Rolls-Royce Unveils All-Electric ACCEL Aircraft

Credit: Rolls-Royce

Rolls-Royce has released the first images of an all-electric demonstrator aircraft the company is developing to fast-track expertise in electric propulsion and stimulate a UK-based supply chain in this growing sector.

Developed in partnership with electric motor and controller manufacturer YASA and startup Electroflight, the ACCEL (Accelerating the Electrification of Flight) is due to make its first flight in the second quarter of 2020. It is aimed at establishing a new speed record for an all-electric powered aircraft by targeting an airspeed of 300 mph (260 kt.) or more.

The tail-sitter aircraft, which is based on a heavily modified version of the diesel-powered Nemesis NXT Big Frog sport racing aircraft, currently is being fitted with the propulsion system. Ground tests of the integrated aircraft and propulsion system already are underway using a test airframe dubbed the “ion bird.” Rolls says “planned tests over the next couple of months include running the propulsion system up to full power as well as key airworthiness checks.” 

Supported in part by the UK government Aerospace Technology Institute (ATI), in partnership with the Department for Business, Energy and Industrial Strategy and Innovate UK, the ACCEL project is based at Electroflight’s Gloucestershire Airport facility in Staverton. Targeted specifically at developing know-how in energy storage and higher power density electrical systems, ACCEL is how Rolls is learning about the integration, packaging and management of lithium-ion batteries as well as gaining a better understanding of the thermal analysis of center cells.

With more than 6,000 cells mounted in the extended nose section to power the propulsion system, ACCEL will have “the most power-dense battery pack ever assembled for an aircraft, providing enough energy to fuel 250 homes or fly 200 mi. on a single charge,” Rolls says. Battery pack temperatures will be regulated using an active thermal management system configured with coolant pumps and a radiator mounted beneath the nose. At max power the system will deliver 750 kW and drive three YASA 750R motors. These will deliver more than 500 hp to the three-bladed propeller, which will spin at a relatively slower rate of 2,400 rpm.

The ACCEL project complements other, smaller-scale electric and hybrid-electric initiatives at Rolls aimed at the personal air vehicle and fledgling urban air mobility markets. For the latter, Rolls-Royce’s Indianapolis group is ground testing a hybrid electric system based on the company’s Model 250 (M250) turboshaft under a program that began in early 2018.

Guy Norris

Guy is a Senior Editor for Aviation Week, based in Los Angeles. Before joining Aviation Week in 2007, Guy was with Flight International, first as technical editor based in the U.K. and most recently as U.S. West Coast editor. Before joining Flight, he was London correspondent for Interavia, part of Jane's Information Group.


Don't we need to know how long the 250 homes would have power? I can't imagine the energy to fly a single engine plane 200 mi would be enough to power 250 homes for very long.
Something doesn't sound right here - 750kW ~= 1,000hp. BUT, the three engines "will deliver more than 500 hp". That means a transfer efficiency of something great than 50%.

Where are the losses coming from? When I've read about other power drive/motor systems the efficiency is 85+% with Tesla doing 94%-96% depending on the driving motor.
One of the great promises of electric power is the elimination of drag inducing air scoops necessary to feed the internal combustion engine and cool it. But this electric configuration unfortunately still needs a drag inducing scoop for the radiator to cool the batteries. But because oxygen is not needed for power production, higher altitudes will not decrease engine power. Higher altitudes in this aircraft should show its efficiency advantage over internal combustion engines.
I believe the term is "iron bird" and not "ion bird"
In addition, the aircraft in the picture looks more like a tail dragger than a tail sitter, unless I am mistaken
Unless I am mistaken, the aircraft is a tail dragger and not a tail sitter as described in the article. I also believe the term is "iron bird" and not "ion bird"
Tail sitter? Aircraft equipped with conventional gear are colloquially referred to as a "tail dragers". Tail sitter is a term reserved for one class of VTOL aircraft that take off and land sitting vertically on their tail, such as the Convair XFY-1 "Pogo".
Someone once said; if it looks good.......
Someone in the U.K still knows how to put a good set of lines to paper.....