Thrust-Vector Control for Supermaneuvering
While supermaneuvering flight maneuvers such as the Cobra can evidently be made with ordinary aerodynamic controls, there is a growing interest in thrust vectoring for supermaneuvering (Gal-Or and Baumann, 1993). Four recent thrust-vectoring flight demonstration programs are
F/A-18 HARV (High Alpha Research Vehicle) Thrust is deflected by three vanes per engine for pitch and yaw control to a maximum angle of 12.5 degrees. Roll control is also available because of the airplane’s two engines.
X-31 Thrust is deflected for pitch and yaw control to a maximum of 15 degrees by carbon paddles, integrated with the flight control system.
F-16D MATV This airplane’s thrust-vectoring system is integrated into the engine, with maximum yaw and pitch deflection angles of 17 degrees (Figure 3.13).
YF-22 Prototype Engine nozzles are deflected in pitch at angles of attack above 12 degrees and airspeeds under 200 knots, blended with horizontal tail deflections. The airplane is controllable at an angle of attack of 60 degrees (Barham, 1994).
10.4 Forebody Controls for Supermaneuvering
Alternatives to thrust-vector controls at the high angles of attack for supermaneu – vering are the blowing or strake controls that act on the vortex systems shed by tactical airplanes’ forebodies. There is an extensive literature on the effects of vortices shed by slender body noses on airplane forces and moments. The intent of blowing and strakes or
tabs is to modify these vortices for control purposes, particularly in the supermaneuvering high angle of attack regime.
Pedriero et al. (1998) demonstrated both the promise and problems of forebody blowing. Rolling and yawing moment coefficients as large as 0.02 and 0.4, respectively, are available with blowing to one side, for a cone-cylinder body with a 70-degree delta wing. However, moment linearity with jet mass flow is too poor for closed-loop control purposes. Adding controlled amounts of blowing to the opposite side improves linearity to the point where closed-loop control is possible, with no sacrifice in available control moment. In tests of forebody blowing for a model with a chine at the body’s widest point, control linearity with mass flow appears to be improved without resorting to blowing to the opposite side (Arena, Nelson, and Schiff, 1995).
The F/A-18 HARV was used to experiment with deflectable foldout strakes on the forward forebody for roll control at high angles of attack, with successful results (Chambers, 2000).