The reduction of quadcopter propeller noise

Fan affinity laws are combined with a simple scaling relationship for fan noise to show that truly significant reductions in propeller noise can be achieved by increasing the propeller diameter while reducing its rotational speed, thereby reducing its blade tip speed, while maintaining a given level of static thrust. Fan affinity laws are also used to show that efficiency improvements accompany the reductions in radiated noise. The significant reductions in noise and increases in efficiency predicted from the scaling relationships are verified experimentally by measuring the radiated noise and power requirements for both large, slowly rotating propellers and small, high-speed propellers, at equivalent static thrusts, where the large propellers serve as possible replacements for the small propellers in typical quadcopter applications. The bulk of the noise reductions offered by large and slowly rotating propellers compared with small, high-speed propellers are shown to be maintained at equivalent net force (thrust minus weight) conditions, as required for practical implementation into a quadcopter UAV, even using readily available hobby grade components. Further significant noise reductions are possible with lightweight and custom engineered components.