Nonlinear H_∞ helicopter control

This paper investigates a new application of the nonlinear H_∞ control to a helicopter whose complete six degree-of-freedom nonlinear equations of motion with coupled rotor and inflow dynamics are considered directly without linearization. A closed-form expression for the nonlinear H_∞ helicopter flight controller is derived from the solution of Hamilton-Jacobi partial differential inequality and is shown to be in the simple structure of proportional feedback. We also solve the problem of how to implement helicopter blade pitch control from the nonlinear H_∞ command. Robustness and global stability are validated in a nonlinear six degree-of-freedom simulation, which reveals that nonlinear H_∞ helicopter control can resist the maximal possible wind gust with varying statistical characteristics, and reveals that much better performance and larger flight envelope can be achieved by nonlinear H_∞ controller.