I‘ ’, 1 NASA -! TP 1921 ’ .I

I 1:. NASA Technical Paper 1921 c. 1

Vehicle Concepts and Technology Requirements for Buoyant Heavy- Systems

Mark D. Ardema

SEPTEMBER 1981 TECH LIBRARY KAFB, NM

NASA Technical Paper 1921

Vehicle Concepts and Technology Requirements for Buoyant Heavy-Lift Systems

Mark D. Ardema Ames Research Center Moffett Field, California

National and Space Administration Scientific and Technical Information Branch

1981 VEHICLECONCEPTS AND TECHNOLOGYREQUIREMENTS FOR BUOYANT HEAVY-LIFTSYSTEMS

Mark D. Ardema

Ames Research Center

Several buoyant-vehicle () concepts proposed for short hauls of heavy payloads are described. Numer- ous studies have identified operating cost and payload capacity advantages relative to existing or proposed heavy-lift for such . Applications mvolving payloads of from 15 tons up to 800 tons have been identified. The buoyant quad-rotor concept is discussed in detail, including the history of its development, current estimates of performance and economics, currently perceived technology requirements, and recent research and technology development. It is concluded that the buoyant quad-rotor, and possibly other buoyant vehicle concepts, has the potential of satisfying the market for very heavy vertical lift but that additional research and technology development are necessary. Because of uncertainties in analytical prediction methods and small-scale experimental measurements, there is a strong need for large or full-scale experiments in ground test facilities and, ultimately, with a research vehicle.

INTRODUCTION world vehicles is about 18 tons. Listed in the figure are several payload candidates for airborne vertical lift that are beyond this 18-ton payload weight limit, Feasibility studies of modern (refs. 1-18) indicating a marketfor increased lift capability. and other studies (refs. 19-27) have determined that Extension of lift toa 35-ton payload is modern air-buoyant vehicles (airships) could satisfy possible with existing technology (refs. 28, 29), and the need for air transport of heavy or outsized pay- future development of conventional rotorcraft up to loads over short distances. a 75-ton payload appears feasible (ref. 29). With HLA There are two reasons that such , called concepts, however,payioad capability of up to heavy-lift airships (HLAs), appear attractive for both civil and military heavy-lift applications. First, buoy- ant lift does not lead to inherent limitations on pay- loadcapacity as does dynamiclift. Large conven- INDUSTRIAL EQUIPMENT tional dynamic-lift vehicles, including rotorcraft, tend AND CONSTRUCTION to follow a “square-cubelaw” in that lift increases MAIN BATTLE TANK CRANE, SHOVEL - 40 ton with the square of the vehicle’s principal dimension, while empty weight increases with the cube, notwith- standing the effect of fixed-weight items. This means thatthe vehicle’s structural weight increases faster CONTAINER (8 x 8.5 x 35 ft) than the gross weight as size is increased; thus, as the OGGING (MINIMUM size is increased, the percentage of the total weight available for useful load decreases. On the other hand, buoyant-lift aircraft tend to follow a “cube-cube law” and thus have approximately1990 the same1980 efficiency 1970 at 1960 1950 all sizes. CALENDAR YEAR Figure 1 shows the history of rotorcraft vertical- lift capability. Current maximumpayload of free Figure 1 .- Potential heavy-lift payloads. 200 tons is possible using existing propulsion-system TABLE 1 .- PRINCIPAL HEAVY-LIFT technology or even, if desired,existing rotorcraft AIRSHIP MARKETS propulsion-system hardware. [From refs. 30,311 The second reason airships appear attractivefor Useful Number of heavy lift is cost. Most HLA concepts are projected Market area load, vehicles to offer lower development, manufacturing, mainte- tons required nance, and fuel costs than large rotorcraft with the same payloads; thustotal operating and life-cycle Heavy lift costsmay be lower. The lower developmentcost Logging 25-75 >I 000 arises from extensive use of existingpropulsion- Unloading cargo in systemtechnology or hardware orboth, making congested ports 16-80 200 major new propulsion-systemdevelopment unneces- High-voltage transmis- sary. Low manufacturingand maintenance costs sion tower erection 13-25 10 accrue because buoyant-liftcomponents are less Support of remote expensive to produce and maintain than dynamic-lift drill-rig installations 25-1 50 15 components. Lower fuelcosts follow directly from lower fuel consumption. As fuel prices increase, the Ultraheavy lift high fuel efficiency of HLAs will become increasingly Support of power- important. HLA costs and fuel efficiency will be dis- generating plant cussed in more detail later. construction 80-900 30 Because the market for vertical lift of payloads in Support of oil-gas off- excess of 20 tons is a new one for aerial vehicles, the shore platform size and characteristics of the market are somewhat construction 5 00 3 uncertain. As aresult, several studies have been Other transportation 25-800 10 undertaken. Many of these studies have been pri- vately funded and theirresults we proprietary, but the results of some have been published (refs. 26,27, 30-33). HLA market-study conclusions have been The availability of vertical aerial lift in this payload generally favorable. Table 1 summarizes the results range will make the expensive infrastructure asso- of one of these,the recentlycompleted NASA- ciated with surfacemovements of heavy or bulky sponsored study of civil markets for HLAs (refs. 30, items largely unnecessary. It would also allow more 3 1). freedom in the selection of plant sites by eliminating the restrictions imposed by the necessity for readily The HLA civil market tends to fall into two cate- accessible heavy suface transportation.Further, it gories. The first consists of services that are now or couldsubstantially reduce construction costs of could be performed by helicopters, but perhaps only complex assemblies by allowing more extensive pre- on a very limited basis. Payloads are low to moderate, assembly at manufacturing areas. This application is ranging from about 15 to 80 tons. Specific markets relatively insenstitive to cost of service. include logging, containership offloading (of interest also to the military), transmission-tower erection, and In the remainder of this paper, HLA concepts will support of remote drill rigs. HLAs would be able to be reviewed. The buoyant quad-rotor (BQR), or heli- capture greater shares of these markets than helicop- stat, will be emphasized because it has been the prin- ters because of their projected lower operating costs. cipal subject of technologydevelopment efforts to Most of these applications are relatively sensitive to date. As a result, there is more technical information cost.The largest market in terms of thepotential available about the BQR than other HLA concepts. number of vehicles required is logging. The next section briefly describes free-flying HLA The second HLA market category involves heavy concepts other than the BQR. The following section payloads of 180 to 800 tons - a totally new applica- discusses the BQR in terms of (1) development his- tion of vertical aerial lift. This market is concerned tory, (2) description of the concept, (3) technology primarilywith support of heavy construction proj- needsas currently perceived, and (4) thecurrent ects, especially power-generating plant construction. NASA research and development program.

