THE SPORTPLANE BUILDER by Antoni (Tony) Bingelis 8509 Greenflint Lane EAA Designee Program Advisor Austin

Home , Elinor Smith

THE SPORTPLANE BUILDER By Antoni (Tony) Bingelis 8509 Greenflint Lane EAA Designee Program Advisor Austin. Texas 78759 PUSH-PULL TUBE CONTROL SYSTEM INSTALLATIONS

f IRST, LET ME set the record straight on one thing Well, since we homebuilders tend to succumb to e matteith n f push-pulo r l control system . cablvs s e impulse buyin d occasionaan g l scrounging, used push- control systems. Some very authoritative books and pull tubes immediately com o mindt e u . Wheryo n ca e manuals state in absolute terms that the main disad- find used aircraft materials? vantage of using cables for control linkages is that their Outsid a luck f o e y a builder-friend'fin t a d s shop, tension must be adjusted frequently due to stretching aircraft salvage yard, "Countr yy Market StorFl r o e " and temperature changes. This simply is not so ... at a major fly-in, your chances of finding used push- not in small sport aircraft. pull rods suitable for your need is slim. Still, you may I guess some expert, many years ago through logi- e ablb o brint e g home some push-pull tubes witd ro h cal reasoning, figured that such tension changes must ends on them that are exactly what you need except for take place in cables and duly recorded his conclusions their lengths. s facr posteritya fo t e yearth followo n st I . e writeon , r One problem with most any used salvage or surplus after another perpetuated that same spiel as gospel. locaty ma tubethas ei u tsyo they will probabl vere yb y However, I happen to have a personal acquaintance old ... World War II stuff. with one 14 year old homebuilt aircraft that has not had its control cables adjusted in all those years . . . nor has the need ever arisen. Another aircraft several years its junior likewise seems to defy the need for "fre- quen infrequentr (o t ) adjustment". Even though cable control systems are without this alleged fault, ther e somar e e aircraft designs thae ar t better suited to push-pull control systems. Maybe yours themf o e i.son

Why Use Push-Pull Control Systems? It is also said in those ancient tomes just refer- enced that push-pull tubes eliminat e probleth e f mo varying cable tensions e proble(eveth f ni m probo in s - . O.K.?)le . m . . Anyway majoe on , r attribut pusha f eo - pull tube is its capability for transfering control move- ments through a single link (tube) positively and in direct proportion to the control input. A single push-pull tubn transfeca e r either tension or compression loads (stresses) wherea a contros l cable syste onln mca y handle tension loads. s wel i e fac refleco t t I lth t n thato t , although indi- vidual cables are lighter than push-pull tubes, the cable systems, particularl n higi y h wing aircrafto d , (Photo by Tony Bingelis) requir e fabricatioth e d installatioan n f mano n y pul- Note the degree of misalignment possible in this push-pull leys, brackets and guards. As a consequence, the cable tube installation. You should be able to rotate the tube slightly installation tends to become heavier and more complex between your finger . otherwis . s. e misalignmeno to t I t than you would expect. Additionally, the numerous pul- great. leys and higher cable tensions generally result in a control system generatthay ma t eneea heavyr dfo con- Naturally, there is really nothing wrong with old trol pressures because of friction. On the other hand, WW-II tubes except that the grease in the rods will push-pull controls are well known for their ease of undoubtedly have become coagulated years ago and the movement so characteristic of friction-free push-pull bearings aren't functioning or they have a lot of drag systems. due to that ungreasy grease in them. Such bearings wil l e cleanehavb o d rejuvet e an d - t Push-PulGe u WherYo ln TubeseCa ? nated (regreased). Unfortunately a homebuilde, f o e r on canno o t o g t Some aircraft supply catalogs list Bearing Regreasers his local discount stores and shop around for the correc tjobe th bearinA . o d than g ca tdegrease a smal s - i r in l length find size push-pull tubes ... so, where do you expensive device wit a hbuilt-i n grease fittinge Th . get them? Outside of making them, that is. gadget is secured to a bearing and the old grease is SPORT AVIATIO5 N3 purged out by forcing new grease through the bearing otheOe nth r hand, goothero n du s ei reasoyo y nwh under pressure from a regular grease gun. Bearing re- couldn't make your own push-pull tubes and rods from greasers cost less than most new bearings do. One new materials. It is a simple matter to select rod ends catch though . . . each size bearing requires a separate to fit a particular size of tubing because the catalogs size degrease t thee welbu rar y buck w l fe wort se th h generally provide this information. Incidentally, when that may be expended. assembling push-pull tubes, t zinapplwe c ya chromat e Whil trus i t ei Worlthad ol tf do ther t stile lo ear a l shankd en corrosior d sfo ro e th fil no m t protection . Wa I vintagI r e push-pull rodtubed an s s showint a p gu the Fly Markets and Country Stores, not all of the old How Push-Pull Tubes And Rods Are Assembled push-pull tube u finyo sd wil e thab l to pro t old e - .Du Thi coveres si Figurn di . e2 ductio d desigan n n changes, aircraft companies scrap excess stock that ofte inty n owa find homebuildes it s r supply channels. These push-pull tube e usuallar s f o y good vere qualitar yd attractivelyan y priced. On the other hand, be careful to examine each tube closely for elongated or mid-drilled holes, poorly driven rivets, dents and other defects which may have been

