Airbus announced three different aircraft concepts for a hydrogen-powered aircraft that is to enter service in 2035. The company is making key technology choices early and still has massive challenges ahead: technological, regulatory and in convincing industry partners to participate. Aviation Week editors Guy Norris, Thierry Dubois and Jens Flottau discuss the key issues ahead.

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Below is a rush transcript of Aviation Week’s Sept. 18, 2020, Check 6 podcast.

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Jens Flottau:

Hello and welcome to this week's Check 6 Podcast. My name is Jens Flottau and I'm the executive editor of commercial aviation at Aviation Week Network. I'm happy to welcome with me on the program, senior editor, Guy Norris and Thierry Dubois, our France bureau chief, who, as you surely know, if you read Aviation Week regularly, is an expert in aerospace technology subjects too. This week, we are going to talk about three aircraft concepts that Airbus presented for the first time. They are very different from each other in many ways, but they do have one thing in common. They are supposed to be powered by hydrogen. And our Airbus' vision in the transformation of aviation into a greener more sustainable future. Exciting ideas, but lots of questions too. Let's take a step back first and Thierry, if I can ask you to just walk us through the plans that Airbus presented this week.

Thierry Dubois:

Sure. Basically, there are three concept planes at the center of the study. They call them concept planes because none of them will actually be built, but there are three directions that they're going to be studied in depth. So one of them is, looks like  a turboprop aircraft configuration. I think the maximum passenger capacity would be around a hundred passengers. The other one, sorry, the first one, I mentioned the turboprop because it would burn hydrogen in relatively conventional way seen from outside, relatively conventional to the turbine engines. The second concept plane is also a conventional tube and wing configuration. It will be powered by two turbofans not turboprops to the fans. Burning hydrogen again, capacity is between 120 and 200 passengers.

And just like the first concept plane on the fuel tank, the hydrogen tank is located at the rear of the fuselage. And the third concept plan is definitely the most spectacular it's a blended wing body. Again, powered by turbofans. So all three concepts planes burn hydrogen in turbine engines, but the big difference, the main feature of the third one is the blended wing body configuration, which means you can much more optimize aerodynamics, and you can also distribute passengers and fuel tanks in a much more efficient way in the airframe. So roughly speaking, these are the three concept planes that Airbus is speaking about.

Jens Flottau:

So we're 15 years out, right? They're talking about entering into service in 2035, but already they're making some very important technology choices. You mentioned liquid hydrogen, for instance. Can you just walk us through again, what are the steps that are coming up in between now and 2035?

Thierry Dubois:

Sure. So between now and 2035, and again, 2035 is the plan date for entering to service. The first main, milestone, if you wish is 2025, by then they expect to have majored some technology bricks as they call them to choose from. And they would launch a program in 2027 or 2028. So that would be a full program launch for industrial program launch in 2027 or 2028. And what would be very, very informative for us to follow is the next five years they plan to do several demonstrations. So they will demonstrate the technology bricks such as hydrogen storage, for example. And one of the first demonstration projects is about hydrogen storage and distribution.

They will start on the ground, but they also plan some demonstration in flight, which could be quite spectacular. And they plan quite... And I'm a bit surprised by this. Maybe we could discuss this afterwards. They plan to start with gaseous hydrogen storage demonstration before moving to liquid. And as they seem to have made a choice already for liquid hydrogen, I'm a bit surprised by the fact they are going to also test gaseous hydrogen.

Jens Flottau:

Yeah. So Guy, Airbus seems to be really enthusiastic about this and it's kind of came out of not nowhere, but it came a bit as a surprise to me. That that enthusiasm isn't really shared by everyone, in the industry, particularly in the engine industry, there does seem to be quite some serious reservations about this. So can you tell us what you're hearing?

