An implementable digital adaptive flight controller designed using stablized single-stage algorithms

Adaptive flight control systems are of interest because of their potential for providing uniform stability and handling qualities over a wide flight envelope despite uncertainties in the open-loop characteristics of the aircraft. Because of the potential for actual implementation of adaptive control algorithms using contemporary, small digital computer equipment, a study has been made to define an implementable digital adaptive control system which can be used for a typical fighter aircraft. Towards such an implementation, an explicit adaptive controller, which makes direct use of on-line parameter identification, has been developed and applied to both the linearized and nonlinear equations of motion for the F-8 aircraft. This controller is composed of an on-line weighted least squares parameter identifier, a Kalman state filter, and a real model following control law designed using single-stage performance indices. The corresponding control gains are readily adjustable in accordance with parameter changes to ensure asymptotic stability if the conditions of perfect model following are satisfied, and stability in the sense of boundedness otherwise. Simulation experiments with realistic measurement noise indicate that the controller was effective in compensating for parameter variations and capable of rapid recovery from a set of erroneous initial parameter estimates which defined a set of destabilizing gains.