Nonlinear Fuzzy Robust Adaptive Control of a Longitudinal Hypersonic Aircraft Model

A multi input multi output (MIMO) robust adaptive fuzzy control is presented for the longitudinal dynamics of a hypersonic aircraft. Because of various sources such as modeling errors, in-flight failure and external disturbances, the vehicle dynamics are partially or completely unknown. Furthermore, the vehicle state variables are unavailable for measure in the complicated flight conditions. As a result, the traditional control methods cannot be used for a hypersonic aircraft. In this article, the unknown dynamics are approximated with fuzzy logic systems, and the state observers are constructed for estimating the state variables. In addition, the ¿dominant input¿ concept is applied, and H^¿control is designed to improve the system performance by attenuating the effects of both the external disturbances and the approximation errors to expected level. Simulation studies are conducted for the trimmed cruise conditions at an altitude of 110,000 ft and at a velocity of 15 Mach to evaluate the response of the hypersonic aircraft to a step function with magnitude of 80 ft/s in airspeed and a sinusoidal function 100sin(0.3 t) ft in altitude. Simulation results demonstrate that the robust adaptive fuzzy control can guarantee the flight stability and also maintain the tracking performance.