Noise Measurements of Unmanned Aircraft Vehicles: Experiences, Challenges and Recommendations for Standards taken from Flight Trials

Over the past decades, drone technology has evolved to become a key element for various purposes in today’s globalized society. Besides the various technical challenges of implementing and utilizing their onboard systems as well as challenges with respect to the integration of these new airspace users into the existing airspace, one major factor for their success is their acceptance by the general public. In order to proactively address the concerns of the public with regards to the noise pollution of drones, the German Aerospace Center (DLR) together with the German Environment Agency (UBA) has undertaken flight trials to measure the noise emission levels of a variety of different types of drones. In particular, one flight test campaign was focused on measuring the sound pressure levels (i.e. pollution levels) of drones overflying static microphones, and another flight test campaign was focused on measuring the sound power levels (i.e. emission levels) of drones using a microphone hemisphere.This scientific publication focuses on three relevant elements of these flight trials and discusses the obtained experiences, mainly from a drone pilots’ perspective, and provides recommendation for future regulations and standards. First, an overview of the measured drones is given including relevant vehicle specifics such as vehicle configuration, take-off mass, and their dimensions. Second, this publication describes the various flight scenarios including specific drone maneuvers that have been performed with the airborne drones during the flight tests. These maneuvers include hovering, forward level flights as well as take-off and landing maneuvers. Third, this publication highlights the challenges encountered when following the applicable EN ISO 3744 standard, which has been used for the second flight tests campaign as a reference document for setting up the measurement equipment required to perform the acoustical measurements. As a result, this publication lists several recommendations for establishing reasonable and practical requirements for future drone noise measurements taken from the obtained experiences coming from these flight tests. For example, one key recommendation is that the standards and regulations on how to measure noise levels of drones should be as detailed as possible and take the drone pilots perspective into account. In essence, this publication aims to pave the way for enhancing the public acceptance of drones by sharing obtained lessons learned from acoustical flight tests and provides recommendation for new regulations and standard that might be used for future drone noise measurements.