17. Stepped repair method. oval shape, or to a rectangular or square shape (preferable having rounded corners). manner as the outer facing. After the inner The individualplies are then cut out as repair has been cured, the entire repair area illustrated in figure 7-17. Each ply is "stepped" should be sanded to the original contour and back 1-1/2 inches and trimmed out using a sharp prepared for refinishing. knife. The sides of the repair should be parallel FOAM TYPE CORE.When the puncture with the weave of the cloth, if possible. penetrates the entire wall, remove the damaged NOTE: Do not cut through more than one core and face laminates to one-fourth inch past layer of cloth. If the layer of cloth underneath is the perimeter of the hole on the inner face. scratched, the strength of the repair will suffer. Make a plaster support to replace the removed The opposite facing is shimmed and backed core, conforming to the curvature of the inside up with a mold and the core material is inserted layer of the inner face. Figure 7-18 illustrates a as previously described. The outer repair plies punctured repair with a plaster support. aresoakedinthe resin and laidover the Afterrepair tothe inner face has been damaged area. An extra layer of thin cloth is laid completed, remove theplaster support and over the repair area to extend one-half inch over continue the repair on the opposite side. the undamaged facing. The repair area is then covered with a sheet of cellophane to apply Finishingof Repaired Areas pressure, and allowed to cure. The inner facing is then replaced in the same In the repair of reinforced plastic parts, the
171 AVIATION STRUCTURAL MECHANIC S 3 & 2
LAW$ATID GLASS final step is to refinish the part with a finish FMK SKINS MORIN ON ROM SIDES FORMED IN PLACI FILLER identical to the original, or an acceptable substi- O HONIVICOMII GOO DAMAOID. tute. In refinishing radomes and other surfaces which enclose electronic equipment, do not use metallic pigmented paints or other electronic reflective type materials because of undesirable shielding and interference effects. Always use the materials recommended in the applicable Structural Repair Manual for refinishing both the interior and exterior surfaces of reinforced DAMAGE plastic components.
PIASTER SUPPORT Reinforced plastic components whose frontal areas are exposed to high speeds are frequently coated with a rain erosion coating. Rain erosion coatings protect the component against pits which arecaused by raindropshittingthe component at high aircraft speeds. These pits or eroded areas can cause delamination of the component glass cloths if allowed to progress unchecked. GOAT 11415 SLIPPAGE OF SECTION A-A SUPPORT WITH PAVING RAIN EROSION RESISTANT COATINGS. AGENT Rain erosion resistant coatings for reinforced plastic components conform to Specification MIL-C-7439. Coatings conforming to this speci- fication are classified as follows: Class I is a rain erosion resistant coating which is furnished in kit form. This kit consists of a primer,accelerator,dilutingsolvent,and neoprene. Class II is a rain erosion resistant coating with an additional surface treatment to minimize
PLASTER SUPPORT radio noise resulting from precipitation static on PLASTER SUPPORT AND REPAIR CUTOUT the coated surface. This coating is also supplied RIPAM MAARIA1 in kit form and consists of a primer, accelerator, diluting solvent, neoprene, and antistatic coat- ing. These kits (MIL-C-7439, Classes I and II) are packaged unaccelerated to provide longer shelf life. The neoprene is ready to use only after the catalyst(accelerator)has been added. The material inthese kits should be mixed and applied in accordance with the instruction sheet REPAIR INSTALLED supplied by the kit manufacturer.
NOTE Safety Precautions REPLACE DAMAGED CORE MATERIAL WITH SPECIFIED FILLER Thefollowinggeneralsafetyprecautions should be observed when making repairs to AM.358 reinforcedplasticcomponents. These safety Figure 7-18.Foam type puncture repair. precautionsshould bereviewedbeforeat- tempting any repairs to reinforced plastics.
172 Chapter 7AIRCRAFT DAMAGE REPAIR
1. Local station safety regulations as to fire De lamination and health hazards must be complied with. 2. Allsolventsareflammable, therefore, Facing-to-core voids of less than 2.5 inches in observe proper handling procedures. diameter can usually be repaired by drilling a 3. Personnel involved in the mixing or han- series of holes 0.06 to 0.10 inch in diameter in dling of catalyzed resin prior to the curing theupperfacingoverthevoidarea. An operation should wear rubber gloves. After using expandable foaming resin, such as Thermofoam rubber gloves, the hands should be cleaned with 607, or equivalent, is then injected through the soap and water and rinsed with vinegar to holes with a pressure type caulking gun. neutralize any catalyst particles. When the void is an the lower surface of the 4. Never mix thecatalystand promoter panel, only sufficient resin must be injected as together as they are explosively reactive as a to completely fill the void. With voids on the mixture. Always mix the promoter with the upper surface, the core area should be filled resin first and then add the catalyst to the until the resin comes out of the injection holes. mixture. These holes should be sealed with a thermo- 5. The toxicity of polyester formulation has setting epoxy resinadhesive, and the entire not been definitely established. Some of the assembly cured with lamps, as required for the components are known to cause nasal or skin adhesive system. irritationtocertainindividuals.Adequate When the void areas are large, it is necessary ventilation should be provided. to remove the facing over the damaged area and 6. The sanding operation on glass cloth re- follow the repair procedures for a puncture. (See inforced laminates gives off a fine dust that may fig. 7-19.) cause skin or respiratory irritations. Inhalation of excessive amounts of this dust should be avoided. Protection should be provided for Punctures respiration and skin. 7. Do not store catalyzed resin in an air-tight A puncture is defined as a crack, break, or container or an unvented refrigerator. hole through one or both skin facings with resulting damage to the honeycomb and/or balsa wood core. The size of the puncture, amount of REPAIR OF SANDWICH CON- damage to the core, assembly to be repaired STRUCTION (HONEYCOMB (rubber, elevator, etc.), and previous repairs to AND BALSA WOOD CORE) the damaged assembly are factors to be con- sidered in determining the type of repair to be The repairsdiscussedinthis sectionare made. Damage to a honeycomb and/or balsa applicable to structural type sandwich construc- wood core assembly that exceeds a specified tionconsistingof aluminumalloyfacings length or diameter in inches or the total number bonded to aluminum honeycomb and balsa of repairs exceeds a specified percentage of the wood cores. total bonded area necessitates replacement of the assembly. Minor Surface Damage NOTE: These figures are found in the ap- plicable Structural Repair Manual. The most common types of damage to the HONEYCOMB CORE.The repair shown in surface are abrasions, scratches, scars, and minor figure 7-19 (A) is used when a puncture through_ dents. These minor surface damages require no one skin facing has caused only minor damage to repair other than the replacement of the original the core material. To repair this type damage protectivecoatingtopreventcorrosion; proceed as follows: Cover the component with a provided no breaks, holes, or cracks exist. The suitable protective covering (polyvinyl sheet or procedures and materials used in replacing the kraft paper). Cut out a section of the protective originalprotectivecoatingareoutlinedin covering that will extend approximately 2 inches chapter 11. beyond the damaged area. Use masking tape to 173 AVIATION STRUCTURAL MECHANIC S 3& 2
MASK AREA AROUND DAMAGE APPROXIMATELY PATCH1 SAME MATERIAL AS DAMAGED TWO INCHES BEYOND PACING. PATCH MUST EXTEND AT LEAST STOP HDLES. I INCH BEYOND STOP HOLES. PATCH ADHESIVE FILL VOID WITH SPECIFIED FILLER.
111111111th11111111;- SECTION AA STOP ONI LL (A) r---1EXISTING STRUCTURE r---1REPAIR PANTS masaCORE FILLER = FILLER 41111111111."."'"ft.PATCHII INCH BEYOND THE HOLE ON ALL SIDES. BEVEL -DOES 45.
CORE REPLACEMENT FILLER
SECTION B-B
4libpATCH
CORE REPLACEMENT.FILLER
PATCH ;sot;
1111111111111111100fioliiiilio SECTION CC PATCH (C) AM.359 (A)Skin facing, minor damage to core; (B)Skin facing, extensive damage to core; (C) Skin facings and core damaged.
Figure 7-19.Sandwich construction pricture repair (honeycombcore).
174 Chapter 7 AIRCRAFT DAMAGE REPAIR
hold the cutout in place. Stop-drill as necessary through the skin facing only. Strip the paint and protective coating 1 1/2
ASSUMED DAMAOE inchesbeyondtheatop- drilledholes.The stripped areais then cleaned with a special cleaning paste. Fill the void with the specified filler material to within approximately 0.063 inch of the skin facing and cure as directed. Prepare a round or oval patch large enough to overlap the damaged area at least 1 inch. Apply sealant to the undersurface of the patch and to the filler and skin surface. Install the repair patch, maintaining correct overlap, and clamp to the assembly to assure contact with the skin facing. Cure as directed. Remove the excess adhesive and refinish as necessary. The repair shown in figure 7-19 (B) is used when a puncture through one skin facing has caused extensive damage to the honeycomb core.Whenthecorehasbeendamaged extensively the damaged material must be re- placed. Prepare the assembly as previously described. Cut out the damaged skin facing with a hole saw or aviation snips.File the edges of the hole smoothly. Using a pocket knife, carefully cut out the damaged core. CAUTION: Do not damage the opposite facing. Install a new core filler and complete the repair as previously described for view (A) of figure 7-19. The repair shown in figure 7-19 (C) is used when both skin facings and the core have been
( 3 damaged. Use the same procedures as described Z,11121ff above for view (A) and (B) to facilitate this repair. BALSA WOOD CORE.The repair shown in figure 7-20 is used when no gain in structural strength is desired and is only to be used for sealing holes of 1 square inch or less in external surfaces. The damaged area should be cut out to a smooth circular or rectangular shape. A 3/8- inch minimum radius must be provided at the corners of rectangular cutouts. AM.360 NOTE: Theafore-mentionedinformation applies to all repairs made to balsa wood core (1) Assumed damage. (2) Damage cut out toa smooth rectangular hole.(3) Inner metal face cut back and panels. In cutting out the damaged area, care beveled. (4) Filler plug.1(5) Filler glued in place, sealed, must -be taken not to separate the metal faces and fabric patches appliid. from the core. This can be accomplished by using a very fine-toothed coping or hacksaw Figure 7-20.Balsa wood repair with filler plug and blade for straight cuts, and cylindrical saws (hole fabric patch. saws) for cutting holes or rounding corners.
175 AVIATION STRUCTURAL MECHANIC S 3 & 2
After the damaged section has been cut out ASSUMED file the edges smooth using a fine cut file only. DAMAGE Then inspect the area for separation of the skin facing from the balsa wood core. If the facing has separated from the core, rebond the two surfaces, using the procedures outlined in the previoussection on skinseparation.Then complete the repair as shown in figure 7-20. 3) Figure 7-21 illustrates one flush .type balsa SECTION AA wood core repair thatis used on puncture damages larger than 1 inch. To facilitate this typerepair,cut out the damagedarea as previously described. After the damaged area has been cut out, the inner metal face is cut back 1 inch and the core material is removed. (See (3) fig. 7-21.) Inspect for adhesion of the face to the core and seal the exposed filler material to prevent the entry of moisture. Lay out the required rivet pattern and drill pilot holes in the panel. (See (4)fig.7-21.) NOTE: The rivetsize,rivet spacing, and number of rows of rivets are given in the appropriate repair section of the ap- plicable Structural Repair Manual. Next, prepare two patch plates; a wood, plywood, or phenolic filler; and a metal filler. (See (5) fig. 7-21.) The outer patch plate should fill the hole in the core, and the inner patch plate shouldoverlapthe holein the core approximately 1 inch for each row of rivets. Locate the patch plates and wood filler. Using the pilot holes in the panel as a guide, drill pilot holes through the patch plates and wood filler. The patch plates and wood filler are then ASSEMBLED bonded to the panel using the specified adhe- REPAIR sive. Next, locate the metal filler and drill pilot holes through both patch plates and the wood filler. All pilot holes are then size drilled, and machine or press countersunk, as applicable. SECTION El Complete the repair by installing the specified rivets. When aerodynamic soothness is not desired, AM.361 a nonflush patch such'the one shown in figure (1) Assumed damage. (2) Damage cut out to a smooth 7-22 can be used. No ice that this type repair rectangle.(3)Inner metal face cut back and core utilizes two patch plates, a wood filler, and removed. (4) Rivet pattern. (5) Patch plates. (6) Wood, nonflushrivets.Otherwise,the procedures plywood, or phenolic filler. (7) Metal filter. (8) Flush described for the repair shown in figure 7-21 are rivets installed. applicable to this type repair. Figure 7-21.Balsa wood repair with flush patch. 176 Chapter 7AIRCRAFT DAMAGE REPAIR
TRAILING EDGE REPAIR Cl) A trailing edge is the rearmost edge of an airfoil (wing, flap, rudder, elevator, etc.). It may ASSUMED DAMAGE be a formed or machined metal strip or possibly a metal covered honeycomb or balsa wood core material which forms the shape of the edge by tying the ends of a rib section together and joining the upper and lower skins. These trailing edges are very easily damaged. The majority of this type damage can be avoided if care is taken when moving aircraft in confined spaces, and/or when positioning ground support equipment around parked aircraft. NOTE: The trailing edges on some high performance aircraft are almost knife edge in construction. Extre:.le care must be taken when working around these surfaces to avoid person- nel injury. The following paragraphs briefly describe the procedures to be used in repairing damage to both the all metal and sandwich construction trailing edges.
ALL METAL
Trailing edge repairs to all-metal construction assemblies and/or control surfaces are performed using basically the same procedures outlined in section one of this chapter, titled "Damage Repair Procedures." The lap or flush patch may be used, depend- ing on the size of the damage, type aircraft, and the assembly or control surface to be repaired. NOTE: Normally, the flush patch is used on control surfaces to insure aerodynamic smooth- ness.
SANDWICH CONSTRUCTION
SECTIONA-A A typical trailing edge repair to a sandwich construction assembly is shown in figure 7-23.
AM.362 RIVETING PROCEDURES (1) Assumed damage. (2) Damage cut out to a smooth rectangle. (3) Rivet pattern. (4) Nonflush patch plates. The AMS must use his knowledge, ability, and (5) Wood filler. (6) Rivet patterns. (7) Nonflush rivets experience when planning an aircraft structural installed. repair. This does not end after the proper Figure 7-22.Balsa wood repair with nonflush patch. materials have been selected. Each type of rivet must be selected and driven in a precise manner to meet riveting specifications. Some of the 177 AVIATION STRUCTURAL MECHANIC S 3 & 2
CUT OUT DAMAGED AREA WITH 0.5 INCH MINIMUM RADIFIN THE CORNERS.
FILL EDGES OF TRIMMED AREA WITH SPECIFIED FILLER. MASK OFF AREA 2 INCHES FROM THE INTENDED CUTOUT. REMOVE PAINT AND CHEMICAL SURFACE TREATMENT. CORE REPLACEMENT FILLER
PATCH
ADHESIVE
I-I/2 INCHES CORE REPLACEMENT FILLER
EXISTING STRUCTURE I INCH (MAX) REPAIR WATS 4101%fhii, CORE FILLER ; 7:1FILLER
I. I3 INCHES (MAK)1 1-1/2 INCHES INCHES AM.363 Figure 7.23. Trailing edge repair (sandwich construction). specifications are rivet spacing and edge dis- by one made of 2017 aluminum alloy unless the tance, diameter of rivethole, aerodynamic 2017 rivet is a size larger. Similarly, when 2117 smoothness, and size of the rivet bucktail. These rivets replace 2017 rivets the next larger size can be accomplished only through determina- should be used. tion, practice, and accurate manipulation of all 2. When rivet holes become enlarged, de- standard layout and riveting equipment. formed, or otherwise damagecl, use the next larger size as replacement. 3. Countersunk-head rivets are to be replaced RIVET SELECTION by rivets of the same type and degree of couatersink, either AN426 or MS20426. The following rules govern the selection and 4. Allprotruding head rivetsareto be use of rivets in making a repair: replaced with universal head, either AN470 or MS20470. 1. Replacements must not be made with 5. Rivets of smaller diameter than 3/32 inch rivets of lower strength material unless they are will not be used for any structural parts, control larger than those removed. For example, a rivet parts, wing covering, or similar parts of the of 2024 aluminum alloy should not be replaced aircraft.
178 Chapter 7AIRCRAFT DAMAGE REPAIR
rivet center. TRANSVERSE PITCH is the dis- tance between rows of rivets and is measured from rivet center to rivet center. EDGE DIST- ANCE is the distance from the center of the r rivet to the edge of the material being riveted. , There are no specific rules which are ap- \ plicable to every case or type of riveting. There are, however, certain general rules which should be followed.
Rivet Spacing Rivet spacing (pitch) depends upon several factors, principally the thickness of the sheet, G-GRIP (TOTAL THICKNESS) diameter of the rivets, and the manner in which D-DIAMETER OF R ',/cT the sheet will be stressed. Rivet spacing should never be lessthan 3D (3times the rivet 1 1/2 D+G=TOTAL LENGTH OF RIVET diameter). Spacing is seldom less than 4D ndr wore than 8D.
Transverse Pitch AM.364 Figure 7-24.Rivet length. When two or more rows of rivets are used in a repair job, the rivets are staggered to obtain 6. Minimum rivet diameter is one times the maximum strength. The distance between the thickness of the thickest sheet to be riveted. rows of rivets is called transverse pitch. Trans- 7. Maximum rivet diameter is three times the verse pitch is normally 75 percent of existing thickness of the thickest sheet to be riveted. rivet pitch but should never be less than 2 1/2D. 8. The proper length of rivet is an important part of the repair. Should too long a rivet be Edge Distance used, the formed head will be too large, or the rivet may bend or be forced between the sheets Edge distance for all rivets, except those with being riveted. Should too short a rivet be used, a flush head, should not be less than 2D (twice the formed head will be too small or the riveted the diameter of the rivet shank) nor more than material will be damaged. The length of the rivet 4D. Flush-head rivets require an edge distance of should equal the sum of the thickness of the at least 2 1/2D. If rivets are placed too close to metal plus 11/2 times the diameter of the rivet, the edge of the sheet, the sheet is apt to crack or as shown infigure7-24. The formula for pull away from the rivets; and if placed too far determining rivet length is specified as follows: away from the edge, the sheet is apt to turn up at the edge. 1 1/2 D+G=L, NOTE: On most repairs, the general practice is to use the same rivet spacing and edge distance where D = rivet diameter, G = grip (total that the manufacturer used in the surrounding thickness of material), and L = total length of area, or the Structural Repair Manual for the five t. particular aircraft may be consulted. Figure 7-25 illustrates rivet spacing and edge distance. SPACING AND EDGE DISTANCE DRILLING RIVET HOLES RIVET SPACING, alio referred to as RIVET PITCH, isthe distance between rivets in the Standard twist drills are used for drilling rivet same row, and is measured from rivet center to holes. Table 7-1 specifies the size drill for the 179 AVIATION STRUCTURAL MECHANIC S 3 & 2
Locations for the rivet holes should be center- punched and the drilling done with a power drill, either electric or pneumatic. Electric drills constitute a fire hazard' when drilling on or near an aircraft due to the arcing of the brushes, r therefore, the pneumatic drill must be used. The center-punch mark should be large enough to prevent the drill from slipping out of position, 0 00 0 but must not be made with enough force to dent the surrounding material. (See fig. 7-4.) The 0 0 0 drilling can be done with a hand drill if no 0 0 power .drillisavailable.All burrs must be removed before riveting by using a larger size drill, or by using a deburring tool.
AEDGE DISTANCE Use of Portable Drills B-RIVET PITCH C TRANSVERSE PITCH Before using a drill, turn on the power and (DISTANCE BETWEEN ROWS) check it for trueness and vibration. Do not use a drillbitthat wobbles orisslightlybent. Trueness may be visibly checked by running the motor freely. AM.365 The most common error made by the in- Figure 7-25.Rivet spacing and edge distance. experienced man is to hold a portable drill at an incorrect angle to the work. Make sure the drill is held at right angles to the work. When drilling Table 7-1.Drill sizes for various size rivets. in a horizontal position, it can be seen if it is too far to the right or left, but it is difficult to tell if the rear of the drill is too high or too low. Until Rivet Drill Drill the AMS learns how to hold a drill at the correct diameter size size angle, he should have another man sight the angle before starting the drill. 3/32 Another common mistake is to put too much No. 41 0.0960 pressure on the drill. Pushing or crowding a drill 1/8 No. 30 .1285 may break the drill point, cause the drill to plunge through the opposite side of the sheet, 5/32 No. 21 .1590 leaving rough edges around the hole, or cause the drill to side slip on the metal causing hole 3/16 No. 11 .1910 elongation. The drill should not be stopped immediately 1/4 No. F .2570 upon breaking through, but should be inserted for approximately half itslength while still 5/16 No. P .3230 running, and then withdrawn. This operation requires judgment and skill since it is very easy II 3/8 No. W .3860 to ream the hole oversize; but if this is done properly, cleaner holes will result. FLUSH RIVETING various size rivets.' Note that there is a slight clearance in each case, which prevents binding of Progression has been made possible towards the rivet in the hole. higherspeedaircraftby improved .design, 180 Chapter 7 AIRCRAFT DAMAGE REPAIR
MALE DIE
MALE DIE GUIDE \\ASOMMO ,ACAZ\NAM% 4\\X`e.\\1\1OM\1\I` OX0\1\1\\.\\\` \\.\\\,....,.,T,,p\ \\\\\\\\\\\\\\\11 ,..,. 0-;;., RAM 1/ EMALE DIE AM.336 Figure 7-26.Dimple countersinking. stronger and lighter aluminum alloys, and more Dimple Countersinking powerful engines. Attention has been turned towards the elimination of protruding head Dimple countersinking is accomplished by rivets on the exterior surfaces of aircraft. In using male and female dies (fig.7-26). The fabricating stressed metal skin on modem air- female die shown in figure 7-26 has incorporated craft, all exposed rivet heads must be counter- in it a spring-loaded ram which flattens the sunk to lie flush with the outer surface of the bottom of the dimple as itis formed. This skin. It is essential to provide an aerodynamical- preventscracksfromformingaroundthe ly smooth surface. dimple. The forming of a dimple is a combined Flush rivets are more difficult to install, since bending and stretching. operation. A circular the parts being riveted must be countersunk, bend Is formed around the hole. As in any which is one extra operation following drilling. bending operation, the tension force the Another hazard is the closeness of the rivet set upper side of the bend (break) creates the radius to the metal during riveting. If considerable skill at the junction of the two surfacesthe top side is not used, the metal will be damaged by the of the sheet and downward bent inner wall of rivet set. Flush rivets are made with heads of thedimpledepression.Thestretch occurs several different angles, but the 100-degree rivet around the hole as itis displaced from its is standard for all Navy aircraft. original position and relocated at the bottom of the dimple. The female die must have a slightly The two methods used in countersinking for larger cone diameter than the corresponding flush riveting are dimple and machine counter- dimension of the male die. This allows for sinking. In some instances, a combination of the material thickness and to relieve the bending two may be used; in other words, the top sheet load at the break in order to avoid circum- of an assembly may be dimpled while the under ferential cracks around the boundaries of the sheet is machine countersunk. dimple. As a further safeguard, a slight radius is
181 AVIATION STRUCTURAL MECHANIC S 3 & 2
THERMO DIMPLE GUN
DIMPLING SQUEEZER
CONTROL UNIT
AM.367 Figure 7-27.Hot dimpling kit. made on the female die at the junction of the more brittle materials is advantageous for the top face with the dimple depression. reduction of cracking and also from the stand- Dimpling dies are made to correspond to any point of dimple shape. The heat is applied to the sizeand degree of countersunkrivet head material by the dies, which are maintained at a available. The dies are numbered, and the specific temperature by electrical heaters. The correct combination of dies to use is indicated in heat is thus transferred to the material to be charts specified by the manufacturer. Both male dimpled only momentarily and none of the and female dies are machined accurately and heat-treat characteristics of the material are lost. have highly polished surfaces. When dimpling a Thereareseveralmodelsofdimpling hole, place the material on the female die and machines used in the Navy, from the bulky floor insert the male die in the hole to be dimpled. models to portable equipment. One of the most The dies are generally brought together, forming popular portable types is shown in figure 7-27. the dimple by a mechanical or pneumatic force. Basically, it has three unitsthe dimpling con- HOT DIMPLING.As newer aluminUm alloys trol unit, dimpling squeezer, and the thermo were deyeloped to increase the shear and tensile dimple gun. strength, they became increasingly difficult to The dirn ling control unit is a small compact form, since these alloys are harder and more unit desig ,ed to regulate automatic control brittle. These aluminum alloys are subject to dimpledie temperatures, prepressure,dwell cracking.1 when formed or dimpled cold. For this time, and final forming pressure. This same unit reason, itis necessary to use a hot dimpling is used with both the hot dimpling squeezer and process. The application of hot dimpling to the the thermo dimple gun.
182 Table 7-2.--Dwell time chart. AT259 Portable squeezer Equipment 7075S-T6Material Tool-temperature MALE --650° F Material thickness . 016 .020 AN426-100° Rivets .025 .032 .040 .051 .064 FEMALE-650° F .072 .081 .091 3/32 Size AT252DA-3 Male Die number s AT251DA-3 Female 1. 5 1.5 1. 5 1/8 AT252DA-4 AT251DA-4 1.51.5 15 1.5 1t) 1.51.5 15 1.5 15 1.51.5' 20 2.01.9 20 2.02.0 30 2.252.0 35 3/165/32 AT252DA-6AT252DA-5 AT251DA-6AT251DA-5 1.5 1515 1.51.5 1515 1.5 1515 1.51.5 15 1.25 20 2.01.5 30 2.0 35.35 40 1/4 AT252DA-8 Key toAT251DA-8 chart: timeDwell in seconds.1.5 15 15 15 15 25 Dwell pressure-in 30 pounds. AVIATION STRUCTURAL MECHANIC S 3 & 2
Thehotdimplingsqueezer isspecially designedfor use where stationary squeezer operation isimpracticalandsometimes DIMPLING DIMPLING impossible. It is capable of working all material PRESSURE HIGH PRESSURE LOW gages up to and including 0.091inch. The squeezer type is designed to dimple in areas that are inaccessible to other types of equipment. STRAIGHT EDGE Male and female dies are independently heated arerear4k=relflaar by heaters operated from an electrical source. The heaters produceashortheat-up and DIMPLING recovery time. The male die is adjustable for PRESSURE CORRECT TEST maximum squeeze for all gages of material. Also SPECIMEN incorporated is a cooling feature which affords ease of handling and also reduces the power loss due to heat interference. The thermo dimple gun is used to dimple in AM.368 the center of panels and in those areas otherwise Figure 7-28.Checking dimple equipment air pressure. inaccessible to yoke type dimpling equipment. When being used on the aircraft, the thermo imaginary lines cross is the information block dimple gun drives the dimple from the exterior denoting the required dwell time in seconds and while the female die and dolly bar are used on dwell pressure in pounds. In this case the dwell the inside. The thermo dimple gun is aircooled, time is 1.5 seconds and the dwell pressure is 20 eliminatingtheneedfor cumbersome heat- pounds. resistant gloves. This tool is small, compact, well When setting up any dimpling equipment, balanced, and easy to handle. follow the sten-by-step procedure outlined in Operation of the Hot Dimpler.Prior to the L Maintenance Manual supplied settingthedimplingcontrolunit upfor the equi Anent. Since equipment types dimpling, the AMS should refer to the equip- vary,itis impractical to specify a standard ment manufacturer's dwell time chart. (1.e( .ie procedure in this course. However, there are 7-2.) Select the proper chart, ta..ing o con- four general requirements of a dimple, and by sideration which type of equipment is to be used examiningeach,itispossibletodenote and the material to be dimpled. Notice in table improper setting up of equipment. 7-2 the type of equipment is a portable squeeze 1. Sharpness of definition. It is possible to typeandthematerialbeingdimpledis get a dimple with a sharp break from the surface 7075S-T6. The temperature required for both into the dimple. The sharpness of the break is the male and female dies is 650°F. The second controlled by two things (1) amount of pressure line indicates the rivet to be used, in this case, and (2) material thickness. 100 degree countersink rivet. The third line 2. Condition of dimple. The dimple must be indicates the gage of material to be dimpled. The checked for cracks or flaws that might be caused lower leftsideof thechartindicatesthe by damaged cr dirtydies, or by improper diameter of rivet to be used and part numbers of heating. both the male and female dies. The chart is used 3. Warpage of material. The amount of warp- in this manner: If 0.040 material was being age may be held to a minimum if the correct dimpled, using 1/8 inch diameter rivets, the pressure setting is held. When dimpling a strip AMS should draw an imaginary line down the with too much pressure, the strip tends to form 0.040 column and across thechart on the a convex shape as shown in figure 7-28. When 1/8-rivet size line. At the point where the two insufficient pressure is used it tends to form a 184 Chapter 7AIRCRAFT DAMAGE REPAIR
FIBRE COLLAR
CHIP OPENING
CUTTER LOCK NUT
BODY STOP V CUTTER SHAFT PILOT ASSEMBLY
AM.369 Figure 7-29.Stop-type countersink. thickness. A countersink has a cutting face beveled to the (Ingle of the rivet head and is kept centered by a pilot shaft inserted in the rivet COUNTERSUNK DIMPLED COUNTERSUNK DIMPLED hole. A stopping device automatically acts as a TOO DEEP rn0 DEEP TOO SHALLOW TOO SHALLOW depth gage so that the hole will not be counter- sunk too deep. Figure 7-29 shows a stop-type countersink. The countersink should always be equipped with the fiber collar shown in figure 7-29, to COUNTERSINK IMPERFECT CROOKED DIMPLING prevent marring of the metal surface. A hand, electric, or air drill may be used to operate the countersink, and should not be operated above AM.370 2,500 rpm. The countersink must be sharp to Figure 7.30. Incorrect countersinking. avoid vibration and chatter. Figure 7-30il- concave shape. This can be checked by using a lustrates several effects of incorrect counter- straight edge. sinking. 4. General appearance. The dimple should be checked with the fastener that is to be used, making sure it meets the flushness requirement. RIVET DRIVING PROCEDURE This is important as the wrong type or size dies are sometimes used by mistake. Before driving any rivets, make sure all holes line up perfectly, all shavings and burrs have Machine Countersinking been removed, and the parts to be riveted are fastened securely together. It is important that Machine countersinkingisused for flush the sheets be held firmly togetherin the rivetingallsheet 0.064 inch and greater in immediate area of the rivet being driven.
185 AVIATION STRUCTURAL MECHANIC S 3 & 2
To adjust the speed of the gun, place it taps may mean "bad rivet, remove and drive against a block of wood. Never operate a rivet another"; and so on. gun without resistance against the set, as the The upset head, often referred to as the buck- vibrating action may cause the retaining spring tail, should be one and one-half times the original to break, allowing the set to fly out. diameter of the original shank in width and one- CAUTION: A rivetset can be a deadly half times the original diameter in height as weapon. If a rivet set is placed in a rivet gun shown in figure 7-31. If the head thus formed is without a set retainer and the throttle of the gun narrower and higher than the dimensions given, is opened, the rivet set may be projected like a more driving isnecessary. If itis wider and bullet. This may cause either severe injury to a shallower, it must be removed and replaced. person or the destruction of equipment. The gun should be adjusted so that the rivet RIVET REMOVAL may be driven in the shortest possible time, but care must be taken not to drive the rivet so hard Rivets must be removed and replaced if they or in such a manner as to dimple the metal. show even the slightest deformity or lack of Practice will enable one to properly adjust a gun alignment. Among the reasons for replacing for any type of work. rivetsarethefallowing:Rivet marred by When the rivet has been pushed into proper bucking bar or rivet set; rivet driven at slant, or position and held there firmly with the set of shank bent over; rivet too short, causing head to the rivet gun resting squarely against the rivet be shallow; rivet pancaked too flat from over- head, the bucking bar is held firmly and squarely driving; sheet; spread apart and rivet flashed against the protruding rivet shank. (In most between sheets; rivet driven too lightly, causing instances, the bucking bar must be manipulated sheets to buckle; two rivet heads not in align- by another man, called the bucker.) The gunner ment; and head of countersunk rivet not flush then exerts pressure on the trigger and starts with outside surface or driven below surface. driving. The gun must be held tightly against the Examples of these incorrectly driven rivets are rivet head and must not be removed until the shown in figure .7-32. trigger has been released. The bucker removes the bucking bar and checks the upset head after the gunner has stoppeddriving. A signal system isusually OVER DRIVENDN WIN At UNDIP Of F CENTER employed to develop the necessary teamwork, SIAS! DRIVEN and consists of tapping lightly against the work. One tap may mean "not. fully driven, hit it again"; two taps may mean "good rivet"; three
HOE I TOO HEAD HEAD NOT DOILY OFF IANDS NICKED FLUSH HOLE CENTER TOO SMALL
N\\\\\\\\\.\\V. ..\\NN.\\\.\\ ,,.\\N" ":"N -L///464,41Wfil7 WWWWPWAVIVIW6 WAWAW/WWWW tix1)
SHEETS NOT HARD RIVET RIVET DIE HOLES IN SHEET HIED TOGETHER IN SOFT NICKED NOT ALIGNED NIVIT FLASHED MITAL SHItT
AM.371 Figure 7-31.Rivet dimensions before and after AM.372 bucking. Figure 7-32.Incorrectly driven rivets.
186 Chapter 7AIRCRAFT DAMAGE REPAIR
Nom FILE A FLAT ON MANUFACTURED CENTERPUNCH THE FLAT. DRILL THROUGH THE HEAD, HEAD. USE DRILL ONE SIZE SMALLER THAN RIVET SHANK.
Art
REMOVE WEAKENED HEAD WITH PUNCH OUT SHARP CHISEL. RIVET
AM.373 Figure 7-33.Removal of rivets. When removing rivets, care should be taken head, the shank should be drilled out. However, not to enlarge the rivet hole, as this would ifthe sheetisfirmly supported from the necessitate the use of a larger size rivet for opposite side, the shank may be punched out replacement. To remove arivet,fileaflat with a drift punch. (See fig. 7-33.) surface on the manufactured head if accessible. It is always preferable to work on the manufac- The removal of flush rivets requires slightly tured head rather than on the one that is more skill. If the formed head on the interior is bucked, since the former will always be more accessible and has been formed over heavy symmetrical about the shank. Indent the center material suchasan extruded member, the of the filed surface with a center punch and use formed head can be drilled through and sheared a drill of slightly less than shank diameter to off, as mentioned above. If the material is thin, drill through the rivet heath Remove the drill it may be necessary to drill completely through and, with the other rivet end supported, shear the shank of the rivet and then cut the formed the head off with a sharp chisel. Always cut head with diagonal cutting pliers. The remainder along the direction of the plate edge. If the of the rivet may then be drifted out from the shank is unduly tight after the removal of the inside. 187 AVIATION STRUCTURAL MECHANIC S 3 & 2
G-II HAND GUN
G-15(SERIES)POWER GUN G-6H DRAW BOLT
G-6H COUNTERSUNK HEAD SLEEVE G-6H UNIVERSAL HEAD SLEEVE
AM.374 Figure 7-34.Self-plugging rivet (friction lock) installation tools.
BLIND RIVET INSTALLATION the G-11 hand gun. The G40 power gun uses the H-40 pulling heads primarily; however, The description and use of blind rivets are through the use of a 226 adapter, G-6H heads covered in chapter 6. The special tools and may be used. Extensions are available for all installation and removal methods are covered in guns using G-6H heads. Figure 7-34 shows the the following sections. Selection of the proper Gil and G15 rivet guns with the G-6H pulling equipment depends on a number of variables; heads. space available for equipment, type of rivets to The heads are manufactured in three different be driven, availability of air pressure, etc. sizestoaccommodatethedifferentrivet diameters. For ease of selection, the sizes are Installation Tools for stamped on the parts of the pulling head. Friction Lock Rivets Installation ProcedUres The guns used for installing this type of self-plugging rivet are the GI 1 hand gun and the It is important that the proper drawbolt and G15 (series) and G-40 (series) power guns. The sleeve be used for the rivet being installed. The G15 power gun uses G-6H pulling heads as does drawbolt should correspond to the diameter of
188 Chapter 7AIRCRAFT DAMAGE REPAIR
head of the rivet firmly, and to insure contact between the parts being riveted. Pull the trigger until the stem breaks. The stem will be ejected RIVET INSERTED through the rubber tube at the back of the gun IN MATERIAL head. It is important that this tube be in place in GUN HEAD order to prevent stems from getting into the gun INSTALLED mechanisms. OVER STEM Inspection DIRECTION OF PULL MI S 1 BY GUN BOLT V /41/ The rivet is satisfactory if the pin is firm and the head is seated tightly on the face of the material. Occasionally, the head will rise slightly STEM PULLED in the area which was under the slot of the AND BROKEN, pulling head. This condition is acceptable if the GUN FREED, RIVET UPSET head is not too badly deformed and the tension characteristics of the joint are not made critical by the deformation of the head. Figure 7-36 illustrates satisfactory and unsatisfactory self- plugging rivets. STEM TRIMMED INSTALLATION Removal COMPLETE These rivets are removed in much the same manner as the common, solid shank rivets, except for the preliminary step of driving out the rivet stem. (See fig. 7-37.) AM. 375 Figure 7-a5.Self-plugging rivet (friction lock) 1. Punch out the rivet stem with a pin punch. installation. 2. Drill out therivet head, using a drill the rivet, and the sleeve should correspond to slightly smaller than the rivet shank. the rivet diameter and head style. Speed of 3. Pry off the weakened rivet head with a pin installation may be increased by inserting a punch. number of nvets in the work and then applying 4. Push out the remainder of the rivet shank the gun. In other instances, such as overhead with a pin punch. If the shank will not push out, work, it is apparent that this method would be drill the shank, taking care not to enlarge the impractical and the rivet should be loaded into hole in the material. If the hole should be the gun and then inserted into the prepared enlarged, finish-drill for an oversize rivet. hole. The rivet must be completely inserted into the slotin the drawbolt, because improper Installation Tools for seating of the rivet may permit the head to Mechanical Lock Rivets break off before the rivet is properly set. (See fig. 7-35.) When using a hand gun, hold the rigid One of the tools used for driving these rivets handle of the gun parallel to the rivet axis. Open is the CP350 blind rivet pull tool. (See fig. 7-38.) the movable handle as far as it will go, then The nose of the tool includes a set of chuck jaws partially close. Repeat this operation until the which fit the pull grooves in the rivet pin and rivet stem breaks, then release the gun by pull it through the rivet shank to drive the rivet; completely closing the movable handle. When an outer anvil which bears against the outer part using the power gun, hold the head of the gun of the manufactured head during the driving parallel to the axis of the rivet. Push the gun operation; and an inner anvil which advances against the work with enough force to seat the automatically to drive the locking collar home
189 AVIATION STRUCTURAL MECHANIC S 3 & 2'
SATISFACTORY UNSATISFACTORY
GRIP LENGTH TOO SHORT FOR MATERIAL THICKNESS
UNDERSIZE OVERSIZE HOLE HOLE
AM.376 Figure 7-36.Inspection of self-plugging rivets (friction lock). after the Und head is formed. A short nose reliefvalveoperationpressureisproperly assembly, interchangeable with the standard adjusted for the size rivets being driven. Also assembly, is available for use in areas where make sure that the rivets are of proper length. there is not sufficient clearance for the standard The tool has only one operating adjustment. nose. This adjustment is used to control the pull on A change in rivet diameter requires a change the pin at which the inner anvil advances. The in chuck jaws, outer anvil, inner anvil, inner desired amount of the pull depends on the anvil thrust bearing, and an adjustment of the diameter of the rivets to be installed, and the shift valve operating pressure as described below. pull is varied by changing the pressure at which A change in the rivet head type from universal the adjustable shift valve operates. To adjust, head to countersunk head, or vice versa, requires proceed as follows: a change of the outer anvil only, if there is no change in the rivet diameter. 1. Remove pipe plug from tool cylinder and Aspecialchuck jaws assemblytoolis connect a pressure gage to the tool. furnished with the tool. To facilitate insertion of 2. Press trigger and release it the instant a the chuck jaws into the chuck sleeve, mount the puff of exhaust indicates that the shift valve three jaws on this assembly to form a cone, and controlling the Liner anvil has shifted. The gage lower the inverted chuck sleeve over the jaws. will then indicate the shift pressure. See table Always be sure that the pull tool is equipped 7-3 for the approximate pressures. with the correct size chuck jaws, outer and inner NOTE: The trigger must be released im- anvils to fit the rivets being driven, and that the mediately as the valve silifts. Otherwise the gage
190 Chapter 7 AIRCRAFT DAMAGE REPAIR
down the line pressure to 60 psi with an air regulator, part number 900-102, attached to the air inlet bushing. When using a CP350C rivet pull toolto drive1/16- and 5/32-inch diameter rivets, use air inlet bushing, part number 81479, and shift valve stop, part number 83731. When driving 1/8-inch diameter rivets, use air inlet bushing, number 83642, and cut down the line pressureto60 psi with airregulator, part DRILL HEAD ONLY number 900-102,attachedtothe airinlet bushing.
Installation Procedures Proper driving procedures are vital to obtain a firm joint. The recommended procedures are as follows: 1. Hold the head of the gun steady and at right angles to the work. 2. Press on the head of the gun hard enough to hold the rivet firmly against the work. Do not use a great amount of pressure unless necessary to bring the part being riveted into contact. 3. Squeeze the gun trigger and hold until the AM.377 Figure 7-37.Removal of self-plugging rivets rivet pin breaks, then release the trigger. The (friction lock). next rivet should not be driven until the return action has caused the gun to latch. A distinct. will record the higher pressure which builds up click will be heard, indicating that the gun is as soon as the valve has shifted. ready for the next installation cycle. 3. To adjust the pressure, loosen the valve- adjusting screw locknut and turn the valve- Figure 7-39 shows the complete installation adjusting screw clockwise to increase pressure, of a self-plugging (mechanical lock) rivet. or counterclockwise to decrease pressure, until The rivetisactually cold-squeezed by the the desired pressureisobtained. Check the action of the pin head drawing against the pressureaftertighteningthevalve-adjusting hollow shank end. Shank expansion through the screw locknut. When rivets of extremely long actionofthe extruding angle, blind head grip length are to be driven an adjustment to the formation, and setting of the mechanical lock in high pressure limit lhould be made. For efficient the rivet head all follow in automatic sequence operation of the too;, the minimum desired line and require but a fraction of a second. In some pressure should be not less than 90 psi and the places such as near the trailing edge of a control maximum not more than approximately 110 psi. surface, there may not be sufficient space When using a CP350 A or B rivet pull tool, it between the two surfaces to insert the rivet. may be necessary to increase the inside diameter In such cases, the pin may be forced into the of the air inlet bushing, part number 81479, hollow shank until the head of the pin just from0.055to0.065inch whendriving touches the end of the shank. Since no further 3/16-inch diameter rivets if the line pressure is shank expansion will result, the drill hole should below 90 psi. When driving 1/8-inch diameter not be enlarged to provide a free fit of the rivets,it may be necessary to use air inlet already expanded rivet. To insert the rivet, use a bushing, part number 82642, having a 0.040 - hollow drift pin which will accommodate the inch inside diameter. If the tool "flutters," cut rivet pin and the locking collar. (See fig. 7-40.)
191 AVIATION STRUCTURAL MECHANIC S 3 & 2
OUTER CHUCK ANVIL JAWS INNER TRIGGER ANVIL LONG NOSE ASSEMBLY CP 350 BLIND RIVET PULL TOOL
AIR INLET BUSHING SHORT NOSE ASSEMBLY PIPE PLUG
LOCKNUT
VALVE ADJUSTING SCREW AM.378 Figure 7-38.Self-plugging rivet (mechanical lock) pull tool.
Table 7-3.Adjustments for CP350 blind rivet pull The mechanical lock feature increases the load- tool. carrying capacity in single shear from about 10.3 percent in the case of thick sheets where joint strength is considered critical in rivet shear, to as much as 63.3 percent in thin sheets where sheet Rivet Shift valve operating bearing is considered critical. diameter pressure Inspection 1/8 30 to 31 psi Visual inspection of the seating of the pin in 5/32 46 to 47 psi the manufactured head is the most reliable and simple means of inspection. If the proper grip 3/16 66 to 67 psi length has been used and the locking collar and broken end of the pin are approximately flush with the manufactured head, the rivet has been properly upset and the lock formed. Insufficient grip length would be indicated by the pin This allows a driving force to be exerted on the breaking below the surface of the manufactured head of the rivet. Drive the head into firm head,andexcessivegriplength would be contact with the sheet and then apply the rivet indicated by the pin breaking off well above the pull tool in the usual manner to upset the rivet. manufactured head. In either case, the locking Due to the mechanical lock feature of the pin collar might not be properly seated, thus form- and sleeve, the driven rivet is substantially the ing an unsatisfactory lock. Table 7-4 gives limits mechanical equivalent of a one-piece solid rivet. for proper pin seating.
192 Chapter 7 AIRCRAFTDAMAGE REPAIR
Mechanical-lock rivet beforeinstallation, (1) Note shorterstem on blind side providing marked improvement forlimited blind clearance applications.
NOTE SHEET GAP
As the stem is pulledinto the rivet sleeve, tnNit immediately forms the 1100 (11 H110 / blind head. The "mechanical-lock alwaysforms the blind head firmly against the blindsheet,
Continued movement of thestem pushes the (3) blind sheet ahead of theblind head until the sheets are firmlyclamped together and the rivet is firmly seated. SHEET GAP CLAMPED TOGETHER
The plugging portion of thestem expands the rivet sleeve to fill thehole and re- (4) duces in diameteras it passes through the rivet sleeve, providing exoelleuthole fill even in oversize holes.
The movement of the stem isstopped by the pulling head at a pointwhere the (5) groove in thestem and the chamfer in the rivet line up to makea receptacle for the locking ring.
The pulling head shiftsautomatically, (s) inserts the positivemechanical locking ring, and fractures the stemflush with the rivet head.
AM.316 Figure 7-39.Self-plugging rivet(mechanical lock).
193 AVIATION STRUCTURAL MECHANIC S 3 & 2
3. Use the proper size drill to drill nearly through the rivet head. For a 1/8-inch diameter RIVET PIN PRESSED INTO SLEEVE BEFOSE INSERTION' rivet, use a number 31 drill; for a 5/32, use a number 24; and, for a 3/16, use a number 15. 4. Break off the drilled head, using a drift pin as a pry. 5. Drive out the remainder of the rivet with a pin having a diameter equal to, or slightly less HOLLOW DRIFT PIN than, the rivet diameter. Installation Tools for Rivnuts AM.379 Figure 7-40.Inserting self-plugging rivet Tools used in the installationof Rivnuts (mechanical lock). include the heading tool and the keyway cutter. The heading tool, as shown in figure 7-42, has a threaded mandrel onto which the Rivnut is Table 7.4. Inspection criteria for self-plugging threaded until the head of the Rivnut is against rivets (mechanical lock). the anvil of the heading tool. This tool normally comesinthreedifferentsizes.Theyare identical, except for the size of their threaded mandrel. The heading tool comes in sizes 6-32, Rivet A B C 8-32, and 10-32 which correspond with the diameter thread sizes of the standard Rivnuts. The key- way cutter is used for cutting a notch in the 1/8 inch 0.012 0.016 0.008 Rivnut hole for the Rivnut keyway. In some 5/32inch .015 .020 .010 instances the keyway cutter cannot be used 3/16inch .018 .024 .0i2 because the material is too thick. If such is the A. Maximum allowable distance of locking col- case, use a small round file to form the keyway. lar above or below rivet head. B. Maximum allowable distance of top of land Installation Procedures on pin above rivet head. C. Maximum allowable distance of top of land The drilling of ho'es for Rivnuts requires the on pin below rivet head. same precision as that required for solid shank rivets. The shank of the Rivnut must fit snugly in the hole. To obtain the best results for a Removal flatheadinstallation,firstdrillapilot hole Removal of this rivet is accomplished easily smaller than the shank diameter of the Rivnut, without damage to the work by use of the then ream to the correct size. Pilot and ream following procedure: (See also fig. 7-41.) drill sizes for Rivnuts are given in table 7-5. The application of flush Rivnuts is subject to 1. Shear the lock by driving out the pin, certainlimitations.For metal which hasa using a tapered steel drift pin not over 3/32-inch thickness greater than the minimum grip length diameter at the small end. If working on thin of the first Rivnut in a series, use the machine material, back up the material while driving out countersink; and for metal thinner than the the pin. If inaccessibility prohibits this, partially minimum grip length of the first Rivnut in a remove the rivet head by filing, or with a rivet series, use the dimpling process. The counter- shaver. An alternative would be to file the pin sunk Rivnut should not be used unless the metal flat, center punch the flat, and carefully drill out is thick enough for machine countersinking, or the tapered part of the pin forming the lock. ,unlesstheundersideisaccessibleforthe 2. Pry the remainder of the locking collar out dimpling operation. Aside from the countersink- with a drift pin. ing operation, the procedure for installing a 194 Chapter 7--AIRCRAFT DAMAGE REPAIR
FILE A SMALL FLAT PRY OUT REMAINDER ON RIVET HEAD ')OF LOCKING COLLAR
CENTERPUNCH FLAT DRILL ALMOST THROUGH RIVET HEAD
DRILL OFF TAPERED PORTION OF PIN WHICH FORMS THE LOCK.
PRY OFF RIVET HEAD
ACCOMPLISH STEPS 1,2,AND 3 ONLY IFRIVET IS IN A THIN OR RESILIENT MATERIAL
SHEAR LOCK TAP SHANK BY DRIVING OUT WITH OUT PIN PIN
AM.380 Figure 7-41.Removing self-plugging rivets (mechanical lock). flush Rivnut is the same as that for the flathead heading tool together until the Rivnut starts to Rivnut. head over. Then release the handle and screw the When installing Rivnuts, always check the studfarther into the Rivnut. This prevents threaded mandrel of the heading tool to see that stripping the threads of the Rivnut before it is it is free from burrs and chips from the previous properly headed. Again squeeze the handles installation. Then screw the Rivnut onto the together until the Rivnut heading is complete. mandrel until the head touches the anvil. Insert Now remove the stud of the heading tool from the Rivnut in the hole (with the key positioned theRivnut byturning the crank counter- in the keyway, if a key is used) and hold the clockwise. heading tool at right angles to the work. Press The action of the heading tool draws the the head of the Rivnut tightly against the sheet Rivnut against the anvil, causing a bulge to form whileslowlysqueezing the handles of the in the counterbored portion of the Rivnut on
195 AVIATION STRUCTURAL MECHANIC S 3 & 2
NOTCHED HOLES
HEADING TOOL
/ /////////////. '/////////./4"/ KEYWAY CUTTER
AM.381 Figure 7-42.Hand-operated Rivnut heading and keyway cutter tools.
Table 7-5.Drill sizes for Rivnuts. after the hole has been reamed. Operate the keyway cutter by inserting it in the hole and squeezing the handles. Always cut the keyway on the side of the hole away from the edge of the sheet. Rivnut size 6-32 8-32 10-32 Pilot drill Inspection size 19(0.166) 8(0.199) 1 (0.228) After the installation of Rivnuts, as well as Ream drill otherfasteners,the AMS must inspect the 12(0.189) 2(0.221)1/4" (0.250) size completedinstallations.TheRivnutsare inspected for the following: Manufactured head is inspected for correct installation of the Rivnut keyway in its keyway slot, insuring it is flush the inaccessible side of the work. This bulge is with the surface in which it is installed. The comparable to the upset head on an ordinary threadedportionoftheRivnutshankis solidshankrivet. The amount of squeeze inspectedfor cracks, stripped threads, and required to head the Rivnut properly is best general condition. Threads that are found to be determined by practice. stripped may have an improperly upset head. When keyed Rivnuts are used, cut the keyway The stripped threads would also prevent the 196 Chapter 7 AIRCRAFT DAMAGE REPAIR
installation of screws. When possible, in open fasteners are covered in chapter 6. The special skin areas, inspect the shank for a properly upset tools and installation and removal methods are head. covered in the following sections. NOTE: Rivnuts which are not to be used at the time of installation, or not used for any Installation Tools for other reason, should be plugged with a screw Hi-Shear Rivets designed specifically for that purpose. This will eliminate pockets, which could hold moisture The special tools required for use with Hi- and cause corrosion if left open. Shear rivets differ from conventional sets only in the design of the collar swaging and trimming Removal features and the discharge port through which excess collar material is ejected. (See fig. 7-43.) Defective Rivnuts should be replaced by the Various tools and combinations of tools are same size Rivnuts whenever possible. When the available for installing rivets in limited access hole has been enlarged by removal, substitution areas. of the next larger size can be made. To remove a Rivnut, select a drill the same size as the original installation Procedures hole.Drillout the Rivnut head, using light pressure and the hollow Rivnut shank as a guide. Figure 7-43illustrates four stepsin the The Rivnut shank should fall out of the hole installation of the pin and collar to form the behind the sheet, or it may be drifted out, using rivet. In step 1, the pin is inserted into the work. a pin punch. A bucking bar is placed against the head of the pin. in step 2, the collar is slipped over the SPECIAL RIVET AND grooved end of the pin. A gun or squeezer set is FASTENER INSTALLATION placed over the collar. As driving pressure is applied in step 3, the collar begins to form into The description and use of special rivets and the grooved end of the pin. Step 4 shows the
MI-smFAA RIVET SEE (STEP I) (STEP 2)
(STEP 3) (STEP 4)
AM.313 Figure.1,43.Hi-Shear rivet installation.
197 AVIATION STRUCTURAL MECHANIC S 3 & 2
USE CHISEL THAT HAS CUTTING EDGE NARROWER THAN COLLAR HEIGHT a.. PUNCH
BUCKING BAR TO /V/S SUPPORT RIVET
I \ / STEP 1. STEP 2. SPLIT RIVET COLLAR TWO PLACES DRIVE RIVET PIN OUT WITH PUNCH
(A) CHISEL METHOD
DRILL BUSHING DRILL BUSHING
STEP 1. STEP 1. DRILL SHANK DOWN DRILL THROUGH TO LOCKING GROOVE RIVET HEAD
DRILL APPROXIMATE DRILL SAME SIZE SIZE OF RIVET AS RIVET
STEP 2. STEP 2. DRIVE RIVET PIN DRIVE RIVET PIN OUT WITH PUNCH OUT WITH PUNCH
(B) DRILL GUIDE METHOD IHOLLOW END MILL
STEP 1. STEP 2. MILL COLLAR DOWN TO EDGE OF PIN GROOVE DRIVE RIVET PIN OUT WITH PUNCH
(C) HOLLOW END MILL METHOD
AM.16 Figure 7-44.HiShear rivet removal.
198 Chapter 7AIRCRAFT DAMAGE REPAIR collar formed or swaged completely into the grooved end of the pin.Excess materialis trimmed off the collar automatically by the tool during driving. Step 1. Pin is inserted from one side of work through pre pared hole. Metal collar is Removal then placed over the pintail. When tool nose ie applied, Hi-Shear rivets may be removed by various chuck jaws grip pull grooves. methods. However, only some of these methods are recommended as the others may increase the possibility of damaging the parts. Cutting the collar off with a chisel or other sharp tool should be done only where other methods are not practical and the structure isfairly rigid. Step 2.Tool pulls on pin and starts drawing sheets (See (A) fig. 744.) Special care must be taken to together. prevent damage to the part or to the hole. The use of a drill guide is recommended in drilling out a Hi-Shear rivet. (See (B) fig. 7-44.) The base of the guide has a conical surface which fits over the drivencollar. A drillwith a diameter approximately equal to the rivet diameter is then used to drill the shank end of the rivet Step 3. As the pull on the pin increases, tool anvil down to the locking groove. The rivet is then swages collar into locking driven out with a small punch. When absolutely grooves and a permanent necessary, the head of the rivet may be drilled lock is formed. out, but a guide should be used on protruding head rivets. A collar removal tool, consisting of a hollow end mill, may also be used to remove the collar. (See (C) fig. 7-44.) The rotating cutter is applied Step 4. Tool continues to to the collar until a sufficient amount of collar pull until pin breaks at the breakneck groove and is ejected. material has been removed to permit a sharp tap Tool anvil disengages from of a hammer to drive out the pin. A stop swaged collar. prevents the cutter teeth from contacting and damaging the work surface.
Installation Procedures for AM.318 Lockbolt Fasteners Figure 7-45.Lockbolt installation. Figure7-45illustratesfourstepsin the installationofthelockboltfastener.This Special care must be taken to prevent damage to fastener is installed using the CP352 pneumatic thestructureortothehole.The most driving tool (similar to the CP350 blind rivet acceptable method of removal isto cut the pull tool illustrated in figure 7-38). collar off, using a hollow end mill in a drill motor. After removal of the collar, the pin may Removal be driven out with a punch. Lockbolt collars may be removed by various Installation Procedures for methods. In general the procedure is the same as Hi-Lok Fasteners for removing Hi-Shear rivets. (See fig. 7-44.) Cutting the collar off with a chisel should be Hi-Lok fasteners may be installed by one done only where the structure is fairly rigid. person working from one side of the work, using
199 AVIATION STRUCTURAL MECHANIC S 3 & 2
COLLAR .
.4
%Wit01.111= 'VW
PIN
I. Insert the pin into 2.Manually screw the collar 3.Insert the hex wrench tip of the the prepared hole. onto the pin o minimum power driver into the pin's hex recess. of two turns.
COLLAR POWER DRIVER INSTALLED FASTENER
21P1111111IMIN1;,///
COLLAR WRENCHING COLLAR WRENCHING DEVICE DEVICE
4. Firmly press the driver against the 5.The. HI-Lok fastener is collar, operate the power driver until installed with the correct the collar's wrenching device has torque value. been torqued off. ( A) HILOK INSTALLATION (Power Tools)
Allen Wrench Allen Wrench Ratchet
Socket Water Pump Pliers (B) H I- LOK FASTENER (C) REMOVAL OF INSTALLED HI-LOK INSTALLATION FASTENER . (Hand Tools ) (Hand Tools )
AM.17 Figure 7- 46. Hi -Lok fastenor installation and removal.
200 Chapter 7AIRCRAFT DAMAGE REPAIR standard power or handtools and Hi-Lok adapter correct torque value as the collars are designed tools. Hi-Lok adapter tools can be fitted to tobreakoff (torque off) at preestablished high-speed power drivers in straight, 90-degree, torque levels. offset, and extension configurations. View (A) figure 7-46 illustrates steps in the installation of Removal Hi-Lok fasteners using power tools. Hi-Lok fasteners may be installed using the Hi-Lok fasteners arc easily removed with followinghandtools:Allen hex key (Allen standard handtoolsina manner similar to wrench) and open-end or ratchet-type wrenches. removing a nut from a bolt. To remove a Hi-Lok (See (B) fig. 7-46.) To install the fastener, insert fastener, insert an Allen wrench in the hex recess the pin into the prepared hole and manually of the pin. Hold the Allen wrench firm and, screw the collar onto the pin a minimum of two using a pair of channel-lock or vise-grip pliers, turns. Insert the proper size Allen wrench into rotatethecollarcounterclockwiseuntilre- the hex recess of the pin and, using a ratchet or moved. (See (C)fig.7-46.) Hi-Lok pins are open-end wrench, rotate the collar clockwise reusable if no thread damage is incurred during until the wrenching device of the collar has been removal. AN or NAS nuts may be substituted torqued off. The fastener is installed with the for Hi-Lok collars.
WRENCH ADAPTER
NOSE ADAPTER HANDLE
STRUCTURE (REF)
AM.299 Figure 7-47.Jo-ilt9t installation tool.
