NASA Technical Memorandum 100035

Civil Applications of High-speed and Powered-Lift Configurations

James A. Albers John Zuk, Ames Research Center, Moffett Field, California

October 1987

National Aeronautics and Space Administration Ames Research Center Moffett Field, California 94035 ABSTRACT advanced to high-disk-loading direct Advanced subsonic vertical and short lift aircraft are discussed, including high-speed and landing (V/STOL) aircraft configurations rotorcraft, subsonic V/STOL aircraft, and sub- offer new transportation options for civil appli- sonic STOL aircraft. Future transportation cations. This paper describes a range of opportunities, along with VTOL and STOL transpor- vehicles from low-disk to high-disk loading air- tation systems, are described. The various con- craft, including high-speed rotorcraft, V/STOL figurations are compared and their advantages are aircraft, and short takeoff and landing (STOL) highlighted. This report indicates that these aircraft. The status and advantages of the vari- aircraft can satisfy many transportation require- ous configurations are described. Some of these ments and that they could be of a great benefit configurations show promise for relieving conges- to civil transportation. tion in high population density regions and pro- viding transportation opportunities for low popu- V/STOL TRANSPORTATION OPPORTUNITIES lation density regions. V/STOL aircraft can provide congestion relief for existing airports of densely populated WORLDWIDE, THERE IS A STRONG DESIRE to improve areas and have great potential as economic tools each nation's economy and quality of life. for developing regions. First, future transpor- Future world population growth, along with devel- tation opportunities for high-population density oping countries' desires to become highly indus- regions will be briefly discussed. trialized, requires efficient transportation HIGH POPULATION DENSITY REGIONS - As ground system. As always, it will be highly desirable congestion increases, short-haul intercity air to transport people and high-value cargo as transportation should increase in importance, rapidly and as economically as possible. Many primarily because of the importance of time to regions of the world lack suitable ground trans- the traveler and the growing efficiency, flexi- portation systems and have formidable geographic bility, reliability, and wider distribution of barriers. In urban developed areas, both ground air transportation services. However, the addi- congestion and air congestion around existing tion of new, large, and conveniently located airports will become severe. In most areas it is airports will be increasingly constrained by difficult, if not impossible, to expand airports, environmental, ground access, and economic fac- particularly because of the congestion and tors. Making better use of existing transporta- noise. Fortunately, there is a solution to these tion hubs and secondary and small community air- transportation problems--V/STOL aircraft. Tech- ports will become increasingly more important to nology advances in materials, propulsion, aerody- avoid serious air transportation congestion and namics, controls, guidance, and the integration ultimately business and economic stagnation. In of these technologies are yielding many promising the future, even with the use of advanced air designs that show the potential for revolutioniz- traffic control technology and wide-body aircraft ing short-haul transportation. technology, runway capacity limits will be Promising designs, including the state of reached in many of the major hub airports. development of the configurations, are described; A good example of current and future air The full range of vehicles from low-disk-loading congestion can be found in the United States.

1 Aviation in the U.S. is highly concentrated, and highways enabling a highly efficient intermodal airline hubs have become popular since deregula- transfer. Existing urban and remote heliports tion of the airline industry in 1978. Under this can also be used for most V/STOL aircraft. Cou- practice, passengers from a number of cities are pling these facility possibilities with existing funneled into a central location, where they general aviation airports, means an extensive change planes for their final destination. This vertiport ground-facility system could be availa- hub concept allows the airlines to fill the ble. Figure 2 is an artist's rendition of an planes but strains the air-traffic control and airport expansion possibility where an airport is runway system. In 1978, the airlines carried saturated with CTOL traffic and is constrained 275 million passengers; in 1987 the total is from expanding externally. V/STOL aircraft can expected to be more than 450 million. Airlines provide high-frequency, short- and medium-haul logged an average of 2000 hours of delays per day service, operating on vertipads or short runways in 1986. Operations at 17 large metropolitan and that generally can be placed on existing air- regional airports exceeded their practical annual ports. The CTOL runways can then be used for the capacity thus leading to an unacceptabe number of longer-haul, wide-body aircraft. Thus, the air- delays. Air travel is predicted to continue port capability can be greatly increased. growth at over 5% a year. As a result, opera- V/STOL aircraft offer a distinct advantage tions at some 65 major U.S. airports are pre- over the CTOL aircraft in impacted terminal-area dicted to exceed capacity before the year 2000. real estate because of the inherent characteris- Besides being a great inconvenience to the tics of V/STOL aircraft to descend and climb at traveller, the monetary costs of these delays is steep gradients. For example, a V/STOL aircraft high. In 1984, the Council of Airport Operators can make an approach to the touchdown zone on a estimates the delays cost air carriers and pas- runway or landing pad at a spiraling descent sengers over $3.2 billion. In 1987, delays have gradient of up to 9". whereas the normal descent increased to the point of being equivalent to gradient for approach to a landing by a CTOL suspending all conmiercial air service for aircraft is 3". On ascent, V/STOL aircraft can one month. follow an equally steep ascent gradient. Even with the current airport congestion and Furthermore, the characteristics of the large anticipated growth, the prospects are cur- V/STOL aircraft make feasible a curving approach rently not very good for building large new air- (or departure) in both VFR and IFR conditions ports because of environmental concerns, availa- (assuming suitable microwave landing navigation bility of suitable real estate, and costs. The facilities) which can provide considerable bene- Dallas-Fort Worth airport, constructed in 1974, fits to and flexibility in the ATC System. For was the last mafor airport built in the U.S. example, after entering the terminal area, an This airport covers about 18,000 acres, but some arriving V/STOL aircraft can proceed on a dis- aviation analysts believe major new airports crete three-dimensional routing to its initial would need 25,000 to 30,000 acres to ensure approach fix. Thereafter, the V/STOL aircraft enough of a noise buffer to avoid restrictions on can make a curving approach going downwind, par- flights. allel to the V/STOL runway, at the same time To reduce the results of airport saturation, descending at a steep gradient to touchdown point conmiunities will have to effectively use existing for a landing. Also, by applying advances in hub and secondary airports, and should consider active control, navigation and guidance systems the high payoff transportation opportunity along with cockpit automation, a V/STOL aircraft offered by V/STOL aircraft. V/STOL aircraft can be preprogrammed to fly a minimal environmen- terminal flight-path control capability will tal impact flightpath. allow the use of terminal-area flight LOU POPULATION DENSITY REGION - Future rules so that they will pose no additional burden V/STOL aircraft economic development opportuni- to crowded airports. ties include passenger service, agriculture prod- Significant airport relief can be obtained ucts, emergency services, mineral development through the use of these vehicles when they do transport, law enforcement, fishing, and high- not use existing airports, but instead carry value cargoes (l).* An example of a region which passengers almost point-to-point using verti- has many V/STOL opportunities is the Pacific ports. Figure 1 illustrates potential V/STOL Basin (2). V/STOL aircraft should be suited as a aircraft landing facilities. These include sea- passenger and high-value-cargo transport for ports along rivers or lakes that my use existing areas that lack ground transportation systems piers or barges, facilities located adjacent to or above other existing transportation modes, such as railroads, light rail or subways; and 'Numbers in parentheses designate references at end of paper.

