The NASA AD-1 – Flying Scissors
Quite possibly one of the most bizarre-looking aircraft that you will ever see, the NASA Ames Dryden 1 (AD-1) was a research aircraft that was designed to test the concept of a pivoting (also known as oblique) wing.
Most other aircraft look symmetrical, standing the Ames Dryden 1 out as an odd-ball that ultimately led to nothing. However, it did show that blue sky thinking can give rather extraordinary results.
Oblique wings have fascinated aviation engineers since the first know design was proposed by Richard Vogt in the middle of World War Two.
With the introduction of the first generation of turbojet engines, many new and unusual designs appeared to take advantage of this new technology. However at the time one of the biggest hurdles was aircrafts’ own wings. Their straight flight surfaces caused significant drag, limiting top speeds.
Vogt decided that the best way around it would be to have a pivoting wing in the center of the fuselage that could move and therefore reduce the drag and enable a higher top speed.
This type of wing is known as an oblique wing, and is a type of variable geometry wing. Variable geometry wings are flight surfaces that can change shape to better adapt to the conditions at hand.
For example, they can reduce their size and therefore drag for high speeds, or increase their size and therefore lift for low speeds.
Whilst Vogt’s design was never produced, in the 1970s Robert Jones, an aeronautical engineer at NASA’s Ames Research Center in California, promoted the concept enough to gather significant attention.
After initial research, Jones stated that a transport-sized aircraft with a pivoting wing would have significantly better performance at supersonic and subsonic speeds than a similar aircraft with conventional wings.
In addition to this, Jones also believed that an oblique wing would reduce the violence of sonic booms.
During landing and take off the wing would be perpendicular to the fuselage just like a traditional aircraft, with the angle increasing with the speed. Whilst it may look strange, this angle would mean that the aircraft could fly at higher speeds and have a longer range with the same fuel usage.
The sweep would only work in a single direction with the right wingtip moving forwards.
After Jones spent many hours in the wind tunnel and experience with scaled down models, a design was put onto paper for a small test aircraft to prove the concept would work. This test aircraft was the AD-1.
It was built by the Ames Industrial Company in New York under a $240,000 contract, and her first flight was on December 21st, 1979 flown by NASA’s research pilot Thomas McMurtry.
The AD-1 was delivered in February 1979.
Due to the relatively low cost of the AD-1, it was not designed to be a high-performance aircraft, but simply a test bed to show that this type of wing could work. As a result, it was small, lightweight, did not have extremely powerful engines and wasn’t capable of supersonic flight.
She was very small with an overall length of just shy of 39 feet (12 m), an unswept wingspan of 32 feet (9.7 m), and a height of 6 ft 9 in (2.06 m). The total gross weight was 2,145 lbs (973 kg). To put that into perspective, that is less than a Mazda Miata.
The aircraft was constructed from plastic reinforced with fibreglass. This kept both weight and costs down, but limited the strength of the AD-1.
The landing gear is fixed but mounted extremely close to the fuselage to help reduce the effects of aerodynamic drag. It made the AD-1 look even more strange whilst on the ground due to such a squat appearance.
She was powered by two Microturbo TRS18-046 turbojet engines mounted on either side of the fuselage. These were extremely small and weighed less than 100 lbs (45 kg) and produced a rather weedy 225 lbs of static thrust (1.00kN) each. This engine was designed for self-launching motor gliders but was adapted to power ultralight and unmanned aircraft. For safety reasons as well as limitations due to the engine, the AD-1 was limited to a speed not in excess of 170 mph (270 km/h).
Its control surfaces were not hydraulically operated, instead relying on cables and torque tubes for movement. Its cockpit was equally primitive, with only the most necessary gauges available to the pilot.
Electrical power came from a pair of generators, one attached to each engine. This powered some of the aircraft’s systems, including the on-board data gathering computer and the oblique wing’s electric control motor.
Research and Testing
The testing commenced in December of 1979 and lasted for three years with a total of 79 flights taking place. NASA tested the AD-1 in their typical way; very methodically, barely pushing the envelope and analyzing all of the data gained each time the AD-1 took to the air.
Due to the size and performance, the main purpose of the AD-1 was to test the low-speed characteristics of an oblique wing.
Under these conditions the AD-1 was reportedly pleasant to fly and easy to control. NASA employed a list of pilots to fly the plane, with each giving their opinions on its handling and performance.
It was not until 1981 that the AD-1 achieved the full 60-degree angle for the wing, allowing NASA to fully exploit all of the data available by flying such an aircraft.
However once the wing angle reach 50 degrees the AD-1 became difficult to control, due to the lack of stability versus a traditional symmetrically designed aircraft. Typically this was whilst maneuvering with the wing fully swept, causing oscillations. Pilots also noted that when pulling on the stick to pull up, she had a tendency to want to roll over.
Part of the problem was that the lightweight materials used in the AD-1’s construction were too flimsy for the job.
Ultimately this type of design never went anywhere. Whilst it was indeed possible and potentially viable for larger transport aircraft, it would have been complicated and expensive to produce on a large scale which combined with the less than ideal flying characteristics meant further development was never pursued.
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After her final flight on 7th August 1982, the AD-1 was retired and put on display at the Hiller Aviation Museum in California where she still resides to this day.
Length: 38 ft 4 in
Wingspan: 32 ft spread, 16 ft 2 in swept
Height: 6 ft 6 in
Gross weight: 2,145 lbs (973 kg)
Powerplant: 2 × Ames TRS-18 turbojets, 220 lbf thrust each
Maximum speed: 200 mph (320 km/h)
Service ceiling: 12,000 ft (3,700 m)