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 featured fixed strakes along the aft fuselage, as well as a pair of movable computer-controlled canards to increase stability and maneuverability. There are no horizontal tail surfaces, only the vertical fin with rudder. Pitch and yaw are controlled by the three paddles directing the exhaust (thrust vectoring). Eventually, simulation tests on one of the X-31s showed that flight would have been stable had the plane been designed without the vertical fin, because the thrust-vectoring nozzle provided sufficient yaw and pitch control.
The X-31 showing its three thrust vectoring paddles.
During flight testing, the X-31 aircraft established several milestones. On November 6, 1992, the X-31 achieved controlled flight at a 70-degree angle of attack. On April 29, 1993, the second X-31 successfully executed a rapid minimum-radius, 180-degree turn using a post-stall maneuver, flying well beyond the aerodynamic limits of any conventional aircraft. This revolutionary 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
The X-31 showing its three thrust vectoring paddles.
During flight testing, the X-31 aircraft established several milestones. On November 6, 1992, the X-31 achieved controlled flight at a 70-degree angle of attack. On April 29, 1993, the second X-31 successfully executed a rapid minimum-radius, 180-degree turn using a post-stall maneuver, flying well beyond the aerodynamic limits of any conventional aircraft. This revolutionary 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
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