2 which are expensive to build or maintain. Unde- independent STOL ports consisting of one or more veloped natural resources are a characteristic of ST9L runways situated at a site removed from a some remote regions. Another characteristic is CTOL airport. the relatively short and unimproved existing STOL aircraft offer a distinct advantage airport runways. Ventures that seem particularly over the CTOL aircraft by using shorter runways suited for such aircraft include mining indus- because of their inherent characteristics to tries, such as copper and aluminum; petroleum descend and climb steeply. STOL operations to exploration; associated wood products; high- and from a STOL port offer a great deal of flexi- value-added manufacturing; and agricultural prod- bility in providing discrete routes to facilitate ucts. Helicopters have virtually monopolized traffic flou. Airspace required by STOL aircraft servicing of offshore oil rigs because they are for takeoff/landing and in terminal-area maneu- more productive than ships. Projecting to the vering is significantly less than that required next century, oil rigs can be expected to be by CTOL aircraft. These characteristics not only located farther offshore and, in general, other facilitate operation of the ATC system in segre- resources such as minerals are expected to be gating STOL and CTOL traffic, but also assist in extracted from more difficult geographic loca- carrying out obstruction-clearance and noise- tions as more readily accessible sources are abatement procedures. The curving, steep- depleted. Other new opportunities may exist, gradient flight paths of STOL aircraft can be such as ocean mining, that may offer other oppor- arranged to avoid adverse effects caused by wake tunities for the application of long-range, ver- vortices from heavy CTOL aircraft. tical takeoff and landing aircraft. V/STOL and Suitable sites for STOL airports can be STOL air transportation may offer a solution for found even in congested cities. Similar to special seasonal needs for industries such as the V/STOL aircraft, STOL airports could be located fisheries. Also, the basic health and welfare along rivers, along the shores of large bodies of needs of citizens located in remote and isolated water, along transportation rights-of-way, or in areas could be served by V/STOL aircraft. Gener- wasteland areas within cities that are unsuitable ally, remote area service requires small air- for housing or industry. For example, a STOL craft, another point in favor of V/STOLs. landing pad could be located along the riverfront A broad range of V/STOL aircraft configu- (e.g., as is the new STOL port in London), or . rations was examined to satisfy the many trans- could be built on the roofs of existing water- portation requirements and opportunities. These front buildings, or on unused piers. In remote are shown as functions of disk loading and air- areas STOL aircraft could be used on short, speed in Fig. 3. Disk loading (defined as thrust unpaved runways that are relatively easy to divided by a representative area, e.g., construct. disk, shroud exit, and Jet nozzle areas) provides a rational basis for comparing various configura- ADVANCED HIGH-SPEED ROTORCRAFT CONFIGURATIONS tions. The disk loadings of the configurations considered in this paper range from 10 to This section will discuss a range of high- 3,000 lb/ft2 and cruise airspeeds range from speed (greater than 200 knots) rotorcraft con- about 200 to 600 knots. These configurations figurations. The designs discussed include the will be discussed in more detail in subsequent tilt rotor, folding tilt rotor, stowed rotor, sections of this paper. compound, and stopped-rotor configurations. A historical perspective of advanced rotorcraft STOL TRANSPORTATION OPPORTUNITIES developments in the United States is given in Ref. 3. Short takeoff and landing (STOL) aircraft TILT ROTOR - The tilt-rotor aircraft com- have the potential for relieving congestion at bines the low-disk-loading VTOL capability of a hub airports, transporting tourist and high-value ,helicopter with standard aircraft cargo, and aiding in the developent of cruise flight. The design has been proved in the regions. STOL aircraft can avoid the problems of XV-15 tilt-rotor research aircraft (Fig. 4). A landing-slot allocation and long arrival and unique feature of this aircraft is the two large, departure delays by utilizing the short segments three-bladed proprotors mounted at the tips of of inactive runways, stub-runways, or special the wings. For takeoff, the axes of the prop- STOL runways which are typically 2,000 ft long rotors and their engines are rotated to the ver- (see Fig. 2). STOL ports can be categorized as tical position where the lift developed is two basic types: Conventional takeoff and land- entirely propulsive. The XV-15 has the ability ing (CTOL)/STOL ports consisting of one or more to fly in one of three different modes: as a STOL runways situated at a CTOL airport; and helicopter, in the partially converted tilt-rotor

