Feasibility Study of Modern Airships, Phase 11 - Executive Summary

NASA ContractorReport 2922

CONTRACT NASZ-8643 NOVEMBER 1977 I TECH LIBRARY KAFB, NY

0061675 NASA Contractor Report 2922

Feasibility Study of Modern Airships, Phase I1 - ExecutiveSummary

Goodyear Aerospace Corporation Akron, Ohio

Prepared for Ames ResearchCenter underContract NAS2-8643

National Aeronautics and Space Administration Scientific and Technical Information Office

1977 t

FOREWORD

GoodyearAerospace Corporation (GAC) under a jointly sponsored NASA/Navy Contract (NAS2-8643) has conducted a two- phaseFeasibility Study of Modem Airships.References 1 through 6 summarize thedetails of thecontractual effort. This document is an overviewof the entire study with emphasis upon the Phase I1 Studyresults. RalphHuston was the GAC ProgramManager of the Feasi- bility Study.Gerald Faurote was theProject Engineer for the Phase I1 Heavy Lift Airship investigation and Jon Lancaster was the Project Engineer for the Airport Feeder and Navy application studies . Dr. Mark Ardema, the NASA Project Monitor, provided valu- able technical guidance and direction to the entire study effort, as did the LTA Project Office of the Naval Air Development Center. The contractor wishes to acknowledge that NASA Ames ResearchCenter (ARC) providedthe use of the ARC 7 x 10-foot Wind Tunnel Facility for the purpose of an exploratoryevalu- ation of the Phase I1 Heavy Lift Airship. Subcontractorsand other industry contributors supporting theGoodyear Study included:

NeilsenEngineering and Research, Inc. Battelle Columbus Laboratories PiaseckiAircraft Corporation Sikorsky Aircraft Corporation General Electric Company RadioCorporation of America Summit ResearchCorporation NorthropResearch & TechnologyCenter

TABLE OF CONTENTS

FOREWORD...... i

LIST OF FIGURES ...... V LIST OF TABLES ...... vi LIST OF ACRONYMS ...... vii

SUMMARY ...... 1 INTRODUCTION ...... 1 PHASEIOVERVIEW ...... 3 HEAVY LIFT AIRSHIP STUDY WSULTS ...... 7 Summary ...... 7 Description of HLA andRelated Performance ...... 13 DesignAnalysis ...... 14 Aerodynamics ...... 14 Flight Dynamics ...... 16 FlightControl System ...... 18 StructuralAnalysis and Materials ...... 20 Economic Analysis ...... 22 OperationalAnalysis ...... 24 TechnologyAssessment Analysis ...... 25 Conclusionsand Recommendations ...... 27 AIRPORT FEEDER STUDY RESULTS ...... 28 Summary ...... 28 VehicleDesign Definition ...... 30 OperationalProcedures Analysis ...... 35 CostAnalysis and Comparison with Alternative Modes ... 36 Mission/VehicleFeasibility and Technology Assessment . . 39 NAVY MISSION STUDY RESULTS ...... 41 MissionDescription ...... 41 Generalized Parametric AnalysisResults ...... 42 Mission SpecificResults ...... 48 Trail Mission ...... 48 SOSUS AugementationMission ...... 48 ASW Barrier Mission ...... 51 Convoy EscortMission ...... 51

-iii- TABLE OF CONTENTS

OverallMission/Vehicle Conclusions ...... 52 OperationalConsiderations ...... 53 Ground Handling ...... 53 Weather ...... 53 Wind ...... 54 Vulzerability ...... 55 Conclusions ...... 56 REFERENCES ...... 57

-iv-

. . " .. LIST OFFIGURES

FIGURE NO. TITLE PAGE

1. FeasibilityStudy of Modem Airships...... 2 2. Phase I: General Approachand Overview...... 4 3. Structural Efficiency of Modemand Historical Neutrally-BuoyantRigid Airships...... 4 4. Basic Methods ofAnalysis (GASP ComputerProgram) 6 5. Specific Productivity of Fully Buoyant Airships . 6 6. Phase I1 Heavy LiftAirship Concept ...... 9 7. Military Payloads Beyond Helicopter Lift Capability...... 10 8. Phase I1 General Arrangement andSelected Performance marateristics1 ...... 13 9. PoweredModel in ARC 7 x 10-Foot Wind Tunnel Facilityin Presence of Ground Plane...... 15 10. Phase I1 HLA Response to Lateral Gust ...... 17 11. HLA Fly-By-Wire ControlSystem Block Diagram. . . 19 12. MajorStructural Components of HLA...... 20 13. Frame AnalysisProcedure...... 21 14. Comparison of S64F and HLA TotalOperating Cost PerPayload Ton Mile at Design Range of HLA . . . 23 15. FinalPhase I1 BaselineAirport Feeder Configuration ...... 29 16. AirportFeeder Concept of Operations...... 30 17. Two-Segmented Payload ModuleCabin Layout (6Abreast Seating) ...... 32 18. Buoyancy Ratio Trends for Maximum Productivity Phase I andPhase I1 Study...... 34 19. Comparison of RepresentativeVehFcle Concepts . . 44 20. StructuralEfficiency Comparison...... 45 21. 11 MCF RigidDesign Characteristics ...... 46 22. HoverCapable Non-Rigid Airship ...... 47

-V- LIST OF FIGURES (Continued)

FIGURE NO. TITLE - ~~~~ PAGE

23. Trail Mission ParametricPerformance Results (Neutrally Buoyant Rigid)...... 49 24. Trail Mission ParametricPerformance Results (Construction Concepts)...... 49 25. TOS Versus ROA for 11 MCF Rigid Airship...... 50

LIST OF TABLES

TABLE NO. TITLE PAGE

I BASELINE CONFIGURATIONWEIGHT SLJ"ARY...... 33 . I1 BASELINE DOC/ASSMCOSTBREAKDOWN ...... 37 I11 SUMMARYOF DOC SENSITIVITY ANALYSISRESULTS. .... 38 IV REQUIRED R&D AREAS ...... 40 LIST OFACRONYMS

A/F AirportFeeder AFCS AutomaticFlight Control System APU Auxilliary Power Unit ARC Ames ResearchCenter ASL AverageStage Length AS SM Available Seat Statute Mile ASW Anti Submarine Warfare Static Lift/Gross Weight CER CostEstimating Relationship CTOL ConventionalTake Off andLanding DOC Direct OperatingCost DOF Degree of Freedom Ew Empty Weight FAA Federal Aviation Administration F BW Fly By Wire FRV Flight Research Vehicle GAC GoodyearAerospace Corporation GASP Goodyear AirshipSynthesis Program Gw GrossWeight HLA Heavy Lift Airship LERTA Lake Erie RegionalTransportation Authority MCF MillionCubic Feet MQ4 Million Cubic Meter NADC Naval Air DevelopmentCenter nm Nautical Mile PAX Passenger PHS Precision HoverSensor pNdB Perceived Noise Decibels PV/E SpecificProductivity, Payload Times Velocity over Empty Weight R Range RABH Revenue Aircraft BlockHours RDTU Research,Development , Test and Evaluation

vii LIST OF ACRONYMS (Continued)

ROA Radius of Action RPV Remotely Piloted Vehicle sosus Sound Surveillance System STU Steward(ess) SURTASS Surveillance TASS TAA Technology Assessment Analysis TAS S Towed Array Sonar System TOC Total Operating Cost TOS Time on Station UL Useful Load VC Cruise Velocity VTOL Vertical Takeoff and Landing WER Weight Estimating Relationship

viii I

A feasibilitystudy of modern airshipshas been completed. In the secondhalf of this study, summarized herein,three promising modern airshipsystem concepts and theirassociated missions were studied: (1) a heavy-liftairship, employing a non-rigidhull and a significant amount of rotor lift, usedfor short-range transport and positioning of heavy military and civilpayloads; (2) a VTOL (verticaltake-off and landing), metalclad,partially buoyant airship used as a short-haulcommercial transport; and (3) a classof fully-buoyant airships used for long-endurance Navy missions. The heavy-liftairship concept offers a substantialincrease in vertical lift capability over existing systems and is projectedto have lower totaloperating costs per ton-mile. The VTOL airshiptransport conceptappears to be economicallycompetitive with other VTOL aircraft conceptsbut can attain significantly lower noise levels. The fully- buoyantairship concept can provide an airborne platform with long endur- ancethat satisfies manyNavy missionrequirements.

INTRODUCTION

Inthe fall of 1974,Goodyear Aerospace Corporation (GAC) was awarded oneof two identicalcontracts by NASA Ames ResearchCenter to study the feasibility ofmodern airshipsunder certain ground rules. Figure 1 summarizesthe tasks that were to beaccomplished in this two-phase study. At theend of the four-month Phase I, promisingconcepts were identified onthe basis of competitivemission value (The GoodyearPhase I results aredetailed in Reference 1).

Phase 11, performedsolely by Goodyear,focused on the design features ofthe selected concepts, with lesser attentionpaid to cost and opera- tionalfactors. This summary reportconcentrates on the results ofPhase I1

-1- e-- PHASE I &PHASE 11 __* ---"------r-._"""""" 1 I NAVl STUDY I I I PA,RAHETRIC CONCEPTUAL i c VEHICLE 1 TO 3 VEHICLES VEHICLE I DEFINITION b DEFllllTION I IA I"-!"! "_""_" II I SURVEY

PROCEDURES

;"L"- """"I COST CORETlIdG CORETIIVENESS T MODES

Figure 1. FeasibilityStudy of Modern Airships ofthe study as reported in References 2, 3, 4, 5, and 6. An abbreviated summary was givenin Reference 7. Of necessity,only the highlights of thestudy are given herein, and the reader is referredto the above referencesfor details.

WhereasPhase I was limitedto civil applications, the Phase I1 effort was broadenedto include missions of potential military worth for the Navy.

Forthe NASA portionof Phase 11, two concepts were selected and analyzed:(1) a 75-ton-payloadYheavy-lift vehicle consisting of an aero- stat and four CH-54 helicopters, and (2) an80-passenger/cargo VTOL transportapproximately the same lengthas a Goodyear advertisingairship butwith double the envelope volume.

TheNavy portion of thestudy focused on theapplication of fully- buoyantairships to long-endurance Navy missions. As contrastedwith the NASA portion of Phase 11, the Navy studyincluded parametric analysis and excludedcost competitive analysis.

-2 - PHASE I OVERVIEW

Beforediscussing the Phase I1 results,Phase I will be briefly summarized. As mentionedpreviously, Phase I resultsare detailed in Reference 1; a more complete summary, includingboth Phase I studies, may befound in Reference 8. Figure 2 depictsthe evolution of Phase I ofthe Feasi- bilityStudy and theinteractions among thefour major tasks.