reason enough for its rejection in the first place. R£n.«JLL TUBES AND RODS If you cannot locate the exact length salvage tube ARE ASSEMBLED BY...... you need, you could probably cut one down to the correct modifiede lengthb o t s . Sinc,ha thid esen onle yon simple rework is an expensive way to get a needed tube. (See Figur) e4 I would point out, however, that it is difficult to impossible for most builders to match drill the rivet holes already drilled through the shank of the rod end fitting salvage fro e cut-ofmth f end couldu .Yo , instead, disregard the existing holes and drill new holes through shand en degree0 k9 d e tubin ro th intd e sgan oth (per - pendicular) to the original holes without weakening shankd en d . ro Alternatively e th coulu yo , d instala l new rod end terminal to replace the old cut-off one. Avoid acquiring push-pull tubes with swager o d necked-down diameter eacn unlesd so hen s their length is correct for your purpose (most can be adjusted ^"-1"). They are more difficult to refit with a rod end after you thad en havt t e ofincludeefcu on swagee sth d areae Th . reason, of course, is that you are left with the full diamete e originawild e tubine th en th b l d f d o rgan ro l . smalo it to r fo l

TYPlCfl- TERMhAL CQMNECTTTRS FOR PUSH-PULL Tyee sRODa S Riveted Assemblies e mosRivetth e t commonlsar y used mean securr sfo - ing rod ends to push-pull tubes. Usually two rivets are inserted perpendicular to each other at each rod end. The rivets must be of aircraft quality (identifiable by the dimple in the rivet heads). Never, ever use commer- cial rivet aircrafn i s t structural applications! Thee ar y the d sure weaan yo toar fai. o e t to o. l k. d sofyou an t . Rod ends with hollow shanks require extra care when riveting. That sort of riveting had best be done with a riveting gun as hammering the rivets down against a metal surface (or squeezing them in a vise) may col- lapse the tubing ends. Of course, rod ends with solid shank betten sca r stand hand riveting.

Bolted Assemblies Another push-pull tube assembly method utilizes a couple of AN3 aircraft bolts secured with fiber lock nuts. I personally think bolts make an ugly push-pull tube terminal connectio smaller fo n r tubing . size . . s one tha catco s t mori t somt n ho eap estruce parth f o -t turd increasan e a e controris f th eko l jam. Further- more, a smaller diameter tube assembled with bolts is somewhat heavier tha a nsimila r riveted assembly. 36 NOVEMBER 1981 Naturally, if a large diameter tube is being fabricated ends adjustable you do have a greater range in adjust- you would have no choice but to use AN bolts. ment shoul neeu . dyo dit Some production aircraft (and homebuilt T-18s, I Push-pull tubes are made of 4130 steel tubes or of believe) use a rather large diameter thin wall tube (2" 2024T3 aluminu me fitte tubear eac n witd do d hen shan x e elevato.035"th r fo ) r linkage. Suc a hthi n wall d bearingroen d r somo s e other fitting. Sometimea s aluminum tube can handle the vibration and bending designer will designate 6061T6 for the aluminum tubing. induce compressioy b d n load d stilan sl provid a ever y Remember that the maximum unsupported tubing light installation. length, diameter, wall thickness and material specifica- tion are an engineering determination and should not be left to an "I guess that's good enough" eyeball de- sign evaluation d betteha u r knoYo . e w ar wha u yo t Welded Assemblies doing when you make and install a push-pull tube (for Welded terminal ends for push-pull tubes are com- e elevatoth r s rathecontroit n example)a o t s ra le Du . monly use de welde b wit o t h d d steeen d l tubesro e Th . long length it might lack sufficient rigidity and flex to the tube should slip into the tube snugly. When order- excessively under higher control surface loads. Further- ing your rod ends, be sure they will fit the tubing you more, the effects of vibration on tubing as well as the must use. connecting linkage must be considered.