3 mode, or in the fully converted airplane mode. with subcontracts to Bell Helicopter Textron and The XV-15 converts from the helicopter mode to the Boeing Vertol Company. The study identified the airplane mode safely and rapidly by continu- the most promising areas of potential application ously tilting the proprotors from the helicopter of the civil tilt rotor. Examples of configura- rotor position to the conventional airplane pro- tions from this study are the 19-passenger and peller position. During the 10- to 15-sec con- 39-passenger civil tilt rotor renditions shown in version period, the aircraft speed increases and Figs. 7a and 7b, respectively. The payload-range lift is transferred from the rotors to the curve for the 19-passenger configuration is shown wing. To land, the proprotors are rotated up to in Fig. 8. For vertical takeoff and landing the position and the aircraft is operations with one-engine-inoperative margin, flown as a helicopter to a vertical landing. The the range is 600 n. mi., whereas for STOL opera- ability of the XV-15 to rotate its proprotors to tion the range can be more than doubled to nearly different angles also makes it possible to oper- 1400 n. mi. The study results indicate that for ate as a STOL aircraft. tilt angles of the civil tilt-rotor to achieve full potential 60°-?Oo produce lift from both the proprotors and benefits of congestion relief, a system infra- wings. Heavier payloads can be lifted in this structure geared to its V/STOL capabilities is STOL mode operation than in helicopter-mode needed. operation. FOLDING TILT ROTOR - The XV-15 research Two XV-15s were built by Bell Helicopter aircraft has demonstrated the tilt-rotor and its Textron under a joint NASA-Army contract. One operational readiness; however, it.was not opti- aircraft is engaged in a flight research program mized for high speed. Studies under way at Ames at Ames Research Center, the other is being oper- indicate that it will be possible to operate ated by Bell Helicopter Textron in Arlington, tilt-rotor configurations to 400 knots with Texas, and is being used for tilt-rotor.develop- advanced technology (6). An improved aeroelasti- ment and military and civil demonstrations. The cally stable rotor-hub configuration is required two aircraft have accumulated over 800 hr of along with a lower drag configuration. Beyond accident-free testing. 400 knots, rotor drag is severe. However, if the The advantages of the tilt-rotor aircraft rotor is slowed, stopped, and folded, while the are many. The ease with which the aircraft can forward thrust is provided by a convertible tur- be converted from one flight mode to another bofan engine, this configuration can attain enhances its maneuverability and permits it to be speeds approaching 500 knots. configured to meet varied mission requirements. As with most V/STOL designs, the folding Also, the unique tilt-rotor aircraft increases tilt-rotor aircraft idea is not new. In 1970-72, mission flexibility by providing a flight enve- considerable research was performed by both Bell lope that overlaps those of the helicopter and Helicopter and Boeing Vertol on folding tilt- airplane. Figure 5 compares an XV-15 tilt-rotor rotor vehicles under NASA sponsorship. The flight envelope with a helicopter and fixed-wing rotor-folding mechanism was tested by NASA and turboprop. Bell in 1972 in Ames' 40- by 80-Foot Wind Tunnel The vibration levels measured in the XV-15 (Fig. 9). Complete stop-index-fold-unfold cycles in the helicopter mode are similar to those for were successfully demonstrated with a 25-ft-diam helicopters. However, in the airplane mode rotor at wind-tunnel speeds as high as vibration levels are much lower and are equiva- 175 knots. An artist's conception by Bell Heli- lent to other turboprop fixed-wing aircraft. copter Textron of a folding tilt-rotor is shown Figure 6 compares measured XV-15 sound expo- in Fig. 10. sure levels with those of Bell 2228, which is The work done in the early 1970s was based representative of modern helicopters. These on the utilization of four engines--two for shaft measurements were obtained from a flyover at power and two for fan thrust. Today the applica- 500 ft (4). Note that the XV-15 tilt rotor is tion of the convertible propulsion technology significantly quieter than the helicopter, even (i.e., an engine that converts from turbofan to though it weighs more than twice as much as the ) could reduce weight. Considerable helicopter, and has a greater disk loading. effort has been expended in analyzing and testing Also, the sideline noise drops off much more engines of this type (7). In Fig. 11, the TF-34 rapidly on the XV-15 than it does on the modified into a convertible engine is shown in helicopter. schematic form. A folding tilt rotor with The Federal Aviation Administration (FAA), today's technology could be designed to operate NASA, and DOD conducted a Joint study of civil at maximum speeds of 475 knots with a altitude tilt-rotor aircraft (5). The Boeing Commercial ceiling of 40,000 ft (8). Airplane Company led the main contractual effort, STOWED ROTOR - Besides folding tilt-rotors, contract to build a technology demonstrator: The other stowed-rotor concepts have been investi-. ABC demonstrator was designed to be flown both as gated where the rotor is stopped, folded, and a pure helicopter and as a compound helicopter stowed in the fuselage and the aircraft is then (i.e., with auxiliary propulsion system). The operated as a conventional fixed-wing aircraft. flight program initiated in 1973 was sponsored by Lockheed conducted both subscale and full-scale the Army, NASA, and Navy, and explored the heli- wind tunnel tests to demonstrate the feasibility copter mode. The flight envelope was then of this concept (9). A full-scale wind tunnel expanded in the compound configuration (Fig. 15) model with a 33-ft diam 3-blade rotor in the Ames with the addition of two 5-60 turbojet engines to 40- by 80-Foot Wind Tunnel is shown in Fig. 12. increase its forward speed and agility (11). The rotor blades in a fully folded position are The ABC achieved forward speeds of about shown in Fig. 13. Mission vehicle studies of the 240 knots and demonstrated good hover charac- stowed rotor configuration indicated that it can teristics, high maneuverability, compact size, obtain speeds similar to the folding tilt rotor. and relative simplicity, but had high vibration For the stowed rotor configuration, a tele- and hub drag at the higher speeds. A flight scoping rotor offers a feasible solution to the envelope is shown in Fig. 16. However, because problem of stopping the rotor in flight. A tele- it was purely a concept demonstrator, the blade scoping rotor is a variable diameter rotor system shape, twist, hub shape, rotor materials, shaft introduced by Sikorsky Aircraft in the 1970s tilt, auxiliary propulsion, empennage, and flight (10). The telescoping rotor minimizes aeroelas- controls were not optimized. The flight program tic stability problems with a lower disc loading was terminated before improvements could be made and can be tuckec. away in a reasonably small in the various aircraft subsystems. A review of stowage compartment leaving an efficient fixed the lessons learned from the flight program wing aircraft for high speed flight. However, a indicated that the following steps could be taken trade-off to these benefits to the added complex- to improve system efficiency: optimization of ity of the telescoping rotor for a given applica- rotor-blade airfoil sections for high-speed tion needs to be considered. Also, the blade flight, modified transmissions and structural geometry variation with span (characteristic of weight, an integrated propulsion system, and modern blades) may have to be compromised. modified empennage and hub for reduced drag. An COMPOUND ADVANCING-BLADE CONCEPT - The prin- optimized ABC design has the potential for speeds ciple of advancing blade concept (ABC) helicopter greater than 250 knots and could have a broad is based on the use of rigid, coaxial, counter- range of applications. A 30-passenger civil ABC rotating rotors. The ABC is a rotor design that has been studied that has a design speed of utilizes more of a rotor's lift potential by 250 knots and range of 500 miles (Fig. 17). overcoming in high STOPPED ROTOR - The X-wing is an aircraft speed. Single-rotor helicopters must produce with a stoppable rotor that will provide a low- equal lift on each side of the disk to keep the disk loading VTOL capability, similar to that of rotor level in roll. To compensate for the a conventional helicopter, combined with high unequal distribution in lift, larger pitch angles subsonic cruise speed. The rotor is stiff, four- are required for the retreating blade than for bladed and utilizes circulation-control blowing the advancing blade. The ABC rotor avoids this over the trailing- and leading-edge surfaces of condition by transferring the lift to the advanc- its syarmetrical blades for lift and control. The ing blades on each side of the disk, producing a X-wing is designed to operate in both the rotary- balanced rolling moment. By overcoming iing and fixed-wing mode and passes through the retreating-blade stall, an ABC rotor requires conversion mode; these are depicted in Fig. 18. less power than a conventional rotor at high In the rotary-wing mode, the X-wing rotor is used speeds and can maintain lift throughout the speed as a conventional helicopter rotor with the envelope (Fig. 14). Hover performance is supe- addition of blowing to augment lift for hover, rior to single-rotor helicopters because the the transition to forward flight, and in forward power train and additional weight of the tail flight at speeds up to approximately 150 knots. rotor, gearboxes, shafting, and controls are At speeds in the range between 150 and 200 knots, eliminated. the X-wing converts from a rotary-wing to a The ABC was developed by Sikorsky Aircraft fixed-wing by reducing rotor speed until the beginning in 1964. Preliminary testing included rotor is stopped in a fixed position with two a 115-scale. powered wind-tunnel model and a blades swept forward and two blades swept back at full-scale, 40-ft diam rotor system run in Ames' 45". The X-wing is designed to operate as a 40- by 80-Foot Wind Tunnel. Based on favorable fixed-wing aircraft at flight speeds between 200 test results, the U.S. Army awarded Sikorsky a and 500 knots. (However, the vehicle drag

