Reduced-Attitude Control of Fixed-Wing Unmanned Aerial Vehicles Using Geometric Methods on the Two-Sphere

As an alternative to reduced-attitude control of fixed-wing unmanned aerial vehicles using roll and pitch angles, we propose to use a global representation that evolves on the two-sphere. The representation of reduced attitude is invariant to rotations about the inertial gravity axis, which makes it well suited for banked turn maneuvers. With the relative airspeed viewed as an exogenous input, a nonlinear controller for almost semiglobal exponential tracking of reduced attitude is presented. For the regulation case, asymptotic convergence is almost global, and the relationship to a classical approach using Euler angles is established. In addition to being singularity-free, a benefit of the presented approach is that the proportional action is pointed along the shortest direction on the sphere. The performance of the controller is demonstrated in numerical simulations