Dufour updates Aero1 fully-electric aerobatic aircraft – the perfect test bed for eVTOL aircraft

The beautiful elliptical wings pictured here are reminiscent of the famed Spitfire of yesteryear. But here, it’s the Aero1 – the world’s first all-electric aerobatic aircraft, officially presented to the world in 2016, and a test platform for Dufour Aerospace.

It’s only been flown by a select few, like Dominique Steffen, one of the three Co-founders of Dufour Aerospace. Dominique has extensive aviation and engineering experience. He is a World Cup Champion in paragliding aerobatics and a Red Bull competition pilot. He thus brings considerable expertise and experience in flight static, aerodynamics, flight-testing and system integration.

 “The Aero1 is a joy to fly,” he said. “We’ve gained a tremendous amount of experience and knowledge from designing and building the Aero1. Indeed, we’ve been working with electric propulsion since 2015, so we know exactly what works and what is challenging. We know what is real in the eVTOL space and what is dead weight,” he said with a laugh. 

“Flying without vibrations and almost no noise is a special experience. Over 200 km/h you can practically only hear the wind noise, the feeling is similar to being in a jet”

In the eight years since its maiden flight, the Aero1 has enjoyed a full flight test program – all manner of aerobatic manoeuvres including rolls, loops, Immelmann, hammerheads and spins. The Aero1 is capable of performing these up to +6 /-4g – and does so nearly silently. When flying above the airfield, you barely notice Aero1 – while traffic from nearby streets and trains further afield is dominant.

“Flying the Aero 1 through aerobatics also differs from normal flying. Flying with just one lever makes everything much easier. The recuperation makes the flown speeds much more constant and overspeeding the motor/propeller is impossible.” said Steffen.

The aircraft is not simply for loops, however. 

The Aero1 was designed to rigorously test the propulsion systems earmarked for future eVTOL aircraft, namely the Aero2 and Aero3 and their tilt-wing innovation. This hands-on, practical approach ensures that the propulsion systems for the Aero2 and Aero3 are thoroughly vetted and optimised for performance and safety. During the past years, the team at Dufour Aerospace updated the aircraft with a new propulsion system and batteries to improve performance and for testing purposes to inform Aero2 and Aero3. 

“The Aero1 provides a real-world platform to test redundant propulsion systems, verify performance data under actual conditions, and observe system behaviour during high power situations,” said Felix Steinmann, Aerospace Engineer and Aero1 project leader. “For instance, this platform provided us with confidence to use Geiger Engineering motor and controller systems for the Aero2 main motors – it fed directly into the development of our tilt-wing aircraft. We learned a lot about cooling of the motor and controller, software architecture and parameterization, system limitations and post-flight analysis,” he said. “It’s all about thermal management of the solely air-cooled drive system – starting with the initial design of the air cooling ducting, testing on ground and in flight, optimizing and re-testing again and again.” 

Depending on the flying environment, Aero1 has about 35-45 minutes of flying time, plus reserves. Test flights occurred in the mountainous Swiss regions, where the initial climb was to 8,000 feet above the ground. 

The Aero1 is equipped with a duplex drive system with a continuous power of 50kW and a peak power of 70kW. With a maximum take-off weight (MTOW) of 420kg and 18.6kWh battery capacity, the Aero1 can comfortably cruise at 150-160km/h at 18kW, or 210 km/hour burning 35-40kW. The Vne – the maximum permitted safe speed – is a sprightly 305 km/h. 

Aero1 will continue to provide important insights for Dufour Aerospace, as it has done in the past. Dufour's decision to rely on a hybrid engine for Aero2 and Aero3 is a direct consequence of the flights with Aero1. While in theory it would be possible to land a fixed-wing aircraft like the Aero1 with the last available battery capacity at reduced power or even in glide, this is not possible with a vertical take-off aircraft like Aero2 or Aero3, where the highest power is needed in the very last phase of the flight – during landing. For this reason, Dufour Aerospace has chosen to design Aero2 and Aero3 with an electric hybrid system, able to recharge batteries during flight and ensuring full battery capacity at the beginning of the landing phase.