Grumman X-29

The Grumman X-29 was a high tech aircraft designed to test the feasibility of forward swept wings.

Background
Grumman’s X-29 looks like a strange apparition, but it is an ‘X-plane’ with a purpose. Germany’s wartime Junkers Ju 287 bomber proved that a forward-swept wing (FSW) can improve performance at high speeds. But the FSW was largely ignored until structural problems associated with the concept could be solved by advanced composite materials, enabling the X-29 to test this wing shape and to bring a wealth of new knowledge to aviation.

History
The benefits of forward-swept wings have been known since World War II, offering enhanced agility, virtually spin-proof handling, lower drag, better low-speed flight and lower stalling speeds, but early efforts were defeated by aeroelasticity - the tendency of wings to twist under normal flight loads. Practical designs had to wait until the strength of available structural materials caught up with theory. After years of work on FSW design, Grumman won a 1981 contract to build two X-29 research planes. The company slashed manufacturing costs by using parts from many aircraft:


 * F-5 fuselage and nosewheel,
 * F/A-18 Hornet engine
 * F-16 main undercarriage.

The result was more than the sum of its parts. In several years of experiments, the X-29 demonstrated an ability to manoeuvre at angles of attack as high as 67°, and showed that the FSW conﬁguration can result in large fuel savings. Test pilots found the X—29 exciting to fly. With its wing shape and agility, it gave meaning to the motto on a sign at Edwards Air Force Base: ‘Toward the Unknown’. Today the X-29 has been retired, but its contribution to aviation is very much alive.

Description
The cockpit of the X-29 is surprisingly simple, with traditional dials and switches. Apart from the large amount of telemetry gear, the only advanced systems were a Litton altitude/heading reference system and the Martin-Baker election seat.

The forward fuselage was based on the Northrop F-5A, using parts taken from ex Norwegian and USAF aircraft. The rear fuselage strakes are a very unusual feature - each strake has a flap on its traillng edge actuated by a slngle Moog servo actuator.

The engine intakes were of simple rectangular design with splitter plates and ﬁxed ramp intakes. The General Electric F-404 engine is a lowebypass ratio turbofan, also used in the F/A-18 Hornet.

The wing sub-structure is built of titanium and aluminium. The wing is extremely thin, and is fitted with leading and trailing edge flaps,The composite materiais of the wing were laid in carefully calculated patterns to avoid the aerodynamic twisting effect of the f0rvvard»swept wing. The variable incidence canards could be rotated as much as 60‘ around their axis. The forward-swept wing gives very good handling characteristics at low airspeed and high angle of attack, making landings very simple.

The undercarriage was from the F-16, but as the X-29 did not need a tactical ‘rough ﬁeld’ capability it used small wheels and narrow tyres, retaining the anti-skid system and carbon brakes.

One of the features that became common in many later ﬁghters was the small nose strakes just behind the pitot tube. These devices improved directional stability at high angles of attack.

The X-29 proved a delight to ﬂy, so much so that test pilot Chuck Sewell could not resist the temptation to roll the aircraft on one of its ﬁrst ﬂights, before it was cleared to do so.

Specification

 * Type: single-seat forward-swept-wing high-agility research aircraft ~
 * Powerplant: one 71.17-kN General Electric F404-GE-400 turbofan (as on F/A-18 Hornet)
 * Maximum speed: Mach 1.87 or 1900 km/h at 10000 m
 * Range: 560 km
 * Service ceiling: 15300 m
 * Weights: empty 6260 kg; maximum B074 kg
 * Dimensions: span 8.29 m, length 16.44 m, height 4.26 m, wing area 188.80 m2