Realistic assessment of efficiencies of micro air vehicle propellers

Propulsive efficiencies of Micro Air Vehicle propellers over operating range is playing very important role in enhancing the endurance of the MAVs. These propellers are powered by brushless mini motors whose efficiencies are low in comparison to bigger size motors and are varying over a range of operation. Generally propulsive efficiencies are evaluated by measuring the input power of drive motor and its efficiencies from commercial catalogue. Uncertainty in propulsive efficiency estimation results from the uncertainty in motor efficiencies which vary with load, speed; local heating of the miniature motors, and also compounded by uncertainty in low velocity air flow measurements. To alleviate this, novel method of simultaneous measurement of propellers shaft torque, thrust and rotational speed is configured by CSIR-NAL and procured from M/s MAGTROL SA, Switzerland along with the computer controlled data acquisition system. Wind tunnel testing in uninstalled condition, measurement techniques and data analysis method adapted has yielded realistic assessment of propulsive efficiencies of mini propellers used in micro air vehicles. Maximum propulsive efficiencies of 70% are measured at advance ratio of 0.65 in comparison to 58% from earlier method for 6inch 3bladed mini propeller and computed values of 3D steady state CFD analysis using ANSYS FLUENT are closer to measured values