After endurance records, the next goal for electric, zero-emission flight is speed. TIM ROBINSON looks at a proposal for the world’s fastest purpose-built electric racing aircraft.

 

Roger Targett and the Electroflight P1e mock-up (Ed Hicks, Flyer.co.uk)

Until today, any word association game with electric aviation might have picked ‘green’ and sustainable’ – but ‘high-performance’ or ‘fast’ would not be among the words chosen.

Solar Impulse, for example, which circumnavigated the world in 2015-16, has a cruising speed of only 56mph. Meanwhile, Airbus’ e-Fan demonstrator, has a top speed of 220km/h or just 136mph. The current speed record for a manned electric-powered aircraft is only 220mph – set in 2013 by pilot Chip Yates using a modified Long-EZ.

However, a UK company, Electroflight, is aiming to change all this, by pushing electric propulsion to the limit in the aim of creating a ‘Formula E of the skies’ or even an ‘electric Red Bull Air Race’. Performance and power are the watchwords – with the aim of going 250mph and beyond. Founded around six years ago by Roger Targett, the goal of Electroflight he says is: “To develop high-powered, high-performance electric propulsion systems for use in aerospace and showcasing them through the P1e aircraft initially, then establishing an air race series based on the P1e aircraft, to push the development of batteries, motors and control systems in aerospace.”

Electroflight say the aim is to build the world’s fastest high-performance, full electric sport aircraft.

The engine

Two high-density YASA electric motors are planned to provide the power for the P1e. (Electroflight)

Key to Electroflight’s plan is a lightweight, electric motor that promises a better than a 1:1 power-to-weight ratio, giving the P1e the kind of face-melting acceleration usually experienced by jet fighter pilots or F1 drivers. (Indeed, this is already being exploited in the motor industry by Elon Musk’s electric car company Tesla – its Model S P100D hit 0-60mph in 2.275 seconds recently in ‘Ludicrous Mode’ – making it the fastest accelerating production car in the world.)

The Electroflight P1e will use axial flux YASA 750R motors. Says Targett: “The motors weigh 37kg and produce 750newton metres of torque at 2,750rpm and can run 200kW (264hp) peak for 60 seconds. Max continuous is half that.”

The first flight of the Electroflight P1e will use a single 750R motor, while the contra-rotating propeller system will be developed and tested on a bespoke test rig, for use in later versions of the P1e or possibly other aircraft. The contra-rotating unit will use two motors in tandem driving two-bladed propellers. In this arrangement, each motor drives a seperate shaft and does not require a complicated gearbox. This is a much simpler mechanical arrangement than in the contra-rotating propeller units driven by piston or turbine engines.

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The power-to-weight of the P1e would be significantly better than the aircraft currently used in the Red Bull Air Race series. We may have to ‘de tune’ the P1e for the typical RBAR race track!"

Power for these motors will come from lithium batteries and, for the record speed runs, Targett says that the battery pack will weigh approximately 120kg. However, as newer batteries improve on energy density and become lighter, Electroflight says it will look to use the lastest technology as it becomes available.

Electric motors for aircraft also come with inbuilt advantages. They are not affected by the attitude of the aircraft, unlike some traditional engine systems. They also do not suffer from thermal shock which can be a risk for piston engines or need the fuel mix adjusting to cope with adjusting to cope with air density – making for much simpler operation. There can also be more streamlined cooling arrangements than used in most piston engine-aircraft, resulting in much reduced drag for high-speed racing.

The impressive torque generated also means that, like the ultimate piston engine fighters of WW2 and the souped-up Reno air racers, a contra-rotating propeller also cancels out what might be dangerous yaw swings as power is applied. Contra-rotating, two-bladed propellers also can be a smaller diameter – meaning the airframe as a whole can be smaller and lighter. “The contra-rotating system will give us a huge amount of power/thrust in a small airframe,” says Targett

 

The airframe

The P1e is a single-seat composite design.

Built around the power and battery package is a highly sleek, all-composite single seat racing aircraft. The power package is also slimmer than a traditional piston engine, like a Lycoming, reducing the frontal area and promising improved aerodynamics. Maximum all-up weight of the P1e, says Targett, is expected to be 450kg but this will be slimmed down to 420kg for the record attempt. For safety, the pilot will sit in a semi-reclined position for improved G tolerance. They are also inside a constructed impact safety cell that is built into the fuselage structure. In addition, the P1e will be equipped with a whole aircraft ballistic parachute system that works at a low altitude/high speed.

 

Performance

The P1e is designed to push electric aviation faster than ever before. (Electroflight)

With a high-power electric motor and lightweight airframe – it is no surprise that the P1e’s performance is expected to be startling for an electric aircraft. Says Targett: “The calculated thrust-to-weight is very close to 1:1 and level flight speed will be in excess of 250mph.” Indeed, the P1e should give Red Bull racers a run for their money. “The power-to-weight of the P1e would be significantly better than the aircraft currently used in the Red Bull Air Race series. We may have to ‘de tune’ the P1e for the typical RBAR race track!” Further development, says Electroflight, could push the P1e past 300mph where it could race in the sport or a dedicated electric class at Reno. Notes Targett: “I feel confident that electric aircraft will be significantly faster than a hydrocarbon powered equivalent.”

The downside, however, of this blistering speed is, of course, endurance. Says Targett: “For the speed run we need a flight time of 3.75 minutes plus 20% reserve. For air racing and air show displays, the P1e will have a flight time of 10 minutes plus 20% reserve.” While the speed of recharging for multiple flights a day is now not an issue, one challenge for the team will be battery temperature management.

 

Project status

Development of the first prototype could be surprisingly quick. (Electroflight)

Having built and displayed a full scale mock-up of the P1e at RIAT and Cranfield Festival of Flight, with initial seed funding Electroflight is now on the hunt for sponsors or partners to provide funds to get the P1e into the air and break the electric airspeed record for Britain – as well as potentially backing an aerial ‘Formula E’ to promote green, clean aviation – with associated STEM education spinoffs. This could be sooner rather than later, if a sponsor is found. Targett: “If we had the required funding tomorrow, we could be flying in just under 12 months.”

 

Summary

Could Electroflight P1e kick-start an whole new electric air sport? (Ed Hicks, flyer.co.uk)

It is important to remember that this project is still in its early stages. Yet, just as the round-the world flight of Solar Impulse sparked excitement about the possibilities of zero-carbon electric flight for endurance, so too could Electroflight for speed – converting die-hard aviation pistonheads into green, zerocarbon evangelists. Intense competition for a ‘Formula E’ of the air could also potentially stimulate new public interest for general aviation and create a whole new airsport. As Roger Targett observes: “We believe that having an electric air race series will help to push the development of electric propulsion in aerospace. History shows that competition drives technology.”

Tim Robinson
3 March 2017