Nonlinear H 8 Flight Control of General Six-Degree-of-Freedom Motions

This paper investigates the application of nonlinear H,~) control theory to flight vehicles whose complete six degree-of-freedom lioiilinear equations of motion are considered directly without linearization. Nonlinear flight control modes such as velocity control, body-rate control, attitude control, and hovering control are designed in a unified framework such that the derived nonlinear H,.,, control law is valid for arbitrary flight vehicles. The most difficult and challenging task involved in applying the nonlinear H,,, control theory is to solve the associated HamiltonJacobi partial differential inequality (HPDI). In this paper we show that the H.PD1 of flight control problems can be solved analytically with simple manipulations. A closed-form expression for the nonlinear H,n flight controller is derived from the solution ofH.PDI and shown to be in the simple structure of proportional feedback. The numerical simulations show that the derived nonlinear H,,, control law can ensure global and asymptotical stability of the closed loop system and have strong robustness against wind gusts with varying statistical characteristics.