Type: skew-wing research aircraft
Powerplant: 2 x 220 lbs.* small turbojet engines (*at sea level)
First flight: December 21, 1979
The NASA/Ames AD-1 (Ames standing for the Ames Industrial company, and AD standing for NASA's Ames-Dryden facility) was a research aircraft designed to investigate the concept of an oblique (or pivoting) wing. The wing could be rotated on its center pivot, so that it could be set at its most efficient angle for the speed at which the aircraft was flying. NASA Ames Research Center Aeronautical Engineer Robert T. Jones conceived the idea of an oblique wing. His wind tunnel studies at Ames (Moffett Field, CA) indicated that an oblique wing design on a supersonic transport might achieve twice the fuel economy of an aircraft with conventional wings.
The AD-1 started as an unsolicited proposal by Rutan Aircraft Factory to NASA in December '75. The oblique wing on the AD-1 pivoted about the fuselage, remaining perpendicular to it during slow flight and rotating to angles of up to 60 degrees as aircraft speed increased. Analytical and wind tunnel studies that Jones conducted at Ames indicated that a transport-sized oblique-wing aircraft flying at speeds of up to Mach 1.4 (1.4 times the speed of sound) would have substantially better aerodynamic performance than aircraft with conventional wings.
The AD-1 structure allowed the project to complete all of its technical objectives. The type of low-speed, low-cost vehicle - as expected - exhibited aeroelastic and pitch-roll-coupling effects that contributed to poor handling at sweep angles above 45 degrees. The fiberglass structure limited the wing stiffness that would have improved the handling qualities. Thus, after completion of the AD-1 project, there was still a need for a transonic oblique-wing research aircraft to assess the effects of compressibility, evaluate a more representative structure, and analyze flight performance at transonic speeds (those on either side of the speed of sound).
The RAF provided the detailed design and loads analysis for the AD-1. As early as December 1976, Rutan Aircraft Factory wrote on the fact they had "completed the detail design of a research airplane for N.A.S.A. utilizing VariEze technology. The N.A.S.A. airplane is a small, one-pilot test vehicle that is intended to test the handling characteristics of a future (1990's) yawed-wing airliner." NASA specified the design based on a geometric configuration provided by the Boeing company. It is interesting to note that Rutan's company later described the AD-1 as "a 15%-size manned, flying model of a Boeing-designed transonic airliner".
RAF did the detailed design of the AD-1 (dubbed the "Skew Wing" or "Scissor Wing") between May 76 and Feb 77 under a $12,000 contract. Ames Industrial Corp. (AIC), of Bohemia, Long Island (N.Y.), won the construction contract and started construction in December 77, under a $240,000 fixed-price contract. The AD-1 was the first non-homebuilt aircraft to use the structural methods developed for the VariEze. In fact, its entire structure was basically similar to a VariEze, with about the same diameter, but was 38.8 feet long and 6.75 feet high with a wing span of 32.3 feet, unswept. It was constructed of plastic reinforced with fiberglass and weighed 1,450 pounds, empty. The vehicle was powered by two small turbojet engines, each producing 220 pounds of thrust at sea level. Due to safety concerns, the aircraft was limited to speeds of 170 mph.
Ames built the AD-1 "on-cost" and "on- schedule", for a total contract cost of $239,000. Until that time, the aircraft industry did not believe it was possible to design and build a manned, skew-wing, twin-jet research aircraft for less than several million dollars. "It is interesting to note that the total work done by RAF and AIC was done at a profit and at far less cost to the taxpayer than the NASA tasks of overseeing the contractors and doing a simulation!" commented Rutan in 1979. "While we expect the AD-1 to provide the basic subsonic skew-wing stability data it was built to provide, we expect its major impact will be that it is possible for the government research agencies to procure a truly low-cost aircraft, working with a small contractor and employing the moldless composite construction similar to the VariEze."
The aircraft was delivered to the Dryden Flight Research Center, Edwards, CA, in February 79 and immediately began taxi tests, including a static load test. The first flight was on December 21, 1979. Piloting the aircraft on that flight, as well as on its last flight on August 7, 1982, was NASA Research Pilot Thomas C. McMurtry. The AD-1 flew a total of 79 times during the research program.
Although the Boeing airliner project has been forgotten, the AD-1 will forever endure as a true-to-form Rutan design and a milestone in aviation research. Another little-known fact is that at some point, Julian Wolkovitch had a contract to modify the AD-1 into a joined wing aircraft, but when he died, this project died with him. The AD-1 now hangs in the Hiller Aviation Museum in San Carlos, California.
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