New Delhi: In January, a test jet pierced the skies 35,000 ft above Mojave Desert and became the first privately funded aircraft to break the sound barrier. American manufacturer Boom Supersonic’s XB-1 achieved Mach 1.122, which is a little under 1,400 km per hour. But no one on the ground heard a sonic boom.
Research on sonic boom–a thunderous shock wave created by aircraft flying faster than the speed of sound–forms the core strategy of the US firm, which was established in 2014. It is now banking on US President Donald Trump’s keen interest in commercial supersonic flight.
In June, Trump signed an executive order titled ‘Leading the world in supersonic flight’ to enter “a bold new chapter in aerospace innovation”. It lifted a 52-year ban on commercial supersonic flight over land in the US, the same restriction that previously prevented Concorde operations on transcontinental flights.
Trump has already signed several executive orders on issues ranging from Artificial Intelligence to cryptocurrency and an energy grid revamp, evidently to establish a global tech supremacy and autonomy. His executive order on supersonic flight centred on the same vision.
“For more than 50 years, outdated and overly restrictive regulations have grounded the promise of supersonic flight over land, stifling American ingenuity, weakening our global competitiveness, and ceding leadership to foreign adversaries,” the order said, adding that the order was a historic national effort to reestablish the US as the undisputed leader in high-speed aviation.
Boom Supersonic told ThePrint that revoking the ban will let manufacturers develop supersonic aircraft at a time when maintaining US leadership in aerospace technology is critical.
“The executive order directs the Federal Aviation Administration to revise its regulations to allow for civil aircraft to fly faster than Mach 1 over land in the US, as long as no sonic boom reaches the ground. The order effectively lifts the ban on supersonic flight over the US that has been in place since 1973,” a spokesperson of the company said.
Historically, supersonic aircraft have only been developed by militaries and governments. In 1947, Chuck Yeager became the first human to break the sound barrier when he pushed the Bell X-1 past Mach 1 during a flight over the Mojave Desert, the same area where the XB-1 flew this year.
XB-1’s supersonic flight, which it calls Boomless Cruise, marks the first time an independently developed jet has broken the sound barrier. The XB-1 test jet provides the foundation for Overture, the company’s planned commercial airliner that has already found takers in leading airlines.
Overture’s order book stands at 130 aircraft, including orders and pre-orders from American Airlines, United Airlines, and Japan Airlines. American Airlines made a deposit on up to 20 aircraft, with an option for 40 more, in August 2022.
Japan Airlines was one of its earliest backers, announcing a strategic partnership to bring commercial supersonic travel to passengers with an option for 20 aircraft. Headquartered in Denver, the company has raised about $600 million from investments.
The science of boom-less flight
Boom Supersonic said it leverages well-established ‘Mach cutoff physics’, where a sonic boom refracts upward due to temperature and wind gradients that affect the local speed of sound. “This is similar to how light bends when passing through a glass of water. By flying at a sufficiently high altitude at an appropriate speed for current atmospheric conditions, Overture ensures that its sonic boom never reaches the ground,” the company’s spokesperson told ThePrint.
Overture’s autopilot is designed to change its speed based on real-time atmospheric conditions. Over land, the jet will attain speeds up to Mach 1.3, with typical speed between Mach 1.1 and 1.2. Over water, Overture aims to reach its top cruising speed of Mach 1.7, which would be about 2,100 km per hour. Overture has a planned flight range of 7,867 km and its planned cruising altitude could go up to 60,000 ft.
But the effort to keep the noise down begins even as the aircraft is on the ground. Overture, according to the manufacturer, will have landing and take-off noise levels similar to any other subsonic long-haul aircraft. “One major difference between Concorde and Overture is that Overture will take off without afterburners – the main reason for the noise levels of Concorde’s take-offs,” the spokesperson said.
It said that Symphony, a turbofan engine that will power Overture, will be quieter than Concorde’s turbojet engines with afterburners. An afterburner injects extra fuel into the exhaust to produce extra thrust in an aircraft. It is known to be loud and a fuel-guzzler but serves the purpose of many military aircraft.
To a query on why there will be four engines instead of two, the spokesperson said they selected a four-engine configuration after extensive R&D and an effort to understand the supply chain. “Using four engines lets us reduce the size of each engine, allowing production to fall within current supply chain and manufacturing capabilities.”
The company said the engines have been mounted on the wings behind the pressurised passenger cabin to minimise risk to passengers in case of engine failure.
As objects travel through the atmosphere at a speed more than that of sound, the air molecules are pushed aside with great force. The bigger the object, the more air it displaces.
“The shock wave forms a cone of pressurised air molecules which move outward and rearward in all directions and extend to the ground. As the cone spreads across the landscape along the flight path, they create a continuous sonic boom along the full width of the cone’s base. The sharp release of pressure, after the buildup by the shock wave, is heard as the sonic boom,” according to a NASA fact sheet.
Executive order & future of supersonic flight
Trump’s executive order said that within 18 months of its signing, which was 6 June, the US Federal Aviation Administration (FAA) will establish a standard for supersonic aircraft noise certification. The norms will define acceptable noise thresholds for take-off, landing, and enroute supersonic operation.
Supersonic flight over land was banned in the 1970s after the FAA and Congress faced public anger following test flights that led to complaints of noise pollution and even damage in some areas.
This move came just a few years before British Airways began its first regular Concorde service from London to Bahrain. Jointly developed by the French and British governments under a 1962 treaty, the Concorde retired in 2003 after three decades in service because it was proving to be financially unviable, other than problems of noise and limited use.
The Trump order said that US officials will engage the International Civil Aviation Organization (ICAO) and key foreign partners to seek global cooperation. The ICAO is a United Nations agency, which has 193 signatory countries who coordinate on global air mobility and flight operations.
“As the United States looks to re-industrialise, repealing the ban allows manufacturers to develop and test new supersonic aircraft, fostering a competitive market at a time when maintaining US leadership in next-generation aerospace technology is critical,” the company said about the presidential order. “We welcome a future where more companies are working to bring back supersonic passenger flight.”
Last year, Boom Supersonic completed construction on its Overture Superfactory in Greensboro, North Carolina, where it plans to build 66 Overture aircraft per year.
Boom Supersonic’s XB-1 is a stepping stone in its plan to develop a commercially viable supersonic airliner, the Overture, capable of carrying 64-80 passengers across the Atlantic in about 3-1/2 hours.
It said there are over 600 global routes that are economically viable for supersonic flight, even without going supersonic over land. And now that the rules are being relaxed in the US, additional routes will benefit from speedups.
“With speeds 40-50 percent faster than conventional airliners, Overture in Boomless Cruise enables passengers to travel from San Francisco to New York in 3 hours 30 minutes instead of just over 5 hours, saving 90 minutes. Passengers can leave Washington, DC at 8:00 AM EST and arrive in Los Angeles in just 3 hours 40 minutes at 8:40 AM PST. Hybrid routes with overland and overwater segments, such as Chicago to Frankfurt, will also see incremental time savings,” the company said.
Boom Supersonic also partnered with NASA recently to capture specialised photography and acoustic data during the XB-1 supersonic flight test programme.
(Edited by Tony Rai)