Boom’s New Engine Plan Is Ambitious… at Best


Boom’s Overture supersonic airplane has been in development for a very long time. And while the company has kept a wildly unrealistic very optimistic timetable — expecting entry into service by the end of the decade — few were willing to believe anything until there was an engine to actually power the airplane. And now… there is. Well, sort of. I mean, it’s closer to an engine than it was before. And this rendering looks pretty cool, so there’s that.

Rendering via Boom

This is not the usual kind of thing I write about, but I’m just so utterly fascinated and perplexed by the attempt to return to supersonic travel that I just couldn’t look away. Boom had planned originally on working with Rolls-Royce to develop an engine, but that partnership fell apart earlier this year.

Why? Well…

After careful consideration, Rolls-Royce has determined that the commercial aviation supersonic market is not currently a priority for us and, therefore, will not pursue further work on the program at this time.

The story behind the failure of the partnership is probably juicy enough for a made-for-TV movie somewhere down the line. Or maybe not. But this rupture did mean Boom would have to look in another direction. And now, it has found that direction with a trio of companies that you probably didn’t even know made engines or had anything to do with them. I’m told some of them may even be actual enterprises with real employees.

  • Florida Turbine Technologies (FTT) will handle design and is not to be confused with ITT Tech
  • GE Additive will do “additive technology design consulting” so its name is apparently accurate for whatever it is that it does
  • StandardAero will work on the maintenance side and is a company I’ve heard of

The new engine has now been deemed “Symphony” which is probably what you’d like to hear instead of a loud sonic Boom when the plane flies overhead. But what is this engine?

It’s nothing, yet, but it will be, uh, well, if you like word salads… “Symphony will be a bespoke design leveraging proven technologies and materials to achieve optimal supersonic performance and efficiency.”

That says a lot of nothing, so let’s get into the nitty gritty here. I want to know what the real plan is. And it’s hard to dig through all the consultanty words here, so let’s try and break this down into smaller pieces, starting with the technical details they’ve released.

Architecture: twin-spool, medium-bypass turbofan engine, no afterburner

This has been the trend of recent attempts to develop a more efficient supersonic engine. It’s what the GE Affinity was going to be before GE abandoned the project when its primary purpose — powering the Aerion supersonic business jet — disappeared. The Aerion would have been easier to develop for, because it was a tiny airplane and likely only needed an engine with 15,000 to 20,000 lbs of thrust unlike the 35,000 lbs that the Overture is said to need. But the Aerion project failed spectacularly and GE quit working on the engine.

That should be a red flag right there. Boom could have taken the Affinity work and in theory put it into a bigger engine for the Overture, but GE thought it was a better plan to just stop and walk away. Now, FTT will try to rebuild something GE couldn’t be bothered with.

But beyond basic regular commercial aircraft engine characteristics, three big things will be different.

Boom-designed axisymmetric supersonic intake

Air comes into a jet engine and passes through, but if you have a wider range of possible speeds ranging from takeoff/landing speeds to higher Mach numbers at cruise, then it would help to be able to alter the shape of the air intake to optimize how much air enters the engine and directing how it will behave. Here’s an image that helped me to understand it better from a 1955 NACA research study.

A variable-geometry low-noise exhaust nozzle

The intake is up front and the exhaust is in the back. This would allow the direction of the exhaust to be shifted as needed at different speeds to make sure the airplane is optimized for performance. It also will apparently help keep noise down.

A passively cooled high-pressure turbine

I understood at least some words in this unrelated press release, but I think what it’s saying is that by using newer materials, an engine can avoid needing to be actively cooled with a heat exchanger and can instead be passively cooled. That reduces weight and complexity… if it works.

Most of the rest if fluff, including the part saying it will be “optimized for 100% Sustainable Aviation Fuel.” (SAF buzzword unlocked ✅) But that doesn’t mean there isn’t more heft behind it.

The next question is… can these three partners deliver? And that’s a tough one to feel confident about right now.

FTT has leading supersonic engine design expertise, including key engineers among the team responsible for the design of the F-119 and F-135 supersonic engines that power the F-22 and F-35..

FTT will be leading the way on design, and it appears there are some engineers on the team that have designed engines for supersonic military aircraft. It should be noted, of course, that military supersonic engines are world-renowned for being fuel efficient and quiet.

FTT was mostly bought out by Kratos Defense back in 2019, a proud member of the military industrial complex which does some super secret stuff. It’s hard to glean exactly what FTT brings to the table, so I will simply say this… the president’s name is Stacey Rock, and that’s a bad-ass name.

