First oblique-wing aircraft

The first piloted oblique-wing aircraft was the NASA AD-1, which made its maiden flight, piloted by Thomas C. McMurtry (USA), on 21 December 1979. The 11.8-m-long (38-ft 8-in) aircraft had a single wing joined to the fuselage by a pivot in the centre. For take-off and landing, the wing would be at a 90-degree angle to the fuselage – like a conventional wing – but once in flight it could be tilted up to 60 degrees, meaning that the wing would be swept forward on one side of the plane and swept backward on the other.

Oblique-wing aircraft have several theoretical advantages over fixed-wing, delta-wing, and variable-sweep designs. These include better low-speed performance, low weight (compared with variable-sweep designs) and lower wave-drag at supersonic speeds.

Richard Vogt of Blohm & Voss was the first to come up with an oblique-wing aircraft design: the B&V P202, which he proposed to the German Air Ministry in 1942. Two years later, Woldemar Voigt at Messerschmitt produced his own design: an oblique-wing biplane known as the P.1109. Neither of these projects are known to have moved beyond the design stage, however, and were certainly never made into actual aircraft.

Work began on oblique-wing research in the US around 1946, but the idea was soon shelved in favour of more aerodynamically straightforward variable-sweep designs. NASA researcher Robert Jones continued to work on the concept on and off, however, and by the mid 1970s had persuaded his superiors to fund the construction of a prototype.

The AD-1 was designed and built by the Ames Industrial Corporation, with design input from Boeing and Rutan Aerospace. It was flown a total of 79 times between 1979 and 1982, but the results from the test programme were not particularly encouraging.

Using the industry-standard Cooper-Harper rating system, pilots rated the aircraft's performance at between 3 ("Fair: Minimal pilot compensation required for desired performance") and 8 ("Major Deficiencies: Considerable pilot compensation required for control"), depending on the wing-sweep angle and manoeuvres attempted. The pilots found that increasing the sweep made the aircraft more unstable, and that right-turning manoeuvres (towards the forward-swept wing) were more difficult than left-turning manoeuvres.

Today the AD-1 is on display at the Hiller Aviation Museum in San Carlos, California. The oblique-wing concept has been revived in recent years for military drone designs, but no further prototypes are known to have been made.