The first task was toconduct a briefhistorical overview of the air- shipvehicles and operations. Included were summariesof major missions, markets,vehicle performance and technicalfeatures, acquisition and operatingcosts, operating procedures, other system elements, andkey sub- systemcharacteristics. The goal was notto obtain a comprehensivecatalog of dataon past airships but to concentrate on data relevant for modern airshipdesigns. Also, part of thistask was a comparisonbetween the technical andeconomic states of the art in 1930and 1974 forthe purpose of assessingthe impact of modern technology. An example of theinfor- mationdeveloped in Task 1 is shown inFigure 3, which depictsthe type of improvementon structural efficiencies that new materials and propulsion technologycan provide.

In Task 2, a survey was conductedto identify potential missions for airshipapplications. Emphasis was on civiltransportation missions althoughother types of missionswere also considered. Included were unique LTA applicationsas well as conventional missions currently performed by othertransportation modes. Becausethe operating characteristics andeconomics of most of the potential modern airshipconcepts had notbeen established and becauseof the broad scope of the study, the mission analysis was necessarily of a primarily qualitative nature.

The vehicleparametric analysis was regardedas the most important taskin Phase I ofthe Feasibility Study. In this third task, the entire spectrumof airship concepts, encompassing both conventional airships and hybrids, was examined.Emphasis was placedon conventional, ellipsoidal- shapedconcepts and a modifieddelta planform lifting-body hybrid. Vehicles

-3- TASK 3: PARAMETRICANALYSIS a GROSS YEIGHT PARAMETERIZATIONOF DESIGN CHARACTERISTICS a CONFlGURAilONCHARACTERISTICS CONVENTIONAL LTA DYNAMIC LIFTUTILIZATION UNCONVENTIOHALVEHICLES 0 STRUCTURAL AN0 PROPULSIVEDESIGN a OPERATING PROCEDURES APPROACHES ! MISSIONS.MRKETS. AN0 COSTS a STOLAN0 VTOL CAPABILITIES """_""" CRUISEVELOCITY a ESTIMTE OF IMPACT OF 1974 SO4 ON ADVANCED TECHNOLOGY DESIGNOPTIONS PARAHETERIZEODATA ---""""" OPTIMIZE0CONFIGURATION CHARACTERISTICS NORWLIZEOPARAMETRIC PERFORMNCE CHARACTERISTICS SURVEY OF CONVENTIONALTRANSPORTATION e OVERALLPERFOWANCE COMPARISON OF I MISSIONS (CURRENTAND PROPOSED) I" GENERAL CONFIGURATIONCLASSES P EXISTINGTRANSPORTATION SYSTEM PERFRO" a EVALUATION OF ADVANCED TECHNOLOGY ANCE LIMITATIONS DESIGNOPTIONS ENVIRONMENTAL, ENERGY, AND SOCIO- ECONOMIC CONSIDERATIONS """"- "" TASK 4: MlSSION/VEHICLEEVALUATION AN0 la IDENTIFICATION OF PROMISINGMISSIONS 1 SELECTION IDENTIFICATION OF MISSIONSUNIQUE MISSION/VEHICLEUNIQUE COMBINATIONS FIGURES OF MERIT FOR SELECTIONAND a CONVENTIONAL TRANSPORTATIONMISSION/ EVALUATION VEHICLECOMBINATIONS a MISSION PECULAROPERATIONAL RESTRICTIONS MULTIMISSIWVEHICLE CONFIGURATIONS a MISSION/VEHICLERANKING AN0 RECOtWENOiO PHASE II STUDY BASELINE

Figure 2. Phase I: GeneralApproach and Overview

- LL 0.04 1 g HISTORICAL AIRSHIPS Y I 3 / 0

u) 2- 003 3 2 MODERN AIRSHIPS Q: F -" / ;002 0 u P > t I w 0.01 0 2 4 6 a 10

MAXIMUM GAS VOLUME (lo5 FT31

Figure 3. StructuralEfficiency of Modern and Historical Neutrally-BuoyantRigid Airships

-4- withgross lifting capabilities ranging from 3000 lbsto 6,000',000 lbs wereinvestigated. The parametricstudies included the effects of im- portantdesign factors such as vehicle geometry, ratio of buoyant lift- to-total lift, and cruisespeed. Since the emphasis of Phase I was on transportationmissions, the principal figures of merit were productivity, definedas either payload or useful load times cruisespeed, and specific productivity,defined as productivity divided byempty weight.(Since theheavy-lift airship concept is not meant forproductivity missions, it was treatedseparately.)

A key partof Task 3 was thedevelopment and use of a vehicle synthesis(integrated conceptual design) computer program. The program is calledthe Goodyear AirshipSynthesis Program (GASP) and Figure 4 shows its functionalcapability. This programcomputes mission perform- ancefor a specifiedvehicle concept, shape, and missiondefinition and canbe used toconduct parametric studies of a wide varietyof both conventional and hybridairships. Although many of thesubprograms in GASP were derived from airship analysis capability which has evolved over many years, a significant amountof effort was requiredto develop weight estimatingrelationships for hybrid airships since these represent a new classof vehicle.

As anexample of the parametric results whichwere obtained for con- ventionalairships, effects oftype of construction and sizeare shown in Figure 5. The dashedlines for the non-rigid concepts at the higher gross weightsindicate a requirementfor improvedseaming technology in this region.This figure shows thatnon-rigids tend to be favored for small sizes,metalclads for mid-sizes, and rigidsfor large sizes but that there is generallynot a greatdeal of difference betweenthe concepts. In fact, all concepts had a structuralweight-to-gross-weight ratio of about 0.4 over- a widerange of gross weights. Figure 5 also shows thatif Kevlar is developedas an envelope material for a non-rigid,then the non- rigid is thesuperior concept for almost all sizes.

-5- ._ ...... ”. .... - ... ._ ...... _...... ”_...... -...... -....._...”.”._ ...... ”...... F

NASACOHMIN PAPAMETER VAR!ATION OPTIMIZATION AND SEI.ISITIVITYITER-

Figure 4. Basic Methods of Analysis(GASP Computer Program)

*O0 r c*-”““

v) *, e”” --. 0 C Y KEVLAR w

0- CLAD METAL 3- 50

// RIGID I I 0 I I 03 1o3 105 1o6 6 x IO6 GROSS WEIGHT, Ib

Figure 5. SpecificProductivity of Fully Buoyant Airships

- 6- After a preliminaryscreening, one hybrid concept was selected for parametricevaluation for productivity missions. This was a lifting body shapewhich had a parabolicplanform with elliptical cross sections; it waschosen because of structural weight considerations and the proximity ofthe centers of buoyancy and pressure. The parametricanalysis focused ondetermining the values of aspect ratio, thickness-to-chord ratio, and cruisespeed which maximized productivityat various values of gross weight (GW), buoyant-to-totallift ratio (B), andrange (R). The results showed that at almost all values of GW and R, thebest productivity was obtained as 8 tendedto zero, i.e., a vehiclewith no buoyant lift (anairplane) is optimum. The lifting body hybridconcept was compared withthe conven- tionalrigid airship at various values of GW, 8, and R. Exceptfor very largevalues of GW, theconventional rigid consistently had a higherpro- ductivitythan the hybrid.

The finaltask in Phase I was toselect promising vehicle/mission combinationsfor further study in Phase 11. Basedon results fromthe othertasks, the heavy-lift and VTOL transportconcepts appeared to be the mostpromising and were selected, with NASA approval,for more detailed studyin Phase 11.

HEAVY LIFT AIRSHIP STUDY RESULTS'

Summary

A majordeficiency in current air transportation. systems is theshort haulof heavy and very heavy outsized cargo and this was identifiedduring Goodyear'sPhase I Studyas a missionuniquely suited to modern airship vehicles. The militaryneed for a heavy verticallift capability is well 2 documentedand thecivil need, while equally apparent, is inthe process ofbeing more completelycharacterized anddocumented in a forthcoming 3 NASA Study. The primarymilitary requirement is theoff-loading ofcargo

1 References 2, 3, and 4 providecomprehensive results relative to the Phase I1 Heavy LiftAirship Study Navy Operational Requirement Nuder W1019-SL PrsmarilyContainerized Cargo

-7- 1111 I

fromships in areas lacking deep water port facilities while the civil needs are centeredin the power generating,petroleum, construction, logging, andheavy equipment industries.There also appears to be a considerableforeign civil market in the off-loading of cargo from ships indeveloping nations lacking deep water ports. Currently, military air- borneheavy liftscenarios consider aggregate loads requiring payload capacities up to 140tons while potential civil applications could involve severalhundred tons. Range requirementsvary from a fewhundred yards in some constructionindustry applications with a rangecapability of severalhundred miles of interest in the movement of miningequipment to remote sites.

Variousheavy lift conceptscombining buoyant and rotor lift have beenproposed inrecent years for performing the emerging heavy lift shorthaul missions. TheHeavy LiftAirship (HLA) evaluatedduring Phase I1 is a conceptfirst proposed by PiaseckiAircraft Corporation (Reference 9) whichcombines buoyant lift derived from a conventional helium-filledairship hull with propulsive lift derived fromconventional helicopterrotors. The buoyant liftessentially offsets the empty weight of thevehicle; thus the rotor thrust is availablefor lifting the useful load and to maneuverand controlthe vehicle. The abilityto off set the entire empty weightof the vehicle with buoyancy permits a quantum in- creasein current and projectedhelicopter lifting capabilities plus potentially a substantial reduction in current vertical lift costs.

The conceptalso eliminates the significant historical airship deficiency ofinterchanging ballast andpayload. In addition, the con- ceptpromises to significantly improve the low speedcontrol and hovering qualitiesof prior airships while also leading to improvedground handling characteristics. The classicalhelicopter problems of high fuel consumption and airframeweight are implicitly minimized inthe concept. Further, significantly improved maintainability and reliability characteristics appearto be availableif dedicated propulsion systems (rotor/turbine/ transmissionmodules) are developed, making the use of existinghelicopters unnecessary. The HLA concept is relatively immune toscale effects and

-8- prioranalyses (References 1 and 10) have shown thatpayloads up toseveral hundredtons can be transported several hundred miles.

The specific HLA configurationstudied in Phase I1 combines four CH- 54B helicopters, by means ofan interconnecting structure, to a two andone- halfmillion cubic foot non-rigid airship hull fabricated of present-day proven airshipmaterials (Figure 6). This HLA has a payloadcapacity of

1 Figure 6. Phase 11 Heavy LiftAirship Concept

68,040 Kg (75tons) and a non-refueledrange of 1.852 x lo5 m (100nauti- calmiles). Without the buoyancy, the collective payload capability of the four helicopters at the same range wouldbe on theorder of50% of that of the HLA. Figure 7 illustratesthe many militarypayloads which canbe lifted by the HLA but whichcannot be lifted by existing helicopters.

