PREPARED STATEMENT OF GERALD G. KAYTEN, ACTING DIRECTOR, STOL TECHNOLOGY OFFICE, OFFICE OF ADVANCED RESEARCH AND TECHNOLOGY, NATIONAL AERONAUTICS AND SPACE ADMINISTRATION Mr. Chairman and Members of the Committee, short take-off and landing (STOL) capability is essential to the development of effective short-haul air transport systems and highly desirable for improvement of long-haul systems. In recognition of its statutory responsibility in aircraft technology, NASA plans to initiate in FY 1972 a multilateral Government/industry cooperative program to develop an experimental STOL aircraft. Coordinated planning activities with the concerned Government agencies have been in progress during the past year; discussions with industry are currently under way. Air transport has not proven an ideal mode for short trips, although it has been most effective for long-haul traffic. Nevertheless, numerous analytical studies have shown that effective short-haul air transportation (stage lengths up to 500 miles) represents both necessity and promise for the future. The importance of the short-haul segment of the national transportation picture can be illustrated by considering that over 10 billion short-haul passenger miles were flown in 1970 alone. It has been shown that STOL capability is essential to the short-haul class of civil transport, primarily for high density areas. After two years of hearings and study regarding air transportation in the Northeast Corridor, the Civil Aeronautics Board determined in September 1970 that a properly implemented "metroflight" service is needed based on a STOL or V/STOL system. The Board found that such a system is economically feasible and will fill a pressing need to reduce air terminal congestion and delay, and to improve the quality of service in the Northeast Corridor, and, in fact, generally throughout the United States. When considering the total air transportation system for passenger service and air freight. the availability of airports generally suitable for STOL operation is significant. This is illustrated in Figure 1, where runway length distribution of 9,400 airports in the United States is plotted. A STOL system capable of operating from 1,500-foot runways and unobstrusive with respect to noise and pollution could use approximately 90 percent of the available airports in the country, whereas a conventional take-off and landing aircraft (CTOL) requiring 7,000 feet can use only 10 percent of the same airports. In the New York area alone, within a one-hundred-mile radius of the city, there are roughly 400 airports capable of meeting a 1,500-foot STOL requirement. A significant benefit of STOL operation lies in its potential for reducing the effects of aircraft noise on the community. A plot of 95 EPNdB noise contours around two representative airports of the CTOL and STOL class is shown in Figure 2. Everything inside the contour receives 95 EPNdB or greater for take-off and landing-in one case for a Boeing 727, and in the second case for a STOL machine using a 1,500-foot runway. The STOL aircraft, with its capability to climb and descend more steeply, permits confinement of the noise produced to a considerably smaller area. It is anticipated that STOL aircraft will approach the runway at a 7.5 degree angle, for instance, while the 727 approach is 2.9 degrees. Thus, STOL operation at conventional airports will alleviate the current noise problem to a significant degree. The steep-path capability can also be advantageous for reduction of terminal airspace requirements and relief of congestion. Studies are in progress to determine the degree to which STOL technology can be applied to conventional long-haul transports to achieve these potential benefits. For later introduction of STOL service closer to centers of population for more effective short-haul transportation, a further reduction in generated noise is required. This noise reduction is a primary objective of NASA's STOL research. The sideline noise of a 727 at a distance of 500 feet is 119 EPNdB. The goal for STOL operation is a sideline noise level of 95 EPNdB at 500 feet, an appreciable reduction over the CTOL aircraft. The chief obstacle to the development of a STOL system has been a cycle of inaction among aircraft manufacturers, air carriers, and local authorities. Aircraft manufacturers have been reluctant to assume the risk of vehicle development without air carrier orders and some assurance of Government certification of the vehicles. The air carriers have been reluctant to place aircraft orders without assurance of the appropriate airport and airways system to accommodate such service. Local authorities have been reluctant to provide airports because of public reaction to aircraft noise and the inability to see the real advantages of the system without an existing vehicle. The nature of the problem requires Government leadership to accelerate the solution. This leadership must take the form of DOT STOL systems studies and establishment of certification criteria; continuation of CAB public hearings leading to route and air carrier assignments, especially in the Northeast Corridor; and the conduct of a technology program upon which the eventual development of an effective, economical, and environmentally acceptable STOL transport aircraft can be based. Because of its traditional role in aeronautics, NASA has undertaken the responsibility for providing the technology for the STOL aircraft development. NASA research over the past 15 years has identified several promising technical approaches suitable for application to commercial STOL transports. Although reduction in field-length requirements can be realized by various combinations of high-lift aerodynamic devices and increases in thrust-to-weight ratio, the more advanced STOL concepts depend on the principle of using propulsion system air flow to augment the wing lift. Representative powered-lift concepts that have been tested are shown in Figure 3. With the externally-blown jet flap, the jet exhaust flow is deflected by the flap and thus produces lift due to