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Evolito’s Breakthrough Axial Motors
  • 16 Apr 2024 07:47 PM
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Evolito’s Breakthrough Axial Motors

By Tom Risen
Vertiflite, May/June 2024

The unique Evolito axial flux motor design gives it a high power-to-weight ratio.

Lightweight electric motors can power a diverse range of aircraft types.

Bicester, UK-based Evolito plans to match demand for electric aircraft once regulators enable large-scale revenue flights by designing electric powertrains that are efficient, lightweight and cost-effective enough to support the nascent sector.

The axial motors, motor controller units and batteries built by the UK propulsion developer can be paired with or customized for a range of aircraft types including rotary-wing, fixed-wing, uncrewed, and electric vertical takeoff and landing (eVTOL) aircraft.

Evolito’s scalable production mindset draws on its experience with the automotive sector as part of YASA Motors before launching as an independent company in 2021. The two separate companies still have a cross-licensing agreement to share all intellectual property, including more than 200 patents that they can each use for electric autos or aircraft.

Evolito’s headquarters is in Bicester, Oxfordshire, about 11 miles (18 km) east-northeast of Oxford, England.

Competitive prices for parts could enable electric airframers to scale up aircraft production if demand grows, Evolito CEO Chris Harris said in an interview, adding, “ideally, that sort of automotive type pricing is in our DNA from day one…. If we can get the pricing right, it enables the industry to take off.”

Building with lightweight polymer instead of heavier metals, when possible, Harris said, is among the ways the company wants to sell cost-effective, streamlined products that can be more easily mass produced. The YASA motor includes a steel backplane for magnets, for instance, while Evolito uses polymer instead.

Evolito also sells compact motor controller units, or inverters, with a dual-lane design that complements the axial motors. Modular architecture in Evolito’s battery solutions allows the electric power system to be tailored for a range of electric and hybrid-electric aerospace projects without needing a tailor-made design.

Axial Motors for Aerospace

The YASA electric motor has an axial, dual-rotor design, differing from the more widely used radial single-rotor design. That powertrain built by YASA for electric automobiles, Harris said, adapts well to aerospace because it is designed for “very high power density, very high torque density, [and] small battery packaging space.”

The 19-lb (8.5-kg) Evolito D250 is designed for low torque for both low speed/low-power or high-speed/high-power applications.

The twin axial-flux electric motors are packaged together with a common driveshaft and lack the extra weight of a central yoke used in a traditional radial motor. Dual motors provide safety through redundancy, while space between parts enables high current densities — compared with a radial motor — with thermal management features, including a dielectric liquid cooling system that runs between the edge coils. 

“This topology allows you to directly cool the coils, which means you get very high efficiency,” Harris said, adding that the ability to operate an axial motor “pretty close to your peak power is a real attribute.”

The Evolito axial motor has two rotors with the magnets opposing each other and a stator in the center to provide the magnetic field that drives the rotating armature, generating the electric current. A stator in turbine engines, in contrast, guides the flow of fluids between rotating parts.

Chopping the stator of the Evolito motor into two halves is designed to add safety through redundancy, Harris said, while minimizing weight on the axial motors reduces the risk that parts of the motor could break through their containment and damage the aircraft.

The 66-lb (30-kg) Evolito D500 (shown here packed in three stacked motors) is designed for mid-torque and mid-speed applications.

Standard Evolito parts share the same core technology and are designed to pair with several aircraft types for fully electric or hybrid-electric propulsion. Customers who order designs that are more bespoke for their aircraft requirements pay extra for the application engineering.

Investor financing and grant funding also helps Evolito navigate the processes of development and certification. During the past two years, Evolito has developed its new 40,000 ft² (3,700 m²) headquarters in Bicester, near Oxford, with manufacturing space that Harris said can scale up to increase production “at the right kind of pricing when the time is right.”

In December 2023, the UK Civil Aviation Authority (CAA) awarded design organization approval (DOA) to Evolito for its electric propulsion products, clearing the way for it to start the type certification process. Evolito expects to gain type certification within the next two years.

Startup Mindset

The 77-lb (35-kg) D1500 is designed for high-torque, low-speed applications where the motor is connected directly to a propellor, without a redundancy stage.

Favoring the startup mentality after years of building YASA gives him a management style of “let’s go make this happen quickly, let’s get on with it, and let’s move quickly, make good decisions and build something,” Harris said.

