Experimental Analysis of Thrust Efficiency and Noise Characteristics of Toroidal Propellers for Fixed-Wing UAVs

Toroidal propellers have emerged as a promising alternative to conventional blade designs due to their potential for reduced noise and improved aerodynamic performance. This study investigates the feasibility of toroidal propellers for fixed-wing UAVs through experimental testing of three propeller variants: a conventional 4-bladed design, a toroidal configuration, and a modified toroidal propeller featuring a tip angle designed to maintain effective angle of attack at the blade tips. Each design was manufactured in three pitch configurations, 9.4×7, 9.4×9, and 9.4×11, and was evaluated in static and dynamic wind tunnel conditions with incoming flow conditions ranging from 2.5 to 10 m/s. The angle of incoming flow was varied from +90° (head-on) to -90° (descent condition) to simulate all possible flight configurations. Particle Image Velocimetry (PIV) was conducted at selected inflow angles (90°, 15°, and 0°) to assess wake structure and flow behavior. The results indicate that the modified toroidal propeller performs better in direct-inflow conditions, while the conventional toroidal propeller excels in oblique and descent angles. The modified toroidal also maintains higher efficiency in a broader range of inflow conditions than standard designs, suggesting its viability for hybrid UAV propulsion systems operating in variable aerodynamic environments.