201 AVIATION STRUCTURAL MECHANIC S 3 & 2
Installation Tools for the correct size for different size and type of Jo-Bolt Fasteners Jo-Bolts. Itis recommended that the holes be drilled undersize and then be brought up to final Special tools are required for the installation size for reaming. After bringing the holes up to of Jo-Bolts. In no case shall power screwdrivers correct size and prior to installing the Jo-Bolts, or drill motors be converted to Jo-Bolt driving the part to be joined must be secured firmly in tools. The handtool illustrated in figure 7-47 position. Cleco fasteners, C-clamps, or any of consists of a tool body, nose adapter, and several varities of temporary fasteners may be wrench adapter which can be used for installing used for this purpose. Figure 7-48 illustrates the all sizes and types of Jo-Bolt fasteners. The nose installation of Jo-Bolts. Insert the correct grip adapter is secured in the tool body and prevents length Jo-Bolt in the hole. The fastener can be the nut portion of the Jo-Bolt from turning pushed easily into a properly prepared hole and during installation. The wrench adapter rides in no case shall it be driven forcibly into the free inside the nose adapter and gets its turning hole. A verylighttapfitis permissible in action from the ratchet wrench. aluminum alloy parts but not in steel. Select the correct nose and wrench adapter for the fastener Installation Procedures and secure them in the handtool body. Place the nose adapter of the driving tool over the slabbed When installing Jo-Bolts it is important that portion of the bolt shank so that it engages the the fastener holes and countersink diameters be head of the Jo-Bolt. On flush head Jo-Bolts the
.NORMAL INSTALLATION DRIVING TOOL WRENCHING END OF BOLT BOLT WRENCH ADAPTER NOSE ADAPTER BOLT BREAK -OFD NUT
COLLAR ////////////fi
Step 1 Step 2 Step 3
Select proper grip length Engage nose adapter of When power is applied, then insert fastener in tool with nut and slabbed the collar is compressed hole. portion of bolt. over the tapered end of the nut. The bolt is notched to break off at a predetermined tension force. < lir IMO INSTALLED PROTRUDING HEAD INSTALLED FLUSH HEAD THREADED BLIND FASTENER THREADED BLIND FASTENER
AM.327 Figure 7-48.Jo-Balt installation.
202 Chapter 7AIRCRAFT DAMAGE REPAIR
dogs on the nose adapter shall fit into the slots turnlock fasteners. Three of the most widely of the fastener head. On the protruding head, used turnlock fasteners are the Camloc, Dzus, including the minable head fasteners, the nose and Air loc. adapter will fit over the fastener head. Hold the tooltightlyagainsttheJo-Bolt head and CAMLOC INSTALLATION TOOLS perpendicular to the surface of the work. Failure to hold the tool perpendicular may result in the The following list of Camloc tools should be stem breakoff before the Jo-Bolt is tight. Hold- available to assure satisfactory Cam loc installa- ing the handle of the tool stationary, turn the tion, but does not represent the minimum tools ratchet handle. As power is applied, the bolt is required for any particular installation: turned whilethenutisheld. The sleeve, compressed between the bolt head and tapered Pliers, No. 4P3. end of the nut, is drawn over the end of the nut.' Snapring tool, No. T26. The sleeve is expanded, forming the blind head Cutters, Nos. 4-G2C and 4-GC. against the inner surface of the part. When the Hole saws, Nos. HS-471D and HS-500. sleeve is drawn up tight, tl, slabbed portion of Flaring tools, Nos. T-55-1 and T-50-1. the bolt is snapped on, cornp:eting the driving Dimpling tools,Nos. 4-G200M, 4-G200F, operation. After driving, the end of the bolt, at 2-S200M, and 2-S200F. the breakoff point, should be touched up with zinc chromate primer. CAMLOC REPAIR PROCEDURE
Removal Repair of Camloc fasteners includes removal of the damaged stud, grommet, or receptacle, The procedure to be used for the removal of a proper preparation of the hole, and installation Jo-Bolt will depend on whether the fastener is of the replacement part. In all cases, alignment clamped up tight or whether it is loose. If the of the stud, grommet, and receptacle must be Jo-Bolt is clamped up tight in the hole, it can be maintained. When structural repair of the access removed by drilling just through the fastener door or access frame is necessary, all repair work head and then driving out the shank portion should be completed before aligning receptacle with a hammer and punch. (See (A) fig. 7-49.) If holes with stud or grommet holes. the Jo-Bolt is loose in the hole, it must be Hole preparation is dependent upon the series prevented from turning by using a drill bushing of fastener specified and the sheet thickness of which has dogs to engage the head slots and a the material to which the fastener must be handle or other device to hold it. (See (B) fig. attached.All holesplain, dimpled, counter- 7-49.) While holding the Jo-Bolt to prevent it sunk,or counterboredshould be predrilled from turning,drillthe bolt portion of the undersize with the size drill (pilot hole) recom- fastener completely out, removing the bolt head mended in the Structural Repair Manual for the and fastener sleeve. After the bolt !lead and particular aircraft. sleeve have been removed, pick out the nut Remove all chips and burrs before installing portion of the fastener. For all drilling opera- fastener parts. Select proper size stud, grommet, tions on Jo-Bolts, select a drill motor that does and/or receptacle. In cases of varying sheet not turn over 500 RPM. thicknesswhich wouldcausehigh locking torque, the stud assembly should be replaced with one of suitable length to insure uniform TURNLOCK FASTENER REPAIR low locking torque. Stud length increments of 0.030 inch allow for varying material thick- A number of approved turnlock fasteners are nesses. The totalgriplength for the stud in use on aircraft. They are used to fasten small assembly includes both top and bottom sheet removable inspection panels, doors, fairings, and thicknesses. Stud selection tables will be listed in otherpartsfrequentlyremoved. The AMS the aircraft Structural Repair Manual. Always should be proficient in inspection and repair of refer to these tables for replacement sizes. 203 AVIATION STRUCTURAL MECHANIC S 3 & 2
Drill Selection Chart Jo-Bolt Column 1 Column II Nominal Diameter Drill Size Drill Size 5/32 No. 42 (0.089) No. 23 (0.154) (0.0935) 5/32 (0,1562) 3/16 No. 35 (0.110 inch) No. 12 (0.189 inch) 1/4 No. 24 (0.152 inch) D (0.246 inch) 5/16 No. 17 (0.173) M (0.295) 3/8 No. 5 (0.2055) 23/64 (0.3594)
STEP STEP II SELECT CORRECT PILOT DRILL FROM COLUMN I OF THE DRILL SELECT CORRECT FOLLOW UP DRILL FROM COLUMN II OF SELECTION CHART, THEN DRILL BELOW THE HEAD THE DRILL SELECTION CHART, THEN DRILL TO THE SHANK JUNCTION OF THE NUT. PILOT HOLE DEPTH.
STEP III USE A HAMMER AND NOMINAL SIZE PUNCH TO DRIVE OUT THE SHANK AND BLIND HEAD.
(A) TIGHT FASTENER
STEP I STEP II PREVENT NUT FROM TURNING BY ENGAGING SELECT DRILL, IN ACCORDANCE WITH COLUMN 1 OF THE STEP III DRIVING TOOL NOSE ADAPTER, HOLDING THE DRILL SELECTION CHART, THEN DRILL THROUGH THE PICK THE NUT FROM THE HOLE WITH A PUNCH. NOSE ADAPTER WITH VISE-GRIP PLIERS. SHANK, SEVERING THE BOLTHEAD. ( B) LOOSE FASTENER
AM.300 Figure 7-49.Jo-aolt removal.
204 Chapter 7AIRCRAFT DAMAGE REPAIR
Grommet selection is determined as follows: The following repair methods apply to the 1. In the 4002 series, the grommet is used in 4002 series Camloc fastener. combination with the stud assembly, but is dependent upon the type of hole required, the Stud Damage total thickness of the material, and the specified counterbore of the snapring. Stud assemblies 4002-1 through -15 are re- 2. In the 2700 series, the spring cup of the moved by compressing the spring with Camloc stud assembly eliminates the use of a grommet. pliers and lifting out the stud. To install a new 3. In the 40551 series, the grommet isa stud, compress the spring and insert the stud nonremovable part of the stud assembly. into the grommet. (See fig. 7-50.) When the NOTE: Lateral movement of the grommet spring is released, the stud assembly cannot fall must be held to a minimum. Vertical movement out. of the grommet, when the fastener is unlocked, Stud assemblies -16 and longer are retained in should be held to a minimum to prevent possible the grommet by a split washer. No pliers are loss or fallout of the grommet. required for removal or installation of these
AM.382 Figure 7-50.Installing Camloc stud.
205 AVIATION STRUCTURAL MECHANIC S 3 & 2
snapring, using snapring tool T26, as shown in figure 7-51. The snapring must be fully seated behind the shoulder of the grommet.
Receptacle Damage
Remove the attaching rivets, using standard removal procedures, in replacing the damaged receptacle. The new receptacle, which should be identical to the original, is then riveted into place.
DZUS FASTENER REPAIR
Dzus fasteners are of two types, the light-duty type and the heavy-duty type. The main dif- ference in repairing is that the heavy-duty type requires an additional operation, as the retaining grommet must also be removed and replaced. The S shaped spring is replaced if damaged or broken.
Installation The light-duty Dzus fastener is installed in three steps. (See (A) fig. 7-52.) The hole is dimpled, using a special set of dies. The correct size of stud is then inserted in the dimpled hole. Using another set of dies, the dimpled material is then forced into the undercut of the stud, which locks the stud in place. The heavy-duty Dzus fastener is installed in four steps. (See (B) fig. 7-52.) A hole is drilled AM.383 to the proper size, and the grommet is inserted. Figure 7-51.Installing snapring behind shoulder of The grommet is then set (partially flared). The grommet. correct size of fastener is then inserted through the grommet. Using a set of dies, the grommet studs. The stud is inserted in the grommet, and material is flared, forcing the grommet to clinch the split washer is placed on the stud shank the undercut part of the stud and the panel. This between the cross pin and the spring cup. The clinching action locks the stud in position. stud cross pin should not be removed under any circumstances. Removal
Grommet Damage The light-duty Dzus fastener may be removed by placing the stud over a hole in an anvil and Remove the grommet by first prying off the striking it with a hammer and drift punch. After snapring and slip the grommet out of the hole. the broken stud is driven out, the hole will be Check for possible damage to the hole size, the too large and will be dimpled on the wrong side. dimple,orcountersink,andforcorrect This may be remedied by flattening the hole dimensions. Remove all burrs and install a new area with a hammer and redimpling with the grommet identical to the original. Install a new proper sizedimpling tool. Removal of the 206 Chapter 7AIRCRAFT DAMAGE REPAIR
DIMPLING DIES CLINCHING DIE
STEP 1 STEP 2 STEP 3 DRILL 0 DIMPLE INSERT FASTENER CLINCH
(A) LIGHT-DUTY FASTENER
SETTING DIES CLINCHING DIES zifirzmz,zz
STEP 1 STEP 2 STEP 3 STEP 4 DRILLaINSERT GROMMET SET GROMMET INSERT FASTENER CLINCH
( B ) HEAVY-DUTY FASTENER
AM.384 Figure 7 52.Dzus fastener installation. heavy-duty Dzus fastener requires a different in the lap patch. procedure, as a grommet is used in the hole and must be cut away before the damaged stud can Repair of a Spring be removed. Insertion of a new grommet is necessary before installing a new stud. When a spring is broken or damaged, replace The heavy-duty Dzus fastener may be re- with an identical spring. Different spring heights moved by cutting away the grommet, using are available for each fastener. There are also diagonal cutter type pliers. The old fastener is special springs which are used for installation in then free to fall out of the hole. Inspect the hole boxcornersandpanels which wouldbe area for damage, and repair as necessary. The subjected to either horizontal or vertical move- new fastener and grommet are then reinstalled in ments. the original hole, as described earlier. AIRLOC FASTENER REPAIR Repair of the Hole The Airloc assembly consists of the recep- tacle, stud, and cross pin as seen in figure 6-10 When the hole is too badly worn to permit (ch. 6). The repair of this fastener is normally reinstallationof the same sized heavy-duty made by complete replacement of the damaged fastener, it is recommended that a lap patch be parts. The stud and cross pin should never be installed over the old hole and a new hole cut in reused due to the press fit, which is necessary the lap patch. The new fastener is then installed for cross pin retention. 207 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.386 Figure 7-54.Inserting cross pin, using special Airloc handtooi.
AM.385 add the thickness of the inner structure and Figure 7-53.Airloc stud head shapes, outerpanels, doors, gaskets, reinforcements, countersunk and round. etc., in thousandths of an inch. Add to this, 0.010 inch to allow for wrinkling and warpage Installation Procedures of materials. Select the nearest even 0.010 inch above the total, for the proper length of stud. The Navy normally uses Nos. 2, 5, and 7 NOTE: When using a floating type receptacle, Air loc receptacles. Each receptacle is held in add to the preceding measurements 0.020 inch place by rivets. The No. 2 receptacle is installed for No. 2 receptacles or 0.030 for Nos. 5 and 7 using 3/32-inchrivets;No. 5uses1/8- or receptacles. 3/32-inch rivets; and the No. 7 uses 1/8-inch After determining the correct length of stud, rivets. Receptacles with flat rivet holes may be insert the new stud into the panel or sheet. replaced by a receptacle with countersunk holes. Using the special Airloc tool, press the cross pin The stud normally comes in two head types, into the stud hole, as shown in figure 7-54. the countersunk and round head. (See fig. 7-53.) When Airloc fasteners do not fasten properly If round head studs are not available, the outer and the studs are known to be the correct sheet may be dimpled and the countersunk head length,excess misalignment isnormally the stud substituted. The head of the studis cause. This condition can often be corrected by stamped to indicate the total grip length. The removing the panel and fastening the studs in a length of studs is available in varying increments different sequence. Fastening the difficult studs of ten-thousandths of an inch. first, or by starting in the middle of the panel To select the proper stud, the AMS must and working toward each end, usually corrects determine the total grip length. To obtain this, this condition. 208 Chapter 7AIRCRAFT DAMAGE REPAIR
Removal
Removalofdamagedreceptaclesis ac- complished by removing the rivets, using stand- ard removal procedures. The stud is removed by pressing out or clipping off the cross pin. The cross pins for I-inch and 1 3/8-inch studs are normally removed by pressing out, using special hand pliers. (See fig. 7-55.) The cross pin for 3/4-inch studs may be removed either by using the hand pliers or by clipping off the cross pin.
AM.387 Figure 7-55.Hand pliers for removing cross pins.
209 CHAPTER 8
AIRFRAME MAINTENANCE
This chapter is essentially a continuation of studying the following NavPers manuals: Fluid chapter 7. While chapter 7 dealt mostly with the Power, NavPers 16193-B, and Basic Electricity, repair of damage to the structural parts of the NavPers 10086-B. airframe,this chapter deals with the main- tenance of nonstructural airframe components. TYPICAL SYSTEM DESCRIPTION In the area of nonstructural airframe com- ponents, the AMS is responsible for such tasks as Typicalamongsimple,unboostedflight removal, installation, and balarcing of flight control systems is the primary flight control control surfaces; removal and installation of system incorporated in the T-28. The flight detachable aft fuselage sections, and replace- control surfaces (ailerons, elevators, and rudder) ment of glass and plastic enclosure components. are actuated through a series of push-pull rods, cables, belicranks, sectors, and idlers. Figure 8-1 schematically illustrates the elevator portion of FLIGHT CONTROL SYSTEMS the T-28 flight control system. The elevators are operated by a fore-and-aft Flight control systems require little routine movement of the controlstick. Raising the maintenance other than inspection and lubrica- elevators causes the aircraft to climb; lowering tion. However, it is very important that these be the elevators causes it to dive or descend. The performed as carefully and conscientiously as elevators are raised by pulling back on the stick, possible. An inoperative or malfunctioning flight and they are lowered by pushing the stick control system can result in aborted flight or forward. total loss of aircraft, cargo, and crew. As can be seen in figure 8-1, each control A flightcontrol system includesallthe stick is mounted in such a way that it can pivot components required to control the aircraft backwards and forwards on its mounting pin. about each of the three axes affecting flight (ch. The front and rear sticks are connected to each 4). A simple flight control system may be all other by a push-pull rod attached to their lower mechanical; that is, operated entirely through ends. A second push-pull rod is attached to the mechanical linkage and cables from the pilot to lower end of the aft stick. Then, as either stick is the control surface. Other more sophisticated moved ,longitudinally the other stick moves in flight control systems may utilize electrical or the same direction and an equal distance, and hydraulic power to provide some or all of the the elevators are deflected proportionately. Built "muscle" in the system. Still others combine into the bracket supporting the rear stick are some of the features of allthree types of adjustable stops which limit the fore-and-aft systems. The emphasis in this chapter is on movement of thesticksand prevent over- mechanical systems; however, the AMS should controlling the elevators (see inset). be familiar with the hydraulic and electrical The push-pull tube (rod) that connects to the components aswell. A basic knowledge of lowest point of the aft control stick extends aft hydraulics and electricity may be attained by to the bellcrank. Notice that the function of the 210 Chapter 8AIRFRAME MAINTENANCE
AM.432 1. Aft control stick. 11. Aft sector. 2. Stop bolts. 12. Elevator fitting assembly. 3. Push-pull tube adjustment. 13. Rigging dimension. 4. Bellcrank. 14. Vertical reference line. 5. Rig pins. 15. Centerlinestick neutral. 6. Bungee. 16. Stick throw limitUP elevator:_ 7. Forward sector. 17. Stick throw limitDOWN elevator. 8. Bobweight. 18. Stick throw rangeelevator control. 9. Turnbuckles. 19. Locating anglevertical reference line. 10. Push-pull tubes. 20. Longitudinal reference line (cockpit floor). Figure 8-1.Typical elevator flight control system. bellcrankisto change the direction of the bungee. The bungeeisspring-loadedto the push-pull action from fore-and-aft to up-and- center position and regardless of the direction of down. The second push -pull tube connects the deflection of the elevators, the bungee will assist forward cable sector and the bellcrank and in returning the system to neutral. causes the sector to rotate in accordance with From the forward sector, the cables extend the stick movements. back through the aircraft to the aft cable sector. The forward cable sector pictured in figure Notice in the drawing, just aft of the cable 8-1 incorporates a bobweight which partially turnbuckles, a zigzag line breaking both of the compensates the system for the weight of the cables. This is a draftsman's symbol used to elevators. As the sector moves the bobweight up indicate that the cables are really proportionate- or down, the elevators move in the opposite ly longer than is shown here but that they have direction. The elevator cables are attached to the been reduced in length so that the remaining forward edges of the sector. Also on the forward essential components of the elevator control sector is an arm which connects to a centering system may all be shown in the one drawing.
211 AVIATION STRUCTURAL MECHANIC S 3 & 2
(.,r STICK LEFT LEGEND
HYDIAUUC PRESSURE = RETURN PRESSURE PIVOTPonrt
LEFT HAND RIGHT HAND CONTROL CABLE CONTROL CABLE
POWER MECHANISM CONTROL VALVES UTILITY HYDRAULIC SYSTEM
LOAD FEEL DUNDEE
NEUTRAL
POWER MECHANISM LEFT AILERON an DISCONNECT
NEUTRAL DKR AILERON moms
AM.1048 Figure 8-2.Aileron control system.
The aft sector is essentially the same as the down. forward sector and acts as a slave to the forward The A-4 aileron control system illustrated in sector. Cables from the forward sector attach to figure 8-2 is typical of a power boost system. the aft edges of the aft sector. A push-pull tube Thissystemis equippedwithapower from the aft sector extends to, and connects mechanism which provides hydraulic power to with, the elevator fitting assembly. operate the ailerons. However, in the event of Theelevatorfitting assembly, commonly hydraulic power failure, the mechanism can be called the elevator "horn," is built onto the disconnected, placing the system in complete elevators and extends outward (usually down- manual operation. ward) from the elevator surface at right angles to Operation of the system is initiated when the the plane of rotation and the chord line of the control stick in the cockpit is moved to the left elevatorsurfaces. As thefitting assembly is or to the right. When the stick is moved, cables moved fore or aft, the elevators are moved up or connected to the bellcrank in the control stick 212 Chapter 8AIRFRAME MAINTENANCE housing are moved to actuate the sector on the cable is corroded, relieve the tension on the power mechanism. With the actuation of the cable and carefully untwist the cable to visually sector, the power mechanism operates, trans- inspecttheinterior. Any corrosion on the ferring the movement to the mechanical linkage interior strands of the cable constitutes failure which in turn actuates the ailerons. and the cable must be replaced. If no internal corrosion is detected, remove loose external rust CONTROL SYSTEM MAINTENANCE and corrosion with a clean dry rag or fiber brush and apply the specified preservative compound. Control system maintenance includes inspec- tion to discover actual and potential defects, servicing with lubricants as required, and the A CABLE WITH BROKEN correction of reported malfunctions and defects. WIRES DISTRIBUTED NOT OVER 6 IN I- INCH DIS- Malfunctions which occur in control systems TANCEIS STILL include frayed and loosened cables, worn and SERVICEABLE--\ loosened bearings, unnatural tightness (binding), 4) / 'i. .S.,...dy and broken or damaged components. Ve f .40'..d.aarIP 4"er*,,,r,0j01 . THESE WIRES Cable Maintenance ARE BROKEN THIS IS A 7X19 CONTROL Cable type control systems require more I''''.r5A' CABLE MADE OF 6 STRANDS . 44e). AROUND I CENTER STRAND. maintenance than rigid linkage type systems and ,' V EACH OF 7 STRANDS HAS 19 WIRES MAKING 7 X 19 OR must therefore be inspected more thoroughly. -,415,:, 133 WIRES IN ALL. o' Cables must be kept clean at all times and must 101"-,11 CABLE WITH MORE THAN 6 be inspectedperiodicallyfor broken wires, WIRES BROKEN WITHIN AI-INCH corrosion, kinking, and excessive wear. DISTANCE MUST BE REPLACED Broken wires are most apt to occur in lengths of cable which pass over pulleys or through fairleads. Tests have proved that control cables may have broken wires and still be capable of AM.433 carrying their designated load. However, on Figure 8.3.Determining serviceable cable. certain periodic inspections, cables are checked for broken wires by passing a cloth along the length of the cable without removing the pre- servative. Where the cloth snags along the cable is an indication of one or more broken wires. The bare hands should never be used in checking for broken wires.
Any 7 x 19 cable that shows more than .6 WIRE NIPPERS broken wires in any 1-inch length, or any 7 x 7 cable that shows more than 3 broken wires in any 1 inch, must be replaced. A maximum of 3 broken wires per inch is allowable in the length PLACE CABLE of cables passing over pulleys, drums, or through PERPENDICULAR 70 CUTTING JAWS fairleads. Figure 8-3 illustrates how to determine AS SHOWN a serviceable cable. Corrosion, kinking, and excessive wear should begivenparticularattentionduringcable inspection. If found to be kinked or badly worn, the cable should be replaced, even though the number of broken wiresisless than that AM.434 specified for replacement. If the surface of the Figure 8-4.Cutting small cable with wire nippers. 213 AVIATION STRUCTURAL MECHANIC S 3 & 2
CUTTING JAWS
AM.435 Figure 8-5.Cable cutting machine. NOTE: Do not use metal wool or solvents to cable assembly. This may be accomplished by clean installed cable as use of metal wool will measuring the old cable assembly, or from embedtinydissimilar metal particles,thus measurements providedinthe Maintenance creating further corrosion problems; and the use instructions Manual for the aircraft concerned. of solventswillremove theinternalcable Cutting of cables may be accomplished by lubricant, allowing the cable strands to abrade any convenient method except an oxyacetylene and further corrode. cutting torch. The method of cutting usually When a cable is found to be unserviceable and depends upon the tools and machines available. a spare cable is not available, an exact duplicate If a cable tends to unravel, the ends may be of the damaged cable may be prepared. This will sweat-soldered, or wrapped with a strip of tape involve cutting a length of cable to the proper prior to cutting. length, attaching the necessary end fittings, and Small diameter cable may be cut satisfactorily testing the assembly. with a pair of heavy-duty diagonal cutters, side
. In determining the proper length to which the cutters, or a pair of wire nippers similar to those new cable will be cut, itisfirst necessary to shown in figure 8-4. Best results are obtained if determine theoverall length of the finished the cutting jaws are held perpendicular to the 214 Chapter 8AIRFRAME MAINTENANCE
cable during the cutting operation. Cables up to 3/32 inch in diameter may be cut in one operation by this method. Larger cables may require two or more cuts. When cutting large diameter cables in this manner, use the end of the cutting blade and cut only a few strands at a time. The most satisfactory method of cutting cables is with a cable-cutting machine having special jaws to accommodate various sizes of cable.(Seefig.8-5.) To usethis machine, position the cable in the proper diameter groove and hold the cable firmly within 2 inches of the cutting blades. Hold the cable at right angles to the cutting blades and pull the operating handle down sharply. A cold chisel used in conjunction with a soft metal block may also be used for cutting cables. This method should be used only as a last resort MECHANICAL because of the way the cable ends will be frayed. TYPE Figure 8-6 illustrates this method of cutting a cable. The chisel should be held straight up, with the cutting blade at right angles to the cable. Using a heavy hammer, strike the chisel with a
SOFT METAL BLOCK
HOLD CHISEL BLADE INLET. AIR PERPENDICULAR TO SUPPLY LINE CABLE
PNEUMATIC TYPE
AM.437 AMA36 Figure 8-7.Hand-swaging toolsmechanical and Figure 8-6.Cutting cable with a cold chisel. pneumatic.
215 AVIATION STRUCTURAL MECHANIC S 3 & 2 hard, sharp blow in order to get o clean, square clean and that all strands remain in a compact cut. group as shown in figure 8-8. Place a drop or After the cable is cut, the next step in making two of light lubricating oil on the cable end, up anaircraftcableisattachment of the then insert the end into the terminal to a depth terminals. Most terminal fittings are SWAGED of about 1 inch. Bend the cable toward the onto the ends of control system cables. Swaging terminal, straightenitback tothe normal is essentially a squeezing process in which the position, then push the cable all the way into cable is inserted into the barrel of the terminal, the terminal barrel. This bending process puts a then by great pressure applied by dies in a kink in the cable end, which provides enough swaging machine, the barrel of the terminal is friction to hold the terminal in place until the compressed or shrunk in diameter so that it swaging operation is completed. It also tends to clasps tightly around the cable, and the metal of separate and spread the strandsinside the the inside walls of the barrel is molded and cold terminal barrel, thus reducing the strains caused flowed by force into the crevises of the cable. by swaging. Figure 8-7 illustrates two types of hand-swaging Both of the hand-swaging tools shown in tools. The one in the upper part of the illustra- figure8-7 are widely used by naval aircraft tion is mechanically operated, while the lower maintenance activities. The procedure for using one is pneumatically operated. both types is described in the following para- When preparing to swage a terminal, cut the graphs. cable to the required length, allowing for the When operating the mechanical type, the elongation (increase in length due to stretching) AMS places the proper size pair of dies on the of thefitting which will occur during the swaging tool. The terminal is then located in the swaging process. The amount of elongation will jaws of the tool as shown in figure 8-9, and the vary with the type and size fitting used. There- swagh ,goperation is performed. As the dies fore, the elongation must be taken into account rotate in such a manner as to pull the terminal whenever making up any cable. Tables are from right to left, the dies compress the terminal furnished in the publication NavAir 01-1A-8, barrel onto the cable and swaging occurs. Rota- Aircraft Structural Hardware, or superseding tion of the dies is accomplished by opening and publication, which provides elongation data for closing the handles in the manner of a pair of all types and sizes of fittings. scissors. Make sure that the cable end is cut square and After completion of swaging and removal of the fitting from the swaging tool, measure the outside diameter of the shank with a micrometer or with the gage furnished with the swaging SQUARE-CUT CABLE ENU outfit to determine whether or not the terminal has been swaged sufficiently. This may be determined by checking the measurement with the applicable cable terminal table in NavAir 01-1A-8. The pneumatic swaging tool shown in figure 8-7 is a lightweight portable unit designed to precision swage the metal of a terminal into the interstices (crevices) of the cable strands. The - SWAGE TYPE CABLE swager may be mounted on a base plate and TERMINAL BARREL used on a bench, or it can be taken to the job. When the swaging tool is taken to the location of the job, it may be held in the hand at the balance point or cradled in the arm while using. The pneumatic swaging kit has several dif- AM.438 ferent sizes and types of dies used for swaging Figure 3-8.Inserting ;Able in swage-type terminal. ball and sleeve type terminals and for cutting 216 Chapter 8AIRFRAME MAINTENANCE
Thefollowingstep-by-stepprocedureis recommended for setting up the pneumatic swaging tool: 1. Connect the air supply to the foot valve. For efficient operation use an inlet air line with at least 3/8 inch inside diameter and 90 pounds minimum line pressure. 2. Connect the swager air line to the foot valve. 3. Clean the dies, remove any steel particles which may have adhered to the die cavity, and apply a light film of oil to the entire die. 4. Insert the dies in the swaging tool as previously described. CAUTION: Do not insert or remove dies until the air supply which is connected to the swager is shut off. With the pneumatic tool set up for use, the followingstepsshouldbefollowedwhile swaging terminals to cables. 1. Position the terminal on the cable, using theold cableas a pattern, or follow the instructions given in the applicable technical directives. When using a ball type terminal, a minimum 11/2 inches of cable must extend beyond the ball to allow room for holding and turning the terminal during swaging. The excess istrimmed,ifnecessary, after the swaging operation. When using MS 20667 terminals, 1/4 inch of cable must extend through the terminal. On all other terminals, the cable is bottomed (inserted all of the way into the terminal). 2. Each terminal is cleaned, using a suitable PNEUMATIC TYPE solvent, then coated with a light oil. 3. With the terminals positioned in the cavity of the forward die, slide the rear die to its AM.439 forward position using the slot provided in the Figure 8-9.Locating the terminal in the swaging yoke for the index finger. tools. NOTE: To prevent damage to terminal or cable during the swaging cycle, maintain light andtrimmingcable.Likethe mechanical pressure on the cable towards the front of the swaging tool, the dies come in matched sets, and swager. This holds the terminal and cable firmly must be used together. The dies are installed by in the forward die cavity. inserting either die through the yoke opening, 4. Depress the foot valve firmly and rotate into the die cavity with the keyway down and the cable back-and-forth in 180-degree arcs or the shank facing to the rear of the swager. Slide complete revolutions. The length of time the the first die back in order to clear the opening foot valve is held depends upon the type and for the insertion of the mating die. The second size of fitting being swaged. This time can be die is inserted with the shank facing forward. found by referring to the chart supplied with the
217 , AVIATION STRUCTURAL MECHANIC S 3 & 2 pneumatic swaging tool. If the terminal will not correct length of the new tube is obtained by rotate, stop swaging immediately, rotate the loosening the checknut and turning the end terminal 90 degrees, and start swaging again. fitting in or out, as necessary. When the push- 5. Release the foot pedal to stop swaging, pull tube has been adjusted to its correct length, and remove the terminal from the swaging tool the checknut must be tightened against the for inspection. If the diameter is oversize or the shoulder of the end fitting. Normally, only one terminal surface is too rough, repeat the opera- end of a push-pull rodisadjustable. The tion. adjustable end has a hole (witness hole) drilled If swaged terminals are to be used on both in the rod, located at the maximum distance the ends of the cable, recheck the overall length of base of the end fitting is allowed to be extended. the cable and trim,ifnecessary,prior to If the threads of the end fitting can be seen installing the second terminal. Make certain that through this hole, the end fitting is within safe all additional fittings and accessories, such as limits. cable stops and fairleads, are slipped onto the When attaching push-pull tubes with ball cable in the proper sequence. The other terminal bearing end fittings, the attaching bolt and nut may then be swaged, using the same procedure must tightly clamp the inner race of the bearing as that used for the first one. to the bellcrank, idler arm, or other supporting All newly fabricated cables should be tested structure. A nut and bolt only finger tight does for proper strength before they are installed in not utilize the bearing for the purpose it was aircraft. The test consists of applying a specified intended. Therefore, nuts should be tightened to tension load on the cable for a specified number the torque values listed in the aircraft Main- of minutes. The proof loads for testing various tenance Instructions Manual. size cables are given intables contained in After installing a new push-pull tube in a Nav Air 01-1A-8, or subsequent publications. flight control system, the control surface must Proof loading will result in a certain amount of be checked for correct travel. Prdcedures for permanent stretch imparted to the cable. This accomplishing this are described later in this stretchmust be taken into account when chapter. If travel is incorrect, the length of the fabricating cable assemblies. Cables which are push-pull tube must be readjusted. made up slightly long may be entirely too long after proof boa ding. Replacing of cables in the aircraft, especially Troubleshooting those routed through inaccessible spaces, can be difficult. One method used is to secure a snaking When the cause and remedy for a reported line to the cable to be replaced, remove the malfunction in a control system are not im- pulleys from the brackets, and pull out the old mediately obvious tothe AMS it may be cable, pulling the snaking line into the cable necessary to troubleshoot the system. Most system run at the same time. Attach the new aircraftMaintenanceInstructionsManuals cable assembly to the snaking line and pull the provide troubleshooting charts which list some snaking line out to pull the new assembly into of the more common malfunctions likely to place. Replace the pulleys and attach the new occur in the system. Each discrepancy is ac- cable in the system. companied by one or more probable causes and a remedy is prescribed for each cause. The Push-Pull Linkage Maintenance troubleshootingchartsareorganizedina definite sequence under each possible trouble, Push-pulltube linkage must be inspected according to the probability of failure and ease closely for dents and cracks and for bent lengths of investigation. In order to obtain maximum of tubing. Damaged tubes may have to be value from these charts, they should be used replaced. End fittings are checked for damage systematically in accordance with the aircraft and for wear and security of attachment. Worn manufacturer's recommendations. A portion of or loose fittings must be replaced. the troubleshooting chart for the control system When replacing a damaged push-pull tube, the illustrated in figure 8-1 is shown in table 8-1. 218 Chapter 8AIRFRAME MAINTENANCE
Table 8-1.Troubleshooting flight control system.
Trouble Probable Remedy cause
Cockpit controls hard to move. Control system not rigged Rerig control system. correctly. Control cable tension too Check tension with tensio- high. meter. Equipment or structure Check routing of linkages interfering with move- and cables, correct as ment of control system. necessary. Control cable fouled on Check vicinity of turn- equipment. buckles. Control cables incorrectly Reroute control cables. routed. Pulley out of alignment. Straighten or replace pulley bracket. Defective or dry bearing Clean and lubricate bearing in the system. or replace if damaged. Defective bungee in Adjust bungee. Replace system. if necessary. Sectors torqued too high. Isolate sector and torque to proper value or replace if defective. Cockpit controls will not move Rig pin left in system dur- Remove rig pin. with the surface controls dis- ing rigging procedure. connected. Bungee jammed. Remove and repair, or replace. Foreign object jammed Remove foreign object and into system. inspect system for damage. Quadrant bolt torque too Torque bolt to specified high. torque as per Maintenance Instructions Manual. Control surfaces will not move. Attaching bolts overtorqued.Torque correctly. Movable' surface striking Replace or repair movable or binding on fixed sur- surface as required. Re- face. Hinge pin bent or place or align. misaligned.
219 AVIATION STRUCTURAL MECHANIC S 3 & 2
Since most present day aircraft incorporate control system is to insure neutral alignment of some form of electrical control and/or hydraulic all connecting components and to regulate and boost intheirflightcontrol systems, main- limit the surface deflection in both directions. In tenance of these systems must include the the elevator system illustrated in figure 8-1, related electrical circuits and hydraulic systems rigging begins at the aft sector. in many instances. Although an AE or AMH is The aircraft manufacturer has determined the generally called upon to locate and correct position of the aft sector when itis in the electrical or hydraulic troubles, respectively, the neutral position. He has furnished a rig ri.ri AMS should be able to check circuits for loose in the sector and a mating hole in the adjoining connections,performcontinuitychecksif structure. (See (5) in fig. 8-1 at aft sector.) With necessary, and perform minor troubleshooting the rig pin inserted in the aft sector and in the ofthehydraulic system. A knowledge of aircraft structure the sector is held firmly in the electrical and hydraulic symbols and the ability neutral position. With the sector in this position, to read electrical circuit diagrams and hydraulic the push-pull tube connecting the sector with system schematics are necessary; therefore, the theelevator fitting assembly isadjusted to AMS should study the training manuals Basic position the elevators to the neutral (stream- Electricity and Fluid Power. lined) position. The neutral position is deter- Loose electrical connectors are located by mined by use of an elevator rigging fixture checking all those in the circuit. A connector illustrated in figure 8-10. The curved section of that can be turned by hand is loose and should the rigging fixture is graduated in degrees on be tightened handtight. either side of the neutral (zero degree) position A continuity check is simply a matter of which is about midway of the curved part of the determining whether or not the circuit to the rigging fixture. applicable unitiscomplete. The check for The rigging fixture is fastened securely to the continuity may be made with a test lamp, which aircraft at indicated points of attachment. When can be drawn from supply. properly mounted, the index marks (gradua- To perform an electrical continuity check, the tions) on the curved section align with the connector at the electrically controlled unit is elevators and indicate the position, in degrees, of firstdisconnected.Then, with all necessary switches and circuit breakers closed, the test lampisconnected into thecircuitat the electrical connector. The lamp thus indicates whether or not the circuit is complete. Continuity checks may also be made with the use of a multimeter. A multimeter is an instru- ment used for measuring resistance, voltage, or amperage. Using this instrument is primarily the responsibility of the AE; however, the AMS may learn to use it by referring to Basic Electricity, NavPers10086-B,Chapter15.Remember, certain portions of this training manual are recommended supplemental reading for all AMS personnel. Satisfactorybackgroundinformationon hydraulic theory may be acquired by referring to the training manual, Fluid Power, NavPers 16193 (Series).
Rigging and Adjustment AM.390 The purpose of rigging and adjusting a flight Figure 8-10.Elevator rigging fixture. 220 Chapter 8AIRFRAME MAINTENANCE the elevators at any time. If, with the aft sector As mentioned in chapter 6, only two methods of rig pin in place, the elevators are not in neutral; safetyingturnbuckles have been adopted as for example, 5 degrees above the neutral mark, standard procedures by the armed servicesthe lengthening the push-pull rod end will push the clip-locking (preferred) method and the wire- elevator fitting assembly forward and thereby wrapping method. lower the elevators. If the elevators are too low, CLIP-LOCKING TURNBUCKLES.The clip- then shortening the rod will bring them up as locking method of safetying uses an NAS lock required. clip. To safety the turnbuckle, align the slot in The next step in rigging and adjusting is the the barrel with the slot in the cable terminal. adjusting and tightening of the pair of cables in Hold the lock clip between the thumb and the system. This is accomplished by tightening fore-finger at the end loop. Insert the straight the turnbuckles on each cable evenly until the end of the clip into the aperture formed by the requiredtensionisobtained.During cable aligned slots. Bring the hook end of the lock clip tightening the rig pinis retained in the aft over the hole in the center of the turnbuckle sector, leaving the forward sector free to turn. barrel and seat the hook loop into the hole. Therefore,whenthenecessarytensionis Application of pressure to the hook shoulder at recorded on one cable, that is also the tension theholewillengage the hook lipin the on the other cable. To insure that the cables turnbuckle barrel and complete the safety lock- were tightened evenly, check the forward sector ing of one end. The above steps are then rig pin hole to see if the rig pin can be inserted repeated on the opposite end of the turnbuckle through the sector and into the structure. If this barrel. Both locking clips may be inserted in the is not possible, then the cables must be adjusted same turnbuckle barrel hole or they may be by loosening one and tightening the other the inserted in opposite holes. (See fig.6-40 in same amount. This will maintain the correct chapter 6.) tension on the cables and at the same time Lock 'clips must be examined after assembly rotate the forward sector to the neutral position. for proper engagement of the hook lip in the The cable section is properly rigged when it is turnbuckle barrel hole by the application of possible to insert and remove the forward sector slight pressure in the disengaging direction. Lock rig pin easily with the aft sector pin installed and clips must not be reused, as removal of the clips the cables tightened to the prescribed tension. from the installed position will severely damage Figure 8-11 illustrates a tool for holding the them. terminals on cable ends to prevent their rotation WIRE-WRAPPING OF TURNBUCKLES. while adjusting the turnbuckle barrel. First, two safety wires are passed through the When all adjusting and rigging on the cables is hole in the center of the turnbuckle barrel, and completed, safety the turnbuckles as necessary. the ends of the wires are bent 90 degrees toward the ends of the turnbuckle, as shown in figure 6-40, Next, the ends of the wires are passed through the holes in the turnbuckle eye or between the jaws of the turnbuckle fork, as applicable. The wires are then bent toward the center of the turnbuckle and each one wrapped four times around the shank, securing the wires in place. When a swaged turnbuckle terminal is being safetied, one wire must be passed through the hole provided for this purpose in the terminal. It is then looped over the free end of the other wire and both ends wrapped around the shank, as shown in figure 6-40. AM.391 RIGGING AND ADJUSTING RIGID Figure 8-11.Tumbuckle rigging clamp. CONTROLS.The push-pull tube connecting
221 . AVIATION STRUCTURAL MECHANIC S 3 & 2 the forward sector and the bellcrank is adjusted ment the elevators should be held in neutral to the correct length by installing a rig pin in the (plusorminustheprescribed number of bellcrank and turning the rod adjustable eye in degrees) by bungee action. If the elevators are or out until the rod can be installed between the too high, shorten the bungee rod end. If they are sector and bellcrank without binding. At this too low, lengthen the bungee. With the bungee point three rig pins are in place and should properly adjusted, tighten the bungee rod end remain in place until the control sticks are rigged locknut and safety it as required. to neutral. When positioning the control sticks to neutral Removal and Installation the rear stick must be adjusted first as we are working forward from the elevator surface. The It is sometimes necessary to remove control push-pull tube connecting the bottom of the surfaces from aircraft for the purpose of repair rear stick with the bellcrank must be adjusted or replacement. The instructions presented in until the stick centerline (15, fig. 8-1) is the the following paragraphs are general instruc- prescribed number of degrees forward of a tions, applicable to several types of aircraft. For vertical reference line (14). The vertical refer- specificinstructions and precautions, always ence line is a position that the centerline of the consult the applicable Maintenance Instructions control stick would attain at a 90-degree angle Manual before removing a control surface from (19) to the cockpit floor (20), as determined by any aircraft. a level protractor. REMOVAL.Removal of a control surface Adjustthelength of the push-pull tube should not be attempted until the aircraftis between the control sticks to position the front placed in a hangar or other area protecting it control stick to an angle identical to that of the from the wind. Before any control surface is aft control stick, and remove all three rig pins. removed from the aircraft, it should be tagged This completes the rigging and adjusting of the with the bureau number of the aircraft and the control system to neutral. All that remains is to location of the control surface on the aircraft. adjust the stops that limit the fore and aft travel The firststepis to remove the necessary of the control sticks and rig and adjust the access opening covers and fairings. To prevent bungee that holds the system in the neutral the loss of these inspection plates and fairings, position. they should be left attached to the aircraft by The stop bolts (2, fig. 8-1) are located, one one screw or by a piece of safety wire. The other each, in front and behind the aft control stick. screws should be put in a container to prevent They are installed so that the stick contacts the them from being lost. stop bolts at the extreme limits of its travel. The Disconnectbonding wires,electricalcon- maximumtraveloftheelevatorsin each nectors,andcontrollinkage.Beforedis- direction is determined by the manufacturer and connecting cable linkage, the tension should be is controlled by the stop bolts. With the rigging relievedatthe most convenient turnbuckle. fixture still in place, move the control stick all Next, support the entire control surface, either the way forward and adjust the stop until the manually or with mechanical supports, in such a elevator DOWN throw conforms to the instruc- manner as to remc eall the load from the tions in the applicable Maintenance Instructions hinges. Remove the hinge bolts, using a mallet Manual. Pull the stick all the way aft and adjust and brass drift pin where necessary. The control the aft stop bolt to obtain the correct elevator surface should be supported and all the hinges UP throw. The stop bolts are safety wired in kept in alignment until the last hinge bolt has place after this adjustment. been removed. On king control surfaces it may The last item to be adjusted in this control be necessary to replace the hinge bolts with drift systemisthe centering bungee. Connect the pins to keep the hinges aligned while removing bungee and adjust its rod end so that with the the remaining hinge bolts. stick against the stop bolt in the full down Secondary and auxiliary control surfaces are elevator position, the bungee is a minimum of sometimes attached with piano wire hinges. 1/32 inch from bottoming. After this adjust- Removal of the piano wire can be accomplished 222 Chapter 8AIRFRAME MAINTENANCE by cutting off the bent ends, securing one end of surface correctly supported, install the hinge the wire in the chuck of a hand drill, and bolts. In the case of a secondary or auxiliary rotating the wire with the drill while withdraw- surface attached by piano hinge wire, a new wire ing it. Excessive spinning will have a wearing should be used. effect on the hinge material and should be After a control surface is installed, the control avoided. The reuse of piano hinge wire is not linkage is then connected and the rigging of the considered safe, therefore, any wire removed system checked. should be discarded. After all the hinges are disconnected, remove Balancing of Flight Control Surfaces the control surface from the aircraft, supporting itcarefully to prevent damage to the hinge All flight control surfaces are balanced at the ,brackets and adjoining surfaces. Replace the time of manufacture by the addition of counter- -- hinge bolts in the hinges to prevent them from weights inside, the leading edge of the control being lost or damaged. surface.Thisbalancemustbemaintained INSTALLATION.Before installing a control (within certain tolerances) throughout the serv- surface, check the identification tag to deter- ice life of the control surface, because flutter or mine the location on thd aircraft. Place the dynamic oscillation of these surfaces in flight is surface in position carefully, being sure that all sensitivetobalance.Balancetolerances are the hinge holes are properly aligned. Drift pins always specified in the applicable aircraft Struc- may be used to align the holes. With the control tural Repair Manual.
BALANCE STAND BRACKET: RUDDER TIP PIN
RUDDER 4 RUDDER HINGE FITTING 411°-11411*111111111111b-. VIEW A
WEIGHTS AND CONTAINER
HINGE CENTERLINE
BALANCE STAND RUDDER SECTION
AM.392 Figure 8-12.Typical balance stand.
223 . AVIATION STRUCTURAL MECHANIC S 3 & 2
Following the repair to (or modification of) been +50to +60 pound/inches, additional any control surface, a balance check should be counterweights would have been necessary. made to determine whether the specified toler- ances of the control surface have been exceeded. This check is made on a specially constructed AFT FUSELAGE SECTION balance stand similar to the one illustrated in REMOVAL AND INSTALLATION figure 8-12. When a control surfaceis mounted on a Most single-engine jet aircraft have the engine balance stand, a downward movement of the incorporated inthefuselage. Access to the trailingedge below thehorizontalposition engine for removal and installation is provided indicates a positive (+) unbalanced moment. An by means of a removable aft section of the upward movement of the trailing edge above fuselage. MI or part of other systems located in horizontal indicates a negative (-) unbalanced the aft fuselage section are the flight control moment. surfaces and systems; landing gear, arresting Before making a balance check, the control gear,andtakeoff assistsystems; personnel surface must be complete with tab and other environmentalsystems;hydraulicpower equipment and the final coat of paint already systems; automatic flight control systems; and applied. The area must be free from drafts in electrical power systems and lighting provisions. order for an accurate check to be made. Strictly speaking, maintenance of aft fuselage TYPICAL BALANCING PROCEDURE.The sections is limited to installation and removal. following procedure is taken from the Structural Should repairs to the airframe become neces- Repair Manual of a typical naval aircraft. sary, such work is effected in accordance with the applicable aircraft Structural Repair Manual. 1. Mount the control surface on a balance It is a responsibility of the AMS to remove and stand, using the two outer hinge brackets as install aft fuselage sections, which hereafter may mounts. (See fig. 8-12.) also be referred to as the tail section, or merely, 2. Suspend a container from the leading edge tail. or trailing edge (as necessary) and add weight to Manyofthefunctionsassociatedwith the container until the control surface is in a removal and installation of tail sections are horizontal position. commonto nearlyallaircrafthavinga 3. Measur^ the distance from the point of removable tail. The procedure presented in the suspension of the container to the control following paragraphs is taken from the Main- surfacehingecenterline.Thisdistanceis tenanceInstructionsManualfortheA-4 designated as X. Distances forward of the hinge (Skyhawk) and is a typical example of the steps line are indicated +X, and distances aft of the involved. The preparatory steps are general in hinge line are indicated-X. nature and apply to all aircraft. 4. Remove the container, and determine the weight of the container and its contents. This REMOVAL weight is designated as W. 5. The total weight, W, multiplied by the The first thing to do after being assigned to distance,X,isequal to the calculated un- remove the tail section from an aircraft is to balanced moment. assemble all the special tools and support equip- EXAMPLE: A control surface in a balance ment specified in the applicable Maintenance stand requires a 7-pound weight (container and Instruction Manual. It is futile to start the job if contents), located 6.5 inches forward of the a needed piece of support equipment is un- hinge line to balance the surface in a horizontal available. position. This indicates an unbalanced moment The second step should be a briefing by the of +45.5 pound/inches in the control surface. crew leader to the crew (four men are required The tolerance for this control surface is +40 to on the Skyhawk) on various phases in the +50 pound/inches; therefore, no correction is tail-removal sequence and thepart each is necessary. Had the tolerance for this surface expected to accomplish. All of the CAUTION 224 Chapter 8AIRFRAME MAINTENANCE and WARNING notesintheMaintenance hooks. The adapter hookstrapsarethen Instructions Manual which relate to the job at adjusted to secure the tail section to the adapter. hand should be read and discussed. At the end The main bolts are now ready to be removed. of the briefing, the crew leader (regardless of The removal of the main bolts must be experience)shouldretaintheMaintenance performed in a definite sequence. In addition, as Instructions Manual containing the steps in the some of the bolts that splice the two parts of the removal sequence so that he may use the list of fuselagetogether are removed, bullet-shaped steps as a checkoff list to make sure no vital step thread protectors are installed on the bolts. The is overlooked or performed dangerously out of thread protectors are also called aft fuselage sequence. attachment aligners, since they are also used to Prior to the actual separation of the tail help align the forward and aft sections of the section from the main fuselage there are many fuselage during reinstallation of the tail. With preparatory steps to be taken. These include the thread protectors in place the aft section will such preparations as the following: not damage the splice bolt threads as the two fuselage sections are disengaged. 1. Insuring approximately even fuel levels in Before moving the tail the entire work area external tanks. should be reinspected for proper disengagement 2. Aileron gust lock installed. of all lines, hoses, quick-disconnects, and elec- 3. Flaps are raised. trical connections. If all is clear, move the tail 4. All ground handling safety equipment is section. supported by the trailer and installation installed. adapter, away fromthe wing and fuselage 5.Allexternalpower(hydraulicand forward section. electrical) is disconnected. 6. Removal of all necessary access doors and INSTALLATION panels. 7. Release of air pressure from the arresting Installation of a tail section is essentially the hook hold-down unit. reverse of the removal procedure. Many of the preparatory steps have to be rechecked to insure After completing the preparatory steps listed that the tail can be reinstalled safely. Just prior inthe foregoing, allelectrical lines, control to actually mating the two fuselage sections an cables, hydraulic and pneumatic tubing, oxygen inspection should be made of the interiors of system lines, and drain lines must be discon- each section and all hardware which must be nected and stowed as per the Maintenance reconnected. Some systems such as the fire Instructions Manual and each of the applicable detection system should be checked out in both line ends or tubing openings covered to prevent the forward and aft fuselage sections separately. contamination while separated. The checking of thefire detection system In order to remove the tail section from the components makes replacement of damaged Skyhawk, the tailpipe clamp and tailpipe must components possible before theaft fuselage be removed next. section is installed. With theaft fuselage installation adapter Extremecaremust beexercisedduring properly secured to the installation and removal installation of the tail to prevent damage to trailer,position thetrailer beneath thetail control cables, electrical cables, hydraulic lines, section. Adjust the height of the installation and the heat radiation shields on the lower sides adapter, using hoist mechanisms on the trailer; of the engine. then insert the pin to secure the arresting hook With theaft fuselage installation adapter attachingfitting.Operatethetrailerhoist installed on the installation and removal trailer, mechanisms to raise the adapter until it contacts and the tail section securely mounted on the the fuselage aft section firmly at the supporting adapter, move the tail section into position for points. Adjust the adapter hooks on the installa- attachment to the forward fuselage section. tion adapter to align with the holes in the left- During the actual attachment of the aft and right-hand sides of the fuselage; engage the fuselage section to the forward section, another
225 , AVIATION STRUCTURAL MECHANIC S 3 & 2
MAINTENANCE ACTIONmow OPSAY FORM 4090/40 (10-011) 3/H.0107.770.4400
I. JOBCONTROL NUMBER 2. TIRE TOUIF 1. BU/SER NO. 4. ACTION S. WOW 1. SAINT. LEVEL 7. ACTION DATE 060. CENTER ORG. DATE SCR SUE ILC3A0A0paa AACD /5o/6ode 3igo igI04.El 1 .41. DI dr.2 0 42 5 S. 4051UNIT CODE S. WHIN DISCO 10. TYPE SAINT, 11. ACTION 12. MAL IS. ITEMS14. MAN. 1S.EMT IS. TAKEN. PROC. HOURS
, 1 ///0 P 8 5 000 4° f4 Ii°/ lo 110 REMOVED (Al 21INSTALLED i1114
.1 mrGIT SERIAL MUSSER .1 MFGII .2 SERIAL NO.
.3 PAH, riumwEm .4 TIME/CYCLES .3 PAST NUMBER .4 TIME/CYCLES
DI CORRECTIVE ACTION
1!:',111DYE hND Te_iii STA LL_ 'EMO V ED AND /A/ST/91_1.6P 7-4 /L 50e.770N POR rip I.,SEc1--/ o/.1 PAK/ER PIA iii,:r-.1_
O. En''1E5 REWIRED SIGNATURE E. CORRECTED BY f.INoro4.1[0 AV G. SUPERVISOR GO..., *1011 Evil r-i MO LOG rj VII 0 Re /Ia$4.44-rrnRaevAtte ...__ ea/lePW ACCIS1 ILICOGO L., .. t.....1, MI OM S 2. iirinel A MSC 30 40. REPAIR CYCLE DATA FAILED MATERIAL I .1 AcT./ .7 .4- .5 DATE MM. OTY PART HOOKA/RIF. KKK OM TOIN KM
I. REMOVED 5. TO AOP
E. RECEIVED 4. OFF AMP MAIL. CONTROL
3. WORK 7. TO ASP
4. COMPLETED 4. OFF ARP
RFI II B Como II R/511 S.
0.
N. PCN PRIORITY OATS DUE
IS OUT J. ACCUMULATED NOM REQUIRED MENIAL ..1 I' DATUTIKE NAME /SHIFT DATE MANHOUPS C.JT RIO. NO. UPON PART NUMBER STY PRI M1P 0o0 KC
-
TOTAL
AM.5 Figure 8-13.-MAF documentation tow dse removal andreinstallation of a tall section.
226 Chapter 8 AIRFRAME MAINTENANCE definite sequence is employed. Many of these handled only with clean cotton gloves. steps require inspection by a Quality Assurance 2. The use of harmful liquids as cleaning Representative as soon as they are completed. agents should be avoided. Once thetailsectionstructureisproperly 3. Fabrication, repair, installation, and main- attached to the forward fuselage, then recon- tenance instructions must be closely followed. nection of all the systems between the aft and 4. Operations which might tend to scratch or forward sections can be accomplished. Every distort the plastic surface must be avoided. Care system that can be checked must be checked for must be taken to avoid scratching plastic sur- proper operationafterreconnection. Other faces with finger rings or other sharp objects. systems may require servicing prior to operation. When the crew has completed their work the Just as woods split and metals crack in areas Quality Assurance Representative willassure ofhigh,localizedstress,plasticmaterials himself on final inspection that the work has develop, under similar conditions, small surface been properly completed. fissures called CRAZING. These tiny cracks are Figure 8-13 illustrates the use of a single copy approxime:ly perpendicular to the surface, very Maintenance Action Form (MAF) for the re- narrow in width, and usually not over 0.01 inch moval of atailsectiontofacilitate other in depth. These tiny fissures are not only an maintenance and the reinstallation of the same optical defect, but also a mechanical defect, tail section. inasmuch as there is a separation or parting of ,naterial. TRANSPARENT PLASTIC Crazing may be caused by improper cleaning, ENCLOSURES improper installation, improper machining, or cold forming. Once a part has been crazed, Because of the many uses of plastic materials neither the optical nor mechanical defect can be in aircraft enclosures, optical crality (quqlity removed permanently; therefore, prevention of promoting good vision) is of great importance. crazing is most necessary. These plastic materials are similar to plate glass in many of their optical characteristics. Ability to locate and identify other aircraft in flight, to CLEANING PLASTIC SURFACES land safely at high speeds, to maintain position in formation, and in some cases, to sight guns For exterior surfaces, flush with plenty of accurately through plastic enclosures, all depend water, using the bare hand gently to feel and uponthesurfacecleanliness,clarity,and dislodge any dirt, sand, or mud. The plastic is freedom from distortion of the plastic material. then washed with a mild soap, specification These factors, in turn, depend entirely upon the P-S-560 and clean water. NOTE: Water contain- amount of careexercisedinthe handling, ing dirt and abrasive materials may scratch the fabrication,maintenance, andrepair of the plastic surface. material. A clean soft cloth, sponge, or chamois may be Plastics have many advantages over glass for used to carry the soap and water to the plastic. aircraft application, particularly the lightness in The cloth, sponge, or chamois should not be weight and ease of fabrication and repairs; used for scrubbing; use the hand method as however, they lack the surface hardness of glass, described for removing dirt or other foreign and are very easily scratched, with resulting particles. impairment of vision. Care must be exercised Dry with a clean damp chamois, a soft clean while servicing all aircraft to avoid scratching or cloth, or soft tissue by blotting the surface until otherwise damaging the plastic surface. dry. Rubbing the surface of the plastic will Specific procedures are described later in this induce (build up) an electrostatic charge that section for lightmaintenance; however, the attracts dust particles to the surface. If the following general rules should be emphasized: surface does become charged, patting or gently blotting with a damp, clean cloth will remove 1. Transparentplastic materials should be this charge as well as the dust.
