The return of supersonic flight

Concorde was the beautiful Anglo-French supersonic airliner which, like the first moon landing, marked its 50th anniversary last year. It took its maiden flight in 1969 – actually three months behind its ill-fated Soviet rival, the Tupolev Tu-144 – and fast became a symbol of tomorrow’s world, flying between London or Paris and New York in around three hours. At least it did for 27 years. 

“But it was just too much of a gas-guzzler, too expensive and had too many seats to fill,” argues Scholl, as to Concorde’s early retirement – though whether Concorde was commercially viable remains debated. Then, in 2000, one of the fleet of 14 aircraft crashed in Paris – the product not of the aircraft itself but debris on the runway – and Concorde’s fate was sealed. And since then? We’ve plodded around the world at some 500mph – much the same as we did over a half a century ago.

Scholl thinks this is nuts. And he’s aiming to put it right. He might be described as the Elon Musk of supersonic passenger flight: much as Musk has launched spaceflight into a new era – a private business that, with money to burn and a lot of chutzpah, has wrestled dominance of space travel from government control – so Scholl’s Denver-based start-up, Boom, is planning do the same for travelling faster than a bullet. Supersonic flight may no longer be the preserve of military jets.

“I’m an airplane guy by passion rather than by training,” the serial entrepreneur concedes, “but I always had this wish to fly supersonic one day. And I ultimately decided that if I was ever going to get to do so in my lifetime, I’d have to start a company to make it happen myself. Six years ago the idea of a start-up building a complicated, hugely advanced, safety-critical machine might have been a crazy idea. And a lot of people said we were crazy. Back then people’s idea of the potential for supersonic travel was, I think, very different. But six years later we have a test aircraft under construction in our hanger. The first privately-developed supersonic aircraft will be flying next summer.”

Boom might well have been considered crazy so recently. One reason why Concorde failed, it’s been argued, is because of the sonic boom it produced. As an aircraft approaches the sound barrier – 767 mph – pressure disturbances build up in waves around it, and rather than pass around the fuselage sequentially as they might at sub-sonic speeds, begin to bunch up together. Collectively, these compressed waves produce the so-called boom, loud enough to reach the ground and give the unsuspecting a jump; loud enough, it was suggested in Concorde’s day, to terrify animals and break house windows. The result? Concorde was only ever permitted to fly supersonically over water. That limited the number of routes it could fly – essentially just trans-Atlantic. That, perhaps, ensured it wouldn’t make money.

Now if you’re expecting a drum-roll – or something much louder – and the announcement that Boom aircraft’s, the Overture, has solved this enduring problem of physics, then stand down. While it’s telling that official attitudes to the sonic boom are softening – this spring in the US the Federal Aviation Authority published a ‘notice of proposed rule-making’ regarding supersonic aircraft noise standards, which means it accepts the situation has changed sufficiently that it needs to look at the issue again – what Boom plans is to work around this problem rather than, in the short term at least, to solve it. In other words, like Concorde, it plans to only fly supersonically over water, and sub-sonically over land. The point though is that this will still be considerably faster than anything flying commercially today. What’s more, technology has moved on in recent years to make such an aircraft work in the way Concorde – which didn’t even have onboard computers – could never have.

Indeed, it’s an idea not lost on other companies. If the new space race gets most of the attention, closer to Earth there’s a clutch of start-ups likewise looking to overhaul supersonic flight, albeit with different intentions. Boom sees its model as being a small airliner – some 55 seats, as opposed Concorde’s 100-plus, with a business class environment for an accessible premium on business class ticket prices. It might not be clear as yet that there are enough people who want to fly faster, rather than just more cheaply, but this is far from being an entirely elitist product. The Boston-based Spike Aerospace is pursuing an 18-seater model that could work for both private owners or airlines. Aerion Supersonic, based out of Nevada, plans for a smaller private jet, seating around 12, again flying supersonic only over the sea.