Guy Norris:

Yeah. Hi there, it is a very interesting time because of course the engine manufacturers, like the airframe manufacturers, they're all facing this cliff of how do we meet these sustainability targets in really 30 years? Seems like a long time, but in the aerospace business, it's really not. They've been approaching this idea of whether to adopt the new transformational approach mostly based on alternative fuels, which would be dropping into the existing infrastructure, the existing propulsion designs and the existing tube and wing configurations that the airframers have loved and developed and perfected for the past 50 years or more. So you can imagine that there is a bit of a shock going on here. So how do we suddenly move all of that towards a hydrogen based ecosystem? Of course, the other thing is that they've saying, well, we have been there before, we've studied this, we studied it in the 1950s, for example, more based for military type applications. Again in the 70s during the fuel crisis when the first global fuel crisis.

And again, in the 90s, when there was the first glimmers of the emerging environmental issues, this time, of course, it's different. As you both said, there is a driving force that has never been there before. And of course the French government tying this incentive package really to sustainability is the big decision-making driver on this. So the fact that there's a much more urgent need now is changing the game, but it doesn't change the fact that there is 70 years of history of safety and certification and development behind a known operational cycle around kerosene. People know how to handle it. They know how to certify it, and this is a whole new ball game.

Jens Flottau:

So why would Airbus get buy in from the other industry participants, if that wasn't possible for one reason or another over the past several decades?

Guy Norris:

Well, one of the reasons is that time does move on and technology has improved. There are ways of coping now. There's a couple of ways to look at it. One is from a big picture perspective, the big challenge that a lot of them see both in and out of aerospace is the fact that the feed stock, the actual production of hydrogen has to be done in a sustainable way to make this entire equation balance out. So, for example, at the moment 95% of the world's hydrogen, generally speaking is produced as a byproduct of burning fossil fuels. So obviously that doesn't work. So what you have to do is go to a sustainable way of producing it, and that of course could involve electrolysis of seawater or pure water by doing that.

Using a nuclear based system, there're all sorts of different ways of approaching that problem, but it just shows you that you're talking about wholesale change in the entire infrastructure. And the second thing is, of course, that there're more ways of skinning the cat here than perhaps just the obvious picture, right? As Thierry says, Airbus project is looking at turbofan, a turboprop and a blended wing body, which opens up the design space to beyond conventional gas turbines, to distributed propulsion systems, which could be driven electrically. So the aspect there of you're opening the prism really to enable lots more options. So it may not just be combustion of hydrogen in an engine, which is almost a wasteful approach to it. It's a much more integrated possibility. So electricity produced by a hydrogen based system, whether it's a fuel cell or another approach to power the hybrid electric system, which would then be used to generate a propulsive force in an engine somehow. So there are several approaches I think.

Thierry Dubois:

But it seems Airbus has already made a choice towards burning hydrogen as opposed to using electricity produced from hydrogen on board. So they seem to be ready to go ahead with turbofans, turbine engines and to some extent, a level of hybridization, which would use smallest fuel cell sorry. And just like on a Toyota Prius, for example, would optimize the overall propulsion chain, but it seems the Airbus projects are making electric propulsion fading away a little bit in some way.

Jens Flottau:

Do you think that this is because of the EU kind of the political situation in the crisis right now? Now the funds are accessible for them because of the French, a research package and the German research package and governance want to see action now. But if you look at the technologies that you think you can mature in a given timeframe, which is 2035, then this is what you have to do rather than fuel cell, it's taking longer other avenues that would probably be promising, but may take a lot longer. Is that what's behind it?

Thierry Dubois:

Yeah. Yes, totally. Just at the beginning of the summer Guillaume Faury, Airbus CEO was saying that his engineers were reviewing all options. And now at the end of the summer, they seem to have made quite strong choices though. They still have to choose between sub choices, sub options if you wish, but they already have chosen apparently liquid hydrogen, as opposed to gaseous and burning hydrogen, as opposed to using it in a fuel cell form producing electricity.