227 . AVIATION STRUCTURAL MECHANIC S 3 & 2
To clean i;;teriorplastic surfaces, dust the to its original thickness when excessive heat is surface lightly with a soft cloth. Do not wipe the applied. The best procedure is to keep either the surface with a dry cloth. Next, wipe carefully wheel or plastic constantly in motion relative to with a soft clamp cloth or sponge. Keep the one another. Keep the pressure against the wheel cloth or sponge free from grit by rinsing it to a minimum, and change the direction of frequently in clean water. buffing often. Cleaning and polishing compound, Specifica- Briefly, the procedure for removing scratches tion P-P-560, may be used to remove grease and is as follows: oil. Apply the compound with a soft cloth, rub A single deep scratch or imperfectionis in a circular motion until clean, and polish with reduced by sanding toa number of small, another soft cloth. shallow scratches. These scratches, in turn, are reduced to alarger number of still smaller scratches on a buffing wheel to which a fine REMOVAL OF SCRATCHES abrasiveis applied. These finest scratches are further reduced or filled in with tallow or wax. The AMS is required to remove and install A final buffing or polishing brings the surface to canopies,escape hatches, and otheraircraft a high gloss. The depth of scratch will determine structures that contain plastic sections. Great how many of these operations are necessary. care must be taken to protect the finish of the However, each step in the process must be plastic. Plastic is very soft as compared to other performed thoroughly, or subsequent polishing aircraft structural materials. The surface is easily willnot remove scratchesleft by previous scratched or damaged, and should be protected operations. by the use of proper protective covers and It is obvious that sanding and buffing cause storage racks which are provided by the aircraft thickness variations in the plastic around the manufacturer or are manufactured locally. It is scratch. If skillfully done, these operations will easier to avoid scratches than to remove them. It cause only minor optical distortions which will is possible, however, to restore even a badly not be serious in most applications. Distortion scratched surface to a good finish by buffing and may be reduced by gently polishing and feather- sometimes sanding. ing a fairly large area around the scratch. In Aircraft Maintenance Instructions Manuals critical optical sections, however, even minor specify limits on the length, width, and depth of distortions may causeserious deviationsin cracks,and in what areas they are allowed. sighting. Such sections, even though scratched, These measurements are normally made by the should not be sanded or buffed. If necessary, use of an optical micrometer. Ifascratch these sections are replaced. exceeds the specified limitations, the surface must be replaced. Sanding Before starting to sand or buff, be sure the plastic surface is clean. The buffing wheels and Transparent plastics should never be sanded compounds should also be free of dirt and grit unless absolutely necessary, and then only when to avoid seriously scratching the surface during surface scratches, which may impair vision, are the polishing operation. If the buffing wheels too deep for removal by buffing. have been used before, remove any hardened When sanding is necessary, the finest smallest tallow by running the wheels against a metal grit abrasive paper that will remove the scratch edge. or other defect should be used first. Normally, It is important to remember that most plastic the AMS will never need abrasive paper coarser enclosures are thermoplastic and soften when than No. 320A; however, abrasive paper as heated. The friction of sanding or buffing too coarse as No. 240A may be used if the situation long or too vigorously in one spot can generate warrants. The abrasive paper is wrapped around enough heat to soften or burn the surface. Also, a felt-covered, wooden or rubber block and the plastic that has been deep-drawn, or formed to defective area rubbed lightly, using plain water compound curvatures, has a tendency to return or water with a 2 percent soap content as a 228 ('hinter8AIRFRAME MAINTENANCE
DO NOT SAND UNLESS ABSOLUTELY NECESSARY TO RE- MOVE DEEP SCRATCHES. HOLD SANDPAPER BY SMOOTH RUBBER OR WOODEN BLOCK. SAND OVER A WIDE AREA TO PREVENT OPTICAL DISTORTIONS. EXCESS PRESSURE IN SANDING OR BUFFING WILL BURN PLASTIC.
SCRATCH
-*---ALWAYS WET PAPER
SAND WITH ROTATING MOTION
/ WRONG
I N.% 2":%%' 0 i ,707 SI%1.1,11 11#..'10..0 00.0.8, 1 oar go,oso
. as.
AM.383 Figure 8-14.Proper method of sanding plastic. lubricant. Use circular strokes as shown in figure sequence: Nos. 400A, 500A, and 600A. Wash 8-14.Neveruseastraightback-and-forth the plastic after each operation. During each motion. Sand an area about two or three times step, the deeper scratches left by the preceding the length of the defect in order to minimize grade of abrasive should be removed. optical distortion and excessive thinning of the plastic. The initialsanding should then be Buffing followed by similar treatments, using successive- ly finer grades of sandpaper in the following In order to remove the fine, hairline scratches
229 , AVIATION STRUCTURAL MECHANIC S 3 & 2 caused by sanding, transparent plastic may be is then used to bring the plastic to a high polish. buffed. It is often possible to remove scratches Both wheels are made up of numerous layers of by buffing alone, provided the scratches are not cloth discs, but the abrasive wheel is made hard too deep. by several rows of stitches, as shown in the There are a number of standard commercial illustration. The finish wheel is unstitched with buffing compounds satisfactory for use on trans- spacers (washers) mounted between every fourth parentplasticenclosures. They areusually or fifth cloth disc. composedof veryfine alumina orsimilar Power for turning the buffing wheel may be abrasive in combination with wax, tallow, or supplied by mounting it in a portable drill, as grease binders. They are available in the form of shown in figure 8-16, or a pedestal-type machine bars or tubes for convenience in applying to the similar to the one shown in figure 8-17 may be buffing wheel. used. Plain tallow is often applied to the buffing At the start of each buffing operation, the wheel. It may be used in addition to buffing plastic must be clean and dry. Some of the compound, or may be used alone. In the latter buffing compounds now available will leave the case, tallow functions similar to wax inasmuch surface clean so that washing is not necessary. as itfills in hairline scratches and gives a high Wherenecessary,however, washingshould gloss to the surface. follow each step in buffing. Buffing wheels are made of cotton cloth or If a panel has been sanded previously or is felt. For removing scratches caused by sanding, deeply scratched, the abrasive wheel should be an 'abrasive" wheel and a "finish" wheel are used first. needed. (Seefig.8-15.) The abrasive wheel, Apply fresh compound to the wheel and buff which is relatively hard and to which buffing lightly along and across all scratches. Keep the compound is applied, is used for removing the plastic or wheel in motion with relation to each deeper scratches. The finish wheel, which is soft, other to prevent generating too much heat, thus damaging the plastic. Complete the buffing operation by using the FINISH WHEEL finish wheel, bringing the plastic surface to a high gloss. After all scratches have' been removed with the finish wheel, a coat of wax should be applied by hand. CAUTION: Hand polishing is recommended in critical vision areas. Overheating transparent plastic, by buffing, induces internal stresses and optical distortions.
INSTALLATION OF PLASTIC PANELS There are a number of methods of installing transparent plastic panels in aircraft, some of which are shown in figures 8-18 through 8-21. ABRASIVE WHEEL Which method the aircraft manufacturer uses depends upon the position of the panel in the aircraft,thestressestowhichitwillbe subjected, and a number of other factors. In installing a replacement panel, always follow the AM.394 same mounting method used by the manu- Figure 8-15.Buffing wheels. tpetuper of the aircraft.
230 Chapter 8AIRFRAME MAINTENANCE
AM.395 Figure 8-16.Buffing wheel mounted in portable drill.
The following general rules apply to all types Sinceplastic expands and contracts three of mountings. Fitting and handling should be times as much as metal, suitable allowances for done with masking paper in place, although the dimensional changes with temperature must be edges of the paper may be peeled back slightly made. Minimum clearances between the frame and trimmed off for installation. and the plastic are listed in Nav Air 01-1A-12. Since transparent plasticisbrittle at low Clearance should be equally divided on all sides. temperatures, installation of panels should be Screw torquing procedures should be in ac- done at normal temperatures. cordancewiththeapplicableMaintenance Plastic panels should be mounted between Instructions Manual. Plastic panels should not be some type of gasket material to make the installed under unnatural stresses. Each screw installation waterproof, to reduce vibration, and must be torqued as specified to enable it to to help distribute compressive stresses on the carry its portion of the load. If a plastic panel is plastic. Minimum packing thickness is 1/16 inch. installed in a binding or twisted position and Rubber, fiber glass impregnate, and nylon are screws are not torqued correctly, the plastic the most commonly used gasket materials. panel may fail while the aircraft is undergoing
231 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.398 Figure 8-17.Pedestal type buffer with stitched and unstitched cloth wheels. normal taxiing and flight operations. each screw is removed from the panel, itis During the removal of a plastic panel, there installed in its respective position on the card- may be several different lengths of screws to be board. This is done with each screw as itis . removed. The AMS will save a lot of time if he removed. acquires the habit of keeping screws separated. During installation of the panel, each screw is An easy way to do this is to draw a diagram of removed from the cardboard and reinstalled in the panel on cardboard. Puncture each screw the same hole from which removed until all of hole, with an awl, through the cardboard. As the screws are reinstalled.
232 Chapter 8AIRFRAME MAINTENANCE
PLASTIC FACE SHEET
PLASTIC SHEET BUTYRAL INNER LAYER
LAMINATED SYNTHETIC FIBER CLOTH LAMINATED SYNTHETIC FIBER CLOTH
AM.398 AM.397 Figure 8-19.Approved edge attachment for laminated Figure 8-18.Approved edge attachment for solid plastic. plastic. AVIATION STRUCTURAL MECHANIC S 3 & 2
PLASTIC PLASTIC SHEET LAMINATE
SYNTHETIC FIBER RUBBER CLOTH LOOP EXTRUSION
SPECIAL EXTRUSION
AM.399 RETAINING Figure 8-20.Typical sighting dome attachment. CABLE
FRAME
SKIN
AM.400 Figure 8.21. Typical loop edge attachment
234 CHAPTER 9
LANDING WHEELS, TIRES, AND TUBES
WHEELS Some wheels are designed for use with tires and tubes while others are designed for use with The AMS must have the knowledge and tubeless tires. Those designed for use with tires professional ability to change wheel and tire and tubes have knurled flanges to prevent tire assemblies, repack and replace wheel bearings, slippage on the wheel. Wheels for use with and build up tires, as well as practice the safety tubeless tires have the wheel sections sealed by precautions related to these procedures. General- an 0-ring and employ special valves which are a ly, the wheels require only normal upkeep and part of the wheel. take up little of the AMS' time; however, he may bestationedwhere wheelassemblies DIVIDED (SPLIT) TYPE WHEEL frequently come in contact with salt water or salt air. In an area such as this, the AMS will Figure 9-1 illustrates a typical divided (split) spend a considerable amount of time stripping type wheel. This type of wheel is divided into paint and treating the wheels to help control or two halves, which are held together-by bolts and eliminate corrosion. Wheels are removed from nuts. The two halves are sealed by an 0-ring on aircraft frequently for tire changes, inspections, wheels designed for use with tubeless tires. Each lubrication of wheel bearings, and inspection of wheel half is statically balanced so that any two the wheel brakes. Familiarity with the various opposite halves of the same size and type (part types of wheels, their construction features, and how they are properly installed on the aircraft are therefore highly important items. This section describes the types of wheels currently used on naval aircraft, illustrates the various components of a typical wheel assembly, and describes the procedure for removing and itia? installing a wheel properly. Installation of each component in its proper order in the wheel hub, and correct adjustment of the wheel bearings are especially'important items. Aircraft landing wheels are made from either aluminum alloys or magnesium alloys. Both of these materials provide a strong, lightweight wheel, requiring very little maintenance. Wheels used on naval aircraft are of two generaltypesthe DIVIDED type and the DEMOUNTABLE FLANGE type. Both of these designs make tirechangingafairlysimple AM.401 operation. Figure 9-1.Typical divided (split) type wheel. 235 AVIATION STRUCTURAL MECHANIC S 3 & 2 no.) may be joined together to form one wheel These designations refer to the features of assembly. Thus, if the outboard half of a wheel construction and the types of tire casings with is damaged beyond repair, a new outboard half which they are used. The dimensions by which can be drawn from supply and assembled to the wheels are identified are not necessarily the old inboard half. This type of wheel is used on dimensions of the wheels themselves, but refer nose, main, and tail gears. to certain dimensions of the tire. Size designa- tions are discussed in the section on tires. DEMOUNTABLE FLANGE TYPE WHEEL Similarity of one wheel to another in size and shapeis no proof that the wheels can be The demountable flange landing wheel is interchanged, since one wheel may be designed made so that one flange of the wheel can be for heavy duty while the other one is designed removed for changing the tire. The flange is held to carry a lighter load. Also, one wheel may be in place on the assembled wheel by a lockring or designed for use with an entirely different type bolts. The wheel is balanced with the flange of brake assembly. mounted on the wheel, and both the wheel and flange are marked. To insure proper balance of TYPICAL WHEEL ASSEMBLY the wheel when assembling, these two marks should be lined up together.Figure 9-2il- A complete wheel assembly is shown in figure lustratesatypical demountable flange type 9-3. The wheel casting (6) is the basic unit of the landing wheel. This type wheel is more common- wheel assembly. It is to this part that all other ly used on the main landing gear. components of the assembly are assembled and upon which the tire is mounted. The demountable flange (4) is assembled to the wheel with the chief purpose being to simplifytireremoval and installation. The demountable flange lockring (3) secures the flange to the wheel. It is fitted into a groove in the wheel casting. The bearing cups (12) and (13) are shrink- fitted into the hub of the wheel casting and are theparts on which the bearings ride. The bearings (5) and (7) are the tapered roller type. Each bearing is made up of a cone and the rollers. This type bearing absorbs side thrust as well as radial loads and landing shocks. Bearings must be cleaned and repacked with grease periodically, as discussed later in the chapter. A three-piece grease retainer retains the grease AM.402 in the inboard bearing and keeps out _dirt and Figure 9-2.Typical demountable flange type wheel. moisture. It is composed of a felt seal (9) and an inner and outer closure ring (8) and (10). A Wheels are further classified into the follow- lockring (11) secures the assembly inside the ing types: wheel hub. The hubcap (2) seals the outboard side of the Type ISmooth contour. hub. Itis also secured with a lockring (1); Type IIHigh pressure. however, on some aircraft the hubcap is secured Type IIILow pressure. with screws. Type IVExtra low pressure. All wheels designed for use on the main Type VILow profile. landinggearareequippedwithbraking Type VIIExtra high pressure. components. These components are attached to Type VIIIExtra high pressure (low profile). the wheel casting and may consist of either a 236 Chapter 9 LANDING WHEELS, TIRES, AND TUBES
AM.403 1. Hubcap lockring. 9. Inboard bearing felt seal. 2. Hubcap. 10. Inboard bearing closure ring. 3. Demountable flange lockring. 11. Inboard bearing closure lockring. 4. Demountable flange. 12. Outboard bearing cup. 5. Outboard bearing. 13. Inboard bearing cup. 6. Wheel casting. 14. Disc drive key. 7. Inboard bearing. 15. Fusible plug. S. Inboard bearing closure ring. Figure 9.3. Typical wheel assembly. brake drum or brake drive keys. The wheel in mayoccurandcauseseveredamageto figure 9-3 is equipped with drive keys (14). This equipment and personnel. To counteract this type wheel is designed for use with disc type situation, aircraft manufacturers have developed brakes. Those equipped with brake drums are a safety device called a fusible plug. The fusible designed for use with expander tube brakes, or plug (15) contains an alloy which will melt and the old shoe type brake which is no longer used permit the tire to deflate in.the event the wheel on naval aircraft. is exposed to excessive heat from overbraking or The trend in the armed forces seems to be other causes. This release of air pressure will larger and faster aircraft, which means heavier prevent damage to personnel or equipment. loads and higher landing speeds. Friction caused Wheels which contain fusible plugs should have a by long rollouts, taxiing, etc, cause heat to be metal tag affixed which reads, "Fusible Plugs absorbed by the wheel. Possible wheel failure Installed." 237 AVIATION STRUCTURAL MECHANIC S 3 & 2
BALANCING OF WHEELS order) they are lubricated with Specification MIL -G -81322 A, wide temperature range grease. Wheel assemblies are statically balanced at the Wheel bearings may be lubricated either by time of their manufacture. The method of pressure equipment or hand methods asil- balancing is such that the limits of the assembly lustrated in figures 9-4 and 9-5. However, the imbalance will not be exceeded by changing pressure method is recommended sinceitis major portions of the rotating assembly, such as easier,faster,reducesthepossibilityof brake drums or demountableflanges.Split contamination, and, when utilized correctly, will wheels are balanced so that assembling the wheel assure a more even distribution of grease within halves in alternate positions or assembling halves critical areas. Felt grease retainers are cleaned or of different wheels together will not unbalance replaced ifsaturated with lubricant. Bearing theassemblybeyondthespecifiedlimits. cups are inspected for wear and damage. Balance weights are securely attached in such a NOTE: Insure bearings are completely dry mannerthatthe wheel performanceisnot priortopacking withlubricant.Water or impaired. Any weights which have been added condensation will cause bearings to rust. to a wheel to bring it within proper balance Fusible plugs are inspected to detect fused or should not be removed. However, if a wheel has partially fused plugs. Figure 9-6 gives examples been rendered out of balance due toloss, of fusible plugs; the top row shows usable plugs, breakage, or accidental removal of the balance the second row partially fused plugs, and the weights, the wheel must be rebalanced in accord- bottom row illustratesfusedplugs.Wheels ance with existing instructions. containing either partially fused or fused plugs must haveallplugs contained in the wheel WHEEL MAINTENANCE replaced. Then the wheel must be inspected for AND INSPECTION damage using the procedures listed in the ap- plicable Overhaul Instructions Manual for that The AMS removeswheelsfrom aircraft specific wheel. periodically for a thorough inspection. Wheels Inreinstalling the wheel on theaircraft, are cleaned, using a suitable solvent, prior to proper adjustment of the bearings is extremely inspection. The wheels are then inspected for important. The procedure is as follows: corrosion, cracks, distortion, condition of paint or protective coatings, and checked for evidence 1. Tighten the axle nut while spinning the of overheating due to braking action. wheel by hand. CAUTION: When an aircraft wheel is to be 2. _When the wheel no longer spins freely, removed from the aircraft, the air must be back off the axle nut one castellation (1/6 turn). removed from the tire prior to removing the When properly installed and adjusted, the wheel wheel. This precaution must be taken because of willturn freely, but willhave no sidewise the possibility that the bolts in split type wheels movement. (This procedure may vary from one might have been sheared from landing, thus aircraft to another; the AMS must refer to the causing the wheel halves to separate when the applicable Maintenance Instructions Manual.) axle nut is removed. In the past, several people 3. Safety the axle nut, and install hubcap and have been killed by, their failure to remove the lock it in place. air from the tire before removing the axle nut. Wheel bolts used to fasten divided (split) type AIRCRAFT TIRES wheels are inspected for cracks or condition. This inspection is normally performed using the Proper care and maintenance of tires have magnetic particle inspection in accordance with always been important items in aircraft main- applicable directives. tenance; however, with the development and use Braking surfaces are checked for looseness of the fast-landing aircraft of today, careful tire and for excessive or uneven wear. Wheel bearings maintenance has become increasingly important. are cleaned with an approved solvent. After the Aircraft tires are built to withstand a great deal wheel bearings are cleaned and inspected (in that of punishment, but only by proper care and
. 238 Chapter 9LANDING WHEELS, TIRES, AND TUBES
. "
Ss %ss
sn' sss :tr.` A
104
: 7"
.
14",.. - 4411,-- k,1))
ti
1011.4111..
AM.404 Figure 9.4. Hand lubrication of wheel bearings. maintenance can th )y give safe and dependable in construction except that they have a rubber service. inner liner that is integral with the inside surface of the tirefor air retention, and they also TIRE CONSTRUCTION employ materials and construction in the bead area designed to form a seal with the wheel Figure 9-7 shows the construction details of a flange.Wearindicators(treaddepth holes tube-type aircraft tire. Tubeless tires are similar located in the tread area or lands located in the 239 AVIATION STRUCTURAL MECHANIC S 3 & 2
The BEADS are multiple strands of high tensile strength steel vire imbedded in rubber and wrapped in strips of open weave fabric. The beads hold the tire firmly on the rims andserve as an anchor for the fabricplies turned up around the bead wires. The CHAFING STRIPS are one or more plies of rubber-impregnated woven fabric wrapped around the outside of the beads. They provide additional rigidity to the bead construction and prevent the metal wheel rim from chafing the tire.Tubeless tires have an additional ply of rubber over the chafing strips which functions as an air seal. The BREAKERS are one or more plies of cord or woven fabric impregnated with rubber. When used, they are located between the tread rubber and the cord body, and provide extra reinforcement to prevent bruise damage to the tire. Breakers are not considered part of the cord AM.1215 body. Figure 9-5.Pressure lubrication of wheel bearings. Tread Patterns bottom of the tread grooves) have been in- corporatedintoselecttires The tread is a layer of rubber on the outer asanaidin circumference of the tire. There are four designs measuring tread wear. of tread patterns available for use on naval The CORD BODY consists of multiple layers aircraft. of nylon with individual cords arranged parallel The tread patterns may be any of the follow- to each other and completely encased in rubber. ing designs. The fabric, therefore, has all its strength in orly one direction.Each layer of coated fabric I.Plain. A plain tread is one with a smooth constitutes one ply of the cord body. Adjacent uninterrupted surface. cord plies in the body are assembled with the 2. Nonskid. A nonskid tread is any grooved cords crossing nearly at right angles to each or ribbed type tread. other. This arrangement provides a strong and 3. Ribbed. A ribbed tread pattern is one flexibleconstructionthat distributes impact having three or more continuous circumferential shocks over a wide area. The main function of ribs. the cord body is to give the tire tensile strength 4. Channel. Channel tread tires are heavier to resist internal pressures and to maintain tire than the respective standard types to reduce shape.It must be able to withstand severe wheel shimmy and improve ground handling of flexing, heat, and impact shocks during normal aircraft. tire operations. The TREAD is a layer of rubber on the outer Tread Construction circumferenceofthetire.Itprovidesthe wearing surface and proteeis the cord body The tread construction will be one of the underneath from abrasion. cuts, bruises, and following types. moisture. NOTE: Other tread types may be provided The SIDEWALL is an outer layer of rubber under specific circumstances or as required by adjoining the tread and extending down to the applicable MS standards or drawings. beads. Like the tread, it protects the cord body 1. Rubber tread. A rubbertreadiscon- from abrasion, cuts, bruises, and moisture. structed from 100 percent new (no reclaim) 240 Chapter 9LANDING WHEELS, TIRES, AND TUBES
USABLE FUSE PLUGS
PARTIALLY FUSED PLUGS
FUSED PLUGS
NOTE: WHEELS CONTAINING FUSED OR PARTIALLY FUSED PLUGS MUST HAVE ALL PLUGS REPLACED.
AM.405 Figure 9.6. Fusible plugs. rubber.It may be new natural rubber, new tread. (See fig. 9-8.) synthetic material, or a blend of new natural and 4. Reinforcedcut-resistanttread. A re- new synthetic materials. inforced cut-resistant tread is one that combines 2. Cut-resistant tread. A cut-resistant tread is thefeatures of both thecut-resistant and one which has improved cut-resistant properties reinforced-tread design. that are imparted to the tire by incorporating into the undertread a barrier that resists penetra- Ply Rating tion of cutting objects. 3. Reinforced tread. A reinforced tread is The reference to the number of cord fabric one constructed with fabric cord or other plies in a tire has been superseded by the term reinforcing materials as an integral part of the "ply rating." This is used to identify a given tire
241 . AVIATION STRUCTURAL MECHANIC S 3 & 2
BREAKERS OR INSERTS TREAD
PLIES
SIDEWALL
CHAFING CORD BODY STRIPS PLY BEAD TURNUPS AREA
BEAD WIRES
AM.406 Figure 9-7.Typical aircraft tire construction.
withitsmaximum recommended loadfor specific types of service. It does not necessarily represent the number of cord fabric plies in a tire. Most nylon cord tires have ply ratings greater than the actual number of fabric plies in the cord body.
Type and Size Designation There are seven types of tires used on aircraft now in service. Figure 9-9 illustrates the various types and how the size of each is designated. Dimension A in the illustration is the outside diameter of the tire. DimensionBis the cross- AM.1216 sectional width of the tire at its widest point. Figure 9-8.Reinforced-tread construction. Dimension C is the inside diameter of the tire.
. 242 Chapter 9LANDING WHEELS, TIRES, AND TUBES
SMOOTH HIGH LOW CONTOUR (SC) PRESSURE (HP) PRESSURE (LP)
TYPE I TYPE H TYPE III
Size designated by A in inches* Size designated by Ax B in Size designated by B-C in inches. for main wheels or A in inches and inches. B is given in inches and decimals. decimals for tallwheels. Example: 32x8 C is given In inches. Example: Mainwhael- 56 Example: 16.00 -16 Tailwheel -12.50
EXTRA LOW LOW PRESSURE (ELP) PROFILE (LPR) EXTRA HIGH PRESSURE (EHP)
TYPE IV TYPE VI TYPE VII
Size designated by Ax 8-C in Size designated by Ax B-C in Size designated by AxB in inches. A inches. inches. A is given in inches. Example: 29x13 -5 is given In Inches. B is given in inche and C may be given in inches and decimals to prevent mistake with or inches and dscimals. Type X tires of similar size. Example: 220.25-11.50 Example: 26x6.6
EXTRA HIGH PRESSURE LOW PROFILE (EHP LPR) Size designated by AxB-C in inches. A is given In inches. B and C may be given In Inches TYPE VIII or inches and decimals. Example: 26x8.0-14
AM.408 Figure 9.9. Types and size designation of tires.
Identification Markings Maintenance Action Forms (MAF) and other requiredmaintenanceforms. Each marking The AMS should be familiar with the mark- which is engraved or embossed on the sidewall ings on the sidewall of tires. Some of this for identification purposes is discussed in this information is needed to facilitate completion of section. 243 AVIATION STRUCTURAL MECHANIC S 3 & 2
SIZE AND TYPE.The size of the tire is plies of the cord body. They relieve air that indicated as previously explained, and the type accumulatesinthecord body by normal is indicated by the Roman numeral designated diffusion through the tubeless tire liner and the for that type of tire. tirecarcass. Vent holes in tubeless tires are PLY RATING.On some tires "ply rating" is marked with a bright green dot. abbreviated as "PR". NOTE: Tubeless tires must be marked TUBE- CORD BODY MATERIAL.Type of material LESS. used in the carcass if other than nylon. In addition to the above markings, all tires are DATE OF MANUFACTURE AND SERIAL marked with the manufacturer's name or trade- NUMBER.The date of manufacture of the tire mark,manufacturer'smoldnumber,and isincludedinthe serial number. The serial country of manufacture (if other than USA). number consists of a maximum of 10 positions. RETREAD TIRE IDENTIFICATION.The The first four positions indicate the date of identification data required of the original tire manufacture in the form of a Julian date (last manufacturer is required to remain on the tire digit of the year followed by the day of the and must be replaced by engraving or embossing year, i.e., 23 May 1968 is written 8144). The if removed during retreading. In addition, the next positions (not to exceed six) selected by retread tire is required to be legibly marked and the manufacturer may be either numbers or identified as follows: The letter "R" or "TR" 'letters, or a combination of both. followed by a numeral "1", "2", or "3", etc., to BALANCE MARKER.The balance marker is indicate the first, second, or third time the tire a rcd dot permanently branded into the sidewall has been retreaded,Juliandate of retread of thetire immediately above the bead. It manufacture, and the name of the retread indicates the lightweight point of the tire and manufacturer and plant location. must be placed next to the balance marker on When a retread tire has a cut repair extending the inner tube when mounting. into the carcass plies, a letter "c" is placed in the CUT-LIMIT IDENTIFICATION.Thecut- new rubberintheshoulderarea directly limit dimension is expressed in thirty-seconds of adjacent to the cut repair. an inch, and is rounded to the next smaller thirty-seconds of an inch increment when a STORAGE OF TIRES fraction of a thirty-second inch is involved. It is molded in a minimum of two places equally The life of a tireisdirectly affected by spaced on each sidewall of the tire. storageconditions.Tiresshouldbe stored TREAD CONSTRUCTION.Tires with fabric indoors in a dark, cool, dry room. It is necessary reinforced tread are marked FABRIC TREAD. that they be protected from light (especially VENT MARKINGS.Tube-type tireswith sunlight) to prevent checking. This may be inflation pressu1es greater than 100 psi and all accomplishedbypaintingthestoreroom tubeless tires must be suitably vented to relieve windows. They must also be protected from trapped air. Tube-type tires are vented in either excessiveheat, strong air current, dirt, and of two ways. The first method uses air bleed dampness. Tires must not be allowed to come in ridges on the inside tire surface and grooves on contact with oils, greases, solvents, or other the bead faces. The ridges and grooves channel petroleum products that cause rubber to soften to the outside the air trapped between the inner ordeteriorate.The storeroomshouldnot tube arid the tire. The second method uses four contain any kind of sparking electrical equip- or more vent holes that extend completely mentthat would produce ozone, nor any through each tire sidewall. They relieve both fluorescent lights. pocketed air and air that accumulates in the `fires should be stored vertically in racks, cord body by normal diffusion through the according to size as shown in figure 9-10. The inner tube and tire. Tube-type tire vent holes are edges of the racks must be planed down or marked with an aluminum or white colored dot. designed so that the tire tread does not rest on a Tubeless tires have vent holes that penetrate sharpedge.Tiresmustneverbestacked from the outside of the tire sidewall to the outer horizontally in piles. The issue of tires from the 244 Chapter 9LANDING WHEELS, TIRES, AND TUBES
AM.1217 Figure 9-10.Tire storage rack. storeroom should be strictly on the basis of age safe service life. Military aircraft inner tubes and from the date of manufacture so that the older tubeless tire liners are made of natural rubber to tires will be used first, preventing the chance of satisfy extreme low temperature performance deterioration of the older tires in stock. requirements. Natural rubber is a relatively poor air retainer. This accounts for the high daily INSPECTION AND inflation pressure loss and the need for frequent MAINTENANCE OF TIRES pressure checks. If this check discloses more than a normal loss of pressure, check the valve There are two types of inspections conducted core for leakage by putting a small amount of on the tires; one is conducted with the tire saliva or water on the end of the valve and watch mounted on the wheel, while the other is for bubbles. Replace the valve core if itis conducted with the tire dismounted. leaking. If no bubbles appear, it is an indication that the inner tube (or tire) has a leak. When a Mounted Inspection tire and wheel assembly shows repeated pressure loss exceeding 5 percent of the correct operating During the first preflight inspection each day, inflation pressure, it should be removed from the tires must be inspected for correct pressure, the aircraft and sent to the IMA. tire slippage on the wheel (tube type tires), cuts, After making a pressure check, always replace wear, and general condition. Tires must also be the valve cap, insuring that it is screwed on inspected before each flight for obvious damage fingertight. The cap prevents moisture, salt, oil, that may have been caused during or after the and dirt from entering the valve stem and previous flight. damaging the valve core.Italso acts as a Maintaining the correct inflation pressure in secondary seal if a leak should develop in the an aircraft tire is essential to obtain maximum valve core.
245 . AVIATION STRUCTURAL MECHANIC S 3 & 2
Objects being pried from the tire frequently are ejected suddenly and with considerable force. Therefore, to avoid eye injury, safety glasses or a face shield must be worn. (A gloved hand over the object may be used to deflect it.) Tires must be removed from the aircraft when the tread pattern is worn to less than 1/32-inch, at any spot, or to the limits of the tread wear indicators; if the tire's sidewall cord body fabric is exposed; or if the tread cuts exceed the depth specified on the sidewall of the tire or in the Technical Manual, Aircraft Tires and Tubes, NavAir 04-10-506.Figure9-12showsthe method for measuring cuts, cracks, and holes.
Dismounted Inspection
Whenever a tire has been subjected to a hard landing or has hit an obstacle,it should be dismounted for a complete inspection to deter- mine if any internal injuries have occurred. The tire beads should be spread and the inside of the tire inspected with the aid of a light. If the lining has been damaged or there are other internal AM.409 injuries, the tire should be removed from service. Figure 9-11.Tire slippage mark. Check the entire bead area and the area just above the bead for evidence of rim chafing and damage. Check the wheel for damage which may Tires which are equipped with inner tubes, damage the tire after it is mounted. and operate with less than 150 psi, and all helicopter tube typetires must utilizetire DISMOUNTING AND MOUNTING slippage marks. The slippage mark is a red stripe painted 1 inch wide afid 2 inches long, extending During mounting and dismounting of tires, equally across the tire sidewall-and the wheel safetyisparamount.Compressedairand rim as illustrated in figure 9-11. Aircraft meeting nitrogen present e.. safety hazard, if the operator the above requirements should be inspected for is not aware of the proper operation of the tire slippage on the rim after each flight. If the inflation equipment and the characteristics of markings do not align within 1/4 inch, the wheel the inflation medium. It is also very important assembly must be replaced and the defective to know the wheel type and be familiar with the assembly forwarded to the IMA for repair. manufacturers recommended procedure before Failure to correct tire slippage may cause the attempting to dismount a tire.For specific valve stem to be ripped from the tube. precautions concerning a particular installation, During the visual inspection of tires for cuts, alwaysconsulttheapplicableMaintenance wear, and general condition, any foreign objects Instructions Manual. such as. stones, glass, metal, or other materials embedded in the tread should be removed. A Dismounting common screwdriver or other blunt instrument may be used. The AMS working in the tire shop should WARNING :Whenprobingforforeign recheck tires for complete deflation prior to objects, extreme care must be used to prevent disassembling the wheel and breaking the bead the probe from penetrating deeper into the tire. of the tire. Breaking the bead means separating 246 Chapter 9LANDING WHEELS, TIRES, AND TUBES
14
1. MEASURE REMAINING TREAD DEPTH. 2. MEASURE DEPTH OF CIT. 3. SUBTRACT THE DEPTH OF THE EVALUATE THIS CUT AS 7/8 IN. LONG REMAINING TREAD FROM THE DEPTH OF THE CUT. THE RESULT IS THE MEASUREMDIT TO BE OZWARED WITH THE LIMITS SPECIFIED IN NAVAIR 04-10-506 OR ON THE mewl OP THE TIRE AS APPLICABLE. DEPTH IS READ AT 4. ALL MEASUREMENTS SHOULD BE THIS POINT MEASURED WITH A TREAD DEPTH GAUGE. FSN 5210-357-5951
4/32
AM.1218 Figure 9.12.Method of measuring depth and length of cuts, cracks, and holes. the bead of the tire from the wheel flange. When recommended by Nav Air 04-10-506. Other com- atire has been completely deflated and set aside mercially available or locally fabricated equip- to await the bead-breaking operation, the valve ment which uses either a hydraulically actuated ease should be removed and a deflated tire flag cylinder or a mechanically actuated device may (as shown in fig. 9-13) installed on the valve also be used, provided the equipment will not stem. The tire flags should be so constructed as damage the tires or wheels. The bead breaking not to be installable unless the valve core has equipment shown in figure 9-14 is available in boon removed, two models. Model Lee-1 is designed for instilla- BREAKING THE BEAD.The use of proper tion and service in shore based facilities and equipment for breaking the bead of the tire Model Lee-IX is an explosion-proof version of away from the wheel flange will save materials the Lee-1 intended for shipboard use. and manhours. Aircraft tires, inner tubes, and The following is a step-by-step procedure in wheelscan be damaged beyond repair by the proper operation of the Model Lee-1 equip- improper mounting and dismounting equipment ment. and procedures. The equipment in figure 9-14 is 1. Insure the tire is completely deflated. 247 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.410 Figure 9.13. Deflated tire flag.
2. Determine the type and size of wheel to be 6. Using the UP pushbutton, raise the center dismounted and assemble the proper parts on of the wheel to line up with the center of the the drive shaft. bead-breaking disc. 3. Push the outer centering rollers toward the 7. Rotate -the tire by pushing the tire rotating front of the machine and roll the wheel (posi- toggle to the right. Position the front beadbreak- tioned with the lockring side facing outward for ing disc against the outside bead of the wheel demountable flange wheels) on the outer center- flange. If necessary, adjust the position of the ing rollers. Using the up and down pushbuttons, hydraulic pump assembly by loosening the raise or lower the drive shaft to the proper position lock pin and sliding the pump to the height for the wheel being dismounted, and pUsh proper position. After turning the rump release the wheel onto. the drive shaft. If an open valve clockwise as far asitwill go, apply rimmed tire assembly is being dismounted omit hydraulic pressure against the bead by pumping step 4 and proceed to step 5. the handle as illustrated in figure 9-15. Use the 4. Insert the locking bar and turn about 90 guide handle to properly position the disc. Push degrees counterclockwise. Mount the wheel cone the bead back far enough to allow the removal on the locking bar and insert the locking pin. of the lockring or loose flange. 5. Push the air valve switch to the right; this 8. Remove the lockring and loose flange. If will clamp the wheel on the drive shaft. necessary use the bead shoes (fig. 9-16) to hold
248 Chapter 9LANDINGWHEELS, TIRES, AND TUBES
UP-DOWN PUSH BUTTONS TIRE ROTATING SWITCH AIR VALVE
AIR SUPPLY HYDRAULIC BEAD INLET BREAKING PUMPS
DRIV SHAFT
LARGE WHEEL CONS AND 110-V POWER PACK LOCKINGBAR ( DRIVE FOR J HYDRAULIC LIFT ) SHOE BEAD SHOES SPREADING AND HOLDER CONE
:fa'if WHEEL SHOES
SMALL WHEEL CONES
AM.411 Figure 9-14.Aircraft wheel holder and tire bead breaking machine. the bead back while removing the lockring. 9.Repeatthebead-breakingoperation Release and retract the front bead-breaking disc against the rear surface of the tire, using the rear by turning the release valve counterclockwise. bead breaking assembly.
249 . AVIATION STRUCTURAL MECHANIC S 3 & 2
BEAD SHOES
r 111111-
AM.412 Figure 9-15.Using bead-breaking pump.
10. On all divided (split) type wheels, after AM.413 the beads are broken, remove all nuts and bolts Figure 9-16.Shaft arranged to hold tire bead while while the wheel assembly is still mounted on the removing lockring. machine. Dismounting Divided(Split) Wheels.Tire bead is broken away from the wheel and nuts hex nut (if any) and push the valve away from and bolts are removed as previously described. the seated position to prevent damage to the NOTE: If the tire is a tube type, remove the inner tube valve attachment when breaking the hex nut (if any) and push the valve away from bead. the seated position to prevent damage to the If trouble is encountered in removing the inner tube valve attachment when breaking the flange while the wheel is mounted on the bead tire bead loose. Remove the wheel assembly breaking machine, remove the tire from the from the tire.If thetireis a tubeless type, machine. Lay the tire and wheel assembly flat remove the wheel seal carefully from the wheel with the demountable flange side up. Drive the half and place it on a clean surface. Wheel seals demountable flange down by tapping with a in good condition may be reused if replacement rubber,plastic, or rawhide-faced mallet,far seals are not available. If the tire is a tube type, enough to enable removal of the locking ring. remove the inner tube. Inner tubes can be reused CAUTION: Extremecare must be taken if in good condition, and if less than 5 years old. when breakingthebeads loose and when Dismounting Demountable Flange Wheels. removing the lockring on some demountable Tire bead is broken away from the wheel as flange wheels. The toe of the demountable previously described. flange on these wheels extends very close to the NOTE:. If the tire is a tube type, remove the tubevalvestem.Excessivetravelofthe 250 Chapter 9LANDING WHEELS, TIRES, AND TUBES demountable flange, when removing the lock- inches long in contrasting colors. It is located on ring, or of the tire bead, when breaking the the valve side of the tube. The balance mark on beads loose, will damage the rubber base of the a tireis a red dot approximately 1/2 inch in inner tube valve. diameter. It is located on the sidewall near the If the tire is a tubeless type, remove the wheel bead. seal carefully and place it on a clean surface. Inflate the tube until it is rounded out and Wheel seals in satisfactory condition may be placethe valve-hole half of the wheel into reusedif replacement seals are not available. position in the tire. Push the valve stem through Turn the tire and wheel assembly over, and lift the hole. Insert the other half of the wheel and the wheel out of the tire. If the tire is a tube align the boltholes. type, remove the inner tube. Inner tubes may be NOTE: All bolts must be magnetic particle reused if in a satisfactory condition. Remember inspected to insure they are not defective. Install to keep the wheel flange and locking ring four bolts, nuts, and wulitrs 90 degrees apart. together as a unit to avoid possible mismatch Start the bolts by hand, and draw up evenly during remounting. until the wheel halves seat. Install the remaining bolts, nuts, and washers. Tighten the bolts in a Mounting crisscross order to prevent distorting the wheel or damaging the inserts. A pneumatic powered Prior to mounting a tire on a wheel, the AMS impact wrench may be used, provided the must inspect the tire for condition and insure torque obtained does not exceed 25 percent of the inside of the tire is free of foreign materials. the specified final torque required for the wheel. The inner tube must be inspected for bead Use a currently calibrated torque wrench and chafing, thinning, folding, surface checking, heat tighten each bolt in increments of 25 percent of damage, fabric liner separation, valve pad separa- the specified torque value in a crisscross order tion, damaged valves, leaks, and other signs of until the total torque value required for each deterioration. The wheel assembly is inspected bolt in the wheel has been reached. in accordance with current directives. NOTE: When "Lubtork" is specified on the Mounting of divided (split) and demountable wheel half, coat all treads and bearing surfaces flangewheel assembliesiscovered here to ofboltheadswithMIL-T-5544antiseize acquaint the AMS with the basic procedures. compound. "Lubtork" must not be used on For specific information in regard to a given tire magnesium wheels. For magnesium wheels use assembly, consult the applicable Maintenance MIL-G-21164 lubricant. All excessive lubricant Instructions Manual. should be removed. MOUNTING DIVIDED (SPLIT) WHEELS. Prior to mounting tubeless tires, check the All wheel halves should be matched by year and tire sidewall for the word "Tubeless." Treat all month of manufacture as closely as possible. tires not so marked as tube type tires. When Wheel assemblies received from overhaul having mounting tubeless tires, install the valve stem matching overhaul dates on both rims should be (valve core removed) in the wheel assembly. maintained as matched assemblies. In the event a Removing the valve core prevents unseating of wheel assembly is received or made up of wheel the wheel seal by pressure built up when the tire halves having different overhaul dates, the wheel is installed. Insert one wheel half in the tire and overhaul should be based upon the earlier date. position the tire so that the balance marker on All wheels shouldfit together easily without the tire is located at the valve stem. Install the forcing. wheel seal, which has been lubricated with a When mounting a tube type tire, dust the light coat of MIL-G-4343 lubricant, on the outer tube with talcum powder and insert the tube in wheel half. Install the other wheel half and align the tire. The tire should be positioned so that the boltholes. Install bolts, washers, and nuts in the balance marker on the tube is located next the same manner as explained earlier for the to the balance marker of the tire. wheel assembly containing inner tubes. NOTE: The balance marker on an inner tube MOUNTING DEMOUNTABLE FLANGE is a stripe approximately 1/2 inch wide and 2 WHEELS.When mounting a tube type tire on a
251 AVIATION STRUCTURAL MECHANIC S 3 & 2 demountable flange wheel, the inner tube is tube type tires which are inflated to 150 psi or prepared and inserted in the tire in the same less. manner as on a split or divided wheel. The wheel A loss of pressure, not to exceed 5 percent, is then positioned on a flat surface with the will be experienced during the first 24 hours fixed flange down. Push the tire on the wheel afterinitialinflation of a new tire. This is assembly as far as it will go, guiding the valve attributed to normal tire stretch and the tire stem into the valve slot with the fingers. Install pressure should be adjusted accordingly. the demountable flange on the wheel, and secure INFLATION OF NEW TIRES.After the the locking ring in accordance with the assembly buildup of a tire and when the tire is ready to be instructions required by the applicable wheel inflated, it is placed within a safety cage for manual. inflation. A typical safety cage is shown in figure When mounting a tubeless type tire on a 9-17. The method of inflation used depends on demountable flange wheel, install the valve stem whether a tube or tubeless type tire is being (valve core removed) in the wheel assembly. inflated. Removing the valve core prevents unseating the Inflation of Tube Type Tires.Remove the wheel seal by pressure built up when the tire is valve .core and place the wheel assembly in the installed. The wheel seal is lubricated with the same lubricant and in the same manner as previously mentioned for split or divided wheel assemblies using tubeless tires. The wheel seal is installed on the flange sealing surface. Install the demountable flange on the wheel, and secure the locking ring in accordance with the assembly instructions required by the applicable wheel manual. Tire Inflation The AMS is required to have a thorough knowledge of servicing tires. The equipment used and proceduresforinflatingtiresare covered in chapter12. The actual inflation medium is covered in the following section. In the past, aircraft tires have been inflated with clean dry air. The trend now is from a clean dryairsourcetonitrogen.Nitrogen, (BB-N4 1 1B) type 1class 1, is preferred because oxygen in the air reacts with the tire rubber at high temperatures and pressure. This causes deterioration, reduces the tire life, and consti- tutes a blowout hazard. If circumstances dictate that air rather than nitrogen must be used, the air line from the compressor must be equipped with a trap to remove all water and oil. All high-pressure inflation sources must be equipped with reducing valves that limit the line pressure to 600 psi or 50 percent above the maximum tire inflation pressure, whichever is the lesser. Slippage marks must be painted on all newly AM.414 mounted helicopter tube type tires and other Figure 9-17.Safety cage for inflation of tires. 252 Chapter 9LANDING WHEELS, TIRES, AND TUBES
from the safety cage, and the cause of the leak determined. If a slow leak is detected, the air retention test should be extended to 24 hours. The tire should not be issued until remedial action is taken if the leakage exceeds 5 percent. Inflation of Tubeless Tires.Tubeless tires inflatedinthe same manner as previously explained for tube type tires except it is not necessary to inflate tubeless tires with the valve core removed.
RETREADING AND REPAIR The Navy considers all aircraft tires to be potentiallyretreadable.Usedaircrafttires should not be discarded or scrapped until it has been definitely determined that they are unfit for further use. All tires removed from aircraft should have the injuries marked with a wax crayon. The tire is then turned in to the Intermediate Main- AM.1219 tenance Activity (IMA) for screening. The IMA Figure 9-18.Remote inflator assembly. willdetermine ifthe tireis serviceable or nonserviceable and take the necessary action. safety cage. Attach a remote tire inflation gage Serviceable Tires assembly (figure 9-18) to the valve stem. Check to make sure the inner tube is not being pinched Serviceable tires are those judged suitable for between the tire bead and the wheel flange. continued service use by the tire shop personnel. Check demountable flange wheels to make sure They should be retained in service until the the demountable flange and locking ring are remaining tread at any spot is 1/32 inch thick or seated properly. Secure the safety cage door and to the limits of the tread wear indicators. inflatethetire:3its maximum operating Defects permitted are cut limits contained on pressure to seat the tire beads agairst the rim the tire sidewall or as listed in the technical flanges. Deflate the tire, install the valve core, manual,AircraftTires and Tubes, Nav Air and reinflate the tire to its maximum operation 0440-506. Cuts are permitted in the sidewall pressure. Allow thetireto remain atthis provided they do not penetrate to the cord body pressure for a minimum of 10 minutes. At the fabric. end of this 10-minute period, there should be no detectable pressure loss. Nonserviceable Tires If no pressurelossisdetected, the tire pressureisreduced to 50 percent of the Nonserviceable tires may be nonretreadable or maximum operating pressure or 100 psi, which- retreadable. ever is the lesser. The tire/wheel assembly is then NONRETREADABLE.Nonretreadable tires removed from the safety cage, a valve cap are coded for condemnation and forwarded to installed, and the assembly stored in a rack, the nearest Property Disposal Officer via the ready for issue. local Supply Department. The following inspec- If there is a significant pressure loss, the tire tion criteria must be used by the tire shop pressure is reduced to 50 percent of the maxi- personnel to determine .those tires that are mum operating pressure, the assembly removed nonretreadable:
253 . AVIATION STRUCTURAL MECHANIC S 3 & 2
1. Blowouts. cloth saturated in a soap and water solution. 2. Punctures extending through the entire Rinse well with tap water. carcassmeasuring morethan1/4inchin diameter/length on the outside and more dull Uneven Tread Wear 1/8 inch in diameter/length on the inside. 3. Loose, frayed, or broken cords evident on If a tire shows signs of uneven or excessive the inner tire surface. tread wear, the cause should be investigated and 4. Cord body fabric damage, visible to the the condition remedied before the tire is ruined. nakedeye withouttheuse of mechanical UNDERINFLATION.Underinflation causes devices. the tire to wear rapidly and unevenly at the NOTE: Exposure of cords on fabric rein- outer edges of the tread as shown in figure 9-19. forced tread tires (which is imprinted on the tire An underinflated tire develops higher tempera- sidewall) is permissible. tures during use than a properly inflated tire and 5. Kinked, broken, or exposed wire beads. this can result in tread separation or blowout 6. Tread separation and bulges exceeding I type failure. inch. OVERINFLATION.Overinflationreduces 7. Tires saturated with rubber deteriorating the tread contact area causing the tire to wear liquids. faster in the center as shown in figure 9-20. 8. Tires exposed to excessive heat. RETREADABLE.All tiresremoved from service which are not condemned are potentially repairable and must be returned to the Supply Department forretreading. The number of retreads a carcass may receive will to based solely on carcass integrity as determined by the applicable inspection criteria.
PREVENTIVE MAINTENANCE Debris on the runways ant: rirking areas causestirefailures and resultsin many tires being removed long before giving full life, as a result of cuts. It is theref6re important that such areas be kept clean at all times. When ground handling an aircraft, do not pivot with one wheel locked or turn sharply at slow speeds, as this not only scuffs the tread off, but also causes internal separation of tide c:Jrcic. Always be sure the aircraft is moving kfore attempting a turn. This allows the tile to roll instead of scrape. Particular care should be observed in prevent- ing oil, grease, hydraulic fluid, or other harmful materials from coming in contact with thz tires. During maintenance, when there is a chance that harmful materials may come in contact with the tires, they should be protected by covers. To AM.1220 clean ,ires which have come in contact with oil, Figure 9-19.Rapid tread wear caused by grease; or other harmful materials, use a brush or underinflation.
254 Chapter 9LANDING WHEELS, TIRES, AND TUBES
-...... AMILA11111111111111
A
AM.1221 Figure 9-20.--Rapid tread wear caused by overinflation.
Overinflation increases the possibility of damage to the cord on impact with foreign objects and AM.1222 arresting cables on the runway or flight deck. Figure 9.21.Rapid tread wear caused by misalignment MISALIGNMENT.Figure 9-21 shows rapid and uneven tire wear caused by incorrect camber. or toe-in. The wheel alignment should be cor- off and landing. 'This makes handling of the rected in accordance with the applicable aircraft aircraft difficult. manual to avoid further wear and mechanical problems. BALANCE.Correct balance of the tire, tube, Nylon Flat Spotting and wheel assembly is important. A heavy spot on an aircraft tire causes that spot to always hit If the aircraft stands in one place under a the groundfirstupon landing, resultingin heavy static load for several days, local stretch- excessive wear at the one spot and an early ing may cause an out-of-round condition with failure at that part of the tire. A severe case of the resultant thumping during takeoff and land- imbalance causes excessive vibration during take- ing.
255 AVIATION STRUCTURAL MECHANIC S 3 & 2
Dual Installations
On dual-wheel installations,tire should be VENT RIDGES matched inaccordancewithdimensions indicated in table 9-1. Tires vary somewhat in size between manufacturers and can vary a great deal after being used. When two tires are not matched, the larger one supports most or all of the load. Since one tire is not designed to carry this increase in load, a failure may result.
Table 9-1 --Tolerances for diameters of paired tires in dual installations.
Tire outside Maximum difference in AM. 1223 diameter outside diameters Figure 9-22.Inner tube vent ridges. Less than 1/8 inch circumference. The reinforcement extends a 18 inches minimum of 1/2 inch beyond that portion of 18 to 24 inches 1/4 inch the tube which contracts the rim. 25 to 32 inches 5/16 inch Type III inner tubes used at inflation pres- sures above 100 psi, and all type VII inner tubes, 33 to 40 inches 3/8 inch have radial vent ridges molded on the surface, as 41 to 48 inches 7/16 inch shown in figure 9-22, to relieve air trapped between the casings and the inner tube during 49 to 55 inches 1/2 inch inflation. 56 to 65 inches 9/16 inch Inner tube valves are designed to fit specific More than 65 5/8 inch wheelrims. However, specialvalve bending inches configurations or extensions to provide access to the valve stem when servicing the tire may be required.
STORAGE INNER TUBES Tubes should be stored under the same The purpose of the inner tube is to hold the conditions as that outlined for tires. New tubes air in the tire. Tubes are identified by the type should be stored intheir original containers. and size of the tire in which they are to be used. Used tubes should be partially inflated (to avoid creasing in storage), dusted with talc (to prevent IDENTIFICATION sticking) and stored in the same manner as tires. Each tube should be plainly marked to identify Tube types are designated the same as for the contents,size,type,curedate,and stock corresponding tires in which they are to be used. number. Under no circumstances should inner For example, a type I tube is designed for use in tubes be hung over nails or hooks. a type I tire. Tube size is the size of the tire the tube is designed to fit. INSPECTION Inner tubes required to operate at 100 psi or higher inflation pressures are usually reinforced Inner tubes should be inspected and classified with a ply of nylon cord fabric around the inside as serviceable or nonserviceable. Usually, leaks 256 Chapter 9LANDING WHEELS, TIRES, AND TUBES due to punctures, breaks in the tire, cuts, and thefollowing defects should be classified as the like, can be detected by the eye, but small repairable: leaks requirea water check. Complete sub- mersion in water is the best way to locate small 1. Bent, chafed, or damaged metal valve leaks. If the tube is too large to be submerged, threads. spread water over the entire surface and examine 2. Replaceable leaking valve cores. carefully for air bubbles. The valve stem and valve base should be swished around to break NON REPAIRABLE.Nonserviceabletubes anytemporaryseals.The tube should be with the following defects should be classified as checked for bent or broken valve sterns, also for nonrepairable: stems with damaged threads. 1. Anytear,cut,orpuncturewhich Serviceable Tubes completely penetrates the tube. 2. Fabricreinforcedtubeswithblisters Inner tubes should be classified as serviceable greater than 1/2 inch in diameter in the rein- if they are found to be free of leaks and other forced area. defects when inflatedwitha minimum of 3. Chafed or pinched areas caused by beads nitrogen required to round out the tube and or tire breaks. then immersed in water. 4. Valve stems pulled out of fabric base type tubes. Nonserviceable Tubes 5. Deterioration or thinning due to brake h ;at. Nonserviceable tubes may be repairable or 6. Folds or creases. nonrepairable. 7. Severe surface cracking. REPAIRABLE.Nonserviceabletubes with 8. No balance marker.
257 CHAPTER 10
TUBING, FLEXIBLE HOSE, AND CLAMPS
In this chapter we will discuss rigid tubing, FLUID LINE IDENTIFICATION flexible hose, and the line clamps that are used to support and bond rigid tubing to the aircraft Each fluid -tine in the aircraft is identified by structure. Modern day aircraft have hundreds of bands of paint or strips of tape around the line feet of tubing and flexible hose running through- near each fitting. These identifying media are out the wings and fuselage. The AMS is not applied atleast once in each compartment. responsible for maintaining the fluid systems in Various other information is also applied to the Navy aircraft, but in many instances he is called lines. upon to assist the AMH and AME in maintaining In most instances, lines are marked by the use their respective systems. Therefore a knowledge of tape or decals. On lines 4 inches and larger in of the materials, tools, equipment required, and diameter, lines in an oily environment, hot lines, the proper procedures to follow in fabricating and on some cold lines, tages may be used in and installing tubing, flexible hose, and line place of tape or decals. clamps is necessary. NOTE: On linesinengine compartments, Many lives have been lost in aircraft accidents where there is the possibility of tapes, decals, or caused by fluid line and/or fitting failure. The tags being drawn into the engine induction following quotes are typical of some found in system, the information can be applied as aircraft accident reports. follows: Type or print (ballpoint pen) the information on white paper or decal and place it "Hydraulic fitting cracked. Probable cause, in position on the tubing. Apply a length of overtorque of nut during line installation follow- clear,heat-shrinkablerubbertubing,MIL- ing system maintenance." R-46846 type V, over the area, 1/2-inch longer "Hole in utility system pressure line. Inves- than the label. tigation revealed chafing of pressure line by port Identification tape codes indicate the func- aileron control cable. Cause, support clamp not tion, contents, hazards, direction of flow, and reinstalledafter hydraulic pressureline was pressure in the fluid line. These tapes are applied replaced following system maintenance, thus in accordance with MIL-STD-1247. This Military allowing the pressure line to contact the control Standard was issued in order to standardize fluid cable." line identification throughout the Department of Defense. Figure 10-1 illustrates the method of "Flexible hose parted at end fitting. Cause, applying these tapes as specified by this stand- incorrect end fittings installed during fabrication ard. of replacement hose assembly by maintenance The function of a line is identified by use of a personnel." tape, approximately 1 inch wide, upon which NOTE: The quotes listed above point out word(s), color(s), and geometric symbols are just a few different maintenance errors that have printed. Functional identification markings, as caused or are suspected of causing aircraft provided in MIL-STD-1247, are the subject of accidents. international standardization agreement. Three-
258 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
CONTENTS PRESSURE
:60/ki;RESSED PHDAN PNEU MAIM #0 PSI W.:1044;-"*.sYr
DIRECTION HAZARD CODE OF FLOW IDENTIFICATION OF FUNCTION
AM.66 Figure 10-1.Fluid line identification application. fourths of the total width on the left side of the line identified by the word "TOXIC" contains tape has a code color or colors which indicate materials which are extremely hazardous to life one function only per color or colors. The or health. function of the line is printed in English across Anesthetics and harmful materials (AAHM). the colored portion of the tape; therefore, even All materials productive of anesthetic vapors and a non English-speaking person can troubleshoot all liquid chemicals and compounds hazardous or maintain the aircraft if he knows the code but to life and property, but not normally produc- cannot read English. The right-hand one-fourth tive of dangerous quantities of fumes, or vapors, of the functional identification tape contains a are in this category. geometric symbol which is different for every Physi:ally dangerous materials (PHDAN). A function. This is to insure that all technicians, line which carries material which is not danger- whether English speaking or not, who may be ous with in itself, but which is asphyxiating in colorblind may still be able to positively identify confined areas or which is generally handled in a the line function by means of the geometric dangerous physical state of pressure or tempera- design rather than by the color(s) or word(s). ture is identified by the marking "PHDAN." Figure 10-2isa listing,in tabular form, of Table 10 -I lists some of the fluids with which functions and theirassociated identification the AMS may be required to work and the media as used on the tapes. hazards associated wit,- each. The identification-of-hazards tape shows the hazard associated with the contents of the line. Tapes used to show hazards are approximately one-half inch wide, with the abbreviation of the RIGID TUBING hazard contained in the line printed across the tape. There are four general classes of hazards Rigid tubing assemblies are made up mainly found inconnection with fluid lines. These of aluminum alloy or stainless steel tubing. hazards are outlined in the following paragraphs. However, copper tubing is used in certain parts Flammablematerial (FLAM). The hazard of some oxygen systems. marking "FLAM" is used to identify all mate- Two aluminum alloys are in common use rialsknownordinarilyasflammablesor alloy 5052 may be used for lines carrying combustibles. pressures up to 1,500 psi and alloy 6061 for Toxic and poisonous materials (TOXIC). A pressures up to 3,000 psi.
259 AVIATION STRUCTURAL MECHANIC S 3 & 2
FUNCTION COLOR SYMBOL
Fuel Red 410. Rocket Oxidizer Green, Gray 2) Rocket Fuel Red, Gray 4) Water Injection Red, Gray, Red NO Lubrication Yellow IN
Hydraulic Blue, Yellow III Solvent Blue, Brown sworm. Pneumatid Orange, Blue Instrument air Orange, Gray It Coolant Blue OW Breathing Oxygen Green Air Conditioning Brown, Gray 1:.
Monopropellant Yellow, Orange lir Fire Protection Brown 4. De-Icing Gray Rocket Catalyst Yellow, Green Compressed gas Orange Ale Electrical Conduit Brown, Orange .k
Inerting . Orange, Green ++
AM.67 Figure 10-2.Functional identification tape data. As a general rule, exposed lines and lines 8 tubing is 8/16 or 1/2; etc. Wall thickness is subject to abrasion, intense heat, or extremely specified in thousandths of an inch. high pressures are made of stainless steel. Replacement tubing assemblies should be Flexible hose is generally used in connection fabricated from the same type materials as the with moving parts or where a line is subject to original part. Most aircraft Maintenance Instruc- considerable vibration. tions Manuals contain a table of acceptable substitutes which lists the original material and TUBING SIZES wall thickness and substitutes with wall thick- nesses for each. The tubing used in the manufacture of rigid tubing assemblies is sized by outside diameter TUBE FITTINGS (OD) and wall thickness. Outside diameter sizes are in sixteenth-inch increments, the number of Fittings for tube connections are made of the tube indicating its size in sixteenths of an aluminum alloy, steel, and corrosion-resistant inch. Thus, No. 6 tubing is 6/16 or 3/8 inch; No. steel (CRES). Fittings are made in many shapes 260 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
Table 101.Hazards associated with various fluids.
