An eVTOL is a modern-day innovative aircraft that uses electrically powered systems to hover, take off, and land vertically. As research & development activities are taking up speed globally, there are still quite a few barriers to the widespread adoption of Urban Air Mobility (UAM) solutions, both in terms of operating performance, and in terms of social impact and acceptance.
This week, I’d like to share with you some insights into eVTOL noise – or rather their lack of noise, as compared to helicopters – including how this relative quietness could help public acceptance, and how engineers can reach their vibroacoustic goals using simulation. Noise is a key discipline where leading OEMs are making incredibly fast progress, bringing the noise to a level much below standard aircraft and helicopters.
Let’s take the example of Joby Aviation - a Californian start-up on a mission to relieve road congestion in urban areas by innovating solutions for aerial ridesharing. Incidentally, Joby’s aircraft happens to use electric propulsion, which, on top of providing congestion relief, also offers a zero-emission solution to move around California – or elsewhere. And it’s a quiet solution too.
At this year’s ESI LIVE 2022, our annual global event about creating a sustainable future that is safe, clean, and productive, we had the pleasure to welcome our customer Greg Goetchius, Lead Engineer for Noise & Vibration at Joby Aviation, amongst the presenters.
As Greg Goetchius highlighted, today, community noise is the number one barrier to the expansion of aerial ridesharing. Helicopters can take off and land vertically, meaning they can be used outside of airports, providing a great Urban Air Mobility (UAM) solution, but the noise they generate creates such an inconvenience for people living in cities that their usage is mainly restricted to emergencies. This is why Joby’s product could be a game changer: “A Joby vehicle taking off vertically is as quiet as 65 dB(A) when standing at a 100m distance, which is roughly 20 dB(A) quieter than traditional helicopters” according to Greg Goetchius.
For eVTOLs, low noise and sustainability are two sides of the same coin. The first winning feature for Joby’s quiet eVTOLs is their “distributed thrust”, using 6 propellers placed in specific locations, with optimized blade design. As a result, the propellers spin at very low Revolutions per Minute (RPM), one of the keys to producing very low noise.
Secondly, distributed propulsion allows for compact, lightweight, fast-responding, and efficient propulsion units – something which, according to Greg Goetchius, is most realistically achievable using an electric power source. So, interestingly, as he points out, a quiet eVTOL is also a more sustainable eVTOL.
Joby measured the actual noise of their eVTOLs using one of their two flying physical prototypes in a physical acoustics flyover test. The aircraft flew at 100 knots and followed a path exactly situated over a microphone, 1,500 feet above the ground. The company’s measurements were compared against NASA measurements as NASA engineers from Virginia measured Joby’s aircraft noise using an array of over 50 microphones. These measurements confirmed noise levels of 45.2 dBA for overhead flight, and only 65 dBA for take off and landing.
Besides the external noise performance of Joby’s next generation aircraft, creating an acoustically pleasant cabin experience is another important field of play for Greg Goetchius’ acoustics engineering team. “ESI has been a fantastic partner in helping Joby develop a first-of-its-kind vibro-acoustic model of an eVTOL aircraft,” says Greg Goetchius.
Besides these incredibly valuable insights shared by Joby, I would like to add that other barriers to the widespread adoption of UAM solutions include passenger safety, and mission performance.
Tackling these challenges requires completely new architectures involving multi-domain expertise. Concurrent engineering often induces great complexity. Multidisciplinary teams need to break silos: their work needs to be integrated in a common backbone to enable fast iterations, and robust data exchange. This is what ESI Group is jointly developing with key aerospace partners, as a core member of the MISSION project, an EU-funded project part of the Clean Sky 2 program. This will be our topic for the next post – let's keep connected!