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Aviation History
1986
1986 - 1132.PDF
TECHNOLOGY Nasa backs joined wing RANCHO PALPS VERDES Nasa has awarded a $500,000, two-year contract to a small, California-based company to build and fly a "joined wing" demonstrator aircraft. ACA Industries will convert Nasa's AD-1 oblique-wing research aircraft to the new config uration for proof-of-concept flights beginning early in 1988. Significant savings in wing weight and useful reductions in drag are the principal advantages claimed for joined wing by ACA Industries presi dent Julian Wolkovitch, who holds one Canadian and two US patents on the design. In a joined-wing config uration the swept-back main wing is connected close to its tips to a swept-forward rear wing. Unlike previous such designs, the rear wing is mounted on top of the fin, and has marked anhedral, the resulting joined wing forming a diamond shape in both plan and front views—an essential feature of the design, says Wolkovitch. The rear wing supports the main wing, allowing wing box strength—and therefore weight—to be reduced. Inde pendent studies have shown a joined wing to be 30 to 40 per cent lighter than an aerodynamically equivalent cantilevered wing and tail, says Wolkovitch. The exact weight and drag benefits depend on the location of the wing join, which can be anywhere from 60 to 100 per cent of main wingspan. Tip-joined wings offer the lowest induced drag, acting like winglets to increase effective span, but allow only a 20 per cent weight saving. Wings joined at 60 per cent span are the lightest, but offer only marginally reduced induced drag. Conversion of the oblique- wing AD-1 to the joined-wing JW-1 will take 13 months. The JW-1 will test three • • - ' -~ •• mil • *i*afia ia^Bc % Summit Aircraft's Trident-3 joined-wing microlight was designed by ACA Industries configurations, first with a 40ft main wingspan and the wing joint at 24ft (60 per cent) wingspan. By using smaller tips, main wingspan will be reduced to 34ft, locating the joint at 80 per cent span. Finally removing the tips altogether for a 24ft overall span will produce a tip-joined configuration. Joined wing is a general concept applicable to a wide range of air vehicles from cruise missiles to transports, claims Wolkovitch. Other advantages claimed include a reduction in transonic drag through the smooth distribu tion of cross-sectional area possible with joined wing, and the possibility of using thin, high-aspect-ratio wing panels. With control surfaces on all wing panels, direct lift and sideforce control is possible. Wolkovitch patented his design in 1976, having built and flown a joined-wing hang- glider in 1974. The US Navy was the first to sponsor work on the concept, funding wind- tunnel tests by Rockwell of a joined-wing, submarine- launched cruise missile. ACA Industries later designed the Summit Aircraft Trident-3 microlight, the handling qualities of which were highly rated, says Wolkovitch. This latest Nasa contract has been awarded under the Small Business Innovation Research scheme, which Wolkovitch says bridges the gap between small companies with ideas, but no resources, and large companies with resources, but no ideas. Under the scheme small companies bid for $50,000 contracts to study the feasibility of their designs. They can then bid for $500,000 "Phase 2" con tracts allowing more detailed studies. To qualify for a Phase II contract, however, a company must have an under taking from a large industrial concern that the idea, if successful, will be put into production. In the case of joined wing, Wolkovitch has a letter from a "well-known" aircraft manu facturer stating that it is interested in joined wing and that it will develop the concept if flight demonstra tion proves successful. ACA will fly the JW-1 from Mojave Airport and flight-test objectives will be to demon strate satisfactory low-speed handling qualities and to gather data for comparison with results from com putational analyses and wind- tunnel tests of a joined-wing model. Joined wing is applicable to a wide range of air vehicles, including this business jet concept Big five get X-31 contracts WASHINGTON D.C. ~ Five major US companies have been chosen by the Department of Defence to undertake initial design work on the X-31 National Aero space Plane (Nasp). They are: Rockwell, Boeing, Lockheed, McDonnell Douglas, and General Dynamics. Contracts worth a total of $32 million will be shared among the five, and will cover extensive research into the necessary technologies, in cluding, for example, new thermal protection materials, active airframe cooling systems, and computational fluid dynamics. Propulsion studies are being carried out by Pratt & Whitney and Gen eral Electric, who are working on hydrogen-burn ing, supersonic-combustion "scramjet" engines that achieve near-orbital speeds in air-breathing mode, switching to rocket mode for orbital insertion. The Nasp programme is shared between the US Air Force, the US Navy, Nasa, the Defence Advanced Research Projects Agency, and the Strategic Defence Initiative Office. The programme is managed from Wright- Patterson Air Force Base, Ohio. In its current shape, a family of aerospaceplane vehicles are foreseen, that would be capable of numerous tasks ranging from rapid deployment of Defence Department payloads into low-Earth orbit, to trans- global passenger transport. The vehicle would be able to cruise within the upper atmo sphere at hypersonic speeds (Mach 12-Mach 25) or ascend directly into low-Earth orbit. The Nasp programme should lead to the construc tion of two flyable prototypes and one ground vehicle for testing in the mid-1990s. Little is being said at this point about how the programme might be affected by the virtual cessation of the US space programme after the Shuttle, Titan, and Delta losses. 40 FLIGHT INTERNATIONAL, 17 May 1986
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