Electric propulsion slowly wings its way to aviation

That electric power is coming, on a mass scale, to motoring is pretty much now taken for granted. Battery and electric motor technology has advanced in giant leaps in the past decade, and since 2008 we have gone from electric cars that struggled to go for more than 100km on a single charge to those that can easily top 400km.

As ever, in the feedback loop world of motoring and aerospace, technological advances in one area beget similar advances in the other. For decades, cars drew on aviation experience for superior fuels, improved fuel injection and other aspects such as tyre and brake designs. Now, it’s just possible that motoring, and its move towards electrification, is influencing aviation. The only caveat is not to hold your breath – this is going to take some time.

How long? "It could be 40 years before we see volume-oriented commercial aircraft that are fully electric powered," says Gavin Campbell, director of engineering and technology development at Bombardier aviation in Belfast. He started with the company when it was still known as Short Brothers, and was chiefly famous for flying boats. He's also a member of the Aviation Technology Institute, a forum for aviation engineers and scientists to promote new developments and improvements.

“In terms of power density and the battery debate, I would go back to 1909, when the first powered flight took place across the English Channel, and it was only last year that the first all-electric flight took place across the channel,” Campbell says. “So if you look back 100 years ago, look at how long it took to go from that first cross-channel flight to flying people transatlantic, to me that gives you an indicator of what rate of advance you’ll see in the technology. Some people might say that in the 21st century we will advance much faster, that we’ll find different techniques. My own view is that human ingenuity will drive that innovation and change at a rate that we haven’t seen before. There’s a technology analogy to Moore’s Law, and when there’s a potential goal in sight, it tends to concentrate efforts.”

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Cross-channel flight

That first cross-channel electric flight took place three years ago, in an Airbus E-Fan prototype aircraft, with pilot Didier Esteyne at the controls – 106 years on from the first cross-channel flight, by Frenchman Louis Bleriot, controversy reigned as another pilot, Hugues Duval, claimed to have beaten Airbus to the electric crossing record. Airbus claimed that Duval's aircraft launched from a conventional 'mothership' aircraft, which made his record invalid.

Whoever got there first, that pegs electric aircraft roughly a century behind current fuel-based aviation technology, and it’s not even as simple an analogy as saying that cars are going electric, so why can’t aircraft? For a start, the modern high-bypass turbofan jet engine is incredibly efficient, far more so than a car’s piston engine, so electric power has a higher hurdle to jump.

On top of that, there’s the old issue of energy density. In spite of the huge advances in battery technology, aviation fuel still has a roughly 30-to-one advantage over battery power when it comes to how much motive power you can extract from a given weight.

Electricity in the air is coming, though, but it might need to take more baby steps between now and when it becomes truly widespread.

A spokesperson for Airbus said: “We are pushing the technologies to be able to develop a 100-seat fully electric aircraft in the 2030s. There are enormous challenges to achieving this, which is why we are investing hundreds of millions on projects and demonstrators to secure this plan. Our sustainability targets are very serious to us and in order to meet them we need to develop new technologies.

“Electrification technology is already being applied to our urban air mobility demonstrators and we believe that in the early 2020s these kind of vehicles will enter commercial service. These are two- to four-passenger vehicles with a range sufficient to cover urban commuting. As the technology progresses higher range and passenger carrying capability will become possible. It’s likely therefore that the shorter distances will be technically feasible before the long-haul.”

Intermediate steps

Campbell agrees with that assessment: “There are some intermediate steps, which will also help the pace of the development. Now, again, we’re a very regulated industry, and the regulator is there to protect the general public, and in some ways is there to stop us from having a hare-brained idea, rushing into it, and sticking it up in the sky. And then all of a sudden the safety standards might start to slip.

“So it’s not just the pace at which we can create the technology, it’s the pace at which we can produce evidence in the way that will satisfy the regulator. There will be regulations which will need to be changed in order to switch over to these systems. So there won’t be a ‘big bang’ moment where suddenly we’re all going to be flying on electric aircraft, you’ll start to see more electric systems, bit by bit, as we go along.”

According to Campbell, what we’ll see first is a ‘more electric’ aircraft, rather than a fully electric one. “The automotive sector can afford to be a bit more iterative – you can try something and see if it works and if it doesn’t then you can try something different.

