TIM ROBINSON looks at the UK budget airlines’ vision to jump-start electric airliner flight within the next ten years. Realistic or not? 

Can easyJet and an US start-up bring electric, green airline travel into service in the next decade? On 27 September, UK low-cost airline easyJet revealed it had partnered with a US start-up, Wright Electric, to help develop a short-haul all-electric airliner – with the goal of bringing it into service within 10 years . The concept revealed shows a 120-seat airliner, with a T-tail and distributed electric ducted fans buried in the wings. The design features eight ducted fans per wing while underfloor battery packs (with ‘advanced cell chemistry’) would be swappable. High aspect ratio wings and elegant double split winglets complete the configuration.

Range would be around 335miles, for flights under two hours, making a signficant amount (about one-fifth) of easyJet’s current city pairs feasible as zero-carbon, zero-emission green flights. An electric airliner will also, according to Wright Electric, be 50% qiueter and cost 10% less to operate than todays jets. 

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The concept is also reliant on battery technology and the pace in which it develops"

US-based Wright Electric, for its part, a start-up that was only formed in 2016, has already leveraged knowledge from a previous electric airliner project for NASA, as well as flying a small electric prototype modified from a LongEZ light aircraft.

While the team have a goal for electric flight in 20% of easyJet’s network in the next decade, such is the pace of progress, they predict that every short haul flight could be electric within the next 20 years.  If realised, this would represent a game-changing leap for aviation and a huge victory for aerospace in meeting (and quite possibly smashing) its sustainable goals. Can this be start of the much needed new era of green, carbon-free flight?  

Major challenges ahead

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easyJet's futuristic electric airliner (easyJet)

Yet despite the excitement there may be grounds for caution. Just developing the new 787 jet airliner (with innovative features such as a composite fuselage) challenged even a highly experienced company like Boeing. A ‘less-risky’ solution re-engining existing airliners with new engines, meanwhile is currently causing major headaches for Airbus. Newcomers to airliner manufacturing, such as China and Japan (with their C919 and MRJ respectively) are also wrestling with development delays and are finding out just how difficult designing, building and testing new civil aircraft can be.

Blazing a trail then, with a radical new propulsion/power system (and associated infrastructure and CONOPS) suggests that a ten year horizon may be an ambitious goal for a new airliner.

Though electric power technology is advancing fast there remain technical challenges for larger aircraft. Weight, the enemy of aircraft designers everywhere, is one, as batteries are a very dense energy source compared to tried and trusted kerosene. Reducing weight of an all-electric airliner then calls for innovative thinking and not just swapping turbofans for a distributed embedded fans. Again there may be challenges. While distributed propulsion offers many advantages (eg redundancy) and is perfectly suited to electric power, swapping one large engine nacelle for several smaller intakes and ducts may incur a weight penalty. Though an electric engine system will not have the extreme temperatures and pressures associated with a turbofan engine, depending on the speed of the embedded fans and their composition, will these also need separate containment disks in case of blade failure or birdstrike?

It is also worth noting another challenge of electric airliners – in that unlike Jet-A1 fuel-powered types weight will not decrease as the aircraft uses up fuel during flight, allowing it to progressively climb higher in the cruise. Fuel burn in flight (or fuel dumping ) also allows for lower landing weights, and a lighter aircraft structure. Will then a battery powered all-electric design need to be tougher structurally to cope with the same weight at take-off and landing?    

The concept is also reliant on battery technology and the pace in which it develops. It is worthwhile remembering that, while battery efficiency (in terms of reduced size/weight and increased power) is improving all the time, it does not follow the exponential ‘Moores Law’ of CPU computer chip power. Increased power with reduced weight will thus demand a shift from lithium-ion into new chemistry, such as lithium-sulphur or aluminum-air or lithium-air/oxygen. A lithium-air battery, for example, has between 5 to 15 times the specific energy of current Li-Ion batteries.  While these are promising it also has to be noted that aerospace’s battery needs and unique requirements (extreme low temperatures when in cruise) are only a tiny niche compared to the larger demand from consumer, IT and automotive sectors. How fast this techology develops and which battery architectures are available thus will not be driven by the aerospace sector itself.      

There may also be operational restrictions or penalties. EasyJet’s concept shows swappable underfloor battery packs – anecessity given the fast turnarounds needed by LCCs for multi-sector operations. However, supplies of ready-charged batteries may also impact diversion airfields and call for a massive electric charging infrastructure.

