Design of a helicopter control system to meet handling quality specifications using H_∞ techniques

This paper describes a method for design of a flight control system for a high performance helicopter. This method uses H_∞ and µ techniques to provide inner loop control laws which decouple the roll, pitch, and yaw rates and vertical velocity, and provide desired bandwidth in those channels. The design is an implicit model following approach in which the weighted H_∞ norm between the actual system outputs and outputs of desired handling quality models is minimized. Stability robustness is investigated by using nonlinear simulations. The H_∞ controller provides excellent performance when the control inputs are small and the system is essentially linear, however performance is degraded for large inputs. The µ controller provides improved response for large inputs.