By Elan Head

An award-winning journalist, Elan is also a commercial helicopter pilot and an FAA Gold Seal flight instructor with helicopter and instrument ratings. Follow her on Twitter @elanhead


Dufour’s tilt-wing eVTOL demonstrator completes initial flight testing

The Swiss startup Dufour Aerospace has wrapped up the first phase of flight testing of its tilt-wing eVTOL technology demonstrator, successfully completing 550 test flights including full transitions from hover to wing-borne cruise flight and back again.

Based in Visp, Switzerland, the company was co-founded by Dominique Steffen and CEO Thomas Pfammatter, who is also a professional helicopter rescue pilot for the Swiss operator Air Zermatt. The two collaborated on the aEro 1 electric aerobatic plane that debuted in 2016. Chief technology officer Jasmine Kent — a software engineer who spent eight years with Google and co-founded the artificial intelligence (AI) startup Daedalean — joined the company in 2017.

In March 2018, Dufour revealed plans for an aEro 2 hybrid-electric VTOL platform, inspired by the experimental tilt-wing Canadair CL-84 that was tested extensively in the 1960s and early 1970s but never entered production. Kent told eVTOL.com that the company was attracted to the inherent efficiency of a tilt-wing design, whether for hybrid or fully electric applications.

Dufour used simulation and subscale models to refine its VTOL design, proceeding to build the fully electric unmanned technology demonstrator last year. The demonstrator’s wingspan of around four-and-a-half meters is smaller than the wingspan envisioned for a production passenger-carrying aircraft, “but it puts the aerodynamics very much in that ballpark, which is why we chose that size,” Kent said.

As lead aerodynamics engineer Felix Rubin explained in a press release, “At larger scales, slipstream airflows over tilting wings become more turbulent and harder to predict, and care is needed to ensure that the aircraft remains stable during transition. With this large-scale unmanned aircraft, we’ve now been able to demonstrate that we can achieve that stability at high Reynolds numbers.”

Flight testing has been taking place this year at Raron airfield near the company’s headquarters in Visp, even during the COVID-19 pandemic. With only around 15 people involved with the project, “we’re a small team so we’ve been able to continue working, especially in the hangar and on the airfield — these are larger open spaces,” Kent explained.

“We started very small and many of the first flights were just hover tests, and we iterated very slowly and carefully and checked that all of the systems were working as expected. We also did quite a lot of control software iteration in the early phases of the flight test campaign,” she continued, noting that Dufour has been working closely on flight control development with the Autonomous Systems Lab at the public research university ETH Zurich.

Dufour eVTOL demonstrator
Dufour’s technology demonstrator is fully electric using lithium polymer pouch cells, but the company expects that its future customers will initially want hybrid-electric aircraft for greater payload and range. YouTube Screenshot

“Once we believed it was ready to go to a full transition, we were able to actually achieve that, without too many further changes to the control system. So, that was quite gratifying to show that our simulation systems and calculations were lining up well with reality,” Kent said.

Dufour is now exploring development of a commercial unmanned platform based on the technology demonstrator, while also using insights from the flight test campaign to continue progress on a larger, crewed VTOL aircraft.

“The goal for us ultimately is to develop a vehicle that is a helicopter replacement, particularly for medical transport,” Kent said. “We believe there is a big opportunity in the market for an aircraft that can do medical transfer flights faster and much more cheaply than a helicopter.”

She said Dufour aims to begin manufacturing a full-sized experimental VTOL prototype next year, with flight testing to begin with a human test pilot by 2022, if “there are no hiccups along the way.”

Although Dufour expects its initial passenger-carrying platforms to have on-board pilots for operational and certification reasons, Kent said the company continues to collaborate on “more forward-looking projects” with Daedalean, which is developing an AI-based autopilot.

“Sometime down the line, it will make sense to make the vehicles autonomous. I think we’re not there yet, but ultimately it will be possible to make them safer if they are autonomous than with a human pilot,” Kent said.

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  1. The goal is to fly “faster and much more cheaply than a helicopter.” Dufour will also have to look deep into rotor/propeller efficiency issues. When both hover (i.e. vertical lift) and cruising are expected from the same propulsion system you deal with a very wide speed range – even if admissions are made in agility and top speed. Fixed pitch propellers won’t do. Out of variable pitch options the new Stallfree propeller concept is recommended. ( http://stallfreepropellers.com/ ) So you can make the best use of available battery power.

  2. What is the “Flight Time”? What is “Altitude Limit”? What is the time to “Recharge”?

  3. For anyone following the fast growing sector of evtol/ectol (including hybrid architecture) prototypes under development in the last few years, this company has been doing his homework and instead of marketing an unfinished product, they have been working behind the scene to continually improve their design. Good questions are asked, and I am sure they are considering all avenues and definitely will do their best to outperform other design in their vision. I believe flight time and altitudes will compete with traditional helicopters. Range will outperform them. Amazing design!

    1. I agree Dominque. I’m glad to see you say that.

      I’ve spoken to Thomas and Jasmine and was blown away by their pragmatic approach and the 5 years they took to come up with this design. Thomas is a search-and-rescue helicopter pilot and really knows his way around that technology in the toughest of environments. He says he wanted to find a better tool than a traditional helicopter. Dufour Aerospace is aiming at reducing the cost of helicopter prices and maintenance.

      I’ve been impressed with this company since it showed its Hamilton aEro1 five years ago. Much as the Swiss cliche is true, they are steadfast, pragmatic, and making sure their ducks are all lined up before going public. It’s refreshing to see and spells good news for our UAM and regional air mobility world.

  4. If vertical flight takes 4 times the thrust of high speed lateral winged flight why not use 3 or 4 props for vertical and 1 or 2 tilt motor-rotors for high speed low power consumption winged flight? While all electric is greenest, using all electric with limited battery capacity (and weight) for the 3-4 motors during vertical flight and a single avgas engine for lateral flight (and battery recharge) will extend range several-fold.

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