EXPERIMENTAL EVALUATION OF HIGH BANDWIDTH HELICOPTER FLIGHT CONTROL SYSTEM DESIGNS EXPLOITING ROTOR STATE FEEDBACK

Achieving robust high gain feedback in helicopter flight control system design is problematic because the rotor and fuselage are dynamically coupled in the frequency range of the desired closed-loop crossover, and the rotor thus becomes an integral part of the dynamic system that has to be controlled. The concept of Rotor State Feedback (RSF) augments the conventional rigid-body feedback vector with measurements of the rotor dynamics to allow explicit control of the coupled body/rotor modes at higher bandwidths than would otherwise be achievable. To this end, DERA, GKN Westland Helicopters and the University of Bristol have been conducting an experimental evaluation of RSF controllers using the University’s Experimental Rotor Rig Facility. This paper details the design and development of H∞ and Eigenstructure Assignment multivariable RSF controllers, and the testing of these controllers on the Rotor Rig. The tests have included frequency sweeps and small, moderate and large amplitude step responses, with the results being related to full-scale in the context of ADS-33D flying qualities requirements. Comparing the performance of the Rig and the RSF controllers with full-scale has demonstrated: • robustness to representative model uncertainty • up to 50% increase in closed-loop bandwidth (approx) The concept of RSF thus yields potentially significant advances in robust high bandwidth control.