A 98 - 37266 High Speed , Low Angle - of - Attack Pneumatic Vortex Control . Ajaa - 98 - 4449

Forebody pneumatic vortex control has previously been demonstrated through full-scale flight test to be effective for directional control of aircraft at low Mach number and high angle-ofattack flight conditions. The objective of the present research was to investigate the suitability of two-axis (wing, and vertical tail) pneumatic vortex lateral/directional control of a current fighter-type aircraft at high Mach number and low angle-ofattack flight conditions. The pneumatic effectors were tested for first augmenting, and then replacing the conventional aileron and rudder on a generic F16 XL configuration. Evaluations were conducted on a high fidelity, nonlinear, six degree-of-freedom, non real-time simulation of this aircraft. Results demonstrate that at low blowing coefficient levels and with conventional effector augmentation, aileron and rudder activity and maximum deflections can be reduced. At higher yet realistic and attainable levels of compressor bleed air, aileron and rudder can be completely replaced by pneumatic devices, yet still allow the aircraft to complete aggressive bank-to-bank maneuvers and simulated penetration strike missions. Introduction Pneumatic vortex control (PVC) using either tangential slot blowing or nozzle blowing to control the forebody vortices generated by aircraft at high angles-of-attack is a generally well understood and mature technology. The viability of the concept for 'Assistant Professor, Department of Aerospace Engineering. Senior Member AIAA. * PVC Program Manager, Air Force Research Laboratory. Senior Member AIAA. Copyright © 1998 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. generating controllable yawing moments has been extensively tested in wind tunnels for several years [15]. More recently, the promise of PVC was successfully demonstrated in full-scale flight test to reduce the loss of directional control power on fighter type aircraft at high angles-of-attack [6-8]. The X29 A aircraft was fitted with compressed nitrogen gas bottles to power PVC nozzles mounted on each side of the forebody, essentially providing yaw augmentation only. The PVC nozzles were controlled manually by the pilot, i.e. open-loop, and not as part of the X-29A digital flight control system. The tests demonstrated that PVC was a viable means of generating well behaved yawing moments at high angles-of-attack and low Mach numbers. The time delays experienced in initiating a PVC event were small, and the responses to PVC inputs were generally fast and acceptable to the pilot. Specific recommendations for extending the PVC research program included using engine compressor bleed air to power the PVC nozzles, and closing the loop on the nozzles within the flight control system. All-PVC control, characterized by pneumatic devices completely replacing conventional aerodynamic effectors, provides the potential for significant reductions in radar detectability by eliminating control surface deflections altogether. To realize this potential in the operational context of low level strike/interdiction missions requires the use of pneumatics as multi-axis control effectors over the full subsonic/transonic flight envelope. Recent wind tunnel testing of PVC has expanded into the low angle-of-attack / high Mach number flight regime, and to other configurations such as the high speed civil transport [9-11]. Results indicated that with sufficient engine compressor bleed air, PVC devices are an attractive control effector for high speed / low angleof-attack flight conditions. Other testing [12,13] successfully demonstrated wing-mounted PVC devices for generating multi-axis moments. The remaining step prior to serious consideration of an all-pneumatic controlled aircraft is