Globally Stable Attitude Control of a Fixed-Wing Rudderless UAV Using Subspace Projection

Abstract

This letter extends recent work on globally asymptotically stable nonlinear attitude control of fully actuated vehicles to underactuated vehicles, specifically, a rudderless fixed-wing airplane. Previous work uses a quaternion attitude representation and Lyapunov theory to establish global asymptotic stability for attitude tracking in a fully actuated fixed-wing airplane, beginning from arbitrary initial conditions. Many small unmanned aerial vehicles are, however, heavily constrained with respect to sensor and actuator resources. A common situation is a flying wing configuration with a pair of elevons that serve the purpose of both the elevator as well as the ailerons. While it is not possible to track an arbitrary attitude in the three-dimensional (3-D) attitude space, we show that it is still possible to track a 2-D subspace of the unit quaternion space. Projecting a desired attitude onto a 2-D subspace is achieved by solving an optimization problem in the quaternion attitude formulation. The resulting controller is verified using simulations that demonstrate satisfactory performance.