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COMPETITIVE ASSESSMENT OF TECHNOLOGY 114 European industry use of primary composite structures has begun in military applications. Composites are also used for the pod for the Rolls Royce RB211 engine and for helicopter rotor blades and rotor heads. Composite research and development in Europe is now concentrated on ways to speed the production process and reduce costs through automation and other methods, as well as on postproduction testing and quality control. This indicates that Airbus will continue to be very aggressive in the application of composites to future aircraft, and given the moderate pace of the current NASA program and the budget pressures it is encountering, Airbus may take the lead in this very important technology. In application of advanced structures to general aviation and regional aircraft, the United States is judged to have an advantage; however, in rotorcraft our position is regarded as no more than equal to that of foreign competitorsâ especially France. Propulsion Integration Propulsion integration of powerplant with wing or fuselage is a relatively mature art for conventional turbofan-powered aircraft. The United States and Europe are regarded as comparable. Analytical techniques are helping to optimize the location of engine nacelles relative to the wing for wing-mounted turbofan installations. Both U.S.- and British-designed nacelles have been applied to U.S. aircraft. The British nacelles show a slight advantage due primarily to shorter engine length. However, competitive nacelle technology is judged about equal. Integration of the propulsion system with the airframe becomes extremely important when high-speed turboprop, powerplants or propfans are used. This advanced technology is widely regarded, both in the U.S. and elsewhere, as holding great promise for improved fuel efficiency. It is especially applicable to general aviation aircraft and regional aircraft. As advanced turboprops exceed M = 0.70 (the region now being contemplated) interference drag becomes exceedingly critical, as do inlet recovery, flow distortion, and interference problems. Mathematical analyses of these complex three-dimensional flow fields are under way, but extensive wind tunnel and flight testing are required to verify and calibrate these analytical models before design decisions can be made. Advanced turboprops also have to contend with high-decibel, and poorly understood, acoustic problems. Analytical models of propeller noise require full- scale flight test data for confirmation. Once propeller acoustic characteristics are understood, methods of minimizing noise and vibration in the passenger cabin must be developed and substantiated.
COMPETITIVE ASSESSMENT OF TECHNOLOGY 115 The development of advanced propellers and their gearboxes, or systems that eliminate the need for gearboxes, is central to incorporation of propfans and advanced transports. Aerodynamic performance of propfans has already been substantiated by tests. Structural design of the thin, swept blades and contrarotating configuration necessary for the higher Mach-number operation has not yet been proven at full scale. Extensive research and development work needs to be done on all aspects of advanced propeller systems before design of advanced high-speed turboprop transports can proceed confidently. Current U.S. propfan R&D is largely limited to NASA-sponsored programs, which are not scheduled to complete demonstration of systems integration in aircraft flight tests until 1988, providing funds are allocated. That schedule will not permit U.S. propfan development to start until the early 1990s at best. The U.S. propfan program has concentrated on very high speed props (M = 0.8), and in that speed range the United States is probably ahead in technology. However, economic studies suggest this speed may be too high. At slower speeds (M = 0.7), the cost per seat-mile is substantially lower, and the Europeans may not be behind, having considerable experience at M = 0.5. The Airbus view of propfan technology would seem to indicate that it is wrestling with the same problems, and Airbus does not forecast an advanced propfan aircraft before the 1990s, if then. The French government has been sponsoring research into propfans for the last three years. How extensive this work is or what results have been achieved to date is not yet known. In rotorcraft the United States is regarded as an equal in propulsion integration. The United States has a substantial technological lead in an advanced version of rotorcraft, the tilt rotor. NASA and the Army have recently validated a new concept in rotorcraft technology having potentially significant civil applications. The XV-15 tilt-rotor, proof-of-concept vehicle has demonstrated that the characteristics and capabilities of turboprop airplanes can be blended with those of helicopters in a single aircraft. DOD has moved rapidly to capitalize on this configuration via the Joint Services Vertical Lift Aircraft Program (JVX), now in preliminary design. A civil derivative of the military JVX could yield a 30- to 40-passenger vertical-takeoff and-landing (VTOL) regional transport rotorcraft in the 35,000- to 45,000-pound gross weight class. The vehicle would be capable of cruising at speeds above 300 knots at altitudes of 25,000 to 30,000 feet over a range of 500 nautical miles. The aircraft would be a synthesis of advanced rotorcraft technology and the other technologies that have been noted.
