Podcast: Is Boom's Supersonic Airliner Closer To Reality?

Listen in as Aviation Week’s propulsion editor updates our chief Boom skeptic on the company’s latest test flight.

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Transcript

Joe Anselmo:

Welcome to the Check 6 Podcast. I'm Joe Anselmo, editorial director for the Aviation Week Network, and editor-in-chief of Aviation Week magazine.

Boom Supersonic's efforts to develop a supersonic airliner have attracted their share of fierce skeptics, who question everything from the project's engines to its economics. Yet, Aviation Week's audience can't seem to get enough of Boom. Whenever we write about Boom, the online metrics are high. When we record a podcast about supersonic air travel, we get tons of listeners. And Boom continues to press ahead, skeptics be damned.

On August 26th, the company's XB-1 demonstrator made its second flight from the Mojave Air & Space Port in California, reaching an altitude of 10,400 feet. Joining us today to talk about Boom, our senior propulsion editor, Guy Norris, who has covered the project since its inception and has some new details to share. Steve Trimble, Aviation Week's resident Boom skeptic. And Jens Flottau, our executive editor for commercial aviation. Guy, let's start off with you. What's new with Boom?

Guy Norris:

Thanks, Joe. Well, as you mentioned, second flight of the XB-1 was recently achieved at Mojave, and I think the key thing about that was that it was a big boost for the Boom development team because on the first flight they'd experienced ... It was a pretty successful first flight, but they were a bit jittery about some of the roll response on the aircraft. So, this flight verified really the fact that it was the roll control itself that needed a little bit of modification. They did some tufting work on the right wing to clarify the fact that, or verify really, that their own predictions about the flow over the aircraft were correct.

So, basically it was a confidence booster for them because it proved that it was, in fact, what they thought it was, which was just the roll control that needed tweaking and not some kind of hidden flow issue that they'd not detected with their analysis. So, that was good.

They also cycled the gear for the first time, which is a massive confidence booster because all of these things clear the way for basically going supersonic in the next couple of flights. So, I think they're back on track for trying to get supersonic in the next couple of months, essentially by the end of this year. So, that's going pretty well.

The other thing that we really should talk about though is the fact that their engine work is progressing quite quickly, perhaps faster than even they thought. And one of the reasons they're saying this is because they don't have an engine maker to work with, they're doing it themselves. So, really strangely, they're seeing faster progress because the airframe team and the air propulsion team are basically one team. So, that's kind of a weird thing that we've never seen before.

Of course, the proof is in the pudding. As you mentioned, Joe, I've got a few more details to share about the engine, but I just wanted to quickly, before I pass to our chief skeptic, I wanted to repeat something that Blake Scholl, who's of course the CEO, said recently in an ask me anything, he said, "We kind of threw down the gauntlet and said, 'We're doing it.'" This is in terms of the engine. "And you'll be able to see it running by the end of next year, and either we'll be right about that or we won't." Okay. Well, anyway, Steve, what do you think? Are you at all convinced on any of this?

Steve Trimble:

So, the chief skeptic thing, I guess I probably deserve that, but at the same time, I'm not rooting against them. I'm also not rooting for them. But I'm sure there's people in the company working very, very hard, very dedicated to doing this. And I don't think I'm saying anything they don't know, or any of us, the rest of us don't know, which is that what they're trying to do is extremely difficult and there's some technical difficulties ahead for them.

You mentioned the engine. Obviously, supersonics have been around for several decades, since 1947. So, that's not sort of inventing new technology, but to apply it and the current regulatory regime with emissions both with fuel and noise, they're going to have to go past the state-of-the-art in those areas, and that implies a development risk that they're going to have to deal with.

But I mean, the technology is one thing. I mean, really the big issue with them, and no matter who it is, that's a startup company trying to do something like this, is the financial risk and the financial challenge. They're trying to obtain FAR Part 33 certification for a commercial supersonic turbofan engine, as well as FAR Part 25 certification for a commercial supersonic airliner. I know in the past, Blake Scholl has said that that's going to cost about $6 billion. I don't know if he's updated that number. I mean, he's been saying that for several years, even at the point where if you go back just five or six years, he was saying that the aircraft would be delivered by last year, right? In 2023, the Overture, the supersonic aircraft itself, not just the XB-1 test bed.

Maybe $6 billion is optimistic. Who am I to say? But it could be optimistic by a factor of two, three, maybe even four, to actually get all that done to the FAA and EASA's satisfaction. And that is hard. They have financial backers, right? Sam Altman was out there as one of the original founding financial supporters. In 2019, Laurene Powell Jobs kicked in $100 million. She's the widow of Steve Jobs, so there's a lot more where that came from.

