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'Work has just begun' as Spirit of Innovation project accelerates aerospace electrification

Professional Engineering

The Rolls-Royce Spirit of Innovation aircraft hit a top speed of 623km/h during flights (Credit: Rolls-Royce)
The Rolls-Royce Spirit of Innovation aircraft hit a top speed of 623km/h during flights (Credit: Rolls-Royce)

On 23 March 2017, the Siemens-powered Extra 330LE aerobatic plane hit a top speed of 343km/h, making it the world’s fastest electric aircraft. On 16 November 2021, just four-and-a-half years later, the Spirit of Innovation flew at 623km/h.

The extraordinarily quick electric aircraft, part of the government-backed Accel (Accelerating the Electrification of Flight) project, took the world records for fastest speed over three kilometres (556km/h) and 15 kilometres (532km/h). But the speed with which it beat the previous holder was almost as impressive as the records themselves, claimed project leader Rolls-Royce.

“Never before in the history of the World Air Sports Federation (FAI) record attempts has there been such a significant increase in speed over such a short timeframe, highlighting the rapid pace at which the electrification of aerospace is advancing,” the firm said.

Close collaboration between industrial partners – including several key British firms – was central to the project’s success, which could enable further advances in zero-carbon flight.

Automotive expertise

Rolls-Royce CEO Warren East gave special thanks to Cheltenham start-up Electroflight, which developed the plane’s powertrain and battery system. The size and weight constraints of aviation presented a particular challenge, says Electroflight technical director Douglas Campbell. ‘Unprecedented’ levels of energy density were needed – but the highest safety standards needed to be met.

The company drew on expertise from the automotive sector, including work on Formula E and hypercar projects, to develop a 756V DC max-voltage powertrain. A total of 6,480 lithium-ion batteries from Japanese firm Murata provided continuous power output of 488kW.

Three separate battery pack channels were housed in a carbon-fibre reinforced polymer composite case, each able to operate independently to add redundancy, and each channel was connected via an inverter to a 750 R axial-flux electric motor from British manufacturer Yasa, selected for its outstanding power density. The motor delivers 790Nm of peak torque and 200kW of peak power, with a speed range of 0-3,250rpm.

Campbell says the level of innovation on the project, part-funded by the Aerospace Technology Institute (ATI), was only possible due to its collaborative nature.

“Electroflight worked directly with Amorim Cork Composites to develop the fire-proofed laminate used within the battery case, a unique invention that is now patented. The team was supported by McLaren Applied to deliver the baseline spec battery management system, while Ansys Mechanical provided modelling software to evaluate the battery system thermal and structural performance. Additional testing was carried out at the Warwick Manufacturing Group (WMG) battery characterisation and testing facilities at the University of Warwick.”

Battery benefits

The project and world record runs provided important data for the development of future electric aircraft, Rolls-Royce said, possibly including all-electric urban air mobility vehicles – commonly known as flying taxis – or ‘hybrid-electric commuter aircraft’.

Technology used in the project will also influence wider decarbonisation of the aviation industry, says Campbell. “In the short-term, our priority was to set an all-electric flight speed record. Longer term, we believe the resulting technology will support the aviation industry as it shifts to a new greener model where power-dense batteries operate in conjunction with traditional power systems, such as turboprops, and new propulsion technology, such as hydrogen fuel cells, to deliver a hybrid powertrain solution.” 

He adds: “Batteries working in conjunction with a traditional engine would offer the first step to decreasing the aviation industry’s carbon footprint. The high bursts of power delivered by battery technologies are ideal for take-off or taxiing scenarios, and would also reduce noise pollution in built up areas.”

The next generation of batteries will need to provide far greater energy density and power, he adds, while also being smaller, safer and lighter to make them commercially feasible. “In other words, our work at Electroflight has only just begun.”


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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.

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