Swashplateless-elevon Actuation for a Dual-rotor Tail-sitter VTOL UAV

In this paper, we propose a novel swashplateless-elevon actuation (SEA) for dual-rotor tail-sitter vertical takeoff and landing (VTOL) unmanned aerial vehicles (UAVs). In contrast to the conventional elevon actuation (CEA) which controls both pitch and yaw using elevons, the SEA adopts swashplateless mechanisms to generate an extra moment through motor speed modulation to control pitch and uses elevons solely for controlling yaw, without requiring additional actuators. This decoupled control strategy mitigates the saturation of elevons' deflection needed for large pitch and yaw control actions, thus improving the UAV's control performance on trajectory tracking and disturbance rejection performance in the presence of large external disturbances. Furthermore, the SEA overcomes the actuation degradation issues experienced by the CEA when the UAV is in close proximity to the ground, leading to a smoother and more stable take-off process. We validate and compare the performances of the SEA and the CEA in various real-world flight conditions, including take-off, trajectory tracking, and hover flight and position steps under external disturbance. Experimental results demonstrate that the SEA has better performances than the CEA. Moreover, we verify the SEA's feasibility in the attitude transition process and fixed-wing-mode flight of the VTOL UAV. The results indicate that the SEA can accurately control pitch in the presence of high-speed incoming airflow and maintain a stable attitude during fixed-wing mode flight. Video of all experiments can be found in youtube.com/watch?v=Sx9Rk4Zf7sQComment: 8 pages, 13 figure

An adaptive flight controller design for a tilt-prop fixed wing uav for all flight modes

© 2020, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In this study, we propose an autonomous flight control strategy (which is valid for all flight modes including vertical flight, hover, and level flight) for a vertical takeoff and landing capable, tilt-prop, fixed wing, tricopter unmanned aerial vehicle. In the inner loop of proposed hierarchical architecture, desired control forces and moments are generated using adaptive control theory, and these forces and moments are realized by tricopter motors and aerodynamic control surfaces with an introduced control allocation methodology. In the outer control loop, a pitch offset command is introduced so that the strategy for transition from hover to level flight (and vice versa) can be adjusted. Using this pitch offset command, one may follow the transitioning path on which lift-to-drag ratio becomes maximum that makes the transitioning maneuver cost efficient. Outer control loop also generates the desired attitude commands and continuous front motor tilt angle using reference velocity commands. Hence, no switch is required in the controller while operating between the flight modes. The success of the proposed control architecture is illustrated through numerical simulations on a Hi-Fi nonlinear tricopter model