X-59: NASA launches “silent” supersonic plane

If you've heard a sonic boom recently, you probably remember it. The loud, explosion-like boom caused by a plane flying faster than the speed of sound can be startling and even shatter windows.

Sonic booms are part of the reason there are no supersonic passenger planes flying today and one of the limiting factors in the success of the Concorde, which last flew in 2003.

The supersonic plane was restricted to subsonic speeds when flying over land or near the coast, and current international regulations still limit the speed of commercial land transport to below the speed of sound (1,235 km/h) to avoid disturbing sonic booms over areas inhabited.

Now, NASA is working to change these regulations, turning the boom into a “thud,” paving the way for a new generation of quieter supersonic aircraft.

The agency is doing this through a program called Quest, which is the result of decades of research and revolves around a new aircraft called the X-59, which was launched on Friday (12).

Distant thunder

The X-59 is the latest in a series of experimental planes that include the X-1, which in 1947 became the first manned aircraft to exceed the speed of sound, and the X-15. The latter still holds the record for the fastest plane ever in a manned flight, at around 8,300 km/h, achieved in 1967.

The new aircraft was designed and built by prime contractor Lockheed Martin Skunk Works in Palmdale, California, under a $247.5 million contract with NASA.

With factory deployment complete, the X-59 will now undergo integrated systems testing, engine running and taxi testing in preparation for first flight. It is expected to take off for the first time later this year, ahead of its first silent supersonic flight.

“In just a few years we went from an ambitious concept to reality. NASA's X-59 will help change the way we travel, getting us closer in less time,” NASA Deputy Administrator Pam Melroy said in a statement.

“It will be significantly quieter than the Concorde or any other supersonic aircraft that exists today,” Craig Nickol, senior advisor at NASA Headquarters, told CNN in 2022.

“It is extremely long and thin: it is almost 30.5 meters long, but it has a wingspan of only about 9 meters. 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 during supersonic travel.

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

When this highly compressed shock wave hits the human ear, it produces a loud boom, which does not occur when the plane breaks the sound barrier, but is a continuous effect that can be heard by anyone in a cone-shaped area below the sound barrier. plane.

The X-59's shape was designed to prevent shockwaves from sticking together. Instead, they spread out, with the help of strategically placed aerodynamic surfaces. The lone engine is also on 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 just 75 decibels of sound when traveling at supersonic speeds, compared to Concorde's 105 decibels.

“What this means is that this aircraft could sound like distant thunder on the horizon or like someone closing a car door around the corner,” says Nickol.

“It may even happen that people don't even hear the bang, and if they do, they certainly won't be scared, because it will be low and spread out, and not at all loud.”

Change of regulation

The X-59 is expected to fly at 1.4 times the speed of sound, around 1,500 km/h. Before then, the Quest team will conduct several flight tests at the Lockheed Martin Skunk Works before transferring the aircraft to NASA's Armstrong Flight Research Center in Edwards, California, which will serve as its base of operations.

The crucial part of the program will begin in late 2024, when a series of test flights will be conducted in half a dozen residential communities across the US, selected to offer a diverse combination of geographic and atmospheric conditions.

“It's going to be a fun part of the project, because we're going to interact with the public and generate some citizen science,” Nickol said.

The plan is reminiscent of an experiment carried out 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.

Things didn't go well. Up to 20% of people opposed the bangs and 4% filed complaints and claims for damages. “We don't want to repeat this, of course, which is why we will test this aircraft first at a restricted range, measuring all the barriers,” says Nickol.

“Only when we are satisfied with the performance will we go to the communities and carefully control the level of sonic booms.”

Once the X-59 flies over selected areas, NASA will engage with local communities to assess their response to noise. The aim is to confirm the theory that a boom of 75 decibels 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 a change in regulations would open the skies to a new generation of supersonic aircraft, allowed to fly on routes that are not permitted now, such as New York to Los Angeles, and cut flight times by approximately half.

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

“Any future design of a commercial aircraft for supersonic flight will certainly be different from this one, although some of the elements of the design may be directly translated,” Nickol said.

He pointed to the extended nose, some of the flight control systems, and the X-59's unique Eeterna vision system, which provides high-definition screens showing the pilot what's ahead in the absence of an actual window facing the sky. forward due to the aircraft's aerodynamic nose.

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 take advantage of the findings from the Quest program, which will likely inform the next generation of supersonic aircraft.

Nickol believes such aircraft, with the ability to fly anywhere, would democratize supersonic travel, marking a big difference from the Concorde's luxury status: “If you look back 100 years, many of the advanced mobility technologies, including railways and airplanes, started out as premium experiences, but as technology advanced and costs decreased, 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 that can't happen.”