Methods for attenuation of unmanned aerial vehicle noise

Unmanned aerial vehicles (UAVs) like drones (quadcopters, hexacopters, octocopters etc.) can be a source of a significant acoustic noise. High noise makes them less suitable for use in densely populated urban areas, particularly during take-off, landing and low level flight, due to the noise annoyance. This paper reviews methods and proposes some concepts for attenuation of UAV noise. Both passive and active solutions are considered. Solutions with piston engine silencer, Q-tip propeller, more propeller blades, absorptive and reflective barrier, ducted propeller, sound absorbing ducts, synchrophaser, multichannel active noise cancellation (ANC) system with secondary sources circularly arranged around the propeller and the system with magnetically excited propeller blades are mentioned.