No one will invest in building an engine for Boom Supersonic. So they’re going to fund the development themselves. They’ve raised money in a ‘down round’ to pay for this. Two years ago they’d supposedly come to an agreement with three companies to provide an engine.

As XB-1 approaches Mach 1, I’m happy to share @boomaero has raised >$100M in new financing, fully funding the first Symphony engine prototype.

Major investors in this round include Alex Gerko, @BessemerVP, Michael Moritz, @paulg, @reidhoffman, @sama, and @ycombinator. (1/3)

— Blake Scholl (@bscholl) December 14, 2024

He goes on to explain,

Goal is to make thrust on the first prototype core in about a year….Core is the high pressure spool, everything from high pressure compressor through the high turbine. We’re developing the high spool first then adding the low spool.

And then he says “To my knowledge it’s never been done this way before. So we’ll see how it goes…” which is not encouraging!

They couldn’t get any of the big engine manufacturers to bite, because no one thinks this project will succeed commercially. If everyone is wrong, and if the smaller players turn out to have the expertise, this would be a huge win all-around. But probabilities are stacked against success.

United Airlines placed an order for Boom Supersonic’s promised jets. Then American Airlines followed suit. Japan Airlines is an investor in the company.

And yet most people in aviation think that the plane will never be built.

• It has a very limited market, relatively short flying range (for an initial plane, at least) and needs to fly overwater due to noise – likely still true even with regulatory changes

• Given the limited market, no major engine manufacturer has seemed willing to step up to make an engine for the plane.

Rolls Royce was supposed to build an engine. They dropped out. GE, Honeywell, and Safran all passed. Pratt & Whitney did too.

An engine manufacturer has to believe that the engine is going to sell well, in order to recoup develop costs and turn a profit. In fact it has to sell better than other things they might deploy development resources against.

The engineering Boom wants to accomplish should be possible. Supersonic jets aren’t a new idea, Concorde accomplished it 50 years ago. They’re just trying to engineer something that’s more fuel efficient – both for operating economics (so airlines can make money) and for environment concerns (airlines have made environmental commitments). They’re also trying to make something quieter.

• No U.S. airline ever purchased a Concorde, though orders were placed by Pan Am, Continental, TWA, American Airlines, Eastern, United and Braniff.

• There were also orders from Qantas, Air India, Sabena, Air Canada, Lufthansa, and even Middle East Airlines and others which never came to fruition.

• Only British Airways and Air France took actual deliveries of new aircraft.

• The only other committed order came from Iran Air, and that was cancelled after the Iranian revolution.

Oddly Braniff did briefly own Concordes for a few hours at a time. They operated service between Dallas and Washington Dulles in conjunction with Air France and British Airways, but to do so they were required to take ownership of the plane for the flight segment in order to operate under their own certificate of airworthiness.

As well as changing flight crews the US approved documentation and procedures had to be present on the flight deck, which meant that the UK/French documentation had to be stored in the forward toilet.

There also had to be a change in the aircraft registration, while being flow on the Dallas – Washington – Dallas routes the “G” or “F” was covered up with white tape. On landing at Washington the ground staff would pull work ladders up to the tail and peel of the F- or G- registration numbers and changed them to an “N” with two letters and the numbers “94″ after that. This was repeated every time the Concordes landed in the US from Europe.

Credit: Boom Aerospace

As long as supersonic travel is more expensive than subsonic, the market will be limited. And the number of city pairs that can work with this plane is limited, too. Limited markets make it tough to recoup development and acquisition costs. Airlines have a hard time making money operating only a couple of planes of a type. The plane needs to be capable of flying long distances, fuel efficiently, and carry large numbers of passengers in order to be economical on a large scale.

Otherwise the market has to be able to support fares significantly higher than for subsonic transport. The ultimate question is: how much is shaving 3.5 hours off of an East Coast transatlantic flight worth, and to how many people?

When American announced their order they said they made a non-refundable deposit but didn’t specify what that means. It could have been $1. They didn’t even produce a graphical rendering of the plane in American Airlines livery. And American didn’t spend the day promoting this on social. For some reason they made the move (claiming to have ordered more planes than United, even) but didn’t go all-out even with the P.R. Their pilots’ union even came out against the move, and they represent the people who theoretically would get to fly the thing!

It’s possible to build a supersonic plane, but inefficiencies and regulation killed the Concorde. Boom can presumably develop a plane, and a top engine manufacturer can produce an engine for it. But will it sell to airlines who see themselves able to operate enough of the planes, to enough places, with enough frequency – given a market that will pay a premium for the option – in order to buy enough planes and engines where the whole thing works out as a business?

Engines can run billions of dollars to design and tens of millions of dollars apiece to purchase. It’s a huge bet for a manufacturer which would need to sell large numbers of engines just to break even. If a manufacturer can’t sell several hundred engines they won’t recoup their development cost, after recouping production costs, let alone turn the project profitable.

Boom has raised about $350 million in the past decade, and will now pay for engine development (which will ultimately cost more than $100 million). They can’t convince manufacturers to fund this, but they’ve convinced Silicon Valley investors to do it – albeit at a lower valuation than they’ve raised money in the recent past.