In the future, regional flights such as Trondheim-Oslo could become much more environmentally friendly with the help of a hybrid aircraft engine. This type of engine combines an electric motor and a combustion engine to drive a propeller. The innovation should be able to reduce CO2 emissions by up to 30 percent.

“The principle that causes emissions to decrease is the same as for hybrid cars – that is, a combination of both fuel and electricity,” says SINTEF researcher Torstein Grav Aakre.

Aviation accounts for about four percent of the EU’s total climate emissions. This solution has the potential to reduce emissions by as much as one percent throughout the EU, according to the researcher.

The focus is on regional flights because it is easier to make these flights greener using electricity.

“The reason is that batteries for electric engines weigh more than regular fuel. And the longer you have to fly, the more energy the plane needs to carry,” Aakre explains.

A lot needs to be developed to create the hybrid aircraft engine, including better aircraft propellers, gearboxes between the electric engine and the combustion engine, electric powertrains, energy management and energy distribution.

“Everything has to 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.

SINTEF and Rolls-Royce are collaborating to develop the electrical insulation for what is called the stator. It is located at the heart of the electrical machine and makes the rotor turn.

“The stator converts current that is sent through coils into an alternating magnetic field that turns 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,” says Røkke.

Building machines that are bigger and more powerful and have more power than before, require using higher voltages and frequencies. There are currently no methods to test this.

“The industry does not have standards for calculating service life at such high voltages and frequencies. They only have figures for how much a given insulation material can withstand up to 1 kilohertz. Here, we’re talking up to about 50 kilohertz,” says Røkke.

She explains that Rolls-Royce, as a supplier to the aircraft industry, must have knowledge of how the materials behave at these frequencies in order to be completely certain that the insulation’s lifespan is long enough.

“Otherwise, we might create something that is dangerous to use.”

But a newly developed test method from SINTEF makes it possible to calculate the service life of this important material.

“Simply put, we test the lifespan by connecting a voltage source to relevant test objects that represent the insulation. We turn the voltage on and off at a given frequency until an error occurs, to see the service lifespan of the test objects.

Based on the test results, we can find out how voltage and frequency will affect the service life of the insulation, says Aakre.

“The test method SINTEF has created is something that we’ve needed at Rolls-Royce for a long time, but that 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,” says Røkke.

“We’ve had a lot of good results, and the experiments are still ongoing,” says Aakre.

As expected, the researchers have confirmed that the lifespan is shorter with a higher frequency.

“That’s what we thought would happen, but we couldn’t know for sure, because no tests have been published on this before,” says Røkke.

Right now, a demo of the aircraft engine is being built and will be tested in France next summer. The ambition of the research project is to have the new hybrid solution on the market by 2035.

He-Art is an EU-funded research project that will demonstrate a hybrid-electric turbine propeller for aviation by the summer of 2026.

Rolls-Royce is supplying the electric motor and the electrical converter for the multinational research project.

Partners in He-Art are: Rolls-Royce, Airbus, ATR, Calyos, Capgemini España, CENAERO, CERFACS, CESA, EC Lyon, CNRS, CATEC, GSC, Ingpuls GmbH, INCAS, Leonardo, NTNU, ONERA, Ratier Figeac, Safran, SINTEF, SINTEF Energy, Skylife Engineering, Thiot Ingénierie, UC Louvain, University of Lodz and VKI.

He-Art is funded by HORIZON EUROPE Climate, Energy and Mobility Grant agreement ID: 101102013.