Flyover Noise Comparison Between Joby Aircraft and Similar Aircraft

Abstract

Joby Aviation is developing a six propeller, all electric vertical takeoff and landing piloted air taxi aircraft. The aircraft is designed for high density operations near residences and workplaces, so it is imperative that the acoustic emissions of the aircraft are minimized for community acceptance. It is important to compare not just the absolute sound levels but also the sound quality with conventional aircraft already known to the public. To showcase the difference between the Joby aircraft and similarly sized aircraft for a level flyover condition, Joby arranged a flight demonstration with two conventional fixed-wing aircraft and three commercial helicopters. All the aircraft were flown at approximately 100 knots (51 m/s) and 1500 feet (457 m) above ground level within minutes of each other in the same location to minimize variability. They were measured with the same equipment and processing methods. The results show that the peak Joby aircraft sound pressure level was 10 to 19 dB(A) below the conventional aircraft. The conventional aircraft noise levels were above the peak Joby level for 43 to 54 seconds during the flyover. The Joby aircraft was measured at 13 to 22 EPNdB lower than the conventional aircraft. Close examination of the spectra showed that Joby aircraft has greatly reduced tonal and low frequency content. When substituting the low ambient noise during the flight test with a realistic urban outdoor cafe environment, the Joby aircraft is below the ambient at all frequencies during the direct f lyover which allows it to blend in with the ambient soundscape. The other conventional airplanes and helicopters exhibited large tones that rise above the cafe ambient for approximately one minute, and would impact a much larger area on the ground that is not directly under the flight path.