Output feedback nonlinear control of an aeroelastic system with unsteady aerodynamics

The paper presents a nonlinear output feedback control system for the stabilization of an aeroelastic system with structural nonlinearities. The aeroelastic model describes the plunge and pitch motion of a wing. The unsteady aerodynamics are modeled with an approximation to Theodorsen's theory. A single control surface is utilized for the flutter control. For the purpose of control law derivation, a judicious choice of output as a linear combination of the plunge displacement and pitch angle is made. Based on a backstepping design technique, a control law for the trajectory control of the chosen output variable is derived. For the synthesis of the controller, only the plunge displacement, pitch angle, and control surface deflection are measured. An observer is designed to estimate the remaining state variables of the system for feedback. In the closed-loop system, including the observer and nonlinear controller, trajectory control of the output is accomplished and the state vector asymptotically converges to the origin. Simulation results are presented which show that the designed control system is effective in flutter suppression. (C) 2004 Elsevier SAS. All rights reserved.