Reduction of structural coupling in advanced fighter aircraft by active structural mode control

To avoid the possibility of the structural dynamics coupling with the rigid-body flight control system (FCS) the current approach is to use structural notch filters to reduce specific structural frequency contents from the FCS signals. With modern fighter type aircraft designed to be naturally unstable it is important that such notch filters do not insert significant phase lags. This paper proposes an alternative approach to avoid structural coupling by actively controlling the lower frequency structural modes. It is shown, in the case of a naturally unstable delta canard combat aircraft, that by controlling the lower frequency structural modes, greatly reduced cross-coupling together with increased structural damping can be achieved.