To keep Evolito agile, Harris said he draws on his decades of work with technology startups. In 2011, Harris joined YASA as its CEO and developed the business with YASA founder Tim Woolmer, who is still chief technology officer at the electric automotive powertrain maker. Woolmer had originally conceived of the technology during his time at the University of Oxford, where he earned a PhD in electrical engineering.

Together, they guided YASA until its purchase by Mercedes- Benz AG in 2021, when Evolito was spun out to focus on aerospace applications, with Harris as CEO of the new company. Between 2014 and early 2023, Harris was also the chairman of UK-based Cambridge Photon Technology, which develops advanced materials to improve the performance of solar panels.

During the nearly three years since its launch, Evolito has hired staff with experience at aviation firms and engine makers, including Collins Aerospace, Safran and Rolls-Royce.

Harris holds a PhD in atomic physics from Imperial College London and said that he shifted from engineering work to managing startups because “I love taking new disruptive technologies through to market.”

Evolito is also leveraging “over a decade of scars” and lessons from motor development at YASA, Harris said, remembering examples, including “the first time we were trying to make a motor, trying to get it into a Jaguar prototype.”

“We start with a higher maturity level than perhaps others that are starting this journey do,” he said of the aerospace startup culture blended with 12 years of electric automotive experience at YASA.

Set Realistic Expectations

When marketing a new and disruptive technology, including electric flight, companies must set realistic expectations to ensure steady support from investors, Harris said.

The eVTOL sector is only part of Evolito’s target market for its off-the-shelf motor products, but it also generates the most public attention, because it has the “potential to become the very biggest market,” Harris said. The years-long path ahead for eVTOL development towards revenue flights, he adds, is a good example of the need to manage expectations for emerging aircraft types and new technologies.

Cautionary tales of startups that have lost market confidence by overpromising or by running out of money, Harris said, can lead to “cycles” where investors gain or lose appetite for entrepreneurship in certain sectors.

Evolito CEO Chris Harris served as CEO of YASA from 2011 until it was purchased by Mercedes in 2021, when Evolito was spun off to focus on the aerospace market.

Evolito has a marketing style that is “not necessarily very flamboyant,” and that it doesn’t often advertise its partnerships or deals to boost its profile, Harris said.

When Evolito does make a statement, they have proof to back it up. In 2016, YASA boosted recognition for its technology through grand demonstrations, for instance, by developing axial electric motors in 2016 for a modified Robinson R-44 helicopter that flew on battery power, as part of a team led by Tier 1 Engineering (see “Tier 1 Engineering Pioneers Electric e-R44, Vertiflite, July/Aug 2022).

In 2021, an Evolito electric motor also powered the Accelerating the Electrification of Flight (ACCEL) battery-powered airplane, a demonstrator built by a team led by Rolls-Royce (see “Momentum Builds for eCTOL and eSTOL Aircraft,” Vertiflite, Nov/Dec 2021) that broke the speed record for battery-powered flight by reaching a top speed of 345 mph (555 km/h).

Evolito motors — whose names refer to the torque class in Newton-meters — span from the low-torque D250 with a peak power density of 12.7 kW/lb (28 kW/kg), to the mid-torque D500 with peak power density of 5.4-kW/lb (12 kW/ kg), which can be stacked for increased torque and power up to 1 MW. Evolito’s D1500 has up to six times the peak torque of the D250 and three times that of the D500, and has more than 1,000 hours of in-flight testing.

The outer housing of an Evolito axial flux motor.

Keeping investors both well informed and in a low-key partnership can help those partners sidestep potential pressure to generate profit from the deal while the startup brings its product to market.

“It typically takes a decade to get a new disruptive technology [ready for] the market, to be accepted and to drive towards profitability,” Harris said. “Don’t over-invest too early, but don’t be late. It’s about getting that balance right.”

Manufacturing powertrains and electric components can be less costly in time and money compared to developing a new aircraft, which could enable Evolito to meet its certification timetable and supply cost-effective parts to a growing electric flight market.

Evolito plans to showcase its standard electric motor components in July at the Farnborough International Air Show.

About the Author

Tom Risen is a business journalist in Washington, DC, who has written about space and aviation for publications such as Cirium, Aerospace America and US News & World Report.

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