Industry interest in electric propulsion for aircraft is growing fast but the first hybrid-electric jetliner is “at least a decade away”, according to one aviation R&D executive.

Ron van Manen is Programme Manager at Clean Sky 2, a joint research programme of the European Commission and the aerospace industry to develop greener aircraft.

Van Manen spoke to EURACTIV’s publisher and editor, Frédéric Simon, on the sidelines of an event organised as part of the GE Garages Brussels 2016.

The Clean Sky programme was launched in 2008 to support research into environmentally-friendly aircraft. Since then, where was the biggest progress achieved in terms of technology?

I would single out two particular areas that seem to be the most far-reaching. They relate to new engine architectures, like open-rotor engines with a very high bypass ratio and without the ducting around the fan blades. And a new design approach to create a laminar flow over the wings – what we call a laminar wing approach.

Through our technology evaluator, we now see a 37% or 38% improvement in fuel burn and therefore an emissions reduction for aircraft equipped with these technologies. So it should be ready around 2025, if the market is ready for them.

That 38% is huge and suggests we may have hit the limits of what could be achieved by improving existing technology. So where are the main opportunities now lying ahead?

We assume that our visionary goals for 2020 will have been satisfied around 2023 or 2025, with available technology and air traffic management improvements in place.

But I stress being in the market place is not the same as being in the aircraft because the next stage is the market’s financial and commercial capability to accept these.

Moving beyond that, Clean Sky 2 has two sets of goals. One is a further 20% in emissions reductions for 2025 compared to the 2015 state-of-the art aircraft, and a 30% emissions reduction for technology to be made ready by about 2035. And this links to the renewal of the so-called ACARE strategic research agenda, which aims at moving beyond this 50% reduction by 2020 towards a 75% reduction in fuel needs by 2050. So 2035 is kind of the mid-way.

So you’re saying there is still a lot of room for improvement on fuel efficiency?

People hardly see what kinds of improvements have already been made. The cylindrical aircraft with twin engines under each wing has been regarded as the state-of-the-art architecture until now. And the question now is, does that architecture run out of runway. We believe there is probably another 20% or even 30% improvement inside that type of architecture. Then you run out of runway.

And the kinds of things that the industry will need to look at moving forward are different means of propulsion, a different thermo-dynamic cycle or even things like electric propulsion. And the aircraft configuration – so the way an aircraft looks – will also have to be reconsidered.

But that seems far off, doesn’t it?

You’re looking at beyond 2035. And the speed at which this develops depends in part on how fast technologies progress – the speed of discovery. And part of it is the economic equation. The low interest rates we’re currently seeing tend to be pro-investment in future aircraft.

But low fuel prices are a huge inhibitor. And the key to that challenge I would say is the cut-over at the level of airlines – how do you finance 20 or 30,000 aircraft. And what may actually be not one but two cycles of fleet renewals. Because if airlines are replacing their current fleet with available new-generation aircrafts like an A320 Neo, an A350 or a 787 – it’s really the generation after that we’re talking about. So it’s two cycles of 30,000 aircraft and $3-4 trillion of investment.

If low fuel prices are an inhibitor for investment in new efficient aircraft, can a strong aviation ETS provide the necessary incentive?

There is no escaping, whether it’s through a market-based system like emissions trading or advantaging one fuel type versus another or simply taxing fuel.

As a natural consequence of finite resources, it will happen. The question is, can it happen on time without some kind of intrusive policy or will it happen so late that the time will be lost.

So you think it should happen sooner rather than later.

The Global Market-Based Measure agreed by ICAO, regardless of whether it is the most aggressive mean, is a start and a necessary start at this point in time.

About electrification, how much of it is happening already now in existing aircraft and how more is expected in the future?

What we’ve seen generally is a trend towards the systems on board being electric-driven and less driven by hydraulics or pneumatics. That allows the engine to be more efficient because there is less off-take from the engine. And you can conduct energy across the aircraft tin a more efficient way. Copper-wire is lighter than high pressure hydraulics.

How much fuel savings would that allow?

It’s in single-digit terms but it’s significant. Traditionally, the real drivers of fuel efficiency have been the architecture of the engine itself – the by-pass ratio, the temperatures in the engine, the materials allowing high temperatures and the thermo-dynamic cycle – and the optimisation of air flow over the wing.

Computer analysis using 3D modelling has also allowed optimisation such as better predictive design routines to build aircrafts without having to go through trial and error. Designers are now capable of optimisation that wasn’t possible in the 80s or 90s. And that trend continues.

Looking forward to future prospects for electrification, what would it be?

The next big step is understanding to what extent electric energy can also augment or perhaps at some stage even replace propulsion based on petrochemicals – whether fossil fuels or biofuels.

There is still a long way towards replacing fossil fuels because the energy density you would need in batteries is probably about a thousand times or more greater than it is now. But if you look at what has happened already in batteries in your cell phone for instance, the pace of change has been tremendous over the past 10 years, not driven by aviation but by consumer electronics and space.

And it will find its way into aerospace as it has been doing already for automotive. But the challenge there is quite a bit more severe than with your mobile phone.

To say the least…

You can contain the thermal aspects of a lithium-ion battery in your mobile phone with the size of a one cent coin a lot better than you can if you need a battery pack of several thousand kilos. So there are real challenges there.

How far off is hybrid-electric propulsion for aircraft?

It’s found its way into Clean Sky 2 and it is developing very rapidly. Initially, the industry told us ‘We might want to look into this when we have time’. Now, I reckon we’ll probably fund €50- 100 million of hybrid-electric activity in the course of Clean Sky 2, it’s developed that quickly.

One question is to what extent you can use augmentation of electric power on top of thermo-dynamic power or distribute it better. This is interesting because the amount of power you need to take off with an aircraft is a lot greater than you need to cruise. If on take-off you could augment the thermo-dynamic power coming on fuel with electric power and then recharge your batteries in flight, then you would be able to get away with smaller engines. Smaller engines are lighter which also means a lighter wing so you get into a virtuous cycle.

Very preliminary guesstimates put the potential benefit of that at about 15-20%, on top of what you can do to make a better fuel-powered engine. So it could be pretty significant.

What timeframe do you foresee for this?

The technology readiness, I would say, is at least a decade away. But that would only be the end of the beginning. So, realistically, I think you’re looking at a 2035 aircraft, not a 2025 aircraft. But it could go that quickly.