What Is Sound Barrier Speed & How Fast To Break It?

Ken Hyde

By Ken Hyde

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Most people do not consider the sound barrier a big deal until they see the media going wild whenever some pilot “breaks” it. But what exactly is this barrier, and why is it such a huge milestone to overcome it in the first place? Keep reading to find out!

What Exactly Is A Sound Barrier?

The term describes the difficulties an object faces when it approaches the speed of sound (or Mach 1).

In normal circumstances, an object moving through the air creates sound waves. Sure, these waves can easily travel ahead of the object at lower speeds. But once the object gets close to the speed of sound, the sound waves can’t get out of the way fast enough! 

how does Sound Barrier work

The result is an instant buildup of pressure and air resistance, and such a sudden increase in drag is what people call the “sound barrier.” These powerful waves of pressure buffet the aircraft and make it difficult to control, even disrupting the airflow around the wings to reduce the lift the jet aircraft can generate. 

If that’s the case, why did so many people claim that a sound barrier is a physical wall?

Back then, the science of aerodynamics around transonic speeds (speeds near the speed of sound) wasn’t fully understood. 

The sudden increase in aerodynamic drag forces and the formation of shock waves felt like hitting a limit – a physical wall – to most pilots at the time. This misconception only increased during World War II, as pilots pushing their fighter aircraft to high speeds reported strange phenomena (like control issues and instrument malfunctions) when approaching the speed of sound. 

Fortunately, with advancements in aerodynamics and numerous supersonic flights exceeding the speed of sound (we will return to that later), it’s clear the sound barrier isn’t a physical obstacle but rather a challenging zone to overcome due to the changing air behavior.

F-18 Super Hornet – Breaking the Sound Barrier

At What Speed Do We “Break” The Speed Of The Sound Barrier?

In this context, “breaking the sound barrier” simply means exceeding the speed of sound. Simply put, the supersonic aircraft is now traveling faster than the speed at which sound waves can travel ahead of it. Obviously, the whole concept is metaphorical since there’s no physical wall to break through.

So, how fast does the object have to be to break the sound barrier? The answer isn’t a fixed value; let us explain why.

As said earlier, the speed of sound is Mach 1 (about 767 MPH or miles per hour). There’s only one problem: the sound barrier is not always the same since it depends on the internal temperature. Sound travels faster when it’s hot (meaning you need more energy and speed to break the barrier) and slower when it’s cold. 

Another issue is “compressibility”. This term refers to when the air gets squished against an object while the latter is moving fast. The object gets hotter and more pressurized – and remember how the speed of sound changes with temperature? Hence, some parts of this object start going faster than the speed of sound, while others aren’t even there yet.

Has Anyone Broken The Speed Of Sound Before?

Yes. 14 October 1947 marked a significant milestone in aviation history. Bell X1 officially became the very first plane to break the speed of sound, piloted by Charles “Chuck” Yeager, captain and test pilot in the U.S. Air Force.

Bell X-1 Glamorous Glennis

Chuck Yeager was selected for his extensive knowledge in air combat during WWII and testing new aircraft models. The entire flight was a secret; only Yeager knew exactly how fast he was going when he established the record.

Yeager took the Bell X1 up to 45,000 feet during this high-speed flight and then started coming back down. He got the plane going at Mach 1.06 (about 813 MPH). That’s when the historic moment happened – the plane finally went faster than the speed of sound, with an instant, loud boom that echoed through the desert.

Others Pilots/Passengers

1. George Welch claimed to have exceeded the speed of sound on 1 October 1947 (before Chuck Yeager) and then again on 14 October that same year.

2. Even though all the evidence strongly supported his claims, the achievement was not officially acknowledged due to the lack of proper monitoring when it occurred. The plane Welch piloted, the XP-86 Sabre, was only confirmed to break the sonic barrier a year later, on 26 April 1948.

3. On 18 May 1953, Jackie Cochran became the first woman pilot to break the sound barrier. She was flying a plane lent by the Royal Canadian Air Force, accompanied by Chuck Yeager himself.

4. On 3 December 1957, Margaret Chase Smith was the first Congresswoman to accomplish this milestone. At that time, she was a passenger of the F100 Super Sabre flown by Air Force Major Clyde Good.

5. In the 1950s, the British journalist Allen Rowley got to climb onto a Super Sabre traveling at 1000 MPH (roughly Mach 1.35). He was among the few non-American citizens (or citizens anywhere, in fact) to have such an unordinary experience.

6. On 21 August 1961, a Douglas DC843 plane (registration N9604Z) went faster than the speed of sound in a supervised dive at Edwards Air Force Base. It was the first time a civilian plane (not a military jet) achieved this record. 

The attendants and witnesses were members of the flight crew: pilot William Magruder, co-pilot Paul Patten, flight test engineer Richard Edwards, flight engineer Joseph Tomich.

What Happens When An Aircraft Breaks The Sound Barrier?

Jet breaking sound barrier

Sound waves pile up before the plane as it moves. Once the plane finally pushes through this pile (or breaks the sound barrier), it creates a noise that sounds like an explosion, a phenomenon most refer to as a “sonic boom.”

Below is a closer look at how it works: 

When the plane travels beyond the speed of sound in air (supersonic speed), it moves so fast that its sound can’t catch up at all. That’s why you can’t hear any sound it makes until the plane’s already passed by! These two phases are commonly referred to as the “silence zone” (when the plane is approaching) and the “action zone” (when it’s already passed).

After the supersonic passenger aircraft passes over you, the pressure waves it created (called Mach waves) spread out and hit the ground, producing a sonic boom. Any area where you can listen to the sonic boom is the “boom carpet.” This boom sounds the loudest directly beneath the plane’s path and gets quieter the further you move away from it.

Some Fun Facts To Know

1. Pilots flying supersonic planes might experience a “Mach tuck,” where the plane tilts horribly downward due to the changed air flow over its wings. To soften the effect, they often make the horizontal stabilizers much bigger, move fuel tanks around, or make other adjustments to the plane.

2. Felix Baumgarner (an Austrian skydiver) jumped from 24 miles above the ground in 2012. His free-fall was so incredibly rapid that the speed recorded during his dive was Mach 1.25, breaking the sound barrier. He didn’t have to pilot any modern aircraft to achieve this!

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This phenomenon is no longer a mystery to humankind. Given a much better understanding of how it works. more and more people are breaking through its metaphorical “barrier.” If you have any other questions, feel free to contact us

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Ken W Hyde

Ken W Hyde

Ken W Hyde is the founder of The Wright Experience™. He is passionate about antique airplanes and has restored many of the Wright brothers' planes, including the 1918 Curtiss Jenny and the 1903 Wright Flyer. He is also a pilot and mechanic who has worked for Capital Airlines, Bendix Corporation, and American Airlines.

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