2 HEAVY-LIFT AIRSHIPCONCEPTS OTHER by Nichols (ref. 20), and by Nichols and Doolittle THANBUOYANT QUAD-ROTOR (ref. 24). References 20 and24, inparticular, describe a wide variety of possible hybrid HLA concepts. The classical fully buoyant airship is unsuitable for Perhaps the simplest and least expensive of the most heavy-lift applications because of poor low- HLA concepts are those which combine the buoyant speed controland ground-handlingcharacteristics. and dynamic-lift elements in discrete fashion without Therefore, almost all HLA concepts that have been majormodification. Examples, takenfrom refer- proposed are “hybrid” aircraft, that is, vehicles that ences 7 and 24, are shown in figure 2. Although such obtain part of their total lift from the displacement systems will obviously require minimal development of air by a lighter gas (buoyant lift) and the remain- of new hardware, there may be serious operational der by dynamic or propulsive forces. Because buoy- problems associated with them. Safety and controlla- ant lift can be scaled up to large sizes at low cost per bilityconsiderations would likely restrict operation pound of lift (as previously described), it is advan- to fair weather.Further, cruise speeds would be tageous from a cost standpoint in hybrid aircraft to extremely low. The concept from reference 24 that is provide as much of the total lift as possible by buoy- shown in figure 2 was rejectedby theauthors of ancy. The fraction of total lift derived by dynamic or reference 24 because of the catastrophic failure which propulsive forces is determined primarily bythe would result from an inadvertentballoon deflation. amount of control powerrequired. Thedynamic An earlyhybrid HLA concept, which has subse- forces therefore provide propulsion andcontrol as quently received a significant amount of study and well as a portion of the total lift. some initial development, is a rotor-and- con- The characteristics of hybrid aircraftand their figuration (called Aerocrane byits inventors,the potential for the heavy-lift mission were clearly recog- All American Engineering Company). Early discus- nized (by the mid-1970s) by Piasecki (refs. 12, 21), sions of thisconcept appear in references 19,20,

Figure 2.- Combined discrete concepts (refs. 7, 24).

3 23-25,34; two versions ofthe Aerocrane are ing a suitable control system. A remotely controlled depicted in figure 3. The original configuration con- flying model was built to investigate stability, con- sisted of a spherical -inflated balloon with four trol, and flying qualities (fig. 4). Results (refs. 35-37) rotors (airfoils) mounted at the equator. Propulsors have shown that the rotor-balloon is controllable and and aerodynamic controlsurfaces are mounted on the that it promises to be a vehicle with a relatively low rotors.The entire structure (except the crew cabin empty-to-gross weight ratio and low acquisition cost and payload support, which are kept stationary by a across a wide range of vehicle sizes. Technical issues retrograde drive system) rotates (typically at a rate of that emerged were (1) the magnitudeand effect of 10 rpm) to provide dynamic rotor lift and control. the Magnus force on a large rotating sphere and Principal applications envisioned for the rotor-balloon (2) the high acceleration environment (about 6 g in are logging and containership offloading. most designs) of the propulsors. Study and technology development of the rotor- Although the rotor-balloontechnical issues are balloon concept have been pursued by All American thought to be solvable, two characteristics emerged as Engineering and others, partly under US. Navy spon- being operationallylimiting. First, large vehicle tilt sorship. Emphasis of the program has been on devis- angles would be required to obtain the necessary con-

ORIGINAL Figure 4.- Aerocrane remotely controlled flying model. n trol forces in some operating conditions. Second, the high drag associated with the spherical shape results in very low cruise speeds,typically 25 mphfor a 16-ton payload vehicle. This low speed means that operation in winds of over 20 mph probably is not possible and that the efficiency of operation in even light winds is significantlydegraded. Even with no wind, the low speed will result in low productivity. Thus, the original rotor-balloon concept was limited to very short-rangeapplications in very light winds. The advanced configuration rotor-balloon depicted in figure 3 (ref. 38) is designed to overcome the operational shortcomings of the original concept. Winglets with aerodynamic control systems are fitted

ADVANCED to allow generation of large lateral-controlforces, thereby alleviating the need to tilt the vehicle. A len- ticularshape is used for the envelope to Figure 3.- Aerocrane concept. decrease the aerodynamic drag. The increase in cruise