Contents Hazard
Air (under pressure) PHDAN Alcohol FLAM Carbon dioxide PHDAN Freon PHDAN Gaseous oxygen PHDAN Liquid nitrogen PHDAN Liquid oxygen PHDAN LPG (liquid petroleum gas) FLAM Nitrogen gas PHDAN Oils and greases FLAM AM.68 JP-5. FLAM Figure 143.Flared-tube fitting. Trichlorethylene AAHM
Flare less-Tube Fittings (MS)
The flareless-tube fitting shown in figure 10-4 consists of a sleeve and a nut. Notice that the tubing is not flared. (In order to effect a seal and forms, each designed to fulfillcertain between the tubing and the sleeve, an operation requirements. The following paragraphs cover called presetting is performed which is discussed two common styles of tube fittingsthe flared later inthis chapter). The connector has a (AN) type and the flareless (MS) type. Also counterbore, a portion of which is beveled 24 covered here is the metal lip-seal fitting, which is degrees. The seat in the connector forms a stop being used on the A-7 and A-4 aircraft. for the tube, and the beveled area causes the sleeve to sealthe connection as the nut is tightened. Flared-Tube Fittings (AN) There are two types of flareless-tube fittings in current use. The newer most widely used type The flared-tube fitting shown in figure 10-3 consists of a long sleeve (MS21922) and short consists of a sleeve and a nut. The sleeve fits nut . (MS21921). The older type consists of a directly over the tube, and one end is counter- shortsleeve(MS21918)andalongnut sunk at the same angle as the tubing flare. The (MS21917). nut fits over the sleeve, and when tightened, Flareless -tube, fittings are made of aluminum draws the sleeve and tubing flare tightly against and steel. The aluminum fittings are identified, the male fitting (connector) to form the seal. visually, by their green and yellow color, which The male fitting has a cone-shaped surface with is caused from the anodizing treatment. Steel the same angle as the inside of the flare. The fittings are cadmium plated, which makes, their sleeve supports the tube so that vibration does colors a silvery-white. not concentrate at the edge of the flare, and distributes the stresses over a wider area for Metal lip-Seal Fittings added strength. Flared-tubefittings are identified by their Metal lip-seal fittings (unions, reducers, and color. Aluminum alloy fittings are blue and steel plugs)areutilized throughout most brazed fittings are black. tubing type systems. Figure 10-5 illustrates a
261 AVIATION STRUCTURAL MECHANIC S 3 & 2
component. The conventional fitting requires the use of an 0-ring seal. The metal lip-seal EAT CONNECTOR SLEEVE NUT fittings utilize an integral metal contact seal (fig. 10-5). When the lip-seal fittings are installed in the AtUalttb\t port of a component and properly tightened, the metal contact seal area provides pressure-assist m I IIINI type sealing without the use of 0-rings. The two COMPONENTS types of fittings are completely interchangeable; however, thelip-sealfittings provide better systemintegrity because of the absence of 0-rings. AM.69 Figure 10-4.Flareless-tube fittings. REMOVAL AND REPLACEMENT OF metal lip-seal plug and union or reducer. These DAMAGED TUBING fittingsareidenticalinapplication to the conventionalfluidfitting common to most All tubing is pressure tested prior to installa- AM's. tion and is designed to withstand several times The major difference between conventional theoperating pressure to whichitwill be type fluid fittings and the lip-seal type is the subjected.If a tube bursts or cracks,itis manner in which they form a fluid pressure seal generallytheresultof excessivevibration, when installedintheport of a hydraulic improper installation, or from damage caused by
INTEGRAL METAL CONTACT SEAL
UNION OR REDUCER
PLUG STANDARD AN010050 BOSS
UNION OR REDUCER INSTALLED IN STANDARD AN010050 BOSS.
AM.933 Figure 10-5.Metal lip-seat fittings.
262 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
collision with an object.All tubing failures produce a square end, free from burrs. Tubing should be carefully studied and the cause of the may be cut with a tube cutter or a fine-tooth failuredetermined ifpossible. Replacements hacksaw. should be of the same size and material as the Correct use of the tube cutter is shown in original or an acceptable substitute. The ap- figure 10-6. The procedure is as follows: Place plicable Maintenance Instructions Manual usual- the tube in the cutter with the cutting wheel at ly lists acceptable substitutes for the original the point where the cut is to be made. Tighten material. the adjusting knob so as to apply light cutter pressure on the tube, then rotate the cutter LAYOUT OF LINES toward its open side, as shown in the illustra- tion. As the cutter is rotated about the tube, A damaged line should be carefully removed continue to apply light pressure to the cutting so that it may be used as a template or pattern wheel by intermittently tightening the knob. for the replacement item. If the old piece of Too much pressure applied to the cutting wheel tubing cannot be used as a pattern, an ac- at one time may deform the tubing or cause ceptable one can be made by placing one end of excessive burrs. After the cut is completed, a piece of soft iron wire into one of the fittings remove all burrs it.side and outside, then clean where the tube is to be connected. Form the the tube to make sure no foreign particles necessary bends in order to place the opposite remain. end of the wire into the other connection. When If a tube cutter is not available, a fine-tooth thetemplatesatisfactorilyspansthearea (32 teeth per inch) hacksaw may be used in between the fittings, it can be used as a pattern cutting tubing. A convenient method of holding to bend the new tube. tubing when cutting it with a hacksaw is to place Select a path with the least total degrees of the tube in a flaring block and clamp the block bend, as this reduces flow loss and simplifies in a vise. After cutting tubing with a hacksaw all bending. Use a path with all bends in the same saw marks must be removed by filing. After plane, if possible. Never select a path that requires no bends. A tube cannot be cut or flared accurately enough CUTTING so that it can be installed satisfactorily without A TUBE CUTTER'IN bends. Bends are also necessary to permit the tubing to expand or contract under temperature c..) changes and to absorb vibration. If the tube is small (under 1/4 inch) and can be hand formed, fQ casual bends may be made to allow for this. If I the tube must be machine formed, definite bends must be made to avoid a straight as- sembly. 0 Care must be taken to start all bends a cc reasonable distance from the end fittings, as the sleeves and nuts must be slipped back along the tube during the fabrication of flares and during inspections. In all cases, the new tube assembly should be so formed prior to installing that it is not necessary to PULL or DEFLECT the as- sembly into alignment by means of the coupling nuts.
TUBE CUTTING AM.70 The ideal objective, when cutting tubing, is to Figure 10-6.Tube cutting.
263 . AVIATION STRUCTURAL MECHANIC S 3 & 2
aircraftgrade,high-strength,stainless-steel tubing, as well as all other metal tubing. It is designed to be fastened to a bench or tripod, and the base is formed so as to provide a secure grip in a vise. The simple hand bender shown in figure 10-8 uses two handlesasleversto provide the mechanical advantage necessaryto bend the tubing, while this type tube bender employs a handcrank and gears. The forming die is keyed SECTION A-A to the drive gear and sect:i-ed by a screw (fig. 10-9). The forming die on the mechanical tube AM.71 bender iscalibrated in degrees similar to the Figure 10-7.-Properly burred tubing. radius block of the hand type bender. A length of replacementtubing may be benttoa filing, remove all burrs and sharp edges from the specified number of degrees or it may be bent to inside and outside of the tube as shown in figure duplicate the bend inthe damaged tube or 10-7. Clean out the tube and make sure no pattern. Duplicating the bend of a damaged tube foreign particles remain. or pattern is accomplished by laying the pattern on top of the tube being bent and slowly bending the new tube to the required bend. TUBE BENDING NOTE: Certain types of tubing are more elastic than others; therefore, it may be necessary to The objective in tube bending is to obtain a bend the tube past the required bend to allow smooth bend without flattening the tube. Tube for springback. bending is usually accomplished with one of the tube benders discussed in this section; however, in case of an emergency, aluminum tubing under TUBE FLARING 1/4 inch in diameter may be bent by hand. A hand flaring tool similar to that shown in Hand Tube Bender figure 10-10 is usually used for single flaring tubing. This tool consists of a flaring block or The hand tube bender (fig. 10-8) consists of grip die, a yoke, and a plunger or flaring pin. four parts handle, radius block, clip, and slide The grip die consists of two steel blocks hinged bar handle. The radius blockis marked in at one end and held in alignment by a pilot pin. degrees of bend ral,cing from 0 to 180. The slide A number of countersunk holes, varying in size bar handle has a mark which is lined up with the to conform with tubediameters and with zero mark on the radius block. The tube is countersinks matching standard flare angles and inserted in the tool; and after lining up the radii, are provided with half of the hole in each marks, the slide bar handle is moved around block. until the mark on the slide bar handle reaches The yoke fits over the two halves of the grip the desired degrees of bend on the radius block. die and has a setscrew which is used to lock the yoke at the desired position. The yoke also Mechanical Tube Bender serves as a centering guide for the plunger. The plunger is tapered to the same angle as the The tube bender shown infigure 10-9 is countersunk holes in the grip die. issued as a kit. The kit contains the equipment To flare the end of a tube with this tool, slip necessary for bending tubing from 1/4 inch to the fitting nut and sleeve onto the tube and 3/4 inch in diameter. place the tube in the proper size hole in the grip This tube bender is designed for use with die. (The end of the tube should extend 1/64 264 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
NOTE: THIS BENDER CAN 1111 SLIPPED OVER PARTIALLY CONNECTED TUBES AS IT IS 1 RAISE SLIDE IAN APPLIED AT DIRECT POINT OF BEND HANDLE UPWARD
RIGHI HAND
HANDLE
LIFT HAND 3PREPARE TO RAISE CLIP OVER TUBE
4 DROP CLIP OVER TUBE NOTE: ZERO MARK COINCIDES WITH MARK ON BLOCK
S WITH RIGHT HAND, CONTINUE LEFT HAND TO BEND TUBE TO DESIRED ANGLE BY PRESSING SLIDE BAR HANDLE AS SHOWN BELOW
MARK 6 TO REMOVE BENT TUBE, LIFT SLIDE BAR HANDLE TO ORIGINAL POSITION AND RAISE CLIP
RIGHT HAND
A BEND OF 90' DONE AS LEFT SHOWN IN ABOVE HAND STEPS
AM.72 Figure 10-8.Tube bending. inch above the surface of the grip die.) Center with a hammer or mallet. Turn' the plunger a the plunger over the end of the tube and tighten half turn after each blow and make sure it seats the yoke setscrew to secure the, tubing in the properly before removing the tube from the grip grip die and hold the yoke in place. The flare is die. After completing the. flare, inspect to insure made by striking the plunger several light blows that no cracks are evident.
265 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.73 Figure 104.Mechanical tube bending tool.
FINISHED DOUBLE DIE BLOCK FLARE clO
TOOL BODY
RAM
FINISH FLARE PUNCH
UPSET FLARE DIE BLOCKS PUNCH
AM.74 AM.75 Figure 10-10.Tube flaring tool (single flare). Figure 10-11.Tube flaring tool (double flare). 266 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
NOTE: The flared end of the tube should not ram lightly until a good scat is formed. Always be any larger than the largest diameter on the check the seat at intervals during the finishing sleeve being used. operation to avoid overseating. Double flares should be used on all 5052 aluminum alloy tubing up to 3/8-inch diameter. A finished double flareis shown in figure Steel tubing need not be double flared. The 10-11. double flare reduces cutting of the flare by CAUTION: When fabricating oxygen lines, overtightening and the consequent failure of the insure that alltools are kept free of oil and tubingassemblyunderoperatingpressure. grease. Aluminum alloy tubing used in low-pressure oxygen systems should always be double flared. PRESETTING FLARELESS Figure 10-11 shows one of the tools used in the TUBE FITTINGS manufacture of double flared tube assemblies. This flaring tool is issued as a kit. The kit Although theuse of flareless-tube fittings contains a tool body, a ram, and a finish flare eliminates all tube flaring, another operation, punch. Also included are a set of die blocks and referred to as PRESETTING, is necessary prior an upset flare punch for each size of tubing to installation of a new flareless-tube assembly. which may be flared with this kit. Presetting is necessary to form the seal between To double flare a tube assembly, prepare the the sleeve and the tube without damaging the end of the tube as shown in figure 10-7. Select connector. thepropersizedie blocks and proceed as Presetting should always be accomplished follows: with a presetting tool as shown in figure 10-12. These tools are machined from tool steel and 1. Place one-half of the die block in the hardened so that they may be used with a flaringtool body with the countersunk end minimum of distortion and wear. It is recom- towards the ram guide. mended that a mandrel be used during the sleeve 2. Installthe nut and skew, lay the presetting operation. A mandrel consists of a tubing in the die block with approximately 1/2 short piece of solid bar of any hard material inch protruding beyond the countersunk end. such as steel. It should have an outside diameter 3. Place the other half of the die block into of 0.002 to 0.005 inch less than the inside the tool. Close the latch plate and tighten the diameter of the tube. Using a mandrel assists in clamp nuts finger tight. attaining an improved sleeve cut during the 4. Insert the upset flare punch in the tool presetting operation. For field use, a short piece body with the gage end toward the die blocks. of drill rod of the proper diameter may be used NOTE: One end of the upset flare punch is as a mandrel. The mandrel should be long counter-bored or recessed to gage the amount of enough to support the tube inside diameter at tubing needed to form a double lap flare. Insert the sleeve cut and also at the point where the the ram and tap lightly with a hammer or mallet sleeve shoulder grips the tube. until the upset flare punch meets the die blocks NOTE: A connector may be ubed as a and the die blocks are firmly set against the stop presetting tool in an emergency. However, when plate on the bottom of the tool. connectorsareused aspresettingtools, 5. Tighten the latch plate nuts with a wrench. aluminum connectors should be used only once Tighten the nuts alternately, beginning with the and steel connectors should not be used more closed side to prevent distortion of the tool. thanfivetimes. The presetting operation is 6. Reverse the upset flare punch and insert it described in the following paragraphs. in the tool body. Insert the ram into the tool NOTE: There are two types of flareless-tube body and tap lightly with a hammer or mallet fittings in current use. The older type consists of until the upset flare punch contracts the die ashortsleeve(MS21918) and a long nut blocks. (MS21917). The newer type consists of a long 7. Remove the upset flare punch and ram. sleeve (MS21922) and a short nut (MS 21921). Insert the finishing flare punch and ram. Tap the The presetting operation for the two types
267 AVIATION STRUCTURAL MECHANIC S 3 & 2
sleeve over the tube, making certain that the pilot and the cutting edge of the sleeve point PRESETTING SLEEVE NUT toward the end of the tube. (See fig. 10-12.) If a TOOL mandrel is used, it should be inserted in the tube at this time. 2. Lubricate the threads of the presetting tool and the nut with the approved lubricant. Hydraulic fluid, Specification MIL-H-5606, is the approved lubricant for hydraulic lines; and pneumatic grease, Specification MIL-G-4343, is the approved lubricant for pneumaticlines. Refer to NA 01-1A-20, Aviation Hose Assembly and Tube Repair, for the approved lubricants for other systems. CAUTION: Hydraulicfluidor any other petroleum base lubricants must not be used as a thread lubricant for oxygen lines. 3. Place the tool in a vise and hold the tubing firm and squ :e on the seat in the tool. (The end of the tube must bottom firmly in the tool.) The 'Lwo`mai tube should be rotated slowly between the thumb and fingers while the nut is turned down SLEEVE PILOT SLEEVE until the sleeve seizes on the tube. When the tube no longer turns, the nut is ready for final tightening. 4. The final tightening force necessary to set the sleeve on the tube depends on the type of fitting. When presetting the older type fittings, tighten the nut (MS21917) 1 1/6 more turns for PRESETTING TOOL CUTTING EDGE allsizes of tubing and alltypes of tubing material. This force sets the sleeve (MS21918) on the tube. SEALING POINTS SPRING WASHER EFFECT When presetting the newer type fitting the longsleeve(MS21922) and theshort nut (M521921)the required tightening force varies. If a mandrel is used, the final tightening force varies with the size of the tubing. If a mandrel is not used, the tightening force varies with the size, wall thickness, and material of the tubing. Tables of these tightening forces (turn values) are presented in NA 01-1A-20. These tables AM.76 should be consulted when presetting this type Figure 10-12.Presetting flareless-tube assembly. fitting. The final tightening force permanently as- sembles the sleeve to the tube. Sleeves should differs to some extent. These differences are not be removed from the tube and reused under pointed outasapplicableinthe following any conditions. discussion. After presetting (fig. 10-13), the nut should 1. Cut the tubing to the correct length, with be uncoupled from the presetting tool, and the the ends perfectly square. Burr the inside and sleeve and tube inspected for the following: outside of the tube. Slip the nut and then the 1. The sleeve cutting lip should be embedded 268 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
4. The sleeve should be slightly bowed and rotation of the sleeve is permitted. A 1/64-inch
SLEEV PILOT SLEEVE lengthwise movement of thesleeveisalso X Y permitted. 5. As a final check to determine that the IhZ-1,0461* fittingis properly preset,it should be proof tested at a pressure equal to twice the intended 1 working pressure.
TUBE INSTALLATION OF TUBE ASSEMBLIES Before a tubing assembly is installed in an AM.703 Figure 10-13.Preset sleeveflareless-tube fitting. aircraft, it should be carefully inspected. Dents and scratches should be removed (if possible without weakening the tube) prior to installa- into the tube outside diameter approximately tion. The proper nuts and sleeves should be 0.003 to 0.008 inch (distance (X) in figure installed and a proper fit obtained where the 10-13), depending on the size and material of tubing is flared. Flareless assemblies should be the tubing. As shown, a lip of material will be checked for proper presetting. Each tube as- raised under the pilot. The pilot of the sleeve sembly should be proof pressure tested to twice. should contact or be quite close to the outside its operating pressure prior to installation. The diameter of the tube. (See distance (Y).) The tubing assembly should be clean and free from tube projection from the pilot of the sleeve to all foreign matter. the end of the tube (distance (Z)) should be The nuts should be hand screwed to the mating approximately as listed in table10-2. These connector,thentightenedwith the proper figures will vary with wall thickness for a given wrench. The tubing assembly should not have to size. be pulled into place with the nut, but should be 2. A slight collapse of the inner diameter of properly aligned prior to tightening. the tube at the sleeve cut and at the shoulder is Tubing which runs through cutouts should be permissable. installed with care so that it will not be scarred 3. The sealing surface of the sleeve must be when worked through the hole. If the tubing smooth and free from nicks and scratches. assembly islong, the edges of any cutouts should be taped before the tubing is installed. It is important to tighten tube fitting nuts Table 10-2.Distance from sleeve to tube end. properly. A fitting wrench or open end wrench should be used when tightening tube con- nections. NOTE: Plieis should never be used to tighten tube connections. Tube size Approximate tube projection
. (inches) Flared-Tube Assemblies 3/16 764 Correct and incorrect methods of installing' 1/4 7/64 flared-tube assemblies are illustrated in figure 5/16 5/32 10-14. Proper torque values are given in tables 3/8 11/64 10-3 and 10-4. It must be remembered that 1/2 3/16 these torque values are for flared-tube fittings 5/8 13/64 only. 3/4 7/32 If an aluminum alloy tube assembly leaks 1 15/64 after tightening to the required torque, it must not be lightened further. Overtightening may severely damage or completely cut off the
269 . AVIATION STRUCTURAL MECHANIC S 3 & 2
DO NOT DEFLECT INTO PLACE; REPLACE TUBE ASSEMBLY INCORRECT WILL DAMAGE FLARE OR THREADS, OR CAUSE SLEEVE TO CRACK' UNDER VIBRATION TIGHTENED
INCORRECT MAY PULL OFF OR ) DISTORT FLARE IF TIGHTENED
CORRECTLY FITTED AND TIGHTENED
9.025 CLEARANCE BETWEEN FLARE AND SHOULDER BEFORE TIGHTENING
AM.77 Figure 10-14.Correct and incorrect method of installing flared fittings. tubing flare or may result in damage to the CAUTION: A nut should never be tightened sleeve or nut. The leaking connection should be when there is pressure in the line, as this will disassembled and the fault corrected. Common tend to damage the connection without adding faults are as follows: any appreciable torque to the connection. I. Flare distorted into the nut threads. 2. Sleeve cracked. Flareless-Tube Assemblies 3. Flare out of round. 4. Flare cracked or, split. Wheninstallingflareless-tubeassemblies, 5. Inside of flare rough or scratched. inspect to insure that no scratches or nicks are 6. Connectormatingsurfaceroughor evident and that the sleeve is properly preset. scratched. Lubricate the threads of the nuts and con- 7. Threads9fconnectorornutdirty, nectors with hydraulic fluid. Place the assembly damaged, orbroken. in the proper position in the aircraft and finger If a steel tube assembly leaks,it may be tighten clamps, brackets, supports, and nuts. tightened 1/6 turn beyond the noted torque in The tubing ends should fit snugly in the con- an attempt to stop the leakage; then if unsuc- nectors and require little pressure to hold them cessful, it must be disassembled and repaired. in place. Undertighteningofconnectionsmay be CAUTION: Hydraulic fluid must not be used serious, as this can allow the tubing to leak at to lubricate fluid line connections in oxygen the connector because of insufficient grip on the systems. flare by the sleeve. The use of a torque wrench Use the torque values listed in table 10-5 will prevent under, thtening. whenever possible while tightening flareless nuts.
270 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
Table 10-3.Torque limits for flared tube fittings.
Torque For AN818 Nut (inch-pounds)
Tubing outside Aluminium Alloy Tubing Steel Tubing Diameter Flare AND10061 or AND 10078 Flare AN D10061 (inches) With Aluminium Nuts With Steel Nuts
Min Max Min Max
1/8 20 30 75 85 3/16 25 35 90 100 1/4 40 65 135 150 5/16 60 80 180 200 3/8 75 125 270 300 1/2 150 250 450 500 5/8 200 350 650 700 3/4 300 500 900 1000 500 700 1200 1400 1-1/4 600 900 1500 1800 1-1/2 600 900 2000 2300 1-3/4 750 1050 2600 2900 2 800 1100 3200 3600
Table 10-4.Torque values for double flared type be impossible to run the nut down with the coupling nuts (ox'igen system fittings). fingers, use a wrench, but be alert for the first signs of bottoming. It is important that the final tightening commence at the point where the nut just begins to bottom. With a wrench, turn the nut 1/6 turn (one flat Tube OD Torque on a hex nut). Use a wrench on the connector to (inch) (inch-pounds) prevent it from turning while tightening the nut. Working torque Maximum torque After the tube assembly is installed, the system should be pressure tested. Should a connection 5/16 100 125 leak,itis permissible to tighten the nut an additional 1/6 turn (making a total of 1/3 turn). 3/i 200 250 If, after tightening the nut,a total of 1/3 turn, !-....kagestillexists, the assembly shouldbed 1/2 300 400 removed and the components of the assembly inspected for scores, cracks, presence of foreign material, or damage from overtightening.
NOTE: Overtightening aflareless-tube nut Iit is not possible to use a torque wrench, use drives the cutting edge of the sleeve deeply into t e following procedure for tightening nuts. the tube, causing the tube to be weakened to the Tighten the nut be hand until an increase in point where normal in-flight vibration could r sistance to turning is encountered. Should it cause the tube to shear. After inspection (if no
271 AVIATION STRUCTURAL MECHANIC S 3 & 2
Table 10-5.Torque values for flareless fittings.
WRENCH TORQUE FOR 304 1/8 H STEEL TUBES Tube Wrench torque outside diameter Wall thickness inch-pounds 3/16 0.016 90-110 3/16 0.020 90-110 1/4 0.016 110-140 1/4 0.020 110-140 5/16 0.020 100-120 3/8 0.020 170-230 3/8 0.028 200-250 1/2 0.020 300-400 1/2 0.028 400-500 1/2 0.035 500-600 5/8 0.020 300-400 5/8 0.035 600-700 5/8 0.042 700-850 3/4 0.028 650-800 3/4 0.049 800-960 1 0.020 800-950 1 0.065 1600-1750 WRENCH TORQUEFOR 304-1A or 3471ASTEEL TUBES
3/8 0.042 145-175 1/2 0.028 300-400 1/2 0.049 500-600 1 0.035 750-900 WRENCH TORQUE FOR 6061-T6 or T4 TUBES 1/4 0.035 110-140 3/8 0.035 145-175 1/2 0.035 270-330 1/2 0.049 320-380 5/8 0.035 360-440 5/8 0.049 425-525 3/4 0.035 380-470 1 0.035 750-900 11/4 0.035 900-1100
discrepancies are found), reassemble the con- Brazed Hydraulic nections and repeat the pressure test procedures. Tube Assemblies CAUTION: Do not in any case tighten the nut beyond 1/3 turn (twoats on the hex nut); Brazed hydraulic tubing systems are appearing thisisthe maximumt efitting may be in many of the later model aircraft within the tightened without the possi lility of permanently Navy. The brazed hydraulic tubing system damaging the sleeve and tube. includes a multi-branch feature which results in 272 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
TUBING
(A)
NUT AND SLEEVE (TYP) ( A )
AM.932 Figure 10-15.Brazed hydraulic tubing assembly.
fewerthreadedconnectionsandthenear tion are covered in Structural Hardware, NavAir elimination of 0-ring seals. A typical example of 01-1A-8. a brazed hydraulic assembly is provided in figure Overtightening of the B-nut on the flareless 10-15. Brazed tubing assemblies are made of type fitting used to connect most brazed tubing rigid corrosion-resistant steel and assembled with assemblies usually results in damage to the sleeve sleeves and coupling nuts. Individual segments of and consists of a necking down or swagging of the assembly are generally identified by separate thetip.This necking down can usually be part number and dash number and are brazed corrected by the use of a sleeve sizing punch together into an assembly. On some aircraft such assembly as 'illustrated in figure 10-16. Because astheA-4F,adirection-of-flowarrowis of the malleability of the sleeve material, sizing electroetched on each individualegment of can be accomplished several times before the each tube assembly. prospect of material failure would require re- Maintenance of brazed tubing is limited to placement of that segment. identificationmarkingmaintena ce,sleeve SLEEVE SIZING.The sleeve sizing proce- sizing, segment repair, or comple assembly dure can be accomplished without removing the replacement. Tubing identificationaintenance line assembly from the aircraft, space permit- consists of installing color band tape on new ting. The tube assembly is disconnected and tubing assemblies and on existing assemblies drained, then the end of the tubing assembly to where the color bands have become lost, worn, be sized and the threaded body on the punch or illegibly. The requirements, location, and assembly are lubricated with hydraulic fluid. precautions for installing color band identifica- Connect the B-nut on the end of the tube
273 AVIATION STRUCTURAL MECHANIC S 3 & 2
NUT CAP PUNCH openings on the tube assembly except two, one 0-NUT at the highest and one at the lowest openings.
SLEEVE Pour solvent (P-D-680) into the highest opening to remove all hydraulic residue. Connect 20'to 40 psi of air pressure upstream of any cutting, burring, and sleeve presetting operations and SLEEVE AND TUBE WALL COLLAPSED insure that the coupling downstream is open for
PUNCH RETRACTED purge air exit. This will prevent entry of metal particles in the hydraulic system. The proce- dures for repair of such tubing assemblies may NUT CAP BODY B- NUT vary slightly in the various MIM's. Following PUNCH EEVE repair, the assembly must be tested. V .4 t,k\, ,/ TUBE low Oxygen System Tube Assemblies
SLEEVE AND TUBE WALL COLLAPSED Care must be taken at all times to keep the tubing clean and free of foreign matter during PUNCH EXTENDED installation. Thread antiseize compounds and tapes should not be used on flared tubing fitting threads. Antiseize tape (MIL-T-27730A) may be AM.934 used on tapered pipe fitting threads. Figure 10-16.Sleeve sizingflareless fitting. Pipe threaded fittings should be started by hand. A torque wrench should be used to tighten allpipe threaded fittings. The torque assembly to the threaded part of the body on values for pipe threaded fittings are listed in the punch assembly fingertight. Using a wrench table 10-6. to hold the body, tighten the B-nut 1/6 turn CAUTION: The importance of the following (one hex side) beyond fingertight. Next, still cannot be overemphasized: It is imperative that holding the body of the pund, assembly, slowly all oxygen equipment, lines, and fittings be kept turn the cap on the punch assembly until the free from GREASE, DIRT, OIL, HYDRAULIC punch is bottomed in the extended position. FLUID, AND LEAKS. Leakage in oxygen sys- Reverse the wrench action to withdrawthe tem connections should be eliminated since the punch. Disconnect the punch assembly from the leakage rate may increase with time and vibra- tube assembly and inspect the sleeve. Slight tion. collapse of the tube assembly is permissible. No nicks or scoring marks are allowed on the sleeve, and no movement of the sleeve except rotation FLEXIBLE HOSE ispermissible. Pressuretest the repaired as- sembly for leakage as specified in the applicable Flexible hose is used in connecting moving MIM. If the pressure test is positive, reconnect parts with stationary parts and in locations the tube assembly to the aircraft system, air- subject to severe vibration. It is heavier than bleed the lines, and service the hydraulic system. aluminum alloy tubing and deteriorates rapidly; SEGMENT REPAIR.Whenever a segment or therefore,itisused only where absolutely a fitting of a brazed tubing assembly has been necessary. The two types, rubber and Teflon damaged, it can generally be repaired. Figure flexible hose, are discussed in the following 10-17 provides an example of typical segment paragraphs. repairs to a damaged assembly. With all pressure relieved in the system to be repaired, disconnect RUBBER allcouplings. Cap or plug allopenings on adjacent lines and components to prevent loss of Flexible rubber hose consists of a seamless fluidandcontamination. Caporplugall synthetic rubber inner tube covered with layers 274 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
DAMAGE DAMAGE TO BRAZED TEE
DAMAGE TO BRAZED TEE
DAMAGE TOO CLOSE TO BRAZED TEE FOR SPLICE REPAI
BRAZED TUBE ASSEMBLY
DAMAGE
-EXISTING FITTING
EXISTING TUBE TYPICAL DAMAGE AREAS ASSEMBLY
REWORKED TUBE ASSEMBLY NEW FITTING NEW FITTING ASSEMBLY NEW FABRICATED TUBE SPLICE ASSEMBLY (4"" NEW FITTING .411, ISO 4111111111114114 NEW FITTING /
REWORKED TUBE ASSEMBLY
REWORKED TUBE ASSEMBLY
N...-REWORKED TUBE ASSEMBLY
REWORKED TUBE ASSEMBLIES
NEW FITTING
EXISTING FITTING
NEW FABRICATED TUBE SPLICE ASSEMBLY
fiEWORKED TUBE ASSEMBLY TYPICAL REPAIR AREAS
AM.935 Figure 10-17.Brazed tubing segment repair. of cotton braid and wire braid, and an outer hose whichiscommonly used in medium- layer of rubber impregnated cotton braid. It is pressure applications. This hose is identified by a provided in low-pressure, Medium-pressure, and Military Specification number, the hose size, the high-pressure types. Figure 10-18 illustrates the quarter year and year of manufacture, and the
275 AVIATION STRUCTURAL MECHANIC S 3 & 2
Table 10.6. Torque values for pipe threaded fittings fittings and are fabricated only by commercial (oxygen system). activities and intermediate or depot maintenance levelactivities,because of the specialtools required.Medium-and low-pressure hoseas- semblies are equipped with detachable type end Torque (inch - pounds) fittings (described later) and may bi-: fabricated at the intermediate maintenance level. Pipethread (inch) Minimum Maximum FABRICATION AND REPLACEMENT
1/8 40 150 Flexible hose must be replaced if peeling, 1/4 60 200 flaking of the hose cover, or exposure of the 3/8 100 400 fabric reinforcement to the elements occur. Whenfailureoccursinaflexiblehose equipped with swaged end fittings, the unit is generally replaced without attempting a repair; that is, the correct length of hose, complete with hose manufacturer's symbol. This information is factory-installed end fittings,isdrawn from stenciled on the hose at intervals of not more supply. than 9 inches the entire length of the hose. The Whenfailureoccursinlow-pressureor stenciled information indicates the natural lay of medium-pressure hose equipped with detachable the hose. type end fittings, the replacement unit is usually The size of flexible hose is determined by the fabricated by the AIMD. Undamaged end fit- inside diameter (ID) and indicated by a number- tings on the old length of hose may be removed ing system identical to that used with rigid and reused; otherwise, new fittings must be tubing. Therefore, the fittings used on No. 6 drawn from supply along with a sufficient length hose will be the same size and have the same of hose. threads as those used on No. 6 (3/8 inch) tubing. NOTE: Inspect bulk hose prior to use to High-pressurehoseisavailabletothe insure that its shelf life has not expired. operating activity in complete assemblies only. Figure10-19illustrates onetype of de- These assemblies are equipped with swaged type tachable end fitting. This fitting is intended for
TWO COTTON BRAIDS - IMPREGNATED WITH SYNTHETIC COMPOUND
Y4011FH0HEASizigoilc320n
4> 4P ...1446. 40. #4,...',1,44*.44t14/.ft s
YELLOW SINGLE WIRE BAND SYNTHETIC RUBIBER INNER TUBE
AM.79 Figure 10-18.Medium-pressure hose.
276 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
SOCKET NIPPLE NUT
ASSEMBLED aimmEns FITTING
IWO
PART NO. 597
AM.80 ASSEMBLY TOOL KIT Figure 10.19. Sleeve type flexible hose fitting (SIZES-3 THRU 12 ) (MS-245871.
AM.81 use with medium-pressure hose which conforms Figure 10.20. Medium - pressure hose assembly tool kit toSpecification MIL-H-8794. Thisfittingis designed for use in flared-tube systems. Other hose fittings which are designed to be used with instructions contained in the applicable Mainte- flareless-tube fittings are also available. nance Instructions Manual. In cases where proof test pressures are not included in' the aircraft Assembly of Sleeve Type Fittings Maintenance Instructions Manual, refer to Avia- tion Hose Assembly and Tube Repair, NavAir A tool kitis available for assembling the 01-1A-20. Table 10-7 lists the prooftest pressures MS-24587 fittingsto MIL-H-8795 (medium- for a few sizes of medium-pressure (MIL-H- pressure) hose. Figure 10-20 illustrates the hose 8795) hose when assembled with MS-24587 assembly tool kit, which contains the assembly fittings for use in aircraft hydraulic systems. tools for use on the smaller sizes (3/16 through 3/4 inch) of hose. If a tool kit is not available, the corresponding size AN-815 adapter may be Installation of Flexible used. Hos: Assemblies Figure10-21illustratesthestepsinas- sembling the MS-24587 fitting, using the proper Flexible hose must not be twisted on installa- size assembltool from the hose assembly tool tion, since this reduces the life of the hose kit. considerably and may cause the fittings to After assbly, always make sure all foreign loosen as well. Twisting of the hose can be matter is reoved from the insi e of the hose by determined from an identification stripe running blowing outith compressed a.. along its length, or as in the case of medium- All shopl-assembledflexiblhose must be pressure hose (shown in figure 10-18) by the proof tested after assembly. Proof testing is stenciled information that is used to identify the accomplished by plugging or c pping one end of hose. the hose and applying pressure to the inside of The minimum bend radius for flexible hose, the hose assembly. varies according to size and construction of the Proof testing of shop fabricated hose assem- hose and the pressure under Which the hose will blies should be accomplished in accordance with operate. Tables and graphs showing minimum 277 AVIATION STRUCTURAL MECHANIC S 3 & 2
(A) (8) (C)
(0) (E)
AM.82 A. Clamp the hose in the vise and cut the required and exposed. Lubricate the inside of the hose and the length with a fine tooth hacksaw. ripple threads with hydraulic fluid or light lubricating B. Secure the socket in the vise. Turn the hose oil. counterclockwise intothe socket untilit bottoms. E. Using a wrench on the assembly tool, screw the Unscrew 1/4 turn. nippleinto the socket and hose. Excercise care to C. Insert the nipple in the nut. Install the proper prevent the hose from turning. A clearance of 1/32 to size assembly too! and tighten, using two wrenches. 1/16 inch between the nut end socket is required so that D. Place the socket in the vise with the threaded the nut will swivel. Remove the assembly tool. Figure 10.21. Assembly of MS-24587fitting to medium-pressure flexible hose.
Table 10-7.Proof test pressures for medium-pressure hose assembled with MS-24587 fittings.
Hose size Operating pressure Proof pressure Burst pressure number (psi) (psi) (psi)
4 3,000 6,000 12,000 5 3,000 5,000 10,000 6 2,000 4,500 9,000 8 2,000 4,000 8,000 10 1,750 3,500 7,000 12 1,500 3,000 6,000
278 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
bend radiiforalltypes of installations are support enough to prevent bending and kinking. provided in Aviation Hose Assembly and Tube 4. Do not permit flexible hose to impinge on, Repair, NA- 01- IA -20.Bends which are too and thus possibly deflect, rigid supporting lines. sharpwillreduce thebursting pressureof 5. Allow a slight slack in the hose line to flexible hose considerably below its rated value. accommodate changes in length that willoccur Flexible hose should be installed so that it when pressure is applied. will be subject to a minimum of flexing during 6. Do not straighten a bent hose that has operation. Hose must be supported at least every taken a permanent set. 24 inches. Closer supports are desired. 7. Do not hang, lift, or support objects from A flexible hose must never be stretched tight Teflon hose. between two fittings. About 5 to 8 percent of its total length must be allowed as slack to provide Maintenance freedom of movement under pressure. When Teflon hose, like all aircraft parts, has definite under pressure, flexible hose contracts in length wearability limits. The chafing caused by hose and expands in diameter. rubbing against other surfaces, for instance, has undermined many parts and systems. Disaster TEFLON consequent to such wear can be averted only Teflon hose isa flexible hose designed to through frequent inspection and maintenance by meetthe requirements of higher operating alert maintenance and quality assurance person- temperaturesandpressuresinpresent-day nel. weapon systems. Teflon hose can generally be INSPECTION.Whereas allrubber aircraft used in the same manner as rubber hose. hose must be inspected for aging and associated Teflon hose consists of a tetrafluorethylene deterioration immediately prior to installation, resin which is precessed and extruded into tube Teflonhose,beingcomparativelyinert,is shape to a desiredsize.Itis covered with exempt from shelf-life control. However, Teflon stainless steel wire which is braided over the hose, assemblies must be visually inspected for tube for strength and protection. The advantages leakage, abrasion, and kinking according to the of this hose are its operating temperature range aircraftinspectionrequirements inthe ap- (-67°F to +450°F), its chemical inertness to all plicable Maintenance Instructions Manuals. The fluids normally used in hydraulic and engine presence and extent of the following possible lubrication systems, and its tong life. At this defects must be determined. time, only medium-pressure and high-pressure Kinking.Kinking is an imperfection induced types are available and are complete assemblies in Teflon when it is bent at a closer angle (or with factory-installed end fittings. These fittings shorter radius) than its characteristics allow. may be either the detachable type or the swaged This is a common cause of failure, because type. When failures occur, replacement must be Teflon hose tends to assume the shape of the made on a complete assembly basis. position in which itis installed and becomes The size of Teflon hose is determined in the semipermanently" set or "preformed" in these same way the size of rubber hose is determined. configurations. These so-called preformed hoses Teflon hose, like rubber hose, has definite kink easily and their walls are severely weakened limits and particular characteristics that demand if they are excessively bent or twisted or if they understanding and attention in the general han- are permitted to follow their natural tendencies dling during installation and removal. To insure to revert to their orientations. They must be its satisfactory fundtion and reduce the likeli- handled very carefully while being removed and hood of failure, the following rules should be should be tied with wire that will hold them in observed when working with Teflon hose: shape pending reinstallation. Excessive Cold Flow.Cold flow is the name I. Do not exceed recommended bend limits. giventhe deep permanent, impressions and 2. Do not exceed twisting limits. cracks in the hose cover caused by the pressure 3. Clamp the hose assemblies at leastevery of the hose clamps. Replace hose when cold 24 inches (more closelyif possible) to lend flow becomes too deep. 279 AVIATION STRUCTURAL MECHANIC S 3 & 2
Weather-Checking.--Weather-checking, the oc- Separation of Outer Cover.When the cotton- currenceofnumerousfinecrackscaused braid or rubber coverings of metal-reinforced by exposuretovarious weather conditions hose become loose, frayed, or chafed to the over extended periods, causes no serious dam- point that the metal reinforcement is exposed or age as long as it does not expo:,c the fabric of damaged, replace the hose. If a hose shows some thehosecover.However, weather-checking wear but the metal is not exposed or damaged, deepened to the point of exposing this fabric wrap the frayed or chafed areas inflexible, can contribute to the weakening and eventual electrical-insulation sleeving and secure it over failure of hose. the hose with support clamps. To examine the extent of weather-checking, Wire-BraidDamage.Wire-braid damageis flatten the walls of the hose together, with force considered excessive when two or more wires in if necessary. If the cord fabric can be seen at any a single plait or six or more in an assembly (or point, replace the hose. Replace the hose also if lineal foot when assemblies are longer than 12 radial cracks at the end of the hose are deeper inches) are broken. Broken wires, where kinking than one-eighth inch or are halfway from the of Teflon hose is suspected, are felt as sharp ends of the hose to the clamps. dents or twists in the braid. Internal Cracking.Fuel hoses, both Teflon CAUTION:Whenperformingwire-braid and rubber, dry out and crack when they lose damage check, the Teflon hose must always be the placticizer that keeps them pliable. Hoses handled with great care so that the wire-braid remain pliable while in active use with gasoline damage does not injure the hands. flowing through them but lose their plasticizers CLEANING.Teflon hoseisnonabsorbent when the fuel is drawn off. and nonadhesive, and is usually unaffected by Therefore, fuel lines of previously used air- fuels,lubricatingoils,coolants, and solvents craftthat are to be returned to service after used around aircraft.Itiseasily cleaned in extended storage must be inspected for internal oleumspirits,kerosene,techlorethylene, or cracking. Those showing internal cracks, which synthetic detergents. When -lipped in or flushed are best revealed by pressing thz hose with the with thecleaning solution, the hose merely fingers to widen imperfections -hould be re- needs a slight brushing to remove the surface placed, while those s'.. ...Ale cracks at debris. either end are co. :tiered satisf story through- WARNING: Because some solvents are highly out. flammable and some toxic, proper precautions
BULKHEAD LINE CLAMPS FITTINGS CLAMP BLOCK,
«manumil War
AP
MIIIINAP0E1
AM.415 Figure 10-22.Methods used to secure fluid lines.
280 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS must be taken when they are used. Prolonged inhalation of fumes must be avoided. STORAGE.When storing Teflon hose, be sure to: 1. Cap or plug the ends of all hose assemblies with metal or plastic plugs. 2. Tape hose ends to prevent wire flarcout. 3. Store hose in straight position if possible. When it is necessary to coil hose, use the widest coil possible. BONDING CLAMPS CLAMPS As stated earlier inthis chapter there are hundreds of feet of tubing and flex hose running throughout the aircraft structure. These fluid lines are routed to follow the configuration of the aircraft structure to provide support for the lines. Clamps, bulkhead fittings, clips, brackets, and clamp blocks not only secure the lines to theadjacent structure, butalsoprovidea dampening effect to prevent harmful vibration. Fluid lines must be kept separated from the aircraft structure and other lines to prevent chafing. Chafizg (rubbing) of the lines can cause failure of the system. As the lines rub against each other or the aircraft structure, the wall thickness of the tubing is diminished until it can no longer withstand the fluid pressure, and the SUPPORT CLAMPS ( CUSHIONED) line ruptures. The three most common methods of securing fluid lines are shown in figure 10-22. AM.78 Figure 10-23.Bonding and support damps. INSTALLATION OF CLAMPS While performing maintenance actions the AMS may be required to remove clamps and/or Support clamps should be installed at 15-inch clamp blocks. In all cases, unless directed by intervals and as close to tubing bends as possible. Aircraft Changes, Bulletins, etc., the clamp(s) In no case should clamps be installed at intervals and/or clamp block (x) with all of the necessary greater than 20 inches. hardware (washers, spacers, nuts, screws and/or When tubing is supported to a structure or bolts) must be reinstalled. other rigid member, a minimum clearance of CAUTION: Do not allow any dropped hard- 1/16 inch must be maintained with the structure ware toremain lying in the aircraft upon or member. A minimum clearance of 1/4 inch completion of maintenance actions. must be maintained betweenthetubing and The most abused and neglected are the line adjacent rigid structure or moving components. clamps which areusedtoproperly bond Extra support clamps may be used in any (provide a path for static electricity) and sup- installation to prevent vibration and chafing, or port rigid tubing and flexible hose. Figure 10-23 to provide line clearance. shows both the plain bonding clamps and the Figure 10-24 illustrates six ways to secure cushioned steel clamp. The cushioning material fluid lines to each other using support clamps to may be either rubber or Teflon. maintain line clearance and prevent chafing due
281 AVIATION STRUCTURAL MECHANIC S 3 & 2
ADAPTER
(C)
D) IF)
AM.416 Figure 10.24.Securing lines using support clamps. to vibration. In view (A) an adapter is used to fluid lines properly. maintain the desired line clearance. View (B) Figure 10-25 shows a flexible hose secured to illustrates the use of a spacer, and views (C), (D), the aircraft structure. The lower view shows (E), and (F) show the ust of support clamps what could happen if too large a clamp were positioned in such a manner as to separate the used.
282 Chapter 10TUBING, FLEXIBLE HOSE, AND CLAMPS
WRONG
ABRASION
CLAMP TOO LARGE
ABRASION
AM.417 Figure 10-25.Installation procedures (right and wrong).
283 CHAPTER 11
CORROSION CONTROL
CORROSION tion of relatively pure metal from its ore and the addition of other elements (either metallic or Modern high-speedaircraftarc dependent nonmetallic) to form alloys. Alloying consti- upon the structural soundness of the metals tuents are added to base metals to develop a which make up the largest percentage of their variety of useful properties. For example, in thousands ofparts.The greatestthreatto aircraft structural applications, high strength-to- structuralintegrity of naval aircraftis metals weight ratios are the most desirable properties in corrosion. With higher strength demands being all alloys. made of aircraft metals and the closer tolerances After refining, regardless of whether o_ not of flight safety demanded, these aircraft would alloyed,basemetals possess a potential or rapidly become inoperative without regular anti- tendency to return to their natural state. How- corrosion attention. ever, potentialisnot sufficientinitself to Corrosion endangers the aircraft by reducing initiate and promote this reversion. There must thestrengthandchangingthemechanical also exist a corrosive environment, in which the characteristicsof thematerialsusedinits significant element is oxygen. It is the process of construction.Materials are designed to carry oxidationcombining with oxygenthat causes certain loads and withstand given stresses as well wood to rot or burn and metals to corrode. as to provide an extra margin of strength for Control of corrosion is dependent upon main- safety.Corrosion can weaken the structure taining a separation between susceptible alloys therebyreducing or eliminatingthissafety and the corrosive environment. This separation factor. Replacement or reinforcement opera- is accomplished in various ways. A good intact tions are costly, time-consumirg, and reduce coat of paint provides almost all of the corrosion usage of the aircraft. Severe corrosion can cause protection on naval aircraft, Sealants are used at failure of parts or systems which is an obvious seams and joints to prevent entry of moisture danger. Corrosion invital systems can cause intotheaircraft;preservatives are used on malfunctions that endanger the safety of flight, unpainted areas of working parts; and shrouds, and such dangers reemphasize the importance of covers, caps, and other mechanical equipment corrosion control. provide varyingdegrees of protection from Metals corrosion is the deterioration of metals corrosive media. None of these however, provide as they combine with oxygen to form metallic 100 percent protection in the long runpaint is oxides. This combining is a chemical process subject to oxidation and decay through weather- which is essentially the reverse of the process of ing; sealants may work out by vibration or else smelting the metals from their ores. Very few be eroded by rain and windblast. Preservatives at metals occur in nature in the pure state. For the best offer only temporary protection when used most partthey occur naturallyas metallic on operating aircraft and the mechanical cover- oxides. These oxides may also be mixed with ings are subject to improper installation and other undesirable impurities in the ores. The neglect. Control of corrosion properly begins refining processes generally involve the extrac- with an understanding of the causes and nature
284 Chapter II CORROSION CONTROL primarily to avoid the establishment of the electrical circuit, or secondly, to remove it as ELECTROLYTE (FRESH OR SALT WATER, soon aspossibleafter establishment before GREASE DIRT ETC .I3 serious damage can result. Figure 11-1 illustrates the electron flow in a corrosion environment (electrolyte)resulting indestructionof the anodic area. Note that the surface of a metal, especiallyalloys of the metal, may contain anodic and cathodic areas due to impurities or alloyingconstituentswhichhavedifferent potentials than the base metal. Electrochemical attack is evidence in several forms, depending upon the metal involved, its size and shape, its specific function, atmospheric conditions, and the type of corrosion-producing agent(electrolyte)present. There are many forms of metals deterioration resulting from electrochemical attack about which a great deal is known. But despite extensive research and experimentation, thereisstill much to be AM.49 learned about other, more complex and subtle Figure 11-1.Simplified corrosion cell. forms. Descriptions are provided later in this chapterforthemore common formsof of this phenomenon. Corrosionis caused by corrosion found on airframe structures. electrochemical or dire7.t chemical reaction of a Since there are so many factors which con- metalwithotherelements.Inthedirect tribute to the process of corrosion, selection of chemical attack, the reaction is similar to that materials by the aircraft manufacturer must be which occurs when acid is applied to bare metal. made with weight versus strength as a primary Corrosion in its most familiar form is a reaction consideration and corrosion properties asa between metal and water and is electrochemical secondary consideration. In the interest of aero- in nature. dyanmic efficiency, even the number of drain In the electrochemical attack, metals of dif- holes is limited until accumulated operational ferent electrical potential are involved and they data indicates a greater drain requirement. Close need not be in direct contact. When one metal attention during aircraft design and production contains positively charged ions and the other isalso given to heat treating and annealing negativelychargedionsandanelectrical procedures, protective coatings, choice and ap- conductor isbridged between them, current plication of moisture barrier materials, dissimilar with floe.as in the discharge of a dry cell metals contact, and access doors and plates. In battery.Inelectrochemicalcorrosionthe other words, every logical precaution is taken by conductor bridge may be any foreign material the aircraft manufacturers to inhibit the onset such as water, dirt, grease, or any debris that is and spread of corrosive attack. capable of acting as an electrolyte. The presence There are many factors that affect the type, of salt in any of the foregoing mediums tends to speed,cause, and theseriousness of metal accelerate the current flow and hence speed the corrosion. Some of these corrosion factors can rate of corrosive attack. be controlled; others cannot. Preventive main- Once the electrical coupleismade, the tenance factors such as inspection, cleaning, and electron flow is established in the direction of painting and preservation are within the control the negatively charged metal (cathode), and the of the operating squadron. They offer the most positively charged metal (anode) is eventually positive means of corrosion deterrence. destroyed. All preventive measures taken with The electrochemical reaction which causes respecttocorrosioncontrolaredesigned metal to corrode is a much more serious factor
285 AVIATION STRUCTURAL MECHANIC S 3 & 2
under wet, humid conditions. The saltin sea water and the salt in the air is the greatest single MONEL RIVET cause of aircraft corrosion. Hot climates speed (SMALL CATHODE ) thecorrosionprocessbecausetheelectro- chemical reaction develops fastestin a warm solution, and warm moisture in the air is usually sufficientto start corrosion if the metals are uncoated. As would be expected, hot dry climates usually provide relief from constant corrosion problems. Extremely cold climates produce corrosion problems if a salt atmosphere is present. Melting snow or ice provides the neces- RELATIVELY LITTLE sary water to begin the electrochemical reaction. CORROSIVE ATTACK Thick structural sections are subject to cor- rosive attack because of possible variations in ALUMINUM SHEET their composition, particularly if they were heat (LARGE ANODE) treated during fabrication. Similarly, when large sections are machined or cut out after heat HEAVY treatment,thinnersectionshave different CORROSIVE ALUMINUM RIVET physical characteristics than the thicker areas. In (SMALL ANODE ) most cases, different in physical characteristics ATTACK provides enough difference in electrical potential to render the piece highly susceptible to cor- rosion. Another corrosion factor regarding size of materials lies in the area relationship between dissimilar metals. When two dissimilar metals are used where possible contact may develop, if the more active metal is small, compared to the less active one, corrosive attack will be severe and extensive if the insulation should fail. If the area of the less active metal is small compared to the MONEL SHEET other, anodic attack is relatively slight. Figure (LARGE CATHODE ) 11-2 illustrates this factor. One of the biggest problems in corrosion controlisin knowing what materials to use, where to find them, and the limitations ap- AM.50 . plicable to their use. Materials used should be Figure 11-2.Effects of area relationships in dissimilar thosecoveredandcontrolledbymilitary metal contacts. specifications,preferablythoseauthorized specifically for use on aircraft. Corrosion control 2. Preservationof NavalAircraft, NavAir information pertaining to materials, methods, 15-01-500. and techniques is scattered throughout many 3. ChartCleaning Materialsfor Naval Air directives and instructions, and this information SystemsMaintenance and Overhaul Operations, is constantly being revised as better chemicals NavAir 07-1-503. and protective methods are developed. The 4. ChartCorrosion Preventive Compounds following is a list of sources of information that used by Naval Air Systems Command, NavAir should be readily available for reference in every 01-1A-518. unit's technical library or in the airframes shop. 5. Corrosion Control, Cleaning, Painting, and 1. Aircraft Cleaning and Corrosion Control Decontamination. (One volume of the Main- forOrganizationalandIntermediateMain- tenance Instructions Manuals for all late model tenance Levels, Nav Air 01-1A-509. aircraft is on these subjects.)
