A 'once in a generation' opportunity may be emerging for the UK to be at the leading edge of the next revolution in aerospace – hybrid-electric flight. TIM ROBINSON reports on the significance of the launch of the Airbus/Rolls-Royce/Siemens E-Fan X prototype.


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The BAC 221, modified from the FD.2 first flew in 1964 to support supersonic testing for the Concorde project. (RAeS/NAL)

Over half a century ago, strange delta-winged aircraft flew in British skies, portending a future of high-speed passenger flight. These prototypes, the BAC 221 (the modified Fairey Delta 2) and the Handley Page HP. 115, were tested in the early 1960s to support the development of a supersonic airliner – which would eventually enter service as the Aerospatiale/BAC Concorde.

That supersonic future faded with the retirement of Concorde in 2003. However, on 28 November at the Royal Aeronautical Society HQ in London, an agreement was signed that may, one day, perhaps be looked back on as one of the key moments in an exciting new era of low-carbon, commercial flight with potentially 50-100 seat hybrid-electric passenger aircraft by the 2030s.

What is more, is that this agreement, signed by Airbus, Rolls-Royce and Siemens, is for a flying hybrid-electric demonstrator aircraft, based on a BAe 146, which is set to fly in 2020 and may potentially be the first British (with international partners) civil X-plane in over half a century.


Enter the E-Fan X

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Layout of the E-Fan X. (Airbus)

The aircraft, called E-Fan X, builds on Airbus's previous experience with electric flight, that has including the smaller E-Fan light aircraft prototypes and is part of a new drive at the company to fly, test and innovate as fast as possible, mirroring the hyper-quick processes in the tech industry and in start-ups such as SpaceX. Indeed, Airbus has now ditched the GA-sized electric E-Fan development in favour of pushing ahead with this larger demonstrator.

The E-Fan X, aimed to fly in 2020 after a comprehensive ground-test programme, will be based on a BAe146 regional jet, with one of its four Honeywell turbofan engines swapped for an electric motor and fan. Additionally, a Rolls-Royce AE2100 gas turbine (normally used in the turboprop for the C-130 Hercules) will be installed in the rear fuselage to power a two megawatt electrical generator. This will be, says Paul Stein, Rolls-Royce Chief Technology Officer, the 'most powerful generator ever' to fly.

Airbus itself will be responsible for overall integration, power distribution centre, flight deck displays, and the HEPS (Hybrid Electric Propulsion System) e-supervisor – as well as the batteries.

Rolls-Royce, meanwhile, will supply the rear AE2100 gas turbine, the two megawatt generator and, with Airbus, will convert the fan to take an electric motor. The fan and nacelle will use an existing R-R design from its AE3007 engine.

Meanwhile, Siemens will supply the two megawatt electric motor, as well as the motor power electronics and the inverter, DC/DC converter, and power distribution system.

While initially one turbofan will be swapped for an electric fan, further along the line, another engine could be converted to electric power.

The result of this major surgery on the 'WhisperJet’ will be an aircraft able to be used as a testbed to research highly promising hybrid-electric flight. The aircraft will explore thermal effects, power management, altitude and dynamic effects and electromagnetic issues of this 3,000volt power system.

Like hybrid cars, a hybrid-electric airliner will be able to optimise power generation and usage in all phases of flight – particularly when extra thrust is needed in take-off and climb – with both gas turbine and batteries working together. Once in the cruise, the fuel efficiency of (smaller than legacy aircraft) gas turbines driving electric motors will make for significant fuel burn efficiency. Mark Cousin, Head of Flight Demonstrators at Airbus, expects that fuel savings could be in the 'double digits'.

There could be other benefits too, ones that up-end the existing preconceptions about aircraft noise, emissions and city airports. Siemens, in particular, has been working hard on lowering noise on its eAircraft prototypes – currently small GA aircraft. If these promising early results can be scaled up, then hybrid-electric regional airliners may open up the possibility of 24hr operations from airports that are now restricted in the amount of flights due to noise concerns.

Fuel savings and potentially lower operating costs also mean that hybrid-electric regional airliners or commuter aircraft could also compete with railways – offering cleaner, cheap, quiet point-to-point travel to local airports and bypassing major hubs.