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. .. speed of the advanced concept is, however, accom- speed and yaw angles of the on their strutsare panied by some increase in design complexityand controlled to keep the airspeed over the wings at a structural weight. constant value, namely, a value equal to the vehicle Amore substantial departurefrom the original cruise speed. Thus, for hover in still air, the wingspan Aerocrane concept has been proposed recently. The axes are aligned with the envelope longitudinal axis. Cyclo-Crane of Aerocranes of Canada (refs. 39, 40) As forward speed is increased, the vehicle rotational is essentially a new HLA configuration concept speed decreases and the wings are yawed until,at (fig. 5). It consists of an ellipsoidal lifting gas enve- cruise speed, the rotationis stopped and thewingspan lope with four strut-mounted airfoils at the midsec- axesare perpendicular tothe forwardvelocity. tion. The propulsors are also located on these struts. Hence, in cruising flight the Cyclo-Crane acts as a This entirestructure rotates about the longitudinal winged airship. axis of the envelope to provide control forces during Preliminary analysis of the Cyclo-Crane has indi- hover. Isolated from the rotating structure by bear- cated that a cruising speed of 50 mph would be pos- ings are the control cabin at the nose and the aerody- sible witha 10-ton payload vehicle and thatthe namic surfaces at the tail. The payload is supported economic performance would be favorable. However, by a sling attached to the nose and tail. The rotation there are obvious questions of structural weight and

I i

HOVER CRUISE

Figure 5 .- Cyclo-Crane concept (refs. 39,40).

5 aerodynamic interference between the various vehicle while in the air. The technique forjoining the vehicles components,and moredetailed investigation is and the controllability of the combined system need required to resolve them. further study. Another approach to heavy lift withbuoyant forces is the clustering of several small buoyant ele- Finally,another HLA conceptthat has received ments. Examples of this are the ONERA concept and some attention is the “ducted-fan hybrid” shown in the Grumman concept (ref. 41) shown in figure 6. In figure 7 (ref.24). In this vehicle, a toroidal-shaped the Grumman idea, three airships of approximately lifting gas envelope provides a duct or shroud for a conventional design such as the one shown are used centrally located fan or rotor. Therehas been too to lift moderate payloads. When heavy lift is needed, little study of the ductedfan hybrid, however, to per- the three vehicles are lashed together temporarily mit an assessment of its potential.

GRUMMAN ONERA

Figure 6.- Multielement concepts (refs. 7,41).

Figure 7.- Ducted-fan concept (ref. 24).

6 BUOYANT QUAD-ROTORCONCEPT Oehmichen’s later effort was a quad-rotor design with tworotors mounted in the vertical plane and two in the horizontal (bottom photograph in fig. 8). History and Description The hull was changed to an aerodynamic shape more characteristic of classical airships. Existing motion The idea of combining engine/rotor sys- pictures of successful of the Helicostat demon- tems with airship hulls is not new. In the 1920s and stratethat the buoyant quad-rotor (BQR) concept , aFrench engineer, E. Oehmichen, not only was proven feasible in the 1930s. conceived this idea but successfully built and flight- Themodern form of theconcept was first pro- tested such aircraft, which he called the Helicostat posed by Piasecki (refs. 12, 21). Piasecki’s idea is to (ref. 26). One of his first designs (top photograph in combineexisting, somewhat modified helicopters fig. 8) hadtwo rotors driven by a single engine with a buoyant hull, as exemplified in figure 9. The mounted beneath a cylindrical buoyant hull. Accord- configurationshown in figure 9 will be called the ing to reference 26, Oehmichen’s purpose in adding “original” BQR concept in this report. The attraction the buoyant hull to the rotor system was threefold - of the idea lies in its minimal development cost. In “to provide the helicopter with perfect stability, to particular,no new major propulsion-system compo- reduce the load on the lift-rotors, and to slow down nents would be needed (propulsion systems are his- descent with optimum efficiency.” torically the most expensive part of an all-new air- craft development). A fly-by-wire master control sys- tem wouldcommand the conventional controls within each helicopter to provide for lift augmenta- tion, propulsive thrust, and control power. Other variants of the BQR idea are currently under study. A design by Goodyear (ref. 42) is shown in figure 10. As compared with original con- cept (fig. 9), this design (called the “advanced” con- cept)hasa new propulsionsystem, auxiliary horizontal-thrusting propellers, and aerodynamic tail surfacesand controls. Thefour propulsionsystem modules would make extensive use of existing rotor- craft componentsand technology but be designed

Figure 9.- Buoyant quad-rotor, original concept (Helistat).

Figure 8.- Oehmichen’s Helicostat flight vehicles. Figure 10.- Buoyant quad-rotor,advanced concept.

7 specifically forthe BQR. Thehorizontal-thrusting TABLE 2.- WEIGHT STATEMENT propellers would be shaft-driven from the main rotor AND PERFORMANCE OF 75-TON engines. These propulsion modules would be designed BUOYANT QUAD-ROTOR, more for high reliability and low maintenance costs ORIGINAL CONCEPT and less for low empty weight than are typical heli- [From refs. 12,161 copter propulsion systems. They would be “de-rated” relative to current systems, leading to further reduc- Gross weight: lb 324,950 tions in maintenance costs. Rotor lift,lb 180,800 In a revival of the Helicostat concept, a buoyant Buoyant lift, lb 144,150 dual-rotor HLA is currentlyunder studyby Aero- Empty weight,lb 148,070 spatiale (ref. 26). It would use the engines and rotors Useful load: lb 176,800 from a small helicopter,but propellers would be Payload, lb 150,000 fitted forforward propulsion and yaw control Static heaviness: lb 3,920 (fig. 11). Payload would be about 4 tons; the princi- Envelope volume, ft3 2.5X106 pal application is envisioned to belogging. Ballonet volume, ft 5.75X lo5 Ballonet ceiling, ft 8,500 Hull fineness ratio 3.2 Design speed (TAS), knots 60 Design range With maximum pay- ”“ load, n.mi. 100 No payload, n . mi. 196 Ferry, n. mi. 1,150

%ea level, standardday, 93% infla- tion, one engine out, reserves for 100 ft/min climb.

