Boom Supersonic rolls into this year’s Farnborough show one-and-a-half years after embarking on an in-house project to develop an engine for its conceptual supersonic airliner Overture.
Taking the project in-house marked a strategy change that added immense complexity and cost to an already incredibly complex and expensive project.
That said, Colorado-based Boom is soldiering on, and chief executive and founder Blake Scholl insists the company will yet make good on its plan to have Overture carrying paying passengers by around the end of this decade.
And the company is making progress. Boom in recent months completed first flight of its supersonic demonstrator XB-1, achieved a supersonic test-flight authorisation, finished construction of its Overture assembly site and started combustor tests of its Symphony engine.
“I like aggressive but realistic schedules. I like challenging ourselves to move through things without skipping any steps,” Scholl tells FlightGlobal. ”We should be able to do this at least as well as anybody else has ever done it.”
Few could accuse Scholl of lacking ambition with Boom’s plan to develop a clean-sheet supersonic passenger aircraft that, if successful, could upend the air travel industry. Boom says Overture will carry 64-80 passengers, fly at Mach 1.7 (revised downward from an initially planned speed of M2.2), cruise at 60,000ft and have 4,250nm (7,870km) of range. It is to have four under-wing Symphony turbofans.
Boom says it has a 130-strong Overture order book, with customers including American Airlines, Japan Airlines and United Airlines having signed agreements to acquire the type.
It has already revealed several programme suppliers. Honeywell will provide its in-development Anthem avionics suite for Overture, French firm Latecoere will supply wiring systems, Spain’s Aernnova will supply wings, Italy’s Leonardo will provide wing-box and fuselage sections, and another Spanish entity, Aciturri, will supply the empennage. Additionally, Overture’s fuel systems will come from Eaton, landing gear will come from Safran, and major systems and components will come from Collins Aerospace, Boom has said.
Scholl insists passengers are clamouring for ultra-fast travel and that airlines long for a competitor like Boom to disrupt the longstanding Airbus-Boeing duopoly. The firm has also partnered with Northrop Grumman to develop special-mission variants of Overture for the US government and its allies, with Scholl saying such a jet would be particularly valuable operating long-distance flights in the Pacific region.
To make good on its ambitions, the start-up will need more funding and must overcome the incredibly challenging certification process – and do so amid heightened scrutiny from the Federal Aviation Administration. Boom is also striking out amid increased societal and government pressure to cut carbon emissions, which pose particular concerns because supersonic aircraft burn more fuel per passenger than subsonic jets. Boom counters that Overture will burn sustainable aviation fuel, a product of uncertain viability.
Challenges aside, Boom continues stepping in the right direction.
The company on 22 March succeeded in getting its XB-1 demonstrator – which Scholl calls the “first independently developed supersonic jet and the first new civilian supersonic airplane since Concorde” – off the ground for its maiden flight. The clean-sheet, triple GE Aerospace J85-15-powered XB-1 took off from Boom’s flight-test base at Mojave Air & Space Port in California and flew for 12min, climbing to 7,120ft and reaching 238kt (441km/h). While not a scaled representation of Overture, XB-1 will help Boom evaluate technologies it intends to carry over to the future sibling.
“Our goal on that first flight was to demonstrate that we could control it well, fly it well and get it back on the ground safely,” Scholl says, adding that the flight also proved the viability of XB-1’s “augmented reality vision system”, which displays to the pilot an image of the runway during landing. The system is necessary because XB-1’s extended nose and high angle of attack at landing obscure visibility, the same issue which led to the development of Concorde’s ‘droop snoot’ nose.
“About nine out of ten things worked exactly like we hoped they would,” says Scholl. “We did find one thing that we’re going to tweak, which relates to the roll axis…it was twitchy in the roll axis.”
To address that issue, Boom already designed and installed on XB-1 a “roll-stability augmentation system” that supplements the jet’s existing pitch and yaw augmentation systems. Scholl says the team had expected XB-1 might require the added technology and says the updated configuration “brings XB-1 closer to Overture”, which will have “active stability control” on all three axes.
XB-1 has yet to return to the skies, but Scholl says the second sortie is forthcoming and will demonstrate to engineers whether more changes are needed. If not, “the cadence of flights is going to pick up” and the team will likely complete 10-15 flights before pushing XB-1 past the sound barrier, a milestone that could come in September or October, he says.
Though far from starting Overture production, Boom in June said construction is complete of a 16,723sqm (180,000sqft) facility at Piedmont Triad International airport in Greensboro, North Carolina where it intends to assemble the jet. Designed for four assembly stations, the facility is intended to accommodate production of up to 33 aircraft annually. North Carolina’s legislature approved $107 million to help fund the project.
Scholl says Boom is now developing manufacturing processes for Overture. It aims within six to 12 months to install at the production site a test cell for evaluating fuselage-join and other assembly processes, and within two years to begin assembling the first Overture test aircraft.
Many hurdles remain.