Jens Flottau:

And as you say, favoring hydrogen means that electric is moving to the right, electric propulsion. And also a lot of the airlines are putting a lot of hope on synthetic fuels in the short term, particularly for long range. Now the business case for synthetic becomes harder, more difficult if hydrogen comes in sooner, right? Because the market is smaller. Guy.

Guy Norris:

Well, not necessarily, Jens. And I think this is an important point that we must make here. If you talk to the engine makers, they really see this hydrogen move as something that would feed everything from a regional small airliner up to about an A321 size category. And they really see that beyond that synthetic aviation fuels will dominate for the next 50 years, basically.

Jens Flottau:

So hydrogen is really short haul, narrow bodies, regional and synthetic is long haul, wide bodies.

Guy Norris:

Yeah. It's sort of, you get that breakdown, but here's the interesting thing is they also see a way of the hydrogen based the move being an enabler to also help produce synthetic aviation fuels at a more affordable cost. So that's sort of interesting multiplier effect, we're just at the beginning of really seeing the possibilities of that. But if you've got government based inertia to help really move to this economy, suddenly you're starting to talk about the investment that's been needed for decades in which they're calling on to sort of say, look, unless the petroleum business and the governments get behind SAF's synthetic fuels it ain't going to happen. And certainly not in a hurry, but now maybe there's a door opening to that. So I think that's an interesting aspect. And as I was saying earlier, of course, the other thing is that we're now looking at a whole new set of technologies, which will still have to be developed.

And to Thierry's point, those are the bricks that Airbus is alluding to. And that involves really looking at things that go beyond just a combustor say in a turbofan, adapting that to burn hydrogen, but also the fuel system, the valving, the metering and the cost critically the fuel tanks. Because if Airbus is going for liquid hydrogen, remember that's a stable equilibrium of temperature, but of it as a liquid is 20 degrees centigrade above absolute zero, which is minus 253 degrees Celsius. So 420 degrees Fahrenheit minus 420. So that's very cold and there's so many challenges.

Thierry Dubois:

All these challenges are probably the reason why Safran CEO, Philippe Petitcolin, is a big believer in synthetic fuel as opposed to hydrogen. So the reason obviously is it's certainly difficult to produce, but then you do have to change the entire infrastructure at the airport level. And not to change that much tanks at all. In fact, in the aircraft. So one major engine manufacturer at least believes in synthetic fuel for every kind of aircraft, not just long haul. He believes that for every kind of commercial aircraft.

Jens Flottau:

So Guy, you mentioned cooling, you mentioned storage in general. I'm thinking center of gravity. Isn't that also a huge issue if you've got these huge tanks in the back and then you burn off a hydrogen over the course of the flight? That's different from storing fuel in the wings, right?

Guy Norris:

Yeah. It is. But you have to think about the whole... For example, in the 50s and 60s, when there were studies over in the U.S about using liquid hydrogen as a fuel, they found out that there was amazing savings in overall weight, for example, of an aircraft and an aircraft that would take a balanced field length of 6,000 feet, sorry 10,000 feet to take off normally would take off in six with a liquid hydrogen fuel. So you do get these very strange trades emerging, and yes, you're right. There's a lot of technical challenges associated with the shift of CG and how to reconfigure your aircraft in flight to accommodate that using more than just traditional Trim systems. There's a myriad of issues to look at. But I think that... And this goes all the way down to the engine side, for example, burning hydrogen in a gas turbine, is not just a drop in fuel at all.

And that's even apart from the infrastructure issues, we're talking about a much more energetic, a very small molecular size gas that will try to get out of every little nook and cranny it can find. It'll burn at a hundred degrees more than kerosene. So you have the issue of that energy. Maybe they call it flashback. There's the danger of it flashing back into the fuel system. There's the Aeroacoustic considerations. It's a very energetic combustion process, but because of that, it means your engine can be significantly shorter. Pratt, for example, Pratt & Whitney developed an engine. I think it was the 304, which they developed for Lockheed's secret Suntan project, which was Kelly Johnson idea for a spy plane in the 50s Mach 2.5. And that engine, they eventually ran a modified version of another small Pratt and Whitney engine to test the concept. And lo and behold, it was a lot shorter because it just didn't need to be that long with a smaller combustor. So there's so many aspects to this. It's very interesting.

