I‘ ’, 1 NASA -! TP 1921 ’ .I I 1:. NASA Technical Paper 1921 c. 1 Vehicle Concepts and Technology Requirements for Buoyant Heavy-Lift 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 Aeronautics 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 (airship) 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 helicopters for such vehicles. 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 flight 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 airships (refs. 1-18) indicating a marketfor increased lift capability. and other studies (refs. 19-27) have determined that Extension of rotorcraft 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 aircraft, 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-balloon con- The characteristics of hybrid aircraftand their figuration