The potential benefits of the forward-swept (backwards) wing have been known for years. Nazi Germany tried to capitalize with the Junkers JU-287 during World War II. It was conceived as a fast bomber that could out-run Allied interceptors with its early jet engines. The forward-swept wings (FSW) offered better lift at takeoff and landing, which was vital because early jet engines were notoriously under-responsive. Two prototypes were built, but they were never put into production.
A major problem with FSW was aeroelastic divergence — the tendency of wings to literally twist at high speeds. By the 1980s, composite materials and precise fly-by-wire controls let engineers catch up to theorists.
In 1981, Grumman Aerospace Corporation (Now Northrop Grumman) won a contract to build two FSW research planes. Just as the Germans did in 1944, Grumman saved money by piecing their airplanes together with parts of other planes. The main fuselage was from an F-5, and the company used parts from F-18s and F-16s to form the X-29.
New carbon-fiber composites meant that the wings would not twist off the airplane mid-flight. The plane was also outfitted with control-canards for stability. Just as important were the computer controls that kept the airplane stable. The 6x redundant controls featured three digital and three analog computers making about 40 corrections per second. The result was a resounding success and made for a very exciting aircraft for the test pilots to fly. NASA’s Dryden Flight Research Center flew the two X-29s a total of 436 times, without incident, from 1986 until the program’s sunset in 1991.
The first X-29 was used as a flight demonstrator. These “Phase 1” flights demonstrated that the aeroelastic composite wing maintained structural integrity in flight. The flights also showed that the computerized controls could keep the aircraft stable. The pilots, according to NASA, reported “good handling qualities.”During Phase 1, the X-29 became the first FSW plane to break the sound barrier.
The second X-29 was outfitted with a spin-recovery parachute and began to stretch the flight envelope a bit, with proof of concept well established in 242 Phase 1 flights. In Phase 2, the X-29 showed it could flow with up to a staggering 67-degree angle of attack.
Pilots from NASA, the United States Air Force, and in-house at Grumman said that the X-29 maintained “excellent control response” at a 45-degree angle of attack, which is an impressive angle even today. They said there was still some control at 67-degrees, which was attributed to the wing and canard design of the X-29.
The X-29 demonstrated an extremely impressive angle of attack without using thrust vectoring — technology seen in later aircraft like the X-31 in which the engine nozzles are moved to push the aircraft in a different direction than it is facing.
The forward-swept wing concept has not been directly incorporated into any production American military aircraft.
“Flight test data from the high-angle-of-attack/military-utility phase of the X-29 program satisfied the primary objective of the X-29 program — to evaluate the ability of X-29 technologies to improve future fighter aircraft mission performance,” NASA said in its official fact sheet of the X-29 program.
An X-29 is on display near the parking lot at Dryden. The aircraft is clearly visible in Google Earth.
Russia has been developing its Su-47 Berkut since 1997. The Su-47 incorporates both FSW and thrust vectoring. Four prototypes have been built.
In popular culture, the video game Fighters Anthology featured the X-29 and X-31 (still with the X names) as playable 21st century USAF fighters/interceptors with limited air-to-ground capability.
The Transformers Autobot named Dogfight transforms into an X-29.
Length: 48 ft 1 in
Wingspan: 27 ft 2 in
Height: 14 ft 9 in
Empty weight: 13,800 lb
Max. takeoff weight: 17,800 lb
Engine: One General Electric F404 turbofan, 16,000 lbf
Maximum speed: Mach 1.8 (1,100 mph, at 33,000 ft)
Range: 350 mi
Ceiling: 55,000 ft
Never armed. Theoretically capable of carrying 4,000 lbs. of ordinance and equipment.
There aren’t many good books that feature the X-29. The best is “X-Planes at Edwards” by Steve Pace. Avoid a promising sounding book called “X-Planes: Pushing the Envelope of Flight” — weirdly enough written by the same author. The photos in the second book are not very good.
Here are some great online resources:
- Wikipedia — Excellent article, very visual, well-cited
- Dryden Flight Research Center fact sheet — An obvious starting point.
- An old Tripod fansite — Example of 90s websites
- Federation of American Scientists — Great technical reference