Flutter investigations on a combat aircraft with a command and stability augmentation system

Modern airplanes like the sweepable-wing combat aircraft Tornado are using sophisticated power control and automatic control systems, which basically are designed to maneuver the aircraft and to provide sufficient damping for the rigid body modes. Since the sensors are attached to a flexible structure, motions of the elastic aircraft also are picked up and may be modified by the system. In order to avoid instabilities it is necessary to predict the response of the airplane with the control system and to correlate with test data. An analytical approach for the complete system including unsteady aerodynamic forces is presented. The elastic structure is described by normal modes which have been modified by results of a ground resonance survey. Results of openand closed-loop calculations are demonstrated in Nyquist and common flutter plots and compared with test data.