5 characteristics have not been determined at high to operate at speeds of 500 knots and at altitude speeds.) In this mode, the aircraft control is ceilings greater than 40,000 ft. provided in part by the blowing system, which replaces the traditional wing control surfaces. SUBSONIC V/STOL CONFIGURATIONS The X-wing evolved from the circulation control work of Ian Cheeseman of the University There is a long history of V/STOL and verti- of Southampton, England, in the 1960s; his work cal takeoff and landing (VTOL) aircraft develop- was followed by research at the U.S. Navy's David ments in the United States (13, 14). This sec- W. Taylor Naval Ship Research and Development tion will consider three types of subsonic con- Center. Early wind-tunnel tests were conducted figurations to illustrate a range of potential by Lockheed California Company, including conver- vehicles and applications: lift-cruise fan, tilt sion of a 25-ft rotor in the Ames 40- by 80-Foot wing, and vectored thrust. Wind Tunnel, Followed by X-wing assessment by LIFT-CRUISE FAN - Lift-cruise fan VTOL air- Boeing Vertol and Sikorsky Aircraft. craft are generally characterized by utilizing The RSRA/X-wing program was initiated in high-bypass-ratio fans for thrust in cruise, and 1983 with a contract to Sikorsky Aircraft with for lift in terminal-area flight. In transition funding from Defense Advanced Research Projects and cruise flight, the lift-cruise fan thrust Agency and NASA. The X-wing on the Rotor Systems vector is rotated down by rotation of the entire 3esearch Aircraft (RSRA) is shown in Fig. 19. nacelle, or by rotation of the nozzle exits and The RSRA is a compound configuration developed as louvers. (The U.S. Navy and NASA cooperatively a "flying wind tunnel'' for evaluating new rotor developed the technology basis for the design of designs under actual flight conditions. The lift-cruise fan V/STOL aircraft for both military current RSRA is limited to 250 knots. and comercial applications.) The design A number of critical technologies are being depicted in Fig. 21 employed three fans driven by developed for the RSRA/X-wing program. These two engines. A full-scale wind tunnel model of include: 1) very stiff composite structures For this configuration was designed and built by obtaining the high natural frequencies of the McDonnell Douglas and tested in the Ames 40- by rotor-wing to avoid aeroelastic problems and to 80-Foot Wind Tunnel (15). The two engines drove provide satisfactory control; 2) digital fly-by- turbofans mounted over the wing. The thrust of wire control systems for good handling in the these two fans could be vectored through a various Flight modes, controlling vibration, and D-nozzle to provide either vertical lift or implementing the control laws for stopping and cruise thrust. A third fan, located in the nose starting the ; and 3) a pneumodynamic of the aircraft, was driven through a gearbox control system that consists of 48 valves that arrangement connected to the two engines. control the air supply to the leading and trail- An example of a design in which the entire ing edges of the blades. In addition, conver- nacelle rotates is the full-scale tilt-nacelle tible engines are being developed for propulsion model designed and built by Navy/NASA/Grumman. system simplication and weight reduction The design incorporates two tilting, high-bypass (Fig. 11). turbofan engines with controllable inlet guide The broad goal of the RSRA/X-wing program is vanes and a system of controllable vanes in the to develop specific technology and demonstrate exhaust flow (Fig. 22). Hover control is conversion between rotary-wing and fixed-wing achieved through direct modulation and angling of modes. These activities are anticipated to pro- the thrust vector, thereby eliminating the need vide the necessary technology base so that a low- for a reaction control system. Aerodynamic vanes risk development program could be initiated for a located behind the nacelles in the fan-core prototype vehicle. The rollout of the RSRA/ engine exhaust provide pitch and yaw control; X-wing vehicle occurred in August 1986 and flight thrust modulation provides height and roll testing is planned for 1987 and 1988. control. Even though the X-wing is extremely complex The tilt-nacelle has evolved from extensive and involves a number of technical hurdles that configuration studies, supported by over 5,000 hr must be overcome before the design becomes feasi- of wind-tunnel tests and flight simulation ble, it has potential for both military and civil (16). Nacelle component development testing applications. A discussion of X-wing potential began in 1976 and has continued to the present For Navy applications is given in Ref. 12. A time. Initial testing concentrated on developing civil version of this concept is shown in two of the key components of the propulsion Fig. 20. An X-wing aircraft with advanced- system--the inlet and the control vane assem- technology convertible engines could be designed bly. These tests and supporting analyses were used to develop a baseline tilt-nacelle

6 configuration (known as the Grunman 698). The control. A schematic of the tilt-wing aircraft tilt-nacelle configuration was tested exten- is shown in Fig. 27. sively, using small-scale wind-tunnel models and The XC-142A aircraft was built as a concept using a large-scale model in both the hover demonstrator and the flight program disclosed facility and the 40- by 80-ft wind tunnel at Ames several mechanical and structural problems (Fig. 23). The wind-tunnel results indicate that requiring further development. However, the the configuration can operate over a broad tran- CL-84 program which flew several years later had sition corridor with ample maneuvering capabil- fewer problems. The XC-142A and CL-84 programs ity. The ground research program indicated no were generally considered successful in that they technical show stoppers. The tilt-nacelle has demonstrated very effectively the VTOL and STOL been proved during extensive tests, and the tech- capabilities of the tilt-wing concept for opera- nology is ready to proceed with a low-risk pro- tional use. The performance envelope for the gram for a manned flight demonstrator. The tilt- XC-142A is shown in Fig. 28. Other development nacelle offers moderate hover endurance capa- work since the XC-142A program indicated a 50% bility, a less complex control system because reduction in propeller and transmission system of no-engine-bleed requirement and a good weight could be achieved with advanced tech- propulsion-airframe match throughout the flight nology. Also, advanced technology could improve envelope. It is particularly suited for long the handling qualities in-ground effect, and endurance, moderate hover, and high-altitude propeller noise levels. missions with high subsonic cruise speed capabil- VECTORED THRUST - The only operational ity. Many missions, particularly civil missions, V/STOL fighter aircraft in the free-world today require no hover endurance, but do require verti- is the Harrier. The U.S. Marine Corps has been cal flight capability. The wind-tunnel model using the British AV-8A Harrier vectored-thrust represented a proposed manned flight demonstrator aircraft since 1971. The Marines now use the aircraft, which would weigh about 16,000 lb and AV-8B version of the Harrier built by McDonnell be powered by TF-34 engines. An artist's concep- Douglas Aircraft Company; it incorporates a num- tion of a civil tilt-nacelle aircraft is shown in ber of modifications that improved range and Fig. 24. payload. The prototype of the AV-8B is currently A study of civil transportation missions for being used as a V/STOL research aircraft at Ames the tilt-nacelle was reported in Ref. 17. A Research Center for investigations into inte- tilt-jet VTOL aircraft was modeled after the tilt grated flight propulsion controls, aerodynamics, nacelle design, using near-term advanced technol- and advanced displays (Fig. 29). The Harrier, ogy levels. The results from this study of pay- being a high-disk loading aircraft, is ideal for load versus range for an executive transport high speed and high maneuverability military mission are shown in Fig. 25. For the mission, applications. Vectored thrust aircraft are gen- the payload was 1,400 lb for a 95OF-day takeoff erally not applicable for civil use because of and a 750-mile range. The study showed that the high noise levels and high downwash of engine tilt-nacelle transport is most cost-effective at exit velocities during hover. long ranges because of its high cruise speed. TILT WING - Propeller V/STOL aircraft have a SUBSONIC STOL CONFIGURATIONS lon? history dating back to the early 1950s when research was intiated on both the deflected slip- A STOL aircraft is generally defined as one stream STOL and the tilt-wing V/STOL. In the that can take off or land over a 50-ft obstacle deflected-slipstream design, near vertical thrust at sea level at its maximum takeoff or landing is obtained by turning the propeller slipstream weight in a distance of about 2,000 ft. Histori- downward with large wing flaps, while maintaining cally, operational STOL aircraft have achieved the wing and propellers in an essentially hori- their short-field performance through light-wing zontal attitude. In the tilt-wing, the wing and loading (25 lb/ft2 or less) and extensive use of propellers are tilted up at a 90O-attitude for high lift devices such as flaps and slats, at the takeoff and landing. The second-generation expense of reasonably high cruise efficiency and demonstrator tilt-wing airplanes built in the ride qualities. Various designs have been pow- 1960s were the LTV-Hiller-Ryan XC-142A and the ered by turboprop-turboshaft and pure jet propul- Canadiar CL-84. The XC-142A was the winning sion systems. Current STOL aircraft that are entry in the Tri-Service V/STOL transport compe- being used for commuter aircraft operations tition of 1961. The XC-142A (Fig. 26) used four include the De Havilland Twin Otters and T64-GE-1 engines with cross-shafting to four Dash 7s. Typically, these aircraft accomodate propellers and a tail propeller for pitch fewer than 60 passengers and cruise at speeds less than 250 knots.

