Effects of Wind on Multirotor UAS Noise Measurements

The aerodynamic and acoustic state of an aircraft depends strongly on its air speed; however, most small multirotor Uncrewed Aerial Systems (UAS), or “drones,” fly autonomously using a fixed ground speed measured using onboard inertial sensors. In this work, a specially instrumented UAS with an air data system based on an ultrasonic anemometer that has been calibrated for installation effects is used to obtain accurate mea surements of the airspeed and wind speed during forward flight. This UAS is used along with a ground-based acoustic array to investigate the correlation between ground speed, airspeed, and wind speed on the sound exposure level and equivalent level during flyovers. Increases in airspeed and ground speed are both found to result in a reduction in the sound exposure level, but an increase in the equivalent level. This indicates that although an in crease in flight speed increases noise generation, the reduced duration of the flyover still results in a decrease in sound exposure. The flyover noise metrics were not shown to be significantly affected by wind over the range of low wind speeds tested (below 2.3 m/s).