The Future of Advanced Air Mobility

On July 16, 2019, Karem Aircraft was granted a patent covering technology it intends to use in the development of the Butterfly eVTOL aircraft. The design will be based on the patented Optimum Speed Rotor technology previously developed by company founder Abe Karem.

Also on July 16, 2019, Karem announced that it has raised $25 million through a Series A funding round. The main backer for this was South Korean industrial group Hanwha Systems. The funding was approved on December 8, 2019, by the U.S. Committee on Foreign Investment in the United States. It will be used to launch a new spin-off company called Overair (earlier referred to as K4 Aeronautics) that will bring the Butterfly to market and establish an air-taxi operation in support of Karem’s partnership with Uber Air. In the future, Karem Aircraft will mainly focus on its activities in the defense market.

In January 2020, Karem Aircraft formed Overair, Inc. as a spin-off venture to lead the development of the Butterfly under the leadership of president and CEO Ben Tigner. This was one of 10 eVTOL aircraft programs selected as a partner in the Uber Elevate air taxi program, but this alliance broke up in late 2020 when Elevate was acquired by Joby Aircraft. Overair had been working to a goal of getting the Butterfly certified and in service by 2023, and the company is reportedly one of several eVTOL pioneers actively working with the FAA on a path to type certification.


Our objective assessment of this program’s probable success.

FutureFlight assesses the probability of success for a new aircraft program by considering the following criteria:

  • Total investment funds available in proportion to the anticipated cost of getting an aircraft certified and in service
  • A company’s in-house capability (in terms of numbers of engineers, technical staff, and customer support teams)
  • The past experience of the company and its senior leadership in developing aircraft
  • The caliber and past experience of key program partners
  • Whether key aircraft systems have been selected and are available for use
  • Whether the preliminary design review has been completed
  • Whether the design for the full-scale prototype has been completed
  • Whether the type certification process has been formally initiated with an appropriate regulator
  • Whether the company has achieved a first flight with a full-scale prototype
  • The number of hours logged in a flight test program
  • Whether type certification has been achieved
  • The number of orders and commitment received for the aircraft
  • Whether the company has adequate facilities to begin series production of the aircraft
Our Methodology

The strong track record in advanced unmanned aircraft development of Karem Aircraft founder Abe Karem provides foundational credibility for the company's plans in the eVTOL market. The 82-year-old engineer was instrumental in creating prominent military drones such as the General Atomics Predator. In January 2020, Overair Inc was formed as a spin-off venture to lead the commercialization of the Butterfly program under the leadership of CEO Ben Tigner.

The $25 million raised in a Series A funding round completed in July 2019 provided fresh resources for the program, which now has the support of South Korean industrial group Hanwha Systems.

However, since its formation, Overair has been almost completely radio-silent on progress with the program, to the extent that it is hard to assess the current state of the timeline projection for service entry of the Butterly in 2023.  The silence may indicate that the company has no need for further investment, for now, and that it prefers to focus quietly on development work. But the lack of visibility on key landmarks, such as the construction of a full-scale prototype and plans for flight testing do little to bolster public confidence in the program. There also remains a lack of transparency over the projected performance and specifications for the Butterfly, beyond the fact that it will be piloted and carry four passengers at speeds of up to around 200 mph. Critically, no range projection has been published, making it hard to assess the aircraft's viability for commercial air taxi services.

Butterfly Models

Butterfly Specifications

local vtol Lift + Cruise


  • Passenger Capacity
  • Range
  • Cruise Speed
    200 mph
  • Powerplant Type
    multi rotor
  • Power Source
  • Endurance
  • Max Altitude
  • Takeoff Distance
  • Landing Distance
  • Empty Weight
  • Payload Weight


  • Length
  • Width
    45 ft
  • Height
  • Wingspan

As of July 2019, Karem Aircraft had provided almost no details about its design for the Butterfly air taxi. The Butterfly design uses Karem’s patented Optimum Speed Rotor technology to drive a vectored thrust powerplant with four large tilting rotors mounted on the wings and tail. According to the company, this will overcome the acknowledged eVTOL tradeoff between hover and cruise flight efficiency. Without providing any projected specifications or performance figures, it claims that the large, slow-turning rotors will provide both efficient lift and low noise levels needed to meet requirements for operating in urban areas. Since late 2019, the aircraft's development has been in the hands of Overair, Inc., which Karem established as a subsidiary to focus on the urban air mobility sector. 

Key Personnel

Ben Tigner is co-founder and CEO of Overair.
Ben Tigner

Chief Executive Officer (CEO), Founder