The Accelerating the Electrification of Flight (ACCEL) team led by Rolls-Royce is confident that over the next few weeks it will set a world speed record for an electric aircraft. A converted NXT Next kitplane called the Spirit of Innovation—with a 400-kW (500+ hp) electric propulsion system developed jointly by the aero-engines group with battery specialist Electroflight and motor and controller manufacturer Yasa—has made the first two of a planned program of 20 flights. It has already logged a speed within three mph of the current 132 mph record set by France’s Jean Luc Soullier in an Extra 330LE aircraft in March 2017.
In a September 24 media briefing at Boscombe Down military airfield in southern England where the flight trials are continuing, Rolls-Royce said it aims to bring the electric propulsion technology into commercial service by around 2025. The company is already developing an electric propulsion unit for Vertical Aerospace’s VA-X4 eVTOL aircraft and is partnered with Italy’s Tecnam to develop the P-Volt all-electric commuter airliner, for which it is providing batteries, motors, and power electronics. Airbus’s CityAirbus eVTOL technology demonstrator has been flying with a Rolls-Royce propulsion system.
Rolls-Royce Electrical customer business director Matheu Parr identified the pilot training sector as a likely early adopter of electric light aircraft and said that the UK government is now looking at this option for its military air training fleet. “Lots of two- and four-seater training aircraft are flying 14 or 15 hours each day from a single fixed base, which makes them perfect for electrification,” he told reporters.
According to Rolls-Royce, the battery pack developed by UK-based Electroflight is the most power-dense ever assembled with a rating of 72 kW/hr. The 1,200 cells are arranged in three parallel channels along with the aircraft’s three sets of motors and inverters in a thermally contained box lined with cork. At 450 kg, the box and its contents are lighter than most equivalent equipment for electric cars, the company said.
Rolls-Royce is also exploring options for hybrid-electric propulsion and intends to demonstrate a new turbogenerator at its German facility in 2023. The UK-based group’s capability beyond turbofan and turboprop engines was significantly expanded by the 2019 acquisition of Siemens’ electric propulsion business. Parr said that its power systems group is well equipped to meet ground infrastructure needs for electrifying aviation by setting up micro-grids and wind and solar power generation systems.
This week, Rolls-Royce director of flight operations Phill O’Dell will be resuming envelope expansion flights in the Spirit of Innovation aircraft. Flights were temporarily interrupted last week when engineers had to resolve a landing gear retraction issue.
The ACCEL team is aiming to exceed 300 mph. To meet the rules for the Fédération Aéronautique International’s aviation records, this will have to be achieved during a flight duration of no more than 30 minutes, logging the same top speed four times over a three-km course. The single-propeller aircraft’s propulsion system can support up to around 10 minutes of endurance at the highest speeds.
The Aerospace Technology Institute (ATI) is providing half of the funding for the ACCEL program, which is a partnership between the UK government’s Department for Business, Energy, and Industrial Strategy and industry group Innovate UK. The government is seeking to demonstrate its commitment to achieving zero carbon air transportation by 2050 as it prepares to host the COP26 climate change conference in Glasgow this November.