286 Chapter 11 --CORROSION CONTROL
6. Periodic Maintenance Requirements Cards should not be done unless corrosion is present. (as applicable). Touchup of new damage to paint finishes will prevent corrosion from starting there. The cleaning of aircraftisan important PREVENTIVE MAINTENANCE function in retaining the aerodynamic efficiency and safety of aircraft. In keeping, with this "An ounce of prevention is worth a pound of importance, acceptable materials, methods, and cure." Where corrosion prevention on naval procedures for use in aircraft maintenance clean- aircraftis concerned the foregoing clicheis a ing are prescribed in current directives and must ridiculous understatement. Compared with the beused.Instances of serious damage have cost of some late model aircraft which runs into resulted to exterior and interior of aircraft due millions of dollars the cost of corrosion pre- to the lack of correct information regarding ventionisa mere pittance. Preventive main- materials and equipment and their use. Ship- tenance is a powerful tool which can be used to board procedures are not necessarily the same as effectively control even the most difficult cor- procedures ashore, but the same materials are rosion problems. availableandcomparableresultsareac- Mostcorrosionpreventionprogramsare complished,al thoughdifferentapplication adjusted by the operating activity to meet severe methods may be necessary. conditions aboard ship and then decreased in How often an aircraft should be cleaned scope when the aircraftisreturned tothe depends on the type of aircraft and the environ- relativelymildconditionsprevailingashore. ment in whichithas been operating. Itis When regular corrosion preventive maintenance important that the aircraft be kept in a clean nnist be neglected in emergencies due to tactical condition and repeated cleaning should be ac- operating requirements, a period of intensive complished as often as necessary. The necessity care should follow in order to bring the aircraft for cleaning is indicated whenever there is any back up to standard. appreciable amount of soil accumulation within Preventive measures most commonly taken exhaust track areas; by the presence of salt with respect to corrosion require the aircraft to deposits or other contaminants such as stack be kept as clean as possible, all surface finishes gases; by evidence of paint surface deterioration intact, correct and timely use of covers and such as softening, flaking, or peeling; and by the shrouds, periodic lubrication, and the applica- presence of excessive oil or exhaust deposits or tion of preservatives where required. Years of spilled electrolyte and deposits around battery experience have proven the needfor such areas. Cleaning is always mandatory immediately measures if the aircraft are to remain airworthy. after exposure to fire extinguishing materials, Where corrosion preventive maintenance is after exposure to adverse weather conditions neglected, aircraft soon become unsafe to fly. and salt spray, after the aircraft has been parked Squadrons with the best corrosion preventive near seawalls during high wind conditions, after programs are likelyto have the best safety low levelflight, and after repairs or service records, most utilization of aircraft, and lowest which has left stains, smudges, or other gross operating costs. evidence of maintenance. A daily cleaning or wipedown is required on all exposed unpainted surfaces such as struts. actuating cylinder rods, SURFACE MAINTENANCE etc. Aircraft must be thoroughly cleaned before Surface maintenance include,. regular cleaning being placed in storage and should also receive a of the aircraft as well as touchup of protective thorough cleaning at the time of depresccvation. paintcoatings.Sincepainttouchupisac- Unpainted aircraft are cleaned and also polished complished after removal of corrosion, coverage at frequent intervals. Aboard ship, cleaning and ' on this subject is included under the heading, removal of salt deposits are necessary as soon as Corrosion Elimination, later in this chapter. This possible to prevent corrosion. does not imply that touchup of damaged paint Componentswhicharecriticallyloaded 287 AVIATION STRUCTURAL MECHANIC S 3 & 2
(designed with minimum safetymargins to using them. (The flashpriat is the temperature conserve size and weight) such as helicopter at which the first flash from the material is seen, rotor parts, and components and parts which are as an open flame is passed back and forth over a exposedtocorrosive environments, suchas sample of flammable liquid being heated in a engine exhaust gas, acid, or rocket blast, are cup.) cleanedasoftenaspossibletominimize Another hazard associated with solvents, and exposure to these corrosive agents. to a certain extent with all cleaning materials, is NOTE: Lubricationand preservationof theeffect on the surface or material being exposed components are necessary to displace cleaned. Some solvents will deteriorate rubber, any of the cleaning solution entrapped during synthetic rubber, asphaltic coverings, etc. This is the cleaning operation. such an important consideration thatit must always be taken into account when selecting Materials cleaning materials.It may do a good job in removing dirt, grease, oil, exhaust gas deposits, Only NavAir specification cleaniag materials etc.,but may also damage the object being may beused on aircraft. Navy specification cleaned or soften and ruin otherwise good paint cleaning materials are made up and compounded coatings. toaccomplish definite results and are made Solvent,Drycleaning.Thismaterial isa available only after complete testing and actual petroleum distillate commonly used in aircraft field acceptance. All specification materials are cleaning. Itis furnished in two types, I and II. inspected and tested before acceptance and Type I material, commonly known as Stoddard delivery to the supply activities. Cleaning agents solvent, has a flashpoint slightly above 100° F. commonly used by Organizational and Inter- Type II has a higher (safer) flashpoint and is mediate maintenance activities are included in intended for shipboard use. the following categories. Innavalaviationmaintenance,Stoddard SOLVENTS.Solventsareliquidswhich solvent (type I) is used as a general all-purpose dissolveother substances. There are a great cleaner for metals, painted surfaces, and fabrics. number of different solvents, but for cleaning Itmay beappliedbyspraying,brushing, purposes, 'organic solvents are most often used. dipping, and wiping. This material is preferable Some solvents are chlorinated. When solvents to kerosene for all cleaning purposes because contain more than 24 percent by volume of kerosene leaves a light oily film on the surface. chlorinated materials they must be kept in MineralSpirits.This is anotherliquid specially marked containers and care must be petroleumdistillate which is used as anall- taken to insure that equipment in which these purpose cleaner for metal and painted surfaces solvents are used are designed and operated as to and as a diluting material for emulsion com- prevent the escape of such solvents, as a liquid pounds, butis not recommended for fabrics. or vapor, into the workroom. Like Stoddard solvent, it may be applied by All personnel occupied with or working near spraying, brushing. dipping, and wiping. chlorinated solvents should be particularly care- AliphaticNaphtha.This is analiphatic fulto avoid breathing the vapors. While the hydrocarbonproductusedasanalternate vapors from some solvents are more toxic than compound for cleaning acrylics and for general others, prolonged breathing of the fumes can be cleaning purposes that require fast evaporation injurious to health. and no remaining film residue. It may be applied In addition to the breathing hazard associated by dipping and wiping. Saturated surfaces must with solvents, they also present varying degrees not be rubbed vigorously, asitisa highly of fire and explosion hazards, depending upon volatile and flammable solvent with a flashpoint thematerial.Itisconsideredthatsolvent below 80° F. Avoid prolonged breathing and cleaners having a flashpoint greater than 105° F skin contact. Use in well-ventilated areas only. arerelativelysafe.Those having flashpoints AromaticNaphtha.Thisisapetroleum below 105° F require explosion proofing of aromatic distillate. This naphtha is a bare-metal equipment and other special precautions when cleaner and is also used for cleaning primer coats
288 Chapter 11CORROSION CONTROL before applying lacquer.Itwill remove oil, control from a light mist or fogging spray to a grease, and light soils. It is also highly flammable full spray with high-pressure water. and reasonably toxic. Avoid prolonged breathing ALKALINE WATERBASE CLEANING andskincontact. CAUTION: Do notuse COMPOUND. -This compound is similar to the aromatic naphtha on acrylic surfaces as it will water emulsion cleaner. It is a general purpose cause crazing (fine surface cracks). cleaner used to remove light to moderate soils. It SafetySolvent.Methylchloroform is is mixed in1 part compound to 9 parts water intended for use where a high flashpoint and less for light soils and 1part compound to 3 parts toxicsolventthancarbontetrachloride is water for removing medium soils. It may be required. Itis used for general cleaning and applied to the surface by mopping, wiping, spray grease removal of assembled and disassembled equipment, or foam producing equipment. It is engine components in addition to spot cleaning, safe for use on fabrics, leather, glass, ceramics, but should not be used on painted surfaces. and transparent plastics. Follow the previously Safety Solvent is not suitable for oxygen sys- described procedure for washing the aircraft and tems although it may be used for other cleaning rinse thoroughly with fresh water before the in ultrasonic cleaning devices. It may also be compound dries to prevent streaking. applied by wiping, scrubbing, or booth spraying. SOLVENT EMULSION CLEANERS.This The term Safety Solvent is derived from the high cleaner, conforming to Specification P-C-444, is flashpoint.Manylaterissuemaintenance intended for heavy duty defining and should be manuals label safety solvent as Trichlorethane used with caution around painted surfaces as it 1,1,1. will soften paint if in contact with the paint Methyl Ethyl Ketone (MEK).This material is finishverylong.Itwillremove corrosion used as a cleaner for bare-metal surfaces. It will preventive coatings and should not be used on not mix to any great extent with water but is a parts thus protected unless it is desired that such. diluent for lacquers. It is applied with wiping protective coatings be removed. For heavy cloths or soft bristle brushes over small areas at a cleaning, the cleaning compound is mixed in a time. concentration of 1 part compound to 4 parts of WATER EMULSION CLEANERS.Emulsion dry-cleaningsolvent(Stoddardsolvent)or cleaners tend to disperse contaminants into tiny mineral spirits. For lighter duty use, it can be droplets which are held in suspension in the mixed at a 1 to 9 ratio. cleaner until they are flushed from the surface. WATERLESS CLEANER.This compound is Wateremulsioncompound conformingto intendedfor use on painted and unpainted MIL-C-22543containsemulsifyingagents, aircraft surfaces in heavy duty cleaning opera- coupling agents, detergents, solvents, corrosion tions where water for rinsing is not readily inhibitors, and water. It is intended for use on available or where freezing temperatures do not painted and unpainted surfaces in heavy duty permit the use of water. It is relatively nontoxic, cleaning operations where milder specification noncorrosive, nonflowing gel or cream, and its materials of lower detergency would not be detergent properties enable it to be used as an effective. It is used in varying concentrations, effective agent for the removal of grease, tar, depending on the condition of the surface. A wax, carbon deposits, and exhaust stains.It concentration of 1part compound to 4 parts should not be applied to canopies or other water, by volume, is recommended for heavier acrylic plastic surfaces. It is safe for use as a soiled surfaces. For mildly soiled surfaces, the waterless hand cleaner. concentration is changed to 1 part compound to MECHANICAL CLEANING MATERIALS. 9 parts water, by volume. Starting at the bottom Mechanical cleaning materials such as abrasive of the area being cleaned, apply the mixed papers, polishing compounds, polishing cloths, solution by spraying orbrushing- toavoid wools; wadding, etc., are available in the supply streaking. Loosen surface soils by a mild brush- system for use as needed. However, their use ing or mopping and follow with a thorough fresh must be in accordance with the cleaning proce- water rinse. The automatic shutoff type water dures outlined in NavAir 0.1-1A-509,..the specific spray nozzle is best for rinsing. It gives hand aircraft Maintenance Instructions Manual, and
289 AVIATION STRUCTURAL MECHANIC S 3 & 2 directions supplied with the material being used factors, such as the amount of cleaning that is if damage tofinishes and surfaces isto be regularly performed, the type of aircraft that is avoided. In cases of conflicting information, being cleaned, the location of the activity, and NavAir 01-1A-509 will always take precedence. the availability of facilities such as air pressure, Aluminum Oxide Paper.Aluminum oxide water, and electricity. paper (300 grit or finer) is available in several Several specialized items of equipment are forms and is safe to use on most surfaces since it available for cleaning aircraft. These include does not contain sharp or needle-like abrasives pressure type tank sprayers, a variety of spray which can embed themselves in the base metal gunsandnozzles,high-pressurecleaning being cleaned or in the protective coating being machines, and industrial type vacuum cleaners. maintained. The use of carborundum (silicon One of thelatestdevices forfaster and carbide) papers as a substitute for aluminum economical cleaning of aircraft is a swivel type oxide paper should be avoided. The grain struc- conformable applicator cleaning kit developed ture of carborundum is sharp, and the material is bythe 3M Company.Officiallydesignated so hard that individual grains can penetrate and Scotch-Brite Conformable Applicator Cleaning bury themselves even in steel surfaces. Kit No. 251,itis designed to clean aircraft Powdered Pumice.This materialis a mild exteriors several times faster than using cotton abrasive cleaner. The pumice is used as a slurry mops or bristle brushes. with water and is applied to the surface with The applicator head of the cleaning kitis clean rags and bristle brushes. curved and flexibleto conformreadilyto Impregnated Cotton Wadding.Cotton which convex and concave aircraft exteriors. A swivel has been impregnated with a cleaning material is joint on the back of the applicator head provides used for the removal of exhaust gas stains and further flexibility. The 5 x 7 inch Scotch Brite for polishing corroded aluminum surfaces. It is cleaning and polishing pad attaches easily to the also used on other metal surfaces to produce a applicator head and provides a more aggressive high reflectance. and efficient scrubbing medium than bristle Aluminum Metal Polish.Aluminum metal fibers. It can be used without fear of scratching polishis used to produce a high-luster, long- aluminum or painted surfaces. lasting polish on unpainted aluminum-clad sur- The swivel and applicator head are attached faces. It is not used on anodized surfaces as it toastandard brush handle. The excellent will remove the oxide coat. conformability of the applicator allows easier Aluminum Wool.Three grades of aluminum application of a constant scrubbing pressure on woolcoarse, medium, and fineare stocked for curved skin panels and eliminates the need for a general abrasive cleaning of aluminum surfaces. maintenance stand to keep brushes in maximum Lacquer Rubbing Compound, Type III.For contact with the surface. the removal of engine exhaust residues and Some larger shore activities maintain a self- minor oxidation, lacquer rubbing compound, containedvehicleFlightLineMaintenance Type III; may be used. Heavy rubbing over rivet Master for use of all tenant activities. The Flight heads or edges where protective coatings may be Line Maintenance Master is self-propelled and thin should be avoided as the coverings may be self-contained. It provides a heated soap solution damaged most easily at these points. with its own water system. It has a 1,000-gallon capacity and is equipped with an extendable Cleaning Equipment boomtoaccommodatecleaningofhigh horizontal and vertical stabilizers. The cleaning of aircraft not only requires the The cleaningsolutionis sprayed athigh use of correct cleaning materials, but also the pressure from the boom or ground level posi- useof properlymaintainedequipmentto tions or both positions simultaneously. Control produce efficient and satisfactory results. A of the boom and cleaning solution can be made specific cleaning area should be prepared and fromthe boom or thevehiclecab. The equipped for performing cleaning operations. maneuverability of the vehicle makes it extreme- The choice of equipment depends on several lyefficientincleaningallexterior aircraft 290 Chapter 11 CORROSION CONTROL surfaces.Brushing of surfaces can be easily components that can be damaged by moisture or accomplishedbytheboomoperator.The the cleaning agent being used. ground hose is equipped with a crank rewind WATER RINSE CLEANING.The water and is 50 feet long. The boom is equipped with rinsemethodis recommended as the most floodlights to accomodate nighttime use of the efficient and satisfactory method of cleaning vehicle. As with other support equipment, the aircraft when they are only lightly contaminated maintenance master should only be operated by with loosely adhering soils and water soluble qualified and licensed personnel. In some cases corrosion products. The aricraft is prepared as' specialized equipment must be manufactured previously outlined, and all materials and equip- locally by the activity, otherwise it is procured ment that will be required during the cleaning through regular supply channels. are ascertained to be on hand and ready for use. Inadditiontothespecialized equipment Theproperwashingproceduretoinsure mentioned above, other items such as hoses, complete coverage is illustrated and described in brushes,sponges,andwipingclothesare figure 11-3. Apply water by progressing upward required for aircraft cleaning. These items are and outward, scrubbing brisklywith a long procured through supply. handled fiber cleaning brush as necessary while Items of personal protection such as rubber the water is being applied. Do not scrub a dried gloves, rubber boots, goggles, and aprons should surface. After scrubbing, rinse the surface from be worn when necessary to protect clothing, the top downward with a high-pressure stream skin, and eyes from fumes and splashing of of water until all the water soluble residues and caustic materials. loosened soils have been completely flushed off the aircraft. Cleaning Methods and Procedures WATER EMULSION CLEANING.The Thefirststep incleaning the aircraftis emulsioncleaning method isused toclean selecting theproper cleaning agentforthe aircraft contaminated with oil, grease, or other method of cleaning to be used. The recom- foreign matter which cannot be easily removed mended type cleaning agent for each method, by other methods. The aircraft is prepared in the including instructions and precautions to be same manner asitwas for the water rinse observed in their use, may be found in Nav Air method. 01-1A-509 andtheapplicableMaintenance Wet down the surface to be cleaned with fresh Instructions Manual for the type of aircraft water. Apply a concentrated solution of 1part being cleaned. emulsion compound cleaner to 4 parts of water The next stepisthe preparation of the totheheavilysoiled areas, such as engine aircraft for cleaning. Ground the aircraft to the nacelles, landing gear assemblies, or other special deck after spotting it in a cool place if possible. areas that will require such a strong solution. If the aircraft has been heated while parked in Scrub these areas and allow the concentrated the sun or areas of the aircraft are heated as a solution to remain on the surface. Limit the size result of operations, it should be cooled before of the area being cleaned to that size which can the start of cleaning by the use of fresh water be easily cleaned while keeping the surface wet. washdown. Many cleaning materials will clean Next apply a diluted solution of emulsion faster at elevated temperatures, but the risk of compound and water, mixed to a ratio of I part damage to paint, rubber, and plastic surfaces is emulsion compound to 9 parts water, to the increased by the cleaners which are concentrated entire surface to be cleaned including those areas by the rapid solvent evaporation caused by the previouslycoveredwiththeconcentrated high temperatures. Static electricity generated solution. Scrub thesurfaces thoroughly and by the cleaning operation will be dissipated allow the solution to remain on the surfaces 3-5 through the ground wire. After securing all the minutes beforerinsing.Rinse from the top obvious openings such as canopies and access downward until all soils have been removed. If a panels, further secure the aircraft against entry high-pressure stream of water is used for rinsing, of water and cleaning compounds as necessary. hold the nozzle at an angle and a reasonable Mask or otherwisecoverallequipment or distance from the surface being sprayed.
291 AVIATION STRUCTURAL MECHANIC S 3 & 2
STEPI WASH THE UNDERSIDE OF WING, SPRAYING FROM THE CENTER SECTION TOWARDS THE WING TIPS.
NOTE: OPEN DOORS AND FLAPS TO FLAPWELLS, DIVE BRAKES, SPOILERS, CONTROLLABLE LEAD ING EDGES,ETC.,TO PERMIT CLEANING OF HIDDEN AREAS.
01 It * 111111116, WASH THE UNDERSURFACE OF 410Mmill amp mom*um,. 4... STEP 2 FUSELAGE AND TAIL SECTIONS FROM 'LANDING GEAR TOWARDS BOTH ENDS AND SPRAY IN THE DIRECTION OF MOVEMENT.
WASH THE UPPER SIDE OF WINGS STEP 3 AND CENTER SECTION OF FUSELAGE. DIRECT SPRAY INWARD WHILE MOVING OUTWARD TOWARDS WING TIPS.
SPRAY THE REMAINING PARTS STEP 4 OF THE UPPER SIDE OF FUSE LAGE AND TAIL SECTIONS MOV ING FROM CENTER TO ENDS. ALL AREAS OF THE AIRCRAFT MUST BE COMPLETELY COVERED BY THE CLEANING SOLUTION.
*mg 4we 1".# re4.
LEGEND 440mmi DIRECTION OF STEPS 40011111 DIRECTION OF SPRAY SPRAYED AREAS
AM.51 Figure 11-3.Aircraft washing procedures.
292 Chapter 1I CORROSION CONTROL
If any areas arestillnot clean, repeat the approximately 10 minutes; scrub and wipe off operation in those areas only. After rinsing, the thoroughly with a clean wiping cloth. Make sure aircraft may be dried with a clean sponge or allsoilsand cleaning materialare removed, cloths to insure against streaking that could be exercisingspecialcare aroundfasteners and caused by emulsion cleaning. Normally, if the unsealed areas. In freezing weather a dry ap- aircraftis thoroughly rinsed, streaking will be plicator should be used in lieu of a dampened held to a minimum. one. SOLVENT-EMULSION CLEANING. Solvent-emulsion cleaning is intended for clean- Post-Cleaning Requirements ing heavily soiled unpainted surfaces and parts and for use in removing corrosion preventive Following cleaning, the aircraft should be coatings. The cleaning compound is mixed in a relubricated in accordance with the Maintenance concentration or 1part compound to 9 parts of Requirements Cards. Insure that all low-point drycleaning solvent or mineral spirits. The solu- drains are open. Apply aircraft preservatives as tion is applied to a water-free surface, otherwise requiredtothose clean, exposed unpainted the water would lessen the solvent action. Since surfaces. The types of preservatives are discussed this cleaner will remove thick preservative mate- later in this chapter. Insure that the felt wiper rials,itshould be used with care to prevent washers on all hydraulic cylinders are moistened unwanted removal of such coatings. with hydraulic fluid and that all exposed strut The solution is applied by brush or with a and actuating cylinder rods are wiped down with high-pressure spray using a nozzle that gives a acleanragsaturatedwith hydraulicfluid. coarse fan-shaped spray. Scrub the surface with Remove any damaged or loosened sealant and a brush as the solution is being applied. Allow replace in accordance with the applicable Main- the solutionto remain on the surface long tenanceInstructionsManualorStructural enoughtoloosenthesoilwithout drying. Repair Manual. Reapply and rescrub the more difficult soiled Figure 11-4 illustrates the documentation of a areas as necessary. Rinse thoroughly, using a Support Action Form (SAF) utilized to account large volume of fresh water to remove all loose for the time spent cleaning an aircraft. The soils and cleaning compound. spaces 1 through 9 and A and B areself- SPOT CLEANING.Light oily soiled surfaces explanatory and should be filled in accordingly. may be spot cleaned by wiping these areas with For detailed instructions on the SAF and its a dry-cleaning solvent. The solvent is applied uses, consult Military Requirements for Petty with a saturated wiping cloth. Brush or wi:+e the Officer 3 & 2, NavPers 10056-C, or OpNav surface as necessary then wipe clean with a dry 4790.2. cloth, removing the solvent residue and loosened NOTE: If the cleaning is done after normal soil. The solvent wipe may leave a light residue workinghours,onSaturday,Sunday,or which may be removed with soap and water declared holidays and the activity concerned is followed by fresh water rinsing. required to record manhour data, a Manhour WARNING: Drycleaning solvent should not Accounting (MHA) Card must be submitted in be usedinoxygen areas or around oxygen addition to the SAF. equipment. The solventisnot oxygen com- patible and will cause explosion and/or fire. USE OF COVERS AND SHROUDS WATERLESS WIPEDOWN.When water is not available, heavy soils and operational films Each aircraft, when delivered by the manufac- may be removed by using waterless cleaner. The turer, is equipped with a complete set of tailored cleaner is applied by dipping a dampened cloth dust and protective covers. A typical set of ir.to the creamlike waterless cleaning material covers is shown in figure 11-5 installed on an and then spreading the material thinly over the A-6A. area to be cleaned. Scrub the surface until the All covers and shrouds should be installed in soil and cleaner become intermixed or emulsi- such a manner that free drainage is assured. Do fied. Allow the material to remain on the surface not create a bathtub which will trap and hold 293 AVIATION STRUCTURAL MECHANIC S 3 & 2
.-- 2 5
E ACT WORN "III ACTION SUPPORT TM . .: MS MAN LOCAL lisp SIGNATURE P ORG CENTER DATE CODE NOEPROC. HOURS CONTROL
BA5A .71-±J. ZJ/0,S1 a LSD.., 2 0A ..4.La_. WoiteAV 1.-1l--I 1 I I
SUPPORT CODES TYPE MAINTENANCE CODES
010OPERATIONAL SUPPORT A GENERAL SUPPORT
020CLEANING /PRESERVATION / DEPRESERVATION C PREFLIGHT INSPECTION
030INSPECTION D POSTFLIGHT / DAILY INSPECTION 040CORROSION CONTROL E ACCEPTANCE/TRANSFER INSPECTION 050GENERAL FUNCTIONS TRANSIENT MAINTENANCE 060BUILD UP AND TEAR DOWN / ENGINE L LOCAL MANUFACTURE TEST STAND OPERATION T SUPPLY SUPPORT 070MISSION SHOP SUPPORT U RECLAMATION AND SALVAGE 080INSPECTION OF AVIATORS EQUIPMENT, SAFETY AND SURVIVAL EQUIPMENT 090NON AERONAUTICAL WORK
AM.6 Figure 11-4.SAF documentation for cleaning aircraft.
AM.52 Figure 11-5.A-6A dust and protective covers.
294 Chapter 1 CORROSION CONTROL water. Shrouds cr covers may also act as a the sand or gravel from shoe soles before climb- greenhouse in warm weather and cause col- ing on aircraft. lection and condensation of moisture under- When removing cowling and access plates dur- neath. They should be loosened or removed and ing inspections the removed hardware should the aircraft ventilated on warm sunny days. not be placed on the deck to blow around and Where protection from salt sprayis required become scratched. If it is not practical to pro- aboard carriers, the covers should be left in place vide pads or cushioning for these components, and the aircraft ventilated only in good weather. they should at least be secured to prevent their Fresh water condensate will do far less damage movement. When using handtools to remove than entrapped salt spray. screws and quick-opening fasteners on the air- In emergencies where a regular waterproof craft exterior, particular care should be taken to canvas covers are not available, suitable covering avoid scratching the pint. Five minutes of extra and shrouding may be accomplished by using time spent in careful use of tools could save polyethylene sheet, polyethylene coated cloth, hours of paint touchup and corrosion removal or metal foil barrier material, all of which are work later. availableinthe Navy supply system. These covers should be held in place with adhesive AIRCRAFT PRESERVATION tapes designed specifically for severe outdoor application.The tapes are alsoavailablein The susceptibility of an aircraft to corrosion supply. damage is greatest during those periods when the aircraft is dirty, inactive, or being shipped. Since GROUND HANDLING REQUIREMENTS aircraft spend more time on the ground than in the air, even in an active squadron, the need for Maintenance Instructions Manuals for aircraft effective protection becomes apparent. usually provide brief and simple ground handling Suitable protection against corrosive attack is procedures which, if observed, can do much achieved essentially by placing a barrier between toward reducing corrosive attack. Little things the cleaned surface that is to be protected and like heading the aircraft into the wind and any possible source of moisture. During manu- installing available covers, battens, shrouds, etc., facture or overhaul of the aircraft, protective to keep water, salt, and dirt out of areas difficult barriers such as electroplate, paint, or chemical to get at and easyto overlook, can save a surface treatment are provided. Surfaces that tremendous amount of maintenance work later. cannot be so treated, and in some instances the There are many other commonsense practices treated surfaces themselves, must be covered which should be observed to minimize paint with specialcorrosion-preventive compounds. damage and thelossof built-in protective The protection these compounds give is effective systems duringnormal ground handling of the only if no moisture, dirt, or active corrosion is aircraft. Much damage is done to aircraft paint present on the treated surface. Itis essential, films byfailure to use the tiedown points therefore, that the aircraft be thoroughly clean provided, or by passing tiedown cables and lines and dry before apreservative compound is over or around supporting structures in such a applied. Itis also necessary that an unbroken manner that the paint finish is worn, chipped, or film of preservatives be applied in as moisture- broken, especially at sharp edges. free an atmosphere as practicable. Painted aircraft surfaces will withstand a nor- Compounds alone do not provide complete mal amount of foot traffic and abrasion by fuel protection. Tapes, barrier paper, and sealing de- hoses and air lines. However, shoe soles and fuel- vices must also be used to seal off the numerous ing hoses pick up bits of sand, gravel, and metal openings on aircraft which, if allowed to remain chips and become acoarse abrasive which open during long-time storage, would permit the scratches and scuffs the protective finish to the entry of moisture and dirt. To provide addi- point where it is rendered completely ineffective tional protection against corrosion a complete under shipboard operating conditions. For this moisture barrier is sometimes provided. Internal reason, time should be taken to wipe or brush areas that have been sealed off are dehydrated 295 AVIATION STRUCTURAL MECHANIC S 3 & 2 by installing dessicants (moisture absorbents) to salt spray is required. Present instructions gen- remove entrapped unless the cavity is protected erally limit its use to seaplanes and amphibian with a vapor corrosion inhibits r. When any area surfaces. cannot be sealed adequately, provision must be Grade 2 is .a soft-film, grease-type material made for ventilation and moisture drainage. that can be used on most operating parts. Its When certain installed equipment in an air- chief disadvantage is the fact that it may be craft is not being used regularly, its components washed off under direct exposure to salt water are required to be preserved. For example, the or may be removed by inadvertent wiping. It guns of an aircraft must be cleaned after each protects under relatively severe conditions and, firing. The type of oil or other protective treat- given adequate maintenance and touchup as ment which isto be applied subsequently de- necessary, can be used for most maximum pro- pends upon the anticipated period of idleness tection requirements. for the guns. Grade 4 preservative forms thin, semitrans- The requirements forthe preservation of parent films through which identification data operating aircraft are of the most concern of a can usually be read. It also sets up relatively dry Third or Second Class AMS; therefore, this sec- to the touch so that preserved parts may be tion emphasizes the use or preservative coatings easily handled. This grade has proved particu- to supplement paint films, prevent salt spray and larly effective in protecting wheel well areas and saltwater damage to operating aircraft,',1c1 other exposed surfaces where film transparency minimize exposure during routine maintenance is required and moderate protective characteris- and repair. tics can be tolerated. The main disadvantages of In maintenance of aircraft surfaces, under this material is that it is easily removed by water operating conditions, preservation means supple- spray and requires replacement at 1-month inter- menting the protection already present, or pro- vals under severe exposure conditions. viding temporary protection to damaged areas, by the use of various protective coatings and Sprayable, Strippable barrier materials. A brief description of some of Coating Compounds the more coinmon materials used in aircraft pres- ervation and readily available in. Navy stock is Activities based outside of the continental included in the following paragraphs. United States occasionally receive aircraft from rework activities or the procuring agency via Compound, Corrosion-Preventive, ocean surface shipment. This is especially true of Solvent Cutback nelieopter and limited range fighter aircraft. These aircraft are protected during shipment This material is familiarly known as "paral- with a sprayable, strippable coating system, con- ketone." It is supplied in three grades for spe- forming to MIL-C-6799, Type II. Type II coat- cific application. All grades of this compound ing systems, which are more common to mainte- may be applied by brush, dip, or spray. They nancepersonnel, arenormallyapplied by may be easily removed with Stoddard Solvent or spraying and have no harmful effects on metal, mineral spirits. These materials are designed for plastic, or painted surfaces. It is also useful for cold application. Some preservative compounds protecting transparent acrylic surfaces, such as must be applied hot; therefore, when intending canopies, against abrasion during maintenance or to use one of the grades of this solvent cutback extended periods of down time. The type II material,thespecificationnumber (MIL-C- system consists of a black base coat and a white 16173) should always be verified. topcoat to provide maximum heat reflection Grade 1 forms a dark, hard-film, opaque during outside exposure. Nylon ripcords with cover. Its general use is limited because of the finger size loops are placed strategically about difficulty in removing aged coatings and also be- the aircraft prior to spraying to accommodate cause of the hiding power of the material when the manual stripping of coatings. When properly it is applied over corroded areas. This material is applied, the coatings can be easily removed. If used only where maximum protection against coatings are sprayed too thin for easy removal, 296 Chapter 11CORROSION CONTROL they can be recoated and allowed to dry. The will show 100-percent protection for a period of top layer will adhere. to previous layers and all 30 days or more. layers may be manually stripped in one opera- Lubrication Oil, General tion. Purpose, Preservative
Corrosion-Preventive Petroleum There are several different types of lubricating (MIL-C-11796) oil, some of which contain preservatives.In order to be absolutely sure that the proper oil is These preservatives are designed for hot appli- used in a given situation, each must be identified cation and are available in two classesClass 1 with its specification number. The specification (hard film) and Class 3 (soft film). Both consist number for the oil discussed in this section is of corrosion inhibitors in petroleum. They are VV-L-800. removed withStoddardSolventor mineral spirits. Where a hard film is not necessary, Class VV-L-800 oil was compounded for lubrica- 3 should always be used as it is easier to apply tion and protection of piano-wire hinges and and remove yet renders the same degree of pro- other critical surfaces and whenever a water- displacing, low-temperature, lubricating oil is re- tection. Class 1 is generally used for long:-time indoor protection of highly finished metal sur- quired. faces and aircraft control cables. Class 3 is used VV-L-800 may be applied, as received, by to provide protection of metal surfaces such as brush, spray, or dip methods. It is readily re- antifrictionbearings, shock-strut pistons, and moved with Stoddard solvent or mineral spirits. other bright metal surfaces. Lubricating Oil, General ClassI must be heated to 170° to 200° F before applying by brush or dip. For brushing Purpose, Low Temperature class 3 material, it must be between 60° and 120° F and for dipping, between 150° and 180° This general purpose oil (Specification MIL-L- F. 7870) is suitable for use anywhere that a general purpose lubricating oil with low temperature, Oil, Preservative, low viscosity, and corrosive-preventive prop- Hydraulic Equipment erties is required. This oil is suitable for brush, spray, dip, or This oil is used in the preservation of hydrau- general squirt-can application. It is not necessary lic systems and components and shock struts. to remove before reoiling or for inspection. This oil is similar in appearance to, but is not interchangeable with, operating hydraulic fluid, Corrosion Preventive therefore before using operating hydraulic fluid Compound (MIL-C-81309) (MIL-H-5606)or thispreservativeoil(MIL- This material is a water displacing corrosion H-6083) for any purpose the specification num- prevention compound and lubricant. It forms a ber should be checked to ascertain that the cor- thin, clear protective coating when applied by rectoilisbeing used. The preservativeoil aerosol, brush, dip, or spray. It offers only short contains oxidation and rust inhibitors, viscosity term protection so must be reapplied frequently. improver, and antiwear agents. Hydraulic parts On exposed surfaces, protection atitsbest and components being turned in for screening would be 7 days between applications and up to and repair are flushed and drip drained with 30 days on internal surfaces which are protected MIL -H -6083 oil prior to being forwarded. from direct outside environments. It is easily re- Designed primarily for hydraulic components moved with drycleaning solvents. 1t is very effec- this oil may be used on any bare critical surface tive when used in the following areas: Piano-wire that needs protection. Operating hydraulic fluid hinges, removable fasteners,B-nuts, linkages, will protect a steel panel immersed in water for bolts and nuts,ejectionseat mechanisms, only about 48 hours. Thesame metal panel canopy locks, control surface hinges, electrical coated with MIL-H-6083 inhibited hydraulic oil connectors, and microswitches. 297 AVIATION STRUCTURAL MECHANIC S 3 & 2
Packaging and Barrier Materials CORROSION DETECTION A minimum of packaging is necessary at the Timely detection of corrosion is essential to operating activity level. However, critical aircraft any corrosion control program. Of course corro- and engine areas require shrouding against con- sion can be detected after a part fails (if the tamination during maintenance and repair. Fuse- aircraft can be recovered), but it is too late to do lage openings require adequate seals when clean- anything about it other than to intensify inspec- ing and stripping materials are used. At least tions of other, similar aircraft. Inspection for three acceptable barrier materials are available in corrosion and deterioration should be a part of Navy stock for sealing and shrouding large air- all routine inspections. There are, on every air- craft openings. craft, certain areas that are more prone to corro- WATER-VAPORPROOF BARRIER MATE- sion than others. One should check these areas RIAL.This material is a laminated metal foil carefully. In order for the corrosion inspection barrier that has good water-vapor resistance and to be thorough the person inspecting must know can be used for closing of intake openings, for the types of corrosion likely to be found and the protection of acrylics during cleaning, and for symptoms or appearance of each type. Some- necessary packaging of removed components times corrosion is hidden and special detection and accessories being returned to overhaul. It is methods are utilized in the search. Various as- heat sealable with a soldering or clothes iron. pects of corrosion detection are discussed in the POLYETHYLENE PLASTIC FILM.This following sections. barrier material is used for the same purposes as the metal foil barrier material and is much less LOCATION OF CORROSION expensive. It is however not puncture resistant. PRONE AREAS The plastic film is heat sealable only with special equipment. POLYETHYLENE COATING CLOTH.This Discussion of corrosion prone areas in this cloth is used to a great extent in ground support section includes trouble spots or areas that are equipment covers. Its use is preferred over the common to all aircraft. For this reason, coverage plastic film material for general aircraft shroud- for any given aircraft model is not necessarily ing because of its greater tear and puncture re- complete. Figure 11-6 illustrates trouble spots sistance. applicable to a jet engine aircraft. Reference to TAPE, FEDERAL SPECIFICATION the Periodic Maintenance Requirements Cards PPP-T-60, CLASS 1.This pressure-sensitive for specific model aircraft will enable inspec- tape is used for closure of small aircraft openings tions to be amplified and expanded to the neces- and for direct contact use on noncritical metallic sary degree. surfaces. The tape has moderate water -vapor re- sistance, which is generally adequate for mainte- nance use. The main disadvantage of this tape is Exhaust Trail Areas that some cloth-backed materials have not been preshrunk, and tape closures tend to pull loose Both jet and reciprocating engine exhaust de- when exposed to high humidity conditions. posits are very corrosive. These deposits are par- PRESSURE SENSITIVE ADHESIVE ticularly troublesome where gaps, seams, hinges, TAPE.This item is a material developed speci- and fairings are located down the exhaust path fically for exterior preservation and sealing used and where the deposits may be trapped and not in aircraft maintenance programs. It is designed reached by normal cleaning methods. Inspection for application at temperatures as low as 0° F of these surfaces should include special attention and should perform satisfactorily over the tem- to the areas indicated in figure 11-7. Inspection perature range from -65° F to 140° F. It is an procedures should also include the removal of excellent general purpose tape for exterior pre- fairings and access panels located in the exhaust servation and sealing operations. path. 298 Chapter 1 1 COR ROSION CONTROL
AM.53 1. Pallet components. 13. Exposed indicator switches. 2. Rudder pedals. 14. Magnesium wheels. 3. Cockpit floor. 15. Exposed rigid tubing. 4. Battery compartment 16. Main wheel well. 5. Piano hinges. 17. Cooling air inlet 6. Control cables. 18. Bilge areas. 7. Cooling air inlet 19. Piano hinges. & Missile rocket blast areas. 20. Relief tube exits. 9. Exhaust areas. 21. Exposed position indicator switches. 10. Extensible equipment platform compartments. 22. Air intake ducts and engine frontal areas. 11. Flap carriage cutout. 23. Exposed rigid tubing. 12. Slat drives and track cutouts. 24. Magnesium wheels. Figure 11-6.Typical corrosion prort 3 areas on jet engine aircraft
JATO, Rocket, and Gun Blast Areas Battery Compartments and Battery Vent Openings Surfaces located in the path of JATO, rocket, and gun blasts are particularly subject to corro- Fumes from battery electrolyte are difficult sive attack and deterioration (fig. 11-8). In addi- to contain and will spread throughout the bat- tion to the corrosive effect of the gases and ex- tery compartment, vents, and even adjacent in- haustdeposits, protective finishes are often ternal cavities, causing rapid, corrosive attack on blistered by heat, blasted away by high-velocity unprotectedsurfaces. The external skin area gases, or abraded by spent shell casings or solid around the vent openings should also be checked particles from gun and rocket exhausts. These regularly for this type corrosion. Corrosion from areasshould be watched for corrosion and this cause will continue to be a serious problem cleaned carefully after firing operations. whenever batteries are used.
299 AVIATION STRUCTURAL MECHANIC S 3 & 2
they may attract and hold moisture, which in turn causes corrosive attack. Inspectors should pay attention to bilge areas located under galleys and lavatories, and to personnel relief and waste disposal vents or openings on the aircraft ex- teriors. Human waste products are very corrosive to the common aircraft metals.
Bilge Areas A common trouble spot on all aircraft is the bilge area. This is a natural collection point for G GC C C C C C C C waste hydraulic fluids, water, dirt, loose fas- teners, drill shavings, and other odds and ends of debris. Oil puddles quite often mask small quan- ,.....4 tities of water which settle to the bottom and UNDER PAIRINGS iAROUND RIVET HEADS & IN SKIN CREVICES set up hidden corrosion cells. Keeping bilge areas ANN x\lniw. vovs free of all extraneous material, including oil, is the best insurance against corrosion.
Wheel Wells and Landing Gear The wheel well area probably receives more punishement than any other area on the aircraft. AM.54 It is exposed to mud, water, salt, gravel, and Figure 11-7.Exhaust trail corrosion points. other flying debris from runways during flight operations and is open to salt water and salt spray when the aircraft is parked aboard ship. CORROSION PROBLEM AREAS Dui tothe many complicatedshapes,as- semblies, and fittingsinthe area, complete coverage with a protective paint film is difficult to attain. Because of the heat generated from braking, preservative coatings cannot be used on jet aircraft landing gear wheels. During inspec- tions, particular attention should be given the following: Mangnesium wheels, especially around bolt- heads, lugs, and wheel web areas. THESE AREAS ARE ALSO POTENTIAL Exposed metal tubing, especially at nuts and' WATER TRAPS ON SOME AIRCRAFT ferrules, and under clamps and identification GAS OUTLET DOOR tapes. Exposed position-indicator switches and other electrical equipment. AM.55 Crevices between stiffeners, ribs, and lower Figure 11.8. Gun blast area corrosion points. skin surfaces which are typical water and debris Lavatories and Galleys traps. These areas, particularly on the deck behind Water Entrapment Areas lavatories, sinks, and ranges, where spilled food and waste products may accumulate, are likely Design specifications require that aircraft have trouble spots if not kept clean. Even if some drains installed in all areas where water may col- contaminants are not corrosive in themselves, lect. However, in many cases these drains may 300 Chapter 1 1 CORROSION CONTROL not be effective, either due to improper location CORROSIVE AGENTS ENTER or because they are plugged by sealants, ex- AT UNSEALED SKIN EDGES traneous fasteners, dirt, grease, and deLris. Daily inspection of drains should be a standard re- SPOT WELD SPOT WELD quirement, especially aboard ship. p fit..0xgIxT, 0 acCelauxteye MW wINA\ Wing Fold, Flap and Speed Brake Recesses CORROSIVE AGENTS TRAVEL Flap and speed brake recesses are potential BETWEEN SKINS, AROUND corrosion problem areas mainly because they are RIVETS AND WELDS normally closed when on the ground. Dirt and CORROSION BUILD-UP CAUSES water may collect and go unnoticed. Wing fold BUCKLING OF OUTER SKIN areas present a different problem and, like wheel wells, contain many complicated shapes and as- semblies which are difficult to cover with a pro- tective paint coating or preservative film. Wing fold areas are extremely vulnerable to salt spray AM.56 when wings are folded aboard ship. Thorough Figure 1 1-B.Spot-welded skin corrosion points. inspection of this area should include a mirror check of the back sides of tubing and fittings. magnesium skin surfaces, with special attention Also, particular attention should be paid to to edges, areas around fasteners, and cracked, aluminum alloy wing lock fittings such as are chipped, or missing paint. used on some current aircraft models. Corrosion of spot-welded skins is chiefly the result of the entrance and entrapment of corro- External Skin Areas sive agents between the layers of metal. (See fig. 11-9.) Some of the corrosion may be caused Most external aircraft surfaces are ordinarily originally byfabricationprocesses, butits covered with protective paint coatings and are progress to the point of skin bulging and spot- readily visible or available for inspection and weld fracture is the direct result of moisture or maintenance. Even here, certain types of con- salt water working its way in through open gaps figuration or combinations of materials become and seams. This type of corrosion is first evi- troublesome under shipboard operating condi- denced by corrosion products appearing at the tions and require special attention if serious crevices through which the corrosive agents corrosion difficulties are to be avoided. entered. Corrosion may appear at other external Magnesium skin, when painted over, is not or internal faying (closely joined) surfaces, but is visibly different from any other painted metal usually more prevalent on external areas. More surface. However, those surfaces which are of advanced corrosive attack causes skin buckling magnesium are identified in the applicable Struc- and eventual spot-weld fracture. Skin buckling tural Repair Manual. When aircraft contain mag- in its early stages may be detected by sighting nesium skin panels, these must be given special along spot-welded seams or by using a straight- attention during inspections for corrosion. Some current aircraft have steel fasteners installed edge. through magnesium skin with only protective finishes under the fastener heads or tape.s over Piano Type Hinges the surface for insulation. In addition, all paint Figure 11-10 illustrates the effect of corrosion coatings are thin at trimmed edges and corners. on the piano wire type hinges used on most air- These conditions, coupled with magnesium's craft. These are not only prime spots for corro- sensitivity to salt water attack, make up a po- sion due to the dissimilar metal contact between tential corrosion problem whenever magnesium the steel pin and aluminum hinge tangs, but are is used. Therefore, any inspection for corrosion also natural traps for dirt, salt, and moisture. should include the location and inspection of all When this type of hinge is used on access doors
301 AVIATION STRUCTURAL MECHANIC S 3 & 2
familiar reddish colored iron rust. When iron and BARE STEEL HINGE PIN itsalloys corrode, dark iron oxide coatings usually form first, and these coatings, such as AL. ALLOY EXTRUSIONS heat scale on steel sheet stock, may protect iron surfaces rather efficiently. However, if sufficient oxygen and moisture are present, the iron oxide is soon converteu to hydrated ferric oxide, which is the conventional red rust.
Aluminum
Aluminum and its alloys exhibit a wide range of corrosive attack, varying from general etching of the surfaces to penetrating attacks along the HIDDEN CORROSION OCCURS internal grain boundaries of the metal. The HERE. JOINT FREEZES AND corrosion products are seen as white to gray LUGS BREAK OFF WHEN powdery deposits and more voluminous than the HINGE IS ACTUATED originalmetal. Inits early stages, aluminum corrosion is evident as general etching, pitting, and roughness of the surface. The surface attack progresses quite slowly at first; however, it will be accelerated if corroding material is not given AM.57 immediate attention. Figure 11-10.Hinge corrosion points. Paint coatings tend to mask evidence of corro- sion, but the fact that the corrosion products are andplates whichare opened only during more voluminous will result in corrosion show- periodic inspections, they tend to freeze in place ing up a3 blisters, flakes, chips, lumps, or other between inspections. The inspection for corro- irregularities in the paint coating. Often white or sion of these hinges should include lubrication gray streaks of corrosion products will become and actuation through several cycles to insure readily apparent at breaks in the paint film. Any complete penetration of the lubricant. such indications should result in further investi- gation to determine the extent that corrosion APPEARANCE OF CORRODED PARTS has progressed.
One of the problems involved in corrosion Magnesium and Its Alloys control is recognizing corrosion products when they occur. The following paragraphs include Magnesium corrosion products are white and brief descriptions of typical corrosion product quite large compared to the size of the base characteristics of the more common materials of metalbeing corroded. The deposits have a aircraftconstruction. Photographs of typical tendency toraise slightly and the corrosion corroded surfaces are provided in Nav Air 01- spreads rapidly. When white puffy areas are dis- 1A -509 and reference to that publication will covered on magnesium it requires prompt atten- enable maintenance personnel to become more tion as the corrosion may penetrate entirely familiar with and be able to identify corrosion in through the structure in a very short time. its various stages.
Iron and Steel Copper and Copper Alloys Possibly the best known and easiest recog- Cdpper and its alloys are generally corrosion nized of all forms of metals corrosion is the resistant, although the products of corrosive
302 Chapter 11CORROSION CONTROL attack on copper are commonly known. Some- tect by forming an actual physical noncorrosive times copper or copper alloysurfaceswill barrier over the steel. Electroplated coatings, tranish to a dull gray-green color and the surface particularly chromium on steel, are somewhat may still be relatively smooth. This discoloration porous, and corrosion eventually starts at these is the result of the formation of a fine-grained, pores or pin holes unless a supplementary coat- airtight copper oxide crust, called a patina. This ing is applied and maintained. patina in itself offers good protection for the underlying metal in ordinary situations. How- Titanium ever, exposure of copper and copper alloys to moisture or salt spray will cause the formation Titanium is becoming more commonly used of blue or green salts indicating active corrosion. in aircraft construction. It is a highly corrosion- These salts will form over the patina since this resistant metal, but it may show some surface crust is not impervious to water (not moisture- deterioration from the presence of salt deposits proof). Copper alloys used in aircraft generally and other impurities, particularly at higher tem- have a cadmium-plated finish to prevent surface peratures. Corrosion products appear as minute staining and deterioration. surface cracks. When used with other metals, in- sulation must be used to prevent dissimilar metal Cadmium and Zinc attack on the other metals. Cadmium, particularly, is used as a coating to FORMS OF CORROSION prc .ect the part to which it is applied and to provide a compatible surface when the part is in Corrosion may occur in several forms, de- contact with other materials. The cadmium plate pending upon the metal involved, its size and supplies sacrificial protection to the underlying shape, its specific function, atmospheric condi- metal because of its greater activity. That is, dur- tions, and the corrosion-producing agents pres- ing the time it is protecting the base metal, the ent. Those described in this section are the cadmium isintentionally being consumed.It more common forms found on aircraft struc- functions in the same way that an active magne- tures. Corrosion has been cataloged and typed in sium rod inserted in the water system protects many ways. For descriptive purposes, the types the piping of a hot water heater. The cadmium are discussed here under what is considered the becomes anodic and is attacked first, leaving the most commonly accepted titles. base metal free of corrosion. Zinc coatings are used for the same purpose, but to a lesser extent Direct Surface Attack in aircraft. Attack is evident by white to brown to black mottling of the cadmium surfaces. The surface effect produced by the direct These indications DO NOT indicate deteriora- reaction of the metal surface with oxygen in the tion of the base metal. Until the characteristic air is a uniform etching of the metal. The rusting colors peculiar to corrosion of the base metal of iron and steel, the tarnishing of silver, and the appear, the cadmium is still performing its pro- general dulling of aluminum surfaces are com- tective function. Wire brushing or removal of the mon examples of surface attack. On aluminum mottled areas of cadmium merely reduces the surfaces if such surface attack is allowed to con- amount of cadmium remaining to protect the tinue unabated, the surface will become rough underlying structure. and eventually frosted in appearance. Pitting Corrosion Nickel and Chromium Alloys The most common effect of corrosion on These metalsare also used asprotective aluminum and magnesium alloys is called pit- agents, both in the form of electroplated coat- ting. It is due primarily to the variation in struc- ings and as alloying constitutents with iron in ture or quality between areas on the metal sur- stainless steels. Nickel and chromium plate pro- face in contact with a corrosive environment.
303 AVIATION STRUCTURAL MECHANIC S 3 & 2
Pitting corrosion is first noticeable as a white or possibility of water accumulation, by avoiding gray powdery deposit, similar to dust, which the creation of crevices during repair work, and blotches the surface. When the superficial de- by elimination of any existing voids which may posit is cleaned away, tiny pits or holes can be become water traps by the use of approved seen in the surface. They may appear as rela- sealants and caulking compounds. tively shallow indentations or deep cavities of small diameter. Pitting may occur in any metal, but it is particularly characteristic of aluminum Intergranular Attack and magnesium. Including Exfoliation Crevice Attack or All metals consist of many tiny building Concentration Cell blocks called crystals. These crystals are some- times called grains. The boundaries between Concentrationcellcorrosionisactuallya these crystals are commonly referred to as grain form of pitting corrosion which is caused by the boundaries. Intergranular corrosion is an attack difference in concentration of the electrolyte or on the grain boundaries of some alloys under theactive metalat the anode and cathode. specific conditions. During heat treatment, these When there is concentration differences at two alloys are heated to a temperature which dis- different points in an entrapped pool of water or solves the alloying elements. As the metal cools, cleaning solution, anodic and cathodic areas may these elements combine to form compounds; result, and the anodic area will be attacked. and if the cooling rate is slow, they form dis- Figure 11-11 illustrates the theory of concentra- crimininantly at the grain boundaries. These tion cell corrosion. This type of attack is gen- compounds differ electrochemically from the erally detected where there are crevices, scale, material adjacent to the grain boundaries and surface deposits, and/or stagnant water traps. can be either anodic or cathodic to the adjoining This type corrosion is controlled and prevented areas, depending on their composition. The pres- by keeping areas cleaned, by eliminating the ence of an electrolyte will result in attack of the anodic area. This attack will generally be quite rac id and can exist without visible evidence. As intergranular corrosion progresses to the LOW METAL ION CONCENTRATION more advanced stages, it reveals itself by lifting up the surface grain of the metal by the force of expanding corrosion products occurring at the grain boundaries just below the surface. This ad- AN. vanced attack is referred to as EXFOLIATION, and its recognition by corrosion personnel and HIGH METAL ION CONCENTRATION immediate action to correct such serious corro- sion is vital to aircraft safety. The insidious na- METAL ION CONCENTRATION CELL RIVETED LAP JOINT ture of such an attack can seriously weaken
HIGH OXYGEN CONCENTRATION structural members before the volume of corro- sion products accumulate on the surface and the
yAer damage becomes apparent. /. At A Metal that has been properly heat-treated is not readily susceptible to intergranular attack; however, susceptibility can develop from local- LOW OXYGEN CONCENTRATION ized overheating, such as could occur from weld- ing, fire damage, etc. If the intergranular attack OXYGEN CONCENTRATION CELL has not penetrated too far and sufficient struc- AM.1128 tural strength remains, corrective procedures as Figure 11-11.Concentration cell corrosion. outlined in the applicable Structural Repair
304 Chapter 11CORROSION CONTROL
Manual could restore the aircraft to a flight unequal cooling from high temperatures during status. heat treatment, and by internal structural re- Whenever intergranular corrosion is evident or arrangement involving volume changes. Stresses suspected, it should be immediately brought to set up when a piece is deformed, those induced the attention of senior personnel who can initi- by press and shrink fits, and those in rivets and ate appropriate action. bolts are examples of internal stresses. Con- cealed stressis more important than design Dissimilar Metal Corrosion stress, especially because stress corrosion is diffi- cult to recognize before it has overcome the de- Galvanic or dissimilar metal corrosion is the sign safety factor. The magnitude of the stress term applied to the accelerated corrosion of varies from point to point within the metal. metal caused by dissimilar metal being in con- Stressesinthe neighborhood of the yield tact in a corrosive medium such as salt spray or strength are generally necessaryto promote water. stress corrosion cracking, but failures have oc- Dissimilar metal corrosion is usually a result curred at lower stresses. of faulty design or improper maintenance prac- tices which result in dissimilar metals coming in Fatigue Corrosion contact. It is usually recognizable by the pres- ence of a buildup of corrosion at the joint Fatigue corrosion is a special kind of stress between the metals. For example, aluminum and corrosion and is caused by the combined effects magnesium materials riveted togehter in an air- of corrosion and stresses applied in cycles to a craft wing form a galvanic couple if moisture or part.NOTE: An example of cyclic stress is contamination is present. When aluminum pieces the alternating loads to which the reciprocating are attached with steel bolts or screws, galvanic rod on the piston of a hydraulic, double-acting corrosion can occur around the fasteners. actuating cylinder is subject. During the exten- Aircraft manufacturer's utilize a variety of sion stroke a compression load is applied and separating materials such as plastic tape, sealant, during the retracting or pulling stroke, a tensile primer, washers, lubricants, etc., to keep these or stretching loadisapplied. Damage from metals from coming in direct contact and thus fatigue corrosion is greater than the combined keep corrosion to a minimum. It is imperative damage of corrosion and cyclic stresses if the that these separating materials remain intact or part was exposed to each separately. Fracture of are replaced, restored, or repaired as necessary a metal part due to fatigue corrosion generally throughout the life of the aircraft. . occurs at a stress far below the fatigue limit in a Since some metalsare more active than laboratory environment, even through the others, the degree of attack will depend on the amount of corrosion is unbelievably small. For relative activity of the two surfaces in contact. this reason, protection of all parts subject to In any case, the more active or easily oxidized alternating stress is particularly important wher- surface becomes the anode and corrodes. In ever practical, even in environments that are plated metal the possibility of dissimilar metal only mildly corrosive. corrosion becomes a factor only if there are de- fects in the plating, which would allow moisture Fretting Corrosion penetration and subsequently the forming of a galvanic cell. Fretting corrosionis a limited but highly damaging type of corrosion caused by a slight Sta:"Qc Corrosion vibration, friction, or slippage between two con- tacting surfaces which are tinder stress and Stress corrosion, evidenced by cracking, is heavily loaded.Itis usually associated with caused by the simultaneous effects of tensile machined parts, such as the area of contact of stress and corrosion. Stress may be internal or bearing surfaces, two mating surfaces, and applied. Internal stresses are produced by non- bolted or riveted assemblies. At least one of the uniform deformation during cold working, by surfaces must be metal. In fretting corrosion, the
305 AVIATION STRUCTURAL MECHANIC S 3 & 2 slipping movement at the interface on the con- chapter 3 of this manual are suitable for detec- tacting surface destroys the continuity of the tion of the depth of intergranular corrosion and protective films that may be present on the stress corrosion cracks or other general defects metallic surface. This action removes fine par- in metal. Special methods to detect intergranular ticles of the basic metal. The particles oxidize corrosion using ultrasonics and eddy current and form abrasive materials which further agi- principles familiar to some specially trained senior tate within a confined area to produce deep pits. Structural Mechanics have been developed. Such pits are usually so located as to increase Knowledge of these more sophisticated methods the fatigue failure potential of the metal. Frett- is not required at the AMS 3 & 2 petty officer ing corrosion is evidenced at an early stage by level. Any time there is even the slightest con- surface discolor.tion and by the presence of cern over the extent of intergranular corrosion corrosion products in any lubrication present. damage or suspected damage, these specially Lubrication and securing the parts so that they developed methods should be conducted by are rigid are the most effective measures to pre- qualified personnel. vent this type of corrosion.
Filiform Corrosion CORROSION ELIMINATION Filiform corrosion is threadlike filaments of When corrosion of aircraft skin or structures corrosion known as underfilm. Metals coated has been discovered, the first step to be taken with organic substances, such as paint films, may should be the safe and complete removal of the undergo this type of corrosion. corrosion deposits or replacement of the af- Filiform corrosion occurs independent of fected part. Which of these actions to be taken light,metallurgical factorsinthesteel, and depends upon the degree of corrosion, the ex- bacteria, but takes place only in relatively high tent of damage, the capability to repair or re- humidity, 65to 95 percent. Although the place, and the availability of replacement parts. threadlike filaments are visible only under clear Any part which has been damaged by corrosion lacquers or varnishes, they also occur with some should be replaced if continued use is likely to frequency under opaque paint films. Filiform result in structural failure. Areas to be treated corrosion can occur on steel, zinc, aluminum, for corrosion deposit elimination must be clean, magnesium, and chromium plated nickel. unpainted, and free of oil and grease. Chips, burrs, flakes of residue, and surface oxides must Microbiological Corrosion be removed. However, care must be taken to avoid removing, at the same time, too much of Micro-organisms contained in sea water can be the uncorroded surface metal. Corrosion deposit introduced into fuel systems by contaminated removal must be complete. Failure to clean any fuel. These fungus growths attack, the sealing surface debris permits the corrosion process to material used on integral fuel tanks. Under cer- continue even after refinishing the affected tain conditions, they can cause corrosion of areas. aluminum probably by aiding in the formation When corrosionispresent, any protective of concentration cells. Residues resulting from paint films must first be removed to insure that biological growth tend to clog fuel filters, and the entire corroded area is visible. After the coat fuel capacity probes, giving erroneous fuel corrosion has been removed the extent of da- quantity readings. mage must be assessed. It is at this point that the determination is made to repair or replace the SPECIAL DETECTION METHODS affected part or to perform a corrosion correc- tion treatment. This treatment involves the neu- A varietyof nondestructiveinspection tralization of any residual corrosion materials methods may be utilized by the Aviation Struc- that may remain in pits and crevices, and the tural Mechanic in detecting flaws in metal. The restoration of permanent protective coatings and metals inspection techniques discussedin paint finishes.
. 306 Chapter 11COR ROS1ON CONTROL
PAINT REMOVAL and stripping, insure that the aircraft is properly grounded to dis3ipate any static electricity pro- Paint removal operations atthe Organiza- duced by the cleaning and stripping cperations, tional and Intermediate level of maintenance arc Using approved tapes and papers, mask all usually confined to small areas, or possibly a seals, joints, skin laps, bonded joints, etc., where whole panel. In allcases, the procedures out- the paint remover may contact adhesives. lined in the applicable Maintenance Instructions Apply the stripper liberally, and completely Manual should be observed. General stripping cover the surface to a depth of 1/32 to 1/16 procedures are contained in Aircraft Cleaning inch, using a bristle brush. The stripper should and Corrosion Control for Organizational and not be spread in a thin coat like paint, since it Intermediate Maintenance Levels, Nav Air 01- will not loosen paint sufficiently for removal 1A-509. and the remover may dry on the surface of the metal, requiring a reapplication. Materials Allow the stripper to remain on the surface for a sufficient length of time to wrinkle and lift Allpaint removers aretoxic and caustic; the paint, which may be from 10 minutes to therefore, both personnel and material safety several hours, depending on both the tempera- precautions must be observed in their use. Per- ture and humidity and the condition of the sonnel should wear eye protection, gloves, and a paint coat being removed. Loosened paint may rubber apron. be removed with fiber scrapers, bristle brushes, PAINT REMOVER, SPECIFICATION MIL- and rags. The surface should then be rinsed with R-81294.This is a new epoxy paint remover water to remove any residual stripper. for useinthe field. This remover will strip After rinsing the area thoroughly, wipe down acrylic and epoxy finishes very satisfactorily. with rags wet with lacquer thinner or an ap- Acrylic windows, plastic surfaces, and rubber proved solvent cleaner such as Stoddard solvent. prodUcts are adversely affected by this material. The next step is to remove all masking tape This material should not be stocked in large and carefully strip away the remaining paint it quantities as it ages rapidly, degrading the results covered, using rags slightly dampened with an of stripping action. approved solventcleaner suchasmethyl - Additional paint removers are discussed in ethyl- ketone (MEK). Use only nonmetallic Nav Air 01-1A-509 and Nav Air 07-1-503. Each scrapers to assist in removing persistent paint remover has a specific intended use. For exam- finishes. ple, MIL-R-81294 is for removing epoxy finishes but could be damaging to synthetic rubber, while non-flammable water soluble paint re- CORROSION REMOVAL mover conforming to MIL-R-18553 is usable in contact with synthetic rubber. In all cases utilize Afterthepainthasbeen removed from the recommended remover that meets the re- corrosion-damaged areas of metal surfaces, it is quirements of the job being accomplished. necessary to remove all corrosion deposits be- fore an accurate assessment of damage can be Procedures and Precautions made. The different corrosion removal processes required by the various aircraft metals include The stripping procedures provided in this sec- chemical treatments to prevent or retard future tion are general in nature. When stripping any corrosive attack. These chemical treatments are aircraft surface, consult the applicable Mainte- discussed as a part of the corrosion removal pro- nance Instructions Manual for the specific proce- cesses in this section. Further chemical treat- dures to be used. ments are applied for the purpose of improving Stripping should be accomplished outside paint adhesion if it is determined that the corro- whenever possible. If stripping must be done in a sion damage is tolerable and the affected parts hangar or other enclosure, adequate ventilation may remain in service. Prepaint treatments are must be assured. CAUTION: Prior to cleaning discussed in a subsequent section of this chapter.