And just last year, they also attracted an investment from the NEOM Investment Fund. Some of our listeners probably know what NEOM is, it's that $1.5 trillion mega-city development project out in the Saudi desert. They also have an investment fund, sort of a venture capital arm. So, I'm sure they've got a lot of money. But they're going to need it, and probably even more than that to get this ... Not just to overcome the technological challenges, but to actually get aircraft certification and engine certification, and then, I'm sure make a profit. That's what the investors wanted to do. Maybe some of them just believe in the charity of supersonic transport, but I think a lot of them really want some money back on their investment at some point. So, that is the challenge I see going ahead. And they know that, but it's just a fact of the situation.

Joe Anselmo:

Jens Flottau, it has been more than 20 years since the Concorde halted service. Do airlines really want a supersonic airliner? And this Mach 1.7 Boom will fly at, is that enough to make it worth the added cost for a passenger?

Jens Flottau:

Good question, Joe. I mean, if we think about supersonic, we all think about, at least I think about transatlantic, Air France flying Paris to New York and BA flying London to New York. And I went back into and looked up a recent International Council for Clean Transportation study on supersonic aircraft, which was really interesting because they looked at the market potential of the various regions. And they came to the conclusion that the transatlantic market will actually be only 5% of a potential future supersonic market.

And why is that? Obviously, transatlantic, there was bankers flying from London to New York, and that's where the short business trips, the one day, the day trips was where Concorde made the most sense. Now, today, I don't think it's reasonable anymore to assume that there will be a market for that, at least of any significant size. And obviously, the reason is sustainability concerns.

And we're all in Aviation Week, we're part of a large corporation, Informa, and when we book travel through our internal travel system in Europe, when I book a flight, I'm always asked, "Would you rather consider taking the train?” Because the CO2 emissions are so much less. And then you get a percentage number. Of course, the train is not an option on transatlantic travel, but you get the idea. Sustainability concerns are front and center, and I just don't see any supersonic aircraft fly in Europe, at least.

Now, back to that study, the ICCT study, it looks at where would be a big potential market, and it's really interesting, 31% is North America. Of that 31%, most of it is intra-North America. And of course, that's assuming there's no restrictions on noise and everything, so you usually have to fly over land. Now, there's a huge question mark over that. If there are restrictions like noise, emissions, and so on, that market shrinks by 95% according to ICCT. The biggest market for a large supersonic aircraft is, we've talked about NEOM, is the Middle East. So, it's people in the Middle East flying to Europe, flying to India, flying to Africa, to Central Asia. Those are the markets that ICCT believes could be viable, but again, only assuming that there there's no restrictions. And there will be restrictions. So, to me, that says not a great business plan.

Joe Anselmo:

Guy, Jens brought up noise, obviously that's a huge impediment, sonic booms, to supersonic travel over land, but Boom is saying that they've made some progress on that front.

Guy Norris:

As Jens mentioned, I think, obviously sustainability and noise are the two great big things here. So, can they beat those two? Well, on noise, one of the things that emerged at Farnborough when we talked in detail about the engine project to Boom was the astonishing length of the nacelle. It's actually going to be 15 meters long, which is about 49 feet. Now, just to put that in context, that's about 19 feet longer than say, the GE90 on the 777. So, it's going to be huge in terms of length, but of course, with only a bypass ratio of 3-to-1, which is more like a business jet engine or like the Tay, for example, which powers the Gulfstream IV or the Fokker 100, for those of you old enough to remember that airliner.

But the point is that it's all relative. So, within that nacelle, they're going to package an engine diameter with a fan diameter of 72 inches. That's about 1.8 meters. To give you an idea of what size that is, that's about the same diameter as the engine that CFM developed for the Airbus A340, which was the biggest fan engine that CFM had done to that date. And the point about the big fan is that you reduce the speed of the tip. So that, that results in obviously lower emitted noise coming out of the front of the engine.

And the point about the length of the nacelle is it gives you plenty of room for acoustic treatments. So, obviously that's going to be in the front and back, forward and aft in the nacelle. Plus, of course, you have room for this large mixer, a lobed mixer, which is going to result in reducing the shear forces which are involved between the core flow and the fan flow. So, all of these are basically ways of reducing the sources of noises.

And the other thing about it with this large nacelle is that when it matches to the wing, it means that you can really put it very, very close at the underside of the wing, and that you can also reduce the disturbance of airflow over the top of the wing. And that's important because although the wing of the Overture is going to be about 30% larger than Concorde's, it will also feature leading-edge and trailing-edge high-lift devices, which of course, Concorde never did.