“heavy” when completelyunloaded. Ineffect, the buoyant lift supports the vehicle empty weight, leav- ing the rotor lift to support the useful load (payload Figure 11.- Modern Helicostat (ref. 26). andfuel). A different approach hasbeen suggested and studied by Bell et al. (ref. 43). Bell et al. pro- posed that @ be selected so that the sup- Performance and Economics ports the empty weight plus half the useful load. It is then necessary forthe rotors to thrust downward The performancecapability of the BQR design when the vehicle is empty with the same magnitude (fig. 9) examinedin the feasibility studies of refer- that they must thrust upward when fully loaded. This ences 12-14 and 16 is listed in table 2. This design same principle has been used in thestudies of the employsfour CH-54B helicopters,somewhat modi- rotor-balloon. Use of the approach suggested by Bell fied, and a nonrigid envelope of 2.5X lo6 ft3. Total et al. (high @),as opposed to the approach assumed in gross weight with one engine inoperative is about table 2 (low p), has the potential of offering lower 325,000 lb, of which 150,000 lb is payload. Empty- operatingcosts (since buoyant lift isless expensive to-gross weight fraction is 0.455 and design cruise than rotor lift) and better control when lightly loaded speed is 60 knots. Station-keeping is estimated to be (because higher rotor forces are available). In compar- possible in crosswinds up to 30 knots. Range with ison, the low @ approach may result in a vehicle that maximum payload is estimated to be 100 n. mi.; with is easier to handle on the ground (since it is heavy the payload replaced by auxiliary fuel, the unrefueled when empty) and one that is more efficient in cruise ferry range would be over 1,000 n. mi. Performance or ferry when lightly loaded or with no payload of the advanced concept (fig. 10) should be much (because of low rotor forces). Selection of the best better than that of the design shown in figure 9. value of 0 depends on these and many other factors In references 12, 16, and 21, the ratio of buoyant- and will require a better technical knowledge of the to-total lift (0) is chosen so that the vehicle is slightly concept.

8 The BQR vehicle will be efficient in both cruise tenance costs. The advanced concept would be partic- and hover compared with conventional-design heavy- ularly efficientwhen cruising lightly loaded (as in lift helicopters (HLH). This arises primarily from the ferry), since it would operate essentially as a classical cost advantages of buoyant lift when compared with fully buoyant airship. rotorlift on aper-unit-of-lift basis, as discussed Studies have shown that precision hover and earlier. Fuelconsumption of the BQR vehicle in station-keeping abilities approaching those of pro- hover will be approximately half that of an equivalent posed HLHs are possible with BQR designs (refs. 12, HLH. Relative fuel consumption of the BQR in cruise 21, 44-46). Automated precision hoversystems may be even less because of the possibility of generat- recently developed for an HLH (ref. 28) can be ing dynamic lift on the hull, therebyreducing or elim- adapted for BQR use. inating the need forrotor lift in cruising flight. Ultimateselection of the original (fig. 9), the When cruising with a slung payload, the cruising advanced (fig. lo), or some other variant of the BQR speeds of HLHs and BQR vehicles will be approxi- concept will dependon the relative importance of mately the same since external load is generally the development cost, performance, and efficiency. This limiting factoron maximumspeed. When cruising choice will obviously depend on the uses to which the without a payload, as in a ferry mission, the speed of vehicle is to be put as well as on the total number of the BQRwill belower thanthat of an HLH. The vehicles to be built. many HLA studies have shown,however, thatthe higher efficiency of the BQR more than offsets this Technology Needs speed disadvantage. Therefore, the BQR should have appreciably lower operatingcosts per ton-mile in The many recent studies of the BQR concept have either the loaded or unloaded condition. all concluded that the concept is basically technically Total operating costs per ton of payload per mile feasible, as was in fact verified by Oehmichen’s lim- in cruise flight are compared in figure 12 (based on ited flight tests more than 40 years ago. However, to data provided by Goodyear). The figure shows that realize the best economic performance and most suit- the advanced BQR concept offers a decrease in oper- able operational characteristics from the concept, as ating costs by as much as a factor of 3 compared with well as to minimize development risk and cost, a sig- existinghelicopters. Of course,much of this cost nificant amount of research and technology develop- advantage results from the larger payload of the BQR ment will be required. There are technology needs in (approximately eight times larger). The low operating the areas of aerodynamics, propulsion,controls, costs in cruise flight of the advanced concept com- structures and materials, and operations. pared with those of the original arise from the use of In aerodynamics, the most important requirement propellersinstead of rotor cyclic pitch for forward is to develop an accurateanalytical characterization propulsion and from lower assumed propulsion main- of the flow field around the vehicle. This character- ization must accountfor aerodynamicinterference