7 Future and larger STOL aircraft must have ride qualities over those of the current low- the necessary short-field and maneuvering enve- wing-loading aircraft. An example of the USB lope to get into and out of hub airports sepa- design is the twin engine YC-14 aircraft. The rately from CTOL aircraft and have minimum envi- high performance of USB aircraft is achieved by ronmental effects at the small secondary urban installing the engines over the forward portion airports. Promising technology for future of the wing. A faired mixing nozzle directs the designs was developed under the U.S. Air Force exhaust gases over the wing‘s upper surface and Advanced Medium STOL Transport Program which flaps to provide increased aerodynamic lift. produced the YC-14 and YC-15 military prototype Lift is improved by taking advantage of the aircraft, the NGSA Augmentor-Wing Research Air- Coanda effect (Fig. 331, where air adhering to craft Program, and the NASA Quiet Short-Haul the surface of the wing continues down over a Research Aircraft (QSRA) Program. This technol- highly deflected flap, converting a large portion ogy can be applied to a new generation of large of the jet thrust into propulsive lift. high-speed transport airplanes with outstanding The four-engine QSRA (19) was developed for short-field capability. Figure 30 illustrates proof-of-concept verification of the USB low- these aircraft and simplified schematics of the speed-flying characteristics and has been used lift-augmentation systems. The externally blown- extensively to investigate terminal-area opera- flap system concept from the YC-15 prototype will tions for STOL aircraft (see Fig. 34). This be used on the C-17, which is currently under four-engine USB configuration offers better development for the Air Force. The lift augmen- engine-out performance than a two-engine config- tation is achieved by flaps deflecting the thrust uration. Flight research with the QSRA has also downward on takeoff and landing, with the flaps confirmed that landing performance at relative retracted during high-speed cruise flight. short field lengths can be achieved at the lower The Augmentor-Wing Research Aircraft ejected thrust-to-weight ratios comparable to those used fan bleed air between wing upper and lower flap in conventional aircraft. The QSRA nominal take- segments for lift augmentation. The Augmentor- off and landing distance is 750 ft and 650 ft, Uing configuration (Fig. 31) was demonstrated as respectively. However, during carrier trials, a powerful lift-enhancing device on a highly the QSRA demonstrated takeoff distances less than modified C-8A de Havilland Buffalo turboprop 300 ft and landing distances less than 200 ft. aircraft. The augmentor was powered by the cold For optimum utilization, a STOL aircraft flow from the front fans and ducted through the requires a high approach angle capability to wing assembly (Fig. 32). Thus true engine-out minimize the required air space into the terminal capability on this two-engine jet STOL aircraft area. The USB nozzle and flaps on the QSRA have was achieved. The aircraft was first flown on been designed for exceptionally high turning of May I, 1972, and its flight research continued at the engine exhaust airflow to enable steep Ames through 1976 (18). It was transferred in approach angles with adequate safety margins. 1976 to Canada, where research uas conducted for The approach path is over twice as steep as that several years. of conventional airplanes; Fig. 35 illustrates The Augmentor-Uing Aircraft successfully this point. Note that the QSRA can touch down demonstrated the augmentor concept by achieving and stop before the CTOL touches down. Since thrust augmentation ratios of about 1.20. It was noise attenuates rapidly with distance (height), the world’s first jet STOL transport demonstra- the higher approach attitude is a big factor in tor. Additionally, it demonstrated and enabled reducing the noise effect on the surrounding evaluating the advantage of using direct-lift cwrmunity. This height is increased even more by thrust control and spoilers in precise steep landing such aircraft away from the boundaries of flightpath control. The aircraft demonstrated the airport. significant gains in CL (up to CL max of 5.5 The QSRA uses the Lycoming YF-102 engine and an operating CL of 3.9). Nominal approach which has a relatively high speeds of 60 knots were routine, and speeds as (6 to 1 ) , which, in turn, is conducive to low low as 50 knots were demonstrated when it flew on noise. The installation has been designed spe- the back side of the power curve. Takeoff and cifically to attenuate the engine noise by landing distances of less than 1,000 ft over a including tuned acoustic linings in the inlet and 50-ft-high obstacle were routinely demonstrated, fan duct. In addition, placing the engine above and ground rolls as low as 350 ft were the wing provides noise shielding to ground achieved. Its high-speed cruise performance was observers. These design features result in an not demonstrated in flight. extremely quiet airplane, as exemplified by com- The upper surface blowing (USB) design uti- paring the 90-EPNdB footprint of a “scaled-upn lizes high wing loading which results in improved QSRA airplane to that of a coamercial jet

a transport (Fig. 36). The noise footprint is at low hover times, the fuel used by vectored significant in that it indicates the effect OF thrust and lift-cruise fan designs is signifi- the airplane's noise on the area around the cant. For these designs it is important to airport. Studies have shown that the noise develop operational techniques and pilot aids to reaching the surrounding conmunity will be well minimize the time spent in hover and at very low below the 90-EPNdB level. For example, even for speeds. Also, notice in Fig. 39 that the X-wing, this "scaled-up" QSRA, the 90-EPNdB noise level khich is representative of stopped-rotor designs, has been calculated to be essentially contained is a means of achieving high speeds while main- within typical airport boundaries. taining good hover efficiency. (However, this Since transport aircraft spend a large por- assumes that the X-wing has a satisfactory lift- tion of their flying time at cruise speeds, an to-drag (L/D) ratio at cruise speeds, a charac- investigation is required to minimize cruise-drag teristic that remains to be determined.) associated with USB. It is anticipated that The effect of configuration on flight per- computational analysis, wind-tunnel testing, and formance can be examined by considering the flight measurements will be required before a flight envelope of the low-disk loading aircraft commitment is made to a production program. (Fig. 40). It can be observed that as speed and Further, verification will be obtained from the altitude increase, the complexity of the vehicle Quiet Short Takeoff and Landing (QSTOL) airplane increases, as well as the cower required, which called the Asuka. The Asuka, using USB technol- results in higher empty-weight fractions (empty ogy, is designed to operate at Mach 0.7, with a weight/gross weight). However, the increased ceiling of 30,000 ft and a maximum range of higher speed or range could make the vehicle 1,000 miles. It began flight testing in October economically feasible. The helicopter is limited 1985 (Fig. 37). The Asuka was developed by the to less than about 200 knots and has empty-weight Japanese National Aerospace Laboratory and a fractions of 0.5 to 0.6. A compound helicopter consortium of Japanese companies. requires additional engine weight and heavier In summary, large transport aircraft that rotor system that increase empty weight. The utilize can offer impressive short- tilt rotor has an aerodynamic lifting surface in field performance, increased payload for CTOL addition to the tilting mechanism, resulting in operations, and reduced noise level. They can an empty-weight fraction of 0.67-0.70. The speed increase the capacity of existing airports by and altitude are further increased by stopping providing service on STOL runways using alterna- and folding the rotors and substituting converti- tive-airport approach paths. These aircraft may ble engines. The additional complexity also also provide airline service to secondary air- increases the weight and power required. For ports that currently have no airline service. example, the stopped-rotor X-wing has high speed and altitude potential; however, complexity and COMPARISON OF CONFIGURATIONS weight increase because of the large rigid rotor system, the associated pneumodynamic system, and Disk loading can be used as an important installation of the convertible engine. Also, parameter to identify the relative merits of the stowed single rotor would have similar configurations. Disk loading is defined as the flight-envelope characteristics with increased maximum thrust produced divided by an appropriate weight and complexity. The result is empty- cross-sectional area of the thrust producing weight fractions from 0.69 to 0.75. device. Generally, aircraft hover performance The Flight envelopes of high-disk-loading can be related to it. As disk loading increases, aircraft are illustrated in Fig. 41. These enve- hover efficiency (thrust per unit power) lope limits are similar to those of CTOL aircraft decreases markedly, as shown in Fig. 38. A lift using the same propulsion system. However, system that imparts a high dounwash velocity is V/STOL aircraft tend to have small wing areas and less efficient because the engine power (and fuel spans because at low speeds they are not depen- flow required to produce the lift') varies as the dent on aerodynamic lift. In addition, some cube of the air velocity. This directly affects designs will have greater wetted areas because hover performance (Fig. 39). The fuel required their total volume will be greater owing to the to hover (expressed in pounds of fuel per minute) inclusion of additional components for propulsion is plotted versus the cruise speed of the air- or, for example, gas ducting and nozzle- craft. Considering that operational aircraft deflecting mechanisms. Also, the aircraft normally only have 0.25 to 0.30 fuel fraction designer has less freedom in positioning compo- available, the hover requirements of the intended nents because of packaging and center-of-gravity mission are an important consideration in design location constraints and limited inlet location selection. It is obvious from Fig. 39 that even

