Forebody vortex control
Published March 29, 1995 by Royal Aeronautical Society in United Kingdom
Much attention has been focussed in recent years on tactical maneuvering in post-stall flight. Such programs as VISTA/MATV, X-31, and X-29A have established that tactical supermaneuverability at very high angles of attack (AOA) is a potent offensive weapon provided that the adversary can be enticed into close-in combat. Never before have the requirements for integrating the pilot and aircraft been so important. The aircraft must have robust control authority in all axes, plenty of excess thrust, and pilot-friendly controls which allow him to fly to the limits of both his and the aircraft's capability.
Modern fighter aircraft operating above about 25° AOA encounter a destabilizing phenomena caused by the complex three-dimensional separated vortical flowfield surrounding it. It is in this same region of flight that the aircraft wings and fuselage begin blanking the rudder, resulting in both degraded directional stability and control authority. Hence, two requirements emerge; increase directional stability and increase directional control authority. Thrust vectoring has been demonstrated as a means to increase control authority at all angles of attack. A potential way to increase directional stability could be by controlling the forebody vortex flow.
The primary object of this paper is to document an attempt to increase the directional stability of an F-16 aircraft at angles of attack up to maximum lift. A wind tunnel test program had previously shown beneficial effects of forebody chines; additional testing provided stability and control data to support a flight test program. Flight tests were conducted with and without chines as a small adjunct to a program investigating thrust vectoring to very high angles of attack, the F-16 VISTA/MATV program. Specific maneuvers up to CLMAX (and beyond) were assessed to determine the major effects of forebody chines, although formal parameter identification was not an objective of the program. This paper describes the results of this effort