Initial Developments Toward an Active Noise Control System for Small Unmanned Aerial Systems

Small unmanned aerial systems have the potential to expand commercial markets from package delivery to infrastructure inspection. Many missions, however, require the vehicles to operate in close proximity to people, where community noise concerns could ultimately limit vehicle acceptability. Therefore, noise control technologies may be needed to achieve an acceptable noise signature and enable widespread use of these vehicles. The purpose of this paper is to assess the feasibility of using loudspeakers attached to the vehicle to actively reduce noise. More specifically, this initial study explores the possibility of using a single loudspeaker to reduce the noise from an isolated rotor. Tests performed in an anechoic chamber with a 7.6 cm diameter speaker and 23.9 cm diameter rotor are used to demonstrate the potential benefits and limitations of the concept. Results confirm that active noise control can work in this application with measured tonal reductions of over 30 dB in specific directions. However, since the radiation characteristics of the speaker are different than the rotor, amplification is observed in other directions. This technology has the potential to create a “cone of silence”, which could be steered during flight operations to minimize the impact on noise sensitive areas.