9 placement to avoid recirculation-reingestion only 198 knots. The lift-cruise fan average problems. cruise speed is 450 knots; however, the 8-min In civil applications, environmental factors hover out-of-ground effect requirement requires are extremely important operational considera- the vehicle to carry more fuel because of its tions, especially for landing sites. Figure 42 hover inefficiency; as a result, its gross weight compares the predicted perceived noise level is 62,000 lb. The ABC was the heaviest vehicle (PNdB) of various thrusting devices that are at 74,000 lb. This was primarily attributed to characterized by disk loading. The power plants the cruise inefficiency resulting from overcoming are at full-power setting and the distance of the the drag of the coaxial hub. noise detector from the aircraft is 400 ft. As a A longer range example is shown in baseline, the noise level of typical city daytime Fig. 45. This transport mission requires a range traffic is 80 to 90 PNdB. Hence, the noise level of 800 miles, taking off vertically at sea level is extremely important in site selection, as well on a 90°F day, and landing vertically at 5,000 ft as in determining the design for the mission. above sea level on a 90°F day. In this case the Generally, the noise level increases as the disk lift-cruise fan is the lowest mission gross loading increases. High-disk-loading vehicles weight vehicle. This is due to both the may have noise levels unacceptable in dense urban increased distance compared with the first exam- environments but acceptable in remote regions. ple and a requirement only to take off and land Another operational problem that must be vertically. Hence, the lift-cruise fan's effi- considered is the downwash pattern from the cient cruise gives it a large advantage over the thrusting device. Figure 43 shows the velocity other designs. The tilt rotor is 1.5 times at ground level due to downwash from aircraft of heavier, whereas the helicopter is almost 2 times various disk loadings (20). Note that the higher heavier. For the ground rules of the study com- the disk loading, the smaller the ground parison, the ABC could not fulfill the mission at boundary-layer thickness and the higher the maxi- any practical gross weight. In addition, the mum boundary-layer velocity. Hence, the high- lift-cruise fan cruise speed is 450 knots, disk-loading vehicles require a prepared clean whereas the helicopter cruise was 100 knots, and surface, whereas the lower-disk-loading aircraft that of the tilt rotor at 260 knots. Thus, the can land on less prepared surfaces and not lift fan arrived in less than half the time adversely affect the surrounding area. Another required by the other two vehicles. For differ- operational factor is the hot exhaust gas ent mission requirements other V/STOL configura- impingement problem prevalent with vectored- tions may have the lower gross weights. It is thrust configurations. The impingement of the also known that vehicle cost is directly corre- hot gases on the landing surface can damage the lated to the vehicle weight. surface and in some cases may break up the sur- It should be added that important civil face and coat or impinge the surrounding area certification requirements, such as fuel reserve witn eroded surface material. Thus, a treated and one-engine inoperative margin, are in the landing pad area may be required to withstand process of being addressed, but not finalized in high-temperature exhaust. the United States. The ability to operate safely To determine the right V/STOL aircraft for a after loss of an engine and being able to fly particular application requires a mission analy- precisely and stably at low landing speeds for sis subject to mission constraints, such as oper- instrument flight-rule operation are essential. ating environment and type of landing site. Two examples of this type of analysis are shown in APPLICATIONS OF CONFIGURATIONS Figs. 44 and 45. The first example (Fig. 44) shows the mission gross weights for a helicopter, As discussed in the sections on V/STOL and ABC, tilt rotor, and lift-cruise fan for a rescue STOL transportation opportunities, many of the mission. The same payload was used for the four configurations discussed can be used for reliev- configurations. The mission requires flying over ing congestion in high population density regions 300 miles, hovering out-of-ground effect for and for passengers and high-value-cargo in low 8 min at 7,000 ft on an 83°F day, then returning population density regions. The greatest near- to the base, which is at 4,000 ft on a 95'F term opportunities appear to be for smaller day. It is seen that the tilt rotor is the low- vehicles (fewer than 50 passengers) which make est gross weight vehicle to perform the mis- the future especially attractive for V/STOL air- sion. Its gross weight is 43,000 lb and its craft. The civil applications of the configura- average cruise speed is 280 knots. On the other tions discussed are summarized in Table 1, along hand, the helicopter's mission gross weight is with estimated operating ranges that vary from over 51,000 lb and its average cruise speed is 300 n. mi. for compound ABC to 3,000 n. mi. for a

10 STOL aircraft. In addition to range, other fac- CONCLUDING REMARKS tors that determine the configuration applicabil- ity are productivity (speed and payload), fuel Future civil opportunities for V/STOL and efficiency, hover, economics, noise, and downwash STOL aircraft are enormous. Large economic bene- characteristics. Generally, the lowest-gross- fits can accrue through the use of these types of ideight vehicle will have the most favorable eco- aircraft to provide rapid and flexible transpor- nomics and fuel efficiency. tation, which overcome the lack of suitable The potential applications are 1) coanmrter airport facilities and formidable geographic airlines, which include airport congestion relief barriers. At the same time, these aircraft can as a benefit where economics and noise are prime relieve congestion at regional airports, advanc- Factors; 2) tourism and "very important persons" ing the potential for unconstrained aviation transport, where economics, noise, and landing growth. In short, these aircraft hold the prom- surface preparation are important; 3) high-value ise to revolutionize short haul transportation. cargo, where speed and range are factors; The tilt-rotor design is closest to readi- 4) resource development, including fishing, high- ness For civil applications because of the timely grade mining and oil: 5) developing-region util- development of the V-22 For military use. How- ity vehicle; and 6) public service, which ever, if planners develop an integrated transpor- includes public safety-law enforcement, where tation system utilizing the capabilities of the noise is important, air ambulance, Fire fighting, V/STOL and STOL aircraft described, several of and disaster relief. the aircraft designs could be operational within By integrating these Factors with the V/STOL a decade (providing a strong conrmitment was made configuration performance and operating charac- by the public and private sectors). teristics, potential applications For the.various Finally, a future scenario is described. An designs were determined (Table 1). The compound airport of the future ts shown in Fig. 46. The ABC, tilt rotor, tilt-wing, and X-wing aircraft year is 2015. An "Orient Express" hypersonic are best suited to commuter airline service. The cruise aircraft is transporting passengers and lift-cruise fan was excluded because of high high-value cargo from Japan in less than 3 hr to downwash. Tourism appears especially attractive a remote super hub airport in the California for the compound ABC, tilt rotor, and X-wing, desert. From here, in addition to the Orient because of the requirement of landing on lesser Express aircraft and conventional CTOL aircraft, prepared surfaces. All designs may be suitable V/STOL and STOL aircraft are operating. These for high-value-cargo and resource development, latter aircraft are enabling the airports to be and as developing-region utility vehicles. The uncongested, to readily accept future growth, and particular vehicle selected would depend on the to provide rapid point-to-point transportation speed, range, and hover requirements. Public from the most densely populated regions through service missions (public safety and law enforce- the most inaccessible regions. Each of the air- ment, air ambulance, fire fighting, and disaster craft configurations described has its merits. relief) are currently being performed primarily Examples of the application of these configura- by helicopters. Public service/law enforcement tions are as follows. The compound ABC helicop- and air ambulance missions greatly Favor the lou- ter carries critical parts to a high technology disk loading, shorter-range vehicles--ABC, tilt computer plant in Orange County. The tilt rotor rotor, and X-wing because of hover require- provides transportation to the Los Angeles cen- ments. In addition to the low-disk loading tral business district. The X-wing rapidly vehicles, the tilt wing, and lift-cruise fan can transports urgently needed medical supplies to a be used For fire Fighting in place of the fixed- New Mexico Indian Reservation. The tilt wing wing aircraft used today--primarily for dispers- transports tourists to Santa Catalina Island. ing fire retardant to contain Fires. Also, all The tilt nacelle delivers an urgently needed part configurations could be utilized for relief in For a Pacific Ocean mining operation off northern cases of man-made and natural disasters. California. Finally, the STOL aircraft trans- If a STOL runway is available and hover is ports businessmen to San Diego. not a requirement, the STOL vehicle has the many We recommend that a detailed study be ini- potential applications shown in Table 1, espe- tiated to evaluate these promising configurations cially if a larger size vehicle is desired. All in order to determine one or two configurations of the described applications are transportation that should be considered for development for opportunities for STOL aircraft. civil applications. The study should include total transportation system cost trade-offs. Some day, civil V/STOL and STOL configurations will be operational realities.