The HLA is controlledfrom the aft left helicopter by a command pilotusing Fly-By-Wire (FBW) techniques.Automatic flight control and

- . . 1 The range capability of an operational HTA configuration using dedicated propulsionsystems reflective of currenttechnology will be substantially greaterthan the Phase I1 configuration(Reference 10). -9- I I- O I

X rD P Y. i, 0 '0 R ID 1 r r. m R hover modes, withthe hover capability enhanced by a Precision Hover Sensor (PHS),would be providedin addition to the manual flight modes. The AutomaticFlight Control System (AFCS), PHS and FBW electronics requiredfor the HLA involveprinciples, techniques, andhardware develop- edand demonstrated during the U. S. Army Heavy LiftHelicopter Program and a NASA-Langley Programduring which Sikorsky Aircraft modified a CH- 54B helicopter to obtain a FBW capability.

The configurationinvestigated during Phase I1 retainsthe entire helicopter with a minimum ofmodification because of the economy involved in using existing hardware assets for an initial flight research vehicle. A significant benefit ofthe coming NASA Studyof the civil heavy lift market will be a market size definition such that a determinationcan be made asto whether a sufficientquantity ofheavy lift vehicles is needed overwhich the development costs of a dedicatedpropulsion system can be costeffectively amortized. This dedicated propulsion system wouldbe usedon the operational version of the HLA alongwith a central control carfor the flight crew.

The majorareas of investigation during the Phase I1 HLA Studyin- cluded: (1) a pointdesign analysis (aerodynamics, flight dynamics, controls,structures, and weights); (2) an economic analysis; (3) anoper- ationalanalysis; and (4) a technologyassessment analysis.

A corporatelyfunded poweredwind tunnel model ofthe HLA was evaluatedduring Phase I1 in the NASA Ames 7 x 10-foot wind tunnel facility. The results ofthese tests indicatethe aerodynamic feasibility of com- bininglarge rotors in close proximity to a largehull. These tests have also shown thatthe cross-wind station keeping capability of the vehicle can beimproved by modifications,such as changing rotor locations, to the current HLA configuration.

As anadditional area of: corporatesupport, a Six Degree-of-Freedom (6 DOF) hybridcomputer flight dynamics simulation was developedto assess the flight dynamicsand precisionhover mode accuracyof the HLA

-11- ......

and toassist in the synthesis of the fly-by-wire control laws and auto- pilotsystem. Based upon the wind tunneland flight dynamics simulation efforts it appearsthat the HLA hassufficient controllability to perform themilitary and civilmissions for which it is beingconsidered over an acceptablerange of atmospheric conditions.

DuringPhase 11, variousstructural arrangements and materialtrade studies were performed inorder to minimize structural weight, while maintainingacceptable acquisition costs. A reasonablydetailed point designanalysis was performedon the arrangement finally selected and as a resultthe empty weightestimates for the vehicle are believed to be reasonablyaccurate.

The Phase I1 economicanalysis indicates the Total Operating Costs (TOC) ofthe HLA on a payloadton-mile basis to be substantially reduced overcurrent large helicopter vertical lift costs basically due tothe economicleverage afforded by thebuoyant lift. Given proper technology programs inthe areas of low maintenancerotor concepts and the inclusion ofcurrent turbine technology, the TOC forthe HLA shouldbe more favor- ablethan estimated herein.

The technologyassessment of the HLA indicatesthat there appears to beno major unresolvable technology problems and thus the concept is basicallyfeasible. However, additionaldata and analysiscapability is needed inseveral technical areas before an operational HLA couldbe designedwith low risk andhigh efficiency. As partof Phase 11, a technologydevelopment program tosupply this information has been out- lined.

A logical step towardsdevelopment of an operational vehicle is a flightresearch vehicle (FRV) program. This would giveresearch capabilities notobtainable in ground based facilities and would serveto verify feasibility ofthe concept. The FRV would makemaximum use ofexisting com- ponentsto minimize program costs.

-12- Description of HLA and RelatedPerformance

Figure 8 presentsthe Phase I1 HLA generalarrangement and selected performancecharacteristics of interest. The designgross weight’ is 147,365 kg (324,950lbs) of which 65,375 kg (144,150 lbs) is buoyant lift and81,993 kg (180,800 lbs) is rotor lift. The fourhelicopters are capableof providing this amountof lift with oneengine out and adequate reservefor a 30.48 m/min (100 ft/min)climb. There are on theorder of fifteenairship hangars remaining in this country that can accommodate two such vehicles.

ROTOR LIFT 160,800 lbr 6UOlANTLIFT 144.150 lbs EMPTINEIGH! 140.070 lbs USEFUL LOA0 176.800 lbs STAIICHEAVINESS. 3.929 lbs ENVELOPEVOLURE 2.5 I 106 CY It BALLONET VOLUME 5.15 a lo5 cu tt IALLONET ccILImc 8.500 It HULLFINENESS RA710 3.2 DESIGNSPEED (TAS) b0 tnata RANGE DESIGN WITH MAX PAYLOAD 100 nm NO PAlLOAO I96 nm f ERR1 1.150 n. NOTf: 1.0 ft - 3.041 I 10-lm. 1.0 lbm - 4.536 a 10-1 tp 1.0 knot - 5.144 a 10” .Is. 1.0 cu ft I 2.032 a 10.‘ cu a342 IT- 1.0 nm - 1.852 I IO’

Figure8. Phase I1 GeneralArrangement and Selected 2 PerformanceCharacteristics

At sealevel, standard day, 93% inflation.

The rangecapability of an operational HTA configurationusing dedicated propulsionsystems reflective of current technology will be substantially greaterthan the Phase I1 configuration(Reference IO).

-13- The buoyantportion of the lift is obtainedfrom a two andone-half millioncubic foot non-rigid hull fabricated from present day proven airship fabrics.Basic fabric andseam strengthsrequired are only slightly greaterthan the maximum ofthe largest non-rigid ever built, the ZPG-3W built by Goodyear forthe U. S. Navy inthe late 1950's. The liftinggas is helium.

The twin-enginehelicopters are attached to the buoyant hull by means ofthe interconnecting structure much ofwhich is "submerged" withinthe envelopeto reduce aerodynamic drag and overallvehicle height. The four Sikorsky CH-54B helicopters havebeen adapted to the interconnecting structure by means of a gimbaldevice. The tailrotors of the aft heli- coptersare replaced with propellers and reorientedto provide sufficient propulsiveforce for forward flight and directionalcontrol at or near minimum grossweight. The tailrotors of the forward helicopters are un- altered andused toprovide side force for increasing the cross-wind station keeping ability.

The FBW controlsystem combines the normal pilot control modes with theneeded automatic flight control and hover modes. The controlsystem technology is similarto that demonstrated in the Heavy Lift Helicopter Programduring which a prototype FBW control system was successfullyflown on the tandem rotor CH-47 helicopterwith over 300 hoursof flight time accumulated .

The Phase I1 configurationpermits center point mooring to be considered whichminimizes mooring area andmooring mast requirements. Additional wind tunneldata are required to permit a finalassessment as to whether theconcept can accommodate all mooringrequirements of operational interest.

DesignAnalysis

Aerodynamics One factorleading to Goodyear's Phase I recommendationof this HLA concept was thejudgment that it possessedfar fewer aerodynamic uncertainties

-14- thanthe other heavy lift conceptscombining buoyant and rotorlift. One uncertaintythat existed was theextent of aerodynamicinterference between thelarge rotors andthe large hull. As a result of thisuncertainty, a joint Goodyear/NASA sponsoredexploratory wind tunnelinvestigation of the concept was undertakenin the NASAAmes 7 x 10-foot wind tunnel facility.

The mode 1, shown in Figure 9 , is 1.22 m (4 f t) long and 0.41 m (16 inches)in diameter. Rotor location, thrust magnitude and inclination(in roll) along with the model angle of sideslip and height abovethe ground planecan be varied. Themodel employs six component balancesin each outrigger and a six-component main balancein the model hull.

Figure 9. Powered Model in ARC 7 x 10-Foot Wind Tunnel Facility in Presence of Ground Plane

-15- The followingrepresent the most significantconclusions from the wind tunneltesting: (1) no appreciableinterference effects in forward flight wereobserved; (2) no appreciableinterference effects were observedfor angles of sideslip less than 60 degrees(at zero degrees angleof attack); (3) rotor-rotor interference was negligible and the effectof the hull on therotors was small; and (4) a considerablein- creasein crossflow drag ofthe hull occurs as a result of theoperation of allfour motors. This last adverse interference effect is a strong function of rotorplacement with the effect decreasing as the rotors are moved outboard.Fore and aftdisplacement ofthe rotors resulted in no appreciablechange in the observed interference effects. The test resultsalso indicate that in a crossflowthe modification of the flow field aroundthe hull by theoperation of therotors may be a usable phenomenon incontrolling the vehicle. More testing, however, is necessary toconfirm this.

Reference 5 provides a comprehensive summary of the modeland in- strumentationcharacteristics and test program results.

Flight Dynamics A preliminary 6 DOF simulationhas been developed using the Goodyear hybridcomputer facility to assess the flight dynamics characteristicsof the HLA. Specific uses ofthe simulation include: (1) synthesis of over- allcontrol system requirements; (2) synthesis of thefly-by-wire control laws and autopilotcharacteristics; and (3) verificationthat the control lawsdeveloped for interface with the AFCS and PHS modes arecompatible with manualmodes.

The elementsinvolved in the simulation and theirrespective location inthe hybrid setup are as follows. The HLA gust model, control lawsand autopilotsare programmed on the 'EA1 7800 analogcomputer. The analog computer is linked,through an EA1 8831hybrid interface system to a Xerox Sigma 9 digital computerwhich contains the equations of motion,airship and helicopternon-linear aerodynamics, and thecross wind hoverinter- ference model developedfrom the wind tunneltest results. Althoughthe simulationhas proved useful in its presentform, many of its elements will have to beimproved and expanded for use in more detaileddesign studies . -16-

. Y . . " InPhase I1 the HLA simulation was "flown"with autopilot control inthe cruise andhover modes. Inaddition, the HLA simulationcan be flownmanually by stickinputs to the analog computer. The simulation operatesin real timeto@rovide realisticflight responses for flight inputs. All results aredisplayed as an output of theanalog computer onan oscillograph or on a cathoderay tube.

A preliminaryassessment of theprecision hover and directional stability characteristics of the HLA were obtainedusing the flight dynamicssimulation. Figure 10 presents typical simulation results indicatingthe vehicle response to a lateralgust.

2 1. 0 w 8OC 6 4 2 0-0 5 1515 10 2525 20 30 35 LATERAL GUST VELOCITY (FPS)

Figure10. Phase I1 HLA Response toLateral Gust

The simulationstudies to-date indicate that the hover and directional stability characteristics of the HLA areadequate for operations over a significantrange of expectedatmospheric conditions.

