Developing a transverse flux machine for Urban Air Mobility

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Developing a transverse flux machine for Urban Air Mobility

Developing electric and hybrid-electric vehicles for the Urban Air Mobility market means overcoming a host of complex challenges.

To support operations and applications in urban areas, eVTOLs (electric vertical take-off and landing) vehicles must be safe at low weight, creating considerable thrust with low-speed propellers to limit noise pollution.

We spoke to Dr Andreas Reeh, Global Head of Electromagnetics and Thermal Design - Electrical, Rolls-Royce, about overcoming these challenges and developing a non-conventional electric machine topology to meet the requirements of our UAM customers.

Tell us about your background

Dr . Andreas Reeh, Global Head of Electromagnetics and Thermal Design, with an image of the novel electric propulsion unit for Urban Air Mobility the Electrical team is working on

Tell us about your background

My background is in physics, engineering and aerodynamics and my doctoral studies focused on wave propagation phenomena in flows. This theoretical basis provided a valuable foundation for my understanding of electrical machines.

I joined Siemens eAircraft, (which would later become part of Rolls-Royce), in 2015 in the field of systems architecture and integration, looking specifically at propeller flows and potential system configurations for hybrid-electric aircraft. Since then, I’ve become more and more involved in electrical propulsion architectures and components.

How were you involved in the development of our topology for UAM?

As well as working on electrical flight demonstrators, my colleagues and I dedicated a lot of our time to further research in conventional and non-conventional propulsion unit topologies. We conducted corresponding technology studies for electrical machines and the opportunities they presented for customers in UAM.

Our aim was to find technologies that could address the challenge of designing an aerospace certifiable high torque, low speed electrical machine that is lightweight and efficient enough for UAM applications without requiring a liquid cooling system.

Different types of machines each have their pros and cons. Looking at the requirements of vehicles in the UAM market and possible system architectures, we derived and down selected an electrical propulsion unit based on an air-cooled transverse flux machine.

We put together and started off with a small technology project team to develop a technology demonstrator out of the concept in an agile manner. The team grew as we progressed to finalising our first demonstrator. In 2020, our machine went to test, validating a lot of our design assumptions and giving us confidence in the next stage of development as part of our UAM project.

What is a transverse flux machine?

The transversal flux machine topology creates a three-dimensional magnetic field to enable high torque density and air-cooling.

What is a transverse flux machine?

The transverse flux machine (TFM) is an innovative electrical machine design that utilises three-dimensional magnetic field guidance to enable a high torque density design which can be air-cooled and doesn’t require a gearbox, reducing overall system complexity.

The TFM concept allows for low-speed direct drive motors which also help in reducing noise levels enabling safe application in urban and densely populated areas. It also has the advantage of providing more design freedom, as well the ability to implement our unique multi-lane architecture and short-circuit proofing. The combination of these requirements is hard to meet with conventional radial flux machine designs.

How did the team work together to develop the TFM concept?

The most recent technology demonstrator of a TFM machine for Urban Air Mobility propulsion in one of our Munich labs.

How did the team work together to develop the TFM concept?

Understanding the challenges of UAM requires an interdisciplinary team. At Rolls-Royce, we were able to bring together years of experience in this exact application and draw on expertise in system design, electromagnetics, thermal design, structural analysis, mechanical design, and manufacturing. This is a real differentiator for us and the technology we develop.

The project has been a great example of agile working and how to foster creativity until physical realisation. Having six of us initially working vastly undisturbed in a dedicated focus area for the first technology realisation, we had a lot of fun.

Today, the number of people working on the project has grown and it is an important part of the UAM programme based across Budapest, Cottbus, Dahlewitz and Munich. It really shows how much the original idea and our understanding of electrical aviation have matured and how much we’re able to accomplish.

What’s next?

We’ll be conducting a second round of tests on the technology soon, as well as delivering a version of the machine for our customer’s aircraft demonstrator. From this, we’ll be able to derive valuable data to inform future designs.

As the technology continues to mature, we’re increasing not only the number of people working on it but also the skills we can bring to its development. We’re increasingly focused on system interactions and the full lifecycle, especially how to achieve the required reliability, serviceability, especially how we can create highest value throughout the full lifecycle up to product recycling.

It has been an exciting endeavour and we’re continuously learning more about the application and the customers’ specific needs further fuelling our innovation journey.

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