Design and Flight Test of a Stability Augmentation System for a Flexible Aircraft

Control law design for flexible aircraft with coupled flight and structural dynamics is currently a challenge. If not correctly addressed during control law design, the aeroservoelastic coupling can negatively affect the lateral-directional stability of the aircraft. In this context, this paper describes a methodology for the design of a stability augmentation system for the Instituto Tecnologico de Aeronautica X-HALE flexible aircraft and proposes a performance index for numerical optimization of the closed-loop feedback gains. Comparisons between open-loop and closed-loop numerical simulation results show how the proposed control system attenuates the Dutch-roll response. An aeroservoelastic analysis is made in which it its demonstrated that the control system has small but beneficial effects on aeroelastic stability. Finally, experimental data obtained via flight tests with the real aircraft demonstrate the effectiveness of the control system in practice.