Model reference single stage digital adaptive flight controller development

Abstract

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 attractiveness of adaptive control and the availability of digital flight computers, a study has been made in order 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 online parameter identification, has been developed. This controller is composed of an online weighted least squares parameter identifier, a Kalman state filter, and a 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 for perfect model following are satisfied,and stability in the sense of boundedness otherwise.

The adaptive controller was tested on the linearized equations of motion for a typical fighter aircraft. Results show 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. Because of the relatively simple gain update logic and the use of the linear parameter and state estimation algorithms the required computation times are such that these functions should be implement able with contemporary mini-computers.