Robust control design for active flutter suppression

Flutter is an unstable oscillation caused by the interaction of aerodynamics and structural dynamics. It can lead to catastrophic failure and therefore must be strictly avoided. Weight reduction and aerodynamically efficient high aspect ratio wing design reduce structural stiffness and thus reduce flutter speed. Consequently, the use of active control systems to counter these adverse aeroservoelastic effects becomes an increasingly important aspect for future flight control systems. The paper describes the process of designing a controller for active flutter suppression on a small, flexible unmanned aircraft. It starts from a grey- box model and highlights the importance of individual components such as actuators and computation devices. A systematic design procedure for an H∞-norm optimal controller that increases structural damping and suppresses flutter is then developed. A second key contribution is the development of thorough robustness tests for clearance in the absence of a high-fidelity nonlinear model.