Many next-gen aeroplanes developed by defence contractors fall under an “X” moniker. These project-planes are normally not intended to be a full-scale production model, and are instead primarily for research purposes. One of these in particular, the X-29, is a shining example of the intense research that is undertaken for the purpose of flight.
Beginning in 1984, the X-29 was the first significant “X” plane project in decades. With its unique forward-swept wing, it initially appears as if the X-29 is flying in the opposite direction. However, the same feature that makes it look odd made it outperform other aircraft in the industry.
For a long time, aft-swept wings were preferred due to structural limitations. However, many of the drag benefits from an aeroplane’s wings are present, regardless of the direction they are directed in. Although the Germans experimented with the forward-swept wings with the Junkers Ju 287 in World War II, the project was eventually abandoned.
There were a few challenges to designing an aeroplane with a forward-swept wing. Normal aft-swept wings had a tendency to twist downwards and relieve the load on the wing, whereas forward-swept wings had the habit of twisting up — increasing the wing load, which would cause additional bending of the wing.
A potential forward-swept wing would thus have to be designed stiff, increasing the weight of the plane.
Further, the plane would have to overcome its instability during flight. It was concluded that the proposed X-29 would be 35% unstable — other aircraft at the time were merely rated at 5% unstable. Given it’s structure, fighter pilots guessed the plane’s performance would be, “not relaxed, but unconscious.”
Because of this, they would not be able to control the plane unless there was a ballast with the same weight as a Volkswagen, on the nose of the plane.
To address these issues, researchers used forward canards and rear flaps — all controlled by fail-safe triple redundant computers, to react simultaneously at 40 times per second. Also included in the X-29 was an aeroelastically tailored composite wing to reduce weight and prevent deformation.
The US’ Defence Advanced Research Projects Agency (DARPA) awarded Grumman a fixed price contract in 1981, and two planes were eventually constructed. It was agreed upon that Grumman would perform the first four flights, whereby the government would take over the project afterwards.
After flying the X-29, pilots gave glowing reviews of the unique fighter plane. It performed greater than 1:1 thrust-to-weight ratio during take-off, and had a limited amount of turbulence when compared to other planes at the time.
Its high angle of attack was also a source of praise — having an excellent response at a 45-degrees. Finally, it was also considered reliable after pilots were able to perform five flights in a row on a single day.
In 1992, after an “X” program record of 434 flights, the X-29 program was eventually scrapped. Some claim it was due to the Department of Defence’s focus on new stealth technologies — the forward-swept wings would potentially interfere with stealth designs.
Other theories include the fact that the Russians had already developed the similar Sukhoi S-37, which was twice as big and had 68,000 pounds of thrust.
The two planes are now on display at Wright-Patterson Air Force Base and the NASA Armstrong Flight Research Center.
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