Installatio Adjustmend nan t Robearingd den s have been know literallo nt y come apart afte e peeninth r g retainin e balgth l races some- MOO (M> MMMC how failed allowin bearinge gth becomo st e disconnected. This sometimes happen e throttlth t a s e control linkage at the carburetor. It is a wise builder who takes the precaution of installing a large diameter washer between the nut and the bearing to prevent its total failure. Te successfub o preventinn i l g this typ f failureo e e th , washer must have a diameter somewhat larger than the hole in the bearing flange (see Figure 3). e self-aligninth f o d Wheen instalu gd nyo ro typ a le f<3URf J bearing, you must be able to see or at least detect a SAFEGUARD KM«T THKOTTLE FAlLUflE slight movemen e push-pulth n i t whed l u tubro nr yo e o rotat t i betweee n your fingers. Chec r thifo ks freedom of motion in both extreme control positions. A self-aligning rod end will accommodate quite a bit of misalignment but be sure you do not exceed its limits. See the photos for an example of where a de- liberate misalignment may be necessary in a push-pull tube installation. The maximum angle of deflection or misalignment will be reached when the outside diameter or the rod end's head touche e fitting e sidth th f s eo , for r clevio k s in whic bolteds i t hi . To obtai e maximuth n d bearen m-d ro benefi a f o t ing, its inner race must be securely clamped to the attaching fitting or structure otherwise the bearing d coulden d , ro e activate b e t th no d actio y an d ma n 9 -/? _ ©I instead, rotate around the bolt. Push-pull tube actuated bell cranks (and similar . •OOCMOMeNnf T NOT( » OMCMk. 1M) MO I Nf VUO 0*LL Nl* Nraf T MOt£S 1 fNDKULW TO push-pull tube linkages) mus e limiteb t n travei d o t l ••€ OLD OMS FCURC 4 preven n inadvertena t t "locking r jammino " n a n i g PUSH-PULD OL L 9CTTENEC TUBEB N SCA O extreme position or by being rotated past center. In addition, push-pull controls should have positive stops built into the system at both ends to limit the travel rang aileronsf eo , elevato stope th rudderd f so an re On . ma locate e controye b th t da l surface. Threaded Rod Assemblies Threaded rods (mal d femalean e e mosar ) t effective in shorter lengths. These push-pull rods may be aluminu r steemo l depending upo e desigth n n application. For That Rnal Inspection Short aluminu mtappee b rod n accepo dt ca s t threaded Afteu havyo re completed your final installation mal d endsro e . Alternatively, short push-pull rodn ca s and have adjusted the linkage to obtain the required als e madob e from standar boltN dA s (1/4 r 5/6"o " f o ) trave d propean l r control surface alignment, checo t k suitable length . . . simply by cutting the bolt head off see that each threaded rod end is screwed into or onto and threadin e boltth f . go Thi thad sen t fabrication its mating terminal sufficiently to engage at least 3/8 e practicamethob y r push-pulma dfo l d assembliero l s to 1/2" of the threads. Rod end bearings with internal not exceeding 8-9" in overall length. threads will have a small inspection hole through their One or both ends of a push-pull rod or tube may be shanks. The mating terminal ends should always be made adjustable althoug t i ha commos n practico t e screwed in far enough that a test wire probe cannot immobilize one end of the rod or tube. Still, with both be poked all the way through the inspection holes.

