Differences in sound emission level of multi-rotor UAS during hover and cruise

UAS noise is an increasing concern in today's society, necessitating effective control and monitoring.One approach to address this issue is the development of reliable UAS noise models.In some studies, the sound emission of multi-rotor UAS was characterized using hover measurements in an anechoic room; however, comparisons with forward-flight measurements revealed discrepancies for certain UAS.To investigate these differences, we conducted measurements during transitions from hover to cruise using an on-board measurement system mounted on the UAS.In addition to recording the emitted sound, the system acquires relevant flight data and the precise UAS position.In this paper, we present initial measurement results comparing the overall emitted sound pressure level (OSPL) at hover and across various flight speeds for two propeller types.For one propeller, the OSPL increases abruptly by 2 dB at low speeds, while a nearlinear trend is observed for the other.The constant rotor speed during these changes suggests that aerodynamic factors are likely responsible.Although further analysis is needed, these findings emphasize the importance of assessing different flight conditions when modeling sound emission of UAS.