Not all plan to fly at similar speeds either, with Spike and Aerion aiming for between 1,074mph and 1,227mph, with only Boom’s Overture aircraft, flying 1,687mph, exceeding Concorde’s 1,565mph. But what unites all of them is a shared belief that, in part thanks to rising wealth, in part down to the demands of globalisation and a faster world, there’s a real demand for such aircraft now, on the right, smaller scale. Concorde notoriously often flew half-empty – with many passengers either free-loading celebrities or ticking off some bucket list experience, rather than set to be frequent fast flyers. 

But if there’s a market, why aren’t the big boys chasing it? It may be hard for the behemoths of airliner manufacturing to produce such an aircraft themselves, given their price-conscious mindset. Although Boeing had its Sonic Cruiser project in the early 2000s, and has recently released concept sketches of a hyper-sonic aircraft it has in mind for two or three decades hence, airline economics have changed in recent years such that the commercial model is dominated by the idea of moving as many people as efficiently and cheaply as possible around the world. That explains the advent of money-making, super-sized aircraft the likes of Airbus A380. Future airliner development is likely to be limited to improving efficiency, and thus profits for the airlines. Yet none is this is to say newer, more nimble companies can’t be disruptive in responding to what they see as an emerging passenger demographic.  

Nor is it just about appealing to oligarchs who are looking to buy into the next status toy either; airlines, conscious that most passengers would prefer shorter flights if feasible, are buying into the idea too. Somewhat akin to NASA recently giving contracts to SpaceX for a planned moon landing mission over the next few years, so Boom, for example, has taken US$6bn in pre-sales for its jet from the likes of Japan Airlines and the Virgin Group – Virgin once tried to buy the mothballed Concordes in a plan to return them to service. Spike has had talks with airlines too. Aerion has Boeing as its anchor investor. So the capital is there too. More critically though, the technology is also already available to make such aircraft feasible. 

“The fact is that people will pay a premium for speed these days, and the speed offered by jets hasn’t really changed for decades. But to bring that speed you don’t have to invent something new so much as convince partners and suppliers that there’s a business case for such aircraft,” explains Matthew Cram, chief commercial officer for Aerion. “We’ve certainly met some scepticism along the way. Concorde was a very noble experiment but there was a lot wrong with it – and we have to get beyond people associating supersonic flight with that. The fact is though that business jet users already pay a premium for speed. This is all about enhancing global mobility. And making that happen is just really all about the execution now.” 

That’s Blake Scholl’s thinking too. A change of policy from the FAA and other authorities would, they say, be progressive, but regardless these would still be the fastest passenger aircraft around. And none require some super-duper technological leap. “Right now we’re basically at the intersection of what there’s a demand for and what’s already technologically feasible,” says Scholl. “There’s no one magic bullet that’s going to make commercial supersonic flight possible again, just a combination of technologies that didn’t exist until recently.”

Back in Concorde’s day, aerodynamics, for example, had to be developed using physical models and wind tunnels; now computer simulation does the same. Concorde was made out of strong, lightweight but limiting aluminium; now carbon fibre offers a material that is not only stronger and lighter – crucially so, since supersonic flight burns up a lot of fuel, and the weight of that hampers speed – but which can also be formed in any shape. And then there are the engines available today. Concorde needed to have after-burners, those components in jet engines that provide the additional, window-rattling thrust required sometimes for take-off and typically for supersonic speeds; now turbo-fan engines of the kind used on most modern airliners can be adapted to go supersonic. The results of all this tech might be aircraft that certainly look akin to dinky Concordes, but they work differently. Boom claims, for example, that it adds up to an aircraft that could be 75 percent more efficient to operate than Concorde, which makes it more affordable to passengers, and makes 500 routes viable from the off.

“Passenger aircraft are still hugely complex, as are all sorts of factors in operating them. When Concorde was launched gas was 25cents a gallon. When it retired it was US$4,” notes Spike’s CEO Vik Kachoria. “But we have the kind of tools now that weren’t available just a few years ago, so we as a small company can do what it would have taken a thousand engineers to do not long ago.”