NOTE: SEA LEVEL AND 50°F between all elements of the vehicle and must be veri- .--(Y fied by experimental data.Many of the other technol- E 2.0 r ogy needs dependon an accurate aerodynamic S-64 HELICOPTER description of the vehicle. Specific aerodynamic items of interest are (1) effect of the hull on the aerody- namicenvironment of therotors, particularly for rotors in the hull wake; (2) effect of the rotor wake on the hull flow field; (3) interactions between the BUOYANT QUAD-ROTOR vehicle and the ground, such as rotor fountain effects WITH 5-64 and suckdown on the hull caused by crossflow; and HELICOPTERS (4) accurateestimation of cruise and hover perfor- a BUOYANT mance in all flight conditions, includingoblique w .4 QUAD-ROTOR WITH ROTOR crosswinds and atmospheric turbulence. MODULES a 1- Propulsion needs include better definition of the 1000 1500 2000 design of BQR propulsion modules based on existing UTILIZATION, hr/year helicoptersystems technology. The effect of rotor/ Figure 12.- Relative heavy-lift operating costs. hull aerodynamic interference on rotor loads must be

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I determined.Rotor/rotor and rotorlground inter- ant quad-rotor aircraft also are being considered for actions, such as groundresonance, must also be the heavy-lift mission. Such aircraft have many tech- investigated. nical similarities tothe BQR (e.g., both will need In flight controls, the most important task is to development of fly-by-wire control systems for multi- define suitable and optimal control-systems concepts. ple rotors).Modern conventional airships are being This will be a formidable task because of the many proposed for coastal patrol and relatedapplications flight-control inputs that are available. A BQR design (refs. 50-53);these aircraft will be required to may employ many or all of the following controls: station-keep andhover andtherefore will require rotor collective pitch (used in unison or differen- development of control systems for hover-capable tially); rotor cyclic pitch; tilting or gimballed rotors buoyant vehicles. in one or two axes (free or forced); aerodynamic sur- faces; buoyancy distribution (e.g., ballonets); auxili- Research and Technology Development arythrustors; deflectedslipstream; and cold jets. Activity at Ames Research Center Also of importance is characterization of handling qualities, which are likely to be quite different from Over the last seven years, many organizations and those of helicopters and other VTOL aircraft. A new individuals, both foreign anddomestic, private and subset of handling-qualitiescriteria will probably public, have studied HLA concepts in general and the need to bedeveloped. Automatic precision hover BQR concept in particular. Foreign countriesthat systems need to be developed or adapted, possibly have conducted or funded published studies include including active control systems for payload support. Canada (the Province of Alberta (ref. 27); the Preliminary work in BQR flightdynamics and con- National Research Council, Canadair (ref. 25); the trols is reported in references 12,21,and 4446. Forest Engineering Research Instituteof Canada New technology in structures and materials could (ref. 32); Aerocranes of Canada (ref. 39); and others); be quite crucial to successful HLA production Japan (Japanese Buoyant Flight Association (refs. 54, vehicles. Perhaps the most importantitem in this 55), and others); France (Aerospatiale (ref. 26), and category is analysis of the propulsion-system/flexible- others); and the U.S.S.R. In the United States, gov- structure/aerodynamic interactions, which may lead ernment agencies with HLA interestand programs to critical design conditions for many vehicle compo- include NASA, the Navy, andthe Forest Service. nents. Design and manufacture of nonrigid envelopes Many private U.S. companies have pursuedHLA and interconnecting structure in the sizes being con- work, some under government sponsorship and some templated is state of the art, provided state-of-the-art with private funds. In this report, only the BQR materials are used. Modern filimentarycomposite research and technology program at Ames Research materials have thepotential for reducing empty Center are reviewed. A comprehensive review of all weight and permeability andtherefore increasing HLA work under way wouldrequire a much more vehicle performance. Theywould, however,need lengthy report. further development for thisapplication. If large- Figure 13 is an overview of Ames Research Cen- sized BQR vehicles are contemplated, rigid-structure ter’s LTA activity from the MontereyWorkshop in envelopes will have to be considered.Preliminary 1974 through the endof 1979. Using the LTA vehicle work in BQR structures and materials is reported in concepts and potential missions collected atthe references 47-49. workshop as a data base, the feasibility studyof As for any lighter-than-air (LTA) vehicle, opera- modern airships provided a preliminary evaluation of tionalfactors will be important. Mooring systems the LTA field.There were two principal feasibility need to be defined and analyzed. The mooring con- study contractors, Boeing Vertol and GoodyearAero- cept will influence operating suitability and econom- space, and funding was provided both by NASA and ics and may affect vehicle design. Flight procedures the Navy. The most important conclusion of the need definition, taking into account the fact that the studies was the identification of thepotential of vehicle will typically be operatingin turbulent air LTA vehicles for heavy vertical lift. near ground level. Finally, procedures and operating Subsequentto the feasibility studies, NASA has systems must be developed to handle all foreseeable focused on technology development of HLA, specifi- inclement weather. cally on the BQR concept. Thus far, the work has BQR technologyneeds have commonalitywith been confined to the areas of aerodynamics and con- needs of other vehicles of current interest. Nonbuoy- trols, in the belief that these are themost critical

10 P

1974 1975 1974 1977 1976 1978 1979 I I I I v

/ SYSTEMS STUDIES &

1 DYNAMICS TECHNOLOGY

HEAVY LIFT/ OF CONCEPTSCONCEPTSOF SHORT HAUL

Figure 13.- History of lighter-than-air programat Ames Research Center.

technical areas. The programconsists of theoretical A small-scale, wind-tunnel test program is cur- analyses,wind-tunnel experiments, moving-base rently in the planning stage (refs. 58, 59). Tests will piloted simulation experiments, and studies. bedone in the 12-Foot Pressure Wind Tunnel at Ames Research Center.The purposes ofthe wind- A theoretical study of BQR aerodynamic interfer- tunnel tests are (1) validation of theoretical analyses, ence has been completed by Nielsen Engineering and (2) establishment of the influence of Reynolds num- Research (NEAR) (refs. 56, 57). In that study, a pre- ber, (3) determination of aerodynamicloads, liminary computer program tocompute BQRflow (4) determination of pressure distributions, (5) flow fields was developed. Figure 14 shows the velocities visualization, (6) determination of the effect of con- induced on the surface of the hull and the circumfer- figurationalchanges on aerodynamiccharacteristics, ential pressure distributions as predicted bythe and (7) provision of experimental data for a flight- NEAR program for a specific case. dynamics analysis andsimulation effort. Figure 15

