Achieving precise lateral motion modeling and decoupled control in hover remains a significant challenge for tail-sitter Unmanned Aerial Vehicles (UAVs), primarily due to complex aerodynamic couplings and the absence of welldefined lateral dynamics. This paper presents a novel modeling and control strategy that enhances yaw authority and lateral motion by introducing a sideslip force model derived from differential propeller slipstream effects acting on the fuselage under differential thrust. The resulting lateral force along the body y-axis enables yaw-based lateral position control without inducing roll coupling. The control framework employs a YXZ Euler rotation formulation to accurately represent attitude and incorporate gravitational components while directly controlling yaw in the yaxis, thereby improving lateral dynamic behavior and avoiding singularities. The proposed approach is validated through trajectory-tracking simulations conducted in a Unity-based environment. Tests on both rectangular and circular paths in hover mode demonstrate stable performance, with low mean absolute position errors and yaw deviations constrained within 5.688 degrees. These results confirm the effectiveness of the proposed lateral force generation model and provide a foundation for the development of agile, hover-capable tail-sitter UAVs.

Abstract--This paper proposes a novel control law for accurate tracking of agile trajectories using a tailsitter flying wing unmanned aerial vehicle (UAV) that transitions between vertical take-off and landing (VTOL) and forward flight. The global control formulation enables maneuvering throughout the flight envelope, including uncoordinated flight with sideslip. Differential flatness of the nonlinear tailsitter dynamics with a simplified aerodynamics model is shown. Using the flatness transform, the proposed controller incorporates tracking of the position reference along with its derivatives velocity, acceleration and jerk, as well as the yaw reference and yaw rate. Specifically, the lack of vertical surfaces enables maneuvers such as fast skidding turns and Transitioning powered-lift aircraft combine the vertical takeoff knife edge flight where the wing points in the direction of and landing (VTOL) and hover capability of rotorcraft travel. In general, it permits uncoordinated flight, where the with the increased speed, range, and endurance of fixedwing vehicle incurs nonzero lateral velocity. Tailsitter aircraft pitch down during transition, so that their rotors naturally shift from lift generation for In this paper, we propose a novel flight control algorithm take-off to propulsion for forward flight. While the large that is specifically designed for tracking of agile trajectories attitude envelope of tailsitters may render them less suitable using the tailsitter flying wing aircraft shown in Figure 1. for manned flight, their relative mechanical simplicity The proposed controller uses differential flatness to track the makes them an appealing option for unmanned aerial vehicle reference position, velocity, acceleration, and jerk (the third (UAV) applications. Increased range and endurance with the derivative of position), as well as yaw angle and yaw rate.