Development of a Wind Tunnel Dynamometer Assembly for Evaluating Unmanned Aircraft Co-Axial Propeller Performance

This paper presents the development of a dynamometer assembly for evaluating the aerodynamic performance of coaxial propellers, widely used in UAVs for their superior speed, maneuverability, and load-carrying capabilities. Despite the advantages of coaxial configurations, the aerodynamic interactions between the front and rear propellers remain underexplored due to the lack of experimental setups capable of accurately capturing their complex dynamics. The developed dynamometer addresses this gap by enabling individual thrust, torque, and power measurements of front and back propellers of a coaxial system. The dynamometer employs a concentric shaft configuration, with a hollow outer shaft rotating the rear propeller and a solid inner shaft rotating the front propeller. Due to this concentric shaft configuration, a specific type of motor and load cells with through-hole designs are used to measure performance of rear propeller; while a more traditional biaxial load cell is used to measure performance of the front propeller. The system is housed in a subsonic wind tunnel with a 3-ft by 3-ft by 8-ft test section, that can accommodate propellers with a maximum diameter of 18 inch. Preliminary experiments validate the dynamometer’s capability to measure performance metrics under varying conditions. While the present work focuses on detailed development of the dynamometer, future work would leverage this setup to investigate effects of several key design parameters on the aerodynamic interference between front and rear propeller of a coaxial system.