Nonlinear simplified LFT modelling of an aircraft on ground

In this paper, a simplified nonlinear LFT model of an aircraft-on-ground is developed and compared to a full nonlinear model. The proposed simplifications are shown to be not so restrictive. The main contribution of the paper consists of an original approximation of the ground forces. Based on this approximation, which yet remains quite close to reality, some strong nonlinearities of the initial model are conveniently replaced by saturations and time-varying uncertainties. Thus, the proposed simplified model boils down to a reduced order LFT where the Δ block only contains time-varying or constant (but uncertain) parameters on the one hand, and saturation-type non-linearities on the other hand. Such a model is then very useful for applying modern analysis and synthesis techniques.