11 October 1990 – Two X-31s were built, with the first flying on October 11, 1990.
“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 under-fuselage intake), the German TKF-90 (wing planform concepts and under-fuselage 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 Computer Numeric Control, 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.
Over 500 test flights were carried out between 1990 and 1995. The X-31 is a canard delta, a delta wing aircraft that uses canard foreplanes for primary pitch control, with secondary thrust-vectoring 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.” (1)
Source (1): Wikipedia