Adaptive LFT control of a transport aircraft on the lateral axis

This paper describes the application of an indirect LFT (Linear Fractional Transformation) -based adaptive control scheme to a rigid transport aircraft, with emphasis on the lateral axis. The plant parameters, namely the stability derivatives, are estimated online using a Recursive Least Squares technique. A modal approach is used to directly synthesize the static output feedback LFT controller, scheduled as a function of the parameters to be estimated, in order to reduce the online computational time and complexity. The study of the stability and H_∞/L₂ performance of the adaptive closed loop is performed by the analysis of an LFT gain-scheduled closed loop which depends on the true values of the plant parameters and on the estimation error. Using this offline method, based on μ analysis, the adaptive aircraft control scheme is shown to be robust with respect to a large transient and asymptotic estimation error, as confirmed by time-domain results on a nonlinear six degree-of-freedom simulator.