Development of Design Structure for Robust Flight Control Law

Abstract. This work presents the development of a flight control law design structure, based on the H∞ and μ synthesis theory. The design criteria includes usual robustness and performance requirements related to parameters uncertainty in the vicinity of the design point. In addition, the conventional mixed sensitivity design scheme is changed to comply with specific requirements of a flight control law design. These changes include the introduction of a feedforward path to reduce the phase delay at high frequencies and a perturbation in the plant input to avoid pole-zero cancellation. Typical uncertainties in the aircraft dynamics are introduced in the μ design. Using μ analysis, the closed loop performance and robustness are compared against a H∞ design that does not consider the uncertainties in the design. The feedback loop and the weighting function adjustment are based on the C* flying qualities criterion, and analysis through other criteria are also briefly shown. The possibility of H∞ and μ synthesis controllers satisfy the C* criterion is demonstrated. The resulting controller order is not excessive, what would make the implementation of a scheduled controller for the whole flight envelope practical. Furthermore, the robustness to the modeled uncertainties can be guaranteed.