Aircraft manufacturers and aviation technology companies worldwide are gearing up for the next frontier in aviation: a regional jet with electrically-powered propulsion, flying passengers for an hour or two with reduced emissions, noise and cost. And that frontier is within the next 10 years, multiple manufacturers are now saying, with new breakthrough partnerships emerging even as disruptive startups are working on the problem.
Chris Droney, an engineer in Boeing’s Research & Technology unit, suggests to Australian Aviation that “we might see smaller hybrid-electric jets for regional travel in the 2020s and short-range commercial aircraft, like a regional airliner or small version of a Boeing 737, operating in the 2030s. It is worth noting that long-range large commercial aircraft, like a Boeing 777 or 787, are unlikely to be displaced by electric aircraft in the foreseeable future.”
“Electric-powered airplanes exist for small short-range applications,” Droney says. “In the future we will certainly see larger, faster, and longer-range electric and hybrid-electric aircraft. Boeing is actively engaged to push the electric aircraft technologies toward larger and longer-range aircraft.”
The successful development of regional and larger commercial aircraft, Droney says, will be paced by the development of improved batteries and electric components such as motors, controllers, generators and distribution systems.
“As with most research and development, there are challenges to consider,” Droney explains. “For electric or hybrid-electric technology, these challenges include energy storage with the right capacity and density, power capability of electrical components, increased voltage of electric power distribution, power infrastructure at airports, and regulatory certification procedures.”
Airbus, too, is studying the challenges and potential of electrification.
“In terms of technology challenges,” Airbus’s general manager of electrification Glenn Llewellyn tells Australian Aviation, “there are electromagnetic compatibility challenges which we, at that power level, need to learn about, and need to integrate into our design principles in order for that to function correctly. We have thermal management challenges at that sort of power level. We have significant kilowatts of thermal energy that we need to manage. Knowing that today there’s a lot of heat in a gas turbine that’s under our traditional tube and wing aircraft, that heat basically gets exhausted through the exhaust of the gas turbine, and gets managed in a very simple way.
“Once we start integrating power electronics and batteries into the aircraft, we need to manage the thermal challenges in a much more integrated way with the aircraft and find ways to use that excess heat to do things like wing anti-ice, where we really take advantage of essentially the thermal losses in the system.”
That will likely mean a future electrically-powered airliner looks radically different to the winged cylinder we see today.
“We’re investigating a lot of aircraft designs for the future, both standard tube and wing and other designs,” Boeing’s Droney says. “For example, Boeing believes the Blended Wing Body vehicle concept we’ve been working on since the 1990s could be developed into a product in the next 10 to 15 years as a subsonic transport, and initial applications could include military cargo vehicles. We’ve conducted successful structures, flight and wind tunnel tests unparalleled in industry and we continue to refine and improve the concept.”
On the material science side of things, Droney notes, “Boeing is focusing our near-term technology development efforts in several focused material areas including thermosets, thermoplastics, resin infusion, direct digital manufacturing, hybrid composite structures, metallic materials and processes, mixed metallic and ceramic additive manufacturing and ultra-high temperature ceramics.”
The Airbus-led E-Fan X partnership builds on existing work to reach the two megawatt threshold
Airbus is working with Rolls-Royce and Siemens to produce E-Fan X, a regional airliner-sized hybrid-electric demonstrator using a modified BAe 146, to show that shorter flights with serious numbers of passengers will be possible in the near future.
Airbus will build the energy storage systems, carry out test flights, and supervise overall integration. Siemens will be responsible for the energy distribution system within the aircraft, as well as the electric motor for the inverter, while Rolls-Royce will supply the electrical power for the propulsion system via a 2.5MW turbine with integrated generator. First flight is expected in 2020.
Ground-breaking collaboration for aero innovation: the E-Fan X combines our pioneering power systems with @Airbus architecture and @Siemens electronics to create the world’s most powerful flying generator #IntelligentEngine #SGAirshow https://t.co/8UYRvcZ4fA pic.twitter.com/spKWpJEVhA
— Rolls-Royce (@RollsRoyce) February 7, 2018
“We believe that we are actually entering and opening the door to the new world of aviation,” Dr Frank Anton, head of Siemens’ eAircraft department said after the E-Fan X’s formal launch, at the Royal Aeronautical Society in London on November 28.
“This will be disruptive innovation. It will be as disruptive as the introduction of the gas turbine from the forties. It will be as disruptive as the introduction of the fan in the late sixties. And what we saw in the late sixties was that aviation relatively quickly took this new technology of the turbine fan and that it very quickly became the propulsion system for aviation.
“So we could think that even this new technology of hybrid electric propulsion might, if it really shows a benefit, equally quickly go into aviation and make another disruptive evolution of the propulsion of aircraft.”
Mark Cousin, Airbus’s head of demonstrators, notes that, “Airbus has a history in electric flights, which started in 2010,” Cousin says, “through to our most recent project, which was the demonstrator E-Fan 1, which we stopped earlier this year. We didn’t stop it because it was not a success: we decided that we needed to be more ambitious because the world and the technology in this area is moving so fast.”
