Helicopter flight control using individual channel design

Abstract
Using the multivariable analysis framework known as individual channel design (ICD), it is shown that for a typical strongly cross-coupled single main rotor helicopter at 80 knots forward flight, the standard 4-input 4-output multivariable control problem, for design purposes, decomposes without significant loss of structural (interaction) information into two simpler 2-input 2-output multivariable problems: one for the longitudinal dynamics and one for the lateral dynamics. Following on this analysis of multivariable structure, the control systems design is built up in a systematic fashion and a novel type of feedforward control is used to overcome a severe lack of robustness as well as to decouple the lateral dynamics into two SISO subsystems round crossover frequency. A diagonal (4*4) feedback controller matrix is then used, the elements of which are designed on the basis of the decoupled lateral and longitudinal dynamics. Resulting closed-loop bandwidths of all four channels are within Level 1 handling quality specifications and step responses are satisfactory with acceptably low cross-coupling.

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