Application of hybrid mu /Hinfinity control to modern helicopters

The paper presents a study of a hybrid mu /H^infinity design and its application to flight control of a helicopter. A new design procedure for H^infinity control of helicopters is developed, which has a novel feature in that the design incorporates directly the concept of precise model-tracking, for following a handling qualities specification for rotorcraft, into the robust controller synthesis. Analysis, utilising structured singular value techniques ( mu ), concurrently with the system development, gave specific and significant robustness indicators at various perturbation points around the plant. These techniques were used iteratively to refine the design. The end result is a flight control system which is stable, robust and ensures desired closed loop handling qualities. Performance tests were carried out, both in frequency-domain and time-domain, by incorporating the designed controller into a Simulink-based evaluation environment specially set up for rotorcraft simulations. Results show both the efficacy of the final design and the engineering visibility of the methodology.