The Future of Advanced Air Mobility

Overair Lifts the Veil to Reveal Its Butterfly eVTOL Aircraft Design

Overair this week emerged from three years in stealth mode to reveal the design for its planned Butterfly eVTOL aircraft. With financial support from its Korean partner Hanwha Systems, the start-up told a press briefing that it is on track to complete FAA Part 23 type certification by the end of 2025 and to be ready to start commercial operations in 2026.

The Butterfly’s performance is based on the patented Optimum Speed Propulsion system developed over the past couple of decades through a sequence of rotorcraft and drone designs developed by company founder Abe Karem. Its four large 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 environmental conditions. The high aspect ratio wings have full-span flaps to support low stall speeds.

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) should be around 30 dBA.

According to Overair, the Butterfly will be able to carry five passengers plus an unspecified amount of cargo on trips of over 100 miles. It is expected to have a top speed of 200 mph and be able to operate in IFR conditions.

Company CEO Ben Tigner told reporters that his team is preparing to start flying a prototype in Southern California during 2022, mainly to finalize the all-electric model’s propulsion system. By 2023, it expects to be flying a conforming prototype.

Overair was established in January 2020 as a spinoff from Karem Aircraft, which is now focusing exclusively on its defense contracts. Abe Karem is widely credited as a significant innovator with unmanned aircraft, having designed military platforms including the Predator (subsequently acquired by General Atomics) and the A160 Hummingbird (now part of Boeing).

The company says it is yielding dividends from more than $150 million investment in supporting technologies through various U.S. Department of Defense and NASA programs. “Think downsized military transport, not an upsized drone,” it said in marketing materials seeking to differentiate itself from rival eVTOL aircraft programs.

Program manager James Orbon said Overair opted to extend the range of its planned eVTOL by incorporating a pair of wings. The four propulsion units are installed in nacelles on the ends of these wings.

The all-composite aircraft is being designed to be able to operate if one, or even two, of the propulsor units, completely fail. Each nacelle contains multiple inverters and batteries to add an extra layer of redundancy so there is no single point of failure. The Butterfly also will feature full-authority fly-by-wire controls and a health and usage monitoring system.

In October 2018, Uber selected Karem Aircraft as one of its manufacturing partners for its planned Elevate urban air mobility network. Uber subsequently sold Elevate to rival eVTOL manufacturer Joby Aviation in December 2020.

The Hanwha Group, which is the seventh-largest company in South Korea, has prioritized urban air mobility as a key growth market. It invested $25 million in Overair Series A funding round last year and is providing technical support in the development of the Butterfly. Overair says it will seek further investments to complete the type certification process.

According to business development manager Josh Aronoff, Overair intends to be involved in operating the Butterfly in commercial service, as well as directly handling maintenance and spare parts supplies. It shares the view of several other eVTOL aircraft developers that a full-service business model is required to fully exploit the technical and financial synergies anticipated from the urban air mobility sector.

Initial on-demand services will likely be in the U.S. and South Korea. Eventually, Overair intends to certify the Butterfly to operate autonomously without a pilot on board. It also anticipates the aircraft being operated for applications such as logistics, freight deliveries, and military support.

Overair said it plans to forge partnerships with a number of other companies. It has not named any of the key system suppliers for the Butterfly.

“This is just fundamentally a different type of aircraft,” Tigner commented. “Butterfly is a transportation system optimized for safety, utilization, passenger experience, and affordability. Our goal is to become a trusted part of our riders’ daily routines and trusted partner for the communities we serve.”

The company is now operating from a new headquarters facility in Santa Ana, California. This includes a large manufacturing area, a machine shop, a composites shop, and an avionics department. Flight testing will likely be conducted in the Mojave desert.