Aerodynamic Optimization Design of an Orthogonal Octo-Rotor UAV in a Hovering State

This paper presents a novel orthogonal octo-rotor Unmanned Aerial Vehicle (UAV) and addresses the aerodynamics of the UAV with varied rotor spacing by both numerical simulations and experiments. Compared with the traditional planar multirotor UAV, this novel orthogonal octo-rotor UAV features a compact structure with four horizontal main rotors for stability and thrust and four vertical auxiliary rotors for lateral movement. Additionally, the attitude and translation dynamics are decoupled with easy manipulations. To obtain a better hover performance, the flow field and hover performance of the UAV were analyzed with rotor spacing ratios i = D/L ranging from 0.55 to 0.9 (i = 0.55, 0.59, 0.63, 0.67, 0.71, 0.77, 0.83, 0.90) and a rotor speed ranging from 1500 to 2300 RPM. The results showed that a rotor spacing ratio of i = 0.55 achieves a better hover efficiency, increasing hover efficiency by 11.27% at 2000 RPM, where the maximal thrust increment is 3.92% and the power consumption decreased by 5.68% at the same time. Computational Fluid Dynamics (CFD) simulations were further validated by streamlines and velocity distributions. It indicated that the rotor interference from the outflow was decreased with the rotor spacing while the increasing rotor speed aggravated the influence of the auxiliary rotor on the downwash airflow of the main rotor. The potential benefit of the rotor interference from the main rotor and the auxiliary rotor improved the hover efficiency of the orthogonal octo-rotor UAV with a higher thrust increment, which offers it the unique capability of resisting wind gusts or even rotor failure, which will be validated with more field flight tests.