Impact of electric propulsion on aircraft noise – all-electric light aircrafts case study

Aircraft electrification is on the verge of radically changing air transportation. Energy-efficient distributed propulsion, vertical take-off and landing capabilities and reduced emissions are some examples of the great possibilities that electric propulsion offers and how it could disrupt air travel and urban air mobility in the future. Next to the many technological challenges associated with such new concepts, important regulatory barriers still need to be overcome to make it come true. One aspect of particular attention is the impact on environmental noise. In this paper, the acoustic performance of two all-electric light aircrafts is assessed based on ground and in-flight measurements. The investigated aircrafts are the Magnus eFusion, first all-electric aerobatic training airplane in the world and the Extra 330LE, world's first electric aircraft to tow a glider into the sky. For both airplanes, the actual impact of electric propulsion on exterior radiated noise during fly-over is quantified - for the first time - using two variants of the same aircraft, equipped with two different propulsion systems: in one case with a conventional piston engine, in the other case with an electric motor. Cabin noise is also assessed for the two aircraft variants. Sound quality metrics as well as sound source localization techniques are used to perform a detailed analysis of the interior and exterior aircraft noise and to get insight into the noise generation mechanisms. The manuscript details the complete set of measurement techniques which are available for acoustic engineers to develop quieter electric aircrafts in the future. It reports about the setup and execution of the test campaign; it describes the processing of the acquired data and discusses the major findings. Results highlight the different footprints of the two types of propulsion in terms of fly-over and cabin interior noise levels.