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X-31 Enhanced Fighter Maneuverability Demonstrator

The NASA Dryden Flight Research Center is using two X-31 Enhanced Fighter Maneuverability (EFM) demonstrators to obtain data that may apply to highly-maneuverable next generation fighters.

The X-31 program is showing the value of thrust vectoring (directing engine exhaust flow) coupled with advanced flight control systems for close-in air combat at very high angles of attack.


"Angle-of-attack" (alpha) is an engineering term to describe the angle of an aircraft�s body and wings relative to its actual flightpath. During maneuvers, pilots often fly at extreme angles of attack -- with the nose pitched up while the aircraft continues in its original direction. With older aircraft designs this would lead to loss of control which can result in the loss of the aircraft, pilot, or both.

Thrust vectoring paddles on the X-31's exhaust nozzle direct the exhaust flow to provide control in pitch (up and down) and yaw (right and left) to improve control. In addition the X-31s are configured with movable forward canards and fixed aft strakes. The canards are small wing-like structures set on the wing line between the nose and the leading edge of the wing. The strakes are set on the same line between the trailing edge of the wing and the engine exhaust. Both supply additional control in tight maneuvering situations.

The X-31 research program is producing technical data at high angles of attack. These data will give engineers and aircraft designers a better understanding of aerodynamics, effectiveness of flight controls and thrust vectoring, and airflow phenomena at high angles of attack. This is expected to lead to design methods providing better maneuverability in future high-performance aircraft and make them safer to fly.

Phase One

Phase I was the conceptual design phase. During this phase the payoff expected from the application of EFM concepts in future air battles was outlined and the technical requirements for a demonstrator aircraft were defined.

Phase Two

Phase II carried out the preliminary design of the demonstrator and defined the manufacturing approach to be taken. Three governmental design reviews were held during this phase to thoroughly examine the proposed design. Technical experts from the U.S. Navy, Federal Ministry of Defense, and NASA contributed to the careful examination of all aspects of the design.

Phase Three

Phase III initiated and completed the detailed design and fabrication of two aircraft. This phase required that both aircraft fly a limited test flight program. The first aircraft rolled out on Mar. 1, 1990, followed by a first flight on Oct. 11, 1990. The X-31 took off from Palmdale, CA, runway 07, piloted by Rockwell chief test pilot Ken Dyson. It reached a speed of 340 mph and an altitude of 10,000 ft during its initial 38 min. flight. The second aircraft made its first flight on Jan. 19, 1991, with Deutsche Aerospace chief test pilot Dietrich Seeck at the controls.

Flight Summary

During the program's initial phase of operations at Rockwell International's Palmdale, CA, facility the aircraft were flown on 108 test missions before starting operations they were moved to Dryden.

At Dryden an international team of pilots and engineers is expanding the aircraft's flight envelope, including military utility evaluations that will pit the X-31 against similarly equipped aircraft to evaluate the maneuverability of the X-31 in simulated combat.

The X-31 achieved controlled flight at 70� angle of attack at Dryden on Sept. 18, 1992.

On Apr. 29, 1993, the No. 2 X-31 successfully executed a minimum radius, 180� turn using a post-stall maneuver, flying well beyond the aerodynamic limits of any conventional aircraft. The revolutionary maneuver has been dubbed the "Herbst Maneuver," after Wolfgang Herbst, a German proponent of using post-stall flight in air-to-air combat.

Evaluation of the X-31 as a fighter maneuverability demonstrator by the ITO is scheduled to conclude by Dec. 1993.

Program Management

An international test organization, managed by the Defense Advanced Research Projects Agency (DARPA), is conducting the flight tests. In addition to DARPA and NASA, the International Test Organization (ITO) includes the U.S. Navy, the U.S. Air Force, Rockwell International, the Federal Republic of Germany, and Deutsche Aerospace (formerly Messerschmitt-Bolkow-Blohm). About 110 people from the ITO agencies are assigned to the program. NASA is responsible for flight test operations, aircraft maintenance, and research engineering.

The X-31 is the first international experimental aircraft development program administered by a U.S government agency. It is a key effort of the NATO Cooperative Research and Development Program.

Gary Trippensee is the ITO director and NASA�s project manager at Dryden.

Pilots of the X-31 EFM aircraft include: NASA pilot Rogers Smith; U.S. Navy pilot Cmdr. Al Groves; German pilots Karl Lang and Dietrich Seeck; Rockwell International pilot Fred Knox; and Air Force Flight Test Center pilot Lt. Col. Jim Wisneski.

Aircraft Specifications

Designed and constructed as a demonstrator aircraft by Rockwell International Corporation's North American Aircraft and Deutsche Aerospace.

The aircraft has a wing span of 23.83 ft (7.3 m). The fuselage length is 43.33 ft (12.8 m).

The X-31 is powered by a single General Electric F404-GE-400 turbofan engine, producing 16,000 lb (71,168 N) of thrust in afterburner.

Typical takeoff weight of the X-31 is 16,100 lb (7,303 kg).

The X-31 design speed is Mach 0.9 with an altitude capability of 40,000 ft (12,192 m).

Gary Trippensee, Dryden Project Manager
(805) 258-3163

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NASA Dryden Flight Research Center
Public Affairs Office
Edwards, CA 93523
(805) 258-3449
[email protected]

Modified: February 2, 1994