307 AVIATION STRUCTURAL MECHANIC S 3 & 2
Corrosion Removal From Aluminum cessing of anodized surfaces, including corrosion removal, should avoid unnecessary destruction There are three types of aluminum surfaces of the oxide film. insofar as corrosion removal is concerned. They Aluminum wool, nylon webbing impregnated are clad, anodized, and exfoliated. with aluminum oxide abrasive, or fiber bristle CL AD ALUMINUM SURFACES.Pure brushes arethe approved tools for cleaning aluminum has considerable corrosion resistance anodized surfaces. The use of steel wool, steel compared to aluminum alloys, but has little or wire brushes, or harsh abrasive materials on any no structural strength. It has been learned that aluminum surfaces is prohibited. Producing a an extremely thin sheet of pure aluminum lami- buffed or wire brush finish by any means is also nated onto each side of an aluminum alloy sheet prohibited.Otherwise, anodizedsurfaces are improves the corrosion resistance with little im- treated in much the same manner as other alumi- pairment of strength. The trade name of this num finishes. aluminum laminate as originated by the Alumi- EXFOLIATED SURFACES.As previously num Company of America is "Alciad." From described, exfoliation is a separation along the this trade name the adjective "clad" and the grain boundaries of metal and is caused by inter- verb "cladding" have been derived. Not all air- granular corrosion. More severe procedures must craft sheet aluminum isclad, especially those be observed when intergranular corrosion is pres- alloy sheets from which small brackets, gussets, ent. The mechanical removal of all corrosion fittings, etc., are made. The pure aluminum is products and visible delaminated metal layers very soft and the fabrication processes would must be accomplished in order to determine the severely damage or destroy the clad surfaces. extent of destruction and to evaluate the remain- To remove corrosion from clad surfaces the ing structural strength of the component. Metal corroded areas should be hand polished with scrapers, rotary files, and other necessary tools household abrasives such as Bon Ami or Ajax, or are used to assure that all corrosion products are with a specification metal polish, MIL-P-6888. It removed and that only structurally sound alumi- (the specificationpolish) effectively removes num remains. Inspection wish a 5 to 10 power stains and produces a high-gloss, lasting polish magnifying glass, or the use of dye penetrant on unpainted clad surfaces. During the foregoing (Chapter 3), will aid in determining if all un- polishing operation, care must be taken to avoid sound metal and corrosion products have been unnecessary mechanical removal of the protec- removed. When complete removal has been at- tive clad layer and the exposure of more sus- tained, any rough edges should be blended or ceptible, but stronger, aluminum alloy base. smoothed out even though this involves the re- If there is any superficial corrosion present, it moval of more metal. Grinding, where required, should be treated by wiping down with an inhib- can best be accomplished by using rubber base itive material such as the Chemical Surface Films wheels into which tiny particles of aluminum for Aluminum Alloy, available under specifica- oxide abrasives have been impregnated. tion MIL-C-5541. (See Chemical Surface Treat- Chemical treatment of exposed surfaces is ap- ment, this chapter.) plied in the same manner as any other aluminum ANODIZED ALUMINUM SURFACES. surface. Anodizing is the most common surface treat- Any loss of structural strength in critical areas ment of nonclad aluminum alloy surfaces. The should be evaluated by cognizant aeronautical aluminum alloy sheet or casting is the positive engineers, particularly if the damage exceeds the pole in an electrolytic bath in which chromic permissible limits established in the Structural acid or other oxidizing agent produces an alumi- Repair Manual for the aircraft model involved. num oxide film on the metal surface. Aluminum oxideisnaturallyprotective. and anodizing Corrosion Removal From merely increases the thickness and density of the Iron and Steel natural oxide film. When this coating is damaged in service, it can only be partially restored by The most practicable means of controlling the chemical surface treatments. Therefore, any pro- corrosion of steel is the complete removal of the
308 Chapter 1 1 CORROSION CONTROL corrosion products (rust) by mechanical means. ready for a protective paint coating. Aluminum oxide abrasive paper or abrasive im- pregnated nylon webbing can be used. However, Corrosion Removal From Magnesium residual iron rust usually remains in small pits and crevices. Vacu-blasting with glass beads re- Magnesium corrosion reprotection involves moves nearlyallrust andisthe preferred the maximum removal of corrosion products, method. the partial restoration of surface coatings by There are approved methods for converting chemical treatment, and a reapplication of pro- active iron rust to phosphates andotherprotec- tective coatings. tive coatings; however, most of these procedures After cleaning the surface and stripping the require shop installed equipment and are there- paint, if any, as much of the corrosion products fore impractical in the field. Another disadvan- as possible should be broken loose and removed, tage of chemically inhibiting iron rust is the using abrasive impregnated nylon webing or glass danger of entrapping these chemicals in installed beads with the Vacu-Blast Dry Honing Machine. assemblies where thorough flushing is difficult, Steel wire brushes, carborundum abrasives, or thereby causing far more corrosion than was steel cutting tools should not be used. After the originally present. corrosion has been removed, treat the surface HIGHLY-STRESSED STEEL SURFACES. with. Specification MIL-C-5541, chemical treat- Any corrosion on the surface of highly stressed ment solution, as outlined in the section on steelis potentially dangerous, and careful re- Chemical Surface Treatment (this chapter); then moval of the corrosion deposits is mandatory. restore the protective paint film. Surface scratches or changes in the surface mo- If extensive removal of corrosion products lecular structure due to overheating can cause from a structural casting was involved, a decision sudden failure. Removal of corrosion products from a structural engineer may be necessary in must be accomplished by careful processing, order to evaluate the adequacy of the structural using mild abrasive papers such as fine grit strength remaining. Structural Repair Manuals aluminum oxide, or fine buffing compounds on for the aircraft models involved usually include cloth buffing wheels. It is essential that the steel tolerance limits for dimensions of critical struc- surface not be overheated while buffing. After tural members and should be referred to if any this careful removal of surface corrosion, protec- question of safety of flight is involved. tivepaintfinishes shouldbe reapplied im- mediateiy. Corrosion Removal From Titanium CADMIUM PLATED SURFACES.As stated previously, cadmium platings are still offering Titanium surfaces that show surface deteriora- sacrificialprotection even when they show tion from the presence of salt deposits and im- mottling ranging from white to brown to black purities are cleaned with Specification P-D-680 ontheirsurfaces. This discoloration should solvent (Stoddard solvent), then any corrosion is never be removed for appearance sake alone. removed by hand using abrasive impregnated Not until the characteristic color peculiar to nylon webbing and followed by final cleaning of corrosion of the base metal appears should steps the surface with water emulsion cleaner solution be taken. (1 part cleaner to 9 parts water). Corrosion present should be removed by rub- NOTE: The use of steel wool, iron scrapers, bing lightly with stainless steel wool. Under no or steel brushes for cleaning or the removal of circumstances should a wire brush, stainless or corrosion from titanium parts is prohibited. . otherwise, be used on cadmium plates surfaces as these will remove more plating than corro- MECHANICAL CORROSION sion. After the corrosion has been removed the REMOVAL BY BLASTING affected area should be swabbed with a chromic acid solution and, after 30 to 60 seconds, rinsed Vapor blasting,. soft grit blasting, and dry with clean water and dried with clean cloths or vacuum blasting are the most effective mechani- low-pressure compressed air. The part is then cal methods of removing corrosion with the least
309 AVIATION STRUCTURAL MECHANIC S 3 & 2 removal of the metal. For use on assembled air- craft,a portable unit such as the Vacu -Blast Aero Dry Honer is the most desirable.
VACU-BLAST Aero Dry Honer
The VACU-BLAST Aero Dry Honer is a port- able self-contained, lightweight unit utilizing the dry vacuum return system. (Dry honing is the only authorized blasting method of removing corrosion on assembledaircraft.)Withthis machine the work is more visible and metal re- moval can be held to closer limits. The machine SUPPLY PRESSURE GAGE is air operated and can be used in shore-based or shipboard operations.
COMPONENTS.The dry honing machine AIR EJECTOR ABRASIVE PUMP illustrated in figure 11-12 is composed of the RECLAIMING SYSTEM following principal components mounted on a VNtUMA)IC two-wheel carriage assembly: SYSTEM VIBRATING SCREEN (INSIDE) MAIN 1. Pneumatic system. AIR SUPPLY ABRASIVE CONNECTION 2. Control and regulator valves and gages. HOPPER 3. Abrasive hopper (storage tank). (STORAGE TANK) AIR FILTER ABRASIVE MUFFLER 4. Aerator and feed tee. SUPPLY HOS 5. Abrasive supply and return hoses. AIR HO (TO GUN DUST BAG 6. Suction bypass line. RAPPER 7. Blast gun assembly. AERATOR 8. Gun set attachments. AND FEED TEE 9. Air ejector pump. 10. Abrasive reclaimer. 11. Dust collector. AM.59 12. Vibrating screen. Figure 11-12.VACU-BLASTDry honing machine (back view). A hose rack and storage compartment are pro- vided on the front of the dry honing machine for storage of hoses, brushes, and accessories. variable pressure regulator is operated to adjust Pneumatic System.The pneumatic system the air supply to the desired pressure before includes a main air supply connection at which entering the airhose to the blast gun assembly. is attached the external compressed-air supply, This pressure is indicated on the blast pressure interconnecting tubing,and airfilter with a gage adjacent to the pressure regulator. drain cock for removal of liquid from the com- Abrasive Hopper (Storage Tank).The abra- pressed air, and an air ejector pump that creates sive storage tank is conical in -Shape to effect the necessary vacuum to return the used abrasive direction of flow of abrasive. It is removed by from the blast gun assembly to the filter bags. release of two spring clamps. The normal capac- The dry honing machine operates satisfactorily ity of the storage tank is 5 pounds of abrasive on air pressures ranging from 80 to 100 psi and material. air-flows ranging from 80 to 90 cfm. Aerator and Feed Tee.The aerator and feed Control and Regulator Valves and Gages.The tee located at the bottom of the storage tank is supply pressure gage indicates the compressed- designed to aerate the abrasive in the storage air supply pressure. The 150-pound maximum tank and feed is to the blast hose leading to the
310 Chapter 11CORROSION CONTROL blast gun. The aeration is effected by mixing of BLAST CONTROL VALVE air with the fine abrasive. When the fine abrasive is aerated, debris par- ticles which may be mixed with the abrasive, settle to the bottom of the storage tank. The AIR abrasive is then drawn through a metering valve, ABRASIVE from a point a short distance above the bottom of the tank, thus preventing recirculation of the debris particles. The abrasive then flows through ABRASIVE the feed tee into the supply hose. RETURN HOSE AbrasiveSupply and Return Hoses.The abrasive supply hose is a 20-foot length of 5/8- inch ID transparent plastic hose, which permits direct observation of abrasive flow. It is attached to the aerator and feed tee and conveys aerated abrasive to the blast gun assembly. The abrasive BLAST GUN ASSEMBLY return hose is 20 feet long and returns used abra- sive and debris from the blast gun assembly to the abrasive reclaiming system. Suction Bypass Line.The suction bypass line is designed to remove abrasive from the blast hose when the machine is shut off in order to eliminate hose surging when blasting is started again. One end of this line is connected to the feed tee opposite the blast hose connection, and the other end of the line extends up into the storage tank. This line terminates in the storage tank above the abrasive level, and the open end isprotected from the abrasive by an interior baffle. When blasting stops, the exhauster re- mainsinoperationtosuckairbackwards through the blast gun assembly, abrasive supply hose, feed tee, and bypass line, conveying any abrasive in the hose back into the storage tank. When blasting, airflow is reversed and the bypass line insures a balanced pressure between the storage tank and the feed tee housing so that abrasive will fall freely through the feed tee into the blast hose. Blast Gun Assembly.The blast gun assembly (fig.11-13) consists of a hand-held gun, blast control valve, nozzle assembly, and connections for air, abrasive supply, and return hoses. The blast gun assembly draws the abrasive material from the abrasive supply hose, accelerates the CUTAWAY V EW abrasive through the blast nozzle, and directs it against the workpiece. This is accomplished through the gun, which employs an eduction principle whereby compressed air is expended AM.60 through an air jet to create a low pressure area in Figure 11-13.Blast gun assembly. the gun housing, and by connecting the abrasive
311 AVIATION STRUCTURAL MECHANIC S 3 &2
BRUSH ACCESSORIES r / fr ties gowl" ,. ,:, , RUBBER _ ...... S\wW -4141# PAD 1 Pv ii Attti..1#'4 4111))))
Y 1 /kW 1 AO 1.1 L r--- lg. -.', ::4 ' FLAT SURFACE INSIDE CORNER OUTSIDE CORNER EDGE CLEANING IRREGULAR SURFACE
AM.61 Figure 11-14.Gun set attachments. supply hose to the gun housing at the point filter bag type dust collector onto which the where this low pressure area is created. reclaimer is mounted. Gun Set Attachments. The three brushes and Dust Collector.The dust collector consists of an irregular surface attachment, illustrated in a number of cloth Liter bags so arranged that figure 11-14, are provided with the dry honing dust laden air rising from the reclaimer cyclone machine,- and permit blasting of most surfaces. is ducted to the bottom of the dust collector Additional care must be exercised with the in- housing where it must pass through the cloth side and outside corner brushes to avoid the loss filter bags before being discharged through the of abrasive. The irregular surface attachment will exhauster. Filter bags are periodically cleaned by conform to most irregularities. a manually operated bag-shaking mechanism to Air Ejector Pump.The airejector pump remove the accumulated dust which drops to the creates the necessary vacuum to return the abra- dust collector box for disposal. sive from the blast gun assembly through the return hose to the abrasive reclaimer, carrying Vibrating Screen.The vibrating screen, incor- the dust still farther to the cloth filter bags in porating a permanent magnet to remove steel the dust collector. particles,islocated between the reclaimer Abrasive Reclaimer.The abrasive reclaimer is cyclone and the abrasive storage tank. The mounted directly above the abrasive storage screen is sufficiently fine to remove any oversize tank and consists essentially of a cyclone separa- foreign particles from the abrasive. The vibrating tor into which abrasive and debris (from the screen is exposed for cleaning and inspection by abrasive return hose) enter. The angle at which dropping the abrasive storage tank. It is vibrated entry is made imparts a cyclonic, or circular, by an air-driven vibrator mounted at the center action to the airstream, causing the abrasive to of the screen on a supporting frame, the amount drop out of suspension. The conveying airstream of vibration being preset by an orifice in the air leaves the separator through the top, carrying line. with it extremely fine particles of dust which are ABRASIVEAlthough blasting equipment no longer usable as abrasive. The reclaimed abra- may use many types of abrasives, only glass sive itself drops to the bottom of the separator beads are authorized for the removal of mild to and then back through a vibrating screen section medium corrosion from naval aircraft. Glass into the abrasive storage tank. Air and dust leav- beads are manufactured of high grade optical ing the reclaimer cyclone pass into the cloth crown glass, soda lime type.
312 Chapter 11CORROSION CONTROL
OPERATING PROCEDURES.The operating procedures listed in this section are general in nature. The dry honing machine must Le uscl with care, and only by a qualified operator. NOTE: A face shield mus be worn a',all times while operating the di, honing machine. To operate the dry honer, fill the abrasive hopper with a full charge of the correct size abrasive material. Less than full abrasive charges may be used for touchup work or for dry honing either highly corroded or relatively small areas ofsteel,Contaminatedabrasivesshould be thrown away after completion of the dry honing operation. No less than one-half charbe (2 1/2 pounds) should ever be used. After filling the machine with the correct abrasive, turn the regulator adjusting screw to the full open position, then turn on the external air supply valve. Set the pressure regulator to the AM.62 desired pressure by placing the gun against a Figure 11-15.Proper operation of gun. scrap piece of metal or rubber and operating the gun. The blast pressure can then be adjusted hours of operation, shut off the air supply to the with the machine in operation. machine and shake down the filter bags by Hold the blast gun firmly against the surface swinging the dust bag rapper down and sharply to be dry honed and press down on the blast returning it to the normal position, Repeat this control valve. Move the gun in a smooth pattern rapper action for 20 quick strokes. After shaking of overlapping strokes, advancing approximately down the filter bags, empty the dust box. 3/4 inch at each pass. Dwell times must be kept Four-Hour Intervals. Open the drain cock at at the minimum necessary to produce complete the bottom of the air filter and drain moisture corrosion removal. every 4 hours, or whenever visible. Additional CAUTION: Excessive dwell times could re- maintenance and lubrication requirements are sult in overheating of the material and/or excess- defined in Nav Air 17-5BM-1. ive metal removal. CAUTION: Care must be taken to prevent Smoothest reversal of direction at the end of damage to the plastic air filter bowl. Mechanical each pass is made by moving the brush in a small damage or contact with common solvents will circular bath as shown in figure 11-15, so that cause it to shatter when pressurized. If necessary the bristles roll smoothly from one direction to to clean the bowl, use only water or a mild the other. To prevent loss of abrasive, fully re- detergent solution. lease the blast control valve each time the dry L IMITATIONS.The dry honing machine honing operation is stopped and/or before the described in the aforementioned sections can gun is raised from the surface. cause damage to aircraft components and sys- INSPECTION AND M AINTENANCE. tems if improperly used. Small quantities of Certain components to the dry honing machine abrasive may be expected to escape from the require inspection and maintenance at calendar blast nozzle during normal use; therefore, the or operating intervals. The two maintenance equipment must not be used in areas or under actions listed below are usually performed by conditions where the abrasive may contaminate the operator. systems or components. CAUTION: The main air supply must be 1. Do not use on engines, gear boxes, or turned off before performing any maintenance other oil lubricating systems. action. 2. Do not use on fuel, hydraulic, or oxygen Two-Hour Intervals.At the end of each 2 system components.
313 AVIATION STRUCTURAL MECHANIC S 3 & 2
3. Mask vents of the above listed systems surface should be painted soon after treating if when blasting near theM to prevent possible con- best results are to be expected. tamina t ion. Soluble salt residues remaining on the surface 4. Use only on exterior surfaces or parts after treatment will accelerate corrosion and can which have been removed from the airframe to cause blistering of paint finishes. Thus, complete prevent possible contamination of interior areas. rinsing with fresh water following the chemical 5. Do not use on airframes skins or structural treatment is very important. Flush the chemical parts which are exposed to over 500° F in serv- with free-flowing water only. DO NOT wipe the ice. area with a damp cloth or brush as this will 6. DonotblastMetallite or honeycomb deteriorate or remove the chemical conversion panels. NOTE: Corrosion PREVENTIVE mainte- nanceisdocumented on a Support Action Form, while corrosion maintenance that is con- sidered as TREATMENT must be documented on the Maintenance Action Form so that a rec- ord of extensive corrosion rework will exist and be available for any Aircraft Logbook entries that may be requird.
CORROSION DAMAGE LIMITS The term "corrosion damage limits" refers to the amount of metal which may be removed from a corroded part and still maintain the re- quired safe margin of strength and function. When removingcorrosion,maintenance per- sonnel must be very careful not to remove more REF. NO. NOMENCLATURE of the metal than is absolutely necessary to I OUTER CYLINDER insure complete removal of corrosion. Figure 2 ACTUATOR PISTON 3 ACTUATOR BODY 11-16 illustrates the maximum corrosion depths 4 TORQUE ARMS 5 WHEEL allowed on the various components of the nose 6 FORK landing gear on one late model aircraft. 1 STEERING UNIT Damage which exceeds those limits specified 8 PISTON
in the applicable Structural Repair Manual or EssCHROME PLATE the Corrosion Control section of the applicable
Maintenance Instructions Manual necessitates re- MAXIMUM CORROSION DEPTH placement of the affected part if actual struc- REF. NO. MATERIAL MAX DEPTH tural repair of the damage is not possible or I ALUMINUM 0.015 -r CHR PLATED STEEL 0.003 feasible. 3 ALUMINUM 0.030 4 ALUMINUM 0.030 5 MAGNESIUM 0.030 CHEMICAL SURFACE TREATMENT 6 HEAT RESISTANT STEEL 0.010 7 HEAT RESISTANT STEEL 0.010 8 HEAT RESISTANT STEEL 0.010 Chemical conversion coatings will increase 8* CHROME PLATED 0.004 corrosion resistance and improve paint adhesion. HEAT RESISTANT STEEL Aftercleaning and removal of any surface oxides, aluminum and magnesium should be treated with MIL-C-5541 chemical treatment. These coatings are often damaged during aircraft AM.63 maintenance or are contaminated by grease, oil, Figure 11-16.A-5 nose gear-maximum corrosion or other foreign matter. Therefore, the treated depths.
314 Chapter 11CORROSION CONTROL
coating, which is sensitive to abrasion prior to 3. Rinse thoroughly as with the aluminum fully drying. treatment and allow to air dry prior to applying CAUTION: Personnel should wear goggles, protective paint finishes. aprons, and rubber gloves when using solutions of MIL-C-5541. Some magnesium parts in later model aircraft have been originally protected by a proprietary (held under patent) electrolytic process. The Chemical Conversion of "HAE" process is identified by the brown to Aluminum Alloys mottled gray appearance of the unpainted sur- face. "DOW 17" coatings will appear as a green The procedure to be used for the chemical to grayish green color. These coatings are gen- conversion of aluminum alloys is as follows: erally thicker than those applied by immersion or brush method such as MIL -C -5541. The elec- 1.Insure that the surface is clean. trolytic finish cannot be restored in the field. 2. Brush MIL-C-5541 solution on areas to be Therefore, when failure of the coating occurs, treated.Repeat application of fresh solution any corrosion should be removed and the bare untila uniform irridescent yellow to blown maenesium should be touched up with MIL- color is produced, then discontinue hrnshing and C-5 5 4 1chemical treatmentsolution.Care allow the solution to remain on the metal for. should be taken to minimize removal of the elec- about 1 minute. trolytic coatings as they afford greater protec- 3. Rinse the complete area with fresh water. tion than the replacement coatings. 4. Allow to air dry (usually not more than 1 hour) before priming. A powdery coating indi- cates poor rinsing or failure to keep the surface CORROSION wet during the treatment. If this occurs, the CONTROL KIT treatment should be repeated. A corrosion control kit is available for operat- NOTE: Chemical treatments conforming to ing activities and is especially useful for small Specification MIL-C-5541 are not all the same detachments. The kit is primarily designed for composition and therefore should be prepared use in treating small areas of corrosion and con- for use according to the particular manufac- tains all the necessary materials and equipment. turer's instructions. A compartment'd case provides orderly storage of materials. Most materials are identical to materials discussed in this chapter. Chemical Conversion of A maskant material is provided to use in paint Magnesium Alloys stripping operations. The maskant is squeezed around the area to be stripped and forms a dam Procedure for the chemical conversion of to protect areas where paint remover is not de- magnesium alloys is as follows: sired. The maskant must be high enough to con- tain the paint remover. After the paint is lifted 1. Insure that the surface is clean. or softened, the loosened paint, paint remover, 2. While the surfaceisstill wet, brush on maskant material are removed by using the MIL-C-5541 chemical treatment solution. Con- knicarta scraper, which is provided in the kit, to tinue application of fresh solution on the metal work the material toward the center of the en-, until a uniform light brown color is obtained. circled area. The residue is then scraped into a NOTE: The solution for magnesium is the disposable plastic bag. A washing bottle is pro- same as used for aluminum and is made up ac- vided for rinsing the area following stripping and cording to the manufacturer's aluminum treat- chemical treatment of the corroded area. ment instructions. The solution will react much The epoxy polyamide primer packages are more rapidly with magnesium than with alumi- supplied in plastic squeezable bags. At least 1 num. hour prior to use, the two components are 315 AVIATION STRUCTURAL MECHANIC S 3 & 2 mixed by pressing the inner bag of component final recommendations for refinishing require- two, so that it breaks, and then kneading the ments when the aircraft is scheduled for Progres- outer bag untilthe two components are sive Aircraft Rework at the Depot level of main- thoroughly mixed. When ready to use, the top tenance. of the bag is opened and the primer brushed on. Topcoat is available in aerosol spray cans. All other materials are common to corrosion SURFACE PREPARATION maintenance personnel. Complete instructions or appropriate reference to the Cleaning and Much of the effectiveness of any paint finish Corrosion Control Manual is provided in each kit and its adherence depends un [he careful pre- with the arrangement of materials supplied in paration of the damaged surface prior to touch- the kit printed on the back of the instruction up. The procedures to be used in paint and sheet. Materials in the kit may be replenished corrosion removal have been described pre- from standard stock as necessary to maintain the viously. The touchup paint should overlap onto kit. the existing good paint finish. The touchup ma- ter i alswillnot adhereproperlytoglossy finishes. Also, any edges of the existing film will AIRCRAFT AND COMPONENT PAINTING show throughthe overlapunlessthey are AND PAINT TOUCHUP smoothed out. To break the gloss of existing finishes and to The amount of paint touchup accomplished feather (smooth out) the edges for overlap, scuff at the Organizational and Intermediate level will sand, using 300 to 400 aluminum oxide paper. vary widely with the activity involved, the avail- Following sanding, a water rinse is used to re- ability of facilities, and the area of operations. move the abrasive residues. The primary objective of any paint finish is Next, all sanded areas and exposed bare metal the protection of exposed surfaces against dete- surfaces are wiped down with 1-BUTANOL rioration. There are secondary reasons for partic- (normal butyl alcohol). ular paint schemes; the reduction of glare by Remove any loosened seam sealants in the nonspecular coatings, the use of white or light area to be touched up and replace as necessary. colored high-gloss finishes to reduce heat absorp- (See Sealants and Sealing Practices in this chap- tion, camouflage or high visibility requirements, ter.) Also, resecure any loose rubber seals, using or special identification markings. There is sel- the type adhesive specified in the applicable dom justification for repainting for appearance Maintenance Instructions Manual. sake only. A faded or stained, but well-bonded, The area to be painted is then outlined with paint finish is better than a fresh touchup treat- tape and masking paper as shown in figure ment improperly applied over dirt, corrosion 11-17. This protects the adjoining surfaces from products, or other contaminants. over-spray and unwanted paint buildup. Complete refinishing, particularly under field conditions, should be restricted to those areas where existing paint finishes have deteriorated, TOUCHUP PROCEDURES through age and exposure, until they fail to per- form their protective function. Renewal of spe- In the past, it was necessary to identify the cial finishes and markings should also be re- specific surface finish (paint system) applied to stricted to those situations where the purpose of an aircraft at the time of manufacture or re- the .special finish is not being served. However, work. Each surface finish (nitrocellulose lacquer, maintenance and repair of paint finishes at the acrylic lacquer, and epoxy) required a specific Organizational and Intermediatelevelisex- touchup procedure that was compatible with the tremely important, from the evaluation of initial present finish. Failure to properly identify the paint finishes at the time of aircraft receipt, present surface finish and apply the specific through the constant surveillance and mainte- touchup procedures, usually resulted in wasted nance of finishes during a service tour, to the manhours and material.
. 316 Chapter 11CORROSION CONTROL
the primer will exhibit unsatisfactory properties, REMOVE MASKING BEFORE such as poor adhesion, poor chemical resistance, APPLYING TOP COAT or inadequately dried film. For mixing, pour the specified amount of part
1 into an empty container, then slowly pour part 2 into the container, stirring constantly. , to CAUTION: Always add part 2 to part 1. To thin the primer for spraying, add 11/2 parts thinner, Specification MIL-T-19588, to 2 parts primer. The thinned primer should be
t I stirred thoroughly, strained, and allowed to stand 1 hour prior to use. If necessary the thin- ning ratio may be varied slightly to obtain the proper spraying viscosity. The 1-hour standing time is necessary to permit the components to enter into chemical reaction,shorten drying 4110;iglik.i1,114A.:4.1,1 time, reduce cratering, preclude part 2 from "sweating out" or migrating, and to allow any bubbles (formed while stirring) to escape. To apply the primer, insure that the surface AM.64 tobe primed has been cleaned, chemically Figure 11-17.Masking prior to paint touchup. treated, and prepared for spraying as previously described in this section. Apply a wet coat of epoxy primer to 1mil thickness and allow to To preclude this and more effectively control dry from 1to 2 hours. One hour is sufficient corrosion, a standardized paint system for Or- when temperature and humidity range is ideal. ganizational and Intermediate level painting and paint touchup has been promulgated by the Naval Air Systems Command. This system con- Acrylic Lacquer Topcoat sists of an improved epoxy primer, Specification (MIL-L-81352) MIL-P-23377B and an acrylic topcoat, Specifica- tion MIL-L-81352, and is compatible with all of This acrylic lacquer is used as a general pur- the various systems presently used in naval air- pose external coating for metal surfaces. It is craft. applied directlyover theepoxy-polyamide primer. It is available in all colors for touchup Epoxy-Polyamide Primer and insignia marking directly over all paint sys- .(MIL-P-23377B) tems presently employed on naval aircraft. To thin the acrylic lacquer topcoat for spray- The epoxy-polyamide primer is supplied as a ing, mix 1 volume of lacquer with approxi- two-part kit, each part of which must be stirred mately 11/2 volumes of thinner. The thinner or shaken thoroughly before mixing. One part used with this lacquer is composed of equal contains the pigment, ground in an epoxy ve- parts by volume of toluene and xylene. The hicle, while the other part is composed of a clear exact thinning ratio must be determined by the polyamide solution which functions as a hardner user and adjusted to the prevailing temperature, for the epoxy solution. This primer is supplied relative humidity, and type of spraying equip- by various manufacturers. Mix only as much ment being used. Increasing the xylene portion primer as needed, as the storagelife of the promotes better flowout and reduces dry spray primer is limited after mixing. CAUTION: Do but also prolongs drying time. not substitute part 1 or part 2 from another After thinning the acrylic lacquer to spraying manufacturer. Established mixing ratios supplied viscosity, it should be applied in two spray coats by the manufacturer must be followed ,otherwise with a 30-minute air-dry interval between coats.
317 AVIATION STRUCTURAL MECHANIC S 3 & 2
Table 11-1.Acrylic topcoat application, possible defects and methods for correction.
Problem Cause/Correction
Webbing. 1.Insufficient thinning. Dry spray. 1. Insufficient thinning. 2. Increase the r.73purtiuil of the slower evaporating xylene in the xylene- toluene mixture.
Orangepeel or poor flowout. 1.Insufficient thinning 2. Increase the proportion of the slower evaporating xylene in the xylene- toluene mixture. 3. Poor spray technique. Slow drying. 1. Increase the proportion of faster evaporating toluene in the xylene- toluene blend. Bleeding through or lifting of 1. Allow epoxy primer to dry longer. primer. 2.First coat of lacquer topcoat was applied too wet (first coat can also be misted on). 3. Too rich solvents used to reduce lacquer topcoat; decrease proportion of thinner.
The total dry film thickness of the acrylic top- gaged in mixing and spraying paint and/or pri- coat should be 0.8 to 1.2 mils. mers. Gloves and aprons should also be used to To apply insignia and/or squadron markings prevent skin contact. The mixing and applica- over the acrylic topcoat, begin masking after the tion of paints and primers should be done in coating has dried tack-free. Apply the tape with well-ventilated spaces only. a minimum of pressure to avoid marking and Paint touchup in the field is a difficult task. possible damage to the topcoat. The insignia Table 1-1lists some of the problems en- and/or markings are then applied directly over countered during paint application, the most the topcoat. NOTE: Do not use epoxy primer probable cause, and methods for correction. when repainting or doing touchup work over Specification MIL-L-81352 acrylic lacquer top- coat. Polyurethane Finish Systems When painting insignia and/or squadron mark- ings over all other paint systems, use the epoxy In its present search for better quality protec- primer and then overcoat with the acrylic lac- tive finishes, the Naval Air Systems Command quer. has authorized that certain aircraft receive ex- CAUTION: The materials used for painting terior polyurethane finishes. and paint touchup are toxic and flammable. Pre- The polyurethane finish is available in kits cautions must be taken to assure respiratory consisting of a two-component materialresin (face mask) and eye protection for personnel en- and catalyst. The touchup kits are prethinned
318 Chapter 11CORROSION CONTROL and ready for use when mixed in accordance radome or leading edge coatings are in bad con- with the instructions in the kit. dition, they should be stripped completely and One-gallon kits are available for production recoated with epoxy primer and acrylic topcoat type spraying. They consist of 3 1/2 quarts of as a temporary measure. If schedules and condi- resin and 1pint of catalyst, providing a 7 to 1 tions permit adequate curing of elastomeric mixing ratio. Thinning with a suitable reducer, coatings, these original coatings may be re- as specified by the manufacturer, is required to placed. obtain a proper spraying viscosity. The repair kits are normally bought open pur- Polyurethane finishes are applied over epoxy chase to insure that fresh materials are available. polyamide primer which has been allowed to dry They should be stored in a cool place or refrig- for 1 hour. The primer is then scuffed with erated, as heat accelerates aging. Stripping of 400-grit paper to remove any dry, rough areas fiberglass surfaces should be in accordance with which could adversely affect the leveling of the current maintenance instructions. Elastomeric polyurethane film. Apply one even, light top- coatings are toxic and flammable and must be coat of polyurethane, allow to dry for 15 to 45 used with care. minutes, then apply a final full topcoat. Insignia whitepolyurethane has a slight translucent characteristic and may require the application of one additionalcoatto obtain an adequate AIRCRAFT PAINTING EQUIPMENT shadow-free finish. The total topcoat dry film AND TECHNIQUES thickness should not exceed 1.5 mils. Glossy colors will normally dry in approximately 6 to 8 The AMS is called upon many times to use his hours. Camouflage colors will dry in approxi- skill and knowledge in the painting of aircraft. mately 4 to 5 hours. This type of work is normally performed during preventive maintenance inspections or when air- Enamel Finishes craft painted surfaces warrant touchup repairs. NeW aircraft normally assigned to an activity Most enamel finishes used on aircraft surfaces are usually required to have the following mark- are baked finishes that cannot be touched up ings painted on the aircraft: Squadron designa- with the same materials in the field. tion (example, VP-8); modex number (example, Minor damage to conventional enamel finishes 5); unit identifying letter or letters (example, ordinarily used on engine housings is repaired by LC;; and at times a large bureau aircraft serial touching up with epoxy topcoat material or air- number (example, 149673). (See fig. 11-18.) drying enamel. Since types of paints were discussed earlier in the chapter, only the equipment and techniques Elastomeric Rain Erosion in painting aircraft are covered in this section. Resistant Coating (MIL-C-7439) PAINTING EQUIPMENT Elastomeric coatings are used as a coating system to protect exterior laminated plastic Spray Guns parts of high-speed aircraft, missiles, and heli- copter rotary blades from rain erosion in fl:;:ht. The spray gun atomizes the material to be They offer good resistanceto weather and sprayed and the operator directs and controls aromatic fuels in addition to rain erosion. Excel- the spray pattern through manipulation and lent adhesion is obtained after a 7-day drying minor adjustments of the spray gun. Spray guns period. are usually classedaseither suction-feed or Repairs to these coatings in the field are im- pressure-feed type. The types can be divided by practicable due to this long curing time. Kits are two methodsby the type of container used to available for repair of coatings where limited hold the paint material, and by the method in touchup is required. These kits contain a primer, which the paint is drawn through the air cap. neoprene topcoat, and antistatic coating. If the assembly.
319 AVIATION STRUCTURAL MECHANIC S 3 & 2
, ' 4t7r4s.
$ (4:11' r.
r1
AM.418 Figure 11-18.Aircraft markings.
SUC T ION-FEED TYPE.-1 liesuction-feed caused by a fleck of dried material in the nozzle, spray gun is designed for small jobs. The con- or the fluid needle packing may be too tight. It tainer for the paint is connected to the spray may also be caused by a bent fluid needle, a gun by a quick-disconnect fitting, as illustrated broken fluid needle spring, or the wrong size in figure 11-19. The capacity of this container is fluid needle for the fluid tip. approximately 1 quart. The fluid tip of this type AIR LEAKAGE.Air leakage is a result of spray gun protrudes through the air cap as improper setting of the air valve. This may be illustrated in figure 11-20. The air pressure rush- caused by a bent valve stem, a broken spring, or ing by the fluid tip causes a low-pressure area in a damaged valve or valve seat. front of the tip. This cause- paint to be drawn JERKY OR FLUTTERING SPRAY.Jerky up through the fluid tip wnere it is atomized or fluttering spray is caused by obstructed fluid outside the cap by the air pressure. passage, loose tip or damaged seat, and air in the PRESSURE-FEED TYPE.The pressure-feed fluid line. The air can be inducted from several type spray gun is designed for use on large jobs points on the equipment, loose packing nut or where a large amount of spray materials is to be dried out packing, loose or damaged coupling used. With this type, the spray material is sup- nut, loose or damaged fluid tube, lack of suffi- plied to the gun through a hose from a pres- cient material, and cup tipped too far. (See fig. surized tank. This spray gun is designed to 11-21.) operate on a high volume and low air pressure. FAULTY SPRAY PATTERNS.Faulty spray This type of spray equipment eliminates evapo- patterns, their causes, and how to correct them ration of the volatile substances of the mixture are shown in figure 11-22. before striking the surface since the paint and air CLEANING SPRAY GUNS.Spray guns are mixed internally; in other words, a wetter should be cleaned immediately after each use. coating is applied. To clean the suction type gun, empty the con- tainer and pour in a small quantity of thinner or Spray Gun Maintenance suitable solvent. Draw the thinner or suitable solvent through the gun by inserting the tube FLUID LEAKAGE.Fluid leakageat the into the container of cleaning fluid. Move the front of the gun is an indication that the fluid trigger constantly to thoroughly flush passage- needle is not seating properly. This may be ways and the tip of the fluid needle. Remove the
320 Chapter 11CORROSION CONTROL
AIR CURRENTS CREATE AyACUUM _01
FLUID TIP PROTRUDES ABOVE AIR CAP
SUCTION OR GRAVITY FEED CAP
FLUID TIP IS FLUSH WITH AIR CAP AIR CAP
PRESSURE FEED CAP
0 AM.420 CUP IS PART Figure 11-20.Suction and pressure fluidtipsand O air caps. 0 OF GUN
in the cleaning fluid as stated above for the suc-
. AM.419 tion type gun. Figure 11-19.Suction-feed type spray gun. NOTE: Do not immerse an entire spray gun in cleaning materials such as cleaning solvents and thinners. These materials dissolve the oil air cap and soak it in solvent. If this does not from leather packings and cause the gun to have clear the small holes in the air cap, remo,re the an unsteady spray. paint material, using a toothpick or broomstraw. LUBRICATION OF SPRAY GUNS.The fol- Do not use wire or other metal objects which lowing parts of a spray gun require frequent lub- may cause permanent damage to the air cap. rication: Fluid needle packing, air valve stem, To clean a pressure-feed gun, proceed as fol- and trigger bearing screw. Remove the fluid lows: Back off the fluid needle adjusting screw. needle packing before using the gun and soften Release the pressure from the pressure tank by it with oil. The fluid needle spring should be means of the relief or safety valve. Hold a cloth coated with a specified grease. (See fig. 11-24.) over the air cap and operate the gun trigger. This forces the spray material back into the pressure Air Compressors tank. (See fig.11-23.) Remove the fluid hose from the gun and pressure tank. Attach hose In order to use spray guns, a source of com- cleaner to hose and run thinner or suitable sol- pressed air is necessary. Figure 11-25 illustrates vent through to clean the hose. Place the air cap two types of air compressorsa portable unit
321 AVIATION STRUCTURAL MECHANIC S 3 & 2
OB ST RUCT ED LOOSE TIP OR LOOSE PACKING FLUID PASSAGE [-DAMAGED NUT OR DRIED SEAT OUT PACKING
LOOSE OR DAMAGED COUPLING NUT
LOOSE OR LACK OF DAMAGED SUFFICIENT FLUID TUBE MATERIAL IN CUP /4,
CUP TI PPED TOO FAR
AM.421 Figure 11-21.--Crones of jerky or fluttering spray. and a stationary unit. Both types al? in common Air Regulators use. The air regulator (or transformer) is used to The portable unit consists of an electric regulate' the amount of air pressure to the spray motor (or gasoline engine) for driving the unit, a gun and to clean the air. The air delivered to the compressor, storage tank, automatit unloader regulator always contains some oil from the mechanism, and wheels and handle for movin compressor and some water caused by condensa- the unit. tion, and many particles of dirt and dust. Air regulators are equipped with a pressure The stationary unit consists of an electric valve and pressure regulating screw. This makes motor, compressor, storage tank,centrifugal itpossibleto regulate exactly the pressure pressure release, pressure switch, and mounting delivered to the spray gun and prevents any pres- feet. sure fluctuations. The air must pass through a sack or cleaner before it leaves the regulator. Some of the more commr .,compressor This cleaner is containedinthe long cylindrical troubles are illustrated in figure 11-26. part of the regulator. 322 Chapter 1 1 CORROSION CONTROL
PATTERN CAUSE CORRECTION DRIED MATERIAL IN SIDE- PORT "A" RESTRICTS PAS- SAGE OF AIR THROUGH IT. DISSOLVE MATERIAL IN zIDE-PORT RESULT: FULL PRESSURE WITH THINNER. DO NOT POKE IN OF AIR FROM CLEAN SIDE- ANY OF THE OPENINGS WITH METAL PORT FORCES FAN PATTERN INSTRUMENTS. IN DIRECTION OF CLOGGED SIDE.
DRIED MATERIAL AROUND THE OUTSIDE OF THE FLUID NOZZLE TIP AT POSITION "B" RESTRICTS THE PASSAGE OF ATOMIZ- IF DRIED MATERIAL IS CAUSING ING AIR AT ONE POINT THE TROUBLE, REMOVE AIR NOZ- THROUGH THE CENTER ZLE AND WIPE OFF FLUID TIP, OPENING OF AIR NOZZLE USING RAG WET WITH THINNER. AND RESULTS IN PATTERN TIGHTEN AIR NOZZLE. SHOWN. THIS PATTERN CAN ALSO BE CAUSED BY LOOSE AIR NOZZLE.
REDUCING AIR PRESSURE WILL CORRECT CAUSE (I). TO COR- RECT CAUSE (2), A SPLIT SPRAY OR ONE THAT IS HEAVY OPEN MATERIM ON EACH END OF A FAN PATTERN AND CONTROL "D" TO WEAK IN THE MIDDLE IS USUALLY FULL POSITION CAUSED BY (1) TOO HIGH AN ATOMIZ- BY TURNING TO ING AIR PRESSURE, OR (2) BY ATTEMPT-LEFT. AT THE ING TO GET TOO WIDE A SPRAY WITH THINSAME TIME TURN MATERIAL. SPRAY WIDTH AD- JUSTMENT "C" TO RIGHT. THIS WILL REDUCE WIDTH OF SPRAY BUT WILL COR- RECT SPLIT SPRAY PATTERN TO CORRECT CAUSE (1) (1) DRIED OUT PACKING AROUND MATE- BACK UP RIAL NEEDLE VALVE PERMITS AIR TO GETKNURLED NUT INTO FLUID PASSAGEWAY. THIS RESULTS (E), PLACE IN SPITTING. TWO DROPS OF MACHINE OIL (2) DIRT BETWEEN FLUID NOZZLE SEAT ON PACKING, AND BODY OF A LOOSELY INSTALLED REPLACE NUT FLUID NOZZLE WILL MAKE A GUN SPIT. AND TIGHTEN WITH FINGERS (3) A LOOSE OR DEFECTIVE SWIVEL NUT ONLY. IN AG- ON SIPHON CUP OR MATERIAL HOSE CAN GRAVATED CASES, CAUSE SPITTING. REPLACE PACKING. TO CORRECT CAUSE (2), REMOVE FLUID NOZZLE (F), CLEAN BACK OF NOZZLE AND NOZZLE SEAT IN GUN BODY USING RAG WET WITH THINNER, REPLACE NOZZLE AND DRAW UP TIGHTLY AGAINST BODY.
TO CORRECT CAUSE (3) TIGHTEN OR REPLACE SWIVEL NUT (G). A FAN SPRAY PATTERN THAT IS HEAVY IN THE MIDDLE, OR A PATTERN THAT INCREASE PRESSURE FROM YOUR HAS AN UNATOMIZED "SALT-AND-PEPPER" AIR SUPPLY. CORRECT AIR PRES- EFFECT INDICATES THAT THE ATOMIZ- SURES ARE DISCUSSER ELSEWHERE ING.AIR PRESSURE IS NOT SUFFICIENTLYIN THIS CHAPTER. HIGH.
AM.422 Figure 11-22.Faulty spray patterns and how to correct them.
323 AVIATION STRUCTURAL MECHANIC S 3 & 2
I- FORCE MATERIAL BACK INTO TANK AUTOMATIC UNLOADER MECHANISM 2- DISCONNECT ELECTRIC MOTOR allows outfit to run FLUID HOSE also supplied idle after maximum with gas engines pressure is reached 3- CONNECT HOSE TO HOSE HOSE CLEANER CLEANER 4- FILL CLEANER WITH A SCLVENT
5- OPEN CLEANER VALVES TO CLEAN HOSE 6 -CLEAN OUT TANK
NOTE: RELEASE PRESSURE IN TANK BEFORE CENTRIFUGAL PRESSURE BLOWING BACK RELEASE MATERIAL: allows compressor to run free until normal A-SHUT OFF AIR TO TANK speed is attained
B- OPEN RELIEF VALVE PRESSURE SNITCH stops motor when C- LOOSEN THUMB SCREWS maximum pressure is reached D-OPEN LID SLIGHTLY
AM.423 Figure 11-23.Cleaning pressure-feed spray gun.
OIL HERE
AM.425 Figure 11-25.Air compressors.
Air regulators are equipped with two gages. One gage shows the pressure on the main line while the other shows the pressure to the spray FLUID NEEDLE gun. A complete compressor and air regulator 'PACKING installation is shown in figure 11-27. FLUID NEEDLE AIR VALVE Spray Gun Technique SPRING PACKING Proper spray gun technique is acquired and AM.424 developed through knowledge of the equipment Figure 11-24.Spray gun lubrication points. and experience of the operator. The spray gun
324 Chapter IICORROSION CONTROL
CARBON ON PISTON DIRTY VALVES
VALVE ASSEMBLY INFERIOR PISTON RINGS IMPROPERLY INSTALLED WORN WRIST PIN PAINT COVERED CYLINDER DIRTY CHECK CLOGGED AIR STRAINER VALVE
"FROZEN" BEARINGS
WORN MAIN BEARINGS
LEAKAGE LACK OF OIL OR DIRTY OIL IN AIR LINE
AM.426 Figure 11-26.Possible compressor troubles.
SLOPE TOWARDS TAKE OFF FROM DRAIN LEG TOP OF LINE PI PE RECOMMENDATIONS I-I AND 2 H.P. OUTFITS AIR REGULATOR 2 MIN. IN. UP TO 50 FT. AND OIL AND OVER 50 FT. IN. WATER EXTRACTOR TAKE OFF 3 AND 5 H.P. OUTFITS MIN. IN. UP TO 200 FT. DRAIN LEG MAIN AIR OVER 200 FT. I IN. LINE AIR REGULATOR AND OIL AND WATER EXTRACTOR
DRAIN HERE DAILY
DRAIN HERE DAILY
AM.427 Figure 11-27.Compressor and air regulator installation.
325 AVIATION STRUCTURAL MECHANIC S 3 & 2
should be held so that the spray is perpendicular to the area to which the finish is being applied. Great care should also be taken to insure that RIGHT the prescribed distance from the gun to the work is maintained. The gun should be held from 8 to 10 inches from the work for spraying lacquer and 6 to 8 1. dEG1N 3. RELEASE inches for spraying enamels, depending on the TRIGGER width of the spray pattern. Generally, with a STROKE 2. MOVE GUN BEFORE THEN PULL IN STRAIGHT LINE COMPLETING TRIGGER narrow pattern, the gun is held the farther STROKE distances from the work (10 inches for lacquer and 8 inches for enamels). In general, a distance of less than 6 inches is .% ARCING CAUSES undesirable, since the paint will not atomize DO NOT UNEVEN ARC STROKE/ \ APPLICATION properly,and"orangepeel"willresult. A distance of more than 10 inches is equally undesirable, since dried particles of paint will strike the surface and cause "dusting" of the finish. Examples of correct and incorrect spray gun SURFACE techniques are shown in figure 11-28. The distance the spray gun is held from the work is very important; however, there are other SURFACE factors which must be considered and mastered. The manner in which the gun is held and operated is illustrated in figure 11-28. Move the WRONG arm and body with the gun to kef:p the spray METHOD perpendicular to the surface. Avoid pivoting or any circular movements of the wrist or forearm CORRECT which will bring the gun closer to the surface METHOD when directly in front of the body. It is important to "trigger" the gun in order to avoid an uneven coat building up at the beginning and end of a stroke. Triggering is the AM.428 technique of starting the gun moving toward the Figure 11-28.Correct and incorrect methods of area to be sprayed before the trigger is pulled, spraying. and continuing the motion of the gun after the trigger has been released. turning to the left gives a fanshaped pattern. Caremust be taken to avoid too much As the width of the spray is increased, more overlapping on each pass of the gun or an material must be allowed to pass through the uneven coat willresult. The rate of stroke gun to get the same coverage on the increased should be such as to produce a full, wet, even area. To apply more material to the area, the coat. operator should turn the fluid needle adjustment Once the job is started it must be carried (fig. 11-29) to the left. If too much material is through to completion without stopping. applied to the surface, turn the fluid needle SPRAY GUN ADJUSTMENTS. Figure 11-29 adjustment to the right. illustrates the principal parts of a typical spray In normal operation of the spray gun, the gun, including the various adjustment points. wings on theair cap are adjusted to the The spreader adjustment dial is used in adjusting horizontalposition,asillustratedinfigure the width of the spray pattern. By turning the 11-30.Thisprovidesaverticalfan-shaped dial to the right, a round pattern is obtained; pattern, given maximum coverage as the gun is
. 326 Chapter 11CORROSION CONTRCL
14. FLUID NEEDLE 11. FLUID TIP- ADJUSTMENT 10. AIR CAP 8. SPREADER 5. SPRAY HEAD ADJUSTMENT DIAL 9. SPREADER ADJUSTMENT VALVE yo li:414/04 SIS
%...*"...."...-.."..., ::.',...... ,..e./..W.,,, .., ..".., .., of,,,,',,,,.., .- .,,,,,, ...... , ..... 7. FLUID NOZZLE ....:, 6. HOLES IN 2. AIR SPRAY CAP VALVE- 12. FLUID INLET 13. FLUID NEEDLE
1. TRIGGER
4. GUN BODY ASSEMBLY
3. AIR INLET
AM.429 Figure 11-29.Sectional view of typical spray gun. moved back and forth parallel to the surface 1. Too high an air pressure alone causes being painted. dusting of finish and rippling. 2. Too low an air pressure, coupled with too SPRAYINGPRESSURES.Normally,the high fluid pressure, causes orangepeel. AMS will be concerned with spray painting 3. Too highfluidpressurealone causes lacquer,enamel, and epoxy materials. The orangepeel and sags. correct air and fluid pressures used with these 4. Too lowfluidpressurealonecauses materials vary and are important in all spray dusting. painting applications. There are several pitfalls of incorrect pressures, some of which are listed When using 20-foot air and fluid pressure below: hoses, maintain a pressure of approximately 45
327 AVIATION STRUCTURAL MECHANIC S 3 & 2
damage or the use of paint removers has loosened existing sealants. Conditions surrounding the requirements for use of sealants govern the type of sealants to be used. Some sealants are exposed to extremely high and/or low temperatures. Other sealants are in contact with fuels, lubricants, etc. Therefore, it is necessary that sealants be used which have been compounded for that particular type of usage. These sealants are supplied in different consistencies and rates of cure. The basic types ofsealantsareclassifiedinthreegeneral categoriesPliable Sealants, Drying Sealants, and Curing Sealants.
PLIABLE SEALANTS AM.430 Figure 11.30. Spray gun nozzle. These sealants are referred to as one-part and are supplied ready for use as packaged. They are solids and change little, if any, during or after psi at the spray gun for lacquer and 50 psi for application. Solvent is not used in this type. enamel and epoxy. This pressure is measured at Therefore, drying is not necessary; and except the gun. Sufficient pressure must be maintained for normal aging, they remain virtually the same at the main line pressure regulator to obtain the as when first packaged, neither hardening nor above pressures and to compensate for the shrinking. The adhesion to metal, glass, and pressure drops encountered if additional lengths plastic surfaces is excellent. Pliable sealants are of hose are employed. The pressure at the gun used around high-usage access panels and doors, should be rechecked if the main line pressure is and in areas where pressurization cavities must changed for any reason. Fluid tank pressure for be maintained. lacquer should be 8 to12 psi. A 3-pound increase above these figures should be used in DRYING SEALANTS the case of enamel and epoxy. A proportionate increaseinpressure for lacquer and epoxy Drying sealants set and cum: by evaporation of should be allowed for additional lengths of hose the solvent. Solvents are used in these sealants to up to 50 feet maximun. One:poundfluid provide the desired consistency for application. pressure may be added for each foot of height of Consistency or hardness may change little or the gun from the fluid tank level. Make frequent much when this type sealant dries, depending on checks with a test gage of air pressure at the gun. the amount of solvent it contains. Shrinkage upon drying is another important consideration, and the degree of shrinkage is dependent upon SEALANTS AND SEALING PRACTICES the proportion of solvents.
Sealants are used to prevent the movement of CURING SEALANTS liquid or gas from one point to another. They are used in an aircraft to maintain pressurization Catalyst-cured sealants have obvious in cabin areas, to retain fuel in storage areas, to advantages over drying sealants because they are achieve exterior surface aerodynamic transformed from a fluid or semifluid state into smoothness, and to weatherproof the airframe. a solid mass by chemical reaction or physical Sealants are used in general repair work in the change, rather than by evaporation of a solvent. fild and for, maintenance and restoration of A chemical catalyst or "accelerator" is added seam integrity incritical areas if structural and thoroughly mixed just prior to sealant 328 Chapter 11CORROSION CONTROL applications. Heat may or may not be employed to speed up the curing process. When using a catalyst, accurate proprotioning and thorough mixing of the two components are vitally important to assure a complete and even cure.
APPLICATION OF SEALANTS Application of sealants varies according to time element, tools required, and the method of application. However, the following restrictions apply to all sealant applications:
1. Sealantshouldbeusedwithinthe approximate application time limits specified by tide sealant manufacturer. 2. Sealant should not be applied to metal which is colder than 70° F. Better adhesion is obtained and the applied sealant will have less tendency to flow out of place while curing if the metal is warmed to a temperature of 90° F to 100° F before the sealant is applied. 3. Sealant should be discarded immediately when it becomes too stiff to apply or work readily. Stiff or partially cured sealant will not wet the surface to which it is to be applied as well as fresh material and, consequently, will not have satisfactory adhesion. 4. Sealant should not be used for faying surface applicationsunlessithas just been removed from refrigerated storage or freshly mixed. While the use of sealants on aircraft surfaces has greatly increased over the past few years, application methods have been mostly through the use of brushes, dipping, extrusion guns, and spatulas. The spraying of sealants has been a recentdevelopment.Sealant,MIL-S-81733, Type III, is the one most extensively used for spray application. If Type III sealant cannot be procured, sealant MIL-S-8802, Class A, may be used by thinning to a sprayable consistency by AM.1224 the addition of toluene. Figure 11-31.Spray applicator In addition to standard spray type equipment, kit special application types have been developed for th.: occasional or small touchup job. There (sealantcontainer).Theessentialfeatures are many types available. Figure 11-31 illustrates include the power unit with a pushbutton spray one type which consists of a self-contained cap on top and on the bottom, and a screw-type power unit with an attachedspray bottle lid which attaches to the sealant container. A 329 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.1225 Figure 11-32.Sealant applied to aircraft exterior surfaces. dip tube extends from the bottom of the power complished by brush coating the contacting unit into the sealant container. The power unit, surfaces with the specified sealant. The applica- which may be procured separately, contains tion of the sealant should be made immediately threeouncesofpropellant.Thesealant before fastening the parts together. container (spray bottle) can also be procured Careful planning and arrangement of work separately. and equipment are necessary in order that faying Figure11-32illustrateswhere sealantis surface seals on large assemblies may be closed applied to protect some of the most corrosion- within the application time limit of the sealant. prone areas on an A-6 aircraft. The sealant is Once the sealant has been applied, the parts applied using spray, spatula, and brush methods. must be joined, the required number of bolts When pressure sealing an aircraft, the sealing must be torqued, and all the rivets driven within materials should be applied in such a manner as this time limit. to produce a continuous bead, film, or fillet over When insulatingtapehas been installed the sealed area. Air bubbles, voids, metal chips, between the faying surfaces to prevent dissimilar or oily contamination will prevent an effective metals contacts, pressuresealing should be seal.Therefore,thesuccess of thesealing accomplished by fillet sealing. operation depends upon the cleanliness of the Fillet sealing is accomplished by spreading the area and the careful application of the sealant specified sealant along the seam with a sealant materials. injection gun. The sealant should be spread in There are various methods of pressure sealing approximately 3-foot increments. Before joints and seams in aircraft. The applicable proceeding to the next increment, the applied StructuralRepair Manualwillspecifythe portion of the fillet should be worked in with a method to be used in each application. sealant spatula or tool. (See fig. 11-33.) This Thesealingof afayingsurfaceisac- working of the sealant is done to fill in all voids 330 Chapter 11 CORROSION CONTROL in the seam and to eliminate as many air bubbles Sealing Compound (MIL -S -8802) as possible. The leak-free service life of the sealant is determined by the thoroughness and This temperature-resistant (-65° to +250° F), care used in working out the air bubbles. two-component, synthetic rubber compound is used for sealing and repairing fuel tanks and fuel cellcavities.Itis produced in the following classifications:
NON-METALLIC SPATULA Class ASealing material, suitable for brush application. Class BSealing material, suitable for applica- tion by extrusion gun and spatula. Class CSealing material, suitable for faying t- MASKING c, TAPE surface sealing. C. Dash numbers after the classification code indicate the application time in hours allowed before the curing cycle will have progressed to the point where it is no longer feasible to apply that particular batch of sealant. Class A dash numbers are -1/2 and -2. Class B dash numbers are -1/2, -2, and -4. AM.65 Class C dash numbers are -20 and -80 (8 hours Figure 11-33.Applying sealant of application time with the remaining time allowed for working the material). Example: Class A-2 designates a brushable After the sealant has cured to a tack-free material having an application time of 2 hours. condition, the fillet should be inspected for any Class B-1/2 designates an extrusion gun material remaining air bubbles. Such air bubbles should having an application time of 1/2 hour. Class be opened up and filled with sealant. C-20 designates a faying surface sealant with an When a heavy fillet is required it should be application time of 8 hours and a working life of applied in layers and the top layer should fair 20 hours. with the metal. Injection sealingisthepressurefilling of Sealing Compound (MIL-S-81733) openings or voids with a sealant injection gun. Joggles should be filled by forcing sealant into This accelerated, room temperature curing the opening until it emerges from the opposite synthetic rubber compound is used in sealing side. Voids and cavities are filled by starting metal components on weapons andaircraft with the nozzle of the sealant injection gun at systems for protection against corrosion. This the bottom of the space and filling as the nozzle sealant containsr percentage of magnesium is withdrawn. chromate as a corrosion inhibitor. The classifica- Fasteners such as rivets, Rivnuts, screws, and tion of this sealant compound is of the following small bolts should have a brush coat of sealant types: over the protruding portion on the pressure side. Washers should have a brush coat of sealant on Type IFor brush or dip application. both sides. Split type grommets should have Type II For extrusion application, gun or sealant brushed into the split prior to installa- spatula. tion. After installation, fillets should be applied Type IIIFor spray gun application. to both the base of the grommet and the Type IVFor faying surface application, gun protruding tube on the pressure side. or spatula.
331 AVIATION STRUCTURAL MECHANIC S 3 & 2
The following dash numbers are used to When using any material designated as flam- designatethe maximum application time in mable, all sources of ignition must be at least 50 hours: feet away from the location of the work. Toxic vapors are produced by the evaporation of Type IDash numbers are -1/2 and -2. solvents and/or the chemical reaction taking Type IIDash numbers are -1/2, -2, and -4. place in the curing sealants. When using sealants Type IIIDash number is -1. in confined spaces such as fuel cells, fuselage or Type IVDash numbers are -12 and -24. wing sections, table or bench operations, etc., adequate local exhaust ventilation must be used SAFETY PRECAUTIONS toreduce the vapors below the maximum allowable concentration, and kept at that level Many of the sealants listed above may be until repairs have been completed. Do not eat or flammable and/or may produce toxic vapors. smoke when working with sealants.
332 CHAPTER 12 LINE OPERATIONS AND MAINTENANCE
Line operations and maintenance is one of the involvedintowing,spotting,and securing most important responsibilities of the AMS3 and aircraft. AMS2. Line operations and maintenance is the term used -todescribe that work which is TAXI SIGNALMAN necessary to insure that operational aircraft, (PLANE DIRECTOR) aircraft equipment, and aircraft support equip- ment are ready and safe for the type of flight or Any time an aircraft is ready to taxi from the operations for which they are scheduled. This flight line or is returning to the line for spotting, work is performed on a flight line, flight deck, it is directed by one or more taxi signalmen as or other place normally used to park aircraft. It necessary. isusuallyperformedprior toor between Thetaxisignalmanshouldassume and scheduledflights,withoutremovalof the maintain a position whore he can see the pilot's air raft from the flight schedule. eyes at all times. If it is necessary for him to lose Line operations and maintenance includes sight of the pilot's eyes in changing positions, or aircraft handling, daily preflight and postflight for any other reason, he should signal the pilot inspections, servicing, lubrication, jacking, and to stop until he has taken up his new position. the use and maintenance of variGus types of The taxi signalman has a definite position to aircraftsupport equipment. Some of these maintain when directing aircraft, calculated to functionsarenotnormallyperformed by give him all possible advantages. His position personnel of the AMS rating, however, many when directing single-engine aircraft should be operating activities use third class petty officers slightly ahead of the aircraft and in line with the of the AM and AD ratings as Plane Captains. As left wingtip. An alternate position, in line with a plant captain, the AMS may be required to the rightwingtip, may be used when itis perform all of these functions. necessary to clear obstructions. When directingaircraftwithside-by-side seating, such as is found on multiengine aircraft, his position is forward of the left wingtip. He AIRCRAFT HANDLING has no alternate position since the pilot of a multiengine aircraft sits on the left-hand side of Although aircraft handling is primarily the the cockpit. When directing multiengine aircraft responsibility of the AB rating,allaircraft in obstructed areas, an assistant taxi signalman maintenance personnel should be familiar with may be used on the right wingtip. The assistant proper ground handling techniques. Practically taxi signalmanwillsignaltheaircrafttaxi all structural damage to aircraft on the ground is signalmanontheleftwingtip.Thetaxi caused by carelessness or lack of knowledge of signalman must always be in a position to see proper ground handling procedures. the assistant taxi signalman and the pilot's eyes. This section describes the duties of the taxi Figure12-1illustratesthetaxisignalman's signalman and discusses some of the problems position directing aircraft.
