The AD-1 is a uniquely designed aircraft by NASA featuring a long wing that rotates around a central point. It has undergone 79 test flights but was never produced for mass production.
Not many aircraft can claim to be one-of-a-kind, but NASA’s AD-1 is certainly among them. The fuselage resembles a slender, pointed cigar, with a single wing that rotates around a central axis, resulting in asymmetry during flight. No other manned aircraft has been built with such a rotating wing design. It flew 79 times during NASA’s research program from 1979 to 1982.
AD-1 oblique wing aircraft during test flight. (Photo: NASA).
The Oblique Wing Aircraft Concept
The unique aircraft concept known as the “oblique wing” originated in the 1940s, but it wasn’t until NASA’s project in the 1970s that the technology was put to the test.
The program demonstrated that the oblique wing concept has the potential to develop highly efficient supersonic passenger aircraft, as well as military applications. However, more than 40 years after the last test flight of the experimental aircraft, no other aircraft has followed suit.
The inventor of this concept, aerospace engineer Robert T. Jones from NASA’s Ames Research Center in California, was a pioneer who sought to challenge traditional conventions.
“One of the unwritten assumptions in aircraft design is bilateral or mirror symmetry,” he wrote in a 1972 scientific study on oblique wings. He acknowledged that the notion that a rotating wing would lead to better supersonic aircraft was surprising, but he hoped to prove the value of the new design.
Before constructing the AD-1, Jones tested a model in a wind tunnel. The results showed that supersonic oblique wing aircraft could save fuel twice as efficiently as traditional wings. They were also quieter during takeoff, producing a softer sonic boom, and had a greater operational range. With this promising data, Jones received funding to develop a full-scale prototype.
Motion of the AD-1 aircraft wing. (Photo: NASA).
Testing Process
At that time, the AD-1 was very inexpensive, with a total cost of only about $240,000, equivalent to less than $1 million today. The detailed design was created by renowned aerospace engineer Burt Rutan.
This single-seat aircraft is approximately 11.5 meters long and only 83.8 centimeters high. It appears quite “short” when standing on the ground due to its short landing gear, which is optimized to reduce drag. The aircraft operates using two small turbojet engines with a maximum speed of only about 320 km/h for safety reasons. Notably, the aircraft is very lightweight, with an empty weight of less than 680 kg, thanks to its fiberglass-reinforced plastic structure. The aircraft is not equipped with any hydraulic systems.
The rotating wing is attached to the fuselage, just in front of the engine, and is operated by electric motors activated by a switch in the cockpit. During takeoff and landing, the rotating wing remains in a neutral position or perpendicular to the fuselage. This component is only activated during flight.
The AD-1 prototype made its first flight on December 21, 1979, with NASA test pilot Thomas McMurtry. The maximum wing rotation angle of 60 degrees was achieved in April 1981. Subsequently, the aircraft continued to undergo testing for about another year.
All pilots involved in the program were required to provide evaluations. Overall, they found the performance of the AD-1 acceptable when the wing was swept to 50 degrees, close to the maximum. Some negative issues arose when exceeding that threshold, but NASA believed improvements could be made with more advanced materials and structures.
Robert T. Jones stands next to the AD-1 aircraft. (Photo: NASA)
Reasons for the “Retirement” of the Oblique Wing Aircraft
Boeing and Lockheed had conducted studies on potential supersonic passenger aircraft with oblique wing designs, preparing to manufacture one at the time the AD-1 was validated. One proposed aircraft was the Boeing 5-7, which would carry 190 passengers. This aircraft would utilize four turbofan engines and fly at a speed of Mach 1.2—faster than sound. It would be 87 meters long, with a wingspan of 61.5 meters in the neutral position, reducing to 40 meters when at maximum oblique angle.
However, the Boeing 5-7 remained just a concept on paper, like all other oblique wing aircraft aside from the AD-1. The AD-1 also made its final flight in 1982, over 40 years ago.
The reason was that the rotating wing was too mechanically complex compared to designing fixed wings specifically for supersonic speeds, accepting that the aircraft would be less efficient at subsonic speeds (below the speed of sound). For example, the aircraft could be equipped with delta wings which are triangular—similar to those on the supersonic Concorde—or simply straight wings optimized for faster-than-sound flight.
The AD-1 program demonstrated the potential of oblique wing aircraft, but it was not enough to entice experts to invest in this complex system, especially when modern designs made the oblique wing concept seem redundant. However, the data collected from the 79 test flights of the AD-1 was incredibly valuable and may prove useful again in the future.
