X-59: NASA's Quest to Build a 'Quiet' Supersonic Plane

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(CNN) — If you’ve heard a sonic boom recently, you probably remember it. The loud, explosion-like bang – caused by a plane flying faster than the speed of sound – can be startling, even shattering windows.

Sonic booms are one of the reasons why supersonic passenger planes don’t fly today, and one of the limiting factors for Concorde’s success, which last flew in 2003. The supersonic aircraft was limited to subsonic speeds when flying over land or near coasts, and current international regulations still limit the speed of commercial land transportation to below Mach 1, or the speed of sound, to avoid the disruption of sonic booms. above inhabited areas.

Now NASA is working to change those regulations by transforming the boom into a “thump,” paving the way for a new generation of quieter supersonic aircraft. The agency does this through a program called Questst – for “Quiet SuperSonic Technology” – which is the result of decades of research and centered around a new aircraft called the X-59.

distant thunder

The X-59 is the latest in a series of experimental aircraft, including the X-1, which in 1947 became the first manned aircraft to exceed the speed of soundand the X-15which still holds the record for fastest crewed flight ever, set in 1967 at Mach 6.7.

Designed and built by Lockheed Martin in Palmdale, California, under a $247.5 million NASA contractThe X-59 is currently undergoing ground testing, pending a maiden flight later in 2022.

“It will be significantly quieter than the Concorde or any other supersonic aircraft in existence today,” said Craig Nickol, project manager of the Quest program at NASA. “It is extremely long and thin: it is almost 30 feet long (30.5 meters), but has a wingspan of only about 29 feet. The nose is a distinguishing feature of this aircraft: it is about a third of the length. ”

The slim shape plays a key role in making the aircraft much quieter during supersonic travel.

What the X-59 might look like in flight.

cr103.com/NASA

But how does a sonic boom come about? When an airplane travels at subsonic speeds, the sound waves it normally creates can travel in all directions; however, at supersonic speeds, the aircraft will leave its own sound and the sound waves will compress and coalesce into a single shock wave starting at the nose and ending at the tail.

When this highly compressed shock wave meets a human ear, it produces a loud bang, which does not occur when the aircraft breaks the sound barrier, but rather is a continuous effect that can be heard by anyone in a cone-shaped area below the aircraft, as long as it exceeds the speed of sound. exceeds.

The shape of the X-59 is designed to prevent the shock waves from coalescing. Instead, they spread out using strategically placed aerodynamic surfaces. The lone engine is also located at the top rather than the bottom of the plane, to maintain a smooth lower profile that prevents shock waves from reaching the ground.

As a result, NASA believes the X-59 will produce only 75 decibels of noise at supersonic speeds, compared to the Concorde’s 105 decibels.

“That means this plane might sound like a distant thunder on the horizon, or like someone closing a car door around the corner,” Nickol says. “In fact, people may not hear the thump at all, and if they do, they certainly won’t be startled because it will be low and scattered, and not that loud at all.”

Changing regulations

The pivotal portion of the program will begin in 2024, when a series of test flights will be conducted over half a dozen residential communities across the U.S. selected to provide a diverse mix of geographic and atmospheric conditions: “That’s going to be a fun part of the project.” , because we engage with the public and generate a little citizen science,” Nickol says.

The plan is reminiscent of a 1964 Federal Aviation Administration (FAA) experiment when supersonic fighter jets flew repeatedly over Oklahoma City to test the impact of sound waves on the public.

It didn’t go well, with as much as 20% of the people to object to the booms and 4% filing complaints and claims. “We don’t want to repeat that, of course, so we’re going to test this aircraft on a limited range first, measuring all booms,” says Nickol. “Only when we are satisfied with the performance do we move to the communities and still carefully control the level of the sonic booms.”

Once the X-59 has flown over the selected areas, NASA will contact the communities on the ground to measure their response to the noise. The goal is to confirm the theory that a 75 decibel explosion is acceptable.

The data collected in this way will then be presented to the International Civil Aviation Organization (ICAO), which is responsible for aircraft noise regulation, to persuade it to update it at an international meeting scheduled for 2028.

A first flight is planned for the end of the year.

Darin Russell/NASA

A new generation

NASA believes a regulatory change would open up the sky for a new generation of supersonic aircraft, which would be allowed to fly over routes that are now prohibited, such as New York to Los Angeles, and cut flight time by about half.

However, we don’t know what those planes will look like and who will build them, because the X-59 is not a prototype, but just a technology demonstration.

“Any future design of a low-boom commercial aircraft for supersonic flight will certainly be different from this one, although some design elements can be directly translated,” said Nickol, pointing to the extended nose, some flight control systems and the aircraft’s unique external vision system. X-59, which provides the pilot with high-definition displays showing what lies ahead, lacking a true forward-facing window due to the aircraft’s streamlined nose.

Several companies are currently developing supersonic passenger jets and plan to fly them in a decade or less, including: Hermes, Tree and Peak. However, it is doubtful whether any of them will be able to benefit from the findings of the Quest program, which is likely to inform the next generation of supersonic aircraft.

Nickol believes that such aircraft, with the ability to fly anywhere, would democratize supersonic travel, making a big difference to Concorde’s luxury status: “If you look back 100 years, many of the advanced mobility technologies, including railways and aircraft, started out as premium experiences, but as technology progressed and costs dropped, they became available to the general public,” he says.

“One of the long-term goals is to make this form of high-speed travel available as a widespread application, and there’s really no reason why it couldn’t happen.”

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