Static H∞ loop shaping control of a fly-by-wire helicopter

This paper introduces a static output feedback version of the design procedure of McFarlane and Glover (1992). Existence conditions for a static output loop shaping controller are given in terms of two coupled matrix inequalities. Simple linear sufficient conditions can be derived from these coupled nonlinear inequalities and the determination of a static, suboptimal, H_∞ loop shaping controller reduces to an optimization problem over linear matrix inequalities. The procedure is demonstrated by its application to the design of a flight control system for the Canadian fly-by-wire research Bell 205 helicopter. The resulting H_∞ controller has just 3 states and would appear to be the simplest flight control system used on this helicopter. The system was successfully flight-tested and high levels of performance were achieved.