(Grumman) X-29 @·AIRCRAFTUBE

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Grumman X-29

The Grumman X-29 was an experimental Faircraft that tested a forward-swept wing, canard control surfaces, and other novel aircraft technologies. The aerodynamic instability of this arrangement increased agility but required the use of computerized fly-by-wire control. Composite materials were used to control the aeroelastic divergent twisting experienced by forward-swept wings, also reducing the weight. Developed by Grumman, the X-29 first flew in 1984; two X-29s were flight tested over the next decade.

Design and development

Two X-29As were built by Grumman from two existing Northrop F-5A Freedom Fighter airframes (63-8372 became 82-0003 and 65-10573 became 82-0049) after the proposal had been chosen over a competing one involving a General Dynamics F-16 Fighting Falcon. The X-29 design made use of the forward fuselage and nose landing gear from the F-5As with the control surface actuators and main landing gear from the F-16. The technological advancement that made the X-29 a plausible design was the use of carbon-fiber composites. The wings of the X-29, made partially of graphite epoxy, were swept forward at more than 33 degrees. The Grumman internal designation for the X-29 was "Grumman Model 712" or "G-712".

Three-surface design and inherent instability

In Jan Roskam's Airplane Design, the X-29 is described as a three surface aircraft, with canards, forward-swept wings, and aft strake control surfaces. NASA Dryden FRC cites "use of three-surface longitudinal control". The canards and wings result in reduced trim drag and reduced wave drag, while using the strakes for trim in situations where the center of gravity is off provides less trim drag than relying on the canard to compensate.

The X-29A demonstrated high maneuvering and control in flight testing. A maximum angle of attack of 67° was reached. The configuration, combined with a center of gravity well aft of the aerodynamic center, made the craft inherently unstable. Stability was provided by the computerized flight control system making 40 corrections per second. The flight control system was made up of three redundant digital computers backed up by three redundant analog computers; any of the three could fly it on its own, but the redundancy allowed them to check for errors. Each of the three would "vote" on their measurements, so that if any one was malfunctioning it could be detected. It was estimated that a total failure of the system was as unlikely as a mechanical failure in an airplane with a conventional arrangement.

Aeroelastic considerations

In a forward swept wing configuration, the aerodynamic lift produces a twisting force which rotates the wing leading edge upward. This results in a higher angle of attack, which increases lift, twisting the wing further. This aeroelastic divergence can quickly lead to structural failure. With conventional metallic construction, a torsionally very stiff wing would be required to resist twisting; stiffening the wing adds weight, which may make the design unfeasible.

The X-29 design made use of the anisotropic elastic coupling between bending and twisting of the carbon fiber composite material to address this aeroelastic effect. Rather than using a very stiff wing, which would carry a weight penalty even with the relatively light-weight composite, the X-29 used a laminate which produced coupling between bending and torsion. As lift increases, bending loads force the wing tips to bend upward. Torsion loads attempt to twist the wing to higher angles of attack, but the coupling resists the loads, twisting the leading edge downward reducing wing angle of attack and lift. With lift reduced, the loads are reduced and divergence is avoided.

Operational history

The first X-29 flew for the first time on 14 December 1984 from Edwards AFB piloted by Grumman's Chief Test Pilot Chuck Sewell. The X-29 was the third forward-swept wing jet-powered aircraft design to fly; the other two were the Nazi Germany Junkers Ju 287 (1944 and post-war by the USSR) and the HFB-320 Hansa Jet (1964). On 13 December 1985, a X-29 became the first forward-swept wing aircraft to fly at supersonic speed in level flight.

The X-29 began a NASA test program four months after its first flight. The X-29 proved reliable, and by August 1986 was flying research missions of over three hours involving multiple flights. The first X-29 was not equipped with a spin recovery parachute, as flight tests were planned to avoid maneuvers that could result in departure from controlled flight, such as a spin. The second X-29 was given such a parachute and was involved in a high angle-of-attack research program. The NASA test program continued from 1984 to 1991. The X-29s flew 242 times.

The NASA Dryden Flight Research Center reported that the X-29 demonstrated a number of new technologies and techniques, and new uses of existing technologies, including the use of "aeroelastic tailoring to control structural divergence", aircraft control and handling during extreme instability, three-surface longitudinal control, a "double-hinged trailing-edge flaperon at supersonic speeds", effective high angle of attack control, vortex control, and demonstration of military utility.

Aircraft on display

The first X-29 is now on display in the R&D/Flight Test Hangar at the National Museum of the United States Air Force on Wright-Patterson Air Force Base near Dayton, Ohio. The other craft is on display at the Dryden Flight Research Center on Edwards Air Force Base. A full scale model was on display from 1989 to 2011 at the National Air and Space Museum's National Mall building in Washington, DC.

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This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article Grumman X-29 of Wikipedia ( authors )

Specifications (X-29)

  • Length : 48 ft 1 in (or 14.7 m).
  • Height : 14 ft 3 in (or 4.3 m).
  • Wingspan : 27 ft 2 in (or 8.8 m).
  • Wing area : 188 ft² (or 57 m²).
  • Empty weight : 13,800 lb (or 6,260 kg).
  • Loaded weight : 17,800 lb (or 8,070 kg).
  • Payload : 4,000 lb (or 1,810 kg).
  • Max. takeoff weight : 17,800 lb (or 8,070 kg).
  • Max. speed : Mach 1.6 (or 1,200 mph, or 1,820 km/h).
  • Service ceiling 55,000 ft (or 16,800 m).
  • Powerplant : One General Electric F404-GE-400 turbofan.
  • Thrust : 16,000 lbf (or 71.2 kN).

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This text is available under the Creative Commons Attribution-ShareAlike License
Source : Article Grumman X-29 of Wikipedia ( authors )
Grumman X-29 : Your comments on this subject
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