SCALEU/Vj = 0.1 /fi INDUCED VELOCITY ON HLA HULL IN HOVER

ROTOR HULL

4 ” v I \\ Q\ I 42.9 I >I x, ft 3 0 48 i I, i CP A -16 FULL-SCALE HEAVY LIFT -100 AIRSHIP CONFIGURATION CIRCUMFERENTIAL PRESSURE (DIMENSIONS IN ft) DISTRIBUTION ON HLA HULL

0 27090 180 360 e Figure 14.- Interference analysis results (refs. 56,57).

11 Further, flight vehicles will be needed eventually to verify theoperational feasibility of theconcept. Many of the remaininguncertainties are connected withoperational aspects, such as groundhandling, adverse weather effects, and manpower and ground facility requirements; these can be adequately inves- tigatedonly by flight test of sufficiently large vehicles. Finally, an FRV will be a valuable aid in establishing the certificationand airworthiness cri- teria for this new and unique class of vehicles. As currently envisioned, thebuoyant quad-rotor research aircraft (BQRRA) would use the propulsion system componentsof an existing small helicopter type. The vehicle would be capable of incorporating a large variety of flight-control schemes and have a cer- tainamount of variable-geometry capability (e.g., changeable location of rotors relative to the hull). Figure 15.- 7- by 10-FootWind Tunnel buoyant Two envelope sizes wouldbe desirable for use in quad-rotor model (ref. 14). investigating twodifferent regimes of buoyant-to- total-lift ratio. The smaller envelope would be sized shows the model used in an earlier test of the BQR. to allow testing of the BQRRA in the future 80- by Thismodel was built by NEAR(funded by Good- 120-foot section of the Ames Large-Scale Wind year) and tested in the 7- by 10-Foot Wind Tunnel at Tunnel. Thiswould allow safe andsystematic Ames. Results of thisearly test were somewhat exploration of the flight envelope and collection of inconclusive because of insufficiently high Reynolds data before manned flight. numbers (ref. 14). A major effort that is under way is flight-dynamics simulation and analysis of the BQR concept. The pri- mary goal of this contracted effort is to develop an CONCLUDINGREMARKS accurate, nonlinear, off-line simulation of the generic BQR, including all aerodynamic interference effects. The contractor, Systems Technology, Inc., will also Thehistory and currentstate of knowledge of develop linearized and real-timesimulations for use several buoyant heavy-lift vehicle concepts have been inpiloted moving-base simulators.Development of reviewed. Many of these concepts appear to have suitable turbulence models and correlationwith promise, andthe technical feasibility of afew has experimental data are important parts of this effort. been largely established. Thebuoyant quad-rotor In future work, theflight-dynamics simulation will vehicle, in particular, hasbeen studied by many be used incontrol-system research for the BQR. organizations, and results to date have been generally Included will be defintiion of suitable control-system positive. Research and technical development of this logic and investigations of handling qualities. Moving- concept is under way at Ames Research Center and base simulators will be used extensively in this work. at several other government and private organizations. Studies will continue to be made primarily in sup- portof the research and technologyprojects. Cur- Ames Research Center rently under way are design studies of BQR research National Aeronautics and Space Administration aircraft and studies of ground handling systems and Moffett Field, California 94035, April 10,1981 procedures. Because the BQR is a new aircraft concept, large- scale testing, and, ultimately, a flight research vehicle REFERENCES (FRV) are essential parts of any comprehensive research and technology program. An FRV is neces- 1. Bloetscher, F.: Feasibility Study of Modern Air- sary to validate the results of analytical and small- , Phase I, Final Report. Vol. 1. Summary and large-scale model experimental research, particu- and Mission Analysis. NASA CR-137692, larly in the areas of aerodynamics and flight controls. Aug. 1975.

12 2. Davis, S. J.; and Rosenstein, H.: Computer Aided Book 111. AerodynamicCharacteristics of Airship Design. AIAA Paper 75-945,1975. Heavy Lift Airships as Measured at Low Speeds. NASA CR-151919, Sept. 1976. 3. Faurote, G. L.: Feasibility Study of Modern Air- ships, Phase I, Final Report. Vol. 111. Histori- 15. Anon.: Feasibility Study of Modern Airships, cal Overview. NASA CR-137692(3), 1975. Phase 11. Vol. 11. Airport Feeder Vehicle. NASA CR-151920, Sept. 1976. 4. Faurote, G. L.: Potential Missions for Modern Airship Vehicles. AIAA Paper 75-947, 1975. 16. Anon.:Feasibility Study of Modern Airships, Phase 11. Executive Summary. NASA 5. Grant, D. T.; and Joner, B. A.: Potential Missions CR-2922,1977. for Advanced Airships. AIAA Paper 75-946, 1975. 17. Huston, R. R.; and Ardema, M. D.: Feasibility of Modern Airships - Design Definitionand 6. Huston, R. R.; and Faurote, G. L.: LTA Vehic- Performance of SelectedConcepts. AIAA les - Historical Operations, Civil and Military. Paper 77-331, Jan. 1977. AIAA Paper 75-939,1975. 18. Ardema, M. D.: Feasibility of Modern Airships - 7.Jones, B.; Grant, D.; Rosenstein, H.; and Preliminary Assessment. J. Aircraft, v01. 14, Schneider, J.: Feasibility Study of Modern no. 11,Nov. 1977, pp. 1140-1148. Airships, Final Report, Phase I. Vol. I. NASA CR-137691,May 1975. 19.Carson, B. H.: An EconomicCompalison of Three Heavy LiftAirborne Systems. In: 8. Joner, B. A.; and Schneider, J. J.: Evaluation of Proceedings of the Interagency Workshop on Advanced Airship Concepts. AIAA Paper Lighter Than Air Vehicles, Jan.1975, 75-930,1975. pp. 75-85.

