Design of a Robust Adaptive Longitudinal Flight Control

Abstract

A recently developed adaptive controller based on a disturbance attenuation problem is applied here to the longitudinaldynamics of theF-18 high angle-of-attack research vehicle. Forcommanded changein angleof attack, the controller blends aerodynamic controls with thrust vectoring. The blending is based on the uncertainty of the aerodynamic control moment coefe cient vs the restriction on thrust vectoring using paddles. The development of a controller for this complex control problem is based on an adaptive controller determined from solving, without any approximation, the disturbance attenuation problem, where the control coefe cient matrix is uncertain. This controller estimates online not only the system state but also the uncertain parameters in the control coefe cient matrix. The control is determined by maximizing a nonconcave function with respect to the uncertain parameters and is a function of the disturbance attenuation bound. In linear simulations, it is shown that as the bound is decreased, the transient response is signie cantly quickened, the thrust vectoring is used more heavily during the transient, and the steady state is achieved with only aerodynamic control.