The E-Fan has been an airshow favourite since its début, not least because of the future technology that it represents. Now, it’s getting a next generation.
“We’ve been working for the last six months with our two partners, Siemens and Rolls-Royce, in putting together an ambitious hybrid flight demonstrator to demonstrate a two megawatt propulsion chain in a regional aircraft,” Cousin explains.
“The objective of this demonstrator is not to produce a product, but just to mature technology which will be the basis of products in the future. What we plan to do is produce a demonstrator with a two megawatt propulsion system, comprising a gas turbine with an integrated generator produced by our partners from Rolls-Royce, a two megawatt motor driving a propulsion fan produced by Siemens, and the whole system integrated with a two megawatt battery and control system produced by Airbus.”
“We’ve provisionally selected the BAe 146 as the platform for this demonstrator,” Cousin says, “mainly because it’s a four-engine aircraft with a suitably-sized gas turbine engine that we can replace directly with an electric motor.”
Four engines for hybrid-electric as the trusty BAe 146 plays a testbed role
The distinctive high-winged four-engined BAe 146 regional jet, which was later developed into the Avro RJ, will of course be familiar to observers of Australian aviation, especially in rural and remote areas. Why the 146?
“What we want to do is replace the gas turbine with an electric motor,” Cousin says, “so we need an aircraft with engines that were about the right size to require about a two megawatt propulsion unit, and we also needed four-engine aircraft for safety reasons. So the BAe 146 is really the only platform that meets that requirement, and it’s just a good platform for the purpose.”
“We’ll replace initially one engine,” Cousin explains. “We’ll make provision for replacing another engine in the future, but that will depend on how the initial testing goes.
“Our intention is to replace one of the test plane’s four jet turbines with a 2MW electric propulsion system in time for the maiden flight, which is scheduled for 2020. That would be the first time that such a powerful electric motor would help to propel an airplane,” Siemens’ Anton elaborates.
This is indeed at the cutting edge of technology, and it is unpredictable how well the various technologies will evolve during what is a very short timescale, so demonstrating using a single engine initially seems sensible.
“The propulsive force will be a Rolls-Royce AE2100 engine, the engine that powers the Lockheed Hercules,” Rolls-Royce’s chief technology officer Paul Stein explains. The engine will be “driving an integrated generator that we build within the overall envelope of the gas turbine, in fact producing two and a half megawatts – a little bit more for spare. The power electronics will convert that power output, which we believe will be the world’s most powerful flying generator, into 3,000 volts DC to distribute to the aircraft.”
“Then the actual propulsive fan is an AE3007 off one of our regional jets,” Stein says. “We’re taking the fan off of the regional jet, mating it to the Siemens motor, and that will fit within the nacelle of the inner starboard engine of the BAe 146.”
“The AE2100 gas turbine will be mounted in the rear fuselage of the passenger cabin in the BAe 146, with a dedicated inlet and exhaust, to feed that gas turbine,” Airbus’s Cousin says. “The two megawatt battery system, which with today’s technology will weigh around two tonnes, will be located in the forward and aft lower hold of the aircraft.
“The power on the 3kW level is then going to the Siemens power distribution and the power electronics, which is an inverter, which is going to fit in the nacelle,” adds Siemens’ Anton. “This inverter is going – on the 3kW level – to drive the Siemens SP2000 motor, which will be connected at voltage to the fans. And this latter part is in the nacelle.”
If electric propulsion is scalable, we are on the verge of entering a third generation of aviation
“Transportation has been the last frontier for electrification,” Rolls-Royce’s Stein says. “We’ve seen electrification in road transport, in the maritime sector, and rail. Frankly, because the technology has not quite been there with us, electrification of aviation has been slow to catch up. But now with improving technology, the start of this new era has begun. It offers the next step change in fuel efficiency, noise and environmental impact, and it now allows us to rethink the whole layout of flying machines for the first time.
“The phrase used by many – ‘this is the third generation of aviation’ – I think is a phrase that is quite rightly applied: the piston engine era, the jet era, and now the electrification era,” Stein says. “We’re involved in one or two hybrid-electric flight programs globally, but this one, we believe, is going to be the one that actually starts chartering the frontiers of civil aviation.”
Of course, says Siemens’ Frank Anton, “in aviation you can only learn by flying. Siemens, with Airbus, started with electric propulsion for aircraft in 2010, and in 2011 together, Airbus, Siemens, and a small company called Diamond Aircraft flew the very first hybrid-electric plane in the world. It was at that time a two-seater. Now we want to scale up, and when we started one and a half years ago, at the beginning of 2016, a big collaboration, Siemens and Airbus developing different sizes of hybrid-electric systems for propulsion of aircraft with the target of doing ground testing. In this collaboration we are developing 100kW, 2MW, but we are also developing 10MW. If you think about a ten megawatt generator, it will use super conductivity, and this is what we are developing there.”
“Thanks to the extensive amount of research we have conducted in advanced lightweight engineering and high-tech materials,” says Wulf Roscher, Siemens’ project manager for the E-Fan X, “we expect to be able to drastically reduce the size and weight of our drives. Although our previous record-breaking motor achieved a continuous performance output of 5.2kW per kilogram of motor mass, we want to significantly improve on this in our 2MW motor.”