-17- FlightControl System The preliminaryflight dynamicssimulation studies have shown that.the availablerotor forces can be appropriately combined tocontrol the vehicle inboth flight andhover modes. Thisactive control system approach eliminates a severedeficiency of past airships (i.e., lackof low speed control)since airspeed is notrequired for ths@2HLA todevelop maximum controlforces. As statedearlier, the HU controlsystem would use FBW controlsystem techniques andhardware similarto those developed and flight tested on a tandem rotor CH-47 helicopter programduring the HLH program.Automatic modes areprovided including automatic hover employing a precisionhover sensor.

The HLA is flownusing standard helicopter controls. The aft left helicopterserves as the command station in which a command and safety pilotare located. The command pilot'sconventional mechanical controls arereplaced with electric cyclic and collectivesticks as well as electricpedals whichgenerate the commands tothe analog FBW flight controlsystem. The remaininghelicopters are slaved to the command heli- copterthrough the FBW commands asindicated in the simplified block dia- gramof Figure 11. Safetypilots could beused inthe slave helicopters withthe conventional mechanical helicopter controls available if needed.

The HLA fly-by-wireprimary flight control system is a dualredundant systemfrom the command pilot's commands tothe input commands toeach helicopterautopilot. The helicopterautopilot, also a dualredundant electronicsystem, flies the helicopter on thegimbal through the electro- mechanica 1 AFCS servo.

Implementationof the control laws indual paths for redundancy is consistent with the CH-54BAFCS conceptwhich has a redundant electrical channelsuch that either or both can beused. The HLA thereforehas three modes ofoperation for safety-of-flight: (1) activepath fly-by- wire; (2) redundantpath fly-by-wire; and (3) a safetypilot using a manual flightcontrol system.9:

* It is envisionedthat an operational configuration would use a central controlcar much like priorairships thus safety pilots would not be requiredand a tripleredundant system similar to the HLH wouldbe implemented. -18- HELICOPTER HELICOPTER HELICOPTER HELICOPTER #1 #2 #3 #4 COMMAND (SMYE) (SLAVE) (SLAVE)

SERVO SERVO SERVO SERVO

CONTROL LAWS FLY-BY-WIRE COMMANDS I t" NIXING I IKPUTS + 1 I"""""- 7 I RATE GYROS I I I I I I I VERTICAL GYRO I I I I I I I I EXISTING I I INTERCONNECTING I I HLH EQUIPflENT I I STRUCTURE L______J L __-__- ---J

Figure 11. HLA Fly-By-Wire ControlSystem Block Diagram

The CH-54B helicopter is ideallysuited to conversion to fly-by- wire controlwith safety pilot override because of the AFCS servo.In fact, a similarconversion has been achieved by Sikorskyfor NASA Langleyfor variable stability test purposes. In that conversion the test pilot's cyclic stick was disconnectedmechanically from the co- pilot stick and electrical transducers with a stick feel system were added. The co-pilot(safety pilot) had theability to override the test pilot at any time withmechanical stick positions taking command of thehelicopter if required.

An autopilot is requiredon the HLA forthe precision hover mode andpitch attitude hold. The precisionhover mode uses a position sensorthat commands theautopilot which provides load spotting accuracy beyond thecapabilities of a pilotmanually flying the HTA viaprimary

-19- .. ..

flightcontrol system in a hover mode. The static trim capabilityafforded by thefore and aftballonets could be integratedinto the pitch attitude holdautopilot function. As notedpreviously the flight dynamicssimulation was used inthe synthesis of the autopilot system and also to experimentallydefine the autopilot gains.

Structural Analysis and Materials Duringthe preliminary studies of Phase I it became obviousthat the HLA conceptintroduces structural design conditions never before en- counteredin airship design. The basicreason for this is thefact that the maximum rotorforces available are in excess of the empty weight of thevehicle and aretherefore capable of creating accelerations far in excess of previousairship experience. Furthermore, the very nature of thevehicle results in rotor locations which provide large moment armsand createthe possibility ofvery large moments aboutall three axes being transmittedto the envelope (Figure 12). These considerations indicate a requirementfor a broadbased suspension system with an arrangement facilitatinglarge rigging tensions in the cables so that no cables go slackin the most severeloadings.

Figure 12. Major Structural Components of HLA

-20- It was alsoapparent that a large structure, sufficient to pre- cludephysical and aerodynamic interference between the rotors and the envelope andbetween adjacent rotors, becomes animportant consider- ation fromthe standpoint of structural integrity and inert weight. It was clear that considerable effort was justified toward defining a structurallysound, lightweight, interconnecting structure. Toward this endnumerous designapproaches were investigated. The selected interconnectingstructural concept consisted of an internal "star frame"which is submerged withinthe envelope as shown in Figure 12. The star frame is fabricatedof three-boomed,welded high performance steel girdersemploying pin ended joints. The outriggers and lift struts whichare external to the envelope are of an aluminum honeycomb sandwichconstruction.

The large number of helicopter and landingloading conditions experienced by theinterconnecting structure led to the development of a series ofcomputer programs combined asindicated in Figure 13 tofacilitate the structural analysis effort.

"""""""" r INTEGMTED CWUTER PROGRRn1 I SUSPENSlOii SYSTEI * I - *GEOXTRY FRAYE JOINT FRCE MER I *STIFFNESS A* LORDS WADS I I *UNIT SOLUTIOHS I

""" t ""-

AND STIFFNESS.

-21- I

The fabricstrength required for thevarious design conditions is dependent upon thefrequency of occurrence of theseconditions and the lengthof time the fabric is under stress inthese conditions. Since inthe design of an envelope the creep rupture strength is usually criticalrather than the quick break strength of the fabric, the quick break strength is reduced by a factor which will guaranteeadequate life ofthe structure. This factor provides not only for creep rupture effects,but also nominal stress concentrations, wear and a scatter factor.Proven fabrics are available for this application and were assumed inthe Phase I1 design. Advanced materials would givesignifi- cant component weightreductions but a verification programwould be required.

A two-dimensionalenvelope shape analysis computer program was developedto define the cross-sectional deformations occurring for boththe unsymmetrical air loads when masted out andsymmetrical riggingloads.

The envelopepressure was selected so thatwrinkling and excessive deformation will notoccur under limit loads.

The envelopeanalysis has indicated that the critical loads which definethe envelope fabric strength requirements are those associated withthe airship being masted out.This indicates that alternatives to center-point mooringshould be investigated.Additional wind tunnel dataare needed toconfirm that the new centerpoint mooringconcept can beused over a suitablerange of operationalconditions. If not, a more conventionalmooring concept will have to be adopted.

1 Economic Analysis

A preliminaryestimate of the Total Operating Cost (TOC) peravail- ablepayload ton-mile (statute) was made as part ofPhase 11. The TOC analysisconsidered an operational configuration that differs fromthe Phase I1 HIA inthat only the helicopter rotor/turbine/transmission

1 All dollarsare constant 1976 dollars

-22- module is retainedon each outrigger and a centralcar is providedfor theflight crew. It is estimatedthat thi,s approach would result in approximately a 20% reduction in the acquisition cost as compared to thePhase I1 configuration which retains the entire helicopter on the outriggers.Flight crew requirements and costs are also based on the operationalConfiguration (i.e., safetypilots not required),

The model usedin calculating the direct portion of the total operating cost is thestandard Air TransportAssociation approach. The indirectelements are derivedfrom costs needed to support large helicopters in commercialoperations.

Comparison of the HLA TOC withthe largest commercial U. S. Heli- copter,the Sikorsky S64F, is made inFigure 14. Both vehiclesare consideredto beperforming a missionthat the helicopter is capable of performingin ter.ms ofpayload weight. The figureindicates the

FAX GROSS WEIGHT BEST ENDU3ANCE SPEED

0 v I000 1500 2000 UTILIZATION - (HRVANNUM) Figure14. Comparison of S64Fand HLA TotalOperating Cost Per Payload Ton Mile at Design Range of HLA

-23- I

generaleconomic benefits to be derived from combining rotor and buoyant liEt. The reducedmaintenance and improved fuel consumption characteristics of a dedicatedcurrent technology propulsion system will serve to further improvethe economics of the HLA. The additionaleconomic benefits that a vehiclecapable of lifting large outsized loads can provide in terms of factoryversus remote site assembly,special highway or roadways receiv- ingonly limited use, etc., must also beincluded in anydetailed market andeconomic analysis.

Forpurposes of the economic analysis, the HLA RDT&E costshave been 6 estimatedat $50 x 10 . The HLA fuelconsumption for the design speed of 60 kts is estimatedto be 0.36 gal/ton-mile. As a matterof interest, withoutthe benefits of buoyancy thefuel requirements wouldbe on the orderof 0.52 gal/ton-mile.

OperationalAnalysis

The HLA concepteliminates or minimizes the significant historical airshipdeficiencies. The most importantof these is theneed to inter- changepayload and ballast which is eliminated by the use ofsufficient rotor lift to give a vehiclewhich is always in a heavier-than-aircon- dition. The severe(in terms ofcurrently postulated uses) historical limitationof lack of low speedcontrol is significantly minimized inthe HLA concept,again due to the large rotor forces being available for control.Prior airships have hadno appreciablehovering capabilities exceptinto a steadyheadwind. However, theflight dynamicssimulation studies,discussed previously, show thatthe HLA has good potentialin thisregard.

Ground handlingof the HLA in comparisonto prior airships will be much improved for two reasons.First, the rotor control forces canbe used on the ground as in flight to control the vehicle when the vehicle is not moored. Secondly,the HLA has a wide basedlanding gear arrangementwhereas prior airships in some cases were limitedto a singlewheel gear. The widebased landing gear arrangement provides a

-24-

. significant improvement in vehicle roll stability on the groundwhich will minimizevehicle response to ground turbulence. The widebased landinggear arrangement will alsodecrease the historical problem that snow and iceaccumulation have represented to past airships when moored. Prior airships, which afterused only a singlewheel landing gear, were verysusceptable to overturning due to snow and iceaccumulation.

A new "centerpoint" mooring concept for the HLA, whichreduces prior mooring datarequirements, has evolved during the Phase I1 Study. The concepttakes advantage of the wide based landing gear arrangement aswell as the "rugged"nature of the suspension system. It appears that with this mooringconcept the HLA can be moored out, and operated fromunprepared fields involving a widerange of soilconditions. The center point mooringsystem utilizes a "stub"mast which interfaces withstructure at the center of theinterconnecting structure. Thus, thevehicle staWLzes, when masted out,broadside to the wind thereby reducingthe mooring area in comparison to that required in the conventional bow mooringarrangement.

Transportor "ferry" of the HJA tothe area of operational need will be accomplished much the same as inthe past airships. The operational HLA configuration will likely usean auxiliary turboprop propulsion systemfor the ferry mission; thus the high fuel efficiency inherent in past airshipoperations will be achieved.

