Applied active control for a nonlinear aeroelastic structure

Linear and nonlinear aeroelastic response is examined using a unique test apparatus that allows for experiments of plunge and pitch motion of a wing with prescribed stiffness characteristics. The addition of a control surface, combined with an active control system, extends the stable Eight region. Unsteady aerodynamics are modeled with an approximation to Theodorsen's theory appropriate for the low reduced frequencies associated with the experiment. Incorporated with a full-state feedback control law, an optimal observer is utilized to stabilize the system above the open-loop flutter velocity. Coulomb damping and hardening of the pitch stiffness are included to examine nonlinear control behavior. The nonlinear model is tested using the control laws developed from an extension of linear theory. Each model is simulated using MATLAB(R) and compared with experimental results of the active control system. Excellent correlation between theory and experiment is achieved. Using an optimal observer and full-state feedback, the linear and nonlinear systems are stabilized at velocities that exceed the open loop flutter velocity. Limited control is achieved when the system is undergoing limit cycle oscillations.