Propulsion Technology to Unlock Urban Air Mobility's Full Potential

April 29, 2024

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The exciting Urban Air Mobility (UAM) market offers new opportunities for travel and transport, alongside promising long-term financial prospects for companies looking to provide those services in the future. The value of those services for end users will be strongly driven by the reliability, availability and performance of the electrical vertical take-off and landing vehicles (eVTOL) which will serve this market, with providers needing to ensure they maintain the very high safety and environmental requirements the industry demands and that are key for social acceptance.

Power and propulsion systems are critical in helping to unlock the full potential of these UAM vehicles. At Rolls-Royce Electrical, we’re creating real lifecycle value through our differentiated portfolio of technologies that can be optimised to customers’ platforms, are high performing and meet the highest safety standards with fail safe features.

We spoke to Markus Christmann, Chief Engineer UAM at Rolls-Royce Electrical about how we’re addressing these challenges from the earliest stages of design through to testing.

How can we create true lifecycle value for customers in UAM?
Low operating costs are key to enabling mobility models that will unlock the volumes operators need to build financial success. The price of passenger journeys per mile is forecasted to be competitive, so every minute on the ground could impact profits.

Therefore, the electrical propulsion units (EPUs) used to power eVTOL need to have very low maintenance and serviceability requirements and long time on wing.

At Rolls-Royce, our experience in Civil Aerospace and Business Aviation means we understand the cost structures involved and bring the right toolset to our design activity so that we’re designing for reduced maintenance and serviceability from the outset.

Our products incorporate differentiated design features that focus on robustness and reliability for the expected lifetime of the aircraft.  

There are a variety of different eVTOL aircraft designs out there. How do we ensure the value of our propulsion solution for each of them?
We can support platform adaptation and optimise systems for individual aircraft and operation through a modular design, which at the same time facilitates maintenance and servicing.

Our electric propulsion unit for UAM, for example, is made of three key components – a transversal flux electrical machine to create the required torque for the propellers, an external load cartridge (ELC) to mount the motor to the aircraft, and the power electronics controlling and protecting the motor (lane control units or LCUs) – and these are all scalable and adaptable to meet different platform power demands. They’re also designed to enable flexible installation on the platform and improved serviceability, reducing downtime.

A solution optimised for the platform provides the opportunity for a lighter and more efficient design for each type of flight profile. Both factors in combination reduce the energy the aircraft uses and enables further range or flying hours between charges, keeping passengers moving without disruption.

Our designs feature novel technology bricks – how will they help to differentiate our offering for UAM compared to more established technologies?
Our technologies are designed to deliver the highest safety and performance, and optimum platform integration.

Torque density plays a big role in performance. This is the torque you’re driving out of the motor divided by its total weight, including all its auxiliary systems. By using air-cooling in our design rather than liquid cooling, we can reduce overall system weight and increase torque density, enabling the highest efficiency for the six to eight propeller aircraft we expect to see in the UAM space. We have also chosen a transversal flux motor topology, which in combination with the air-cooled approach maximises the achievable torque.

The torque requirements for our motor design are guided by the UAM market’s need to operate at minimum aircraft noise, as they will be operating in cities that are densely populated. Our motor design therefore allows for slower propeller rotations and reduced noise levels.

We are also building on our experience and knowledge of the operating environment and ability to design for it, meeting the requirements operators will need as the industry develops.

How are we ensuring the highest safety levels for our UAM products?
UAM vehicles are intended to be able to fly everywhere, including highly populated and congested urban areas with often long operating hours. Therefore, our solutions will need to meet the highest industry safety standards and our ambition is to deliver propulsion systems with significantly higher fault-tolerance and redundancy than current standards for helicopters today.

Our multilane architecture allows us to manage failures within the electric propulsion unit and still deliver up to 65% of the total power. It also helps to reduce overall system weight without compromising on safety.

Through developing our Electrical Distribution System, we’re also looking at what the automotive industry has done in terms of insulation monitoring and considering the benefits this could deliver within aerospace. Our extensive testing capabilities mean that we can test a variety of insulation materials at high voltages, as well as different environmental loads like temperature, humidity, vibration, and potentially harmful particles like sand. Our aerospace heritage while learning from the automotive industry means we are combining the best of both industries when delivering our propulsion systems that will power this exciting new Urban Air Mobility market.

Source : Rolls-Royce