The return of the X planes and why they hold the key to supersonic travel

In 1947, the first indication that spectators at a military airfield in Muroca, California experienced a sound barrier was a noise that sounded like thunder or a bomb.

This was the ninth flight of the experimental powered Bell X-1 aircraft, and on board the pilot struggled with the controls as the ship’s stability changed as speed increased.

the legend of X planes born in USA mid 40s and flourished until the 1960s, when rocket planes flew limits of space.

The flights of modern aircraft such as the X-1 and X-15 paved the way for the eventual success of the Apollo program and Neil Armstrong’s first steps on the moon. The fastest of the X-planes will accelerate its human pilots to over six times the speed of sound.

Now, in 2023, the last X plane, X-59 aircraftWhat’s the SST (Quiet SuperSonic Technology) aims to replicate the feat accomplished by the first X-plane: breaking the sound barrier again. Only this time, if everything goes according to plan, no one on earth will notice.

silent aircraft

In 1973, the US government banned commercial supersonic flights over the country. With this ban and others like it, cases of aircraft like the Concorde disappeared.

This might change if years of research on how to create quiet sonic boom they come true. NASA and Skunk Works (the official alias for Lockheed’s advanced development program) are trying to build an aircraft with this feature.

Despite advances in computer modeling and wind tunnel technology, it is still too risky to build a silent supersonic airliner without real evidence that the technology will work.

“I think X-59 could make a big difference,” says Christopher Combs of the University of Texas at San Antonio. “You are demonstrating for the first time in a real vehicle that you can produce silent sonic booms, and this could open the door for the commercial industry to start building aircraft like this.”

The X-1 looked like a plane designed to break the sound barrier. It was bullet-shaped with two straight wings (during the design, American aircraft designers did not fully understand the advantages of swept wings, such as reduced drag) and a rocket engine.

The fighter-like X-59 is a much more elegant and economical solution to a complex problem. The aircraft reuses parts from other aircraft, including landing gear from the F-16 fighter, a canopy and ejection seat from the much older T-38 supersonic trainer, and part of the engine system used in the U. reconnaissance aircraft.

Everything about the X-59 is designed to create a quiet sonic boom at a Mach 1.4 (1,074 mph) checkpoint at 16,800 meters, which is the range a commercial airliner can fly.

This will be done by minimizing the amount of shockwaves coming from the aircraft and spreading them more widely through the airframe so they don’t turn into a loud bang.

The long nose of the aircraft (which at 12 meters is equivalent to a third of the total length of the aircraft) is designed to separate the shock waves coming out of the nose from the waves created by the wing.

The engines are above the wing rather than below it like the Concorde, so the waves don’t hit the ground. The underside of the aircraft is also unusually smooth for an aircraft; this is to minimize the amount of shock waves it produces.

human pilots

The new X plane will also be human-controlled, rather than computer-controlled, to help build trust in the communities it flies over.

The aircraft is equipped with the so-called eXternal Digital Vision System (XVS). This system uses one high-definition camera in the nose and one below to provide the pilot with a display equivalent to a forward-facing window.

“We always joked that the X-1 broke the sound barrier, and now we are trying to fix it,” says Catherine Bachm, project manager Low Boom Flight Demonstrator (LBFD).

“His sonic boom won’t be loud enough for people to notice. It will be like distant thunder, or your neighbor’s car door closing, sounds that blend into everyday life.”

However, for the new era of supersonic passenger aircraft to be economically viable, aircraft will need to fly at supersonic speeds, for example, from North American airports to Europe.

“So we want to change not only American standards, but also global standards,” Bakhm adds.

integration of ideas

For some, creating an X-plane that produces a quiet rumble is a far cry from the glory days of breaking the sound barrier. This means that aviation is a mature technology that has run out of great new ideas. Others disagree.

“Integrating new ideas or new technologies is integral to what you do with the X-59,” says Christian Gelser, chief historian at NASA’s Armstrong Flight Research Center.

