Joby claims results from recent NASA-backed flight tests with its eVTOL aircraft prototype demonstrate that noise from the four-passenger air taxi vehicle would be barely audible from city streets below. On May 10, the company published findings from a two-week trial as part of NASA’s Advanced Air Mobility National Campaign.
During the flights, the Joby aircraft registered the equivalent of 45.2 dBA while cruising at an altitude of 500 meters (1,640 feet) at a speed of 100 kts (115 mph). Recordings made by NASA engineers also demonstrated an acoustic profile for the aircraft while taking off and landing that was below 65 dBA, which Joby said represented a noise level comparable to a normal conversation at a distance of 330 feet from the flight path.
The measurements were conducted using NASA’s Mobile Acoustics Facility, which has more than 50 pressure ground-plate microphones. These were positioned in a grid array at the facility Joby calls its Electric Flight Base near Big Sur in California.
To isolate as much of the aircraft’s ambient noise output as possible over the background noise, the Joby prototype flew at a low altitude over this grid six times at 100 kts. NASA then processed the data recorded by the omnidirectional microphones into a so-called “acoustic hemisphere” representing the sound emission in all directions below the aircraft out to a 100-foot radius.
From this, Joby’s engineers used standard spherical spreading and atmospheric attenuation techniques to come up with the average free-field overhead flight acoustic reading of 45.2 dBA.
A further 20 flights were made to measure noise outputs during takeoff and landing. The aircraft flew at a variety of acceleration rates and climb angles to represent anticipated real-world operations.
Joby is working to certify the all-electric aircraft, which has expected range of 150 miles and speeds of up to 200 mph, in time to start commercial air taxi operations in 2024. The company said that, with NASA, it will publish further details of the noise analysis at various industry conferences in the coming months.