Robustness analysis versus mixed LTI/LTV uncertainties for on-ground aircraft

In this chapter, the robustness properties of the adaptive anti-windup controller designed in Chapter 7 are evaluated, with special emphasis on the high uncertainty level affecting the nonlinear ground forces. It is first shown how to convert the initial nonlinear problem into a fairly standard robustness analysis problem versus mixed time-invariant/time-varying uncertainties. An original approach, based on the notion of semi-positive realness, is then introduced to solve the problem. The application of this method to the on-ground aircraft finally reveals the good robustness properties of the lateral controller despite uncertainties and saturation effects. It also gives some relevant information that enables further improvements to be made to the design.