Variable structure adaptive wing-store flutter control by output feedback

The paper treats the question of wing-store flutter control based on the variable structure model reference adaptive control technique. The system represents a typical section of a thin airfoil with an underwing store in two dimensional incompressible flow. The circulatory component of the aero loads is modeled using the Jones's approximation to the Theodorsen function. It is assumed that the parameters of the wing-store as well as of the transfer function which approximates the Theodorsen function are unknown. For the design of control system, an output is defined which is a linear combination of the plunge displacement, pitch angle of the airfoil, and the pitch angle of the store relative to the airfoil. A VSMRAC (variable structure model reference adaptive control) law is designed for the regulation of the output. The control system includes two relays whose outputs are the functions of certain auxiliary error signals. In the closed-loop system, the state vector converges to zero. Simulation results are presented to show that in the closed-loop system, flutter suppression is accomplished in spite of the uncertainties in the system parameters using only output feedback.