PRACTICAL ROBUSTNESS TESTING FOR HELICOPTER FLIGHT CONTROL SYSTEMS

This paper describes practical tests which can be applied to helicopter flight control system designs to verify that the solutions are robust in the presence of the non-linear and highly coupled dynamics representative of a typical helicopter. It shows that systems designed with methodologies involving full state feedback may meet “Singular Value” robustness criteria, but fail when the real non-linearities and realistic plant and control matrix variations are introduced. Robustness tests are performed on a baseline design which has already undergone flight validation. The design procedure which produced that design is summarized. It is based on a physically understandable decoupling technique, which converts the helicopter multiple input - multiple output problem into a sequence of straightforward single input - single output loops. The result is a high gain, explicit model following system which easily meets the practical robustness test criteria. Comparisons are made with example optimal designs that provide excellent results with high order, linear models of the same helicopter, but fail robustness tests which expose them to the real plant non-linear dynamics.