As well as collecting real data. “The engineers working on the X-59 need information for the same reason as those who worked on the X-1,” says Geltzer. “They are trying to see if they can predict what the plane will be like without actually building it.

“No one has ever built anything like this before.”

Prior to the X-plane, scientists serving on the National Advisory Committee for Aeronautics (Naca), NASA’s predecessor, conducted their research in wind tunnels and modified aircraft, gaining a worldwide reputation for quality.

Then, in the 1930s, everything changed. Aerodynamics expert John Stack outlined his idea for a purpose-built, large-scale research aircraft capable of reaching the speed of sound up to Mach 1.

Ten years later, Stack and a small group of engineers were working on turning this idea into a high-speed test car project.

What was an unofficial project grew in importance as rumors of experiments with German aircraft and rockets grew. The USAAF (United States Air Force) learned about the project and wanted a major change: the aircraft was to be equipped with a rocket engine.

Rocket-powered planes may seem ridiculous to us, but they were perfect for breaking the sound barrier, as they had much higher acceleration and speed than jet planes of the same size.

flying laboratory

The current supersonic flight builds on what the X-1 has taught engineers about supersonic airflow, the performance of materials at high speeds, and the most efficient forms of propulsion, as well as the data they have provided on how supersonic flight affects human physiology.

“Sustainable subsonic flight has been going on since the days of the Wright brothers, and all of a sudden you have an aircraft that you have designed to exceed those speeds,” says Combs. “This really sets the X-1 apart as one of the most impressive aircraft ever built. This is a huge milestone that sets the bar high for the rest of X-plane.”

The golden age of the X-aircraft reached its zenith in the late 1950s with the first flight of the American X-15 in 1959. “The X-15 was a great project, it dominated everything and did outstanding things,” he says. Gelzer.

It was a hypersonic demonstrator and still holds the record for the fastest manned hypersonic flight. Between 1959 and 1968, the X-15 demonstrated that it was possible to travel to and from space without the aid of a parachute capsule. He flew eight of the 12 pilots to the edge of space and back.

However, behind the glamor of the space race, the X-15 was, in fact, flying laboratory. Approximately 765 research papers have been written on such matters as the biomedical effects of high gravity and weightlessness flight, stability and control issues in flight and reentry, aircraft design performance at very high temperatures, and wind accuracy. tunnels.

“The X-15 spawned a ton of research, but one of the things that is really overlooked is what it taught us about the human factor,” explains Amy Shira Teitel, author of Breaking the Chains of Gravity: A History of Space Flight Before NASA “. “.

“We’ve learned a lot about how to train pilots who drive non-traditional vehicles and how to teach pilots to handle going beyond the ordinary.”

The beginning of a new era?

Many of these studies are still relevant today, especially when it comes to hypersonic flight. “There were definitely lessons learned from that show that we still talk about, like how to maneuver at hypersonic speedsays Combs, who has a hypersonic wind tunnel in his own lab.

The X-15 program was closed in December 1968 after 199 flights. This was followed by a new generation of X aircraft. Instead of manned rocket planes designed to fly higher and faster, the new X aircraft were often unmanned and intended for specific, unglamorous technical tasks, and they failed to attract attention. the public.

Rocket planes like the X-1 and X-15 were just an insurmountable obstacle. “You had a handful of pilots flying to the far reaches of space, and they were at the forefront of this new era,” says Teitel. “There was a sensuality about it that also attracted people. It wasn’t just amazing technology. It was the future.”

However, there have been many X-planes in the last 30 years and records continue to be broken. Bahm worked on several of them.

The Lockheed Martin X-33 Venture Star was a demonstrator in the NASA-Lockheed Martin project to build a successor to the Space Shuttle.

It was canceled in 2001 before test flights could take place due to a fuel tank failure during testing, although construction was 85% complete.

Now the purpose of the X-59 is not to go faster, but to be quieter. But this is only the beginning.

“The X-59 is sort of the scale of a fighter jet,” says Combs. “Next question: can you build a bigger one, the size of a Boeing 737?”

This story was published on BBC Future. Click here to read the original version (in English).

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