A comparison of different H/spl infin methods in VSTOL flight control system design

This paper investigates the application of different H_∞ design methods to multivariable flight control system design for a VSTOL aircraft. Designs are based on linearised models at an airspeed of 120 knots. Although based on linearised operating points a key issue considered is robust stability and robust performance of designs away from the design operating points. Four different design approaches are used. The first three approaches treat uncertainty as unstructured. Two of these optimise closed-loop objectives, and one specifies open-loop objectives. The fourth design uses a μ-synthesis approach which makes use of structured uncertainty information to optimise closed-loop objectives. The designs are evaluated using unstructured singular values and the structured singular value, μ.