"VORTEX CONTROL USING A MOVEABLE NOSE WITH PRESSURE FEEDBACK"
Darden, L.A., Peterson, K.G., and Komerath, N.M.

AIAA 95-3468, Atmospheric Flight Mechanics Conference, August 1995

ABSTRACT
This paper studies the dynamic rolling moment induced on a wing-body configuration at high angle of attack by dynamic lateral asymmetry of the forebody vortices. A moveable nose tip is used to rapidly induce and control lateral asymmetry of the forebody vortices. The configuration is constrained in roll so that the measurements are performed at zero bank and sideslip angle. The difference in surface pressure across the Zero Vorticity Contour of the forebody vortices is used as a sensor of asymmetry. Correlations between nose motion, wing rolling moment, and pressure difference are examined. Square wave and sinusoidal nose motions are used, at frequencies from 0.1 to 1 cycle per second. Long-period square waves and sine waves are used to confirm the time lags for the pressure and the moment. Adverse yaw-roll coupling is observed at 40+ degrees incidence. At 35 degrees and lower, the initial moment effect is followd by a slower-developing, counteracting moment. This difference is attributed to the effect of vortex bursting or multiple states of wing flow separation. Surface pressure feedback is seen to be a viable method of controlling rolling moment, with the presure on the forebody responding with a very short time scale to the nose motion. The time lag in roll moment response is seen to be an order of magnitude longer than the freestream convection time, and the anomalous moment effect to take another order of magnitude longer. Steady state moment variations with nose position are consistent with the adverse roll-yaw coupling at 40 and 45 degrees incidence, whereas the counteracting moment effects greatly reduce the moment sensitivity at 35 degrees and lower incidence. The experiments indicate the presence of at least three widely different time scales in the roll-yaw coupling of maneuvering aircraft, visible even in roll-constrained experiments.

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