A noise modelling approach for multicopter type unmaned aircraft systems

Abstract

The operation of small unmanned aircraft systems (UAS) is connected with noise generation and radiation within urban and thus highly populated areas. This operational aspect requires at first a proper noise prediction of the UAS generated noise as such and the subsequent noise prediction in the relevant environment including e.g. noise reflection at buildings. The present work targets the description and prediction of UAS generated noise with special focus on small UA systems with four to eight rotors. Noise measurements were undertaken on three different UA systems. One octocopter equipped with two rotor sets and two quadcopters were measured. All flights were performed at low altitude in order to achieve a minimum signal to noise ratio of about 10 dB and to be able to determine the US system’s altitude by optical means with sufficient accuracy. During this first drone noise assessment one single ½” free field microphone was used. All noise data were acquired with a 48 kHz sampling rate finally providing narrow band sound pressure level spectra up to a maximum frequency 20 kHz noise and an analysis bandwidth of delta_f = 4 Hz. Flyovers were achieved under controlled meteorological conditions. Wind speeds were measured in a height of 10 m and did not exceed velocities of 6 kts. However, to account for the effect of wind speed on noise generation, flights were conducted in head and tail wind direction.