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.
