Electric Planes: They Have Arrived    • Electric Planes: They Have Arrived  


Rolls Royce have been at the forefront of aero engines for over 100 years and are no strangers to the record books. The Rolls Royce Eagle was the engine in the Vickers Vimy, the first aircraft to cross the Atlantic in 1919. But the ACCEL, an acronym for “Accelerating the Electrification of Flight” seems to hark back to the late 1920s when Supermarine were chasing down the Schneider Trophy for racing seaplanes. In those days, amphibians seemed to be the future of aircraft: you see, before WWII, long, well paved runways were about as rare as an honest politician. It was a Supermarine S.6B powered by a supercharged Rolls-Royce R engine that broke the world airspeed record in 1931, reaching a speed of 407.5 MPH. This race series was one of time period’s great drivers of airplane innovation. Most remarkably – the invention of engine cooling without radiators, by ducting coolant under the skin of the aircraft’s surface. Foreshadowing RR’s proclivity for novel solutions to high performance aeronautical challenges.
Following in the tradition of their racing heritage, Rolls Royce are building the ACCEL, a sleek race plane based on the airframe of the Sharp Nemesis NXT that’s capable of a blistering top speed.

The ACCEL is propelled by three lightweight axial electric motors driving a single three-blade propeller in a conventional sport class format.
The 82 lb / 37 kg YASA 750 R motors will deliver more than 500 horsepower to the Accel’s propeller. The Supermarine of days past had to make do with highly inefficient fixed pitch propellers, but the ACCEL’s electronically controlled variable pitch prop will allow the torque and motor speed to be tailored on the fly. The high power density axial motors operate at a lower RPM than a conventional plane, increasing stability and reducing noise.

The ACCEL’s high energy density pack has enough juice to fly 200 miles – from London to Paris on a single charge. Once again, it’s cooling that provides a significant challenge on such a power dense unit, this time the 750kW battery rather than a 2,800 Horsepower V12.

The 6000 battery cells are tightly packed to the fore of the pilot, and would melt your popsicle without a vigorous heat exchange campaign. Liquid cooling is used to transfer the heat into radiators ducted so smoothly into the fuselage that they’re almost invisible – look out for the NACA duct intakes just behind the propeller, a popular choice for a low drag duct entrance. Also notice the bulge under the batteries where the radiators and pumps are housed. That said, today’s engineers have much less heat to contend with than the intrepid technicians who worked on the Supermarine. With a system efficiency over 90%, we can expect that only 75kW (100hp) of power must be transferred out of the aircraft as heat loss. By comparison, it’s estimated that the Supermarine S6B had over 750kW (1000hp) of excess heat to dissipate from its powerful but inefficient engine – the same as the full power of the ACCEL’s powertrain. This allows the engineers to get away with a relatively small radiator unit which can be seen on the test rig, the IonBird, along with the large inverter and other power electronics that give a sense of scale to the crafts athleticism.
The record to beat stands at 213 mph (343 km/h) set by Siemens in 2017 in a modified Extra 300.

The ACCEL project is aiming for a top speed of over 300 MPH with their first aircraft, ‘the spirit of innovation’

Rolls Royce have since bought Siemens’ eAircraft unit. The broader purpose of the ACCEL project is to bring together electric power specialists and develop the technology and supply chains to suit future ventures.


As we’ve seen in the automotive world, with companies competing for bragging rights in souped up race cars, innovations learned on the track can translate into real world performance enhancements. The goal is for the optimizations made in high performance electric powertrain design to trickle down to broader commercial applications.


The racer is only the beginning of electric aviation for Rolls Royce and just one strand of their R&D efforts.