Why Did Boom Supersonic Ditch Rolls-Royce to Build Its Own Jet Engine?
How Boom Supersonic's partnership with Rolls-Royce collapsed in public, and why building the Symphony engine in-house made boomless supersonic flight possible.
What happened between Boom Supersonic and Rolls-Royce?
Boom Supersonic spent years trying to get Rolls-Royce to build a custom engine for its Overture airliner, and the deal collapsed in 2022 when Rolls-Royce walked away publicly, without warning Boom first. According to Boom founder and CEO Blake Scholl, the partnership fell apart because of internal politics at Rolls-Royce (a CEO firing, a leadership vacuum, and executives worried about their own careers) combined with a harder technical problem: the engine platform Rolls had proposed was based on next-generation technology the company had quietly stopped developing. Boom ended up building its own engine, called Symphony, and that decision turned out to be the thing that made boomless supersonic flight possible.
TL;DR
- Boom originally planned to build its own engine but pivoted early on after its first engineer argued that Rolls-Royce’s engines were the easiest to adapt for supersonic flight, potentially saving an entire development cycle.
- The Rolls-Royce deal nearly closed in early 2022, reaching a board meeting for contract approval, but the vote coincided with the sudden firing of the Rolls-Royce CEO, which froze all decision-making.
- Rolls-Royce broke off the relationship publicly in 2022 after American Airlines and United Airlines placed pre-orders for Overture, a move that Scholl says spooked Rolls executives worried about owning a failed, embarrassing bet.
- The proposed Rolls-Royce engine wasn’t even capable of what Boom needed: it was adapted from a subsonic design and couldn’t support boomless cruise, the flight profile where a sonic boom never reaches the ground.
- Boom hired a team of former Pratt & Whitney supersonic engineers who had left the company after a facility consolidation, and used that team as the foundation for its in-house engine program.
- Building the engine in-house let Boom’s engineers optimize airframe and engine together, which is what ultimately enabled boomless supersonic flight, something Scholl says never would have happened with an outsourced engine.
- The whole process took years, from a first engine sketch in mid-2022 to Boom’s XB-1 demonstrator aircraft breaking the sound barrier in early 2025.
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Why did Boom outsource its engine in the first place?
Boom wasn’t originally planning to outsource engine development. Early in the company’s history, when Boom had only four or five employees, its first engine-focused hire argued that Rolls-Royce engines were more adaptable to supersonic flight than competitors’ designs, and that partnering with Rolls could save Boom an entire engine development program. Scholl says the team got “drunk on that” idea, reinforced by industry convention: when people asked who was building Boom’s engine, the expected answer was one of the big three engine makers (Rolls-Royce, GE, or Pratt & Whitney). Pursuing an established partner also signaled credibility to a skeptical aerospace industry.
For a while it worked well enough to look like a winning strategy. Scholl says the relationship advanced far enough that Rolls-Royce executives brought a contract proposal to their own board for approval in early 2022.
Why did the Rolls-Royce deal collapse?
Two things broke it, one political and one technical.
The political trigger: the Rolls-Royce board meeting where executives sought approval to negotiate a contract with Boom coincided with the board firing the company’s CEO. The ousted CEO stayed in his seat during the search for a replacement, which meant nobody wanted to make a consequential decision, and every executive angling to become the next CEO was calculating how the Boom relationship would look politically rather than evaluating it on the merits.
The technical trigger surfaced later. The engine Rolls had proposed was based on a next-generation engine platform the company had internally stopped developing, without telling Boom. Rolls had effectively promised capability it no longer had a path to deliver.
Then came the move that blew it up in public. In August 2022, American Airlines placed a pre-order for Overture, following United Airlines’ earlier commitment. Scholl expected the momentum from two airline pre-orders to pressure Rolls-Royce into finalizing the engine deal. Instead, Rolls-Royce executives grew alarmed that Boom suddenly looked like a company that might actually succeed, which made an eventual failure to deliver an engine far more embarrassing. Rolls went to the press and ended the relationship publicly, without warning Boom first.
How did the breakup affect Boom?