the downward thrust; in addition, an appreciable lift increment is derived from the increased air flow induced over the flapped section. The effectiveness of the blown flap is enhanced by the use of moderate wing sweep, which allows spreading of the flow along the flap span. With internally-blown systems, high-pressure bypass air from the jet engine is ducted into a plenum inside the airfoil. The air from the plenum is directed over the flap to create the same effect as the externally-blown flap, except this time the flow is ducted along the entire trailing edge of the wing and thus works over the whole wing area. The augmentor wing concept is a refined internally-blown system in which the jet flow is further augmented by an induced secondary flow of air drawn from the upper surface of the wing. One fundamental relationship that governs the performance of any aircraft is the wing loading factor. Wing loading, measured as weight of the aircraft divided by wing surface, has a direct relationship to runway length, with runway requirements increasing as wing loading increases. Increased wing loading, however, is dictated for reasons of cruise efficiency, economy, flight speed, and passenger comfort. Figure 4 relates the runway length to the wing loading of the aircraft. These curves indicate that without power-augmented lift, short runway lengths can be obtained only at the expense of reduced wing loading— hence, reduced efficiency and reduced passenger comfort. The Ford tri-motor, for example, could get off the ground in 1,200 feet; however, it had a wing 'loading of 16 pounds per square foot, compared with about 100 pounds per square foot for present-day jets. Present-day STOL aircraft (shown as triangles) have wing loadings below 45 pounds per square foot. The shaded area indicates the target range of wing loading and runway length for effective STOL transports. The externally-blown flap and the augmentor wing are two powered-lift STOL systems capable of achieving such performance. A significant amount of basic research on these STOL approaches has been completed. Analytical studies have been performed along with cost studies; wind-tunnel tests have been conducted; simulator studies have been performed; and flight tests on selected numbers of components and systems have been performed and continue to be performed. The major problems and questions that remain now to be solved involve dynamic behavior and cannot be addressed in model tests and flight simulations. These remaining questions will require largescale flight research on representative experimental aircraft as a prerequisite to their solution. An experimental aircraft flight program is planned to validate the technology for turbofan STOL transport development to provide the baseline information needed for establishment of certification and operational criteria and to provide essential data relative to STOL transport avionics and subsystem requirements. The flight program will provide verification of analytical and smallscale experimental data, particularly with respect to dynamic conditions. It will permit the determination of performance and safety margins, and the evaluation of propulsive lift control and engine-out control, low-speed stability and control, flight path and touchdown dispersion, cross-wind and wind-shear effects, and the gust response of a STOL aircraft. The experimental aircraft will produce essential baseline information on STOL handling qualities, terminal navigation, and guidance. Most importantly, the program will permit investigation of noise profiles and effectiveness of noise alleviation techniques. The planned experimental STOL aircraft program will provide a foundation of technology upon which Government and industry can base the development of operational STOL systems. The proposed experimental vehicle and the flight research program are critically needed now because of the extensive development period which necessarily precedes the introduction of a new transport system. Several STOL concepts are being considered for use in the experimental aircraft design, with particular emphasis on the externally-blown flap and the augmentor wing. The augmentor wing has been the subject of the research program discussed in the V/STOL Aircraft section of the Aerodynamics and Vehicle Systems statement; it offers potentially greater STOL performance and some promising avenues for noise reduction, at the cost of additional mechanical complexity and technical development. The blown-flap concept represents the smallest departure from conventional aircraft design. It is mechanically less complex and has the added advantage of being adaptable in the experimental aircraft size to available high bypass engines. As established by extensive wind-tunnel development, the blown-flap performance is adequately representative of turbofan powered-lift transport operation. The experimental aircraft program for STOL transport technology development is planned as a four-pronged activity. The basic wind-tunnel and simulator tests will be continued, together with the analytical studies; an airframe development will be initiated along lines currently being determined in discussions with the airframe industry. A quiet STOL propulsion system study will be continued and an engine development undertaken when substantiated by the studies. Finally, flight testing of the aircraft will be conducted, to be followed by retrofit of a quiet propulsion system. A tentative schedule of the program is shown in Figure 5. The additional tunnel and simulator testing will be on a selected basis as required to support the aircraft development. Large-scale tunnel tests will be performed on the final aircraft configuration for safety-of-flight and correlation purposes. Flight simulation will be required to determine optimum cockpit displays to evaluate control systems and to measure ground effects. Some of this effort has been initiated in FY 1971 and will continue in FY 1972. The aircraft development will be initiated in FY 1972. Two airplanes will be EXPERIMENTAL STOL VEHICLE |