TechnologyAssessment Analysis

The final task ofthe HLA Phase I1 Study was a TechnologyAssessment Analysis (TAA). Thisincluded three major subtasks:

(1)Identification of areas whereadvanced technology could contribute towardimproved safety,performance, or economics of the vehicle.

(2) Identificationof the need forflight research vehicles.

(3) Identificationof costs and schedulesfor technology development and flight research vehicle programs.

Onlythe first two items will be summarized herein.

-25- Although no technicalbarriers to development of the vehicle concept were discoveredin the course of the HLA Phase I1 investigation,there areseveral areas in which further analysis and dataare needed. In aerodynamics,the immediate requirement is forfurther small-scale testing. An obviouschoice for this work is the12-foot pressure tunnel at NASA Ames ResearchCenter since the variable density feature of this tunnel will allowtesting significantly above the critical Reynolds number. Test results will provideaerodynamic data for: (1) flight dynamics simulation, (2)verification of the theoretical techniques for predicting aerodynamic interferenceeffects which are currently being developed, (3) definition of a finalconfiguration (e.g., selection of rotor location, hull fineness ratio, and tailsurface configuration, if any), (4) envelopeanalysis, and (5) mooringsystem analysis.

Finalaerodynamic data from testing in a largetunnel such as the 49 x 80 foot wind tunnelfacility at Ames will beneeded. This facility allows a model ofsuEPicient size such that articulated rotors can be used.Articulated rotors are necessary to assess unsteady aerodynamic ef E2cts.

A key technicalrequirement is continueddevelopment and refinement offlight dynamicssimulation. The following is needed in terms of up- gradingexisting simulation capabilities: (1) complete, experimentally verified G DOF aerodynamics;(2) improved representatim of the rotor dynamics; (3) improved turbulencespectra; (4) improved representationof theinteraction of the turbulence with the vehicle; and (5) inclusionof aeroelasticeffects. The main uses ofthe flight dynamics simulation will beto support (1) controlsystem design and analysis, (2) ground-based simulatorexperiments, (3) developmentof design criteria, and (4) structural design and analysis.

Thereare several areas in structures and materialswhich need technologydevelopment. One need is fordevelopment of structural design criteria. A detailedstructural dynamicsanalysis will berequired to assure a vehicle structure freeof instabilities. A comprehensiveanalysis ofthe envelope and suspension system will also be necessary. The large

-26- deformations(as compared toprior airships) of the HLA will require new envelopeanalysis techniques. A program toexperimentally validate advancedmaterials, particularly fabrics and films, would leadto substantially improved vehicleperformance.

A technologyprogram which would leadto economic benefit is thedevelopment of a low maintenancepropulsion system. The projected maintenancecosts of the Phase I1 HTA are dominated by the maintenance requirementsof the helicopters. The availability ofbuoyant lift to offsetthe weight of the rotor system components can permit greater marginson the dynamic components and thiscould be exploitedin the designof a propulsionsystem for low maintenance.

The TAA has indicated the desirability of a FlightResearch Vehicle (FRV). The primarypurpose of an FRV wouldbe toobtain research capa- bilitiesthat cannot be duplicatedin ground-based facilities or in ground-basedcomponent and sub-system testing. If the FRV is patterned afterthe Phase I1 HLA, it would also be capableof providing concept verification and operatingcost data under actual mission conditions. Use of existing helicopters and other off-the-shelf componentswould result in a low cost FRV program.

One approachto an HLA FRV program is todevelop the FRV concurrently withthe technology development program and this approach was adopted in Reference 2. The FRV initially wouldbe constructedusing existing, proventechnology insofar as possible so thatflight testing could begin at a relativelyearly date. The results fromthe technology program would then be integratedinto the FRV as they became available.

Conclusionsand Recommendations

Significantconclusions resulting from theinvestigation of the heavy lift airship concept are: (1) The conceptappears to be technicallyfeasible andhas the potentialfor meeting the need forthe heavyand very heavy vertical lift oflarge outsized cargo. (2) The buoyancy, inaddition to permitting a substantialincrease

-27- insingle vehicle vertical lift capability, should provide a significant reductionin current vertical lift costs. Additionally, the buoyancy reducesthe fuel requirements for lifting and transportingcargo in comparison to current helicopter sys tems. (3) The conceptminimizes or eliminates significant operational deficiencies of past airship designs. (4) The technologyassessment analysis has indicated that signifi- canttechnology efforts (e.g. wind tunneltesting, flight dynamics simulation,structural dynamics analysis) are needed toassure the successfuldevelopment of the concept. Other technology programs (e.g. inmaterials and propulsionsystems) would substantially improve the performanceand economics. (5) The technologyassessment analysis also has indicated the great utility of a flight research vehicle for research and proof-of- conceptpurposes.

Significant recommendations resultingfrom the investigation ofthe HLA conceptare: (1) A marketstudy is requiredto better define the commercial marketsize and the optimum vehicle andmission parameters. (2) A series of technologyprograms are needed to acquire sufficient analyticaltools and empiricaldata to successfully develop the concept. Otherprograms to improve the vehicle performance and economics should also be pursued. (3) A flightresearch vehicle wouldbe highly desirable and should bedeveloped in a timely manner.

AIRPORT FEEDER STUDYRESULTS

S umma ry

The AirportFeeder Vehicle is a VTOL semi-buoyantairship capable of transportingpassengers or cargo to major CTOL hub terminalsfrom suburbanand downtown depots. The baselinePhase I1 configuration is

- 28- shown inFigure 15. One operationalconcept is shown inFigure 16.

Principlevehicle design characteristics and capabilitiesinclude:

Pressurizedmetalclad construction 3 3 Volume - 12,135 M (428,500 Ft ) GrossWeight - 30,618 kg (67,500lb)

8 = StaticLift/Gross Weight - 0.35

80 Passenger Capacity

Modularizedcargo/passenger design

VTOL

Figure 15. FinalPhase I1 BaselineAirport Feeder Configuration

-29- AIRWAYS TO MOR AIRPORTS Alie+V OR ADJACENT CITY CEKTER

~.~.. .

Figure 16. AirportFeeder Concept of Operations

The Phase I1 studyeffort was organizedinto four tasks: 1) Vehicle DesignDefinition, 2) OperationalProcedures Analysis, 3) CostAnalysis andModes, and 4) Mission/Vehicle Feasibility andTechnology Assessment. The followingsections describe the workdone inthese tasks.

Vehicle Design Definition

The vehicle design definition was a combinationof point design analysis and parametricvehicle sizing andperformance optimization. The objective was todefine the vehicle characteristics of an 80 passengerairport feeder for maximum specificproductivity. The propulsionsystem design andperformance characteristicsrequired for oneengine-out VTOL receivedspecial emphasis. The majorparameter of interest was theratio of buoyant-to-total lift (B).

-30- Severalalternate passenger seating arrangements and carconfigur- ationconcepts were evaluated. The selectedconcept is a modularcon- figurationwith two-forty passenger modulesand six abreast seating as shown inFigure 17. Either all passenger, allcargo, or combined oper- a tions are possible.

Propulsionsystems evaluated included four engine fully cross-shafted propeller,four engine fully cross-shafted ducted fan, and sixengine uncross-shaftedconfigurations. The fourengine fully cross-shafted configuration was selectedas the baseline configuration based on minimum weight, VTOL and cruise power requirements,and VTOL sidelinenoise levels.

The final configuration definition study was performed by incorpor- ating the results ofpoint design analyses into the Goodyear Airship SynthesisProgram (GASP). The optimizationcriteria for the study was maximum specificproductivity, i.e. payload times velocitydivided by empty weight, PV/E, evaluatedat the design range, which was 740 kilo- meters (400 n mi) plus a 74 kilometerdiversion (40 n mi) plus a 20- minutehold at a speedfor maximum endurance. The independentvariables consideredin the optimization study included cruise altitude, cruise velocity, B , grossweight and finenessratio for two types of construction: pressurizedmetalclad and pressurizedKevlar non-rigid.

The Phase I1 results,consistent with the Phase I trends,indicated thatthe pressurized metalclad type of construction was slightlysuperior tothe pressurized non-rigid for maximum PV/E. A weight.statementof the selecteddesign is givenin Table I. The pressurizedKevlar non-rigid couldpotentially offer a lower cost, more operationallyflexible airport feedervehicle andshould be retainedas a potentialcandidate in future studies.

The Phase I1 results are shown inFigure 18 alongwith a comparison ofthe Phase I Studytrend. An optimum 8 of 0.35 was found forthe Phase I1 vehicle,although the sensitivity of PV/E between B's offrom about 0.3 to 0.5 is small. The differencebetween the Phase I andPhase I1 trends

-31- I

OVERHEADBAGGAGE STORAGE

Figure 17. Two-Segmented Payload Module CabinLayout (6 Abreast Seating)

-32- Table I - BASELINECONFIGURATION WEIGHT SUMMARY

HullStructure 11,150 Lb

CarStructure 4,600

Modular PAX Compartment(2) 7 ,000

Empennageand Controls 3 ,100

LandingGear 1,120

PropulsionSystem 15,050

Fueland Fuel System 7 ,400

FlightInstruments and APU 1,200*

FurnishingslSeatsand Belts 1, 820*

Crew (2)STU's (2) and Gear 660*

80 PAX (3 160 Lb/PAX + 20 Lb/PAX Baggage 14,400*

TAKEOFFGROSS WEIGHT 67,500 Lb

* Basedon NASA "StudyGuidelines for Conceptual 1985 V/STOL Aircraft"

NOTE: 1 Lb = 0.453 kg

-33- ~ .. ~

?reaaurized lSO Ihtalclad t \ AirportFeeder

VI 100 - w 0 % Y

I .Y 50 - n. ?base I1 Result. = 0.35 BOP1

0, I I I I I I I 1 I I 0 0.2 0.4 0.6 0.8 1.0 6

NOTE: 1 ft 0.3048 m, 1 lb - 0.4536 kg.1 knot-0.5148 nls

Figure18. Buoyancy RatioTrends for Maximum Productivity: Phase I and Phase I1 Study canbe traced to the car structurelpassenger accommodations design and weightrequirement and thepropulsion system requirements for one-engine- out VTOL capability. The cruisevelocity for maximumPV/E was67 m/s (130knots) atan altitude of 610 meters(2000 ft). All NASA specified design andperformance criteriadefined for the mission can be met or exceeded. The noiseat takeoff is 86.5 pNdB, 8.5 pNdB underthe specified constraint.Fuel Consumption is about0.25 gallons/ton mile.

The majorareas of technical uncertainty were identifiedto be the hoverltransitionphase stability and thecontrol characteristics and flyinglridequalities in turbulent air.

