A Survey on Structural Coupling Design and Testing of the Flexible Military Aircraft

Structural coupling (i.e., aeroservoelasticity) between the flight control system with multiple motion sensor feedbacks and the aeroelastic modes of the flexible airframe can be a serious problem in high-performance aircraft. In a military specification document, MIL-STD-9490D, adequate stability margin requirement is required to be complied with for all frequencies at or beyond the first aeroelastic mode in all flight conditions. To minimize the structural coupling effect to satisfy the stability margin requirement in flying qualities aspects, various design methods are adopted during the aircraft development stage as follows: to reinforce aircraft's structure on which sensor is mounted, to minimize weight/inertia of control surfaces, to select the optimal sensor position, to optimize control gains, to design notch filters for minimizing phase lag in low-frequency band, to design phase advance filters, to apply additional active control technique, and so on. In this paper, we identify major design considerations which have been applied to the production fighter aircraft to minimize the structural coupling. The reviews regarding the prospects on design technologies would be most helpful to the structure and flight control law engineers.