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Boom Supersonic's XB-1 -

In January 2025, a US company's prototype jet broke the sound barrier in a demonstration it hopes will pave the way for a successor to the Concorde.

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A milestone event -

The XB-1 achieved the milestone at the Mojave Air & Space Port in California. During the test flight, the aircraft reached an altitude of 35,000 feet (10,600 m) before accelerating to 844 mph (1,358 km/h)—10% faster than the speed of sound!

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Intrepid aviator -

Flying the XB-1 was Boom's Chief Test Pilot, Tristan "Geppetto" Brandenburg, a graduate of the United States Naval Test Pilot School. He's just one of a long line of illustrious aviators charged with testing the airworthiness of experimental aircraft and taking them beyond the sound barrier. But exactly is the sound barrier?

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What is the sound barrier? -

Technically speaking, the sound barrier is a sharp rise in aerodynamic drag that occurs as an aircraft approaches the speed of sound.

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What is the speed of sound? -

The speed of sound is approximately 768 mph, or 1,236 km/h, at sea level.

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Speed of a passenger plane -

The average cruising airspeed for a commercial passenger aircraft that flies long distances is approximately 547–575 mph (880–925 km/h).

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Speed of a fighter jet aircraft -

Modern fighter aircraft on the other hand, for example an F-16, can reach top speeds of 1,304 mph (2,100 km/h).

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The sonic boom effect -

This speed is more than enough to break the sound barrier. As an aircraft pushes into the sound barrier, a sonic boom occurs. This indicates that the aircraft has surpassed the speed of sound.

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Sound barrier -

The sonic boom is just that—a noise that sounds like a thunderclap. The supersonic shockwave is illustrated by the white cloud formed by decreased air pressure and temperature around the tail of the aircraft.

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The physics behind the boom -

Put another way, if an aircraft flies at less than sonic speed, the pressure waves (sound waves) it creates outspeed their sources and spread out ahead of it.

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Sonic speed -

However, once an aircraft achieves sonic speed, the waves are unable to get out of its way. The moisture in the air condenses into water vapor as it breaks through the sound barrier.

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Other sources of a sonic boom -

Other objects that create sonic booms include natural phenomena like volcanic eruptions, meteor showers, and earthquakes.

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Bullets and bullwhips -

Objects as small as bullets and some common whips, bullwhips for example, are able to move faster than sound: the sharp crack of a whip, in fact, indicates that the tip of the whip has exceeded the speed of sound.

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How was the sound barrier broken? -

Sonic booms are mostly associated with aircraft. But what are the historical events that led to the sound barrier being broken in the first place?

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The "speed of sound" -

The term "speed of sound" came into use during the Second World War. It was used to describe the effects of compressibility experienced by pilots of high-speed fighter aircraft.

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Compressibility issues -

Compressibility is the ability of something to be reduced in volume or size under pressure. In aviation, this refers to a number of adverse aerodynamic effects that deter further acceleration.

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Impeded flight -

Researchers discovered the phenomenon seemingly impeded flight at velocities close to the speed of sound. These difficulties represented a barrier to flying at faster speeds and fueled a public debate about whether or not a piloted airplane could ever safely exceed what was poetically described as the "sound barrier."

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Ernst Mach (1838–1916) -

The ratio of the speed of a flow or object to that of sound is named the Mach number, in honor of Austrian physicist Ernst Mach. Any pilot achieving Mach 1, which indicates a speed in excess of 750 mph (1,200 km/h), would be the first to break the sound barrier. 

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Early attempts -

As early as 1941, the British had initiated top-secret projects to determine the feasibility of breaking the sound barrier. But it was an American aviator named Ralph Virden who in November of that year attempted to do so in a pre-production Lockheed YP-38 Lightning. To achieve the acceleration needed to fly through the sound barrier, Virden put his plane into a steep dive. He reached a speed of 535 mph (860 km/h) before the YP-38 broke apart, killing him instantly.

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New air speed record -

Edward Donaldson, a Royal Air Force pilot, came close in September 1946 when he established a new official world record of 615 mph (989 km/h) in a Gloster Meteor F.4.

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Another failed attempt -

Geoffrey de Havilland Jr., the son of Geoffrey de Havilland, the English aviation pioneer and aircraft designer, almost triumphed the same month when he flew his tailless, swept-wing de Havilland DH 108 Swallow to Mach 0.9 before the plane crashed. His body was recovered from the sea 10 days later.

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Chuck Yeager (1923–2020) -

The following year, United States Air Force officer Chuck Yeager became the first pilot in history confirmed to have exceeded the speed of sound in level flight.

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The Bell X-1 -

Yeager took to the air on October 14, 1947, at the controls of a Bell X-1, named Glamorous Glennis in honor of his wife.

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The sound barrier is broken -

The test pilot broke the sound barrier at Mach 1.05 at an altitude of 45,000 feet (13,700 m) over the Mojave Desert in California. Aviation had entered the supersonic age.

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A better understanding of supersonic flight -

In the wake of Yeager's accomplishment, the science of high-speed flight become more widely understood, knowledge that led to the eventual awareness that the sound barrier could easily be penetrated, under the right conditions. By the 1950s, many combat aircraft could routinely break the sound barrier in level flight.

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Tupolev Tu-144 -

The development of supersonic airliners began in earnest in the 1960s. In December 1968, the Soviets unveiled the first supersonic passenger airliner, the Tupolev Tu-144. In May 1970, it became the world's first commercial transport to exceed Mach 2.

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Concorde -

The first flight of Concorde took off from Toulouse on March 2, 1969. The Anglo-French supersonic airliner could fly at more than twice the speed of sound and set a world record when it flew between New York City and London in two hours, 52 minutes, 59 seconds.

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Tu-144 grounded -

The Tu-144's airworthiness was brought into question after a production aircraft crashed during the 1973 Paris Air Show. Six crew members perished. In May 1978, a second Tu-144 was forced to make a crash landing after a fuel leak led to an in-flight fire. Two died in this incident. Complaints about reliability and passenger comfort caused a lack of interest in the Tu-144, which ultimately led to the demise of the Tu-144 program.

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Concorde canceled -

Concorde's air safety record was flawless until July 25, 2000, when Air France Flight 4590 crashed shortly after takeoff from Charles de Gaulle Airport in Paris. The disaster ultimately led to the cancellation three years later of Concorde, and threw into question the future of supersonic travel.

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A new supersonic era? -

Now, more than two decades after the tragedy in Paris, supersonic travel is set to make a comeback after the successful demonstration of Boom Supersonic's XB-1 prototype jet.

Sources: (Boom Supersonic) (AP News) (Air Force) (San Diego Air & Space Museum) (National Geographic) (CNN)

See also: What's changing in air travel in 2025? 

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