Drone on: A preliminary investigation of the acoustic impact of unmanned aircraft systems (UAS)

Increasingly, operations with unmanned aircraft systems (UAS) are occurring in populous regions. Commercial entities propose increasingly frequent, very low-level flights of a diverse range of small craft (particularly quadrotors) in urban environments. There is a significant body of research addressing safety, security, and privacy issues for UAS and an even greater amount dedicated to manned craft. However, our review reveals relatively little available information on the characteristics of UAS noise sources, factors influencing propagation, the people impacted and the psychoacoustic factors influencing their response. This work begins to analyse the problem by investigating the effect of quadrotor propeller-blade numbers on acoustic annoyance. Frequency spectra for each propeller type are compared against that for a DJI Phantom 4. The effect on loudness, sharpness, and fluctuation strength is also discussed. A number of technical mitigation measures are hypothesised, including flight path planning for reduced exposure, and legislative restrictions. Propeller designs taking inspiration from low noise fans are recommended as a method of reducing the acoustic impact of routine UAS operations over populous areas.