The sky’s the limit
Are electric planes about to revolutionise aviation? Perhaps
• High in the sky Frank Anton reaches cruising altitude, signs off with the air-traffic control tower and signals to his passengers that they can take off their headsets. They are always surprised when they do: there’s no roar of engines, just a quiet humming from the propeller, and no vibration. “The eFusion makes so little noise that I would be allowed to take off and land at any time at any airport in the world,” says Anton.
In theory that could be the way it works. But this experimental electric-powered aircraft is still unlicensed. And even with a fully charged battery it can only travel 50 kilometres (30 miles). With better storage systems it would have a longer range, says Anton, a 60-year-old pilot and physicist who is the head of Siemens’ eAircraft division. “But as the aircraft get bigger, it gets harder to implement purely electric propulsion.” The batteries would be too big, too heavy and too expensive. “So for the foreseeable future there won’t be any fully electric passenger aircraft capable of travelling long distances.”
For the long haul, Anton envisages an environmentally friendly variant: hybrid-electric propulsion. The combination of a gas turbine and an electric motor would be quiet like the eFusion and more efficient than established technology. The aircraft could travel several hundred kilometres without a problem. “With hybrid technology we are opening the door to a new era in aviation,” he says.
By “we” Anton means colleagues from Siemens, Airbus and the aircraft-engine manufacturers Rolls-Royce. At the end of 2017 the three companies announced plans to equip a 100-seater jet with a hybrid propulsion system that will take to the skies by 2020. It is known as E-Fan X and it is the biggest electrical project to date for commercial aircraft. In this airborne hybrid, a turbine in the fuselage fuelled by kerosene-based jet fuel drives an electric generator. The turbine can operate constantly in its optimum speed range, which saves kerosene. The electric current then drives the rotors. In this way power can be distributed to several small electric motors with propellers on the wings or at the rear of the aircraft. This allows totally new aircraft designs and better aerodynamics.
According to Anton, this kind of hybrid electric plane could be fitted with a safety-approved battery adapted to how the aircraft is to be flown. For example, the turbine could be designed to produce just enough current needed for the flight. During the energy-intensive take-off and landing the batteries would provide extra thrust. With a somewhat bigger turbine the then largely empty batteries could be recharged during the flight. “We anticipate fuel savings of a double-digit percentage,” says Anton.
Mirko Hornung, however, has his doubts as to whether any achievable advantage would be economically relevant. He is the director of science and technology at the Bauhaus Luftfahrt research institute in Munich and for years he has been studying the potential of hybrid aircraft. Every year the aviation industry invests billions in developing more efficient technologies, he says. “On average every new aircraft generation consumes 15% less kerosene than its predecessor,” says Hornung. “Hybrid aircraft must offer the prospect of savings of 20% – or ideally more.” In his experience, assessments of gains in efficiency always have to be trimmed by a couple of percentage points over time. And that is the crux of the matter: “If the hybrid planes fall short of savings of 15%, no airline will buy them.”
Hornung also points to the extra weight of the electric motors, batteries, gas turbine and generator compared with traditional jets. “Can I really make up for these disadvantages with the aerodynamic advantages of a spread of electric motors? As yet we have zero reliable statements about that.”
By contrast, Mark Cousin, the British head of the flight demonstrator programme at Airbus, considers that question to have already been largely settled: “We definitely believe in the potential of a hybrid aircraft – the only question now is when we can get it off the ground.” He and his colleagues in Ottobrunn, near Munich, are now planning procurement for the E-Fan X: the latest generation of lithium batteries, a 2.5 megawatt gas turbine from Rolls-Royce, an ultra-compact 2 megawatt electric motor from Siemens, generators, power electronics – and a 80s model BAe 146, a medium-sized four-engine regional jet due to be retired this year.
The Ottobrunn base is currently a building site, where the E-Aircraft System House – with a test bed for hybrid technology – is already going up. Cousin is confident it will be ready for use in a couple of months. About 50 people are already working on the E-Fan X, from all three companies, and that number will grow. The new powertrain – all the main components that generate and deliver the power – could be ready to install in a year and a half. Anton from Siemens reckons it is a rather ambitious schedule: his team is supplying the e-motor, among other things. “In proportion to weight, it will be the most powerful unit in the world,” he says.
It would not be possible without the help of a digital twin, an exact model of the engine in the computer, he says. “We can make changes faster on the virtual prototype, and push to the limits of what is technically possible, without the risk of causing serious damage.” The firms don’t want to waste any time – they are competing for pole position in the aviation market of the future.
Only one of the four conventional BAe engines will be replaced initially. “If our predictions are confirmed after the test flight, we will fit a second and retest. And then hopefully begin designing a new hybrid-electric aircraft,” says Anton. He assumes that by 2035 there will be hybrid-electric jets that can carry up to 100 passengers for 1,000 kilometres.
