On Constrained Nonlinear Tracking Control of a Small Fixed-wing UAV

The problem of constrained nonlinear tracking control for a small fixed-wing unmanned air vehicles (UAV) is considered. With the UAV equipped with low-level autopilots, the twelve-state model of the UAV is reduced to a six-state model with heading, air speed, and altitude command inputs. Three different approaches based on the state dependent Riccati equation (SDRE), Sontag’s formula, and aggressive selection from a satisficing control set are proposed to design the heading and air speed control commands. Those approaches are compared with each other graphically to show their strength and weakness under different scenarios. High-fidelity simulation results on a six-degree-of-freedom twelve-state fixed-wing UAV model are presented to demonstrate the performance of the three approaches.