Rockwell-MBB X-31

https://en.wikipedia.org/wiki/Rockwell-MBB_X-31

The Rockwell-Messerschmitt-Bölkow-Blohm X-31 was an experimental jet fighter
designed to test fighter thrust vectoring technology.

It was designed and built by Rockwell and Messerschmitt-Bölkow-Blohm (MBB), as
part of a joint US and German Enhanced Fighter Maneuverability program to
provide additional control authority in pitch and yaw, for significantly more
maneuverability than most conventional fighters. An advanced flight control
system provided controlled flight at high angles of attack where conventional
aircraft would stall or lose control. Two aircraft were built, of which only one
has survived.

The X-31 design was essentially an all-new airframe design, although it borrowed
heavily on design elements and sometimes actual parts of previous production,
prototype, and conceptual aircraft designs, including the British Aerospace
Experimental Airplane Programme (choice of wing type with canards, plus
underfuselage intake), the German TKF-90 (wing planform concepts and
underfuselage intake), F/A-18 Hornet (forebody, including cockpit, ejection
seat, and canopy; electrical generators), F-16 Fighting Falcon (landing gear,
fuel pump, rudder pedals, nosewheel tires, and emergency power unit), F-16XL
(leading-edge flap drives), V-22 Osprey (control surface actuators), Cessna
Citation (main landing gear's wheels and brakes), F-20 Tigershark (hydrazine
emergency air-start system, later replaced) and B-1 Lancer (spindles from its
control vanes used for the canards). This was done on purpose, so that
development time and risk would be reduced by using flight-qualified components.
To reduce the cost of tooling for a production run of only two aircraft,
Rockwell developed the "fly-away tooling" concept (perhaps the most successful
spinoff of the program), whereby 15 fuselage frames were manufactured via CNC,
tied together with a holding fixture, and attached to the factory floor with
survey equipment. That assembly then became the tooling for the plane, which was
built around it, thus "flying away" with its own tooling.

Two X-31s were built, with the first flying on October 11, 1990. Over 500 test
flights were carried out between 1990 and 1995. The X-31 is a canard delta, a
delta wing aircraft which uses canard foreplanes for primary pitch control, with
secondary thrust-vectoring control. The canard delta had earlier been used on
the Saab Viggen strike fighter, and has since become common on fighters such as
the Eurofighter Typhoon, Dassault Rafale and Gripen which were all designed and
flew several years before the X-31. The X-31 featured a cranked-delta wing
(similar to the Saab 35 Draken and the F-16XL prototype), and fixed strakes
along the aft fuselage, as well as a pair of movable computer-controlled canards
to increase stability and maneuverability. There are no moveable horizontal tail
surfaces, only the vertical fin with rudder. Pitch and yaw are controlled by the
canard with the aid of the three paddles directing the exhaust (thrust
vectoring). Eventually, simulations and flight tests on one of the X-31s showed
that flight would be stable without the vertical fin, because the
thrust-vectoring nozzle provided sufficient yaw and pitch control.

During flight testing, the X-31 aircraft established several milestones. On
November 6, 1992, the X-31 achieved controlled flight at a 70° angle of attack.
On April 29, 1993, the second X-31 successfully executed a rapid minimum-radius,
180° turn using a post-stall maneuver, flying well outside the range of angle of
attack normal for conventional aircraft. This maneuver has been called the
"Herbst maneuver" after Dr. Wolfgang Herbst, an MBB employee and proponent of
using post-stall flight in air-to-air combat. Herbst was the designer of the
Rockwell SNAKE, which formed the basis for the X-31.


Role
Experimental aircraft

National origin
United States / Germany

Manufacturer
Rockwell / Messerschmitt-Bölkow-Blohm

First flight
11 October 1990

Primary users
DARPA
NASA
DLR

Number built
2

Serial numbers
BuNo 164584,
292 flights – crashed on January 19, 1995, north of Edwards AFB, California. The
crash was caused by ice inside the pitot tube, sending incorrect airspeed data
to the flight control computers. Contributing factors included the replacement
of a heated pitot tube with an unheated Kiel probe, and ground crew/pilot
ignorance of an option to override computer control. The pilot ejected safely.
NASA issued in 2005 a film, "X-31: Breaking the Chain," reviewing the events.
The novelty of the X-31 trials was computer control of its revolutionary flight
controls (the canard wing and engine baffles) to effect maneuvers impossible for
conventional jet fighters. The film discusses at length the combination of
independent errors (e.g. that the accompanying chase pilot could not hear the
test pilot's radio conversation with his base) in prompting loss of control,
when the test pilot (correctly) ejected to save his life. Film of the crash
shows the aircraft in unusual attitudes as the computer applied its false data
to attempt to control flight after the pilot ejected.

BuNo 164585,
288 flights, the last one being in 2003. Put on Permanent Display at Deutsches
Museum Flugwerft Schleissheim in Germany.

Specifications (X-31)

General characteristics
Crew: 1
Length: 13.21 m (43 ft 4 in)
Wingspan: 7.26 m (23 ft 10 in)
Height: 4.44 m (14 ft 7 in)
Wing area: 226.3 m2 (2,436 sq ft)
Airfoil: Rockwell 5.5%
Empty weight: 5,175 kg (11,409 lb)
Gross weight: 14,600 kg (32,187 lb)
Max takeoff weight: 15,935 kg (35,131 lb)
Powerplant: × General Electric F404-GE-400 turbofan engine, 71 kN (16,000 lbf)
thrust

Performance
Maximum speed: 1,449 km/h (900 mph, 782 kn)
Maximum speed: Mach 1.28
Service ceiling: 12,200 m (40,000 ft)
Rate of climb: 218 m/s (42,900 ft/min)
Wing loading: 64.5 kg/m2 (13.2 lb/sq ft)




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