By Theo Leggett
Business correspondent, BBC News
From a small office overlooking an airfield, once home to the UK's first Spitfire squadron, a tiny British start-up is hoping to make a little history of its own – as one of the pioneers of commercial electrified aviation.
Faradair is planning to develop and sell a hybrid-electric passenger plane, aimed at the regional aviation market. It would have up to 19 seats and would be propelled by a fan driven by an electric motor. The necessary electricity would be provided by a small gas turbine.
In order to provide extra lift, and allow take-offs and landings from short runways, it would also have a triple level wing. This would give it a passing resemblance to a World War One fighter, despite having state-of-the-art aerodynamics.
The company's chief executive, Neil Cloughley, argues that such a plane would have far fewer moving parts than a conventional propeller aircraft, making it cheaper to run. It would also be much quieter, and produce fewer emissions.
"Why do we not use aeroplanes like we would a bus?" he asks.
"The reason is cost of operation, primarily. Also if you start using lots of aeroplanes it creates a lot of noise, and of course we have now got into an age where sustainability really is a key part of our future.
"So we decided we would come up with an aircraft that would not only be economic to use, and therefore cost-effective, but would also be quiet and sustainable."
The Faradair design, he says, would allow short hops between cities such as London and Manchester for £25 each way – less than the cost of a rail ticket.
In more remote or inaccessible regions, meanwhile, such planes could provide a transport lifeline from small airstrips, avoiding the need for major investments in road or rail lines.
It plans to have the aircraft flying by 2025 with commercial use starting in 2027.
Faradair is far from alone in seeing the potential of electric aviation, at a time when governments around the world are searching for ways to reduce carbon emissions. Nor is its project the most ambitious.
California-based start-up Wright Electric, for example, plans to bring a fully-electric 100-seat aircraft into service by the middle of the decade. It would be based on the existing Bae146, with its four turbofan engines replaced by electric motors.
The company, which has a partnership with Easyjet, says the aircraft would be used to carry out one-hour flights, allowing it to serve routes such as London-Paris, New York-Washington or Hong Kong-Taipei.
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However, in testing, the plane will run as a hybrid. Initially just one of the four engines will be replaced by an electric motor, with others following if the tests are successful.
According to Wright Electric's chief executive, Jeffrey Engler, potential customers think this is a good approach and one they could also follow when the aircraft enters production.
"When we spoke to the airlines, they said, 'Well why don't you go hybrid initially, instead of full electric from the start?'" he explains.
"Just like the car industry started with hybrids as well. So that's something we're looking into."
The main reason electrifying aircraft is so difficult is that even the best batteries contain far less energy per kilogram than traditional aviation fuels, making them much too heavy to power an airliner over long distances.
"The specific energy of today's batteries is far from what you would need," explains Dr Andreas Strohmayer, head of the University of Stuttgart's Institute of Aircraft Design.
The Institute has been researching the potential of electric and hybrid aviation since the mid-1990s, and first flew its own experimental two-seater electric plane, the e-Genius, more than a decade ago.
"We build our own battery systems for our electric aircraft," he explains
"We are getting in the region of 200 watt [hours] per kilogram, where we would need 1,000 or 1,500. So we are far from what we would need for a large aircraft."
His view is that small, light electric aircraft, of up to six seats can be built with today's technology.
He also believes it should be possible to build a larger commuter aircraft, with up to 19 seats while still relying purely on battery power, though it would be "at the edge of what is currently possible".
The Alice, a nine-seater plane being developed by Israeli firm Eviation, would fit into this category. The aircraft, which has been under development for several years, has been designed to fly up to 600 miles, purely on electric power.
Anything larger, meanwhile, would need to be a hybrid, combining electric motors with conventional engines or on-board generators.
For Dr Strohmayer the potential is there for both types of aircraft to create new aviation networks, with small all-electric planes delivering passengers on short hops from local airfields to regional hubs. There, larger hybrid aircraft would be available to carry them on journeys of up to 500km.
"It would be a denser aviation network," he explains.
"It would be of most use in regions like Scandinavia or in mountainous areas, where you can't really just build networks of high-speed railways.
"There are places like Indonesia, Polynesia, where you have all these islands that have to be connected. There are places in the world where such networks are desperately needed."
Eviation is planning its first test flights of Alice this summer.
But such technology is unlikely to be much use over long-distance routes and that may explain why the European aerospace giant Airbus has decided its own priorities lie elsewhere.
In 2017, the company began developing a prototype hybrid plane, the E-Fan X, in partnership with Rolls-Royce and Siemens. Like Wright Electric's project, it was based on the existing Bae146.
But three years later, the programme was cancelled. Dr Sandra Bour-Schaeffer, the chief executive of Airbus Upnext, the division responsible for researching new technologies, thinks it was the right decision.
"Our focus is to achieve carbon neutrality by 2050," she says. "In order to achieve that we need to look at two different technologies, associated with different time horizons."
In the short term, to reduce emissions, the company is focusing on using sustainable aviation fuels made from renewable sources and waste.
Beyond that, Airbus has its sights fixed firmly on using hydrogen to power a new generation of clean aircraft.
"Our ambition is to bring the first zero-emission commercial aircraft based on hydrogen to the market in 2035," she explains.
"I already have teams working on cryogenic and superconducting technologies. We are already exploring what will come next."
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By Theo Leggett