Geometric Reduced-Attitude Control of Fixed-Wing UAVs

Featured Application Although the focus in this article is on unmanned aerial vehicles, the geometric reduced-attitude controllers presented apply to all fixed-wing aircraft with fully actuated rotational dynamics. The proposed approach could also be applied to other bank-to-turn vehicles such as missiles. The method can be particularly useful for situations where the vehicle experiences large deviations from the attitude reference. This paper presents nonlinear, singularity-free autopilot designs for multivariable reduced-attitude control of fixed-wing aircraft. To control roll and pitch angles, we employ vector coordinates constrained to the unit two-sphere and that are independent of the yaw/heading angle. The angular velocity projected onto this vector is enforced to satisfy the coordinated-turn equation. We exploit model structure in the design and prove almost global asymptotic stability using Lyapunov-based tools. Slowly-varying aerodynamic disturbances are compensated for using adaptive backstepping. To emphasize the practical application of our result, we also establish the ultimate boundedness of the solutions under a simplified controller that only depends on rough estimates of the control-effectiveness matrix. The controller design can be used with state-of-the-art guidance systems for fixed-wing unmanned aerial vehicles (UAVs) and is implemented in the open-source autopilot ArduPilot for validation through realistic software-in-the-loop (SITL) simulations.

Automated summary

This article introduces geometric reduced-attitude controllers for unmanned aerial vehicles, utilizing vector coordinates and Lyapunov-based tools to achieve almost global asymptotic stability. Additionally, the use of adaptive backstepping to compensate for aerodynamic disturbances and the establishment of ultimate boundedness of solutions under a simplified controller are highlighted.