9. Lancaster, J. W.: Feasibility Study of Modern 20. Nichols, J. B.: The Basic Characteristics of Airships, Phase I, Final Report. Vol. 11. Hybrid Aircraft. In: Proceedings of the Inter- Parametric Analysis. NASA CR-137692, Aug. agency Workshop on Lighter Than Air 1975. Vehicles, Jan. 1975,pp.415-430.

10. Lancaster, J. W.: Feasibility Study of Modern 21. Piasecki, F. N.: Ultra-Heavy Vertical Lift Sys- Airships, Phase I, Final Report. Vol. IV. tem: The Heli-Stat - Helicopter-Airship Com- Appendices. NASA CR-137692, Aug. 1975. bination for Materials Handling. In: Proceed- ings of the Interagency Workshop on Lighter 11. Lancaster, J. W.: LTA Vehicle Concepts to Six Than Air Vehicles, Jan. 1975, pp. 465-476. Million Pounds Gross Lift. AIAA Paper 75-931,1975. 22. Keating, S. J., Jr.: TheTransport of Nuclear Power Plant Components. In: Proceedings of 12. Anon.:Feasibility Study of ModernAirships, the Interagency Workshop on Lighter Than Phase 11. Vol. I. Heavy Lift Airship Vehicle. Air Vehicles, Jan. 1975, pp. 539-549. Book I. Overall Study Results. NASA CR-151917, Sept. 1976. 23. Perkins, R. G., Jr.; and Doolittle, D.B.: Aero- crane - AHybrid LTA Aircraft for Aerial 13. Anon.:Feasibility Study of Modern Airships, Crane Applications. In: Proceedings ofthe Phase 11. Vol. 1. Heavy Lift Airship Vehicle. Interagency Workshop on Lighter Than Air Book 11. Appendices to Book I. NASA Vehicles, Jan. 1975,pp. 571-584. CR-151918, Sept. 1976. 24. Nichols, J. B.; and Doolittle, D. B.: Hybrid Air- 14. Anon.:Feasibility Study of Modern Airships, craft for Heavy Lift - Combined Helicopter Phase 11. Vol. I. Heavy Lift Airship Vehicle. and Lighter-then-Air Elements.Presented at

13 30th Annual National V/STOL Forum of the 37. Putnam, W. F.; and Curtiss, H. C., Jr.: An Ana- American Helicopter Society, Washington, lytical and Experimental Investigation of the D.C., Preprint 814, May 1974. Hovering Dynamics of the Aerocrane Hybrid Heavy Lift Vehicle. Naval Air Development 25. .Anon.:Feasibility Studyon the Aerocrane Center Rept. OS-137, June 1976. Heavy LiftVehicle, Summary Report. Can- adair Rept. RAX-268-100,Nov. 1977. 38. Elias, A.L.: -Tip-Winglet Propulsionfor Aerocrane-TypeHybrid Lift Vehicles. AIAA 26. Helicostat. Aerospatiale brochure, undated. Paper 75-944,1975.

27. Anon.:Alberta Modern Airship Study, Final 39. Crimmins, A.G.: The Cyclocrane Concept. Report.Goodyear Aerospace Corp. Aerocranes of Canada Rept., Feb. 1979. GER-16559, June 1978. 40. Curtiss, H. C.: A Preliminary Investigation of the 28. Niven, A. J.: Heavy Lift Helicopter Flight Con- Aerodynamics and Control of the Cyclocrane trol System. Vol. I. Production Recommenda- Hybrid Heavy Lift Vehicle. Department of tions.USAAMRDL-TR-7740A, Sept. 1977. Mechanical and Aerospace Engineering Rept. 1444, Princeton University, May 1979. 29. Rosenstein, H.: Feasibility Study of a 75-Ton Payload Helicopter. Boeing Company Rept. 41. Munier, A. E.; and Epps, L. M.: The Heavy Lift DZ10-11401-1,June 1978. Airship - Potential, Problems, and Plans. Proceedings of the 9th AFGL Scientific Bal- 30. Mettam, P. J.; Hansen, D.; Byrne,R. W.; and loon Symposium, G. F. Nolan, ed., AFGL-TR- Ardema, M. D.: A Study of Civil Markets for 76-0-306, Dec. 1976. Heavy Lift Airships. AIAA Paper 79-1579, 1979. 42. Kelley, J. B.: AnOverview of Goodyear Heavy LiftDevelopment Activity. AIAA Paper 31.Mettam, P. J.; Hansen, D.; andByrne, R. W.: 79-1611.1979. Study of Civil Markets for Heavy Lift Air- ships. NASA CR-152202, Dec. 1978. 43. Bell, J. C.; Marketos, J. D.; and Topping, A. D.: Parametric Design Definition Study of the 32. Sander, B. J.: The Potential Use of the Aerocrane Unballasted Heavy-Lift Airship. NASA in British Columbia Logging Conditions. CR-152314, July 1979. Forest Engineering Research Institute of Canada Report, undated. 44. Nagabhushan, B. L.; and Tomlinson, N. P.: Flight Dynamics Analyses and Simulation of Heavy 33. Erickson, J. R.: Potential for Harvesting Timber Lift Airship. AIAA Paper 79-1593,1979. with Lighter-Than-Air Vehicles. AIAA Paper 79-1580,1979. 45. Meyers, D. N.; and Piasecki, F. N.: Controllabil- ity of Heavy Vertical Lift Ships, The Piasecki 34. Anon.: The Model 1050 Aerocrane,A 50-Ton Heli-stat. AIAA Paper 79-1594, 1979. Slingload VTOL Aircraft. All American Engi- neering Co., undated. 46. Pavlecka, V. H.: Thruster Controlfor Airships. AIAA Paper 79-1595,1979. 35. Putnam, W. F.; and Curtiss, H. C., Jr.: Precision Hover Capabilities of the Aerocrane. AIAA 47. Brewer, W. N.: Structural Response of the Heavy Paper 77-1174,1977. Lift Airship (HLA) to DynamicApplication of Collective Pitch. AIAA Paper 77-1188, 36. Curtiss, H. C., Jr.; Putnam, W. F.; and McKillip, 1977. R. M., Jr.:A Study of the Precision Hover Capabilities of the AerocraneHybrid Heavy 48. Vadala, E. T.: Triaxially Woven Fabrics of Lift Vehicles. AIAA Paper 79-1592,1979. Kevlar, Dacron Polyester,and Hybrids of

