A highlight of the Farnborough Airshow was the introduction of the new and freshly designed configuration for what is set to be the world’s next mass supersonic transport vehicle – the Boom Overture. The concept for this airplane has been floating around since 2016, when it was first unveiled. Back then, it was set to be a twinjet, and then a trijet, adding the third engine for the purposes of achieving 180 minutes ETOPS.

But since then, the Overture has undergone rigorous simulation testing and dozens of design cycles to perfect the configuration of the production jet. CEO Blake Scholl unveiled the design changes to a packed audience of journalists, prospective clients, and stakeholders on day two of the airshow. He commented on the redesign,

“The design that we've seen, and love, actually is engineering and that's more than five years old. Since then, we've had more than 26 million core hours of simulation. We've iterated through over 50 design cycles for Overture, and we've confirmed our designs with five windtunnel tests. And all of that results in a breakthrough new Overture configuration to design for the airplane that we're all going to get to fly.”

A render of a Boom Supersonic Overture parked at an airport gate.
Photo: Boom Supersonic

Amongst other design changes was something very obvious – the trijet is now a quadjet. But why?

Why four engines?

Adding an extra engine to the Overture might, at first, seem counterproductive. Considering the jet’s claim to net zero operations, and the rapid phase-out of other quadjets in the aviation world, adding an additional powerplant seems contrary to the mission of sustainable supersonic flight. But Boom has some well-thought-out reasons for this particular design change. A spokesperson confirmed to Simple Flying,

We selected a four-engine configuration after extensive R&D and efforts to understand the supply chain capabilities of our partners. Using four engines lets us shrink the size of each engine, allowing production to fall within current supply chain and manufacturing capabilities—all while reducing the noise levels of the aircraft.

The use of four engines instead of three also keeps weight and temperature within existing technology constraints while allowing Overture to work within established supply chain and maintenance norms.

Boom Supersonic Overture 2022 design
Boom says the required propulsion can be achieved by four smaller engines, which will help with maintenance, production and other factors. Photo: Boom Supersonic

The engines are pitched to be clean, quiet, turbofan engines, without the noisy and inefficient afterburners seen on Concorde. This, the firm says, will ensure it’s a plane people can look forward to arriving at their local airport, rather than worrying about their windows being rattled as it takes off again.

Location, size, and supply chain

Key to the four-engine decision is the capabilities of the supply chain. Boom is confident the Overture will be able to achieve supersonic speeds without afterburners, using four high bypass turbofans.

Boom is also designing for maintenance, deciding that having four engines under the wing will be far easier for customers to maintain than two on the wing and one on the tail. The company explained,

An earlier three-engine design included an engine in the tail, and using four identical engine installations reduces costs and streamlines maintenance for our customers.

Boom Supersonic Overture 2022 design
Smaller, co-located engines will make for easier maintenance. Photo: Boom Supersonic

Having four powerplants also means each engine can be smaller too. Blake Scholl noted that the company had probed the supply chain and how engines are built to understand the limitations of mass production. Starting at the turbine blades and working backwards brought Boom to the conclusion that four smaller engines are a far easier manufacturing prospect, and will help the airplane fit in the existing supply chain with ease.

It's kind of like the Concorde and the 747 had a baby – Blake Scholl, CEO, Boom Supersonic#

The final aspect of the engine redesign worth understanding is the location of the powerplants. From the original design, the engines have shifted towards the back. Part of this is for the purpose of balancing the aircraft, but it comes with an added safety benefit.

Boom Supersonic Overture 2022 design
The engines are positioned further back, adding to passenger safety. Photo: Boom Supersonic

Subsonic airplanes with engines under the wing have a known ‘rotor burst’ zone – an area that could be affected in the event of an uncontained engine failure. Incidents as a result of this are rare but, as was the case with the Southwest Airlines 2018 accident where part of the engine broke a window and killed a passenger, the risk is real. Moving the Overture’s engines further back means the rotor burst zone is behind the passenger cabin, so even in the unlikely incident of a turbine blade puncturing the cabin, passengers would remain safe.

Engine placement was selected to conform to the strictest passenger safety requirements. Overture’s engines are located behind the pressurized passenger cabin (behind the aft pressure bulkhead), which minimizes risks to passengers in case of engine failure.

The elephant in the room

While all this sounds great and well thought out, there is still the elephant in the room to address. Boom has no engine manufacturer lined up, and until they do, the Overture is nothing but a rather pretty glider. Rumors of partnerships with the likes of Rolls-Royce have since been quashed, and Boom is still working to find the company that will build the next supersonic engines for the Overture.

Boom Supersonic Overture 2022 design
Photo: Boom Supersonic

Asked about progress on the engines, Scholl commented,

“We've made a lot more progress in propulsion than we're sharing today … We're looking at multiple different options, multiple different commercial cores that are relatively straightforward to adapt for supersonic flight. And we're also looking not just at the technology solution, but we also want to make sure we have the right business solution for our customers … there are some breakthroughs on that front that I'm incredibly excited about. But today's not the day to share.”

Boom still has time. The company aims to start production in 2024, with the first complete airframe rollout in 2025. By 2026, we should see it in flight for the first time, if those timelines can be maintained. Nevertheless, some news on the propulsion for the aircraft soon will be crucial to quelling the naysayers who doubt this project will ever fly.