NASA AD-1
Experimental · USA · Cold War (1970–1991)
The NASA AD-1 (Ames-Dryden 1) was a small, single-seat experimental jet built in 1979 to test a single radical idea: an oblique wing — a single straight wing pivoted to slant across the fuselage, swung forward on one side and aft on the other. Designed by Burt Rutan and built by Ames Industrial Company at NASA's request, the AD-1 made 79 flights between 21 December 1979 and August 1982. The flight envelope reached a wing-pivot angle of 60° at speeds up to 200 knots, validating an idea NASA's Robert T. Jones had proposed in the 1950s but no aircraft had ever flown.
Aerodynamically the oblique wing has the same drag-reduction logic as variable sweep — high sweep delays shockwave formation at high speed, low sweep gives high lift at low speed — but the entire wing rotates as a single rigid piece, dispensing with the heavy and complex pivot mechanism that variable-sweep aircraft like the F-111 and F-14 need. In theory an oblique-wing supersonic transport could fly at Mach 1.4-2.0 with much lower drag than a fixed-sweep configuration. In practice the AD-1 revealed serious roll-pitch coupling at high pivot angles — when one wing leads and the other lags, the aircraft does not roll cleanly around its longitudinal axis.
The AD-1 was a small subsonic-only proof-of-concept aircraft — not the supersonic transport prototype the Robert Jones theory would require. Powered by two tiny Microturbo TRS 18-046 turbojets (220 lbf each) and weighing only 2,150 lb, it could not push past Mach 0.4 even at zero sweep. Burt Rutan kept costs minimal: the airframe was made of fibreglass-reinforced foam composite, and the cockpit instruments were borrowed from a Rutan VariEze. Total programme cost: USD$240,000. NASA pilots Tom McMurtry, Fitz Fulton, John Manke, Bill Dana, and Einar Enevoldson all flew the aircraft.
The AD-1's bottom-line finding was that oblique-wing roll-coupling at large sweep angles was severe enough to demand fly-by-wire stability augmentation that 1979 technology could not yet provide cheaply. NASA shelved the configuration after the AD-1's last flight; periodic interest has resurfaced (a NASA-Boeing oblique-wing supersonic-transport study in 1991, a small Kelly Aerospace concept in 2005) but no follow-on hardware has flown. The AD-1 is preserved at the Hiller Aviation Museum in San Carlos, California.
For Kids — a shorter, friendlier version
The NASA AD-1 was a strange experimental jet from 1979. It had one straight wing that could pivot across the body — slanting forward on one side and backward on the other. This is called an oblique wing.
The plane was designed by famous aircraft maker Burt Rutan. It was built by Ames Industrial Company at NASA's request. The AD-1 made 79 flights between December 1979 and August 1982.
The idea of the oblique wing came from a NASA scientist named Robert Jones in the 1950s. Jones thought a single wing that pivoted could give you the good parts of swept wings at high speed and the good parts of straight wings at low speed. The AD-1 was the first plane in the world to actually fly with an oblique wing.
The AD-1 was small and slow — only about 200 knots top speed. It is smaller than most fighter jets, at about 38 feet long. The wing could pivot up to 60 degrees in flight. The AD-1 program ended in 1982, and no full-size oblique-wing plane has ever been built.
Fun Facts
- The AD-1 had a single straight wing that could pivot across the body.
- It was designed by famous aircraft maker Burt Rutan.
- The AD-1 made 79 flights between December 1979 and August 1982.
- It was the first plane in the world to fly with an oblique wing.
- The wing could pivot up to 60 degrees in flight.
- The idea came from NASA scientist Robert Jones in the 1950s.
Kids’ Questions
Why an oblique wing?
At low speeds, a straight wing gives a lot of lift, perfect for takeoff and landing. At high speeds, a swept wing reduces drag. Most planes pick one shape or the other. An oblique wing pivots from straight to swept in flight, giving the plane the best of both worlds without complex variable-sweep machinery.
Why has no real oblique-wing plane been built?
An oblique-wing plane wobbles in odd ways that other planes do not. Pilots need very smart computer flight controls to fly one safely. By the time computers got good enough, the idea was no longer a priority for any country. The AD-1 proved the wing works, but no air force or airline has needed one badly enough to build a full-size version.
Variants
- AD-1 (NASA 805)
- Single airframe built. First flight 21 December 1979. 79 flights through August 1982. Wing pivot range 0°-60°, top speed Mach 0.4. Preserved at the Hiller Aviation Museum, San Carlos, CA.
Notable Operators
- NASA Armstrong (Dryden) Flight Research Center
- Sole operator. Conducted the entire 79-flight programme from Edwards AFB. Flown by NASA test pilots Tom McMurtry, Fitz Fulton, John Manke, Bill Dana, and Einar Enevoldson plus astronaut/test pilot Richard Truly.
Frequently Asked Questions
What is an oblique wing?
A single straight wing mounted across the fuselage on a centre pivot, so it can rotate as a rigid piece — one tip forward, one tip aft. At high speed the wing is rotated to a high oblique angle (high effective sweep, low drag). At low speed it returns to perpendicular for high lift on takeoff and landing. The idea was first published by NASA's Robert T. Jones in the 1950s.
Why hasn't an oblique wing aircraft entered production?
The AD-1 revealed serious roll-pitch coupling at high pivot angles — the asymmetric airflow over a wing tilted across the airframe couples roll and pitch axes in non-intuitive ways the pilot can't fly through manually. Modern fly-by-wire systems could likely suppress the coupling, but the development cost has never been low enough to justify a production programme.
Who designed the NASA AD-1?
Burt Rutan — the same designer who later created Voyager (the aircraft that flew nonstop around the world in 1986), SpaceShipOne (the first private suborbital spaceflight, 2004), and the Beechcraft Starship. Rutan's Scaled Composites approach kept the AD-1's airframe at fibreglass-foam composite and the cockpit at minimal cost.
How much did the NASA AD-1 cost?
About USD$240,000 (1979 dollars) for the airframe and engines — a tiny fraction of a typical X-plane budget. Rutan's cost discipline came from composite construction (no expensive metal forming), borrowed components from the VariEze programme, and a deliberately subsonic-only flight envelope.
Where is the AD-1 today?
On permanent display at the Hiller Aviation Museum in San Carlos, California, near where many of the engineering drawings were prepared (NASA Armstrong fact sheet).
Sources
See Also
- Bell X-5 — Earlier variable-sweep research aircraft
- General Dynamics F-111 — Production swing-wing strike aircraft
- Grumman F-14 Tomcat — Production swing-wing fleet defender
- Grumman X-29 — Sister NASA forward-swept research aircraft
- Scaled Composites Proteus — Later Burt Rutan high-altitude research aircraft