-34- OperationalProcedure Analysis

A generalizedanalysis of operational characteristics of a "most probable"airport feeder system operating within the existing trans- portationinfra-structure was performed.Both a non-localeoriented effort and a sitespecific analysis were investigated.Important in- stitutionalconsierations and theimplied operational requirements are summarizedbelow.

The system will likelyserve business travelers. Therefore, the user must perceiveconvenience and/or time advantageover alternatives. From the use.r 's pointof view, the system shouldprovide adequate trip frequencies,scheduled departures, CTOL flight safety in virtually all weather, and reasonableride quality andcomfort.

From thenon-user/community acceptance point of view, noise, air pollution andground congestion should be minimized, as well as any adverseimpact on property value and hazarddue to accidents. These considerationsdictate quiet operations and carefulterminal and land accessplanning. An extensivepublic program may beneeded todefine the benefitsof the system to the public.

Airportoperations represent the first level of contract with user/ non-usergroup. The major areas of concerninclude the income potential of theairport feeder (A/F) system and thecompatibility with existing operations.Ideally, the system should reduce congestion and terminal delaysresulting from airportaccess. This indicates that the feeder must be integrated into or becompatible with existing airport operations. A preliminaryevaluation of the market size for the A/F systemindicated thatonly'the largest 7 - 10metropolitan areas may havepassenger demand sufficientto support an A/F service. The marketpotential for an Airport Feedertype of service is animportant factor which unfortunately is not well-definedat present.

The Lake ErieRegional Transportation Authority (LERTA) service region was selectedfor a site-specificevaluation. The physical

-35- restrictionsassociated with airport access to the proposed lakeport site may result in a uniquerequirement for and benefit from a short haulairport feeder system. The resultsof the LERTA analysisconfirmed many ofthe operational requirements derived in the generalized analysis and providedthe guidelines for developing the A/F operationalprocedures.

Severalapproaches to the loading and unloadingof passengers and cargowere examined. The selectedconcept is a modularpassengerlpayload modulewhich can be transferred fromthe basic Airport Feeder with all passengersaboard or can use CTOL type ramp facilitiesfor passenger access.This operational concept offers substantial improvements inthe landinglon-groundoperations of the A/F vehicleas compared withpast airships. The low valueof B alsoshould facilitate groundhandling.

CostAnalysis andComparison with Alternative Modes

The objective ofthe cost analysis was toestimate the operating cost ofthe Airport Feeder final baseline vehicle defined previously, operating inthe short haul passenger transportation market. Extensive use was made of several NASA developedcost estimating relationships (CER's). Costdata is in 1975 dollarsunless otherwise noted. Major areasof uncertainty in RDT&E include Government supportof RDT&E, FAA Certification Requirements, RDT&E requiredfor the "SecondEver'' Metalclad and the cost of developingthe terminal facilities.

The approachused was toinvestigate the RDT&E costsparametrically and todetermine the variations of the operating costs as a function of the RDT&E costs. The baseline RDT&E costestimate for the A/F System was $80,000,000. The upper andlower bounds consideredin the sensitivity analysis were$160,000,000 and $40,000,000, respectively.

The acquisitioncost estimates for the Airport Feeder vehicle con- ceptwere calculated for production quantities of 1, 25,and 125 vehicle productionruns. Established aircraft cost estimating relationships (CER's)were used forlearning factors, aircraft systems, passenger pro- visions and furnishings , propulsiongroup, and thecar structure and

-36- passengeraccommodations. GAC referencedata was used todevelop modificationsto the basic CER's forthe car structure, the hull structure and the empennage.

Operatingcost estimating relationships developed for short haul passengerturboprop aircraft operations (Reference 11) were utilized toestimate IOC and DOC. Baselineassumptions for the analysis were 125 unit fleet size, 3000revenue aircraftblock hours per year, fuel costof 30 cents/gallon,block speed based on 13 m/s (25 knot) wind speed(half head wind, half tail wind), and anaverage stage length of 74 km (40 n mi). The resultingbaseline DOC breakdown is shown in Table 11. The DOC sensitivityto alternate assumptions is shown inTable 111.

TABLE 11. BASELINEDOC/ASSM COST BREAKDOWN

I tem DOC (Cents /ASSM) % of DOC

Depreciation 1.37 25 Flight Crew Expense13.7 0.75 Fuel Oil andTaxes 22.8 1.25 Insurance 4.7 0.26 Maintenance Air Frame 0.41 8.5 Engine 0.42 7.6 MaintenanceBurden 0.95 17.3 Helium0.11 Replenishment 0.3

DOC (Cents/Available SeatStat Mi) = 5.52 Cents/ASSM 99.9%

NOTE: 1 StatuteMile = 1.609 km

-37-

I TABLE 111. SUMMARYOF DOC SENSITIVITY ANALYSISRESULTS

ParameterValues DOC /ASSMCENTS /ASSM Parameter

- A ~ Baseline +A -A baseline^_____ .

RDTdrE $ lo65.71 5.52 5.4540 160 80

RABH HRS4000 3000 2000 6.37 5.10 5.52

ASL N.MI. 15 40 5.07 1005.52 6.80

Fue 1 c/GAL 156.62 5.5230 4.92 60 .

NOTE: 1 n.mi. = 1.853 km

The DOC per availableseat statute mile (ASSM) rangesfrom about 5c/ASSM toabout 7c/ASSM over a widerange of average stage lengths, (ASL) yearlyutilization, (Revenue AircraftBlock Hours, RABH peryear) fleetsize and fuelcosts. DOC sensitivityto fuel costs suggest that optimum operating addesign characteristics ofthe Airport Feeder vehicle shouldvary with fuel cost.

Incomparison with recent results of studies ofconceptual short-haul airplanes,the A/F appearsto be economically competitive. In comparison withactual helicopter airline experience, the A/F is estimatedto be superior by a factorof two basedon direct operating cost per available seatstatute mile. Fuelconsumption per available set statute mile is estimatedto be approximately 30% betterthan current technology helicopters. As mentioned earlier, the A/F noiselevel at takeoff is considerablybelow thestudy objective of 95 pNdB and therefore belowmost if not all heavier- than-airdesigns.

-38- Mission/Vehicle Feasibility andTechnology Assessment

The greatestarea of uncertainty associated with the Airport Feeder concept is themarket for the service provided. Several key questions. havebeen identified which should be investigatedin more detail. These includemarket size, vehicle performance/design requirements for maximum economic viability, user acceptance,non-user reaction, and a more detailed investigation ofcargo operations.

Detailmarket studies need to beperformed tofurther define the demand and. potentialutilization for the Airport Feeder system concept. Thisanalysis should be integratedwith further vehicle design, perforrn- ance and operationaltrade studies. Promising study areas would include vehicle DOC minimizationas a function of designpassenger capacity, fuel costs, andbuoyancy ratio.

No unknowns havebeen defined which present technological barriers tothe successful development of the vehicle concept. Many areas have beenidentified which require additional research anddevelopment; primary among theseare hover performance/stability and control,aerodynamics,vehicle response to turbulence associated with CTOL airport andsuburban/downtown operations,flyinglride qualities, anddevelopment andintegration of cyclic propeller/prop-rotor technology for hover control. Table IV summarizeskey areasrequiring further RDT&X. Overall,the specifieddesign andperformance requirements appear to be achievable basedon the results todate. The resultsindicate that in terms of operatingeconomics, fuel consumption, and noiseperformance, the AirportFeeder vehicle concept is at least as promising as competing aircraft.

-39- Aerodynamics/Stability and Control/Flight Dynamics R&D Areas

Hull/RotorInterference Effects (Hoverand Cruise) Gust Environrnent/VehicleResponse in Airport and City Center Regions RideQuality During Cruise at Low Altitudes Stability and Control in Transition andHover Flight Applicationof Active Controls Technology Aerodynamic ConfigurationModifications for Improved Lift/Drag

Mission/Marke t Analysis R&D Areas

MarketAnalysis vs Vehicle Design and Performance Capability PissengerAcceptance of Low Altitude Ride Quality DesignOptimization based on Return on Investment DesignOptimization at High FuelCost

General R&D Areas

Operational Development/Verification ofTether/Winch Landing Sys tern Propeller Interference during Transition Low Cost Materials Handling/Manufacturing Approaches PassengerCompartment Noise Level Reduction Environmentaland Operational Limitations of MinimumGauge Metalclad Hull Structure DesignImplications of HighGround-Air-Ground Cycle Operations Applicationsof Advanced Materials

-40- NAVY MISSION STUDY RESULTS

Mission Description

The primarypurpose of the Navy portion of Phase I1 was to assess the technical feasibility of utilizing LTA vehicles or LTA vehicular systemsto perform pertinent Navy missions. The analysisaccounted for thetradeoffs and interactions among aerodynamic, structural,and pro- pulsiveefficiencies dictated by themission requirements. Vehicle concepts withbuoyant-to-total lift ratios, (f3) domto 0.8 were considered. Fourmissions were identified for these fully buoyant airships: (1) submarine trail, (2) SOSUS (soundsurveillance system)/ocean surveillance, (3) ASW Barrier, and(4) convoy escort.

Inthe submarine trail mission,the airship is self-sufficientand capableof independent operations from land bases for periods requiring multiple crews and crew facilities. The missionobjective is to maintain close contact with submarines subsequent to localization by other means. The primarysensor is anadvanced nonacoustic system currently underinvestigation by the Naval. Air Development Center. A reacquisition capability is necessary,and a limitedself-defense capability is de- sireable.In addition to the overtmode, a covert mode using towed arrays was alsoconsidered.

The SOSUS/Ocean Surveillancemission objective is to detect, classify andmaintain surveillance of submarine targets in ocean areas where the land-based SOSUS performance is pooror temporarily out of operation. The primarysensor is a SURTASS (Surveillance TASS) equivalent thin line toved array. A hybridprocessing system is includedonboard the airship which permitsthe data to be displayed and processed onboard the airship and/or data linked to shore for use in the land-based main evaluationcenters. ASW supportforces from land-based or sea-based operations could be vectoredto support the airship system in conducting localization, classification, andnegation portions of the ASW missions.Secondary operations

-41- such as air and surface surveillance could be performed in some approaches to the SOSUSIOcean SurveillanceMission.'

The ASW barrier mission will require an LTA vehicle which is self- sufficient andcapable of independent operations from land bases for periodsrequiring multiple crews and crew facilities. It will besupple- mentaryto both surface and aircraft resources, thus relieving the burden on theseforces in situations where economics or threat levels make the longendurance LTA attractive. Insimplistic terms, it is intendedto fill the gapbetween relatively slow-speed,long endurance, large payload surfaceships and high-speed, short endurance, small payload aircraft. It will be able to use dipped, towed or retrievable sensors because of its onstationhover capability. The missionobjective is tomaintain a counting or detection only barrier across submarine transit routes. Barrier lengthsof 1300 km (700 n mi)and onstationendurance of 20 to 30 days were general mission objectives.

