Is a silent supersonic aircraft possible? NASA’s X-59 is in the kitchen

“A sonic boom rattled the window panes of the city. It was the sound of a supersonic plane, one of the few still flying in those days. People stopped to look up at the sky, surprised to see such a powerful and fast aircraft, something that had been a rarity in recent years,” writes the chat of artificial intelligence ChatGPT-3.

Break the sound barrier without the sky cracking

2023 is the year that a sleek new supersonic plane, endorsed by NASA, will take to the skies with passengers on board. But X-59 will not rattle the windows of city buildings as described by ChatGPT-3. Artificial intelligence has not taken into account in its story that the technological prodigy of the expected plane is its silence. Breaking the sound barrier without cracking the sky is a challenge in testing.

X-59 will fly at Mach 1.42, which is equivalent to about 1,760 km/h, about one and a half times the speed of sound, and is the first prototype of a future commercial airliner. At the moment it has capacity for a single pilot and an observer, but the plan is that in 2030 it will carry passengers on board. For example, we will travel between Madrid and Paris in half an hour, and we will cross the Atlantic in four. Space and time will have been compressed.

The reasons for the sonic boom

Supersonic planes met the challenge of traveling faster than sound in the 1940s, and that, while quite a feat, makes them some of the most thunderous machines ever created by man.

The speed of sound is the speed at which pressure oscillations are transmitted in a fluid, in this case air. It depends on several factors, but at sea level it is about 1,234 km/h.

The phenomenon occurs when a particle collides with the one next to it, and this one with the next one, etc., transmitting the vibratory state as if they were pieces of a domino. If an object like the plane moves in the air, it will make noise. But if this object moves faster than the sound transmission waves, then a shock wave (which makes a lot of noise) is produced and generates what we know as a sonic boom or boom sonic.

The white disk that forms is nothing more than water vapor condensing as a result of the shock wave. This phenomenon is known as the Prandtl-Glauert singularity.

The noise generated by supersonic planes is so disturbing that their flight over urban areas or protected spaces is not allowed, because it also affects flora and fauna.

In addition, they also have against them that they require a large amount of fuel to reach and maintain high speeds, which makes them more expensive and less ecological than subsonic flights. And the commercial failure of the Concorde, finished off by the accident of its last flight with Air France, is still in the collective memory.

The key: its silent geometry

NASA has spent years working to mitigate these problems and its answer is the X-59 QueSST aircraft, a working prototype manufactured by the Lockheed Martin aerospace company.

This is a ship with a swept wing span of 29 meters and designed to fly at about 55,000 feet (16.8 km) above sea level.

Its design is the result of innumerable virtual simulations that allow hundreds of designs to be analyzed in computational fluid models (CFD for its acronym in English). Every little detail of the plane can ruin its silent geometry.

For example, the fuselage is very long and penetrating, and it does not have the typical cockpit that we are used to. A normal airplane cockpit would break the flow and create noise, so the X-59 pilot views the sky through a monitor.

The swept wing allows it to penetrate the atmosphere smoothly. The tail contains the GE F414 engine at its top, and this is also not accidental. Each of these details counts for contributions to the boom sonic particles are small and separate and spread out as the plane moves away, instead of coalescing (joining together) as usually happens in supersonic planes.

There is a virtual sound of the X-59 that is used to test it, and determine if it meets the requirements established by the FAA (Federal Aviation Administration).

Its smaller size and improved cycle engine make it more fuel efficient and less polluting than other supersonic aircraft. In addition, it is equipped with formation flying technology, which allows it to fly alongside other aircraft to reduce air resistance and improve fuel efficiency.

With all these improvements, NASA hopes to pave the way for supersonic commercial aviation again, this time to stay. Will he get it? The first test flight is expected this year. Let’s not miss the appointment.

Alejandro Manuel Gómez San Juan, Assistant Professor in the Area of ​​Aerospace Engineering, University of Vigo

This article was originally published on The Conversation. Read the original.