Taking H∞ control into flight

A flight control law for the longitudinal motion of a Harrier jump jet has been developed using H_∞ techniques. Linear design is carried out using loop shaping of the plant, and robustness is achieved using normalised coprime factors. Implementation issues such as gain scheduling and actuator saturations for multivariable H_∞ controllers have been addressed. Results of piloted simulation on the Defence Research Agency advanced flight simulator are given. The control law provides a demonstrator for the application of H_∞ techniques to a real control problem. The Harrier application is particularly interesting because of the use of vectored thrust. Many of the design problems encountered may therefore be relevant to the recent interest in using limited authority vectored thrust for manoeuvre enhancement