Jens Flottau:

Yeah. And this is just the onboard part of it. There's one huge issue, regulatory. And this is not one regulator, this is globally. Right. Thierry, any thoughts?

Thierry Dubois:

Not that much, except that it seems like culturally hydrogen is more accepted now than it would have been many 20, 25 years ago. It seems that in Europe, you no longer have this immediate reaction that when you speak about hydrogen, someone says, Hey, remember the Hindenburg in the 30s. That's no longer the case. And both because it's being used successfully in space and in the industry various application on the ground. And it has not caused any major problem recently. So I don't expect major debate around safety.

Guy Norris:

Yeah. And Thierry, is absolutely right. It's definitely a changing vision of what the safety is. And just to emphasize that anecdotally during the Suntan project, the U.S Air Force was really worried about the safety of it too. So to prove that it was okay, the Lockheed people did tests in Burbank, where they had a hydrogen fuel source and a kerosene fuel source, and they deliberately blew them up to see what the difference was and to try and provoke an explosion. And the hydrogen would not explode basically. And the kerosene was violent when it exploded. So they were able to say, well, actually what you are running is not as safe as hydrogen and it did convince Lockheed.

The one thing Jens, I think we should briefly talk about also is the potential impact on the climate. The whole idea here, as we've said before, is to become a sustainable, add to the sustainability of aviation and something has to be done, but there are implications of hydrogen. It's not a panacea necessarily, particularly in two regions that I know of. And Thierry, you may have thoughts on this as well, but one is, if you're direct combusting hydrogen, you've got to be careful that because of that high temperature, I mentioned you don't start producing more nitrous oxides as a result of reduced... You may reduce your carbon, but you may also by burning at a hotter temperature, produce more nitrous oxides, which could be just as bad from a greenhouse gas perspective. So that's a really important aspect. The other thing is, of course, in the 1950s, when NASA or predecessor to NASA, NSCA flew a modified Canberra with liquid hydrogen adapted engine over the U.S the first thing they were amazed at was the fact that it produced this dense contrail.

Whereas the normal engine, there was no contrail. So even though there may be fewer condensation nuclei in the emissions of a liquid hydrogen jet, because you're not burning kerosene itself. So you don't have those little particles of carbon in the air, you're basically adding water. You're just pushing water straight into the atmosphere. And if it's at a very low temperature, of course, that will actually attract water from the surrounding atmosphere. And you will condense immediately into quite a substantial layer. The opposite side of that effect is of course it will diminish, and it will evaporate out more quickly potentially. So you hear the short-term effect of a very big contrail, but probably won't last that long. So there's all those sorts of things. Thierry, you're a big watcher of these things, aren't you?

Thierry Dubois:

What I heard recently. Well, my conclusion would be that this would have to be re-tested, re-demonstrated as large scale as possible. What I heard recently from someone in the automotive industry, someone who specializes in fuel and fuel research and who was quite knowledgeable with the automotive industry has done with hydrogen, Toyota, for example, is producing a hydrogen car called Mirai. Is that thanks to the absence of soot. So thanks to the absence of nuclei you were referring to, you could expect less contrails from the outset. So I think that the two theories need to be tested well, they're both valid theories and tests are needed.

Jens Flottau:

Guys. That was excellent, but I'm afraid that's all we have time for today, but I'm sure this will not be the last podcast on the subject. Please make sure to read the story in the Aviation Week magazine and our coverage of this and many other issues. The next print issue will come out on Monday. Guy, Thierry. Thanks a lot. Thanks also to our podcast producer Guy Ferneyhough in London. And finally, needless to say, there will be another, Check 6 Podcast here next week. That we all hope you will listen to again.