One of the things that I find intriguing is that yes, the Boom model is based on ... They're not pretending that they're going to be able to defeat the sonic boom, quite the opposite. They're embracing the fact that it's a simpler design because of that, and they're only going to be able to fly supersonic over water. The speed that they've got, Mach 1.7, is obviously twice that of the current subsonic fleet. So, what's the benefit of that?

And one of the things they are saying is that they're also going to be capable of up to 20% higher speeds over land because they're right up there at the transonic area without significant drag. So, that's going to be an interesting element for bringing locations or entryways within country borders, so that you'll be able to integrate the routes rather than basically being able to just fly from coastal cities, in other words. You'll be able to bring in sort of areas that are with inland destinations. And Steve, I'm seeing some doubt again in your face.

Steve Trimble:

Well, let's just unpack the noise a little bit because it's a huge issue. And I mean, just for the fundamentals of it are that you want to go supersonic, ideally you want to accelerate a small volume of air faster than a larger volume of air more slower, which means you're going to a lower bypass ratio engine, which is what they're doing, but that has effect on noise. So, that's why they're creating that much longer nacelle to have all those acoustic treatments, which are, let's admit it, unproven at this point. I mean, this is something nobody's done to this extent for this kind of level of performance in noise suppression. So, that's part of the risk that they're taking on.

But even they acknowledge sort of tacitly that it's probably not going to be enough, because in addition to that, they also say that they are going to equip the aircraft with what they call an automated noise reduction system. And there's been no detail on what Boom has in mind specifically for that. But we do know that has been proposed before in NASA papers and other industry papers, and AIA reports, and on the NASA Technical Reports Server.

And if you dig down into those things, what those talk about with a variable noise reduction system, they don't call it automatic, but it's probably the same thing. It's automated because the computer controls it, not the pilot. But as you do the takeoff roll, as the wing starts doing more of the job in producing lift, the computer is able to calculate very precisely how much they can de-rate the thrust in real-time as it's taking off, to minimize the amount of noise that it's creating as it's lifting up. Of course, and that's the real impact on community noise, because as it gets above the airport, that's when the noise starts propagating to the surrounding area. That's what they want to minimize the most.

Now, of course, by doing this, they are reducing the noise through that de-rating the thrust, but at the same time, they're having, presumably, a shallower climb out, right? Now, I don't know that for a fact. And Guy's shaking his head. They can get the same amount of climb out with a lower thrust. And go ahead.

Guy Norris:

Well, so here's the thing, Steve, and this is really interesting. So, Concorde, as you know, didn't have any lifting surfaces. I mean, sorry, didn't have any high-lift devices, and it relied entirely on vortex-generated lift and its rotation. It didn't also have a tail. So, if you look at the design of the Overture, the one thing that they've had to really compromise on is giving the thing quite a large tail. And the reason this is important is obviously that gives you a rotation authority when you're taking off. And it means that Concorde had to accelerate and climb out, as you mentioned, at a very shallow angle, which was a nightmare for noise. It also had to use afterburner on takeoff, which is a pretty big no-no these days in the 21st century.

But anyway, the Overture will neither require afterburner, of course, nor will it have that shallow climb-out angle. It will have a relatively steep climb-out angle because A, it's got high-lift devices, flaps, and leading-edge slats. It's also got the big tail. And the engines, because it's got four engines rated about 35,000 pounds each, it means that they're going to be ... They've got what I'm described, what I've been told are there's bags of power. They've got ample margin. So, they will not be needing to do a maximum power takeoff even for a max gross takeoff weight, because basically, runway limit's what they're looking at. So, it means that their takeoff profile is going to be nothing like Concorde. It's going to be much more like any of today's subsonic aircraft. And I think that's a huge factor as far as community noise is concerned.

Steve Trimble:

Well, sure, but they'll still have half the bypass ratio of a modern turbofan engine while it's doing that, with four engines instead of two usually. So, I mean, they still have a challenge there. And this type of noise reduction system has never been certified before, at least that I'm aware of. So, that's another part of the risk that they're taking on just in the certification.

Guy Norris:

Yeah, absolutely. And they're not minimizing that challenge at all. And just one of the things that they are saying is that they're adding in about three to five dB margin over chapter 14, because they think they're going to need that going forward, because they think there's a whole new chapter 24 coming in the mid-2030s, which without meeting that, they're not going anywhere.

Joe Anselmo:

Well, gentlemen, thanks for a great discussion. I actually learned quite a bit just with this exchange back and forth, and we'll definitely have to come back and talk about this some more because this story is not going away. But for now, that is a wrap for this week's Check 6 Podcast.

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Speaker 5:

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