The cost of bringing clean-sheet commercial airliners through design, testing and certification is enormous – running several billions dollars, if not much more, according to aerospace analysts. Such financial burdens pushed former supersonic aircraft developer Aerion – once a Boom competitor – out of business in 2021.
Boom’s investors will need to reach deeper into their pockets to keep the project tracking. Scholl declines to discuss the privately held firm’s finances, but in November 2023 Boom reported having landed total funding of more than $700 million.
“We continue to have great support from our backers,” Scholl says. “We know it’s a multi-billion dollar programme. But what we’ve demonstrated with XB-1 is, we can actually build and fly an airplane five to 10 times more capital-efficiently than anyone else has ever done.
”We really crossed an important mark with XB-1 getting into the air because we’ve now demonstrated the capital efficiency of this company.”
IN-HOUSE ENGINE
Many engineering challenges are still to be overcome, not least of which is developing the Symphony engine, which poses perhaps the greatest uncertainty to the Overture programme.
Rolls-Royce had completed engine studies for Overture before backing out in 2022. At that time, other major engine makers also declined to participate, citing the need to focus development dollars on more-efficient engines for subsonic jets.
Without an engine partner, Boom in December 2022 revealed it was launching internal development of Symphony, a 35,000lb (156kN)-thrust, medium-bypass turbofan. Symphony is to have a 72in (1.8m) diameter fan, three low-pressure compressor stages, six high-pressure compressor stages, one high-pressure turbine stage and three low-pressure turbine stages.
Boom hired senior-vice president Scott Powell, a former 38-year Boeing veteran who led propulsion engineering for programmes including the 787, to head Symphony development. It partnered on the project with Florida Turbine Technologies (FTT), a Kratos Defense & Security Solutions division charged with completing much of Symphony’s design.
FTT’s work has traditionally included developing and testing engine compression and turbomachinery, producing jet engines for cruise missiles and providing commercial and military propulsion engineering services, its website says.
Other Symphony partners include maintenance partner StandardAero, and GE Aerospace subsidiary Colibrium Additive, which is providing additive-manufacturing consulting.
“We knew we were taking a bet on ourselves when we launched this, and so far that bet is paying off real nicely,” Scholl says of Symphony. “With FTT, we were able to scoop up the best supersonic engine design team on the planet.”
In June, Boom said FTT had started combustor rigs tests for the Symphony engine. “Nearly 80 pressure sensors measure flow details from the high-pressure compressor, around fuel nozzles and through the combustor,” Scholl tweeted. “Test results will help calibrate our digital engineering and allow us to maximise Symphony’s fuel efficiency.”
Developing and certificating aircraft engines is among aerospace’s most-challenging endeavours – even for major, long-established players. GE Aerospace is years late in achieving certification for its Catalyst turboprop, which is to power Textron Aviation’s Beechcraft Denali, and Safran Aircraft Engines’ troubles with its Silvercrest turbofan prompted Textron in 2019 cancel development of Cessna’s Hemisphere business jet.
But Scholl insists Symphony will succeed, pointing to Boom’s embrace of a low-cost development model proven successful by other start ups, including SpaceX. The model involves assigning small teams of highly skilled engineers to quickly develop actual prototypes – “rapid hardware prototyping, rapid testing [and] lots of rig testing”, Scholl says.
He says legacy aerospace manufacturers tend to move much slower because they complete exhaustive and expensive design work in a bid to perfect concepts on paper before actually building and testing prototypes – and then, late in the process, issues crop up.
“My philosophy is, go build the prototype quickly, learn and iterate. Ultimately it’s going to be faster and it’s going to be cheaper,” Scholl says. “In very short order it is going to be obvious if it’s working…what we are going to find is that there’s an engine running way sooner than anyone’s going to expect.”
BEYOND MACH 1.7
As if Overture is not challenging enough, Scholl is already eyeing an Overture successor that flies faster and farther. In October 2023, he applied for a patent covering a conceptual propulsion architecture for a future supersonic aircraft. The concept calls for a jet powered both by traditional low-bypass turbojets and by a separate system composed of multiple deployable fans.
At supersonic speed, the turbojets would provide thrust and the fans would be stowed within the aircraft’s structure, out of the airstream. But at slow speed, particularly during take-off and landing, the fans would extend out and provide thrust, says his patent application, published in April by the United States Patent and Trademark Office.
The hybrid turbojet-fan architecture could provide optimal fuel efficiency in the supersonic realm and be sufficiently quiet to meet airport noise regulations, the application says.
Such an architecture could let engineers avoid limitations imposed by turbofans alone, Scholl adds, noting high-bypass turbofans are sufficiently quiet but less efficient at supersonic speed than low-bypass turbojets, which are too loud to meet noise restrictions.
The patent application includes sketches of an aircraft with four traditional turbojets hung under gull-shaped wings, and with groups of fans that can be stowed behind panels or doors. One possible configuration has eight fans stowed in the aircraft’s tail; another has fans stowed within its wings.
“This is not going to be on Overture one,” Scholl says of the idea. “This is really next-generation technology, and we put a marker out there with the patent.”
