Multivariable control of the longitudinal and lateral dynamics of a fly-by-wire helicopter

This paper describes the design and flight-testing of a multivariable helicopter flight control system. The system consisted of separate longitudinal and lateral controllers, each designed using H-infinity optimization. The design was based on a low-order aircraft model. The system was successfully flight-tested on a fly-by-wire research helicopter. It was considerably simpler than other H-infinity controllers tested during the same research program. It also outperformed them in most respects, achieving bandwidths of 3.7 rad/s in roll, 2.5 rad/s in pitch and 1.5 rad/s in yaw, and virtually eliminating pitch–roll coupling.