Existing airliner diversion and fuel reserve rules may also eat into the attraction of electric flight and reduce practical range. (Unlike the smaller VTOL electric air taxies envisaged which may be able to claim exemptiosn based on their ability to land anywhere in an emergency)

Speed too may be a factor. The high-aspect ratio wings and ‘under two hours’ endurance (for a range of 335 miles) suggest a lower cruising speed than today's jet airliners. While not as important on shorter routes as on long-haul operations, will that affect utilisation and operational efficiency if five instead of six sectors can only be flown per day – one of the secrets of easyJets success against rivals?      

The balance between optimising battery charge and high power may also lead to operational trade-offs. For example, a battery-powered airliner could conserve precious charge by a shallower climb. However – this would have the effect of prolonging the noise footprint for those living under underneath. This then might create a paradox for electric flight – which is more important the local community (via noise) or the global community (via reduced energy usage as a whole)?

Indeed while electric aircraft can be optimised to be very quiet, it is worth noting that the majority of noise on landing now is airframe noise caused by the fuselage, flaps and landing gear, rather that the engines. The battery mass and, therefore weight, of an all-electric airliner means noise on approach may still be a factor.     

Finally there is the certification challenge for a brand-new airliner – an extensive and complex undertaking at the best of times, but far more challenging for entirely new propulsion and/ operating concepts. For example, Leonardo’s civil tiltrotor, the AW609, was first flown in 2003, some 14 years ago and has yet to enter service, despite tiltotor technology dating back to to the 1980s or even earlier. 

Deja vu for future flight…

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This open rotor easyJet model (now at the RAeS) was unveiled in 2007.

Those with longer memories may recall that this is not the first time that the UK budget airline has pushed for game-changing propulsion in airliners. In 2007, easyJet revealed the ‘ecoJet’ concept airliner featuring two open-rotor engines shielded by a twin U-tail that was designed to halve CO2 emissions and could cut fuel burn by 15%. The airline was reported at the time to be talking to Airbus and Boeing, as well as Rolls-Royce about this concept with the news that it could be ready for service by 2015.

Two years later than that in-service date - it is clear that progress has been far slower than expected. Both Airbus and Boeing opted to re-engine their existing narrowbody designs in the form of the Airbus 320neo and 737 MAX respectively, dashing the hopes of those who dreamed of exotic new shapes gracing the skies in 2020.

Meanwhile, a stubbornly stable low oil price, contary to the concerns of ‘peak oil’ of the early 2000s has meant that the promising Open Rotor technology (which comes with its own noise challenges) has for the second time in history (after the 1970s oil crisis inspired GE UDF)  had the rug pulled from underneath its development. A planned fly-off between Rolls-Royce and Safran Open Rotor demonstrator engines in the EU’s Clean Sky project has now be reduced to just ground tests by Safran’s model.

Open Rotor, therefore, seems no nearer to airline service, now than it was in 2007. Will battery-power electric airliners suffer the same curse as easyJet’s ecoJet?      

Innovation on the quiet

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UAVs for aircraft inspections can save time. (easyJet)

While Open Rotor airliners and battery-powered electric aircraft certainly grab headlines and simulate debate – more practical near-term savings and efficiencies may come from easyJet incorporating the latest in ‘BigData’ and autonomous systems into its operations. For example, at the Paris Air Show earlier this year, easyJet revealed how it had been using new predictive maintenance software from Airbus to spot failures and avoid aircraft on the ground (AOG) issues, before they happen. Early results look promising. Additionally, the airline  also revealed that after trials with drone aircraft inspections (which saved time and improved safety), it will now roll out regular inspections in 2018.  

Steady progress with these sorts of predictive mainatenance and digitasation efforts may win fewer headlines than developing electric airliners – but could generate big savings over time, as well as help save the planet.

Summary

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First applications for electric aircraft may be in smaller vehixcles such as GA and personal air taxis. (Volocopter)

Championing this leap to electric flight is a bold and visionary move – and easyJet must be praised for its commitment to sustainable aviation goals. The innate conservatism of some parts of the aerospace industry too means that it is easy to knock radical future concepts – when they may help shape the debate, stimulate competition and spark innovation. (Witness the backlash now against some of Elon Musk’s ambitious plans).   

However, a more sober analysis would also conclude that easyJet and its partner Wright Electric have their work cut out to realise this in the next ten years. A more feasible plan might have been to aim for the easier goal of a hybrid-electric airliner – a logical half-way step to an all-electric short-haul and a way to gain experience about this new game-changing propulsion. An experienced airframer too as a partner, would help reduce the risks, particularly when it comes to certification.

The electric flight revolution is now taking place, but it is in the light aircraft and even 'personal air taxi' fields where the first practical uses will be.   

In short, keep a close eye on this but don’t get too ‘amped-up’ about booking your first electric airliner flight just yet…. 

Tim Robinson
6 October 2017