14 Kevlar and DacronPolyester. AIAA Paper 55. Iinuma, K.: Japan Takes Decision to Develop 77-1 180,1977. New Airships. Japan Commerce and Industry, vol. 3, no. 2, Dec. 1978. 49.Horn, M. H., and Pigliacampi, J. J.: High Strength Fibers for Ligher-Than-Air Craft. AIAA Paper 79-1601,1979. 56. Spangler, S. B.; Smith, C. A.; and Mendenhall, M. R.: Theoretical Study of Hull-Rotor Aero- 50. Williams, K. E.; and Milton, T.: Coast Guard dynamic Interference on Semibuoyant Vehic- Missions for Lighter-Than-Air Vehicles. AIAA les. AIAA Paper 77-1172,1977. Paper 79-1570,1979.

51. Rappoport, H. K.: Analysis of Coast Guard Mis- 57. Spangler, S. B.; and Smith, C.A.: Theoretical sions fora Maritime Patrol Airship. AIAA Study of Hull-RotorAerodynamic Interfer- Paper 79-1571,1979. ence on Semi-Buoyant Vehicles. NASA CR-152127, April 1978. 52. Brown, N. D.: Tri-Rotor Coast Guard Airship. AIAAPaper 79-1573,1979. 58. Schwind, R. G.; and Spangler, S. B.: Small Scale Wind TunnelTests on Heavy Lift Airship 53. Stevenson, R. E.: The Potential Role of Airships Configurations. AIAA Paper 79-1 591, 1979. for Oceanography. AIAA Paper 79-1574, 1979. 59. Schwind, R. G.; and Spangler, S. B.: Comprehen- 54. Nagabhushan, B. L.; and Tomlinson, N. P.: Flight sive Plan for a Small-Scale Wind-Tunnel Test Dynamics Analyses and Simulation of Heavy Program for Heavy-Lift Con- Lift Airship. AIAA Paper 79-1 593,1979. figurations. NASA CR-152290, March 1979.

15 "" - .. 1. Report No. 2. Government AccessionNo. 3. Recipient's CatalogNo.

" ~ .. - I . - .. 4. Title and Subtitle 5. Report Date WHICLE CONCEPTSAND TECHNOLOGYREQUIREMENTS FOR September 1981 BUOYANT HEAVY-LIFT SYSTEMS 6. Performing Organization Code

" . . . ~~ 8. Performing Organization Report NO. 7. Author(s) " i Mark D. Ardema A-SO22

"" - "" 10. Work Unit No. 9. Performing Organization Name and Address 505-42-51 Ames Research Center, NASA 11, Contract or Grant No. Moffett Field, Calif. 94035 13. Typeof Report andPeriod Covered . . " "- 12. Sponsoring AgencyName and Address Technical Paper~ -~ National Aeronautics and Space Administration 14. Sponsoring AgencyCode Washington, D.C. 20546

". .. " - 1

~ ~~ "_ . .. .~. 16. Abstract i Severalbuoyant-vehicle (airship) concepts proposed for short hauls of heavypayloads are described. Numerous studies have identified operating cost and payload capacity advantages relative to existing or pro- posed heavy-lift helicopters for such vehicles. Applications involving payloads of from15 tons up to800 tons havebeen identified. The buoyant quad-rotor concept is discussed in detail,including the history of its development, current estimates of performance and economics, currently perceived technology requirements, and recent research and technology development. It is concluded that the buoyant quad-rotor, and possibly other buoyant vehicle concepts, has the potential of satisfying the market for very heavy vertical lift but that additional research and technology development are necessary. Because of uncertainties in analytical predic- tion methods and small-scale experimental measurements, there is a strong need for large or full-scale experi- ments in ground test facilities and, ultimately, with a flight research vehicle.

1.18. Distribution Statement Airships Advanced technology Unclassified - Unlimited Hybrid aircraft Heavy-lift vehicle concepts SubjectCategory 05

" ~ . "1 " 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. NO. of Pages 22. Price' Unclassified Unclassified A02 1. . -~ I 'For sale by the National Technic4 Information Service, Springfield, Virginia 22161

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