The race to electric

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Zumun Aero, backed by Boeing is also working on a hybrid-electric regional airliner. (Zumun Aero)

This programme is not happening in isolation but is part of a wider drive towards electrification of aircraft all around the world, with teams in the US, Europe and elsewhere working hard on projects large and small. Earlier this year, for example, UK budget airline easyJet announced that it was working with a US start-up, Wright Electric, to develop a short-haul, narrowbody electric airliner. Boeing, too, is set to enter this field with its new Horizon X venture capital arm backing Zumun Aero, which is currently working on a hybrid electric 12-seater to flying in 2022. At the Paris Air Show, Israeli company eAviation revealed a concept an electric King Air-sized aircraft.

Speaking to media at the press event, R-R’s CTO Paul Stein said there are three opportunities in electric flight.

The first is in personal electric flight – for 'aerial taxis'. Some 300+ start-ups (and established aerospace companies) are now working on this technology which, only a few years previously, would have been considered science-fiction.

Second, he noted, was in using electric power to increase aerodynamic efficiency in larger aircraft by boundary layer control. This could be via rear tail propulsor or by many distributed electric fans.

Finally, was through hybrid electric aircraft – aimed at the regional airliner market – and this is the area which eFanX is designed to explore.



Electric efficiency is a challenge, but Siemens has already made strides in lightweight, but powerful motors for GA aircraft.

However, there still remain challenges. Dr Frank Anton, Head of eAircraft at Siemens, speaking at the press conference on Monday, outlined three of them.

First, he said was the technical one of boosting efficiency – in electric motors and batteries – by an order of magnitude to get more power out of the same weight. Kerosene remains an extremely dense source of energy and is ideal for flight, where (unlike automotive) you cannot stop and pull into a charging station mid-flight.

The second challenge, he noted, is in certification. Existing conventional aircraft must undergo strict safety certification and a new hybrid-electric power configuration would undoubtedly mean that regulators would have to create new rules or adapt existing ones. For example, what would be the rules for reserve fuel (power?) for diversions with hybrid-electric aircraft? Would electric fans (or propulsors) need the same 'blade-off' or containment bands as the fan blades for a turbofan? With certification authorities already concerned about lithium-ion batteries (and previous 787 incidents in mind) there may well be an extra focus on dealing with battery fires. Finally, some also point to the issue of shielding the power cables against high-altitude discharge. All these will require study.

The third challenge, Anton noted, was not such much the technology itself but in the willingness of those to approve, greenlight and build new aircraft that may incorporate the biggest transformation in civil aviation since the introduction of the jet engine in the 1950s. Even back then, convincing conservative airlines of the capability of jets was not an easy task. Boeing's Chief Historian observes that early crashes of the dH Comet made airlines suspicious of jet airliners. To win sales for its new 707, Boeing took the unusual step of appealing directly to airline passengers of the advantages of smooth, quieter jets over turboprops.


Prospects for success

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Rolls-Royce is also working on turbo-electric flight under the DARPA Lightning Strike project. (DARPA)

Yet, while challenges remain and some of the more fanciful electric aviation ideas (especially involving VTOL flight) may turn out to be dead-ends, this week’s announcement represents a huge boost for hybrid-electric. Why then, might this succeed?

First, is that although the concept is revolutionary for aerospace, hybrid-electric is a smaller step than a pure-electric airliner. It is thus not reliant on wholly reliant on massive strides in battery efficiency which would introduce extra challenges (and is dependent on power storage technology that is being driven by the consumer and automotive sector). The team also foresee regional airliners, with a shorter range as the first application – rather than jumping straight to narrowbody short-haul. Said Mark Cousin: “"There are no fundamental technology blockers."

The demonstrator too, is based on an existing airliner, (with extra engines for safety) rather than attempting to trial a new airframe and power configuration simultaneously.

Secondly, is that the agreement brings three world-class, highly experienced partners together, who individually have been looking into the potential of electric flight. Airframer Airbus is the No2 aerospace company in the world with huge engineering resources and a history of introducing new technology, such as FBW and composites, into civil aviation. More recently, Airbus has instituted a drive to embrace disruptive technologies and is currently working on two separate 'flying car' projects that use electric power.

Rolls-Royce is one of the big-three of the civil engine giants with a track-record of excellence in aero-engines from the Eagle, through the Merlin to the Trent. It too has been investigating the potential for electric flight – and in the US is teaming with Aurora Flight Sciences (now acquired by Boeing) on DARPA’s turbo-electric Lightning Strike VTOL prototype.