333 AVIATION STRUCTURAL MECHANIC S 3 Lic. 2
of the Armed Forces so that there will be no misunderstanding when a taxi signalman of one service is signaling a pilot from another. These signals are for the most part given with the hands; at night plastic wands attached to regular flashlightsareused. Thesignals should be definite and precise to eliminate any possible misunderstanding and toinspire thepilot's confidence in the taxi signalman. TheAirmanManual,NavPers10307-C, chapter 12, lists and explains the standard taxi signals used by all branches of the Armed Forces for the operation and movement of aircraft on the ground, including helicopter landing, take- off, and ground handling signals. Aircrafthandlingprocedures andsignals peculiar to shipboard operations which would be ofinteresttoplanecaptains andother maintenance personnel assigned to the flight deckarelistedinthe CVA/CVS NATOPS Manual. A similar manual is provided for the use of personnel assigned to Amphibious Assault Ships (LPH). The General Information section of each AM.190 aircraft Maintenance Instructions Manual lists Figure 12-1.Position of taxi signalman. the necessary special signals required for that specific aircraft and not covered by the standard When towing aircraft, the same positions are taxi signals. used as for directing an aircraft moving under its own power. The taxi signalman must keep the occupant of the cockpit (usually the plane TOWING AIRCRAFT captain), the driver of the towing vehicle, and assistant taxi signalmen in sight at all times. Towing aircraft can be a hazardous operation, Aircraft being taxied on land within 25 feet causing damage to the aircraft and injury to of obstructions must have a taxi signalman at personnel, if done recklessly or carelessly. The each wingtip. If an obstruction is present on one following paragraphs outline the general proce- side only, a man at that wingtip is required. durefortowing aircraft;however,specific Aircraft must not be taxied at any time within 5 instructionsfor each model of aircraft are feet of obstructions. Aircraft being taxied on detailed in the General Information section of water must not be taxied closer than 50 feet to the applicable Maintenance Instructions Manual obstructions except inmooring or docking and should be followed in all instances. procedures or when dictated by nature of the NOTE: Most naval aviatioa activities issue mission. Extra precautionis necessary when specific instructions concerning aircraft towing. directing aircraft at night. The taxi strip and These instructions usually contain the composi- parking area should be inspected for workstands tion of the tow crew, tow tractor speed, and and any other mobile equipment which can variousotherinstructionsconcerninglocal damage an aircraft. conditions. These instructions must be complied with. Standard Taxi Signals Aircraft are generally moved (towed)' by a tow crew. The tow crew is usually composed of Standard taxi signals are used by all branches a tractor driver, a plane captain (to man the 334 Chapter 12 LINE OPERATIONS ANn nn A iNTENANCE cockpit), and one man to watch for clearance at for use with only one type of aricraft. The each wingtip and the tail. universal tow bar is designed to tow a number of The man assigned to operate the brakes must different types of naval aircraft. be thoroughly familiar with the particular type The universal tow bar (NT-4) which is now aircraft. His main function is to operate the being used by the Navy is shown in figure 12-2. brakes in case the tow bar should fail or come This tow bar is designed with sufficient tensile unhooked. He must also be familiar with the strengthtopullmostaircraft, butisnot operation of various systeMs such as the ejection intended to be subjected to torsional of twisting seat, power canopy, wing fold, and the safety loads. Although the universal tow bar has small precautions associated with each. wheels that permit it to be towed behind the The men assigned to observe the wings and tow tractor when going to and from an aircraft, tail should proceed at their assigned stations as it will suffer less damage if it is loaded aboard the aircraftis being towed. It is the respon- the tow tractor and hauled to the aircraft. When sibility of these men to keep a sharp lookout for the bar is attached to the aircraft, all engaging obstructions and signal the tractor driver in time devices should be inspected for damage or to prevent collisions. Signals may be given with malfunctions before moving the aircraft. the hands or a whistle. Theuniversaltowbar, when usedfor Only qualified personnel should attempt to nosewheel towing (fig. 12-3) is secured to the tow an aircraft. Driving a tow tractor requires nosewheel axle by means of two pins and a specialized training as well as a valid Navy tensioning chain and knob. driver's license. To mounttheuniversal tow bar on a nosewheel, the tensioning knob is loosened and Tow Bars the chain is released. After the bars are lifted and the pins inserted into the axle ends, the There are two types of tow barsuniversal chainis drawn tightly through the bar and and special. Special tow bars are those designed hooked in the slot which is provided to lock it in
CHAIN STOWAGE HOLES
TENSIONING CHAIN
AX E PIN LOCI(
HOOK
TENSIONING KNOB SAFETY PIN AXLE PIN
AM.193 Figure 12-2.Universal tow bar (NT-4).
335 AVIATION STRUCTURAL MECHANIC S 3 & 2
AM.194 Figure 12-3.NT-4 tow bar installed on nosewbeel. place.Tightening thetensioning knob then rings by means of hooks which are mounted on applies enough pressure to hold the bar pins in the ends of the bars. A spring-loaded safety pin the ends of the axles. secures the hooks in the rings. Holes are provided in one bar to stow the pin Special tow bars are designed to be secured to on the loose end of the tensioning chain. Placing the aircraft in various ways. The information this pin in one of these stowage holes eliminates contained in the applicable Maintenance Instnic- thepossibilityof damagingthechain by tions Manual should always be followed when dragging it on the deck as the aircraft is being attaching special tow bars to an aircraft. towed. When towing the aircraft, the towing vehicle The universal tow bar may be used to tow speed must be reasonable, andall persons aircraft from rings mounted on the fuselage or involved in the operation must be alert. Only landing gear. The tow bar is secured to these reliable, competent personnel should be assigned
336 Chapter 12LINE OPERATIONS AND MAINTENANCE to operate tow tractors. When the aircraft is determine how the aircraft should be secured. spotted, the brakes of the tow tractor should The tiedown procedures provided in the General not be relied upon to stop the aircraft. The man InformationandServicingvolumeof the in the cockpit should be alert for the possible applicableMaintenanceInstructionsManual need of aircraft brakes along with those of the include normal weather tiedown procedures and tow tractor. heavy or severe weather tiedown procedures. NOTE: Before towing an aircraft, insure that Some MIM'salsoincludespecialtiedown all landing gear ground safety locks are installed. procedures to be used when jacking an aircraft Landing gear ground safety locks are pins and aboard ship while the ship is underway. Figure clamps which are used to insure that the landing 12-4 illustrates the severe weather and shipboard gear does not retract accidentally while ground tiedown arrangement for the A-6A aircraft. One handling the aircraft. tiedown per fitting is designated as sufficient for normal weather tiedown. SPOTTING AIRCRAFT Carrier Aircraft Based An aircraft can be spotted on the flight line Aboard Ship under its own power, by the use of a tow tractor, or manually, by pushing. If it is spotted Aircraft aboard carriers are tied to pad eyes manually,the handlingcrewshouldbe which are welded into the flight deck and the instructed not to push on any control surfaces hangar deck. These pad eyes are quite similar to or other areas on the aircraft which are stenciled the pad eyes found embedded in the concrete "no push," as damage to the aircraft may result. parking areas of naval air stations. Regardless of the method used to spot the The tiedownofaircraftaboardaircraft aircraft, a qualified man must be in the cockpit carriers is practically the same as that specified to operate the brakes. for aircraft based ashore. However, since the A qualified signalman should also be used to carrier is subject to movement, the aircraft must directtheaircrafttoitsassignedspot. be tied down securely as soon as it is parked. Sometimes the spots will be painted on the Most carriers require the use of at least three parking ramp, but in many cases he will have to tiedowns as soon as it is parked and more if it is be familiar with the parking area so he can spot to be left unattended. The total number of the aircraft in the best position for securing it to tiedowns necessary depends upon the operating the tiedown pad eyes. The position of the taxi conditions. The Genera! Information section of signalman during spotting is the same as for the aircraft Maintenance Instructions Manual taxiing, and he should be able to see the eyes of contains information concerning tiedown points, the man in the cockpit at all times. type tiedowns to be used, and the number of Whenspottingaircraftatnight,extra tiedowns to be used on each aircraft'. The Air precautions should be taken to insure that the Department of the carrier may have additional parking area is clear of all workstands and other instructions which may require more tiedowns equipment. Assistant taxi signalmen should be than specified in the applicable Maintenance used at each wingtip to insure that the path is Instructions Manual. clear and that there is no danger of hitting other The tiedown commonly used aboard carriers aircraft or obstructions. isillustrated in figure 12-5. The chain type When the aircraft is spotted inits proper tiedown (TD-1) is used to secure aircraft aboard position, the brakes should be applied and held ships and ashore. It has a rated capacity of until the main landing gear wheels are chocked. 10,000 pounds. Each TD-1 tiedown weighs about 12 pounds. AIRCRAFT TIEDOWN The TD-1 tiedown consists of a chain and a tensioning device. The chain is inserted into the The tiedown of aircraft is a very important tensioning device and locked by a spring-loaded part of ground handling. When tying down lock. After the chain is locked in the tensioning aircraft, the expected weather conditions will device the tiedown may be tightened by turning
337 AVIATION STRUCTURAL MECHANIC S 3 & 2
NSIONINO GRIP QUICK "RELEASE LEVER
CHAIN ADJUSTABLE LOCH HOOK ASSEMBLY CHAIN POCKET
MECHANISM BODY
TENSIONING AND QUICK-RELEASE MECHANISM
CHAIN AND HOOK ASSEMBLY
AM.198 Figure 12-5.Chain type tiedownTD-1.
at one end and have an eye splice at the other. Put one end through the tiedown ring or point on the aircraft and the other end through the pad eye, thread the whipped end through the eye splice and tighten up on the line. Then AM.1210 secure the line, using half hitches or a rolling Figure 124.Tiedown arrangementA-6A. hitch together with half hitches. CAUTION: When manila lineisused,it should be carefully adjusted to provide for the tension nut in the direction of the arrow on shrinkage due to moisture. However, excessive the end of the nut. The TD-1 tiedown is released line slack which would allow shifting of the by pulling the release lever up and back. aircraft should be avoided. The number of tiedown lines or chains to use Land and Carrier Aircraft when securing the aircraft is governed by the Based Ashore anticipated weather conditions. The normal and heavy weather tiedown procedures are given for Aircraft ashore on naval air stations are tied each type aircraft in the applicable Maintenance down on concrete parking areas equipped with Instructions Manual. ringlike fittings called pad eyes. These pad eyes Mostaircraftareequipped with surface are installed when the concrete is poured and are control locks which should be engaged or installed flush with the surfaces of the concrete installed 'whenever the aircraft is secured. Some The aircraft to be tied down is spotted in the aircraft control surfaces are locked by simply parkingarea in the bestpositionforfull moving a lever and aligning the controls in the utilization of the pad eyes. If high winds are neutral position. However, some aircraft require anticipated, they should be headed into the the use of gust locks such as the one shown in wind. The aircraft may be tied down with chain figure12-6.Sincethe method of locking type tiedowns or manila line. controls will vary on different type aircraft, When manila line is used, it should be whipped check the applicable Maintenance Instructions
338 Chapter 12 LINE OPERATIONS AND MAINTENANCE
INSTALLATION ARIL PIN RETRACTING LEVERS APART ANO LEG BRACE MOVE ASSEMBLY AFT _UNTIL ANCHOR PINS LINE. UP WITH HOLES UNDER LEG BRACES. RELEASE LEVERS ALLOWING ANCHOR PINS TO ENGAGE.
BMOVE STICK INTO ALIGNMENT WITH SLOT IN STICK LOCK FORK. INSTALL FIN. NO GAP HERE WHENCSLIDE SPRING LOADED COLLAR AFT ON PINS ARE IN RUDDER LOCK BAR. HOOK YOKE PIN OVER HOOK ON LEFT RUDDER PEDAL ARM. RELEASE COLLAR. DAOJUST RUDDER PEDAL CRANK TO TRIM RUDDER icANCHODING WITH FIN. SA PIN INSTALL AILERON BATTENS AT WIND VELOCITIES OF 60 KNOTS. CONTROLS LOCK A
PIN RETRACTING LEVERS
STICK LOCKING FORK
PEDAL ADJUSTING CRANK
RUDDER LOCK BAR HOOK ON LEFT RUDDER PEDAL ARM
.71.1411,0010
AM.197 Figure 12-6.Surface control locking device and batten installation.
Manual fOr the proper installation or engaging hangar, the aircraft should be turned so that it procedure. faces into the wind. All covers and guards which When extremely high winds are anticipated protect the canopy, wing butts, air intakes and and the aircraft cannot be moved into the other parts of the aircraft should be installed.
339 AVIATION STRUCTURAL MECHANIC S 3 & 2
These protective covers should also be installed if the aircraft is to remain secured on the line for any length of time. A specialheavy-duty tiedown(fig.12-7) commonly referred to as afull power chain assembly is used to secure the aircraft to the C deck while the engine is being run up to full power for check and adjustments. The full power tiedown assembly consists of a coupler, chain and a deck fitting. The coupler adapts to the catapult holdback fitting on the aircraft. The chain is made of welded links and is attached to the coupler and deck fitting with removable shackles. The deck fitting assembly permits 360 degrees horizontal travel around the TUU FUNK deck and 0 to 45 degrees vertical angle from the CHAIN AMMO deck. The deck fitting assembly adapts to the various types of pad eyes. Only specifically tested and designated pad TAR TNDOWN eyes should be utilized for high power turnups.
Inotherwor.ds,allpadeyesthatwill DECK FITTING accommodate the full power chain assembly should not be considered strong enough to withstand the stress of a full power turnup. When carrier aircraft are tied down with their wings folded, a ju& strut which gives extra support to the folded part of the wing must be installed. When aircraft must be left on the flight deck of a carrier in extremely heavy weather (winds in excess of 100 knots), the wings should AM.199 be left in the spread position. Figure 12-7.Full power tiedown. Aircraft are spotted and tied down aboard the carrier with just inches between each aircraft. Therefore, it is of utmost importance that they and protective devices. Protective covers are be secured properly to prevent any excessive usually provided for canopies, engine air intakes movement when the ship is maneuvering or and exhausts, wing and vertical stabilizer fold encountering heavy seas. Excessive movement of areas, and various other ducts or inlets. just one aircraft may cause serious damage to Protective covers should be tightly installed. several aircraft. All straps and locking devices should be secured. Loose ends should not be left to blow in the USE OF COVERS AND SHROUDS wind. The loose end of a strap, particularly one with a metal clip or buckle, will severely damage Protective covers and shrouds are provided by the finish of an aircraft. the aircraftmanufacturerfor each aircraft. Care should be taken when handling protec- These covers are designed to protect various tive covers to insure that grit or trash does not areas and components of the aircraft from the collect on the inner liner. The installation of a elements, to protect personnel, and to prevent dirty cover may scratch the finish of the aircraft foreign objects from entering vital areas during or severely damage transparent plastic canopies periods of extended inactivity. The applicable and glass windshields. Maintenance Instructions Manual contains in- All protective covers should be installed in formation concerning the installation of covers such a manner that free drainage is assured. Care 340 Chapter 12LINE OPERATIONS AND MAINTENANCE
should be taken not to create an area which will noticeable, but important,is the respiratory trap and hold salt water. Covers may also act as irritation which may be caused. agreen house in warm weather and cause The two most important hazards of jet engine collection and condensation of moisture under- exhaust are the high temperature and high neath. Covers should be loosened or removed velocity of the exhaust gases from the tailpipe. and the aircraft ventilated on warm sunny days. High temperatures will be found up to several hundred feet from the tailpipe, depending on wind conditions. Closer to the aircraft, these FLIGHT LINE SAFETY temperatures are high enough to deteriorate PRECAUTIONS bituminous pavement. Quite frequently when a jet engine is being Inadditionto the more specificsafety started, excess fuel accumulates in the tailpipe; precautions presented in various other chapters when the fuel ignites, long flames are blown out and in other sections of this chapter, there are a of the tailpipe. The possibilities of this hazard number of miscellaneous precautions which should be known by flight line personnel and all must be observed when working on the aircraft flammable materials should be kept clear of the flight line. The following are especially impor- danger area. tant. During maximum power settings, the high velocity of the exhaust gases may pick up and Intake Duct Hazards blow loose dirt, sizable rocks, sand, and debris several hundred feet. Therefore, due caution When working withreciprocatingengine should be used in parking an aircraft for runup. aircraft, the propeller represents the greatest TheGeneralInformationsectionofthe single hazard to personal safety; however, the jet applicableMaintenanceInstructionsManual engine presents several major hazards. The air contains information concerning the exhaust intake duct of operating jet engines represents areahazards.These instructions shouldbe an everpresent hazard to both personnel working strictly adhered to. NO ONE should foolishly near the inlet duct of the aircraft and to the experiment with the safety margins specified. engine itself if the turnup of ea around the front After engine operation, no work should be of the aircraft is not kept clear of debris. This done to the exhaust section for at least one-half hazard is, of course, greatest during maximum hour (preferably longer). If work is necessary power settings. immediately, asbestos gloves must be worn. The airinlet duct may develop enough suction to pull hats, eyeglasses, loose clothing, Engine Noise and rags from pockets. All loose articles should be made secure or removed before working Modern jet engines produce noise capable of around the engine. In some engines the suction causing temporary as well as permanent loss of is strong enough to pull a man up to, or partially high frequency hearing. The proper precautions into the inlet. Needless to say, precautions must are as follows: be taken to keep clear of the inlet. Protective screens are supplied as part of the 1. Wear the proper ear protection (earplugs ground handling equipment for most jet aircraft. and/or sound attenuators). These screers should be installed prior to all 2. Do not exceed the time limits on exposure maintenance turnups. to the various sound intensities. 3. Have periodic checks on hearing ability. Exhaust Area Hazards Engine noise is broadcast from the aircraft in Jet engine exhaust creates several hazards. patterns which vary in direction, distance, and Tests show that the carbon monoxide content of intensity with engine speed. Generally, the most jet exhaustis low; however, other gases are intense sound areas are in the shape of two lobes present which are irritating to the eyes. Less extendingoutandaftfromtheaircraft
341 AVIATION STRUCTURAL MECHANIC S 3 & 2 centerline. However, dangerous intensities are Seat Ejection Mechanisms also present to the side and forward of the aircraft. Allsafetyprecautionsmust bestrictly Damage to hearing occurs when the ear is observed whenworkingaround aircraft exposed to high sound intensities for excessive equipped with an ejection seat. These safety periods. The higher the sound intensities, the precautionscannotbeoveremphasized,as shorter is the period of exposure which will accidental actuation of the firing mechanism can produce damage. Above 140 db sound intensity, result in death or serious injury to anyone in the any exposure without ear protection can cause cockpit area. damage. Each ejection seat has several ground safety NOTE:Soundintensityismeasuredin pins, the exact number depending upon the type decibels (db). A decibel* is a number which of seat. These safety pins are provided on relates a given sound intensity to the smallest redflagged lanyards for use at every point of intensity that the average person can hear. potentialdanger.Theymustbeinstalled The wearing of regulation ear protection whenever the aircraft is on the ground or deck, (earplugs and/or sound attenuators) will raise and must never be removed until the aircraft is thelimits of time exposure. All personnel ready for flight. working within danger areas should be familiar The following general precautions should with calculated db levels (as specified in the always be kept in mind: applicableMaintenance Instructions Manual) andshouldwearthenecessaryprotective 1. Ejection seats must be treated with the equipment. same respect as a loaded gun. 2. Always consider an ejection seat system loaded and armed. Movable Surface Hazards 3. Before entering a cockpit, know where the ejection seat safety pins are and be certain of Movablesurfacessuchasflightcontrol their installation. surfaces, speed brakes, power operated canopies, 4. Only authorized personnel may work on and landing gear doors constitute a major hazard ejection seats and components and only in an to flight line personnel. These units are normally authorized area. operated during ground operations and main- tenance. Therefore, care should be taken to Overheated Wheel Brakes insure that all personnel and equipment are clear of thearea before operating any movable In the event an aircraft has been subjected to surface. excessive braking, the wheels may be heated to the point where there is danger of a blowout or Power operated canopies have safety locks fire. NOTE: Excessive brake heating weakens which must be installed during ground handling tire and wheel structure, increases tire pressure, operations.Thesesafetylocks preventthe andcreatesthepossibilityof firein the accidentalclosingof the canopy andthis magnesium wheel. When thebrakes on an eliminates the possibility of personnel being aircraft have been used excessively, the fire crushed as the canopy closes. department should be notified immediately and TheGeneralInformationandServicing all unnecessary personnel should be adviied to section of each Maintenance Instructions Manual leave the immediate area. contains specific information concerning the If blowout screens such as the one shown in various movable surface hazards and specifies figure 12-8 are available, they should be placed the safety locks which must be used. Personnel around both main wheels. These screens help to involved with line operations and maintenance eliminate the possibility of damage or injury in should pay particular attention to this informa- the event of a blowout. tion since some of these units move extremely Upon sudden cooling, an overheated wheel fast and with terrific power. may fracture of fly apart, which would hurl
342 Chapter l2 LINE OPERATIONS AND MAINTENANCE
AM.200 Figure 12.8. Use of blowout screen on overheated brakes. boltsorfragments through -theairwith board to puncture the tires and release their sufficient speed to injure personnel. If the tire is pressure. (See fig. 12-9.) flat, explosive failure of the wheel or tire will The recommended procedure for cooling not result. overheated wheel, brake, and tire assemblies is Required personnel should approach over- to park the aircraft in an isolated location. Then heated wheels with extreme caution in the fore allow the assembly to cool in ambient air. The or aft directionsnever in line with the axle. use of cooling agents to accelerate cooling is not CAUTION: The area on both sides of the tire recommendedunlessoperationalnecessity and wheel, in line with the axle, is where the dictates their use. The application of the agents fragments would be hurled if the tire were to exposes personnel to danger by requiring their explode and is therefore called the danger area presence near the overheated assembly. How- (fig. 12-8). ever, if it is necessary to accelerate cooling, a Heat transfer to the wheel will continue for straight stream of water or fag is recommended. some period of time until the brake is cooled. The water should be applied in 10- to 15- Therefore, the danger of explosive failure may second periodic bursts, not in a continuous exist after the aircraft is secured if action is not discharge. Each application should be separated taken to cool the overheated brake. by a waiting period of at least 30 to 60 seconds. NOTE: When a wheel/brake assembly over- A minimum of 3 to 5 applications is usually heats, making rapid deflation of aircraft tires necessary. necessarytopreventawheelassembly When fog is used, the fog is deflected to the explosion,_ ground personnel should direct the brake side of the wheel for a period of 5 to 10 pilot to taxi the aircraft over a tire blowout seconds. Each application should be separated 343 AVIATION STRUCTURAL MECHANIC S 3 & 2
MATERIALS LIST 1/4 x12 x 20 STEEL PLATES (2 REQ) 1/2x 20 STEEL STUDS (34 REQ) 1/2 x20 JAM NUTS (34 REQ) 2 x6x 20 WOOD BOARDS (2 REQ) a
5" 0 0 0 0 0 0 0 0 0 1/2" STUD 2" 12" GROUND TO POINT 0 0 0 0 0 0 0 0 JAM NUT
I
20" MANILA STRAP Agaaatalymigcm/2i,
AM.1226 Figure 12-9.Emergency tire deflator. by a waiting period of at least 20 seconds. This Once the brake has been properly cooled, method is applied as long as it is necessary to permit the wheel to cool in ambient air. A controlthetemperatureoftheaffected crosswind or forced air from a blower or fan will assembly. Never use CO2 for cooling. assist in cooling the wheel.
344 Chapter 12LINE OPERATIONS AND MAINTENANCE
The aircraft should not be moved for at least attenuators, flight deck shoes, flotation gear, 15 minutes following cooling operations. and an adequately secured whistle and survival light. Any maintenanceperformedonaircraft FLIGHT DECK SAFETY whichwillrequirewingspread/fold,respot, PRECAUTIONS turnup, blade track, jacking, etc., or main- tenance that will prevent the aircraft from being The flight deck of an aircraft carrier is one of moved regardless of how much or how little the most hazardous places in the world and one time is required for the work to be performed of the busiest during launching, recovery, and must takeintoconsideration the factthat respotting of aircraft. Plane captains and other approval to proceed with such maintenance maintenance personnel assigned specific duties actions must be approved through the activity's associatedwiththeflightdeckmustbe MaintenanceControl.Theactivity'sMain- constantly aware of this dangerous environment. tenance Control, before it can grant approval, The predeployment training lectures for such must have obtained permission from the Aircraft personnel should include shipboard handling HandlingOfficerviatheAirWing/Group procedures,flightandhangardecksafety Maintenance Liaison Officer or his representa- precautions, responsibilities during launch and tive. recovery of aircraft, tiedown requirements and When participatinginaircraft turnup or techniques, and special shipboard maintenance jacking operations make sure that the permission procedures and safety precautions. This training of theAircraftHandling Officer has been requirementisinadditiontothegeneral received as previously stated and that all ship's indoctrination givenall personnel concerning regulationsareobserved.Safety men with flight quarters, general quarters, fire, abandon sufficient line to block off the area must be ship, man overboard, and other general drills; stationed around the aircraft. ship conditions, smoking and safety precautions Each ship may have safety precautions unique and watch standing requirements peculiar to to that ship due to special circumstances and shipboard operations. operationalrequirements. Pettyofficersare The previously discussed flightline safety charged with the responsibility of knowing and precautionsareapplicabletoflightdeck enforcing those that apply to their area of work operations. The primarydifferenceisthat and their men. because of the limited space and tempo of operations experienced on the flight deck the situation is increasingly more dangerous. ARMED AIRCRAFT PRECAUTIONS During launching and recovery of aircraft all personnelnot required by such operations Maintenance personnel must remain alert to should leave the flight deck and catwalk areas. the potential danger of the weapons utilized on The safe parking area aft of the island is an the various types of aircraft. Shore stations unauthorized space for personnel during aircraft utilize a specified area for arming and dearming recovery.Personnel should not stand inor aircraft.Aircraft returning from flights with otherwise block entrances to the island structure hung weapons are required to be dearmed (by or exits leading off the catwalks. Never turn qualified Aviation Ordancemen) in the landing your back on aircraft taxiing on the flight deck. area or just clear of the landing area. If forward Be alert for the unexpected at all times. There is firing weapons are involved the aircraft must be no roomforcarelessness, daydreaming, or stopped with a clear area ahead of the aircraft skylarking on the flight deck at any time. and dearmed prior to taxiing into designated All personnel assigned flight quarters on Of recoveryspots.Allaircraftlandingwith above the hangar deck must wear appropriate unexpended weapons should be dearmed as soon jerseys and helmets. Personnel on the flight deck as possible in ALL cases prior to commencement during flightquarters must wear the cranial of any postflight checks, servicing, or refueling impact helmet or its equivalent, goggles, sound of the aircraft. 345 AVIATION STRUCTURAL MECHANIC S 3 & 2
PREVENTION OF FOREIGN OBJECT available. The need for the services of the fire DAMAGE TO JET ENGINES crews can, in most cases, be avoided by the prompt and efficient use of firefighting equip- Foreignobject damage is an ever-present ment which is available at all times on the flight hazard to the operation of jet engines. It is the line. It is of the utmost importance that every responsibility of all aircraft maintenance person- man working on the line be familiar with the nel to conscientiously adhere to and follow location and use of the firefighting equipment. preventive procedures and policies to eliminate CO2 bottles arethe most common fire ingestionof foreign objects by jet engines. extinguishers used on the line. These bottles Several areas of concern are parking and storage contain a sufficient quantity of CO2 to handle areas and procedures, engine installation, and most small fires started on the flight line. An engine ground operation. Frequent and periodic aircraft should never be fueled, defueled, or its inspection of engine nacelles, inlet ducts, and engines started without having one or more men storage areas is recommended. When required, standing by with CO2 bottles. carefulcleaningoftheseareasshould be Some aircraft carry one or more small CO2 accomplished. All maintenance personnel must bottles. These bottles are intended for use in exercise extreme care whiiv performing main- flight and should never be used in ground tenance procedures in and around the aircraft to operations except in extreme emergency. In the prevent foreign object damage to the engines. eventthat they areused,they should be The greater size of the newer jet engines creates replaced prior to the aircraft's next flight. greatersuctionpressures and larger suction Whenever an engine is started, personnel with areas. The higher suction pressures enable the adequatefireextinguishers must always be engines to pull objects from greater distances maintained in the immediate vicinity of the into the engines compressor section. Objects engine. When available, a 15-pound CO2 fire may be picked up from the deck areas or from extinguisher is the minimum which should be some areas within the aircraft which are directly used when starting an engine. or indirectly open to the engine bay or intake duct. Therefore, it is mandatory that personnel performing maintenancein and around the Firefighting Procedure aircraft account for alltools, hardware, and components after all maintenance procedures If a fire starts in the tailpipe of a turbojet and operations. engine as it is being started, the engine should be The turnup and taxi area of the jet engine given a dry start; that is, a start (motoring of the must be cleaned frequently to insure that the engine) with the switches which control the fuel area is free of such foreign objects as nuts, bolts, in the OFF and CLOSED position. washers, tools, cotter pins, safety wire, stones, If the fire persists, CO2 can be discharged into rags,etc. Numerous jetengines have been the inlet duct so that it can be drawn through completely demolished because someone failed the engine while it is being given the dry run. to police the turnup and taxi area for loose gear CO2 should not be discharged directly into the before the engine was started. engine exhausts as this may damage the engine. Anyone working in the vicinity of jet aircraft In case the fire is on the ground under the should insure that all personal effects such as engine overboard drain, the CO2 should be hats, gloves, pens, and cigarette lighters are discharged on the ground rather than on the secured. These items may also cause foreign engine. This holds true also if the fire is at the o ct damage. tailpipe and the fuel is dripping to the ground and burning. EXTINGUISHING FIRES The methods described here are for emer- DURING GROUND TURNUP gency use only, because the fire department should always be notified when there is a fire in At air stations or aboard a carrier, experi- or near an aircraft.If thefire cannot be enced crash crews and fire crews are readily extinguished with the equipment at the scene, 346 Chapter 12LINE OPERATIONS AND MAINTENANCE secureall switches, abandon the aircraft and standardized between two or more countries. No stand by to assist the fire department upon their productisallocated more than one NATO arrival. symbol, and a number once assigned is never used for any other product. The NATO symbol AIRCRAFT SERVICING is clearlydistinguishablefrom allother markings; for example j F-22 twill be used by all Servicing of aircraft includes replenishing of NATO countries to identify 115/145 aviation thefuel,oil,hydraulicfluid,andother gasoline. consumable materials. Also included under this headingarecheckingthetiresfor proper Refueling Safety Precautions inflation, struts for proper extension, and the various air storage units for proper pressure. Aviation gasoline is a highly volatile liquid NOTE:Allaircraftservicingshouldbe which gives off a vapor. This aircraft fuel vapor performed in accordance with the applicable set is heavier than air and will settle to the ground, of Maintenance Requirement Cards. The set of accumulating in dangerous amounts in depres- cards covering the daily inspection contains the sions, troughs, or pits; and when combined with servicing instructions for each system. Further air in the proper proportions, forms an explosive instructions concerning servicing may be found mixture. intheapplicableMaintenanceInstructions The ignition of vapor from aircraft fuel may Manual. occur from static sparks, sparks from tools, hot exhaustpipes,lightedcigarettes,electrical FUEL REPLENISHMENT devices, and similar sources. A violent explosion followed by fire will result if liquid gasoline is Identification of Aircraft Fuels present. On the other hand, fuels such as JP-4 have Aircraft engine fuels currently in use are some of the same characteristics of gasoline, but classified into types and grades as follows: by no means the same substance. Different characteristics such as lower vapor pressure and 1. Reciprocating engine fuels; i.e., AVGAS higharomaticcontentexistinthisfuel; (aviation gasoline). therefore,special precautions in its handling must be taken. NATO All existing fire precautions must be adhered GRADE SYMBOL COLOR to during the fueling process. Smoking is not permitted in the aircraft during fueling. Also, no 80/87 Red smoking or naked lights (such as are produced 91/96 Blue byoillanterns,candles, matches, exposed 100/130 Green electric switches, sliprings or commutators, a 115/145 Purple dynamo ormotor,any spark-producing electrical equipment, or any burning material) 2. Turbine engine fuels; i.e., JP (jet fuel). are permitted within 100 feet of an aircraft being refueled, or of fuel storage tanks. No lights NATO other than approved explosion-proof lights are GRADE SYMBOL DESCRIPTION permitted within 50 feet of these operations, and no light of any sort may be placed where it JP-4 I F-40 I Low vapor pres- may come in contact with spilled fuel. Warning sure type. signsshould be postedasaprecautionary measure. JP-5 I F-44 I High flashpoint kerosene type. All accidental spillage of aircraft fuels or other combustible liquids must be immediately The NATO symbol is a code number assigned removed by washing, covered with a foam to a product after it has been classified as blanket to prevent ignition, or neutralized by 347 AVIATION STRUCTURAL MECHANIC S 3 & 2 other means. The proper fire authorities must be creates a dangerous fire hazard, and painful notified any time a large amount of aviation fuel blisters may be caused by direct contact with is spilled. fuel in the same manner as fire bums. When fuel Aircraft fuel tanks must be filled, purged, or has entered the eyes, medical attention should have an inert gas (such as CO2) over the gas in be obtained immediately. the tanks before storing aircraft in hangars, since When an aircraft is to be fueled by a truck, it this leaves no space for explosive vapors to form. should not be located in the vicinity of possible Nonspark tools must be used when working sources of ignition such as grinding, drilling, or on any part of a system or unit designed for welding operations. When practicable, a storing or handling combustible liquids. minimum of 50 feet from other aircraft or The use of leaky tanks or fuel lines is not structures and 75 feet from any operating radar permitted. Repairs must be made on discovery, set should be maintained. Consideration must be with due regard to the hazard involved. given to the direction of the wind so that fuel Gasoline must be strainedif there isthe vapors will not be carried toward a source of slightest chance that water may be present in the ignition. fuel.Mostfuelingtrucksandunderground The tank truck should be driven to a point as storagesystems havefilter/separators which distant from the aircraft as the length of the automatically filter water out of the gasoline hose permits, and preferably to the windward before delivering it to the aircraft tank. These (upwind) side of the aircraft. It must be parked filter/separators should be checked daily for dirt parallel to or heading away from the wing, or in and water. This system serves the same purpose such a position thatit may be driven away as the sediment bulb or tank in an automobile quickly in the event of fire. As soon as the gasoline system. fueling operation has been completed, the truck Aircraft should be fueled in a safe place. Do should be removed from the aircraft's vicinity. not fuel or defuel an aircraft in a hangar or other The truck manway covers should be kept closed, enclosed space except in case of emergency. except when a tank is actually being loaded, or Aircraft should be free from fire hazards, have when pumping fuel at 25°F or below, because at engine switches off, and chocks placed under the such temperatures vent valves may be inoperative. wheels prior to fueling or defueling. NOTE: The operation of fuel trucks at many As an AMS striker, one of your duties might air stations is performed by civilian crews. Even be standing by with a CO2 fire extinguisher or though the Aviation Structural Mechanic S may other firefighting equipment while the aircraft is not be called on to operate or drive fuel trucks, being refueled. The AMS striker assigned to he must be thoroughly familiar with the entire stand by the fire extinguisher should insure that proceduretoinsuresafetyof thefueling the extinguisher is full (by inspecting for the operation,inwhichhewillbeinvolved lead seat on the release mechanism) and that he frequently. is familiar with the release mechanism on the Refueling crews usually include a minimum of type extinguisher in use. When fighting a fuel three men. One person stands by with the fireitis most important that action be taken firefighting equipment; another stays with the immediately; therefore, the fire watch should be truck; and the third man handles the fuel hose at alert at all times. the aircraft and fills the tanks. A member of the CAUTION: Guard against breathing hydro- crew makes sure that both the aircraft and the carbon (fuel) vapors as they may cause sickness truck are properly grounded to prevent sparks or may even befatal. Do not let fumes from static electricity. A check should be made accumulateuse adequate ventilating measures. to see that all radio equipment and unnecessary Also, avoid getting fuel on clothes, skin, or in electricalswitchesareturnedoff.Outside the eyes, because of the high lead content. electrical power should not be connected to the Fuel-saturated clothing should be removed as aircraft unless itisnecessary to operate the soon as possible, and the parts of the body equipment involved with refueling. Care should exposed to fuel washed thoroughly with soap be taken to identify the aviation fuel before and water. Wearing clothing saturated with fuel beginning therefueling operation.Refueling
348 Chapter 12LINE OPERATIONS AND MAINTENANCE trucks have the type fuel contained in the tanks The nozzle should always be grounded prior painted across the side of the tank in black to being placed in the filler neck in order to letters. An AMS who is involved with servicing prevent sparks caused by static electricity. The aircraft should become familiar with the various nozzle should be supported while in the filler grades of fuel and the aircraft's fuel require- neck to prevent damage to the filler neck and in ments in order to insure that the appropriate the case of aircraft which use bladder type fuel fuel is always used. cells(cells made from a type of rubberized nyloncloth)topreventthepossibilityof Gravity Fueling damaging the cell with the end of the nozzle.
Many naval aircraft are refueled by the gravity Pressure Fueling fueling system. (See fig.12-10) Some aircraft may be refueled by either the gravity or pressure Most of the newer naval aircraft are refueled fueling system and other aircraft are fueled from by the pressure fueling system. This system is a single point by the pressure fueling system. employed to enable faster "operational turn Gravity fueling is accomplished by grounding around" of the aircraft. the nozzle, inserting the nozzle in the cell filler Pressure fueling is usually accomplished from neck, and filling the tank to the bottom of the a single point. Fuel from this point is supplied to filler port neck. the various wing and fuselage tanks. In some
AM.201 Figure 12-10.Gravity fueling.
349 AVIATION STRUCTURAL MECHANIC S 3 & 2
PUMA Mao NUM ANC DAMNS cm MCI ADAM VAMN *WIN ?MU ,,, 11J11.014 rare.CROWN DIP MI
SWITCH PANIC
PRISM ROM ANC KrUILING NOZZLI 'POUND CNN MANUAL ROW AND NOROW UAW
AM.202 Figure 12.11. Pressure fueling. cases,thedroptanks andflightrefueling standard on all aircraft which use the pressure package may also be refueled from this point. fuelingmethod.Theelectricalpaneland The pressure fueling station on the aircraft is controls differ from one aircraft to another, equipped with a pressure fueling and defueling depending upon the complexity of the fuel receptacle and an electrical control panel. (See system. The more complex systems may require fig.12-11.) The pressure fueling receptacle is severalswitchesandlights.TheGeneral 350 Chapter 12LINE OPERATIONS AND MAINTENANCE
InformationandServicingsectionofthe opening handle is free to turn whenever fueling applicableMaintenanceInstructionsManual is to be started. To start fueling turn the handle contains illustrations and instructions concern- to the FULL OPEN position. Rotating the ing the pressure fueling system. opening handle more than 180 degrees opens the The pressure nozzle shown in figure 12-11 is poppet valve in the nozzle ai.i locks it in the permanently attached to the refueler hose. The OPEN position. Position the appropriate switch pressure nozzle is equipped with a ground wire on the fuel panel to the FUEL position. The fuel which is used to drain off any static electricity should shut off automatically when the cells are that may have built up in the nozzle. However, full. once the nozzle is attached to the aircraft, it acts CAUTION: During pressure fueling the fuel on its own ground. system should be inspected carefully for leakage. As the connection ismade, the pressure If any leaks are apparent, fueling should be nozzle opens a spring-loaded valve within the stopped and corrective action should be taken. inlet to the fuel tanks. Once the connection is 7. When fueling is complete, the pressure made, there is no further need for grounding the fueling nozzle is removed by rotating the lifting other cells or tanks. Aircraft which employ the handles counterclockwise until the nozzle is pressurefuelingsystemare equipped with unlocked from the fueling receptacle. The dust automatic equipment for shutting off the fuel cover should be pulled up over the nozzle face flow when the tanks are full. immediately and the safety cap replaced on the The following isa general procedure for aircraft receptacle. pressure fueling an aircraft. Since the controls Every safety precaution must be taken to differfromoneaircrafttoanotherthe insure that no dirt or foreign matter enters the applicableMaintenanceInstructions 'Manual nozzle and that the nozzle nose is completely should always be checked prior to pressure clean before it is connected to the aircraft. The fueling an aircraft. dust cover must be kept on the nozzle at all 1. Remove the pressure fueling receptacle times except when actually fueling an aircraft. safety cap by turning counterclockwise. Pull the The pressure fueling nozzle can be damaged pressure fueling nozzle dust cover up and to one by careless handling. Guard against dropping the side of the outer shell. nozzle or allowing it to swing heavily against 2. Groundthenozzlebyinsertingthe structures or equipment during handling. Never groundingplugintoitsreceptacle on the drag the nozzle on the deck. aircraft. Never force the operating action of the 3. Lift the nozzle by its handles into position nozzle. If the unit does not couple freely or and engage the lower slot over the lower lug on open or close readily, locate and correct the the fueling receptacle. Tip the nozzle so that the misalignment or mechanical jam. upper slots engage the upper lugs. Press the nozzle in firmly so that all three nozzle lock Defueling keys are depressed. Lock the nozzle by rotating the lifting handles clockwise. Defueling may be necessary for a variety of 4. Set the refueling panel switches in the reasons such as fuel cell repairs, removal of proper position and apply electrical power to externalfueltanks,failure of fuel system the aircraft. components, and changing of fuel loads. 5. Position the vent monitors as necessary in Aircraft which utilizepressure fueling are accordance with the applicable Maintenance normally defueled from the pressure fueling Instructions Manual. NOTE: The vent monitors adapter which allows the entire system to be are assigned to the various fuel system vents to defueled from a single point. Some older aircraft insure that the aircraft's fuel cells are venting are equipped with one or more defueling valves. properly. Should the cells not vent properly, Some residual fuel will generally be left in the there is a possibility of rupturing the cell and bottomoffuelcellsfollowingdefueling. even causing major structural damage. Residual fuel can usually be emptied or drained 6. With thenozzle lockedinplace, the through the fuel cell water drain valves, using a
351 AVIATION STRUCTURAL MECHANIC S 3 & 2 specialdrawingadapterand appropriate while others are lubricated entirely with a dry container to catch the fuel. When defueling sumptype.Wetsumpenginesstorethe external fuel tanks, it may be necessary to insert lubricatingoilintheengineproperlike the defueler hose in the filler port. automobile engines, while dry sump engines Defuelingwillnormally be accomplished utilize an external tank mounted on or near the outsidethehangarandundercontrolled engine. Oil in jet engines serves the two-fold conditions as specified in the General Informa- purpose of lubricating and cooling. tion and Servicing volume of the applicable Servicing of the engine oil system is usually a MaintenanceInstructionsManual.Ifitis simple task of checking the tank for the proper absolutely necessary to defuel an aircraft in the oillevel and bringing the oil level up to the hangar,doors shouldbeopentoprovide required amount. On aircraft with a dry sump ventilation through the hangar and all shop system,servicingmayconsistof pumping doors leading into the hangar should be dosed. uncontaminated oildirectlyinto the supply No work should be accomplished on or around tank. However, on some aircraft the tank is the aircraft during the defueling operation and located in an inaccessible compartment, and a all sources of ignition should be prohibited in pressure tank is required to fill the oil tank. the area. The safety precautions defined in Figure 12-12 provides an example of the Nav Mat P 5100, the applicable MIM, and local pressure oiler, the engine oil pressure fill station directives should be strictly adhered to at all located in the engin,e nacelle, and the penlight times. (PONS -75) used in servicing the engines on E-2A and C-2A aircraft.Servicing consists of the OIL REPLENISHMENT following steps: 1.Set the penlight switch to ON, with the Identification of cap in place. The bulb should light. Aircraft Engine Oils 2. Remove the cap and insert the plug into the OIL TANK FULL test jack (at thefill Aircraft engine oils are identified by their station). The bulb should go on. If the bulb does militaryspecification number and/or 4-digit notlight,oilIf Ivelis low and servicing is numbers;forexample,1065.The4-digit required. numbering system identifies the intended use of 3. Remove the penlight from the oil tank fill the oil and its viscosity. The first digit designates test jack and with the switch still ON insert into the intended use, lxxx series being for aircraft the DRAIN PLUG CHECK jack. If the bulb engine lubrication. The last three digits indicate lights it is an indication of an accumulation of theviscosity;for example, 1065 oil has a metallicmaterial on either or both engine viscosity rating of 65, 1080 oil has a viscosity magnetic chip detectors. Call such indications to rating of 80, etc. Viscosity is defined as the the attention of the appropriate supervisory internalfluidresistanceto flow caused by personnel. If the bulb remains out proceed with molecular attraction. servicing. NOTE: Both the Navy and the Air Force use 4. Reinsert the penlight into the OIL TANK the Saybolt Scale for determining viscosity. FULL test jack. Sayboltviscositynumbersshouldnotbe 5. Insure that the pressure oiler is properly confused with SAE numbers. filled. Prime the supply line, reset the quantity The synthetic oils used in most turbojet meter to zero, and connect the oiler filler line to enginesarereferredtobytheirmilitary the pressure fitting and the overflow line to the specificationnumber;forexample,MIL- return fitting at the fill station. L-23699. 6. Pump oil into the system until the penlight bulblights and note the quantity on the Servicing Engine Oil Tanks quantity meter.If oil consumption exceeds limits. notify the appropriate maintenance chief. Some aircraft engines utilize a combination 7. Ifoilconsumptioniswithinlimits, dry and wet sump type of lubricating system continue pumping oil at a slower rate until oil 352 Chapter 12LINE OPERATIONS AND MAINTENANCE
QUANTITY PRESSURE METER GAGE
HAND FILLER PUMP LINE
OVERFLOW LINE
PRESSURE OILER
OIL TANK FULL TEST JACK DRAIN PLUG CHECK JACK gt44,,Ik;snommvuotopOsgool,,t4, FILL N., STATION
RETURN FITTING PRESSURE rs FITTING
FITTING CAPS 4
BULB SWITCH PLUG CAP
PENLIGHT PON5-75 AM.1211 Figure 12-12.Oil System servicing equipment (E-2A/C-2A). flow is observed at the overflow discharge in the complished within a specified time limit after pressure oiler. engine shutdown. In most cases if the engine is NOTE: Checking and filling of the engine oil not serviced within these time limits, the oil systemof most jetengines must beac- system must be drained and refilled to insure a 353 AVIATION STRUCTURAL MECHANIC S 3 & 2 proper quantity of oil or the aircraft could be navalaircraft.Useonlythespecifiedoil turned up to scavenge oil from the engine gear indicatedintheGeneralInformation and case to the oil tank. In all cases follow the Servicing volume of the MIM for the particular servicinginstructionsprovidedintheap- aircraft being serviced. Improper lubrication can propriate Maintenance Instructions Manual. cause internal damage and disastrous failure. To If unusually high oil consumption is noted, allow for normal expansion and some foaming maintain an accurate record of consumption as of the oil under use, do not overfill the oil tank. specified by the applicable inspection require- NOTE: The synthetic oil used in some aircraft ments or the MIM. Oil consumption can be a engines and CSD assemblies is harmful to human reliable indicator of impending engine malfunc- skin and respiratory tract, and has a deterio- tionand adetermining factorindeciding rating effect on rubber and painted surfaces. whether an engine is acceptable for flight status. Handle in such a manner as to prevent skin CAUTION: Do not overfill engine oil systems. contact and/or damage to the aircraft finishes. The system previously discussed requires filling Thepresenceofcontaminationinthe to overflow, however, some aircraft oil systems lubricating system of aircraft engines and CSD require that adequate space be allowed for units can be as disastrous to their operation as normal foaming of the oil and expansion when thepresenceof contaminationinoxygen, the engine is operating. hydraulic, and fuel systems. Proper handling of lubricants and servicing equipment and strict Servicing Constant Speed conformance to servicing instructions provided Drive Assemblies in the MIM will minimize the possibility of introducingexternal contamination. Any Severallatemodel reciprocating and jet suspected contamination should be immediately engine aircraft utilize a constant speed drive calledto the attentionof the appropriate (CSD)assemblytomaintaintheaircraft's maintenance supervisor. generator(s) at a constant speed. The assembly transfers and converts variable speed rotation of HYDRAULIC FLUID REPLENISHMENT the aircraft engine into a constant speed rotation necessary to drive the generator at a constant Identification of speed which will meet all the aircraft's electrical Hydraulic Fluid demands. At least one aircraft features a combination Aircraft hydraulic fluids are identified by constantspeeddrive/starter (CSD/S) which their military specification number. Hydraulic provides both pneumatic starting for the engines fluid, MIL-H-5606C, is now being used in the and constant speed drive for the generator. This hydraulic systems of all naval aircraft. This fluid CSD/S canbeoperatedinenginestarter, isalsoused inthe shock struts, shimmy constant speed drive, or air turbine motor modes dampers, and brake systems of allaircraft. of operation. MIL-H-5606C hydraulic fluid is colored red and Proper operation of any CSD assembly is is available in I-quart, 1-gallon, 5-gallon, and extremely dependent on proper servicing by 55-gallon containers. personnel assigned to line maintenance. In most NOTE: Hydraulic fluid MIL-H-6083C is a cases the CSD or CSD/S must be serviced within preservative type hydraulic fluid used in the a specified period after engine shutdown to preservation of hydraulic systems and com- obtain an accurate oil level reading. If this time ponents. While it is red in color and generally is exceeded the oil reservoir must be drained consideredcompatiblewithMIL-H-5606C prior to servicing with the required volume of hydraulic fluid, it should NOT be used to service specified lubricating oil or the aircraft turned up aircraft hydraulic systems. so that the oil level can be checked within the designated time limit. Servicing Hydraulic Systems Several types of lubricating oils are utilized in the various types of CSD assemblies found in Older type aircraft hydraulic systems are 354 Chapter 12LINE OPERATIONS AND MAINTENANCE serviced by checking the fluid level (on a sight fluidtoopenairorotheratmospheric gage which is usually located on the side of the contamination. In addition, waste of hydraulic reservoir) and filling to the prescribed level. fluid is reduced since a partially used can,. Before adding fluid to this type reservoir, always fluid does not have to be thrown away but cPri check the reservoir instruction plate for proper be retained in its contamination-free condition, filling instructions. The instructions plate will be in the unit, untilitis needed and used on attached either to the reservoir or to the aircraft another job. structure near the filler opening of the reservoir. This type of servicing unit comes unpainted The instruction plate contains the following and isto remain as such to eliminate the information: possibility of paint chips getting into the aircraft hydraulic system and contaminating them. All Total capacity of the system. exposed parts of the unit have either been plated Reservoir capacity. or are of hard anodized aluminum. The unit is Refill level. also constructed sothatitcan stand on a Specification and Color of fluid. 15-degree slope without turning or sliding and Correct position of all actuating cylinders has a neoprene strip on its base to prevent during filling. scratching or marring any surface on which it rests. Any other information considered necessary In addition, this unit provides exceedingly during the filling of the reservoir. fine filtration through the use of 3-micron filters NOTE: After opening a can of hydraulic which remove minute particles that may be in fluid, the entire contents should be poured into the fluid. With the use of this unit, the can of the fill stand or servicing unit immediately. This fluid is sealed into the unit, and the fundamental willeliminatethepossibilityof thefluid featureofpreventingcontaminationfrom absorbing dust and grit from the air. Current exposing the fluid to the atmosphere and other instructions require that any remaining fluid left external contamination is accomplished. in the hydraulic fluid container, after servicing a Mo St of the newer type aircraft have a visible fillstand/servicing unit, be discarded and that means (usually sight gages) for checking fluid the empty fluid container be destroyed im- level; however, some are equipped with lights mediately and not used to store or handle any which indicate fluid level. other fluid. Informationconcerningservicingofthe Hydraulic systems can only be serviced with hydraulic reservoirs of a particular type aircraft approved 3-micron absolute filtered dispensers. is contained in the General Information and Figure 12-13 shows a fill stand used to service Servicing volume of the applicable Maintenance some aircraft hydraulic systems. The fill stand is Instructions Manual. connected to the aircraft hydraulic system at a quick disconnect which is provided for reservoir PNEUMATIC SERVICING filling. The fill stand can be operated with air pressure or using the handpu.mp. Some aircraft Landing gear struts, hydraulic accumulators, systems provide for filling several reservoirs from and various air storage bottles throughout most a single point while others have provisions for naval aircraft must be serviced with compressed filling each reservoir individually. air of nitrogen. Another type of hydraulic servicing unit, shown in views A and B of figure 12-14, is a Pneumatic Servicing Equipment portable hand-operated unit designed to accept the standard 1-gallon can of hydraulic fluid and The three main types of pneumatic servicing to dispenseit contamination free to aircraft equipmentarethe portableairbottle,, the hydraulic reservoirs. This is done by pumping nitrogen/air or nitrogen servicing trailer, and the the hydraulic fluid from the original container, portable, high-pressure air compressor. which functions as the unit's reservoir, directly PORTABLE NITROGEN/AIR BOTTLES. into the aircraft's reservoir without exposing the Theportablenitrogen/airbottle isa
355 AVIATION STRUCTURAL MECHANIC S 3 & 2
AIR PRESSURE REGULATOR HYDRAULIC PRESSURE GAGE AIR PRESSURE GAGE
SELECTOR VALVES
HYDRAULIC PRESSURE HYDRAULIC PRESSURE ADJUSTABLE RELIEF AND RETURN LINES VALVE
AIR PRESSURE SHUTOFF VALVE
AIR PRESSURE
AM.204 Figure 12.13. Hydraulic fill stand.
