Control of an aeroelastic system with control surface nonlinearity

Nonlinearities in aircraft mechanism are unavoidable, especially in the control system. Correct modeling of the nonlinearities is necessary for the aeroelastic analysis and control. In this paper, a rational polynomial (RP) approximation model is introduced based on actual measured force-deflection relation in aileron system. Numerical examples prove that the model can be used to describe both freeplay and hysteresis nonlinearities. So the switching point problem may be avoided in the numerical integration process. Then state-dependent Riccati equation method is used to derive a state feedback suboptimal control law for flutter suppression of a three degree-of-freedom typical airfoil section with RP nonlinearity in control surface. With the control law designed in this paper, the closed-loop dynamic system is solved by Runge-Kutta numerical approach. Simulation results are presented to show the efficacy of the designed control system. And the effects of RP nonlinearity on aeroelastic closed-loop responses are also investigated.