The Concorde successor trying to crack the Achilles heel of supersonic travel

Telegraph

08-03-2025

Of all the factors that killed off Concorde more than two decades ago, it was the jet's thunderclap-loud sonic boom that ensured its demise.
Soaring maintenance costs, an eye-watering fuel bill and a crash that killed 113 people may have prefaced the plane's grounding – but it was the boom that left it fundamentally flawed.
Banned from flying over land as a result of the window-rattling roar and lacking the range to cross the Pacific, Concorde was left confined to ferrying the ultra-rich across the Atlantic, a market that proved too limited to sustain the iconic jet.
However, with advances in engine design, aerodynamics and science putting high-speed flights back on the agenda, one company is planning to eliminate the Achilles heel of supersonic travel by tackling the boom head-on.
US-based Spike Aerospace reckons the 110-decibel bang can be reduced to a mere thud by limiting both its volume and the way it is dispersed through a technique called aerodynamic shaping.
That should pave the way for supersonic flights over land, said Vik Kachoria, Spike's founder and chief executive.
'We call it a sonic thump,' he said. 'It should be the sound of a car door closing about 100 feet away. A very quiet sonic boom.
'We're positioning the fuselage, nose cone, wings and engines in such a way that there's still a boom but you're directing it upwards into the sky and minimising how it coalesces.
'What normally happens is the shock waves from different parts of the aircraft coalesce and that's what magnifies the intensity.'
Spike is working on a plane the size of a business jet that will have between 18 and 28 seats, costing potential buyers around $125m (£97m), according to Mr Kachoria – which is the same price as a Boeing 737.
The jet, called the S-512 Diplomat, would cruise at 50,000 feet, where the air is thinner, and speed along at Mach 1.6 (1,220mph), twice the pace of a modern jumbo jet, though slower than Concorde's Mach 2.
The design features a so-called cranked delta wing that minimises the shock wave while bringing the added bonus of reduced drag and improved efficiency, Mr Kachoria said.
The result should be a perceived loudness level for people beneath the flight path of less than 75 decibels, regarded as the maximum acceptable for supersonic flights over land.
The company is betting that the noise reduction will allow the plane to operate across Europe and the US, as well as between Europe and the Middle East, and throughout Asia.
Flights the length of Africa or the Americas would also be possible given sufficient demand.
The boom doesn't just happen once as a supersonic aircraft goes beyond the speed of sound, but is constant as air molecules are pushed aside with great force – creating a shock wave much like a ship produces a bow wave.
Anyone within 50 miles of the flight path will hear a boom, with the noise dissipating the further the listener is from the plane, though Mr Kachoria said people were not the only concern when contemplating supersonic flights over land.
He said: 'Concorde was criticised for shaking buildings and breaking windows.
'Then there are animals. The migratory patterns of birds are going to be affected by a loud sonic boom and really disrupted. And marine animals that use echolocation to figure out where they are and to find mates and prey.'
Boom Supersonic, a rival start-up which has been leading the bid to revive faster-than-sound flight, is also exploring ways of reducing the impact of boom – having initially suggested its plans would be limited to services over the ocean.
The company last month said it planned to offer 'boomless cruise' over land after its XB-1 demonstrator broke the sound barrier three times without shock waves reaching the ground during its first supersonic flight in January.
Mr Kachoria said that minimising the noise of a supersonic aircraft on take-off was as important as reducing the boom given the latest US and European regulations.
Spike plans to use a modified version of an off-the-shelf engine from one of two potential suppliers, he said, while declining to name them.
Meanwhile, General Electric halted a supersonic engines project with the collapse of Spike rival Aerion in 2021, while Boom Supersonic is developing its own engine in conjunction with defence contractor Kratos Defense.
Spike is targeting its first launch in the early 2030s, with its latest subsonic demonstrator aircraft to be built this year, followed by supersonic flights and a full-scale prototype.
Nasa's X-59 low-boom flight demonstrator aircraft, under development at Lockheed Martin 's Skunk Works, should provide some guidance on what sonic boom levels are acceptable, said Mr Kachoria.
The X-59 is scheduled to begin flight testing this year with the aim of creating a 75-decibel perceived noise level at Mach 1.42.
Mr Kachoria said certification of a supersonic plane was the biggest challenge facing Spike, requiring it to clear not only noise-related hurdles but to address issues such as how to survive engine failure or sudden decompression 10 miles high.
The Boston-based company has set aside a third of its budget to address regulatory concerns and estimates that the testing process will take more than three years, including a minimum of 3,000 hours of flight tests.
Spike is also betting that service entry will coincide with the availability of synthetically produced sustainable aviation fuel (SAF) capable of reducing lifetime CO2 emissions by around 80pc compared with kerosene.
That should help neutralise arguments from those who oppose a return to supersonic travel on the basis that it flies in the face of net zero.
Mr Kachoria said: 'One of the reasons for our timeline is to line up with SAF's widespread availability. It's got to be available globally and I think, by then, it will be.
'We spent a lot of time looking at alternative fuels, hydrogen, battery, and none of them were really viable. So it really it's fossil fuels or SAF.'
Spike sees the core market for the plane as business people wanting to travel together to meet with customers and suppliers, as well as government officials on urgent missions.
Mr Kachoria said airlines had also shown an interest, predicting they could charge a premium of up to 30pc above a standard business-class ticket.
That could indicate an annual market of around 25m passengers and a requirement for about 850 planes over the course of 20 years, he said.
Development costs will run into 'several billion dollars', he said, adding that Spike is backed by 'a small group of very wealthy individuals'.
As for the supersonic experience itself, Spike will prioritise speed over luxury.
Unlike most premium cabins, the jets will have no lie-flat beds, although they will be able to cross the Atlantic in three and a half hours – as Concorde was able to do.
Spike's plane would also be windowless, barring a handful of panels required for safety reasons, making the fuselage sleeker while eliminating engine and wind noise to deliver a cabin that would be 20 decibels quieter.
Mr Kachoria said: 'We've removed the windows and put in a digital screen with camera feeds from the outside. We bring in images and stitch them together to create one large landscape view.
'Or a passenger can have their own individual portal, just like at home, watching movies or making a PowerPoint presentation.'