PREPARED STATEMENT OF GERALD G. KAYTEN, DIRECTOR, SUPERCRITICAL TECHNOLOGY OFFICE, OFFICE OF ADVANCED RESEARCH AND TECHNOLOGY, NATIONAL AERONAUTICS AND SPACE

ADMINISTRATION

Mr. Chairman and Members of the Committee, in previous years, we have reported on the aerodynamic research that has produced the supercritical airfoil (Figure 1) and the supercritical wing concept which promise important improvements in transonic flight characteristics for both transport and combat aircraft. This work has progressed along several fronts during the past year and will, during FY 1972, be carried further toward productive practical application. The Supercritical Technology Program includes: further development of the supercritical wing concept; development of the related aerodynamic refinement and integration approaches required to permit realization of the supercritical wing performance potential; identification of compatible advances in other technical disciplines which, in combination with the supercritical aerodynamics, would provide the foundation for a superior new generation of aircraft; and definition of the technical development process required to assure achievement of the desired advances. The program is conducted in three major elements as indicated in Figures 2.

As was shown in last year's testimony (Figure 3), the supercritical wing, together with aerodynamic configuration refinement to minimize wave drag and local interference losses, can be utilized to delay the transonic drag rise and permit efficient transport cruise at very close to the speed of sound (Mach 1). In an alternative application, the concept can be employed, on commercial or military aircraft designed for moderate subsonic speeds, to permit the use of thicker wing sections, reduced sweep, or both-with the resulting benefit of significant reductions in structural weight. These potential gains be utilized directly for performance improvement, or they can be traded to compensate for the penalties associated with the imposition of more stringent environmental constraints such as noise and pollution reduction. For combat aircraft, the use of the supercritical wing to delay or eliminate shock-induced boundary-layer separation can permit the attainment of higher buffet-free lift coefficients (increased maneuverability) in the transonic regime.

During the past year, progress has been made in each of the program elements. In exploratory flight research, design and construction of a high-speed supercritical wing for flight testing on a Navy-furnished TF8-A airplane have been completed. The wing is being ground tested and fitted to the TF8-A airframe (Figure 4). Flight tests are scheduled to begin in the Spring of 1971. These tests will provide the first flight validation of the supercritical wing concept, as well as information on over-speed margins and off-design performance, and on the effects of manufacturing roughness and environmental conditions. During this period, studies will be conducted to determine the need for a follow-on project in which a more typical transport wing would be constructed to permit investigation of of the effects of transport-type aeroelastic structures, highlift devices, and lateral control provisions.

In a related program being conducted jointly with the Navy, a T-2C aircraft has been modified for tests of a "thick" supercritical wing. The T-2C aircraft with a conventional 12%-thick wing and with a 17% -thick supercritical wing are shown in Figure 5. The modified aircraft was flight tested and some early results are shown in Figure 6. On the left side of the figure is a plot of drag coefficient against Mach number showing, in fact, that in flight there was essentially no drag increase for the 17% supercritical wing. As indicated previously, the use of a supercritical airfoil section may greatly increase the buffet-free maneuverability of a combat airplane. This has been verified by the flight test data on the right side of Figure 6, where lift coefficient for buffet onset is shown plotted against Mach number. Although an increase in thickness is generally accompanied by a degradation in buffet boundary, the thicker supercritical wing in this instance shows a significant improvement in buffet-free maneuver capability throughout the design speed range. The T-2C testing is being continued to obtain additional data on handling qualities, boundary layer effects, and the influence of secondary design and construction variables.

Fundamental technology activity has been expanded, with initial emphasis on providing a base of aerodynamic data on two-dimensional wings and on wingbody combinations, and on establishment of improved analytical methods for

design and prediction of characteristics. The fundamental technology efforts are now being broadened to cover the other disciplines involved in the practical design of new aircraft incorporating the supercritical aerodynamics.

Systems studies have been initiated during this past year and will constitute a major portion of the activity in the coming year. Preliminary analysis of a near-sonic commercial transport has indicated that this high-speed application of supercritical technology may offer appreciable benefits in operational economy. A program of more intensive design and economic analyses is being initiated to study the influence, on long-range transport aircraft, of technology advances in propulsion, structures, materials, flight controls, and avionics in combination with supercritical aerodynamic advances. The objectives of the study program are: to identify the technology advances most likely to result in significant improvement in air transportation quality (i.e., safety, environmental acceptability, reliability, performance, and economy); to assess the state-of-readiness for the critical technology advances; and to define the additional research and development required to assure that the selected advances will be sufficiently mature for application to a superior next-generation subsonic long-range transportation system.

To provide valid aerodynamic data in support of the systems studies, windtunnel tests of a supercritical transport configuration (Figure 7) are being conducted and will be expanded in the coming year. As shown in Figure 8, the desired drag-rise delay for this near-sonic application of the supercritical aerodynamics has been achieved in the model tests. Variations in configuration parameters, some of which are shown in Figure 9, will be tested to provide additional data and facilitate design optimization. Additional supporting data will also be developed for advanced propulsion systems. Upon completion of the studies, a basis will have been established for definition of a program to develop by the late 1970's the advanced technology from which a superior new generation of U.S. air transports to the benefit of both the traveling and the nontraveling public can evolve.