Robust control of angle of attack using dynamic inversion combined with quantitative feedback theory

Abstract

We describe a novel flight control design in which dynamic inversion is used to linearize the aircraft dynamics, and then quantitative feedback theory (QFT) is used to yield robust performance in the presence of model uncertainties. The approach is applied to the unstable, nonlinear, short-period dynamics of an F-16 aircraft. A second-order, dynamic inversion linearizes the alpha dynamics before applying QFT. Comparisons are made between three dynamic inversion designs and a baseline linear control design obtained by direct application of nonlinear QFT. The baseline controller demonstrates considerable robustness, successfully following large-alpha commands at flight speeds ranging from 53 to 150 m/sec while subjected to +/- 20 percent variations in pitch moment derivatives. Including dynamic inversion in the control law permits significantly lower loop gain, leading to reduced control usage at all flight speeds; however this control scheme is less robust to perturbations of the pitch moment terms. (Author)