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Bye Aerospace’s Sun Flyer 2 completes first flight with Siemens electric propulsion motor

Bye Aerospace’s electric Sun Flyer 2 successfully completed the first official flight test with a Siemens electric propulsion motor 8 February at Centennial Airport, south of Denver, Colo.


The Sun Flyer family of aircraft, including the 2-seat Sun Flyer 2 and the 4-seat Sun Flyer 4, aims to be the first FAA-certified, practical, all-electric airplanes to serve the flight training and general aviation markets.

Siemens will provide electric propulsion systems for the Sun Flyer 2 airplane—the 57 lb. SP70D motor with a 90 kW peak rating (120 HP), and a continuous power setting of up to 70 kW (94 HP).


Siemens SP70D motor.

Sun Flyer brings the full promise of electric propulsion to the market with safe, practical and reliable electric aircraft. The all-electric operation requires no aviation fuel and results in zero emissions and significantly lower noise pollution compared to conventional aircraft. The sleek Sun Flyer design also features enhanced speed and altitude performance with extremely low operating costs.

George E. Bye, CEO of Bye Aerospace, the developer of the Sun Flyer, said the initial flight with the Siemens motor went flawlessly.

The airplane performed exactly as planned. My thanks to the entire Siemens team for their participation as we enter this next, important flight test phase of Sun Flyer 2 with the Siemens electric propulsion system.

—George Bye

Sun Flyer 2’s program application to the FAA was accepted under FAR 23 certification criteria in the spring of 2018. The Sun Flyer 2 prototype will conduct extensive additional flight test activities in 2019 and continue to work closely with FAA representatives on certification activities.

Current flight test focus areas are propulsion system, envelope expansion and systems optimization.

This successful test flight is a proud moment for the Siemens and Bye Aerospace teams and marks a milestone in bringing the age of electric flight to life. The Siemens electric propulsion system offers a clean, cost-efficient and silent propulsion alternative to the flight training market without compromising performance or safety.

—Dr. Frank Anton, Executive Vice President and Head of eAircraft, Siemens

Globally, Siemens eAircraft technology is helping lead the aviation industry in electrification and hybrid propulsion, system integration, service and condition-based monitoring.

The company has previously equipped European light and sport aircraft with electric propulsion systems up to 260 kW for test purposes and is also developing propulsion technology in power classes up to 10 MW to enable electrification of aircraft in the commercial air transport sector.

Siemens electric motor technology has powered aircrafts to set two speed records, achieve the world’s first aero tow by an electric plane, and set a new world climb record with an altitude of 3,000 meters in four minutes and 22 seconds.

Bye Aerospace is developing the Sun Flyer family of aircraft in addition to a family of advanced, high-altitude, long-endurance solar-electric unmanned aerial vehicles called “StratoAirNet.”



No visible cooling fins on that motor.  It doesn't appear to be designed for good heat dissipation.

Thomas Pedersen


The picture says:
Cooling: water/glycol


Or there is hardly any heat loss worth mentioning to make provisions for forced cooling other than air convection.


The motor/batteries liquid cooling system is used to heat cabin? A very good first start for quieter training e-planes.

Future higher performance batteries, e-motors and lighter plane body will extend endurance?


Will be interesting to compare the results of this new motor with the initial flights completed in Nov/2018; Still the key to this configuration is the performance of the battery, as always. I expect soon to see a hydrogen hybrid in light aero.

Tim Duncan

This is incredible, I am so surprised to see more electric airplanes. Except for flight schools and possibly some very small niche roles, today's GA market does not seem like a fit for electrification. 2600rpm is higher than most propeller planes cruise at. RPM Is a trade off with dia to keep blade tips subsonic, while longer blades are generally more efficient. It is so disingenuous to say this is zero emissions. Disappointing there was no battery discussion. No mention of range, useful load, performance or cost. .

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