Anton estimates that prototypes and smaller hybrid business planes for four to six passengers could be ready for take-off by 2022. A US startup called Zunum Aero is aiming to have a 13-metre (42ft) hybrid jet that could carry 12 passengers ready by then. Powered by two 500 kilowatt e-motors, the plane is designed to reach a speed of 550kph (340mph) with a range of at least 1,100 kilometres. Between the fuel savings and the low-maintenance electric drive, Zunum expects up to 80% lower operating costs and 75% less noise than the aircraft flying today.
“That means we can avoid the ban on night flights, which will make operations even more profitable,” says Sandi Hwang Adam, a Zunum executive. “There are still plenty of aircraft in the US flying on regional routes with inefficient technology dating from the 60s.” But it is not just American airlines that are open to modernising their fleets, she believes, suggesting the global regional aircraft market is worth $1tn.
That figure evidently convinced Boeing’s venture capital division, Horizon X. Together with JetBlue Technology Ventures, it took a stake in Zunum just under a year ago. How much was invested has remained as confidential as the development of the battery. Ashish Kumar, head of Zunum, is expecting to make major progress with the batteries. He expects his hybrid jet to have a range of about 2,400km by 2035. It may even be able to do without the electricity generator.
Anton takes a more sceptical view. Storage capacities are gradually improving, but he does not think a breakthrough is in sight yet. “In the coming decades we will only see pure e-planes in niches such as short-haul transport in mega-cities.” Cousin at Airbus is also convinced that hybrid aircraft will prevail: “When the technology is there, it will reshape aviation for decades.” One reason is that compared with the battery-only solution, the hybrid is safer: “Although having two energy sources on board – turbine and batteries – means more weight, on the other hand if one fails then the other can take over.”
Safety issues are also becoming a hurdle for the many fully electric air-taxi projects, says Rolf Henke, aviation director of the German Aerospace Centre (DLR). “A lot of prototypes are already flying, and that is a great achievement, but licensing them for widespread use in urban areas is a completely different matter.” By that he means take-offs and landings in all sorts of places, such as parks or streets. “If I have to get to the airport, then take an air taxi to the next small airport and then take a car or train, it completely loses its appeal,” says Henke.
Things look rather different if you are at the airport and want to get to the city centre. Here, the air-taxi startups believe a speedy shuttle service down a clearly defined route could be a profitable business model that might win official approval.
Airbus wants to get in on the action: its CityAirbus prototype, with four fixed rotors and capable of carrying four people, is scheduled for lift-off this year. Henke sees that as a possibility on selected routes, “but just imagine that even 1% of the population of Berlin wants to fly flexibly through the city – you would have 30,000 flying machines dotted across the sky.” And they would need plenty of space for take-off, landing or parking on the ground, too. “Someone still needs to explain to me how that could work in safety in the foreseeable future.”
In fact, there are as yet no regulations governing the licensing of such craft. The European Aviation Safety Agency may put some forward this year. Meanwhile, Henke has thought of even more challenges, such as strong downwinds in skyscraper canyons, which can reach 100kph. “That is roughly the speed of the aircraft, so the planes would struggle to maintain their course or keep a safe distance from one another.”
But Henke does not wish to appear too negative. “I am not saying that it is all impossible; we are working on these issues in the German Aerospace Centre. And we too want to develop solutions and, of course, we are doing so.” But it all takes time. As an expert, he predicts that – provided issues of licensing and approval are resolved – the air taxis that that can be produced fastest would be the first to be officially allowed to take off. But for technical reasons fully electric or hybrid electric aircraft, especially large transport machines with e-motors, would require significantly longer. According to Henke, electrification will be a long haul, spread over the next 20 years.
‘Substitute electric flight for the moon’
We talked to aviation expert Bernhard Schmidt, Corporate Business Developer Aerospace and Mobility at the Fraunhofer-Gesellschaft in Munich, about the challenges facing the industry
brandeins: What is the airline industry’s view on electrically powered flight?
Schmidt: The situation resembles the time of the Apollo missions. In 1961 John F Kennedy announced that an American would walk on the moon by the end of the decade – and return safely to Earth. At that time computer technology was nowhere near sufficiently developed to even think of flying to the moon. But within a few years they pulled it off. So, substitute electric flight for the moon, and batteries and electric motors for computer technology, and the race is on.
Kennedy was out to beat the Russians to it. What motivation can aircraft manufacturers have for such a tour de force?
Success hinges on whether the aircraft are quiet enough and can take off and land without emissions. Not just because environmental requirements will be even stricter in the future but also because society increasingly demands this. We see electric mobility on the roads; we see digitisation in our lives. And aviation is judged by that. So, at the moment, it is really on the verge of a fundamental change.
We can see from the automotive industry that change does not proceed without pain.
And that is exactly what the aviation industry is facing. And here, too, the change from traditional aircraft engine technology to batteries and electric motors will affect the whole chain of value creation. And of course it will force many operators out of the market who cannot or do not want to adapt. In turn, others will seize their chance. There are already quite a few startups.