Aerodynamic study on tilt angle optimization for enhancing wind resistance of non-planar hex-rotors

Horizontal wind disturbances critically decrease the aerodynamic stability and flight efficiency of multi-rotor unmanned aerial vehicles (UAVs) by introducing flow interactions and intensifying wake interference. This study investigates a non-planar hex-rotor subjected to horizontal wind speeds ranging from 0 to 5 m/s, demonstrating its enhanced wind resistance relative to conventional planar designs. Combining wind tunnel experiments and computational fluid dynamics (CFD) simulations, the influence of rotor tilt angles ranging from 0° to 50° on system performance is systematically assessed. A theoretical model that accounts for inter-rotor interference and wind effects is developed to interpret experimental and numerical results. Key performance metrics, including thrust, power, power loading (PL), and figure of merit (FM), are measured, and CFD analysis characterized by the flow features such as pressure distribution and velocity field is also presented. Results indicate that horizontal wind significantly increases power demand and reduces thrust due to disrupted downwash symmetry and enhanced rotor-wake interactions. Variations in PL and FM show that specific tilt configurations induce constructive interference, thereby improving both thrust and overall efficiency. At a rotor spacing of L = 1.2D, optimal wind resistance is achieved at a tilt angle of θ = 30° for a wind speed of 2.5 m/s, and θ = 50° for 4 m/s. These optimal configurations correspond to stabilized inflow in face-to-face rotor pairs and suppressed vortex shedding in back-to-back units, which effectively mitigate separation loss. The findings provide valuable guidance for optimizing the aerodynamic performance of non-planar multi-rotor UAVs operating under wind disturbances.