H∞ control laws for a high performance helicopter

Concerns the application of linear multivariable control theory to the design of a full authority flight control system for a typical high performance single-main-rotor helicopter. A comprehensive nonlinear dynamic model the rationalized helicopter model is used. It is configured to represent the characteristics of a LYNX-like helicopter. The open-loop dynamics of this type of aircraft are unstable throughout the flight envelope, and the levels of cross-coupling between the various axes of the aircraft are high. In particular, the longitudinal and lateral dynamics tend to be particularly strongly coupled, which makes it difficult to consider these axes in isolation, as is often done in the design of flight control systems for fixed-wing aircraft. In order to improve the handling qualities of the unaugmented aircraft, limited authority stability augmentation systems are often fitted. These systems are usually restricted in authority to approximately 10% of the total available actuator displacement. Electromechanical interlinks may also be used to reduce levels of cross-coupling. Whilst such devices markedly reduce the pilot workload, it is still widely felt that flying this type of aircraft for any period of time is fatiguing