356 Chapter 12LINE OPERATIONS AND MAINTENANCE
(A) CB)
AM.902 Figure 12-14.Loe Hydraulic Servicing Unit, Model H250-1. small high-pressure cylinder in a tubular steel naval air activities for servicing aircraft hydraulic frame. It has a pressure regulator and two gages. and pneumatic systems. This trailer is designed One gage indicates cylinder pressure and the to carry six air or nitrogen storage cylinders and other indicatesregulatedpressure. A valve the necessary flow controlling mechanism. It has mounted on the cylinder allows the user to shut a 30-foot hose which is stowed in a box the nitrogen/air off when the bottle is not in use., mounted between the top two bottles. Each portable nitrogen/air bottle has recharge The air or nitrogen servicing trailer has a and servicing instructions printed on a plate purifier (dehydrator) assembly. This purifier which is attached to the frame. Only dry filtered assembly is essentially a reservoir which contains air or nitrogen should be used in recharging a a chemical drying agent. This chemical drier is nitrogen/air bottle which isto be used in provided to remove any moisture which may servicing aircraft components. When recharging a haveadheredto the valves or have been portablenitrogen/airbottle, care should be accidentally introduced into the system. The taken to insure that the cylinder pressure does chemical is contained in a metal cartridge or can not exceed that listed in the instructions. which is changed periodically. The gas passes AIR OR NITROGEN SERVICING through the drier just before itenters the TRAILER.A servicing trailer similar to the one servicing hose. shown in figure 12-15 will be found at most The bottles on the air or nitrogen servicing
357 AVIATION STRUCTURAL MECHANIC S 3 & 2
MANIFOLD 0, , ' CONTROL ,VALVES
HANDBRAKE LEVER;,, psi
BLEEDER, 17.1 VALVES'
'SHUTOFF VALVES''
AM.207 Figure 12-15.Air or nitrogen servicing trailer. trailer may be recharged using a high-pressure air or nitorgen servicing trailer, insure that the compressor. cylinder pressure does not exceed the pressure NOTE: When recharging the cylinders on the specified for the equipment being recharged. 358 Chapter 12LINE OPERATIONS AND MAINTENANCE
When operatingtheservicingtrailer,the 5,000psi.Handling ofcompressedairat following precautions for safe operation should pressures up to 5,000 psirequires extreme be observed. caution. The following servicing instructions will Only a qualified operator should operate the help to insure a safe job: trailer while charging a system or component. 1. Always use a remote control pressure gage Complete familiarity with the trailer is a basic that is not defective and is properly calibrated. prerequisite to safe operating techniques. NOTE: In accordance with current instruc- Theservicinghoseend andinstallation tions,allgagesusedinservicingaircraft connection fittingshouldbethoroughly hydraulic and pneumaticsystems must be inspected prior to servicing and any particles of calibrated periodically to insure their accuracy. foreign material removed. 2. Never use an uncontrollable source of Never charge a system or component without high-pressure air. Always use a regulator in the the proper fusible safety plug and blowout disc air system. in the trailer charging system. 3. Always open the control valves slowly. Always know the pressure existing in the Inflate the component slowly-10 psi system to be filled and the pressures in all the incrementsuntil the recommended pressures cylinders to be used up in the cascading process are reached. trfore commencing charging operation. High-pressure air compressors like the air or A malfunctioning pressure regulator should be nitrogen servicing trailer are equipped with one disconnectedfromtheline by closingits or more dehydrators. The cartridges used in associated shutoff valve. The trailer can then be these dehydrators must be replaced periodically, operated with the remaining regulator. depending upon the weather conditions. In The charging hose must never be tightly damp, humid weather it will be necessary to stretched to reach a connection. Position the replace the dehydrator cartridges more often trailer so that the hose is not under tension then in dry, arid weather. while servicing an aircraft. Afterservicinganaircraftsystem,the Servicing Landing Gear Struts servicing hose should be stowed in its container to insure that itis not damaged by dragging For efficient operation of shock struts, the along behind the trailer. proper fluid level and air or nitrogen pressure AIR COMPRESSORS.Therearemany must be maintained. In order to check the fluid models of compressors in use throughout the level, the shock strut must be deflated and in the Navy. Such a variety makes it difficult, at best fully compressed position. Deflating a strut can for the average man to be master of all. The beadangerousoperationunlessservicing situation is further complicated by the variety of personnel arethoroughlyfamiliar with the configurations of dialsand gages, regulator high-pressureairvalve and observeallthe controls, hoses, and hose fittings on the same necessary safety precautions. model compressor. The high-pressure air valve shown in figure Most air compressors have an instructions 12-16 is used on all naval aircraft. This air valve plate mounted on the control panel to aid in (referred to by its MS number, MS 28889-1) is properoperation.Theseinstructionsplates used on struts, accumulators, and various other should be kept in good condition, that is, they componentswhich mustbeservicedwith should not be painted over or scratched and high-pressure air or nitrogen. The MS 28889-1 marred. If the instructions plate is not available high-pressure air valve has no valve core. Turning on the compressor, the Operation and Service the 3/4-inch swivel nut clockwise draws the InstructionsManualfortheparticularair valve stem seat up into the valve body, thereby compressorwillcontainallthenece3sary formingametallicsealwhichtrapsthe instructions for the operation and maintenance high-pressure air or nitrogen in the component. of the compressor. The following is a complete procedure for Most of the newer high-pressure type air deflating a typical shock strut, servicing with compressors will supply air pressure from 0 to hydraulic fluid, and reinflating. 359 AVIATION STRUCTURAL MECHANIC S 3 & 2
on the shock strut instruction plate. Figure 12-17 illustrates the instruction plate found on one type aircraft main landing gear strut. NOTE: DUST The instruction plate may be found on the strut CAP or on the wheel door near the strut. 7. Reinstall the air valve assembly, using a VALVE STEM new 0-ring packing. The recommended torque is 100 to 110 inch-pounds. 8. Lockwire the air valve assembly to the strut, using the holes provided in the hex body 3/4 - INCH nut. SWIVEL NUT 9. Inflate the strut, using a regulated high- pressuresourceofdryairornitrogen. LOCKWIRE HOLE CAUTION:. Under no circumstance should any 3/4-INCH PIN type of bottle gas other than compressed air or HEX SECTION nitrogen be used to inflate shock struts. "0" RINGS NOTE: On some shock struts the correct VALVE BODY THREADS amount of inflation is determined by measuring STEM SEAT the amount of extension (in inches) between two given points on the strut and comparing this figure with the amount of air in the strut. (See AM.208 fig. 12-17.) The proper procedure will always be Figure 12.16.High-pressure air valve, type MS 28889. found on the instruction plate (fig. 12-17). If the instructions on the instruction plate are not legible, reference should always be made to the 1. Position the aircraft so that the shock General Information and Servicing section of the strutsare inthe normal ground operating applicableMaintenanceInstructions Manual. position. Make certain that personnel, work- Shock struts should always be inflated slowly to stands, and other obstacles are clear of the avoid excessive heating and overinflation. aircraft. 10. Tighten theswivel hex nut. Recom- NOTE: Some aircraft must be placed on jacks mended torque is 50 to 70 inch-pounds. for servicing the shock struts. 11.Remove the high-pressure air line chuck 2. Remove the dust cap from the air valve. and install the valve cap. Tighten the valve cap 3. Release the air pressure in the strut by fingertight. slowly turning the swivel nut counterclockwise. CAUTION: Do not remove the high-pressure CAUTION: When loosening the swivel nut, air line chuck before securing the swivel nut. make sure the 3/4-inch hex body is either Since some aircraftstruts requirespecial lockwired in place or held tight with a wrench. servicing procedures, the General Information If it is loosened before the air pressure has been and Servicing section of the applicable Main- released, serious injury may result. tenance Instructions Manual should always be 4. Make sure that the shock strut compresses checked prior to servicing the shock struts of as the air pressure is released. In some cases it any aircraft. may be necessary to rock the aircraft after deflating to insure complete compressing of the strut. Servicing Air Storage Bottles 5. When the strut is fully compressed, the valve assembly may be removed by cutting the Some aircraft use nitrogen/air storage bottles safety wire and turning the 3/4-inch hex body for the various emergency operations which are nut counterclockwise. necessary for the safe operation of the aircraft 6. Fill the strut to the level of the air valve and the safety of the crew. Air storage bottles opening, using the type hydraulic fluid specified are used for such functions as emergency brakes, 360 Chapter 12LINE OPERATIONS AND MAINTENANCE
INFLATION INSTRUCTIONSIN UT tan DIM, I P. S I. IIIIIAMILISS VIACOM' NINNY IS 7/1I lea AEROL NO VINT IMMTION, STINT PULLS SIT. NIP IV ITININSION.11.111 MI ASSIKS140 a44 11111 THE CLEVELAND PNEUMATIC TOOLCO. VAN NI TN TAM TO 1/0 111 0111401 OP LLLLLLLLL PN ISMAT IC TM L111,0016 WITCO/NINON 5 011 A 1/11 414 INONT11114 INC. .0114)," TO TNATis STINT. All SNOULD TO4 PPONAN Al AAAAAA ININININ IN 455 LOIN 1 de 1.41 SI A0010 ON AS IlA 411 VO 1110I111110. 441 I/O 451 1/4 411 UMW. NO. ONOIN NO. 474 454 rrec DESIGN NO. WI /NO 510 VS 514 SPLCIFICATION NO. I/O NIS 5/11 he TO CHECK FLUID LEVEL IN lee I.NINON AAAAA CAP PROM MIN INISSUNI AIN TALVI AAAAA NHL 1/0 NNW OCOLINC ALL AIN IV TONING IMINCIL NUTITUIN COOP SOS TINCLOCINIIIII NOT NAN 04 COUNAINI II MUM IONIC ST AON SWINL MIT 111 SIT IPPON 201014.1Tt AN VIMA1111111.MUMI6 PILL 5/5 141 INNS ULM/TO CIVIL OP M NOLONOLO 1/1111 STMR VI III I IN 411111144 MOWN POSITION. I/11 SIN IIIPL ICC COWL( 71 all VOLVO AIIIMLT Ae011 .0111 /01110110 0/e 710 17,4440140:41140..4114.ACC LOCI MU TUN MILAN WW1. T5 I. ANO TISPITIN NUN CAP. T 1 T115 TO INFLATE STRUT 7/ III L NINON NLYI UP APO ATTMN AN NAIR CANN TO NISH PINISLIM 5/4 eye AN VAN, us 1.00MIN MIN. NOT 111011 CIAMITINCLOCIIIMI) A NAN OP II VS PUN n N1 AIN INUIT" 1111VT 11144 ANIPIO 4111.011 SAU UNIT 0/S 15 NIMINNII M ACCNIMANCI V115 NIPLAt101101111RICI1OMI. 1/4 1014 1. TIMITIN ITIMIL IM TO WIT 1111U1111.Topout 1/INN ILUNIP1141 1/0 MSS WWI AN 14411101LMN,CNICII PCMILIIINSMONIPLICI W401 1110 CAP. I VS IOU 1114 ISIS 3/ INT FULLY COMP
AM.209 Figure 12-17.Landing gear strut servicing instruction plate. emergency landing gear extension, and behind the control panel and utilizes a source of emergency canopy operation. low-pressure air to operate the booster or pump Some aircraft have a pneumatic system which which is used to boost the nitrogen to the will maintain the required pressure in these required pressure. bottlesinflight.However, most of these Since gases expand with heat and contract pneumatic systems requireservicing on the when cooled, air storage bottles are usually filled ground with an external source of high-pressure to a given pressure at ambient temperature. A air or nitrogen prior to each flight. graph similar to that shown in figure 12-18 is The canopy bungee cylinder on the A-4E usually mounted on a plate or decal on or near aircraft is an example of a storage unit which the bottle or air filler valve. If the instructions requires pneumatic servicing. This unit aids in plate is missing or not readable the information openingandclosingthecanqpyandin may be found in the General Information and emergencies removes the canopy from the Servicing section of the applicable Maintenance aircraft. The Maintenance Instructions Manual Instructions Manual. specifies the use of high-pressure nitrogen in this unit; therefore, the nitrogen booster is used in Pressure should be added to air storage bottles servicing (See fig. 12-18.) slowly in order not to build up heat from rapid The nitrogen booster shown in figure 12-18 transfer. Care should be taken to insure that air has one 1,800 psi bottle of nitrogen enclosed storage bottles are not overinflated.
361 AVIATION STRUCTURAL MECHANIC S 3 & 2
BUNGEE CYLINDER WARNING: RELEASE NITROGEN IN CYL
BEFORE DISASSEMBLING 3000
INFLATION INSTRUCTION: FILLER VALVE 1100 I. WITH CANOPY IN OPEN POSITION
CHECK LATCH MECHANISM FOR 1100 SWIVEL NUT POSITIVE ENGAGEMENT.
2. INFLATE CYLINDER PER 1100 INFLATION CHART WITH NITROGEN.
3. SEAT HEX. CAP AND CHECK VALVE, 7100 AND FILLER PLUG FOR LEAKS. 0 40 10 120 leo
DO NOT OVERINFLATE 10111111 11,11111111111 1
GREASE CYLINDER ROD PACKING PRESSURE GAGE PER MILL4343 VALVE CAP
WARNING
COCKPIT ENCLOSURE BUNGEE SAFETY PIN MUST BE INSTALLED WHEN SERVICING, TO PREVENT INADVERTENT CANOPY JETTISONING
COCKPIT ENCLOSURE JURY STRUT NITROGEN BOOSTER
ENTRANCE LADDER
AM.211 Figure 12.18. Servicing the A-4E canopy bungee system.
Inflation of Tires. datamay alsobefoundintheGeneral InformationandServicingsectionof the Correct air pressure must be maintained to applicable Maintenance Instructions Manual. receive satisfactory service from aircraft tires. Overinflation reduces the contact area of the Air pressure must be checked daily with an tire, causing it to wear faster at the tread center. accurate gage. Tires must be inflated to the Failure due to carcass ruptures and breaks in the pressures specified for the type of operation tirecords which result from contacts with (ashore or afloat) and the gross weight of the foreignobjects are usually caused by over- particular type aircraft. Tire inflation data is inflation. usually found as illustrated in figure 12-19. In Underinflationincreases contactarea and case the plate is missing from the aircraft, this causes the tire to wear rapidly and unevenly at
362 Chapter 12LINE OPERATIONS AND MAINTENANCE
shouldbe added from aregulatedsource. CAUTION: An unregulated high-pressureair sourcefortireinflationisahazard.Tire inflationsource pressure should be carefully monitored. If high-pressure cylinders such as the portableairbottleortheairornitrogen servicing trailer are used, the regulator must be used to prevent inadvertent overinflation. A remote inflator unit should always be used when inflating tires. The operator of this unit shouldalways stand atright angles tothe
RIGHTHAND MAIN landing gear axle, directly in front or in the rear MAIN LANDING GEAR DOOR of the tire. The operator should also stand at the LANDING (LEFT-HAND DOOR full length of the inflator unit hose. This will GEAR STRUT TYPICAL) prevent the operator from being struck by pieces of the wheel in case of failure. CAUTION: When an aircraft wheel is to be removed from the aircraft, the air must be removed prior to removing the wheel. This MAIN WHEEL TIRE precautionmustbetaken because of the INFLATION PRESSURES possibility that the bolts in split type wheels 360 EN ., .. might have been sheared from landing, thus 341.1ma.....samemem www.2 tem 11111MUMUNIIMMIf. causing the wheel halves to separate when the Inn 1111111111111MMINIIMMEINrMAIN LANDING axle nut is removed. In the past, several people MINIMOMINIM a. GEAR WHEEL MOW 28011111MIN E AMEN TIRE INFLATION have been killed by their failure to remove the Ammo PRESSURE CHART E. 260MNIMMIN iii.. MIMEO air from the tire before removing the axle nut. 140 MEMO. 41111MINEIMI MEMO NNINININ MIMMIM /MEIONNEN 220sosirmorauunolauwwwiiiu 200mown mow 11 12 14 16 18 20 22 AIRCRAFT LUBRICANTS AIRPLANE WEIGHT 1000 1.11S AND LUBRICATION PLATE NO. 2679611 The proper lubrication of modern high-speed, AM.212 high-altitude aircraft is an extremely important Figure 12-19.Tire inflation chart. partoflinemaintenance.All maintenance personnel should be familiar with the various types of lubricants, their specific use, and the the outer edges of the tread. An underinflated method and frequency of application. tireflexesexcessivelyanddevelopshigh temperatures which weaken the tire cords. An LUBRICANTS underinflated tire may also slip on the wheel when landing and shear off the valve stem. Lubricants are substances which are spread in To determine the proper inflation pressure, a thin coat or film over surfaces which move check the inflation chart. For example, using the across each other to reduce friction and wear chart in figure 12-19, if the gross weight of the between the surfaces. Lubricants also help to aircraftis20,000 pounds, thecorrecttire dissipate heat generated in bearings, prevent pressure for that aircraft when shore based corrosive attack on bearing surfaces, and protect would be 310 psi. When carrier based, the the bearings from foreign particle contamina- pressurewouldbemaintainedat 350 psi tion. If adequate lubrication is not provided as regardless of the gross weight. specified in the various inspection requirements If the tire pressure is found to be low, air and Maintenance Requirements Manuals, bearing 363 AVIATION STRUCTURAL MECHANIC S 3 & 2 failure, binding of mechanisms, etc., can be NOTE: MIL-G-81322 grease is not compatible expected. with other lubricants. If itis to be used as a Lubricants are classified as greases, oils, or dry recommended substitute for another type of film lubricants. Greases and oils are the two grease, insure that all traces of the original grease most common lubricants; however, certain dry are removed first. film lubricants are in limited use and others are AIRCRAFT GENERAL PURPOSE being evaluated. GREASE. MIL -G-771 Iis designated for use in Greases used in roller element type bearings gearboxes, anti-friction bearings, and plain generally consist of an intimate dispersion of a bearings where operation at both low and high thickening agent with oil. The oil can be a temperatures(-40°to+250°F)maybe petroleumderivative(mineral)orchemical required. synthesis (synthetic) depending on the expected AIRCRAFT AND INSTRUMENT GREASE, temperatures encountered in its application. The GEAR AND ACTUATOR SCREW. thickener keeps the oil in suspension and acts as MIL -G -23827 is intended for use in ball, roller, a reservoir. As the moving parts come in contact and needle bearings; sliding and rolling surfaces with the grease,oil adheres to the bearing of instruments, cameras, electronic gear, and surfaces. Bleeding of the oil from the grease aircraft control surfaces; aircraft gears, actuator takes place gradually so that a small quantity of screwmechanisms,andotherequipment oil sufficient for proper operation is continuous- requiring a lubricant with a high load carrying ly supplied. The oil that is picked up by the capacityoveratemperaturrange between moving parts of the bearing gradually deterio- -100° to +250°F. It can withstand tempera- rates from the effects of oxidation, is lost by tures up to 300°F for short periods of time. evaporation, or is thrown free by centrifugal NOTE: MIL-G-23827 supersedes MIL- force. As this process continues, the oil content G-3278, 7118, and 7421, which are still listed in of the grease is depleted and the lubricant will many Maintenance Instructions Manuals as of no longer give adequate service. It is for this this writing. MIL-G-23827 grease should not be reasonthatduringlubricationallthe old used in contact with rubber and painted or lubricant should be forced from each lubrication acrylic surfaces as it will damage these surfaces. point until new lubricant appears. Bearings should be clean and free of other greases, oil, and water before application. While Types of Lubricants thisistrue inlubricating allbearings itis especiallyimportantwhenapplyingMIL- Itisimpracticaltocover each type of G-23827 grease. lubricant approved by NavAirSysCom and in use PNEUMATIC SYSTEM GREASE. at the present time. The types of lubricants MIL-G-4343B is intended for use as a lubricant recommended for various aircraft applications between rubber and metal parts of pneumatic will vary with each type of aircraft to some systems. It isalso used on pressurized cabin degree depending on the aircraft manufacturer. bulkheadgrommets andother mechanisms Some of the more common types are discussed where rubber-to-metal lubrication is required. in the following paragraphs. MOLYBDENUM DISULFIDE GREASE. AIRCRAFT GENERAL PURPOSE GREASE, MIL-G-21164C is intended for use as a lubricant WIDE TEMPERATURE RANGE. MIL -G -81322 foraccessorysplines,heavy loaded sliding is used in the lubrication of aircraft accessories surfaces, and for antifriction bearings carrying operating at high speeds over a wide temperature high loads and operating through wide tempera- range (-65° to +350°F).It was specifically ture ranges. The molybdenum disulfide affords designed for use in aircraft wheel bearings, better than average reliability in preventing or anti-frictionbearings, gear boxes, and plain delaying seizure in the event of marginal or bearingapplicationsthatfallwithinthe inadequate lubrication. operating temperature range. It is available in AIRCRAFT BALL AND ROLLER BEAR- 1-pound cans, 35-pound pails, and 14-ounce ING GREASE.MIL-G-25013D is intended for cartridges. useinantifriction bearings exposed to low 364 Chapter 12LINE OPERATIONS AND MAINTENANCE torque at temperatures as low as 100°F and Grease guns are used in conjunction with will provide adequate lubrication for extended "zerk" fittings for lubrication of landing gear periods at temperatures as high as +450°F. actuators and other similar components. The NOTE:MIL-G-25013DsupersedesMIL- operation of the zerk fitting is similar to the G-27343A which may appear in some Main- one-waycheckvlavesfoundinhydraulic tenance Instructions Manuals and (03) Overhaul systems. When the grease gun is removed, a Manuals. spring-loaded ball check is seated, preventing the GENERAL PURPOSE GREASE. grease in the unit from escaping back through MIL-G-23549Aisa molybdenum disulfide fitting. grease intended for general purpose use on A special flush type grease fitting is now being automotive and ground support equipment that used on many installations to replace the old could be exposed to high:pressure steam, salt zerk type fitting. They are press fitted into the water, high load, and high temperatures and low unit and require a special lubrication adapter, speed. It is not generally designed for aircraft which can be attached to the grease gun. use. Figure 12-20 illustrates both types of guns NOTE: Inallcasesutilizethe type of with the adapter. The grease guns may be lubricant designated in the General Information and Servicing volume of the applicable Main- tenance Instructions Manual and the applicable Maintenance Requirements Cards. GENERAL PURPOSE LUBRICATING OILS.Oil procured under Specification MIL- L-7870, is used primarily for general squirt can lubrication. It is used on canopy tracks, aileron and trim tab hinges, and many other locations on the aircraft where a light, low-temperature, LEVER TYPE corrosion-preventive lubricant is required. Federal Specification VV-L-800 is a preserva- tive type lubricating oil which contains cor- rosion and oxidationinhibitors and water- displacing agents. This type lubricating oil is specified for use on most aircraft as a lubricant for all piano hinges.
METHODS OF APPLICATION The different types of lubricants can be applied by any one of the following methods, as applicable.
Grease Guns
Grease guns are used for general heavy-duty PRESSURE TYPE lubrication. There are numerous types and sizes of grease guns available for different purposes. The hand-operated type guns are the most common; however, pressure-operated types arc AM.213 also available. Figure 12-20.Grease guns.
365 AVIATION STRUCTURAL MECHANIC S 3 & 2 equipped with a flexible hose instead of the rigid andServicingsectionoftheMaintenance extensions as shown in figure 12-20. instructions Manual. These instructions appear in the form of tables and charts. Oil or Squirt Can A table of lubricants similar to the one illustrated in figure 12-21 lists all of the various Oilor -squirt cansarcusedforgeneral types of lubricants to be used in lubricating the lubrication,using thespecifiedoilsfor the entire aircraft. Additional information, such as component or part being lubricated. Always frequency symbols, application symbols, check to make sure the squirt can contains the specification numbers and symbols, and the proper lubricant before using it. NATO symbol, is provided on this table. The lubrication of most new type aircraft is Hand performed using the applicable Maintenance Requirements Card as 0 guide. Lubrication is Thismethod oflubricationisgenerally required at the intervals specified on the various employed for packing wheel bearings. Maintenance Requirement Card sets (Preflight, Daily, Postflight, Special (7 day, 14 day, etc.), Brush Conditional, and Calendar).Figure 12-22 il- lustrates the front and back of one of these This method of lubrication is employed when cards which covers the lubrication of the A-4E itis necessary to cover alarge area with a aircraft. The card shows the types of lubricants lubricant or for coating tracks and guides. required,number of lubricationpoints, an illustration of the unit to be lubricated, and the LUBRICATION CHARTS method of application. NOTE: The frequency symbols used in figure The lubrication requirements for each model 12-21 arenotnecessarilystandardforall of aircraft are given in the General Information aircraft. In reading the lubrication chart for a
TABLE OF LUBRICANTS - FREOUENCY SYMBOLS MILITARY NATO SPECIFICATION SYMBOL SYMBOL NOMENCLATURE NUMBER
NONE ANTISEIZE COMPOUND, FELPRO (5 FELT PRODUCTS CO., CHICAGO, ILL.
CT CORROSION PREVENTIVE COMPOUND, MIL-C16173, SOLVENT CUTBACK, COLD APPLICATION GRADE 3 AND 4 ODD EVEN BRW GREASE, AIRCRAFT., BALL AND ROLLER MIL-G-81322A INSPECTION INSPECTION BEARING, WIDE TEMPERATURE RANGE
GIA G-354 GREASE, AIRCRAFT AND INSTRUMENT MI L-G -23827 GEAR AND ACTUATOR SCREW GGA G-355 GREASE, GRAPHITE, AIRCRAFT MILG-7187 LUBRICATING GMD GREASE, MOLYBDENUM DISULFIDE MIL-G21164 SPECIAL OH( C-635 HYDRAULIC FLUID, PETROLEUM -MIL-H.6083 BASE, PRESERVATIVE "OH GPS LUBRICATING GREASE, PNEUMATIC SYSTEM MILO-4343 III GREASE GUN OGR LUBRICATING OIL, GEAR, PETROLEUM BASE MIL-I. 6086
OGP 0 -142 LUBRICATING OR, GENERAL PURPOSE LOW MIL-L-7870 OILCAN BRUSH HAND TEMPERATURE ADP PLSPECIAL LUBRICATING OIL, GENERAL PURPOSE, V V-1. -BOO ADAPTER FOR GUN PRESERVATIVE
NONE MOLYBDENUM DISULFIDE POWDER, MIL-M.7866 LUBRICANT
AM.214 Figure%21.Table of lubricants for an aircraft.
366 Chapter 12LINE OPERATIONS AND MAINTENANCE
TASK WORK CARD PUBLICATION NUMBER CHANGED ELEC PWROFF MIN AREA 49.4 NAVAIR01-4oAvc-6-4 HYDPWROFF I.
5.0 2 3. Lubricate Forward and Aft Nose Tending Gear Doors asFollows:
ITEM NOMENCLATURE NO. OF POINTS SPECIFICATION
1. Nose Landing Gear Actuating Cylinder Upper Fitting 2 MIL-G-21164 2. Nose Gear Aft Door Hinge 1 MIL-L-7870 3. Nose Landing Gear Position Indicating Pin 1 MIL-L-7870 4. Forward Door (fore and aft) Latch Mechanism Actuating Cylinders 2 MIL-G-21164 5. Forward Door (fore and aft) Latch Moving Parts (except sealed bearings) 2 MIL-L-7870 6. Forward Door (fore and aft) Latch Rooks 2 MIL -G -21164
I
( A )
I CARD PUBLICATION NUMBER FORWARD AND AFT NLC ICHANGED 49.5 NAVATR 01-40AVC-6-4 DOORS LUBRICATION
OK ! 1
(9)
AM.215 Figure 12-22.Maintenance Requirements Card for lubricating an aircraft. (A) Front; (B) back.
367 AVIATION STRUCTURAL MECHANIC S 3 & 2
particular aircraft, always refer to the applicable (MAF's, and SAF's, etc.) have been completed table of lubricants for the correct interpretation and turned in for processing. Throughout this of all symbols. manual various examples of this documentation have been shown with their intended use. GENERAL LUBRICATION In order to achieve the highest possible state PROCEDURES of aircraft readiness and reliability at the lowest costinmanpower, money,andmaterial, Prior to lubricating any components or parts, maintenance documentation cannot be over- allforeign matter should be removed from stressed. Detailed instructions on the use and joints, fittings, and bearing surfaces. A clean soft preparation of the various maintenance docu- cloth saturated with a cleaning solvent can be ment forms are provided in Military Require- used for this purpose. The lubricant should be ments for Petty Officer 3 & 2, NavPers 10056 applied sparingly to prevent accumulation of (Series) and Op Nav Instruction 4790.2 (Series). dust, dirt, and other foreign matter. When applying lubricants through pressure type fittings with a grease gun, make sure the AIRCRAFT JACKING lubricant has emerged around the bushing. If no grease appears around the bushing, check the The AMS should be familiar with the jacking fitting and grease gun for proper operation. of an aircraft in order to be able to assist in Always make sure the grease gun is properly performing routine maintenance. Since jacking attached to the fitting and wipe up all excess procedures and safety precautions vary for grease when finished.If the new flush type different types of aircraft, only general jacking fittingis being used, the grease gun must be procedures and precautions are discussed in this equipped with the flush type adapter, and it chapter.Consult the applicable Maintenance must be held perpendicular to the surface of the Instructions Manual (General Information and fitting when greasing, if possible. Servicing section)for specific jacking proce- dures. NOTE: Some of the high-speed mechanisms on modern aircraft are critical as to the lubricant The aircraft to be jacked must be located in a required. If the exact lubricant specified in the level position, well protected from the wind. A MaintenanceInstructions Manual cannot be hangar should be used if at all possible. The obtained, and thereis no substitute listed, a Maintenance Instructions Manual for the aircraft substitute should berequested from higher being jacked should be checked for the location authority, and only their recommended substi- of the jacking points. These jacking points are tution should be used. usually located in relation to the aircraft center of gravity so that theaircraft will be well Clean up all spilled or excess oil or grease balanced on the jacks. However, there are some after the aircraft is lubricated. Never allow oil or exceptions to this. On some aircraft it may be greasetocomeincontactwithoxygen necessary to add weight to the nose or tail to equipment. Some types of synthetic compounds achieve a safe balance. Sandbags are usually used are harmful to rubber, neoprene, and electrical for this purpose. material. They will also soften paint and should be removed as soon as possible with a clean Tripod jacks similar to the one shown in cloth. figure 12-23 are used when the complete aircraft is to be jacked. A small single-base jack similar to the one shown in figure 12-24 is used when MAINTENANCE DOCUMENTATION only one wheel is to be raised. The jacks used for jacking aircraft must be maintained in good The numerous maintenance tasks that are condition; a leaking or damaged jack must never performed on the line are never complete until beused.Also each jack has a maximum the necessarymaintenancedocumentation capacity, which must never be exceeded.
368 Chapter 12LINE OPERATIONS AND MAINTENANCE
JACK TNACAND FKTFNSION
JACK PISTON LOCK NUT
I
AM.216 Figure 12-23.Typical tripod jack.
AM.217 PROCEDURE FOR JACKING Figure 12-24.Typical single-base jack. COMPLETE AIRCRAFT Prior to the actual jacking of the aircraft, an jack pads. A final check for alignment of the overall survey of the complete situation should jacks should be made before the aircraft is be made to determine if any hazards to the raised, as most accidents that occur during aircraft or personnel exist. Tripod jacks of the jacking are the result of misaligned jacks. Figure appropriate size for the aircraft being jacked 12-25 illustrates two typical types of jack pads. should be placed under the aircraft jacking When the aircraft is ready to be raised a man points and perfectly centered to prevent them should be stationed at each jack. The jacks. from cocking when the aircraft is raised. The should be operated simultaneously to keep the legs of the jacks should be checked to see that aircraftaslevelaspossibleand to avoid they will not interfere with the operations to be overloading any of the jacks. This can be performed, such as retracting of the landing accomplished by having the crew leader stand in gear, after the aircraft is jacked. front of the aircraft and give instructions to the Jack pads, which are used as adapters between men operating the jacks. Figure 12-26 illustrates the jacks and the aircraft jacking points, are an aircraft being jacked. carefully installed and must fit perfectly. The CAUTION: On many jacks the piston can be jacks should be extended until they contact the raised beyond the safety point; therefore, never 369 AVIATION STRUCTURAL MECHANIC S 3 & 2
minimum, and no violent movements should be made by persons who are required to go aboard. Safety jacks or cradles designed to support the aircraft while on jacks should be put in place as soon as possible, particularly if the aircraft is to remain jacked for any length of time. Jacking procedures aboard ship require an extrameasureof caution because of ship movements. Permission to jack the aircraft must be given by the activity's maintenance control. No jacking will be authorized unless the weather is calm and the ship is expected to be on a WING JACK PAD ASSEMBLY straight course during the time the aircraft will be on jacks. Figure 12-27 illustrates the shipboard jacking arrangement for the A-4E aircraft. Additional TD-1 tiedown chains may be utilized to anchor the jacks in position as a further measure of safety. Additional tiedown chains may also be added to landing gear and other tiedown attach points if drop checking operations permit. When removing the aircraft from the jacks, insure that all obstructions, including stabilizing jack, are clear of the aircraft. The same number of people are required as for jacking. The jacks should be pumped up slightly to release the piston lock nuts. The locknuts should be turned FORWARD JACK FITTING upward on the piston screw threads at about the same rate as the pistons are descending. The AM.218 levelattitudeoftheaircraftshouldbe Figure 12-25.Typical jack pads. maintained at all times. Removal of the jack pads fromthe jack receptacles should be accomplished as soon as the jack is moved clear. raise an aircraft any higher than is necessary to The weight of the pad is generally enough to accomplish the job at hand. cause the pad to fall out of its receptacle or if CAUTION:Avoidoverextensionofthe not removed immediately the possibility of threadedextension.Whileitscompression overlooking their removal exists. In either case, a strength is equal to the compression strength of safety hazard is caused. More than one case of the jack as a whole, its thin cross-sectional area an aircraftflying with the jack pad inits makes it particularly susceptible to bending and receptacle has been recorded and points to the breaking under side loads, especially when near fact that human error can go undetected. While its full extension. errors of this sort- should have been noticed by NOTE: While jacking, the piston locknuts the supervisor, quality assurance inspector, the (fig. 12-23) should be moved down as the piston plane captain, and the pilot who ultimately flew israised. Thiswill prevent the jr.;:kfrom the aircraft, the maintenance man should not collapsing in the event of a sudden loss of Mid. rely on others to see a job through to .a safe When jacking is complete, the locknuts should completion. be locked snugly against the jack body. NOTE: When lowering some aircraft from Thearea around theaircraftshould be jacks, it is necessary to place metal plates (skid secured while the aircraft is on jacks. Climbing plates) under each tire on the main landing gear. on the aircraft should be held to an absolute These skid plates must have a film of grease
370 Chapter 12LINE OPERATIONS AND MAINTENANCE
NOTE
WING JACK PAD ASSEMBLY If major equipment has been removed from forward fuselage and engines are installed, use aft fuselage jack point to steady aircraft.
FORWARD JACK FITTING
1. Defuel aircraft to landing weight to reduce structural loads. -97.///////////////..../ / WARNING 2. Inflate landing gear struts. See Warning note. / ///. 0040WWWWW,Viiiiii.%/ 3. Install forward fuselage and wing jack pads. Lower Aft fuselage jack before any other jacks 4. Jack wing and forward fuselage points evenly. to prevent structural damage.
5. When aircraft is jacked to desired height, set Do not use more than 1000 PSI air. ram safety nuts. smirce when inflating struts.
AM.219 Figure 12-26.Jacking a complete aircraft between them to allow the upper plate to skid as tailwheel, it must be locked. The wheel should the weight of the descending aircraft increases, be raised only high enough to clear the deck. permitting the main gear to assume its neutral Figure 12-29 shows a wheel being raised using a rest position (See fig. 12-28.) single-base jack.
PROCEDURE FOR JACKING ONE WHEEL MISCELLANEOUS GROUND HANDLING EQUIPMENT When only one wheel has to be raised, as for changing a tire or greasing wheel bearings, a When assignedto thelinedivision,the single-base jack is used. Before the wheel is AMSAN AMS3 may be required to assist in the raised, the remaining wheels must be chocked starting of aircraft engines or ground testing of fore and aftto prevent movement of the various items of aircraft equipment. To do this it aircraft.If the aircraftis equipped with a will be necessary to know how to operate 371 AVIATION STRUCTURAL MECHANIC S 3 & 2
AIRCRAFT T1EDOWN OAR
_A-4E AIRCRAFT
AM.1213 Figure 12-27.Shipboard jacking arrangementA-4E.
equipment such as mobile electric powerplants coverage is provided in this manual on the NC-5 and gas turbine compressors. Special training and the NC-7B. andin some cases licensingis required of Operation and servicing instructions for the operators of such equipment. various types of mobile electric powerplants can be located by referring to the applicable Nav Air 19 (Series) Operating and Servicing Manual for MOBILE ELECTRIC the specific model equipment as listed in the POWERPLANTS (MEPP) Nav Air Publications Index, NavAir 00-500A. There are many different types of mobile NC-5 Power Unit electric powerplants in common use. Some types are self-propelled and others must be pushed or The NC-5 is a self-propelled electric power towed to the aircraft which is to be serviced. unit. It may be driven from place to place in the The NC-5, NC-7, NC-10/10A, NC-12 and 12A, same manner as any other motor vehicle. and the Mobile Motor Generator (MMG) units It has provisions for delivering three different are still in use throughout the Navy and possess kindsofpowerconstantvoltagevariable similar controls and operating features. Since current d-celectrical power for starting jet special training is required and provided by aircraft engines; constant voltage d-c power for ground support equipment personnel to insure startingreciprocatingaircraft engines or jet that such equipment is operated only by fully aircraft engines in aircraft having a single bus qualifiedoperators,onlybriefdescriptive typeelectricalsystem;and115/200-volt, 372 Chapter 12LINE OPERATIONS AND MAINTENANCE
GREASE
LOWER SKID UPPER PLATE SKID PLATE
VIEW LOOKING FORWARD AM.220 AM.1227 Figure 12-29.--Jacking one wheel. Figure 12-28.Skid plate. cause damage tothestructure around the 3-phase, 400-Hz alternating current for checking receptacle. and operating a-c equipment, each through a Insure that the power unit exhaust is not near separate cable. the skin of the aircraft. The heat from the The power cables are plugged into the aircraft exhaust could cause damage to the skin or the electrical system at an external power recep- paint finish. tacle. Figure 12-30 shows the NC-5 and the Servicing an aircraft with an NC-5 should external power receptacle similar to that found always be a two-man job. The driver should on most new aircraft. Aircraft with this type remain at the wheel and operate the generator external power receptacle require the use of drive unit and the throttle. The second man only one type power,115/200-volt, 400-Hz should operate the unit's electrical system and alternating current (a.c.). plug the power cables into the aircraft. Some aircraft require the use of 28-volt direct Before engaging the generator drive unit, current (d.c.) for starting reciprocating engines. make sure that the transmission is in neutral. Figure 12-31 shows the external power recep- Much damage is caused throughout the Navy by tacle used on an aircraft which requires both carelessness in the operation of mobile electric 400-Hz a.c. and 28 volt d.c. NOTE: The shape power units. No one should attempt to operate of the plug and the spacing of the pins in the any type of mobile electrical equipment unless receptacle make it impossible to plug the wrong heisa qualified operator. NOTE: Ground type cable into the aircraft. support equipment schools are being operated at When applying electrical power to an aircraft, all naval air stations to train operators of units park the NC-5 in a position so that the cable will such as the NC-5. All activities require a special reach without causing a load on the external operator's permit for the operators of these power receptacle. The weight of the cable might units.
373 AVIATION STRUCTURAL MECHANIC S 3 & 2
- AC EXTERNAL POWER SWITCH GUARD
AC EXTERNAL POWER SWITCH
POWER DISCONNECTED
A-C MOIRE maw POWER PLANT
RECEPTACLE GUARD WPM 10S111010
---POWER PLANT CAME PLUG
AM.221 Figure 12-30.External power application using NC-5 mobile electric power unit.
After completing the turnup or checkout of by a V-8 gasoline engine and contains two d-c equipment, the power cable should be removed generators, an a-c generator, a control console from the external power !receptacle and stowed for control of the engine and both electrical in the container which is provided on the unit. systems, and a propulsion system for moving the Many times a year aircraft are damaged by unit under its own power. Access doors are careless NC-5 operators driving off from the providedforthecontrol,console,engine, aircraft with the cable still plugged in. Care battery, cable stowage, and tool compartments. should be taken to insure that the cable is not The a-celectricalpower system provides dragged on the taxi way behind the pow r unit. 120/208-volt3-phase,400-Hzpowerfor Dragging severely damages the cable,.ancables servicingaircrafta-ccomponents.The d-c are quite expensive. Before driving the urt away generators provide an output of 28 volts and are from the aircraft, check to insure tat the rated at 750 amperes continuous and 1,000 generator drive unit is1disengaged. amperes intermittently. The outputs from the two d-c generators are used for jet engine NC-7 Electric Power Unit starting and servicing d-c components. Also, the output from one of the d-c generators is used to The NC-7 shown in figure 12-32 is powered power the self-propulsion system. 374 Chapter 12 LINE OPERATIONS-ANDMAINTENANCE A hand control unit is provided on the tow bar for controlling the unit during self-propelling 0 ACPOWER RECEPTACLE operations. 110/200 YOU, 30,400flt CAUTION: Do not move the power unit by u000aaa D J means of the self-propulsion mechanism while DCPOWER RECEPTACLE supplying power toanaircraft. Under no 2a VOLT DC condition is the unit to be used as the prime J mover for towing other equipment. 3 The self-propelling feature should be used a only when moving from one aircraft to another or from the line to the hangar and back as necessary if the distance is not too great. For
ACCESS DOOR greater distances the unit should be towed. 00JDD D000 Most of the electrical power units tend to be slightly topheavy. When driving or towing such units the speed should be held to a minimum to prevent the possibility of turning the unit over. AM.223 For example, the towing speed for the NC-7 is Figure 12-31.External power receptade. 20 MPH maximum.
4
FIRE EXTINGUISHER BATTERY COMPARTMENT
AM.1214 Figure 12-32.Mobile Electric Powerplant (NC-78).
375 AVIATION STRUCTURAL MECHANIC S 3 & 2
GAS TURBINE COMPRESSORS NOTE: The NCPP-105flyawayassembly cannot be hung as an external store and must be The gas turbine compressor is used to provide transportedinside a transport or cargo type pneumatic power in the form of compressed aircraft. bleedairfortheoperationof pneumatic The control panel, shown in figure 12-35, is equipment. Such as aircraft engine starters and part of the flyaway assembly and is located on air-conditioning systems, and for testing units one end of the NCPP-105 unit. The control suchastheram-airturbine.Gasturbine panel contains the operating instructions for the compressorsarelargelyself-containedand operation of the unit. Table 12-1 is a list of all require only an outside source of fuel and oil to the controls, 'ndicators, and connectors located maintain a constant output. on the NCPP-105 control panel and should be The model NCPP-I05 compressor power unit, used in conjunction with figure 12-35. shown infigure12-32,isacomplete, self- The NCPP-105 is intended for ground use contained unit consisting of a flyaway assembly only and because it is skid-mounted, should be enclosed in a skid-mounted, weather-resistant strategically placed along the line so that it can enclosure. Some models of the NCPP-105 are be usedtoservice more than oneaircraft mounted on trailers for ease of movement from without having to be moved. aircrafttoaircraft or placeto place. The NCPP-105suppliescompressedair,at two Only qualified operators should attempt to pressure ratios_ (5:1and 3.6:1), for aircraft operate this type equipment. Training on this engine starting, and a-c and d-c electrical power type equipmentisusuallyincludedin the for operation of aircraft a-c and d-c electrical aviation support equipment school operated at components. The NCPP-105 is equipped with a naval air stations. remote cable assembly, an a-c output cable, a d-c Gas turbine compressors may be damaged by output cable, and a bleed air duct assembly. trash, tools, or other foreign objects which may The unit enclosure consists of a forward and be left near Lhe inlet duct. When the compressor aft enclosure (hinged together), a cable stowage is operating, the following precautions should be enclosure, muffler assembly, fuel tank, structure adhered to: assembly, and a base assembly. The flyaway assembly, shown in ;, 1. Stand clear of the air inlet. Like aircraft jet is normally operated while in thei'....i?-105 unit engines, these units take in large quantities of enclosure, with the d r..,,cr supply mounted air. in the forward e cfowever, when it is 2. Stand clear of the exhaust, and position required to transpo, tne flyaway assembly by the unit so that the exhaust does not strike the aircraft to a temporary location, the d-c power aircraft. supply is removed and relocated on the flyaway 3. Stand clear of the plane of rotation of the assembly structure. The fuel line and a-c and d-c turbine compressor. This area is clearly defined electrical output cables are disconnected, the and marked on the equipment. forward and aft enclosures are lifted off the 4. Do not connect or disconnect the ducting structure assembly, and the flyaway assembly is while the unit is operating. then removed from the base assembly. The 5. Donotconnectordisconnectthe flyawaY assembly, with its remote cable, a-c and electrical cables wh..:'e the switches are ON. d-c electrical output cables, and bleed air duct 6. After servicing the aircraft, always stow assembly, upon arrival at its temporary location, the cables and ducting in the space designed for can be operated by attaching it to a fuel supply. them.
376 Chapter 12LINEOPERATIONS AND MAINTENANCE
MUFFLER ASSEMBLY BLEED AIR OUTLET
CABLE STOWAGE ENCLOSURE \
CONTROL PANEL ASSEMBLY
STRUCTURE ASSEMBLY
BASE ASSEMBLY
BLEED AIR DUCT STOWAGE
FORWARD AND AFT ENCLOSURE (HINGED)
FUEL TANK
AM.903
Figure 12.33.Model NCPP-106 compressorpower unit.
,. 377 AVIATION STRUCTURAL MECHANIC S 3 & 2
DC POWER SUPPLY (RELOCATION)
11111-- -.-___
In.
AM.904 Figure 12-34.NCPP-106 flyaway asiembly.
378 Chapter I 2LINE OPERATIONS ANDMAINTENANCE
AM.905 Figure 12-35.NCPP-105 control panel.
379 AVIATION STRUCTURAL MECHANIC S 3 & 2
Table 12-1.Controls, indicators, and connectorsNCPP-10c.
Index No. Preliminary (figure 12-35) Nomenclature Function Setting or Indication
1 Indicator (M1) Indicates engine rpm in percentage. zero 2 Dome Assembly (DS7) Illuminates panel. off 3 Meter (M6) Indicates a-c voltage. zero 4 Dome Assembly (D58) Illuminates panel. off 5 Meter (M5) Indicates a-c amperes. zero 6 Dome Assembly (D59) Illuminates panel. off 7 Meter (M4) Indicates d-c amperes. zero 8 Meter (M3) Indicates d-c voltage. zero 9 Switch (S8) Selects meter indication of output OFF or battery. 10 Switch (57) Controls d-c power. OFF Dome Assembly (DS4) Indicates d-c power. off 12 Dome Assembly (DS6) Indicates a-c overvoltage. off 13 Dome Assembly .(DS5) Indicates a-c power. off 14 Switch (S6) Selects meter indication of a-c phase. OFF 15 Dome Assembly (DS11) Illuminates panel. off 16 Switch (S5) Controls and resets a-c power output. OFF 17 Circuit Breaker (CB2) Controls control circuit. off 18 Circuit Breaker (CB1) Controls power switches. off 19 Switch (54) Controls panel lights. OFF 20 Dome Assembly (DS10) Illuminates panel. off 21 Switch (S3) Selects air ratio output. OF F 22 Dome Assembly (DS2) Indicates airflow. off 23 Dome Assembly (DS1) Indicates ready for power delivery. off 24 Dome Assembly (DS3) Indicates high oil temperature. off 25 Switch (S2) Controls power to starter relay. off 26 Switch (S1) Controls power to panel. off 27 Indicator (M2) Indicates engine exhaust temperature. zero 28 Gage Indicates engine air pressure. zero 29 Gage Indicates engine oil pressure. zero 30 Circuit Breaker (CB3) Controls power to starter. closed 31 Circuit Breaker (C135) Controls d-c power to output cable. closed 32 Receptacle (.112) Auxiliary d-c starling and charging input. *33 Receptacle (J10) Connection for remote cable. 34 Plug (ill) Provision for battery heater. *Used on power units bearing Part No. 64A90-Fl. For power units bearing Part No. 64A90-F1-2, connection for remote cable is located on the aft enclosure.
380 INDEX
Accessories manuals, 22 tread, 240-241 Acrylic lacquer, 317-318 types, 242 Advancement, 3-10 inflation, 252-253, 362-363 active duty requirements, 5 maintenance, 245-246 inactive duty requirements, 6 mounting and dismounting, 246-252 preparing for, 4-10 preventive maintenance, 254-256 qualifying for, 4 retreading and repair, 253-254 Air storage bottle servicing, 360-361 storage, 244 Aircraft Application List, 14 Airframe construction: Aircraft cleaners, 288-290 fixed wing, 57-72 Aircraft cleaning equipment, 290-291 arresting gear, 71 Aircraft cleaning procedures, 291-293 control surfaces, 63-66 Aircraft handling: flaps, wing, 65 firefighting procedures, 346-347 fuselage, 57-59 protective covers, 340-341 landing gear, 66-72 safety precautions, 341 slats, 66 spotting aircraft, 337 speed brakes, 66 surface control locks, 338 spoilers, 65-66 taxi signalman, 333-334 spring tabs, 65 taxi signals, 334 stabilizers, 62-63 tiedown procedures, 337-340 tabs, spring, 65 tow bars, 335-337 tabs, trim, 64-65 towing aircraft, 334-335 tail gear, 69-71 tail skag, 71-72 Aircraft jacking, 368-371 wings, 59-62 Aircraft lubricants, 363-364 rotary wing, 72-76 Aircraft manuals, 17-22 fuselage, 72 Aircraft preservation, 295-298 landing gear, 72-73 Aircraft servicing, 347-363 pylon, 75-76 air bottles, 360-361 'rotary rudder blades, 76 air compressors, 359 rotary rudder head, 76 defueling, 351-352 rotor head, 75 engine oil, 352-354 rotor wing, 74-75 fueling, 347-351 Airloc fasteners, 127-128, 207-209 hydraulic system, 354-355 Air valves, 360 pneumatic system, 355, 357-36.1 Aliphatic naphtha, 288 shock struts, 359-360 Allowance lists, 17 tire inflation, 362-363 Alloying of metals, 35 Aircraft spotting, 337 Aluminum alloys, 3742 Aircraft tiedown, 337-340 Aluminum, corrosion of, 302 Aircraft tires: AM rating, 1-3 Construction, 239-244 duties, 3 identification, 243-244 paths of advancement for, 1-2
381 AVIATIONSTRUCTURAL MECHANICS 3 & 2
Approach magazine, 27 idler arms, 154 Armed aircraft precautions, 345 push-pull rods, 154 Aromatic naphtha, 288-289 Copper and copper alloys, 42-43 Arresting gear, 71 Copper, corrosion of, 302-303 Corrosion control, 284-332 Bar folder, 112 appearance of corroded parts, 302-303 Bars, tow, 335-337 chemical surface treatmfmts, 314-316 Bel !cranks, 154 corrosion control kit, 315-316 Bend allowance, 114-116 corrosion elimination, 306-316 Beryllium copper, 43 removal of corrosion, 307-314 Blast, vapor, dry honing, 310-314 vapor blasting, 309-314 Blind rivets, 121-123, 188-197 removal of paint, 307 Bolts, 129-133 corrosion prone areas, 298-302 Brake: covers and shrouds, 293, 295 box and pan, 111-112 damage limits, 314 cornice, 109-111 detection methods, 45-51, 306 Brakes, overheated, 342-345 penetrant inspections, 45-51 Bronzes, 42-43 interpreting results, 50-51 Bucking bars, 87-88 forms of corrosion, 303-306 Bulletins, 24-26 ground handling requirements, 295 Bungees, 154 painting, aircraft, 316-328 preservation, aircraft, 295-298 Cables, 146-147 preventive maintenance, 287-298 fittings, 147 sealants, 328-332 guides, 150 surface maintenance, 287-293 Cadium, corrosion of, 303 cleaning methods, 291-293 Camloc fasteners, 125-126, 203, 205-206 materials, 288-290 Carbon steels, 36 Vacu-Blast dry honer, 310-314 Casting alloys, aluminum, 41 Countersinking: Changes, aircraft, 24-26 dimple, 181-185 Chrome-molybdenum steel, 31 machine, 185 Chrome-nickel (stainless steels), 37 Coupling, V-band, 144 Chrome-vanadium steels, 37 Covers and shrouds, use of, 293-295 Chromium steels, 37 Cutting tools, 90-91 Clamps, installation of, 281-282 CO2 bottles, 346 Damage classification, 155 Compressors, 359 Defueling, 351-352 Connector links, adjustable, 149 Dimpling, hot, 181-185 Controls, mechanical, 144-154 Directional flight, 83-84 cable system, 146-154 Directives Application List, 14 cable fittings, 147 Dissimilar metal corrosion, 305 cable guides, 150, 152 Drilling rivet holes, 179-180 cables, 146-147 Drycleaning solvent, 288 connector links, adjustable, 149 Dye penetrant inspection, 45-52 pulleys, 152-153 Dzus fasteners, 128, 206-207 quick disconnects, 149, 151 sectors and quadrants, 153-154 Edges, reinforced,112-113 turnbuckles, 148-149 Ejection seat hazards, 342 rigid control systems, 154 Electric power units: bellcranks and walking beams, 154 NC-5, 372-374 bungees, 154 NC-7, 374-375
382 INDEX
Emulsion cleaners, 289 Flight control surfaces, 63-66 Enamel finishes, aircraft, 319 basic controls, 63-64 Engine oils, 352-354 miscellaneous flight controls, 64-66 Enlisted rating structure, I slats, 66 Epoxy primer, 317 speed brakes, 66 Equipment Applicability List, 13-14 spoilers, 65-66 Equipment and Subject Applicability List, 14 spring tabs, 65 Extractors, screw and bolt, 98 trim tabs, 64-65 wing flaps, 65 Flight control systems: Fasteners: maintenance, 213-224 Heli-Coil inserts, 133-134 control cable, 213-218 Hi-Lok, 133 push-pull linkage, 218 Jo-Bolt, 134 removal and installation, 222-223 lockbolt, 124 rigging, 220-222 miscellaneous: troubleshooting, 218-220 pins, 140-141 rigging rigid controls, 221-222 cotter, 141 balance, 223-224 flathead, 140-141 turnbuckles, 221 tapes, 140 Flight deck safety, 345 rivets (See Rivets.) Flight line safety, 341-345 skin: Fluid line identification, 258-259 Cleco, 88-89 Flush patch, 160-163 threaded, 129-134 Forms of corrosion, 303-306 bolts, 129-13 3 Fretting corrosion, 305-306 heads, 130-131 Friction lock rivets, 122, 188-189 identification, 131-133 Fuselage (fixed-wing), 57-59 material, 131 Fuselage(rotary-wing), 72 threads, 131 Fuselage sections, aft, 224-227 nuts, 135-136 installation, 225-227 nonself-locking, 135 removal, 224 -225 self-locking, 135-136 screws, 139-140 machine, 139-140 Galvanic metal corrosion, 305 self-tapping, 140 Gas turbine compressors, 376 setscrews, 140 Gravity fueling, 349 structural, 139 turnlock, 124-128 Airloc, 127-128 Handtools, 86 Camloc, 125-127 Hardness testing methods, 36 Dzus, 128 Heat treatment, 33-35 Fatigue corrosion, 305 Heli-Coil inserts, 133-134 Ferrous aircraft metals, 35-37 Hi-lok fasteners, 133, 199-201 Filiform corrosion, 306 Hi-Shear rivets, 120-121, 197-199 Firefighting procedure, 346-347 Hole finder, 88 Flaps, wing, 65 Hose, flexible: Flared-tube fittings, 261 rubber, 274-279 Flareless-tube fittings, 261 Teflon, 279-281 Flexible hose (rubber), 274-279 Hovering, 81-83 fabrication and replacement, 276-277 Hydraulic fill stand, 355 installation, 277-279 Hydraulic system servicing, 354-355
383 AVIATION STRUCTURAL MECHANICS 3 & 2
Identification of aluminum, 38-40 squaring, 101 Idler arms, 154 throatless, 101-102 Illustrated Parts Breakdown, 21 unishear, 102 Inner tubes, 256-257 turrent punch, hand operated, 102 Inspection of metals, 45-52 Metal forming machines, penetrant, 46-51 bar folder, 112 interpreting result, 50-51 brake: 109-112 Instructions and Notices, 26-27 box and pan, 111-112 Intergranular corrosion, 304-305 cornice, 109-111 Iron and steel, corrosion of, 302 rotary machine, 105-107 slip-roll forming machine, 102-105 Jack pads, 369-370 Metal lip-seal fittings, 261-262 Jacking, 369-371 Metal working processes, 31-33 Jo-Bolt, 134, 202-203 Metals, aircraft, 28-45 alloying of, 35 K-Monel, 43 ferrous aircraft metals, 35-37 hardness testing, 36 Landing gear (fixed-wing), 66-72 SAE numerical index, 35-36 arresting gear, 71 types. characteristics, and uses, 36-37 main landing gear, 67-69 heat treatment, 33, 35 nose gear, 69-70 aluminum and its alloys, 37-42 tail gear, 69-71 copper and copper alloys, 42-43 tail shag, 71-72 magnesium and magnesium alloys, 43-44 Landing gear (rotary-wing), 72-73 nonferrous aircraft metals, 37-44 main landing gear, 73 titanium and titanium alloys, 42 tail landing gear, 73 properties, 28-30 Lap patches, 159-160 qualities, 30-31 Layout practices, 116, 118 substitution and interchangeability, 45 Leadership, 3 Methyl ethyl ketone (MEK), 289 Letter type publications, 24-27 Microbiological corrosion, 306 Line operations, 333 Mineral spirits, 288 Lock rivets: Monel, 43 friction, 122 mechanical, 122 NATOPS Flight Manual, 17 Lockbolt, 124, 199 Naval Aviation News, 27 Locking devices, 338 NavTra 10052, 9 Lubricants, 363-365 Navy Training Manuals, 9-10 Lubrication charts, 366 NC-5 power unit, 372-374 NC-7 power unit, 374-375 Machine screws, 139-140 Nickel, corrosion of, 303 Magnesium and magnesium alloys, 43-44 Nickel steels, 37 Magnesium, corrosion of, 302 Nitrogen trailer, 357-359 Main landing gear, 67-69 Nonferrous aircraft metals, 37-44 Maintenance Instructions Manuals, 18-20 Nonmetallic materials, 52-56 Manual type publications, 16-24 N1'-4 tow bar, 335-337 MECH, 27 Numerical Sequence List, 12-13 Mechanical cleaning materials, 289-290 Nuts, aircraft. (See Fasteners) Mechanical lock rivets, 122, 189-194 Outfitting Lists, 17 Metal cutting equipment, 100-102 shears: Packaging and barrier materials, 298 hand bench, 102 Paint removal, 307
384 INDEX
Painting, aircraft, 316-328 technical inforination file of support equip- Paints, aircraft, 317-319 ment, 23-24 Patches: numbering system, 16, 25 flush, 160-163 letter material, 25 lap, 159-160 manuals, 16 Penetrant inspection, 45-52 security of, 15-16 Periodic Maintenance Requirements Manual, 20 Pulleys, 152-153 Personnel Qualification Standards (PQS), 7-8 Push-pull rods, 154 Plane director, 333-334 Pylon, 75-76 Plastic enclosures, transparent, 52-55, 227-232 installment of panels, 230-232 Qualifications Manual, 4-7 removing scratches, 228-230 Quick disconnects, 149 surface cleaning, 227-228 Plastics: Rapid Action Change (RAC) System, 16 reinforced, 55-56, 165-173 Rating structure, 1 transparent, 52-55 Reading List, iv Pneumatic system servicing, 355, 357-361 Record of Practical Factors, 8 Polyurethane finishes, aircraft, 318-319 Refueling aircraft, 347-351 Powerplants, mobile, 372-375 Repair material, 157 Preservation materials, 296-297 Repair, trailing edge, 177 Preservation of aircraft, 295-298 Rig pins, 99 Presetting, flareless-tube fittings, 267-269 Rigid tubing, 259-262 Pressure fueling, 349-351 Rivet cutters, rotary, 86-87 Pressure oiling, 352-354 Rivet head shaver, 94 Protective covers, 293-295, 340-341 Rivet installation: Publications, aeronautic, 12-27 blind, 188 Index, 12-16 friction lock tools, 188 Aircraft Application List, 14 Rivet removal, 186-187 Directives Applications List, 14 Rivet set, 87 Equipment and Subject Availability List, Riveters, pneumatic, 94-97 14 Riveting: Equipment Applicability List, 13-14 flush, 180 Numerical Sequence List, 12-13. procedure, 177-178, 185-186 Updating, 15 Rivets: letter material, 24-27 blind, 121.123 Bulletins, 24-26 pull-thrc ugh, 122 Changes, 24-26 Rivnut, 122-123 Instructions and Notices, 26-27 'self-plugging, 122 Technical Directives, 24-26 High-Shear, 120-121 manuals, 16-24 identification, 121 accessories, 22 solid, 119-120 aircraft, 17-22 composition, 120 flight manual (NATOPS), 17 identification code, 119-120 general aircraft manuals, 22 Rivnut, 122-123 IPB, 21 installation of, 194-197 MIM, 18-20 Rotary machine, 105-107 PMRM, 20 beading, 105-106 structural repair, 20 burring, 106-107 weight and balance, 21-22 crimping, 106 safety precautions, 23 turning, 106 support equipment, 23-24 wiring, 106
385 AVIATION STRUCTURAL MECHANICS 3 & 2
Rotary rudder blades, 76 Tail gear, 69-71 Rotary rudder head, 76 Tail skag, 71-72 Rotor head, 75 Taps and dies, 98 Rotor wing, 74-75 Taxi signalman, 333-334 Rubber hose, flexible, 274-279 Taxi signals, 334 TD-1 tiedown, 337-338 Technical Directives, 24-26 Safety precautions: Technical Information File of Ground Support armed aircraft, 345 Equipment, 23-24 engine noise, 341-342 Teflon hose, flexible, 279-281 exhaust area hazards, 341 Tensiometer, 90, 93 flight deck, 345 Theory of flight (rotary wing), 76-84 foreign object damage, 346 Threaded fasteners, (See Fasteners.) fueling, 347-349 Throw boards, 99-100 intake duct hazards, 342 Tiedown, aircraft: overheated brakes, 342-345 afloat, 337-338 seat ejection mechanisms, 342 ashore, 338-340 Safety Precautions Manual, 23 Tire inflation, 252-253 Safety wire, 141-142 Tires, aircraft, 238i256 Sandwich construction, (honeycomb and balsa Titanium and titanium alloys, 42 wood core), 56, 173-176 Titanium, corrosion' of, 303 Screws (See Fasteners.) Tools: Sealants, 328-329, 331-332 custody, 85-86 Sealants, application of, 329-331 inventory, 86 Seams, sheet metal, 113-114 procurement, 85 Sectors and quadrants, 153-154 Tools: Self-tapping screws, 140 cutting tools, 90 -91 Setscrews, 140 extractors, screw and bolt, 98 Shears, 101-102 miscellaneous tools, 90, 92 hand bench, 102 rig pins, 99 squaring, 101 riveting tools, 86-89 throatless, 101-102 bucking bars, 87-88 unishear, 102 hole finder, 88 Skin repairs, 157, 159-165 rivet cutters, rotary, 86-87 Skin replacement, 163-165 riveters, pneumatic: Slats, 66 corner riveters, 96 Slip-roll forming machine, 102-105 fast hitting, 96 Solvent-emulsion cleaning, 289 gun selection, 96-97 Solvents, 288-289 one shot, 96 Spanner wrenches, 90 slow hitting, 96 Speed brakes, 66 squeeze, 96 Spoilers, 65-66 rivet head shaver, 94 Spring tabs, 65 rivet set, 87 Stabilizers, 62-63 taps and dies, 98 Stainless steels, 37 throw boards, 99-100 Stress corrosion, 305 wrenches: Striking tools, 89 spanner, 90 Structural Repair Manual, 20 strap, 98 Support Equipment Manuals, 23 torque, 90 Surface control locks, 338 Torque wrenches, 90-93 Surface maintenance, 287-293 Touchup painting, 316-317
386 INDEX
Tow bars, 335-337 Turnbuckles, 148-149, 221 Towing aircraft, 334-335 Turn lock fasteners. (See Fasteners.) Trailer, air/nitrogen, 357-359 Turrent punch, 102 Trailing edge repair, 177 Trim tabs, 64-65 Tube assemblies, installation of: Unishear, 102 brazed, 272-274 Universal tow bar, 335-337 flared, 269-270 Vacu-Blast dry honer, 310-314 flareless, 270-272 V-band coupling, 144 oxygen system, 274 Tube bending: Walking beams, 154 hand bender, 264 Washers, 136, 138 mechanical bender, 264 Water emulsion cleaning, 291, 293 Water rinse cleaning, 291 Tube cutting, 263-264 Weight and Balance Data, Manual, 21-22 Tube flaring, 264-265, 267 Wheels, landing, 235-238 Tubes, inner, 256, 257 balancing, 238 Tubing, damaged: demountable flange type, 236 layout of lines, 263 divided (split) type, 235-236 removal and replacement, 262-263 maintenance, 238 Tubing, rigid: Wing, rotary, 74-75 fittings, 260-262 Wings, 59-62 sizes, 260 Wrought alloys (aluminum), 38
387 *U,S. GOVERNMENT PRINTING OFFICE : 1974 0 - 542-195 (17-4