X-59: NASA’s quest to build a “silent” supersonic aircraft

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

Sonic booms are part of the reason there are no supersonic passenger planes in flight today, and one of the limiting factors in the success of the Concorde, which last flew in 2003. The supersonic airliner was limited to subsonic speeds when flying over land or near coastlines. , and current international regulations still limit the speed of commercial land transport to less than Mach 1, or the speed of sound, to avoid disturbance from sonic booms over populated areas.

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

distant thunder

The X-59 is the latest in a series of experimental aircraft that includes the X-1, which in 1947 became the first manned aircraft to exceed the speed of sound, and the X-15, which still holds the record for fastest ever manned flight, set in 1967 at Mach 6.7.
Designed and built by Lockheed Martin in Palmdale, California under a $247.5 million contract with NASA, the X-59 is currently undergoing ground tests, in anticipation of a first flight later. in 2022.

“It will be significantly quieter than the Concorde or any other supersonic aircraft that exists today,” says Craig Nickol, NASA’s Quesst program project manager. “It is extremely long and slender: it is almost 100 feet long (30.5 meters), but has a wingspan of only about 29 feet. The nose is a distinguishing feature of this plane: it is about a third of the length.

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

What the X-59 might look like in flight.

What the X-59 might look like in flight.


But how does a sonic boom occur? When an airplane travels at subsonic speeds, the sound waves it normally creates can travel in all directions; at supersonic speeds, however, the aircraft will leave its own sound behind and the sound waves will compress and merge into a single shock wave that originates at the nose and ends at the tail.

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

The shape of the X-59 is designed to prevent shock waves from merging. Instead, they spread out, using strategically placed aerodynamic surfaces. The solitary engine is also at the top rather than the bottom of the aircraft, to keep a smooth underside profile that prevents shock waves from reaching the ground.

As a result, NASA believes the X-59 will only produce 75 decibels of sound when traveling at supersonic speeds, compared to 105 decibels for the Concorde.

“What that means is that this plane can look like distant thunder on the horizon, or someone closing a car door on 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 in regulations

The crucial part of the program will begin in 2024, when a series of test flights will be conducted in half a dozen residential communities across the United States, selected to offer a diverse mix of geographic and atmospheric conditions: “It will be a fun part of the project, because we will engage with the public and generate a bit of citizen science,” says Nickol.

The plan recalls an experiment conducted by the Federal Aviation Administration (FAA) in 1964, when supersonic fighter jets repeatedly flew over Oklahoma City to test the impact of sonic booms on the public.
It didn’t go well, with up to 20% of people opposing the booms and 4% filing complaints and damage claims. “We don’t want to repeat that, of course, so we’re going to test this plane first on a restricted range, measuring all the booms,” says Nickol. “Only when we are satisfied with the performance will we go out into the communities, while carefully controlling the level of the sonic booms.”

Once the X-59 has flown over the selected areas, NASA will engage with communities on the ground to assess their response to noise. The goal is to confirm the theory that a boom of 75 decibels will be acceptable.

The data thus collected will then be presented to the International Civil Aviation Organization (ICAO), in charge of aircraft noise regulations, to persuade it to update it at an international meeting scheduled for 2028.

A maiden flight is planned before the end of the year.

A maiden flight is planned before the end of the year.

Darin Russell/NASA

A new generation

NASA believes a change in regulations would open the skies to a new generation of supersonic aircraft, allowed to fly over routes that are not currently permitted, such as New York to Los Angeles, and cut flight time in half.

We do not know, however, what these planes will look like and who will build them, because the X-59 is not a prototype but simply a technology demonstrator.

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

Several companies are currently developing supersonic passenger planes and plan to have them flying within a decade or less, including Hermeus, Boom and Spike. However, it is unlikely that any of them will be able to take advantage of the discoveries of the Quesst program, which will probably inform the next generation of supersonic aircraft.

Nickol thinks that such an aircraft, capable of flying anywhere, would democratize supersonic travel, marking a clear difference with the luxury status of Concorde: “If you look back 100 years, many advanced mobility technologies, including including railroads and airplanes, started out as high-end experiences, but as technology advanced and costs fell, they became accessible 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 that shouldn’t happen.”

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