Aeroelastic investigation of a fighter aircraft including flight control systems

Modern fighter aircraft are using high sophisticated power control and automatic flight control systems, which basically are designed to maneuver the airplane and to provide sufficient damping for the rigid body modes. Since the sensors are attached to the flexible structure, motions of the elastic aircraft also picked up and may be influenced by the system. In order to avoid instabilities it is necessary to predict the response of the aircraft with the control system and to correlate with flight test data. An analytical approach for the complete system including flight mechanics and unsteady aerodynamic forces is presented. The elastic structure is described by a set of normal modes which have been updated by results of ground resonance survey tests. Flutter calculations in open and closed loop on different flight conditions as well as incidence variations are demonstrated as common flutter plots. For the flutter analysis a set of notch filter is required, which should be determined in an integrated design step.