Boom plans new Symphony supersonic engine design

Faced with the reality of no major commercial jet engine manufacturers willing to invest in a commercial supersonic engine, Boom Supersonic now has a new plan. The company will develop its own – dubbed Symphony – in partnership with Florida Turbine Technologies (FTT) for engine design, GE Additive for additive technology design consulting, and StandardAero for maintenance.

Through the Symphony program, we can provide our customers with an economically and environmentally sustainable supersonic airplane—a combination unattainable with the current constraints of derivative engines and industry norms.

– Blake Scholl, Founder and CEO of Boom Supersonic

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Boom is clear that the engine will be very similar in many regards to the existing options on the market today. It is a medium-bypass engine with 35,000 pounds of thrust at takeoff.

It will also include notable design differences. These include a “Boom-designed axisymmetric supersonic intake, a variable-geometry low-noise exhaust nozzle, and a passively cooled high-pressure turbine.”

The new design will also take advantage of additive manufacturing of complex parts, reducing weight, part count, and assembly cost.

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No longer a derivative engine architecture

In early 2018 Boom’s 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.

That is no longer the plan. Boom will no longer be able to take an existing commercial aircraft engine and twist a few design knobs.

NTT’s expertise, according to the company, lies in “the development and production of small, affordable, high-performance jet engines for cruise missiles and unmanned aerial systems (UAS).” Boom also highlights FTT’s 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.”

Historically Boom wanted to avoid anything related to military solutions because of the complexity and cost in converting them to civilian production. Again, the company was forced to pivot as its desired options proved elusive.

The companies must now translate NTT’s experience into a commercially viable solution. And, unlike with a major commercial engine manufacturer driving development, this program will almost certainly rely on Boom for the bulk of the funding. Adding that on top of the airframe development and testing costs just made the bill to deliver the first aircraft significantly higher.

Scholl also now is selling the Boom-led engine development program as a more efficient, more reliable (25% more time on wing) and lower cost (10% TCO reduction) option compared to the derivative previously planned. That none of the major manufacturers wanted to partake certainly forced Boom’s decision in this case.

The company is focused on the silver lining, however. Scholl is all in on the reliability and TCO benefits for airlines making up for the increased development costs and timeline Boom now faces.

Yet another schedule slip

The announcement also includes another slip in the company’s production schedule. In prior updates Boom held to the plan of rolling the first Overture out of the factory in 2025. A first flight was planned for 2026.

With the engine announcement this week Boom’s aircraft development timeline also slips another year. Boom now is forecasting the first aircraft to roll out of the factory in 2026 and fly in 2027. The commercial service entry date, however, did not change. The company still touts 2029 for delivery to airlines. That timing is arguably even less likely than the 2023 EIS forecast in 2018, given the need to certify a wholly new engine design rather than a derivative.

Alas, Boom does not have a strong record when it comes to its promised timelines.

At the 2017 Paris Air Show Boom expected XB-1 to fly in 2018. Overture was to enter commercial service in 2023.

Two years later, at the 2019 edition of the Paris Air Show, XB-1 hoped to roll out by the end of 2019. Overture took an even longer delay, with first flight was expected in 2025, and EIS in 2027.

The timeline has repeatedly slipped since then.

In early 2020 the XB-1 demonstrator’s first flight slipped to 2021. Then the target became end of year 2022. With just two weeks remaining and no word about XB-1 being trucked to Mojave for high speed ground testing, that’s almost certainly not going to happen. But the company did pull the plane out of the hangar and fire up the engines at the beginning of this year.

Environmental challenges remain

Scholl continues to hype the ability for the engines to run on 100% SAFs. Unfortunately, however, that does not address the overall environmental impact of supersonic flight.

A joint report published by researchers from Massachusetts Institute of Technology (MIT) and the International Council on Clean Transportation (ICCT) suggests “environmental limits will sharply constrain the potential supersonic market.” The MIT/ICCT study sees a market for just 240 supersonic aircraft by 2035, assuming zero restrictions on noise or fuel burn operating conditions.

With noise or emissions concerns that demand drops by 95% or more, essentially disappearing.

The study also projects fuel burn to be 7-9x per seat mile than a subsonic aircraft in 2035. Boom’s position has always been that its planes would be developed to support 100% Sustainable Aviation Fuel (SAF), sidestepping the conversation about emissions.

Even burning 100% SAFs, the emissions impact from a supersonic jet might not be as climate-friendly as the marketing pitch would have one believe. The MIT/ICCT report suggests that, because of the way the SAFs burn and the higher altitude at which Overture would fly, “a small fleet of supersonic aircraft, providing between 0.1% and 0.6% of the total number of seat-km of the projected subsonic fleet, could cause ozone depletion equivalent to up to 8% of the total impact of CFC emissions” at their peak.

Nothing about this new engine design appears to change these impacts.

More on Boom’s evolution towards supersonic service:

• An investment Boom from Japan Airlines
• Engine selection “core” to Boom Supersonic’s success
• Boom’s supersonic timing slips
• PaxEx Update: FTE Asia edition
• Behind the scenes with Boom Supersonic
• Supersonic sound standards set; Boom schedule slips
• Boom Supersonic picks an engine manufacturer (for further discussions)
• Virgin Galactic makes a move in supersonic travel
• United Airlines plans supersonic Boom with new order
• Boom fires up the engines on XB-1 supersonic demonstrator
• Boom building at Greensboro, new environmental concerns revealed
• Boom Overture adds engines in design revamp
• American Airlines buys in to Boom, despite significant uncertainties
• Boom plans new Symphony supersonic engine design