In the baseline convoy escortmission the mission objective is to providedetection, classification, and early warning of air, surface,and subsurface Lreats. An enduranceof 7 to10 days without replenishment will provideunrefueled trans-Atlantic escort mission capability. In- flightrefueling and replenishment from surface ships is also possible for extendedmissions. The LTA vehiclehas a limitedonboard capability for self-defense,and will rely primarily on other air andsurface units for pro- tectionagainst air/surface threats. Similarly, a limitedonboard capability is availableto localize and attack close-in ASW targets; however, it will rely primarily on other air ASW vehicles for prosecution of its surfaceand subsurface detections. The primaryacoustic sensor is an advanced,thin line, tactical array.Sprint-and-drift tactics thatexploit the LTA vehicle's speed capability permit a high percentage of search time whilemaintaining the convoyspeed of advance.

Generalized Parametric Analysis Results

Vehicleconcepts ranging from approximately 42,500 cubic meters (1.5 millioncubic feet, MCF) toover 1.133 million cubic meters, MCM

-42- (40 MCF) were evaluatedin the parametric study. Figure 19 illustrates conceptsover this study range as compared with the Akron size airship (0.21 MCM, 7.4 MCF) and the most recent Navy non-rigid airship the ZPG-3W -(41,300cu m, 1.5 MCF).

A technologyassessment and design option evaluation was conducted forgeneralized endurance mission applications. This included considera- tion of propulsionsystem cycle, stern propulsion, active controlstech- nology,vectored thrust/low speed dynamics and control, towing performance and control,structures and materials, andaerodynamically augmented flight. Two significantdesign options are the optimum fineness ratio for the four different construction concepts andthe optimum valueof 8.

The optimum length to diameter ratio was found to dependon vehicle structuralconcept. The sandwich monocoque optimized at thelowest value allowedduring the study of3.5, thenon-rigid airship at 4.75, the pressurizedmetalclad airship at 5.2, and therigid airship at 7.0. The optimum fineness ratios resulted from theinteraction between aerodynamic dragand structural weight fraction. Thesevalues are validfor vehicles inthe 0.283 to 0.425 MCM (10 to15 MCF) volume range. NASA Phase I results(Reference 1) indicate a finenessratio dependency on grossweight. Forexpediency, these values were usedduring this study. The comparison ofthe structural weight fractions of the four different construction concepts at the optimum fineness ratio is shown in Figure 20.

Aerodynamicallyaugmented flight(vertical takeoff capable) canin- crease theperformance (time on station) of a constant volume vehicle. The optimum f3 is missiondependent and depends upon the maximum design missionvelocity, the radius of action, the minimum allowableloiter speed, the speed profile associated with the on-station time, and the transit velocity.In general, 8 which will maximizeon stationendurance is in the rangeof 0.85 to 0.9 forthe vehicle configurations and missions investigated during this study.

-43- 7.40 MCF RIGID USS AKRON

-44- Figure 20. StructuralEfficiency Comparison

As a result ofthe combined mission/technologyanalysis, two point designconfigruations were selected for further analysis: The first is a 311,500cubic meter, (11 MCF) rigidairship (Figure 21) using modem designtechniques and subsystems. This design can perform the entire spectrum of specified missions independent from other than home base support. The second is a 42,480 cu m (1.5 MCF), hover-capable,non-rigid airship(Figure 22) capableof performing some less demanding missions(such as coastalsurveillance and defense) indepen.dently and the convoy escort mission if supported by surface vessels.

-45- "" "- - 832.0 FT t- (253.6m)

DESIGN CHARACTERISTICS

HULL VOLUME HULL 11.2 MCF (0.317 hlChl) HELIUM VOLUMEHELIUM 10.53 MCF (0.298 hlCM) DESIGN SPEED 80 KNOTS (41 M/S) PROPULSION : CRUISE - VECTORABLETURBOSHAFT 4 @ 1340 HP/ENGINE LOITER - FIXED PROPELLER DEISELS 2 @ 325 IIP/ENGINE

WEIGHT WT-LBS (KG)

GROSSWEIGHT (5000' DESIGN ALT) 562 I 500 (255150) EMPTYWEIGHT (VEHICLE) 253,400 (114942) MISSION/CRE\VSYSTEMS WEIGHTS 24,900 (11295) AIRPLANE COMPARTMENT 5,860' (2658) CREW QUARTERS (36 MAN) 12,190 (5529) ASW COMPARTMENT & EQUIPMENT 4,180 (1896) REPAIR FACILITIES OPERATINGWEIGHT EMPTY 278,300 (126237) USEFUL LOAD 284,100 (128868) PAYLOAD (SOSUS) 72,500 (3288G) FUEL, OIL AND CONSUMABLES 211,600 (95982)

PERFORMANCE

AIRSPEED FUEL RATE 75 1680 LBS/HR (762 KG/HR) 30 128 LBS/HR (58 KG/HR)

-46- 141.5"--~ " 264.5' -.

182.2"

3.4

4-+ \ L100.0"1 t p-ll2.o""--cl 2.2O I" 93.5""---c1

DESIGNCHARACTERISTICS

HULL VOLUME 1.49 MCF (42197h13) D ESIG N SPEEDDESIGN 90 MOTS (46 M/S) PROPULS ION MAIN PROPULSION 2 AVCO LTClK TURBOPROPS CROSSSHAFTED ON TILT WING STERNPROPULSION 2 ALLISONC250-20B TURBOSHAFTS "V" RUDDER DEFLECTEDSLIPSTREAM WEIGHTS LBS (KG) GROSS WEIGHT ( 6 = 0.86) 96500 (43772) OPERATING WEIGHT EMPTY 51100 (23178) PAYLOAD + CREW 24340 (11040) FUEL & OIL 21060 (9553) PERFORMANCE ENDURANCE @ V 3 30 KTS 88 IIOURS

Figure 22. Hover Capable Non-Rigid Airship

-4 7- Mission Specific Results

Trail Mission

Ninety-five percent of the time on station of the trail missionpro- file is at low altitudeand loiter speed. Five percentof the time on station is spent at the maximum (dash)speed at 1524 m (5000 feet) altitude. The performancerange of interest includes TOS from 10 to 30 days,radii ofaction (ROA) from1853 to 4632 km (1000 to 2500 nauticalmiles) and dashspeeds from 38.6 to 64.35 m/s (75knots to 125 knots). The trail missionpayload is 20,400kg (45,000 lbs) whichincludes a 20 man crew.

Representative performance capabilities of neutrally buoyant rigid airships are shown in Figure 23 in termsof TOS as a functionof ROA, cruisespeed and vehicle volume. Time on station is relativelyinsensitive to radius of action for large volume vehicles (greater than 0.2 MCM, 7.0 MCF) but is highly sensitive to the design dash speedeven though only 5% ofthe mission time is spent in dash.

Figure24 compares the performance of the four different construction conceptsin terms of time on station versus hull volume. Inthe 0.142 MCM to 0.283 MCM (5to 10 MCF) range,the rigid, non-rigid and metalclad concepts are approximatelycompetitive. The figureindicates that the minimum size vehicle for a 30-day on station capability will beachieved by the rigidtype of construction. Conventional rigid airships in this volume range are a near term, low risk extension of the conventional rigid airship state-of-the-art.

SOSUS Augmentation Mission~..

Threeoperational concepts were consideredfor this mission: 1) the airshipdeploys an off-boardarray and monitors via a data link, 2) the airship towsan advanced thin line array at low speed,and 3) theairship deploys a powered sea sled which provides the array tension force.

Array drag is significant(approximately 20 times theairship drag for low speedtow). Figure 25 summarizes TOS vs ROA forthe conceptual

-48- loo0 NAUT RI

2500 MUT nr

10 15 10 20 25 30 35 HULL VOLW (+-lo6 CU FT)

Figure 23. TrailMission Parametric Performance Results (Neutrally Buoyant Rigid)

0 10 20 30 tuu VOLM (v& cu n) 24. TrailMission Parametric Performance Results (ConstructionConcepts)

-49- largerigid vehicle in the towand off-board modes. In the tow mode of operation, TOS capabilitiesof from 15 to 22 days, depending on ROA, can beachieved. In the off-board mode of operations TOS of 20 to 30 days can be achieveddepending on ROA. 11.2 MCF RIGID TOWING THIN-LINESURVEILLANCE ARRAY

I" = 20 I f!E E v) E 15

<52 10 v) I I 6-KNOT TOW SPEED I I e5

0 " 1000 2000 3000 ROA (NAUT MI)

11.2 MCF RIGID MONITORING OFF-BOARD ARRAY Q 35

CI I- 30 zr TIME v) 25 =z? CI 20

0 1000 2000 3000 ROA (NAUT MI>

Figure25. TOS Versus ROA for 11 MCF RigidAirship

-50- The SOSUS augmentationor openocean surveillance mission concept is a promisingairship mission. Vehicles on theorder of 200,000 to 317,000 cu m (7 to 11 MCF) which are near term, low riskairship concepts can provide 2 to 3weeks on-stationcapability in a towmode. The TOS can be increased or vehicle size reduced via the use ofoff-board array operational concepts. The tradesbetween the tow mode, off-boardarray and sled operationalapproaches needs further examination, including an assessment ofsecurity from jamming, array linearity, and array performance in both theoff-board and tow modes. Operationalconcepts which use multiple arrays to enchance localization and classification operations warrant further investigation.

ASW Barrier Mission

Resultsobtained from an abbreviated analysis of a towed array ASW barrier operation indicate that for vehicles in the 0.283 to 0.425 MCM (10 to 15 MCF) sizerange, the "backup" factor (numberof airships required to maintain one station continuously) for a 2500 nautical mile radius of action is below 2 in all cases. If towed arraydetection ranges on theorder of 463 Km (250n mi) can be achieved, the numberof airship stations required to mount a 1300 Km (700 nmi) ASW detection barrier will be less than 2.

Convoy Escort

Any vehiclesized for the trail mission,the SOSUS augmentation mission or the ASW barrier mission will be sufficent to conduct the independent convoy escortoperations. Substantial excess payload or per- formancecapability would be available from the vehicle sizes on the orderof 0.317 MCM (11 MCF) which are required for the trail and SOSUS missions.

An alternate operationalapproach to the convoy escortmission utilizing at sea replenishmentcan substantially reduce the vehicle sizerequred. Vehicles the size of the last Navy non-rigidairship, the ZPG-3W canperform the convoy escort mission utilizing advanced

-5 1- 1

thin line towed arrays in a sprint/drift operational mode. Refueland replenishmentfrom surface vessels on a one to two day cycle is sufficient dependingon mission specifics. An additionaloperational capability could be realized by utilizing the same vehicle, reconfigured for airborne early warning and/or suface surveillance to perfcrm AEW/SS operations as well as overthe horizon command, controland communications andtargeting. Several operational/tacticalapproaches appear promising for either small vehicles or large vehicles in convoy escort missions.

