Thrust vectoring: a new angle to air superiority.

Jet fighters fitted with engines that vector or direct thrust obliquely can perform spectacular maneuvers, which could provide the edge in close-in aerial combat.

Despite the growing capabilities of beyond-visual-range missiles, front-line fighter pilots and Pentagon planners agree that

an edge must also be maintained in dogfighting to ensure success in future air combat. "Sophisticated electronic warfare techniques, radar-evading stealth technology, and the need for visual identification all increase the chances of fighters stumbling onto each other in the merge and getting into a knife-fight," said Col. Michael S. Francis of the Advanced Research Projects Agency (ARPA) in Arlington, Va.

In a close encounter (within visual range) between two supersonic fighters, both aircraft typically lose speed and height (what pilots call "energy") as they jockey for a firing position, trying to kill before counterlaunch. Much of this maneuvering goes on as each aircraft is oriented at a high angle of attack (AOA), a high-drag condition in which the wings form a steep angle with the oncoming air flow. As airspeed drops, stability is degraded, and conventional aerodynamic control surfaces - flaps - become less effective.

Airfoils lose lift or "stall" at these high angles of attack. "Post-stall" refers to flight conditions in which it becomes suddenly more difficult to maintain control, even for fighters, whose airframes are usually designed to minimize loss of control at high AOAs.

A lesser-known method by which a jet aircraft can modify its attitude regardless of airspeed is by directing the thrust of its jet engine obliquely from the center-line, a technique known as thrust vectoring. "Thrust vectoring is a new fundamental force and moment generator that works at slow speeds and in conditions in which conventional control surfaces don't work," said Francis, who serves as the ARPA manager for the X-31 Enhanced Maneuverability Fighter program, one of several research projects that have recently demonstrated vectored-thrust technology.

Skeptics have claimed that post-stall flight could easily lead to catastrophe. In a one-versus-two dogfight, for example, any excursion to high angles of attack dumps a fighter's energy, potentially leaving the plane a sitting duck. However, studies conducted in recent years by U.S. government agencies including the Air Force, Navy, ARPA, and the National Aeronautics and Space Administration, as well as by airframe and aero-engine manufacturers, have shown that thrust-vectoring capability often helps a fighter to prevail in mock engagements. These advanced aircraft can gain dogfight superiority by performing spectacular maneuvers never seen before except on flight-simulation computer screens.