Bringing the electric aero revolution to large aircraft

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Bringing the electric aero revolution to large aircraft

There are two axioms when it comes to electric power for aircraft. One, that it will start with small aircraft in the near future and regional aircraft in the medium-term, and two, that it doesn’t currently work for large, long-haul, aircraft because there is no technology that is light enough.

Both are broadly true – but there is a less heralded development that, if not revolutionise, will help transform the future of aviation in the large sector.

That development is the design of future aircraft that are “more electric” – taking power from the engine to drive hydraulic systems such as landing gear and brakes as well as cabin air conditioning or using energy storage to support the aircraft when its need for power is greatest.

The prize is still substantial – a fuel burn improvement of up to five per cent, which contributes to the industry’s wider goals of significant de-carbonisation. Rolls-Royce is actively supporting the ACARE (Advisory Council for Aviation Research and Innovation in Europe) goals of a 75 per cent reduction in CO2, 90 per cent reduction in NOx and 65 per cent reduction in noise by 2050.

Rolls-Royce is already on the journey to more electric solutions – its Trent 1000 engine powers the Boeing 787 Dreamliner, which utilises electrical power to drive the cabin air conditioning and wing anti-icing systems rather than the traditional pneumatic methods which utilise air bled from the engine. To achieve this, generators on the Trent 1000 deliver a total of one megawatt of electrical power.

Now, Rolls-Royce has its sights set on further large aircraft electrification projects that may reach maturity by end of the 2020s.

Alan Newby, Director of Aerospace Technology and Future Programmes, said: “We know that battery technology presents an issue for large aircraft in the near term – the energy density of kerosene is 30 times better than the best batteries today, so the sheer weight implications of substituting kerosene with batteries makes it an impossibility. But that doesn’t mean we can’t continue to expand the role of electric systems on large aircraft and make a significant environmental contribution.

“Some of those technologies are in development right now – for example we’ve already carried out tests on an electrical starter generator on an Adour engine, which presents opportunities to streamline the engine profile and replace traditional mechanical units such as fuel and oil accessories.

“Another possible efficiency gain would be the elimination of the accessory gearbox by integrating the electrical generator, power storage and power distribution systems. This reduces weight and also further streamlines the engine – which actually supports another de-carbonising factor, improved design integration between the engine and the airframe.

“That is one thing we understand, you only get the true benefit of more electric if you don’t think in terms of simple product substitution, but in terms of using the greater design freedom the electrical alternative brings. That is also a reason why these developments will really need to be incorporated into an all-new aircraft design rather than be retrofitted into what already exists.”

Other potential solutions include multi-shaft power extraction and transfer – Trent engines currently take power offtake from either the HP or IP shafts, but the ability to take power off any three shafts could be optimised to the varying power needs of the aircraft through the flight envelope, increasing efficiency.

Alan added: “That also provides options with energy storage – a bit like the KERS system on a Formula 1 car. If I have that energy available I could add it when the engine is delivering its greatest power at its highest temperatures. That might take some of the load, reduce some of the engine temperatures, and therefore give me an additional engine life benefit.”

Rolls-Royce already has the key skills to support more electric developments, having a long history of integrating complex systems and understanding the controls, speeds, thermals and certification issues that are involved.

Alan added: “We also wanted to put those skills to real use with research programmes involving smaller aircraft, such as E-Fan X and Accel. By flying those aircraft, we are going to get even more learning and rigour, which will also help us with these more electric solutions.

The drive to more electric solutions is part of a wider Rolls-Royce strategy to support aviation sustainability, one that retains a focus on improvements in current gas turbine technology – in large engines through the UltraFan® demonstrator programme, improving integration between the engine and airframe, continued support for the introduction of sustainable aviation fuels, and electrification.