Next up is GE Additive. “Additive” is, coincidentally, the opposite of what GE has been doing to its portfolio businesses for many, many years now.

Symphony will benefit from GE Additive’s proven track record of designing additively manufactured engine components—enabling more streamlined development, reduced weight, and improved fuel efficiency.

This is a real thing… it’s basically 3D printing, but an advanced and super cool version of it. In short GE Additive can make components lighter and more efficient since the process involves building from nothing instead of traditional methods. But I don’t know what additive technology design consulting means. Does that mean they will just advise on which parts can be made this way in the design process? I guess so. Maybe that’ll result in actual manufacturing, but none of that has been announced yet.

And finally…

StandardAero will ensure that Symphony is designed for maintainability.

This seems like a good thing. So I guess FTT will propose a design and StandardAero will say “are you insane? You can’t make the nacelle out of uranium, we’ll never be able to maintain that.”

Boom is saying the right things here, but saying and doing are two very different issues. This announcement suggests that the big engine companies aren’t taking Boom seriously, so the company has had to dig deep to find anyone willing to help. Even with this, the company says first flight will be in 2027, and I haven’t seen anything saying entry into service will be delayed beyond this decade. That seems nearly impossible.

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25 comments on “Boom’s New Engine Plan Is Ambitious… at Best

  1. “FTT has leading supersonic engine design expertise, including key engineers among the team responsible for the design of the F-119 and F-135 supersonic engines that power the F-22 and F-35..“

    Wow, those seem like some old engine experts if they were truly any kind of key player on engines designed that long ago. F-35 alone first flew as the f-35 in 2006, the x-35 in 2000 (I assume the same engine on both?). The F-22 in 1997. If that was their first flight, those engines would’ve been designed long before that.
    Not meaning to be ageist by pointing that out, but these engineers would be getting to late 60s and 70s, at best and close to retirement, not spending the next few years grinding out a brand new engine.

    1. I’d imagine that anyone who is in their early to mid career with expertise working on supersonic engines is probably better off staying with P&W, GE, or other major company that they currently are at. And switching companies will be complicated by NDAs and maybe restrictions on classified data and technology if employees are working on anything military at P&W or GE.

  2. Florida Turbine technologies is now Kratos Turbine Technologies. The first line on their website reads:

    “Kratos Turbine Technologies is focused on the development and production of small, affordable, high-performance jet engines for cruise missiles and unmanned aerial systems (UAS).”

    Since the Symphony project involves jet engines that will neither be small nor affordable and since the Overture is certainly not going to be unmanned, this is a quantum leap forward from this company’s existing technology. The term “supersonic” is not even mentioned on their website. Depending on the online source, they appear to have between 79 and 100 employees total.

    This announcement further solidifies the notion that this plane will never, ever exist.

  3. “It should be noted, of course, that military supersonic engines are world-renowned for being fuel efficient and quiet.”

    Quite possibly one of the best sentences you’ve ever written. My brother was an F-14 pilot and used to love slapping bumper stickers on my hippy brother’s car that read “I love jet noise.” Thanksgivings were always a good time.

    1. Was it sarcasm? Thanks – I knew too little to figure that out. Should have a mark like the ‘buzzword’ which I totally agree on SAF.

  4. I don’t know anything about engines or the science of flight, so any opinions about this project would be meaningless.

    BUT… the thing critics (and supporters) need to keep in mind, is that the road to ultimate success is always littered with scores of failures. So, even if this experiment never takes flight, it will still yield enough new information and knowledge that could eventually fuel a breakthrough.

    1. “Could eventually” is doing a lot of work there.

      I don’t know much about jet engines (let alone supersonic jet engines) but I know that they’re extraordinarily difficult and expensive to design and the prospects for developing a clean sheet engine in four years with a motley crew of “who?” are… dim.

      Looking forward to making my 2023 prediction about the future of this silly airplane.

    2. Or they will shut down and/or indefinitely delay their project, and become a patent troll long into the future. This could be the only way for them to recover some of their investments, and be burdensome for any other company that came along later attempting to build a supersonic passenger plane in the US or other “friendly” (IP respecting) country.

  5. The Boom guys seem to think they’re reincarnations of William Boeing and are trying to do the equivalent of what Boeing did, leverage his experience in the timber industry to make wooden airplanes, except that a hundred years later it’s titanium, composites, and 3D metal printing. They seem not to realize that it’s the 21st Century. If they have a plan, it’s Plan Nine From Outer Space.

