Design and robustness issues for highly augmented helicopter controls

The paper discusses design procedures for achieving a multiple-input , multiple-outpu t, fly-by-wire flight control system for helicopters. It defines an interpretation of ''highly augmented as requiring tight stabilization of all commanded states, including automatic trimming. Design procedures are given that provide physical insights into how control decoupling and desired bandwidths are achieved, using a contemporary attack helicopter as the model. A high-gain, explicit model-following system is shown to meet practical robustness criteria that are designed to validate performance and stability when extremes of the helicopter nonlinear dynamics become part of the control problem. Comparison of this system's performance with published optimal designs based on the same high-order, linear helicopter model is made, showing that these other designs will not meet the proposed practical robustness tests.