This utilisation of the latest technology is vital for another reason too. Given increasingly radical environmentalism, air travel doesn’t exactly have the best image right now. Some, the likes of the International Council on Clean Transportation, have pointed out that the environmental case against the idea of the skies filled with largely conventional supersonic aircraft is a strong one; that, say, 2000 supersonic planes in the air by 2035 would dump prodigious amounts of carbon into the atmosphere, equivalent to some 20 percent of aviation’s entire global carbon budget. That’s why both Aerion and Boom – which, if all goes to plan, expect to have aircraft in service by 2026 and the end of the decade respectively – plan aircraft that will fly on alternative/bio-fuels. Providing the fuel can be made available at each airport, these new supersonic aircraft will, it’s claimed, have a lower carbon footprint than today’s subsonic airliners. 

“I do think this new community [of supersonic aircraft builders] really has to get this message across – that we’re taking the approach that we can build a supersonic passenger aircraft that’s kind to the planet,” stresses Cram. “A lot of airlines have made the commitment to be carbon neutral in the next 10 or so years, but we want to be that from day one.”

That’s forward-thinking of course, yet such developments also feel something of a stop-gap – lacking the romance of a technological advance that would allow supersonic aircraft to fly without restrictions. That means beating the boom, the noise pollution as much as the air pollution, which has been Spike’s position from the outset. It has its patent-pending ‘Quiet Supersonic Flight Technology’ in the pipeline, set to undergo its first supersonic test flights next year. And this, the promise is, will allow for a supersonic aircraft that, as Kachoria, puts it, “will be supersonic everywhere”.

“There’s a business model for what the likes of Aerion and Boom are doing, but the fact is that 80 percent of flights are over land. People want to be able to fly supersonically out of Dubai or Shanghai,” he adds. “And to that end we need an aircraft that may still produce some kind of boom, but one that isn’t so audible on land.” 

Getting this is a process of finding the right combination of aircraft size, weight and shape, notably in swept wing design and in the extension of the nose, such that it cuts through the air without creating those noisy pressure build-ups. Indeed, it’s akin to the thinking being applied by an organisation with the experience, knowledge and funds, but in no rush to get any product to market soon – NASA. It’s been working on its $248m, 94-foot long, X-59 Long Boom Flight Demonstrator (LBFD) since 2016, not a proposal for a commercial aircraft per se, but a test aircraft for certain cutting-edge technologies. 

These include attempts to improve fuel efficiency and reduce emissions. But, more excitingly, also to reduce that boom. While it’s believed that totally eliminating the boom is impossible, the idea is to carefully shape every component of the aircraft so as to be able to control the strength and position of each sonic shockwave such that they at least don’t coalesce. The result is less a singular boom as a low thump – at ground-level something close to the sound of a car door closing. “You wind up with a smeared acoustic signal,” as Peter Coen puts it. 

Coen is NASA’s integrated mission manager for the LBFD and he knows that what works in the lab doesn’t always work as expected in the real world. So next summer he plans to start the process of gathering unbiased data from what are known as community overflight tests – essentially flying the aircraft in different climates, over different geographies and types of housing, to gauge from those down below whether the thump is still too much to bear. He’s open-minded as to the likely response but hopes it will show only a minority of people are bothered by it. 

“If you consider the global community’s growing sensitivity to noise – as indicated perhaps by rules that have come in addressing acceptable levels of noise from aircraft during take-off and landing – then we have to be conscious of the impact even a thump will make,” he says. “Why are we especially sensitive to the sonic boom, given that we already deal with so much noise in our lives? I suppose it comes back to the whole question of environmental sensitivity now. In the 1960s, back with the advent of Concorde, there was more the attitude that all technological advance was good, even with the awakening of the environmental movement at the time too. 

“But even then regulations came in before Concorde, such was the feeling that the sonic boom was just an incredibly invasive phenomena [for those on the ground],” he adds. “And if regulations are going to change now, there needs to be some hard science demonstrating that lives won’t be adversely affected. I don’t think we can impose a mode of transport at a cost to those not using it.  And we need supersonic aircraft that can operate supersonically over land too.”

That, surely, needs to be the end goal. While the return of supersonic passenger flight in any form might be welcomed, the vision of supersonic flight that the pioneers of Concorde had in mind so many years ago was not one limited in the territory one could fly over. Speed restricted in direction might return us to where air travel was in the middle of the 20th century, but it’s a more 21st century notion of mobility that, ultimately, fulfils the dream.