Badly, at least in the short term. Scholl describes Boom becoming effectively unfundable overnight: engine companies wouldn’t return calls, airlines went quiet, and reporters confronted him at industry conferences asking why every engine maker said they weren’t working with Boom. The aerospace trade press covered the breakup as a major story. Boom responded by publicly committing to announce an engine strategy by the end of 2022, partly to buy time while the team worked out what to do next.
How did Boom end up building the Symphony engine itself?
While negotiations with Rolls-Royce were unraveling behind the scenes (a process Scholl says had actually been falling apart since February 2022, months before the public breakup), Boom was already exploring alternatives in parallel. One path, which Scholl says privately appealed to him from the start, was building the engine in-house.
Without shadow IT.
The turning point came through a contract engineering team made up largely of former Pratt & Whitney supersonic engineers. That team had originated at a Pratt & Whitney office in West Palm Beach, Florida, which the company had decided to shut down and consolidate into its Hartford, Connecticut headquarters as a cost-cutting move. Most of the Florida engineers didn’t want to relocate, so they left and formed an independent consulting group doing turbine-related contract work, including projects for Siemens.
Boom brought that team on to anchor its own engine program, alongside smaller partnerships (including a limited additive-manufacturing arrangement with GE and a maintenance partner) meant to build some credibility that Boom could pull off an engine without one of the major manufacturers. Scholl also credits a talk by Airbnb co-founder Brian Chesky, given at a conference, with crystallizing the decision: Chesky’s framing was that during a crisis, companies should lean further into their core identity rather than compromise it. Scholl says he left the talk convinced Boom needed to build its own engine.
Is building your own jet engine actually a good idea for a startup?
In Boom’s case, Scholl argues yes, and for reasons that go beyond avoiding another breakup. He contends that even if a major engine manufacturer had signed a contract, it likely never would have delivered, because large legacy engine makers mostly modify existing designs rather than build genuinely new engines, and operate through slow, multi-layered supplier networks. He points out that most of the engineers actually working on Boom’s engine design at Rolls-Royce weren’t Rolls employees at all, but outside contractors, which is part of what gave him confidence Boom could assemble a comparable team directly.
The bigger argument is technical. Boom’s “boomless cruise” concept, flying at a transonic speed where the sonic boom refracts upward and never reaches the ground, requires an aircraft and engine tuned together for strong transonic performance. The Rolls-Royce engine, adapted from an existing subsonic design, could not support that flight profile. Once Boom controlled engine design directly, its engineers could continuously optimize the airframe and engine as a single system. Scholl says the team discovered, in reviewing data ahead of XB-1’s first supersonic flight, that incremental engine optimizations had already solved the sonic boom problem roughly six months before anyone realized it.
The cost was time. Scholl says the first rough sketch of what became the Symphony engine dates to around June 2022, the program was announced publicly by the end of that year, and Boom’s XB-1 demonstrator didn’t fly supersonic until early 2025. With limited financial resources, Boom had to sequence its priorities rather than pursue the airframe and engine simultaneously at full speed.
Frequently Asked Questions
What is Boom Supersonic’s Symphony engine?
Symphony is the engine Boom Supersonic developed in-house for its Overture airliner after its partnership with Rolls-Royce collapsed in 2022. It was built with a team that included former Pratt & Whitney supersonic engineers.
Why did Rolls-Royce stop working with Boom Supersonic?
Rolls-Royce ended the relationship publicly in 2022 after a leadership shakeup left the company’s board unable to approve a contract, and after Boom’s pre-orders from American Airlines and United Airlines raised the stakes of an engine program Rolls had internally lost confidence it could deliver.
What is boomless supersonic flight?
Boomless supersonic flight (sometimes called boomless cruise) is a flight profile where an aircraft travels at a transonic speed such that its sonic boom bends upward in the atmosphere and never reaches the ground. It requires precise tuning of both airframe and engine performance.
Could Boom have achieved boomless flight with a Rolls-Royce engine?
According to Blake Scholl, no. The engine Rolls-Royce proposed was adapted from an existing subsonic design and lacked the transonic performance needed, meaning the physics of boomless flight were sound but the available engine couldn’t support it.
How long did it take Boom to build its own engine?
Based on Scholl’s account, early engine concepts began around mid-2022, the engine program was announced publicly by the end of that year, and Boom’s XB-1 test aircraft achieved supersonic flight in early 2025.
