Variability of small multirotor aircraft noise measurements

Experimental procedures are developed to measure and characterize the variability of noise radiated by small multirotor aircraft during outdoor flight. These procedures were applied to characterize the noise of a Tarot X8 octocopter. Large (up to 10 dB) variations in A-weighted sound pressure level (SPL) are observed between repeated measurements of the same flight conditions. However, the measured peak SPLs are found to be insensitive to changes in flight speed. This results in a reduction of sound exposure level with increasing flight speed. The A-weighted sound exposure level varies by as much as 6 dB across repeated overflights. Variability in noise is assessed both across repeated runs of the same condition and within a run using an array of microphones parallel to the flight track. Variability is found to increase as the distance between the microphone and aircraft increases. Variations within a run are significant (2.2 dB) and are similar to the variation in peak SPLs observed between runs (2.5 dB).