The Future of Advanced Air Mobility

Overair Starts Ground Tests with Butterfly eVTOL's Propulsion System

Overair has started ground testing the propulsion system for its five-seat Butterfly eVTOL aircraft. The California-based start-up this week released a video showing a full-scale example of the propulsion system, including its distinguishing large tilting propellers, being run on a truck in a desert.

The company reported that it is on track to achieve its objective of a first production-conforming prototype flight in 2023. With backing from Korean partner Hanwha Systems, Overair aims to achieve type certification under FAA’s Part 23 rules in time for commercial flights to begin in 2026. It expects the Butterfly to have a range of over 100 miles and a top speed of 200 mph.

The all-electric aircraft’s projected performance is based on the patented Optimum Speed Propulsion system created over the past couple of decades through a sequence of rotorcraft and drone designs developed by company founder Abe Karem. Its four 20-foot-diameter tilting propellers spin slowly in hover and even slower during cruise flight, which Overair says results in reduced power consumption that boosts payload, as well as safety margins for operating in challenging environments. The high-aspect-ratio wings have full-span flaps to support low stall speeds.

Overair says the large blade area of the propellers, combined with their slow rotation speed and low disk loading, will minimize pressure disturbance, which is also expected to deliver low noise by comparison with both helicopters and other eVTOL designs. According to the company, the noise level at hover (measured at a distance of 100 meters) is estimated at 55 dBA, while at cruise (measured at 500 meters) it should be around 30 dBA. The company believes this factor will be critical to winning community acceptance for eVTOL flights.

“Achieving our full-scale propulsion test goals is an exciting milestone for the Butterfly program,” said Overair program manager Jim Orbon. “Not only does it allow us to validate our design choices and correlate our simulation results to real-world data, but it also proves the team’s technical capabilities and ability to execute our development plans. But this milestone is a means to an end...a full-scale prototype with long-lead-time parts [is] currently underway.”