Experimental Evaluation of Coaxial Micro-UAS Propellers

Coaxial, counter-rotating rotors from six to nine inches in diameter were evaluated to measure thrust and torque with variations in rotor spacing, thrust level, and the propeller pitch of the upper and lower rotors. The upper rotor was trimmed to specific thrust targets while the lower rotor was trimmed to produce zero overall torque. For the range of propeller pitch models tested, the data showed that increasing the propeller pitch on the lower rotor decreased the combined thrust of the coaxial system, but increased its efficiency. The rotor efficiency was insensitive to thrust level and rotor spacing, down to 0.116R. The lower rotor share of the overall thrust increased with increasing rotor diameter and with decreasing lower rotor pitch.