Application of Non-Linear Dynamic Inversion to Rotorcraft Flight Control

With an increasing trend toward Bearingless Main Rotor systems in modern rotorcraft, two major topics of interest within the handling qualities community are (1) the issue of "Carefree Handling" protection of hub moment limits, and (2) the use of Rotor State Feedback, either directly or indirectly, to counter air resonance and hence enable high bandwidth closed-loop control systems. This paper details the application of a control law design technique based on the principles of Non-Linear Dynamic Inversion. In so doing, the paper shows how the technique embodies explicitly the concept of Rotor State Feedback and allows for intrinsic Carefree Handling without recourse to complex estimator or prediction algorithms. Finally, given the requirement for rotor state measurement, the paper discusses a scheme for Fault Detection, Isolation and Reconfiguration.