In Flight Evaluation of UAV Noise

This research project was conducted in collaboration with Manna Drone Delivery,

an Irish commercial sUAS operator. An experimental acoustic testing campaign using

Manna aircraft was conducted to assess the noise emission during flight conditions that represent

realistic delivery missions. Tests were conducted for both stationary hover and fly-by

at heights of 10m, 14m and 50m. Fly-by cruise speeds ranged from typical mission speeds

of 16m/s to 22 m/s. Flyover measurements were captured using a linear array of five ground

mounted microphones. In-flight measurements of sound power were conducted over 360°

for a drone in a stationary hover with an angular resolution of 30°. An in depth investigation

into the magnitudes of broadband and tonal components was conducted, with correlations

of the tonal components with the blade pass frequencies. The directionality of the noise

emission was assessed through the generation of noise hemispheres. Flyover testing was

conducted to evaluate the sound characteristics of forward flight through the computation

of conventional metrics and psychoacoustic sound quality metrics. The utility of the measurement

campaign was assessed and the methodologies employed were evaluated. The

impact of flight conditions on sound levels is assessed. An accurate GNSS RTK positioning

system was used in the navigation system of the sUAS, enabling repeatable measurements.

The results of this testing campaign presented clear directivity in the noise emission of the

UAV and presented novel information on the characteristics of noise emission from a drone

delivery sUAS in terms of sound pressure levels, sound power levels, spectral characteristics

and psychoacoustic sound quality metrics.