Rolls-Royce’s lift motor for eVTOL aircraft is air-cooled and direct-drive.
Rolls-Royce plans to begin ground-testing its lift motor for electric vertical-takeoff-and-landing (eVTOL) aircraft this month and is under contract to deliver units to Embraer for Eve Air Mobility’s full-scale technology demonstrator.
“We are taking this through a few loops in terms of getting to the final production version,” Rolls-Royce Electrical President Olaf Otto told the Vertical Flight Society’s Electric Aviation Symposium in Oshkosh, Wisconsin, in late July. “Our Loop 1A is ready to go on test this August.”
Eve is planning to begin building its first full-scale prototype in the third quarter, aiming for a first flight early in 2024. The aircraft will have eight lift propellers for vertical flight and a pusher prop for wingborne cruise. Production aircraft will use motors developed by an Embraer/Nidec joint venture.
“We are providing strategic support to Embraer in the development of the Eve platform, and this includes the supply of electrical propulsion units for their upcoming proof-of-concept platform,” Julia Hetz, head of marketing for Rolls-Royce Electrical, tells Aviation Week.
Rolls is under contract to supply the same lift motor to UK startup Vertical Aerospace for its production VX4 eVTOL. Vertical’s full-scale demonstrator is powered by motors supplied by UK company Equipmake. The aircraft crashed Aug. 9 during testing, but a second demonstrator is being built.
Weighing less than 55 kg (121 lb.), Rolls’ lift motor produces 150 kW of continuous power and 1,600 newton-meters maximum torque. The motor is air-cooled, with a transverse flux architecture. This is a motor-winding configuration that enables the 3D flow of magnetic flux, increasing low-speed torque.
The eVTOL lift motor is one of three products under development at Rolls-Royce Electrical following its decision to shelve the certification program for an electric propulsion unit (EPU) for small propeller aircraft. “We don’t for us see that the market size and speed is significant enough,” Otto said.
Rolls is beginning assembly of a high-power, mid-speed EPU for Part 23/CS-23 commuter aircraft. This is planned to be on test at the end of 2023. The power level for the production unit still is being decided in discussions with customers. The starting point is 320-400 kW for a motor that weighs less than 160 kg.
“It seems the upper end of this range is more attractive,” he said. “This is a radial flux machine, so scaling up is possible within a certain range. I think this will top out somewhere around 430-435 kW if you still want it to be completely air-cooled.”
Rolls’ third product in development is a clean-sheet 600-1,200-kW turbogenerator for hybrid-electric propulsion systems. “This is on the test stand in our facility in Berlin and being tested and paired with a generator. And the first runs of the complete system are to take place next year,” said Otto.
“There is a completely new gas turbine that is being designed from the ground up for sustainable aviation fuel and to be hydrogen [H2] compatible,” he said. “We can simply exchange the burners and then burn H2 in this gas turbine as well.” Power-to-weight ratio for the turbogenerator is 4 kW/kg.
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