11 REFERENCES 11. Ruddell, A. J., et al., "XH-59A ABC 1. Cobetz, F. W., Assarabowski, F. W., and Technology Demonstrator Envelope Expansion and LeShane, A. A., "Applications of Advanced Operational Tests," U. S. Army Aviation Research Transport Aircraft in Developing Countries," and Development Command TR-81-D-35, NASA CR- 145343, 1978. Fort Eustis, VA, Dec. 1981. 2. Albers, J. A. and Zuk, J., "V/STOL 12. Linden, A. W. and Biggers, J. C., Aircraft Configurations and Opportunities in the "X-Wing Potential for Navy Applications," 41st Pacific Basin," SAE Paper 872-403, Nov. 1987. Annual Forum of the American Helicopter Society, 3. Hard, John F., "Rotorcraft Research - A Fort Worth, Texas, May 15-17, 1985, pp. 435-450. National Effort," The 1986 Alexander Nikolsky 13. Nelms, W. P. and Anderson, S. B., Honorary Lectureship, Journal of the American "V/STOL Concepts in the United States, Past, Helicopter Society, Vol. 32, No. 2, Apr. 1987. Present. and Future," Paper in ACARD-R-710, Spe- 4. Brieger, J. T., Maisel, M. D., and cial Course on V/STOL Aerodynamics, Apr. 1984. Cerdes, R., "External Evaluation of the XV-15 14. Lindenbaum, B., "V/STOL Concepts and Tilt Rotor Aircraft ," Paper No. B-87-SW-32-DO00, Development Aircraft. Vol. I - A Historical Annual National Forum of the American Helicopter Report (1940-86)," Air Force Wright Aeronautical Society, Arlington, Texas, Feb. 1987. Laboratories TR-86-307 1 , Vol . I, Nov. 1986. 5. "Civil Tilt Rotor Missions and Applica- 15. Cambucci, B. J., Aoyagi, K., and Rolls, tions: A Research Study," NASA CR-177452, Jul. L. S., "Wind Tunnel Investigation of a Large- 1987. Scale Model of a Lift-Cruise Fan V/STOL Aircraft 6. Johnson, W., Lau, B. H., and Bowles, with Extended Lift-Cruise Nacelles,'t J. V., "Calculated Performance, Stability, and NASA THX-73164, 1976. Maneuverability of High Speed Tilting Proprotor 16. Lehman, C. and Crafa, V., "Nacelle Aircraft," Vertica, Vol. 11, No. 112, 1987, Design for Crunman Design 698, V/STOL," SAE pp. 317-339. Paper 831492, Oct. 1983. 7. McArdle, J. C. and Wenzel, L. M., 17. Wilson, S. B., Bowles, J. V., and "Experimental Program for the Evaluation of Foster, J. D., "Analysis of Selected VTOL Con- Turbofan/Turboshaft Conversions Technology,'' cepts for a Civil Transport Mission," AIAA NASA TH-82988, 1982. Paper 81-2655, 1981. 8. Eisenberg, J. D. and Boules, J. V., 18. Cuigley, H. C., Innis, R. C., and "Folding Tilt-Rotor Demonstration Feasibility Crossmith, S., "A Flight Investigation of the Study," Paper No. 06-01, Vol. 2, Annual National STOL Characteristics of an Augmented Jet Flap Forum of the American Helicopter Society, STOL Research Aircraft," NASA THX-62,334, May Washington, D.C., 1986. 1974. 9. Carlson, R. H., Donham, R. E., Blay, 19. Cochran, J. A., Riddle, D. W., and R. A., and Codfrey, D. W., "Extending Helicopter Youth, S., "Application of Advanced Upper Surface Speed Performance, Lockheed Horizons, Issue 6, Blowing Propulsive-Lift Technology," SAE July 1967. Paper 820956, Aug. 1982. :O. Fradenburgh, E. A., nApplication of a 20. Kohlman, D. L., "Introduction to V/STOL Variable Diameter Rotor System to Advanced VTOL Airplanes," Iowa State University Press, Ames, Aircraft," Paper No. 913, Annual National Forum Iowa, 1981. of the American Helicopter Society, Washington, D.C., 1975.

12 Table Civil Applications of Configurations

Configurations and Range

Compound LifWCruise ABC Tilt Rotor X-Wing Tilt Wing Fan STOL Application 300 n. mi. 600 n. mi. 1000 n. mi. 600 n. mi. 1800 n. mi. 3000 n. mi.

Connnuter (Airport Congestion Relief) , X X X X X

Tourism/VIP X X X

High Value Cargo X X X X X X

Resource Development Fishing X X X X X X High Grade Mining X X X X X X Oil X X X X X X

Developing Region Utility Vehicle X X X X X X

Public Service Public Safety/ Law Enforcement X X X Air Ambulance X X X Fire Fighting X X X X X X Disaster Relief X X X X X X (a) SEAPORT (b) RAILWAY PORT

(c) FREEWAY PORT (d) REMOTE HELIPORT

Fig. 1 Potential V/STOL landing facilities.

VECTORED THRUST

N 1000 -5r 9 0- t 100 0 COMPOUND sa y 10 2 STOPPED, FOLDED, 0 HELICOPTER STOWED 1 I 0 100 200 300 400 500 600 AIRSPEED, knots

Fig. 2 Airport expanded operations. Fig. 3 Disk loading versus speed.

14 CENTERLINE I

I BELL 222A

I !""In / XV-15 \ e RIGHT I LEFT --L ''=r SIDELINE SIDELINE 1000 500 0 500 1000 SIDELINE DISTANCE, h TRIW(IITI0N Fig. 6 XV-15 sound-level comparisons.

Fig. 4 XV-15 tilt rotor research aircraft.

'ROP

-1 400 AIRSPEED, knots

Fig. 5 XV-15 envelope comparison.

b) Fig. 7 civil tilt-rotor configurations. a) 1 +passenger ; b 1 39-paSSenger.

15 1

24

------7 I I SHORT TAKEOFF I ‘I I ,VERTICAL I v) I a TAKEOFF I %8 (ONE ENGINE I INOPERATIVE) I 40 \ I I -L 200 400 600 800 1000 1200 -1400 1600 ‘:t RANGE, nmi.