The E-Fan X is driven by “a triangle of energy management”
“This configuration of aircraft is not a pure battery aircraft, for those not in the aviation industry,” Rolls-Royce’s Stein explains. “We have a gas turbine, a Rolls-Royce gas turbine powering a generator, and the generator distributes the energy through a number of fans, which will eventually lift the aircraft in a different way than you would today.”
“We are not betting on batteries, we are betting on the hybrid,” says Anton of Siemens. “Hybrid-electric means that you have a generator producing the power on board that is needed for the cruise flight. The batteries just add the additional power that is needed during takeoff and climb – that means that with today’s battery technology you can already do something, and do not have to wait for some kind of completely unexpected battery technology. With hybrid technology, you could see it, by 2030, being large‑scale available so that hybrid‑electric aircraft can fly.”
“Any hybrid-electric configuration requires energy storage to make it work,” says Airbus’s Cousin. “One of the benefits that you could envisage is a downsizing of the gas turbine and then supplementing it during the other phases by energy storage. Today, the most advanced method of energy storage for aviation would be batteries. Will that be the case in five or ten years time? We don’t know, but yes, energy storage is definitely part of it, which is why this demonstrator is built of three elements: the gas turbine with the generator, the electric turbine driving a thrust-producing fan, and a battery system storing energy. It’s a triangle of energy management.”
Airbus is building on the E-Fan program as it develops E-Fan X
“We started around 2010 on our journey of exploring the possibilities for hybrid-electric propulsion,” Airbus’s Llewellyn tells Australian Aviation.
“One of the best-known demonstrators that we built is E-Fan. E-Fan crossed the English Channel in July 2015, and we learned a huge amount from that project. It was very successful in teaching us the potential of electric propulsion as applied to aviation, and it taught us a lot in terms of the lessons that we need to learn in terms of electric propulsion in order to design bigger and bigger aircraft.”
It’s not just the aviation industry that is making major advances, however, Llewellyn says. “In parallel with our development of these demonstrators, what we’ve seen in the car industry is a huge growth in terms of electric car stock. If we compare 2010 to 2016, we’ve basically gone from zero to 2 million in terms of electric car stock globally. That has had a huge impact on the technology which we rely on in terms of aviation. So we’ve seen improvements in performance, we’ve seen improvements in power density of power electronics, of electric motors and electric generators. And that has allowed companies like Siemens in 2016 to fly the Siemens Extra 330, which is an aerobatic aircraft, and it has roughly five times the power of what our E-Fan had in 2015 when it crossed the Channel.”
As far as airlines go, “We haven’t had official discussions with them, but there are a number of airlines who are very interested in the development of this technology, and when it might be feasible to replace some of their smaller aircraft that they operate today with electric or hybrid-electric vehicles,” Airbus’s Mark Cousin says.
“Some airlines have already signed agreements with startups in this business. There are a couple of startups in the US, so the interest is quite high. I think that interest will grow dramatically as they start to understand the technology. I already have two requests to go and explain to certain of our airline customers the potential of this technology for the future.”
Beyond airlines, Airbus is also working on making flying cars a reality
Urban air mobility “is an adventure which has already started for us,” Llewellyn says. “We plan to fly our first urban air mobility vehicle called Vahana this year – it’s a one-seat demonstrator. It’s got eight electric motors, eight propellers, it’s got a tilt-wing, and it is being built in our A3 Silicon Valley facility in the US.”
“Next year we will have the first flight of a four-seat demonstrator, the City Airbus, with a different type of architecture at the vehicle level. And those demonstrators form the backbone for our technology demonstration for the urban air mobility market segment,” Llewellyn summarises.
“There are obviously technical challenges that we need to overcome, and that’s why we’re building the vehicles and we want to demonstrate the technology. Some of the biggest challenges we need to overcome are about air traffic management and regulation,” Llewellyn notes, and indeed there are major concerns about safety and a variety of types of environmental impact on larger cities in particular.
“We’re going to have these vehicles flying in cities – they’re going to be much more local to people in order to serve the populations that are going to really benefit from them. That will require quite significant working together between the regulators and the operators and manufacturers of these vehicles in order for urban air mobility to really have a positive impact on society.
“There are already cities where we have seen a benefit from this type of concept. We have a project already piloted in South America where we’re looking at facilitating the transportation in São Paulo. We’re already piloting the urban air mobility concept by using Airbus helicopters. That is showing us that already today, in certain cities, we’re at the point of saturation in terms of ground transportation. There is already a market for urban air mobility,” Llewellyn says.
Cities the size of Sydney, Hong Kong, or London “are for sure candidates for this kind of societal benefit”, Llewellyn says, “I think the simple fact that with urban air mobility we’re talking about using a three-dimensional space means that it will be much more capable of absorbing traffic than the 2D space which is our current road network system.”
Regulators will have to be persuaded, of course, for this even more than a hybrid-electric system for regional jets, and of course within those regulators – as within the industry more widely – a major upskilling will be required. The government agencies dedicated to keeping aviation safe even as manufacturers push the boundaries of technology may well see some of the toughest challenges of all.