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Breaking the Sound Barrier | The Greatest Moments in Flight

Chuck Yeager
Chuck Yeager and the X-1 research plane that broke the sound barrier. It can be seen today at the Smithsonian Air & Space Museum in Washington, D.C.
Credit: Air Force Test Center History Office

This is part of a SPACE.com series of articles on the Greatest Moments in Flight, the breakthrough events that paved the way for human spaceflight and its next steps: asteroid mining and bases on the moon and Mars.

A booming thunder roared across the clear skies of the Mojave Desert on Oct. 14, 1947, as U.S. Air Force Capt. Chuck Yeager nudged an experimental rocket-powered plane faster than the speed of sound. Though only a handful of people realized it at the time, an aviation record had been set.

In 1935, a simplified explanation of the challenges of supersonic flight led to the creation of the term "sound barrier," which seemed to imply a physical wall that could not be overcome. Bullets and cannon balls had exceeded the speed of sound for hundreds of years, but the question loomed as to whether or not a plane—or a man—could withstand the pressures that accompanied it. The U.S. Air Force set out to answer this looming question.

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The plane

Bell X-1
The Bell X-1 broke the sound barrier with Col. Chuck Yeager at the controls on Oct. 14, 1947.
Credit: NASA

A bullet-shaped plane, the Bell X-1 (originally designated the XS-1), was modeled after a .50 caliber machine gun bullet, an object known to be stable as it exceeded the speed of sound. Four rocket engines propelled the X-1, and it was built to absorb 18 times the force of gravity. Unlike most planes, it didn't take off from the ground, but was instead dropped from the belly of a B-29 Superfortress, rapidly accelerating in the air on only a few minutes worth of fuel before gliding back to the dry lakes below.

The historic plane, nicknamed the "Glamorous Glennis" for Yeager's wife, slowly approached the sound barrier over the course of nine flights. Muroc Air Force Base—now known as Edwards Air Force Base—in the empty southern California desert provided an ideal spot for testing a variety of experimental vehicles, including the X-1.

The pilot

The man who would go down as the most famous test pilot in American history was born in West Virginia on Feb. 13, 1923. Charles Elwood "Chuck" