Should the Boom Supersonic jet take flight later this decade there’s a very strong chance it will be powered by Rolls-Royce engines. The companies announced “an engagement agreement to explore the pairing of a Rolls-Royce propulsion system with Boom’s flagship supersonic passenger aircraft, Overture.” While this is not a formal engine model selection it does advance the project and provides further indications as to how the program might take flight.
We’ve had a series of valuable collaborations and co-locations with Rolls-Royce over the past years to lay the groundwork for this next phase of development. We look forward to building on the progress and rapport that we’ve already built with our collaboration as we work to refine Overture’s design and bring sustainable supersonic transport to passenger travel.
– Blake Scholl, Boom founder and CEO
The propulsion system choice has been a glaring gap in the public-facing details for the program. Just over two years ago CEO Blake Scholl indicated that an “existing core” would be key to the process so that the supplier would not be forced to invent a completely new design:
It is not a new technology engine, it is a new design engine. You’ve got knobs on an engine like bypass ratio and pressure ratio and they’re set in certain places for the 787 and you want to set them in different places for this airplane. It is moving the knobs, it is not let’s invent variable cycle or something that’s never been certified before.
The announcement leaves open the possibility that this approach might come up short. Rather than specifying the Trent platform as the power source for Overture, “The teams will investigate whether an existing engine architecture can be adapted for supersonic flight, while Boom’s internal team continues to develop the airframe configuration.”
While the implied goal is to get to an engine selection point as a result of this deal the companies leave open the potential that will not happen. They “expect to make significant progress towards finalizing Overture’s aircraft configuration and propulsion system” as a result of the collaboration.
That is very different from announcing an engine selection.
For its part, Rolls-Royce can lean on some of its history to help support the program. The company provided the Olympus power-plants that gave Concorde its supersonic boost. Carrying that legacy over to the Overture program would be an impressive link. As Simon Carlisle, Rolls-Royce’s Director of Strategy, notes, “We’re now building on our valuable experience in this space as well as our previous work together to further match and refine our engine technology for Boom’s Overture.”
Other engine and aircraft manufacturers are also playing in the supersonic space. Aireon and GE Engines announced a similar deal three years ago to explore how they could work together on the AS2 jet platform. The AS2 aims for a lower top speed of Mach 1.4 compared to Overture’s target of M2.2 cruise speed.
Timing and emissions challenges for Boom’s Overture
The companies also note that they will work towards a net-zero carbon future and to “address sustainability in Overture design and operations.” Exactly how that will come to pass given the significantly higher fuel burn per seat-mile flown at supersonic speeds is less clear. The ICCT identified expected emissions levels for supersonic transport at 5-7x compared to subsonic travel. This raises questions about the supersonic options and regulatory approval.
The Overture program is also not included in the FAA’s noise standard guidelines, which could eventually create challenges. The company is “Actively engaged with the FAA” and expects to slide into the noise profiles as they expand to cover larger aircraft.
The overall timing on the project also remains questionable. The XB-1 demonstrator is slated for its formal unveiling in October 2020 and first flight in 2021. When the first XB-1 flight was planned for early 2020 the Overture program anticipated a 2025 first flight and 2027 entry in service. Those likely now slip by at least a year. And they remain very aggressive timetables even without considering the XB-1 delays.
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