Siemens, meanwhile has a fast-growing eAircraft division that has already developed a small (50kg) yet extremely high-power (260kW) electric motor that has enabled a modified Extra aircraft to set new records in speed and climb rates.

A third factor is that the British political, industrial and institutional appetite for risk and innovation has changed in the past decade. The release of the UK's industrial strategy this week means that, as a whole, Britain is now keen to harness and exploit coming revolutions in fields, such as AI, green energy and transport. Even a UK spaceport, which 20 years ago would have be seen as sci-fi folly, is now being embraced, thanks to the potential commercial market of the small satellite revolution. For a while now the UK aerospace industry has been calling for demonstrators and flying prototypes as the best way forward, particularly when new and novel configuration or propulsion systems need to be tested. In the US, too, NASA is flying its first manned X-Planes since the 1990s, to investigate electric distributed propulsion and supersonic flight.

Finally. there is another driver - Brexit. At the press conference, Airbus' Mark Cousin revealed that the eFanX team were in discussions with the UK Government over funding for the project through the UK's Aerospace Technology Institute (ATI). Although the ATI has had very successful track record in distributing funding for long-term aerospace R&D since it was formed in 2013, the looming threat of UK companies being excluded from European aerospace R&D programmes (such as Clean Sky 3) post-Brexit, means that the importance of ATI as a national strategic agency has now jumped up several levels. Already, some have called for UK national R&D to be boosted to compensate for losing out on EU-funded projects and ensure the UK's competitiveness going forward.


A UK testing site for E-Fan X?

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Cranfields new AIRC was opened in October. (Cranfield University)

While a first flight of the demonstrator is set for 2020, at the press conference, the project partners were coy on where the aircraft might be modified and test flown. Traditionally, the involvement of Airbus might point to Toulouse, where Airbus already runs a sophisticated flight test centre to support new aircraft. Indeed, a EU-funded laminar flow demonstrator and Europe's largest civil X-plane, the A340 BLADE took to the skies earlier this year to investigate the frontiers of aerodynamics.

However, for the E-Fan X, with a UK-built aircraft (the BAE Systems RJ 146) and (potentially) UK Government funding through the ATI, it may be that this hybrid-electric demonstrator is flown from the UK.

One location immediately springs to mind – which is Cranfield University's new Aerospace Integration Research Centre (AIRC). This state-of the art research facility, only open since October, is partly funded by two of the E-Fan X partners, Airbus and R-R, to help investigate new and novel technologies for civil aerospace. Furthermore, AIRC (and Cranfield) already has experience of modifying BAe146s into specialist aircraft – with the FAAM atmospheric 146 being based there, and another BAe146 being modified for the ETPS test pilots school only earlier this year.

This is of course, speculation but, should ATI funding be secured, there is the distinct possibility that, for the first time in decades, the UK will be home to a prototype testbed designed to investigate new technology for commercial aviation.

Aside from Cranfield's AIRC as a test centre, it is also important to bear in mind that the opportunities for the UK in hybrid-electric flight extend far beyond swapping out a kerosene engine for an electric fan. The new configurations for civil aircraft (such as distributed propulsion) may open up massive opportunities for engineers, designers, technicians, operators and entrepreneurs far across the whole supply chain. A revolution in hybrid-electric and electric flight may see also see the need to rethink aviation infrastructure - especially around urban areas and cities where noise and emissions currently limit further growth. The benefits then could be far-reaching. Says Paul Stein, R-R: “It’s the dawn of a whole new era in aviation propulsion”.



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A historic agreement at the RAeS HQ. L-r - Dr Frank Anton, Head of Siemens eAircraft, Mark Cousin, Airbus Head of Demonstrators, Paul Stein, CTO, Rolls-Royce. (Airbus)

In short, then, the E-Fan X (and the electrification of flight) represents a once in a generation opportunity for the UK to collaborate on what might well be one of the most significant leaps in aviation technology since the dawn of the jet age – and position itself to compete and collaborate in a post-Brexit world – by helping to lead the 'third revolution in aerospace'. What is more is that, with the right political will, this ground-breaking project could potentially see a UK-built test aircraft, modified in the UK (with international partners) fly in UK skies - a sight not seen in over half a century.

Tim Robinson
1 December 2017