Airbus is gearing up to commercialise a light aircraft project with a hybrid-electric propulsion system, as a blueprint for an eventual move into the 90-seat regional transport market.
By slashing noise and emissions, Airbus believes a practical electric fan propulsion system will eventually open opportunities for regional routes currently closed owing to night flight bans – and give it a way into a market largely dominated by Bombardier and Embraer.
Group chief technical officer Jean Botti will not commit to a timetable for the so-called E-Thrust 90-seater. However, speaking on 25 April at Bordeaux-Merignac airport – where Airbus made the first public demonstration flight of its E-Fan pure electric twin-engined prototype, and unveiled models of the two- and four-seat concepts that will follow it into production at a purpose-built factory adjacent to the airport – he drew a straight line between E-Fan and E-Thrust.
It will take a large step forward technically, he says, to go from two motors drawing 60kW to fly the prototype to the megawatt system – with a power density of 10kW/kg – needed for E-Thrust. However, Botti expects further strides in battery technology to make this possible.
Meanwhile, the all-electric E-Fan 2.0 two-seater – intended as a flight school trainer – or hybrid-electric E-Fan 4.0 four-seater that will follow, provide Airbus engineers with challenges in power systems, lightweight construction, aerodynamics and robustness.
However, says Botti, E-Thrust will ultimately be a big version of the E-Fan 4.0.
The link between the two aircraft is clear, in the 4.0’s concept of a “range extender”. This unit – which takes up what might be luggage space in the four-seater – will be a small engine, probably kerosene-powered, carried to top-up the battery charge and maintain flight duration of up to 3.5h with a 60 litre (16USgal) tank.
The 2.0 and 4.0 are new ideas from Airbus. At the 2013 Paris air show, Botti showed off the E-Fan aircraft – although it had not yet flown – while models at the Airbus chalet outlined the E-Thrust concept, being developed with partners including Rolls-Royce for a distant “2050s” timescale.
For now, Airbus has committed itself to the E-Fan aircraft, which it will manufacture and market through a 100%-owned subsidiary called Voltair. The prototype has flown roughly 20 times and undergone a crash development programme, going from conception to flight in just 18 months.
Now, 2.0 and 4.0 chief designer Bruno Saint-Jalmes has arguably a more daunting task: to realise a commercially viable 2.0 and achieve first flight before the end of 2017. Certification, he says, will have to come no more than one year later. Within 10 years, Airbus plans to be making 80 aircraft a year at the Bordeaux plant. Ground will be broken – on land donated by the city – within weeks.
The prototype is a remarkable starting point. Test pilot and designer Didier Esteyne describes it as flying like a conventional aircraft, but perhaps smoother. However, it will not be certificated and is far from being a saleable machine. It carries 137kg (302lb) of lithium-polymer batteries in its maximum take-off weight of 580kg, which includes about 50kg of test equipment, a recovery parachute and a pilot’s parachute. Charging time is 1.5h, or 30min on a quick charge, and endurance is 45min-1h.
Esteyne adds that a T-tail was chosen to save time – he had considered a U-shaped design, but that would have taken a great deal of analysis and design work.
The more capable – but not physically much larger – 4.0 will follow the 2.0 in “a couple [of] years”, says Botti. The two aircraft will be 93% similar – the difference in length is only centimetres, and both carry Garmin 1000 avionics.
For Saint-Jalmes, the follow-on project has implications far beyond its own wing-tips. Battery development remains a crucial ingredient, and will draw on expertise from Airbus worldwide. To get to E-Thrust, he says, the key will be to master integration of a complicated programme, drawing on a crop of partners and technologies that fall outside the traditional turbofan airliner supply chain. That is one of the reasons why E-Fan 4.0 is a twin-engined aircraft – scaling up is part of the plan.
Airbus’s decision to base its electric aircraft manufacturing operations in Bordeaux is no accident – the city and Aquitaine regional government see themselves as partners in the venture.
Joining Airbus at Bordeaux-Merignac airport to unveil the E-Fan project, Aquitaine region president Alain Rousset spoke of E-Fan and “factories of the future” as two of 34 “roadmaps” outlined in a national plan for industrial rejuvenation. Rousset likes the phrase “creative destruction” to describe this renewal of the industrial base. Also, Aquitaine intends to play its trump cards to benefit from a drive to train a new generation of engineers and technicians.
The E-Fan factory will be a test bed for technologies that could be used elsewhere in Airbus. Virtual reality, for example, at E-Fan will be a day-to-day tool for comparing work to plans – not just a design tool. The plant will also play a role in training mechanics to service the 20,000 new airliners scheduled for delivery in the coming decade – just as the aircraft it produces will help train their pilots.
Historically, says Rousset, Aquitaine has been a centre of the French defence industry, given its Western location far from Germany. A decision to diversify into civil aerospace, with the significant contribution of Dassault Aviation’s presence, makes the region a natural choice for Airbus’s civil electrics research and production.
Only a regional government, he believes, can lead this sort of initiative to connect the scientific and business communities, adding that such decisions cannot be taken in Paris. And Aquitaine, he adds, has a track record of innovation in this regard – the world’s first research institute dedicated to studying the impact of climate change on viniculture is in the region.