SPORT AVIATION 37 push-pula f o Eac d hen l tube wit adjustabln ha d en e fitting should be safety-wired or locked securely with t (checknutnu a thim nja ) snubbe d againsp u dro e th t end to keep it from unscrewing. Activat l push-pulal e l control system assemblies through their entire range of movement to be sure that none of the tubes exhibits even the slightest binding or frictional resistance throughout the entire range of movement sure B . ee termina platherth o n n yi s ei l fit- tings or in the rod ends — and if you treated your push- pull tubes gently during installatio u wilyo nl have avoided scratchin r dentingo e installatiog th the d man n (Photo by Tony Bingelis) should look as good as it works. A typical push-pull tube installation. This one is fitted with fora d k fitan -d self-alignina en ) bearine (1 on d n en go d gro ting (2) on the other. Flap hinge (3) has a built-in uniball bearing.

AVIATRIX — By Elinor Smith. Harcourt Brace Jovano- vitch, New York and London, 1981. 304 pages, 35 photos. $13.95.

e mid-1920 Th n excitina s wa sg tim r thosfo e n i e aviation. To capture the big $25,000 prize offered by Raymond Orteig for the first to complete a flight from New Yordreae th Pario kt s everf mo swa y pilot. Roose- velt Field on Long Island became the center for the aviation worl s thos da pilot w coulo efe wh sd obtain backing prepared their aircrafe attemptth r fo t . With Lind- bergh's successfu y 1927l d thosfligho Ma an , wh en i t followed, the American public's awareness of flying was • flow 8 differen15 n t model f aircrafto s e becamSh . e arouse d ever recorw dan yne d flight became front page Aviation e populaEditoth r fo r r Liberty magazind an e news. NBC Radio's aviation commentator. So when a 17 year old girl pilot flew under New York's Elino e famouth r f kneo sl waviatioal n personalities four East River bridge singlea n so solo fligh Octoben o t r of the time — Lindbergh, Bert Acosta, Casey Jones, Al 22, 1928e attainesh , d instant fame. Elinor Smitd ha h Williams, Clarence Chamberlin, Eddie Stinson. She soloed in a Waco at the age of 15 and became the young- was friends with Amelia Earhart (she has harsh words t licensees de Unite piloth n i td States when Orville . PutnamP . foG r , Amelia's husban t surprisingno — d ) Wright signe r F.A.Idhe , certificat Augusn o e , 192814 t . and other women pilots of the time — Bobbie Trout, But Elinor had worked diligently to pile up flying time Pancho Barnes, Viola Gentry, Louise Thaden, Gladys and honed her flying skills toward her personal goal O'Connell. Lady Mary Heath was a good friend, much of becomin gprofessionaa l "aviatrixn piloa — t " (woman admired e crowninTh . g achievemen r Elinofo t r camn i e pilot). October 193 s name0 wa whe e d nsh "Bes t Woman Pilot" e "bridgeTh " fligh d beeha tn mad o redeet e ma of the year by the American Society for the Promotion wager made by one of Elinor's reporter friends. It was of Aviation, a prestigious group made up of top names soon apparent that this flight was more than a lucky e aviatiointh r elationhe n r o idot industry he ,d l ad o T . stunt thir fo ,s young lads sooywa n setting flight records d frienan d Jimmy Doolittl s namewa e d "Best Aviator" in quick succession. In August 1928 she had set a new at the same time. world's altitude record for light planes in a Waco. In Elinor Smith has brought an honest, straightforward January 1929 she set a solo endurance record for women account of the hazards and glories of this period in in a Bird biplane — 13 hours 16 minutes. In April of aviation history in this book. Her free-flowing, natural the same year she raised that figure to 26% hours to styl writinf eo g makes thi sbooa wil u kyo l wan reao t t d t anothese r recor a Bellanc n di a Pacemaker therd An .e e sitting on s highli t t a I . y recommende s cleait r rfo d wer r showai e d demonstratioan s n flights which added insight into the personalities and events of those ex- r experiencehe 193y o t e passeMa 0 sh n e testI . th d s citing time. e covetefoth r d Transport license. Eventually d shha e — George Hardie, Jr., EAA Historian 38 NOVEMBER 1981