EXPERIMENTAL AND ANALYTICAL INVESTIGATION OF TRANSONIC LIMIT-CYCLE OSCILLATIONS OF A FLAPERON

Forced oscillation testing of a control surface on a rigid model is conducted in a transonic tunnel to identify the possibility of limit-cycle oscillations (LCO) induced by aerodynamic sources. Identification is possible through an energy concept by observing the direction of hysteresis loop in the test data. Two flow devices have also been tested and their effectiveness in eliminating the LCO examined. In addition, test data of hinge moment response in forced oscillation at various frequencies are analyzed through Fourier functional analysis to result in a generalized forcing function in an indicial form. The latter is used in the structural equation of motion for the control surface deflection angle. The resulting nonlinear equation is integrated by Hamming's predictor-corrector method to investigate the effect of structural freeplay. It is demonstrated that if the curves of hinge moment response vs deflection angle in dynamic testing exhibit triple hysteresis, LCO is possible. However, whether the latter actually occurs depends on the initial excitation. Structural freeplay is shown to induce LCO at M = 0.97 for the model tested.