    I would love to fly on this thing. I really would. I’m happy United’s got them on order. I am not happy that my home United hub would probably be the only United hub where this thing wouldn’t go. I’m happy that Boom talked someone into providing at least a glimpse of a potential powerplant. But this does not fill me with confidence. I know I haven’t got much time left in this world and I would love to break the sound barrier while sipping a crisp chardonnay. But these guys aren’t going to provide me with that.

  6. Honest question here to all. Reading all of the blogs that picked this story up, everyone of them have been hypercritical. I get that is what most of the internet is, but what is the point? Should the deficiencies be pointed out and discussed? Sure. Should there be scores of over-the-top pessimistic statements that seem to insinuate anyone that disagrees with the author must be a simpleton? Or that the Boom folks must be morons for even trying? Not so sure.

    I assume so much is being put out on the topic in such a way so that in case it does go belly up, each can link back to 3 articles where they said “see told you so.” I’m just curious though, if this thing works or yields some sort of technological advance for the industry, will there be post showing all of the crow being eaten? In the end, they haven’t asked for any of my money, so I’m not out either way. Pretty sure they haven’t asked for anyone’s on this site either. Just not sure why the constant dogpiling…

    1. Hotintx – The whole point of this site is to opine about things that I find interesting. So if I just ignored everything that counts as a dogpile, I probably wouldn’t have much to write about.

      There’s no question that someone needs to take these steps to achieve future success, and it’s usually not the company that does it. I always think of MCI (the company, not the airport) which was instrumental in building fiber cabling under the Atlantic, unlocking the world of cheap or free data and communications. But MCI did the hard work and then others reaped the benefits after it failed.

      I would like to be excited about supersonic, but this effort isn’t that.
      It doesn’t solve the sonic boom issue, and it doesn’t seem like the right partners are involved to make it happen. The timeline is also just so insanely optimistic, it’s hard to take seriously. (Not that they can’t have an airplane flying by the end of the decade, but having it certified to carry passengers…) That’s what I was focusing on in this piece.
      Please, Boom, prove me wrong. I would love nothing more than to eat crow.

  7. The statement about military supersonic aircraft and engines is indeed bound for the history books.

    perhaps the real reason why Boom doesn’t have a great future and why engine makers aren’t terribly interested is because the plane has a lot less range than is needed to serve some of the longest range routes that are increasingly driving long-haul travel.
    Perhaps the most important thing that Boom should be working on is getting civilian aircraft approved for in-flight refueling – like the military does – so that the plane has a much bigger market without having to get heavier and heavier.

    And given how many new energy technologies are occuring – including the successful fusion in California – the idea of supersonic travel might fall victim to technologies that reduce costs and result in more capable aircraft.

  8. A few additional comments
    FTT was founded by former PW folk from their WPB location. So there was a core of experienced people.
    Passively cooled HPT is every engine design since the 1940s. Airflow is directed through the turbine blades to cool them. Nothing new.
    100% sustainable fuel is more about the fuel spec and the fuel production process. The engine doesn’t care provided the spec is the same.
    GE Additive is the world leader in application of additive to aviation. They have the expertise to design parts in a way suitable for additive, to minimize part count by designing single print parts that replace entire subsystems, and not only that but actually FAA certify and produce them.
    And just to state the obvious, the reason that the big guys declined is that it costs a minimum multiple hundreds of millions, and yes sometimes over a billion, to design and certify a commercial engine. If the market isn’t large enough you can never make this back. Very unclear how this consortium plans to get funded to do this work, the cash profile requires enormous deep pockets to expend all the cash, before you see dollar one at delivery of a certified product.

  9. Supersonic travel is just going to be a pipe dream in my opinion. The issue is, you have to have a plane that can fly at supersonic speeds over water, but at subsonic speeds over land, and to do so economically.

    It would be difficult to make it work on routes like DFW or Chicago to Europe, or anything but the West Coast to Japan, and similarly routes from Europe to South America typically involve long portions over land. And it wouldn’t work at all on routes between Europe and Asia or Africa.

    As an example, consider DFW-London. That flight is 4700 miles…but 2800 of those miles are over land, either the US, Canada, or the British Isles. Let’s say you make Mach 2.2 over water. You would have 1900 miles in about an hour and 15 minutes…and the rest in 4 hours and 45 minutes. Total time is 6 hours, compared to 9? Not much savings for the cost.

