A modal approach for designing controllers for active flutter suppression

Flutter is an important topic to be considered during an aircraft development mainly due to its potentially catastrophic behavior. Typically a new aerial vehicle can require the addition of mass and limitations on its flight envelope to be flutter free. As an alternative, active control technologies can be used employing actuators and sources of power, and there are different techniques for computing the actuator’s force. In general, many approaches depend on describing the aeroelastic system through the state-space representation in the time domain. However, the state-space dynamic matrix typically contains nonphysical eigenvalues due to the unsteady aerodynamic forces approximations. In this context, this article introduces an algebraic arrangement for designing a modal controller to suppress the flutter phenomenon. The approach considers the modal state-space realization combined with the linear quadratic regulator to compute a control gain. The gain is converted from the new modal domain to the physical, and the control force introduces an effect of incremental damping for all flight envelope, although the controller is designed particularly for the flutter speed. To demonstrate the approach, numerical simulations are carried out considering the three-degree-of-freedom airfoil. The results show that this technique allows stabilizing the system.