Overall Mission/Vehicle Conclusions

The overall parametric analysis conclusions indicate that vehicle sizesof approximately 0.317 MCM cu m (11 MCF) can satisfy the mission requirementsfor all fourmissions as definedfor this study. Twenty to thirty day times-on-station are achievablewith current technology rizidairships which are near term, low riskvehicles. Airship applications utilizing towed arraysensors represent a uniqueaccommodation ofsensor requirements and platform capabilities.

The metalclad,rigid and non-rigid construction concepts are all competitivein the range from0.141 to0.317 MCM (5 to 11 MCF) for the longendurance missions investigated. In general, the rigid concept results in the minimum volume required to achieve a specified time-on- station. A designspeed of 38.6 m/s (75knots) and an altitude of 1524 m (5000 feet) can satisfy all missionrequirements specified for the four missions.Higher speeds up to 51.9 m/s (100knots) can be achieved with modest penalties in vehicle empty weight and propulsion system require-. ments. The penaltyin on-station performance associated with the higher speed capability results primarily from theduration of the mission time spent at thehigh speed as opposed tothe actual design capability. Improvements in vehicle empty weight due to modem materials andpropulsion technology allow higher payloads or altitudes to be achieved for a given volume.

-52- - ""

The ratioof on-station time tomission time for the airships operatingin the conceptual missions is high; 70% to 90% dependingon theradius of action. Thus, a highpercentage of thetotal yearly utilization will bespent on station. An importantcharacteristic of longendurance LTA vehicles is the low (lessthan 2) backup factor required to maintain a station.

Operational Considerations

Prior airships were operationally inferior to the capabilities of potential modem LTA vehicles. Two areas ofoperational deficiency were dashspeed and low speed control. Current technology provides the capabilityto largely overcome thesedeficiencies. Lightweight gas turbinesallow higher dash and cruise speed capability at lower installed propulsionsystem weight fractions. Modem V/STOL technology,including advancedautomatic flight control systems, provide the capability for fullyhover capable, low speed controllable, VTOL capable LTA vehicles. Precise low speed and hover control results in improved ground handling operationsand expands the mission applicability of modem Naval LTA vehicles.

Ground Handla-__

Duringthe late 1950's,the U. S. Navy developedmechanized ground handlingequipment and mooring techniques for the ZPG-3W airships.Landing andmooring of the ZPG-3W requiredonly 10 to 18 personnel in the ground crew. Dockingand undocking were performedwith 11 to 12 men; takeoff requiredapproximately the same number. The mooringand ground handling equipmenttechniques developed for the 3W airship are applicableto the larger airships considered for future naval missions.

Weather

No vehicle is truly an all-weather vehicle in that it can effectively perform its assigned mission in any weather condition (except possibly a submarine). However, many vehicles can survive severe weatherconditions

-5 3- and resume operations after the weather haspassed; modem airships would . be such vehicles.

In 1954,the Office of Naval Researchassigned to the Naval Air Develop- ment Unit at South Weymouth, Mass., conducted a projectto demonstrate the all-weathercapability of the airship. Technical guidance and instru- menation were furnished by the National Advisory Committee for Aero- nautics. The conclusionsof the official Navy report(Reference 12) on the projectincluded the following:

11AirshIp ground handling evolutions can beaccomplished in virtually all weather conditions."

"Routineground maintenance can be accomplished under extremelyadverse weather conditions.

"Rime ice accretion at normal airship operating altitudes is notconsidered a deterrent to proper station keeping

for protracted periods of time .I1

"Maintaining a continuous barrier station over the Atlantic Ocean appearsto be feasible under all weathercondit5ons."

Wind

Wind is animportant weather element in airship operations. However, whilehigh winds in themselves are no threat to the structural safety of an airship in flight, historically the low airspeed necessitated that high headwinds be avoided by flying the pressure patterns. Higher speed capability ofmodem Naval LTA vehicles will allow them to remainopera- tional at higher windspeeds.

Significant progress in forecasting general and local meteGrologica1 conditionshas been realized since the last rigidairships were flown. The adventof weather satellites, onboardradar, improved navigation, and improvedcommunlcations will result in safety benefits andimproved operational capability.

-5 4- Vulnerability

Any discussion of the use of airships in military operations must addressthe question of the vulnerability of these large vehicles. This has always been a foremostargument against the military use of airships, bothrigid and non-rigid. Although the military rigid airship evolved during World War I as a bombing platform designed to operate against for- midableopposition, it did not prove to be effective in this role and has neversince been considered seriously as a combat vehicle.Current technologyhas not reversed this decision but has contributed to the improvement in expected survivability when the airship is used in military rolessuch as the sea controlmissions.

From a technicalaspect the large rigid airship could probably sustain hits, from a number of air-to-air missiles or surface-to-air missiles withoutserious consequences. In this respect it is much more survivablethan a C-SA, for example,where a single missile hit would normallybe catastrophic. Furthermore, the airship can be equipped with a verycredible self-defense capability. This could consist of early warningand fire control radar, anti-air andanti-missile missiles or other advancedweapon systems, ESM equipmentand a variety of electronic counter- measuressuitable to the threat.

In spite of this capability to sustain damage, to conductinflight repair and to provide for its own self-defense,prudent military operation would not permit the afrship to be used in situations that were beyond its limited combat capabilities.In short, the answer to achieving acceptable levels of survivability lies in employing the airship in missions for which it is particularly suited, and in tactical environmentsfor which it hasbeen designed. A preliminaryexamination (classified) of the self-defense capability of LTA's using an advanced weapon system was performedby the Northrop Researchand Technology Center. The results are encouragingand could expand the potential tactical environmentsfor modem Naval airships.

-55- Conclusions

TheNavy MissionFeasibility Study concluded that: (1) LTA vehicle sizesof approximately 311,500 million cu meters (11 MCF) can satisfy all specifiedmission requirements; (2) 20 to 30 daystime-on-station is achievable;(3) three constructionconcepts -- rigid,non-rigid, and metzlclad -- are generallycompetitive; (4) design speeds of 39 m/s (75knots) and altitudes of1524 m (5000 feet) can satisfy all specified missionrequirements; and (5) higher speeds and altitudes to 4572 m (15,000 feet) are feasiblebut would requirelarger vehicles. Rigid airships in the required volume range are low riskextensions of pre- vious LTA vehicles.Small (non-rigid) airships may alsosatisfy less demanding missionssuch as shipsupported convoy escort.

The primarysensors for all missionstend to be items either towed ordeployed, expended or retrieved by the LTA platform. One sipificant advantageof using an airship as a tow platform is virtual elimination ofpropagation of tow platformnoise into the medium. The airshipalso appearsto be an idealplatform for the carriage, deployment, monitoring, andrecovery of off-board arrays and for RPV launchand recovery operations.

-56- REFERENCES

1. "FeasibilityStudy of Modern Airships,"Phase I, Volumes I, 11, 111, & IV; GoodyearAerospace Corporation; NASA CR-137692, July 1975.

2. "FeasibilityStudy of Modern Airships,"Phase 11, Volume I, Book I; GoodyearAerospace Corporation; NASA CR-151917; September1976.

3. "FeasibilityStudy of Modern Airships,"Phase 11, Volume I, Book 11; GoodyearAerospace Corpration; NASA CR-151918, September1976.

4. "FeasibilityStudy of Modem Airships,"Phase 11, Volume I, Book 111; GoodyearAerospace Corporation; NASA CR-151919, September1976.

5. "FeasibilityStudy of Modem Airships,"Phase 11, Volume 11; Goodyear AerospaceCorporation; NASA CR-151920, September1976.

6. "FeasibilityStudy of Modern Airships,"Phase 11, Volume 111; Goodyear AerospaceCorporation; NASA CR-151989, July1977.

7. Huston, R. F. and Ardema, M. D.: "Feasibilityof Modern Airships - Design Definitionand Performance of SelectedConcepts;" AIAA Paper 77-331, January 19 7 7.

8. Ardema, M. D.: "Feasibility of Modern Airships - Preliminary Assess- ment;"Journal of Aircraft,vol. 14, no. 11, November 1977.

9. Piasecki, F. N.: "Ultra-Heavy Vertical Lift System - The 'Heli-Stat'," Proceedingsof the Interagency Workshop onLighter Than Air Vehicles, FTL Report R75-2, January1975.

10. "Development of Weight EstimatingRelationships for Rigid and Non-Rigid Heavy Lift Airships," GoodyearAerospace Corporation; NASA CR-151976, March 197 7.

11. "Study of Short-HaulAircraft Operating Economics," Final Report; Douglas Aircraft Company; NASA CR-137685, September1975.

12. "Summary of Airship All WeatherCapabilities," USN, Bureauof Aeronautics, Navy Department,Washington, DC, MemorandumAER-AC-721, April6, 1956.

- 57 - ~ 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. NASA CR-2922 .". ~~ 4. Title and Subtitle 5. Report Date November 19 77 "Feasibility Studyof Modern Airships, Phase I1 Executive Summaryll 6. Performing Organization Code

. ~~ 7. Author(s1 -18. Performing Organization Report No.

. .. .-" 10. Work Unit No. 9. Performing Organization Name and Address GoodyearAerospace Corporation 11. Contract or Grant No. 1210 Massillon Road Akron, Ohio 44315Akron,Ohio of 13. Type Report and Period Covered 2. Sponsoring Agency Name and Address National Aeronautics E Space Administration 14. Sponsoring Agency Code Washington, D.C. 20546 5. Supplementary Notes

". .. ." .. " 6. Abstract A feasibility studyof modern airships has been completed. In the second half of this study, summarized herein, three promising modern airship system concepts and their associated missions were studied: (1) a heavy-lift airship, employing a non-rigid hull and a significant amount of rotor lift, used for short-range transport and positioning of heavy military and civil payloads; (2) a VTOL (vertical take-off and landing), metalclad, partially buoyant airship used as a short-haul commercial transport; and (3) a class of fully-buoyant airships used for long-endurance Navy missions. The heavy-lift airship concept offers a substantial increase in vertical lift capability over existing systems and is projected to have lower total operating costs per ton-mile. The VTOL airship transport concept appears beto economically competititve with other VTOL aircraft concepts but can attain significantly lower noise levels. The fully-buoyant airship concept can provide an airborne platform with long endurance that satisfies many Navy mission requirement s.

"- "- ~.-. 7. Key(Suggested Words AuthorM) by 18. Distribution Statement Airships Lighter Than Air Technology UNCLASSIFIED-UNLIMITED

.- . . 3. Security Classif. (ofthis report) 20. Security Classif. (of this pagel UNCLASSIFIED $3.75

*For sale by the National Technical Information Service, Springfield, Virginia 221 61 NASA- Langley, 1977