“We need to look at all the interactions, and a lot of what goes on in aircraft engineering at the moment is all that kind of unseen technology, and how systems interact with each other. How you separate power distribution lines from control and communications lines, how your route them around and away from potential high-risk zones, such as around the engines. That’s why aviation is such a safe means of transport – because we’re regulated to ensure that designs are done in a very strict and controlled way, so that really everything comes back to safety.

“So one of the themes in this that we’ve been pursuing at Bombardier is the idea of ‘more electric’ aircraft. Over the past five or 10 years, for instance, on our Global Express aircraft, we’ve introduced e-brakes, which are electrically powered and actuated brakes, instead of hydraulics. There are a number advantages, including ease of servicing and system reliability and maintenance, but it also reduces the overall weight, because you’re not carrying around all of that hydraulic fluid, pumps, accumulators, pipes and so on.

“It also helps that we have a backup – a thrust reverser on the engine, which has the power to stop the aircraft if for any reason there’s a failure of the wheel brake. We’ve been exploring a number of other systems in the aircraft. At the moment, all of our control surfaces – flaps, slats, rudders, ailerons, elevators – are all hydraulically actuated, so there’s a lot of work looking at can you get the same sort of benefits in terms of simplification, reliability and reduction of weight, by using electric actuation.

“And then of course the regulator comes in and points out that we have 80 years of experience with hydraulic systems, volumes of data, stats and so on. So as an industry we’re going to have to build up the data to prove that an electrical system could be better than what we have now, which is a 10 to the minus six probability of systems failure, and that we can design backup systems that can do the job too, because on an aircraft there’s always one and sometimes two backups, so if your primary system fails your secondary or tertiary system can kick in.”

Safety has already become a hot-button issue for electric aircraft. Earlier this year, an experimental Magnus eFusion electric aircraft crashed, killing both pilot and co-pilot. While many predictions are made for the speed of electric aircraft development, one has to remember that current aviation technology was built on the sudden, shocking advances made in the course of two world wars, and on the willingness of postwar test pilots to put their lives on the line trying out cutting-edge new aircraft.

Many paid the ultimate price, as did some passengers and even visitors to air shows, most infamously at the Farnborough in 1952, when an experimental De Havilland DH110 jet fighter broke up in mid-air, killing the pilot. Worse yet, 29 spectators also died when parts of the aircraft, including its engines, fell into the crowd below. To get to the safe, reliable aviation world of today cost scores of lives, and there’s no way a push for electric aviation would be allowed, in the risk-averse modern world, to do the same.

Savings

Electric flying is, without question, coming all the same. According to Florian Martini from Siemens, which is developing electric turbofan engines for aircraft, the savings are just too compelling for it not to be.

“We have seen estimations for reductions in fuel consumption for hybrid-electric aircraft ranging between 15 and 50 per cent,” Martini says. “Even at the lower end of the scale, these are significant savings. On top, electric motors promise to have reduced maintenance requirements compared to combustion machines. This would drastically reduce operating costs, depending on type of aircraft and configuration. We can already see the technology appearing in smaller planes. We expect that electrical and hybrid-electrical propulsion systems will become established in small airplanes in the next five years.”

Airbus, in collaboration with Siemens and Rolls-Royce Aerospace, is currently building a prototype aircraft based around an Avro RJ85 four-jet passenger aircraft (if you’ve ever flown CityJet from Dublin airport, you’ve flown on one of these) which will have three conventional turbofan engines, and a single two-megawatt electric engine for hybrid electric propulsion.

“From my perspective, from my experience with the Aerospace Technology Institute, we can see that there’s a concentration of investment starting to happen in this area, and it’s not just about aviation,” says Campbell. “One of the big common investments is in the Faraday Challenge, where the [UK] government has come in behind both the automotive and aviation sectors, and there’s a lot of co-investment going on. It’s led by the industry, but it’s backed by government.

“And very often that’s on a pound-for-pound basis, which makes it a very powerful lever of development. By getting cross-sectoral interest such as that, with the government and industry co-investing, that’s how you get to see the pace of innovation hotting up. All of a sudden, you get innovators around the world sitting up and taking notice, and we become a more interesting place to be doing that kind of work. So you do see strategic moves such as that somewhat forcing the pace.”

Shortly after this interview was conducted, Bombardier announced significant job losses at its Belfast facility. Which sadly goes to show that even at the cutting edge of aviation technology, the ancient laws of supply, demand and cost still apply, as does the toxic, smothering effect of Brexit.