by If you’ve heard a sonic boom lately, you probably remember it. The loud, explosion-like bang – caused by planes flying faster than the speed of sound – can be terrifying, and even shatter windows.
Sonic booms are part of the reason there are no supersonic passenger planes flying today, and one of the factors limiting the success of Concorde, which last flew in 2003. The supersonic airliner was restricted to subsonic speeds when flying over land or near coastlines. , and current international regulations still limit the speed of commercial transport over land to below Mach 1, or the speed of sound, to avoid the disturbance of sonic booms over inhabited areas.
Now, NASA is working to change those regulations by changing the boom into a “thump,” paving the way for a new generation of quieter supersonic aircraft. The agency is doing that through a program called Quesst, which is the result of many years of research and is focused on a new aircraft called the X-59, which debuted on Friday.
distant thunder
The X-59 is the latest in a series of experimental aircraft including the X-1, which in 1947 was the first manned aircraft to exceed the speed of sound, and the X-15, which holds the record for his fastest ever. manned flight, set in 1967 at Mach 6.7.
The new craft was designed and built by prime contractor Lockheed Martin Skunk Works in Palmdale, California, under a $247.5 million NASA contract. With the factory commissioning now complete, integrated systems testing, engine runs and taxi testing will be carried out in preparation for the first flight of the X-59. It is set to take off for the first time later this year, ahead of its first silent supersonic flight.
“In the last few years we have gone from an ambitious concept to reality. NASA’s X-59 will help change the way we travel, bringing us closer together in much less time,” NASA deputy administrator Pam Melroy said in a statement.
“It will be much quieter than Concorde or any other supersonic aircraft that exists today,” Craig Nickol, a senior adviser at NASA Headquarters, told CNN in 2022. “It’s incredibly long and thin: it’s almost 100 feet long (30.5 meters), but its wingspan is only about 29 feet. The nose is a distinctive feature of this aircraft: it is about a third of the length.”
The sleek shape plays a key role in making the aircraft much quieter when traveling supersonic.
But how does a sonic boom occur? When an aircraft travels at subsonic speeds, the sound waves it creates can normally travel in all directions; however, at supersonic speeds, the aircraft will leave its own sound behind and the sound waves will compress and condense into a single shock wave that originates from the nose and ends at the tail.
When this highly compressed shock wave hits the human ear, it produces a loud boom, which does not happen when the plane breaks the sound barrier, but is a continuous effect that can be heard by anyone in a shaped area cone under the plane, as long as it exceeds the speed of sound.
The shape of the X-59 is designed to prevent the shock waves from merging together. Instead, they spread out, with the help of strategically placed aerodynamic surfaces. The single engine is also at the top rather than the bottom of the plane, to maintain a flat lower profile that prevents shock waves from reaching the ground.
As a result, NASA believes the X-59 will produce only 75 decibels of sound when traveling at supersonic speeds, compared to Concorde’s 105 decibels.
“What that means is that this aircraft could look like distant thunder on the horizon, or like someone closing a car door around the corner,” says Nickol. “People may not even hear the boom at all, and if they do they certainly won’t be surprised, because it will be low and spread out, and not that loud at all.”
Change regulations
The X-59 is expected to fly 1.4 times the speed of sound, or 925 mph. Before that, the Quesst team will conduct several flight tests at Lockheed Martin Skunk Works before the aircraft is transferred to NASA’s Armstrong Flight Research Center in Edwards, California, which will serve as its base of operations.
The critical part of the program will begin later in 2024, when a series of test flights will be conducted over half a dozen residential communities across the US, chosen to offer a diverse mix of geographic and atmospheric conditions: “That’s fun. as part of the project, because we’re going to reach out to the community and create a bit of citizen science,” said Nickol.
The plan is reminiscent of an experiment run by the Federal Aviation Administration (FAA) in 1964, when supersonic fighter jets were flown repeatedly over Oklahoma City to test the impact of sonic booms on the public.
It did not go down well, with up to 20% of people opposing the boom and 4% filing complaints and damage claims. “We don’t want to do that again, of course, which is why we’re going to test this aircraft on a restricted range first, measuring all the boosts,” says Nickol. “Only when we are satisfied with the performance will we go out to the communities, and even then we will carefully control the level of sonic beats.”
When the X-59 is flown over the selected areas, NASA will contact the communities on the ground to gauge their response to the noise. The goal is to confirm the theory that a 75 decibel boom will be acceptable.
The data collected in this way will then be presented to the US Federal Aviation Administration and international regulators.
A new generation
NASA believes that a change in regulations would open up the skies to a new generation of supersonic aircraft, which would allow them to fly over routes that are now not allowed, such as New York to Los Angeles, and would cut flight time by about half.
However, we do not know what those aircraft will look like and who will build them, as the X-59 is not a prototype but only a technology demonstrator.
“Any future design of a low-boost commercial aircraft for supersonic flight will certainly be different than this, although some of the design elements may carry over,” Nickol said, referring to the extended nose, some of the flight control systems, and the unique X-59 External Vision System, which provides the pilot with high-definition displays showing what lies ahead, in the absence of a real window to face forward due to the streamlined nose of the aircraft.
Several companies are currently developing supersonic passenger aircraft and plan to fly them within a decade or less, including Hermeus, Boom and Spike. However, it is doubtful that any of them will be able to benefit from the results of the Quest program, which will inform the next generation of supersonic aircraft.
Nickol believes that such aircraft, with the ability to fly anywhere, would democratize supersonic travel, which represents a stark contrast to Concorde’s luxury status: “If you look back 100 years, a lot of the advanced technologies of mobility, including railways and airplanes. as great experiences, but as technology advanced and costs came down, they became available to the general public,” he says.
“One of the long-term goals is to make this type of high-speed travel available as a widespread application, and there’s really no reason why it can’t happen.”
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