Fig. 8 Pay1.oad-range for 19-passenger civil tilt rotor.

(C) Fig. 9 Folding tilt rotor in 40- by 80-ft wind tunnel. (a) FJily extended: (b) partially extended; (c) completely folded.

16 QRPGINAL PAGE I!3 OF POOR QUALITY Fig. 10 Folding tilt rotor configuration.

Fig. 12 Full scale stopped rotor.

CLUTCH \

/ EXHAUST VARIABLE NOZZLE PITCH FAN

Fig. 11 Convertible engine schematic.

Fig. 13 Full scale fully folded rotor.

17 ABC

LA W s .12 :I HELICOPTER \

I I I 0 .6 1.2 0 50 100 150 200 250 ADVANCE RATIO AIRSPEED, knots

Fig. 14 ABC lift characteristics. Fig. 16 ABC flight envelope.

Fig. 15 Compound advancing blade concept (ABC) Fig. 17 Compound ABC civil aircraft research aircraft. configuration. ROTARY-WING MODE CONVERSION MODE

U I 150-200 knots 200300 knots 0-150 knots

Fig. 18 X-wing flight modes.

Fig. 19 RSRA/X-wing aircraft. Fig. 20 X-wing civil aircraft configuration.

19 Fig. 21 Lift-cruise fan full-scale model.

HI GH-BY PASS TURBOFAN \

W STRAKES

Fig. 22 Tilt nacelle aircraft schematic. Fig. 23 Tilt nacelle full-scale model.

20 Fig. 24 Artist's conception of a civil tilt- Fig. 26 Tilt wing research aircraft (XC-142A). nacelle aircraft.

TAI L-PROPELLER SHAFTING TAI L-PROPE LLE R zoool CLUTCH AND BRAKE AI

TAKEOFF U 5 1000 1000 Ib RESERVE H/ I FUEL

GEARCASE

0 250 500 750 1000 GEARCASE AND CLUTCH RANGE, nmi. (AFT OF EACH PROPELLER)

Fig. 25 Tilt nacelle payload-range. Fig. 27 Tilt wing aircraft schematic.

21 I 1 I I 0 100 200 300 400 AIRSPEED, knots

Fig. 28 Tilt wing flight envelope. Fig. 30 High-speed STOL designs.

Fig. 29 V/STOL research aircraft (YAV-8B). Fig. 31 Augmentor-Wing Research Aircraft.

22 DUCT AND NOZZLE

APPROACH LANDING 10- 7 \-- STOL (CERA) z 8-- FLAP HINGE POINT - QSRA TOUCHDOWN

TOUCHDOWN CHOKE

-6 -5 -4 -3 -2 -1 0 1 2 3 4 APPROACH AND LANDING DISTANCE, ft x 10-3 Fig. 32 Augmentor wing duct assembly. Fig. 35 Landing performance.

EXHAUST AIR TURNING DUE TO COANDA EFFECT

CERA (SCALED TO MEDIUM CTOL TRANSPORT SIZE) MEDIUM TRANSPORT 6: \ FORWARD THRUST 90-EPNdB FOOTPRINTS

Fig. 33 Upper surface blowing. Fig. 36 Noise footprints comparison.

Fig. 34 Quiet STOL Research Aircraft (QSRA). Fig. 37 Asuka aircraft.

23 VECTOR ED 12 TRUST 40 1 a / FAN f COMPOUND & STOPPED ROTOR Be a Y .2 a TILT WING 24 f I- LIFTlCRUlSE FAN VECTORED TILT1 WING I C , 1 I I 10 100 1000 10,Ooo 0 100 200 300 400 500 600 DISK LOADING, Ib/f? AIRSPEED, knots

Fig. 38 Hover efficiency comparison. Fig. 41 Flight envelopes of high-disk loading aircraft. m VECTOR ED loo0 .-E THRUST .E 0 8W VECTORED a* THRUST Y> ROTORS s6oa ZI LIFT/CRUISE z COMPOUND FAN L - TILT Y '400 HELICOPTER 0 3 \ ROTOR STOPPED. p 110 Y a Y; 200~e2.:g~~ ROTOR 0 3 I- U o o on 0 100 200 300 400 500 600 Y "-3 30 300 3000 30,000 AIRSPEED, knots E DISK LOADING, lb/ft2 Fig. 39 Fuel required in hover. Fig. 42 Noise comparisons.

BOUNDARY LAYER STOPPED, FOLDED, THICKNESS 6 AT 100 ft STOWED ROTOR HELICOPTER - 8.0 ft 40- 'h TILT WING - 3.5 ft 7 +VI-- LIFT/CRUISE FAN - 1.1 ft 0 VECTORED THRUST - 0.7 ft x 30 - Y .cr

13 U E 20 LIFT/CRUISE i TILT WING HELICOPTER, COMPOUND, AND TILT ROTOR I 0 100 200 300 400 500 0 50 100 150 200 AIRSPEED, knots DISTANCE FROM CENTER OF WWNWASH PATTERN, ft

Fig. 40 Flight envelopes of low-disk loading Fig. 43 Downwash comparisons. aircraft. 120 -

110 -

8o r m loo- k 90- X 80- I-- =!? 70- W E 60- v) g 50- Q z 40- 0 - 30- = 20- 10 -

TILT LI OL HELICOPTER ABC TILT ROTOR CRUISE FAN CONFIGURATION CONFIGURATION

Fig. 44 Analysis comparisonn for 300-mile search Fig. 45 Analysis comparison for 800-mile and rescue mission. transport mission.

r, \i

Fig. 46 Airport of the future.

25 ~~~ ~~ ~~ Report Documentation Page

____..- 1. Report No. 2. Government Accession No. 3. Recipierit’s Catalog No.

TM-100035 NASA .__-. - . - 5. Report Date

October 1987 -- __- _. Civil Applications of High-speed Rotorcraft and 6. Perforniirig Organization Code Powered-Lift Aircraft Configurations

-______._ - . -.-. 7. Authorlsl 8. Performing Organization Rep011 No.

James A. Albers and John Zuk A-8339-______- 10. Work Unit No. 505-6 1-5 1 9. Performing Organization Name and Address -- - 11. Contract or Grant No. Ames Research Center 94035-5000 Moffett Field, CA - - __ .. .. - - . 13. Type of Report atid Period Covered 12. Sponsoring Agency Name and Address Technical Memorandum National Aeronautics and Space Administration 14. Sponsoring Agency Code Washington, DC 20546-0001

15. Supplementary Notes Point of Contact: James A. Albers, Ames Research Center, M/S 200-3, Moffett Field, CA 94035-5000 (415) 694-5070 or FTS 464-5070

16. Abstract . Advanced subsonic vertical and short takeoff and landing (V/STOL) air- craft configurations offer new transportation options for civil applica- tions. This paper describes a range of vehicles from low-disk to high-disk loading aircraft, including high-speed rotorcraft, V/STOL aircraft, and short takeoff and landing (STOL) aircraft. The status and advantages of the various configurations are described. Some of these configurations show promise for relieving congestion in high population-density regions and providing trans- portation opportunities for low population-density regions.

17. Key Words (Suggested by Auttiorlsll 18. Distribution Statement V/STOl aircraft configuration Unclassified-Unlimited STOL aircraft configuration Transportation options Civil applications- Subject Category - 03

19. Security Classif. (of this report1 20. Security Classif. (of this pagel 21. No. of pages 22. Price

Unclassified Unclassified 27 A03