Innovation for aviation Rolls-Royce and SINTEF Develop a Hybrid Aircraft Engine

Rolls-Royce and the Norwegian Research Organisation SINTEF are working on an innovative hybrid aircraft engine aimed at significantly reducing CO₂ emissions in aviation. This technology could enable savings of up to 30 percent and represents an important response to the challenges faced by the aviation industry.

Currently, a prototype of the aircraft engine is being constructed and is set to be tested in France next summer. The research project's ambition is to bring the new hybrid solution to market by 2035. However, the expert team still faces several challenges because achieving a minimal weight is crucial in aviation. At the same time, the batteries required for electric flight are considerably heavier than fuel.

Much development is needed to create the hybrid aircraft engine, including improvements to aircraft propellers, gearboxes linking the electric and combustion engines, electric powertrains, and energy management and distribution systems. “Everything must be as light as possible in aviation, so one of our main tasks is to reduce the weight of the aircraft engine as much as possible,” says Astrid Røkke.

Røkke works at Rolls-Royce Electrical Norway, which is collaborating with SINTEF on one of the project’s many work packages.

Researching the heart of the machine

SINTEF and Rolls-Royce are collaborating to develop the electrical insulation for the stator, which is located at the heart of the electrical machine and causes the rotor to turn. “The stator converts current sent through coils into an alternating magnetic field that spins the rotor. The coils require insulation to prevent short circuits, and this needs to be as thin as possible—without compromising the insulation’s lifespan,” Røkke explains.

Testing the insulation lifespan

Building larger and more powerful machines that operate at higher voltages and frequencies poses new challenges, as there are currently no methods to test this. “The industry lacks standards for calculating lifespan at such high voltages and frequencies. They only have data on how much a particular insulation material can withstand up to 1 kilohertz. Here, we're talking about up to approximately 50 kilohertz,” says Røkke.

She adds that Rolls-Royce, as a supplier to the aerospace industry, must understand how materials behave at these frequencies to ensure that the insulation’s lifespan is adequate. “Otherwise, we might create something that is unsafe to use.”

However, a newly developed testing method from SINTEF makes it possible to calculate the service life of this critical material.

Testing voltage and frequency

“Simply put, we test lifespan by connecting a voltage source to relevant test objects that represent the insulation. We turn the voltage on and off at a specified frequency until an error occurs, in order to determine the service lifespan of the test objects. Based on the test results, we can assess how voltage and frequency will affect the insulation's lifespan,” says Aakre.

“The testing method that SINTEF has developed is something we’ve needed at Rolls-Royce for a long time, but we haven't been able to find or had the expertise to develop ourselves. In other words, SINTEF has solved a real problem for us,” Røkke adds.

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Regional flights as the initial target

Initially, the hybrid aircraft engine is set to be tested and utilised for regional flights to reduce CO₂ emissions. Furthermore, it is easier to adjust battery capacities and weight on relatively short flights. The extent to which this new technology will be applicable in other segments of manned aviation will become clear as development progresses.