    You could tweak the route, and fly straight east from DFW to the Atlantic instead of taking the straight shot polar route. That would be 1300 miles to the Atlantic…3700 miles over water…and 200 miles over land at the end. That would be about 500 extra miles but it would take about 5 hours counting descents. Is that savings enough to balance the cost? And it would be even worse from the west coast.

    Very limited application for a massive outlay.

    1. Agree with the issue about supersonic booms over land. That (still) seems like one of the biggest obstacles to routine supersonic pax flights on many routes, even if cost/efficiency is no object. If anything, your analysis is probably a little optimistic, as it assumes no time/space required to accelerate & decelerate.

      Playing devil’s advocate here, how “empty” (in terms of population density and/or political influence) does land have to be before regular supersonic passenger flights are allowed over that land?

      Thinking specifically of the arctic/desert/outback regions, I doubt countries like the US/Canada/Norway/Australia would allow big supersonic booms over their very lightly populated areas on a regular basis. If they tried, there would probably be protests, as I’m sure that the booms would be bad for the animals/environment in some way.

      HOWEVER, I suspect that there are some areas that WOULD allow supersonic flights over large portions of their land if the price were right (key caveat), such in areas such as the Sahara or Siberia (pre-invasion, didn’t Russia normally charge airlines exorbitant ATC fees for flying over Siberia, given how vital that airspace is to efficient routing of planes between Europe & Eastern Asia?).

      I don’t know that concessions like that would be widespread enough to make the concept economically viable (and such concessions would likely increase the costs/flight even MORE significantly), but it’s a fun thought exercise, and I can absolutely see leaders/governments in certain areas trying to make a buck from this.

  10. Well written article and thoughtful responses. I worked at Pratt & Whitney in advanced development in the 1980’s. We worked on supersonic combustion ramjets and scramjets in addition to turbine engines. I do appreciate Hotintx comment on “dogpiling” as its easy to be a critic. That said the fundamental challenges are all still there from the days of the Concorde. All this “It took us twenty years to go 600 mph and we’ve gone knowhere since” is not a technical development issue as much as a business issue. Supersonic flight is 4X the drag of subsonic and the boom you can manage but not design around to eliminate. Imagine if a car at 60 mph transitioned to 4x drag? So your mileage goes from 20 mi/gallon to 8 mpg above 60 and it becomes extremely noisy? Would cars be on the road that go over 60 mph? Its fundamental physics. Inefficiency in a world of climate consciousness not good. Do we as a society really want to forgive the rich for screwing up the atmosphere? I know that sounds woke but all the development in aerospace over last thirty years is higher engine efficiency and turning commercial aircraft into powered gliders with very efficienct aerodynamics. Now, that said, the business case IS there for selected long haul routes where your booms are over water and the time savings is substantial.

    1. But how much demand is there really for such routes?

      The demand has to be enough to pay for the design and development of a supersonic aircraft, enough of them to make it profitable.

      The routes would basically be limited to the eastern US to Western Europe and the western US to Asia. Maybe US to Australia but the range would be crazy.

      Can you profitably make a plane where there are maybe 100 of them at most? Highly doubtful to me.

    2. I agree with Michael Vos, it is fundamental physics, that supersonic travel is not practical, or makes sense economically.

      Boom is located here in the Denver area, we hear a lot from them in the local media, they must have a big PR dept.

      Here is an article from long time Seattle Times journalist, Dominic Gates, about the Boom engine announcement.

      (Seattle Times gives you a few free looks, before the pay wall comes up.)

      Other articles written by Dominic Gates

      1. Scott Hamilton wrote today, 19 Dec. 2022, in Leeham News about the new engine plans for Boom.

        Pontifications: Nope, not convinced about Boom’s new entrant engine plans.

        Scholl claimed last week the first flight of Overture will be in 2026. Not a chance. Not for a prototype pre-production airplane. It takes years to develop an engine, sometimes decades. Just ask GE/Safran/CFM, Rolls-Royce, and Pratt & Whitney—those that know their business when it comes to airliner engines and military supersonic fighter engines.

    1. How about adding Northern Pacific to that list?

      Or what was that weird airline that wanted to fly to northern Europe with a 747?

  11. The development costs the 737max and A320neo were in the billions. The original developer of airbus a220 was going bankrupt.

    I do not want to be negative. Are the developement costs/timeline realistic?

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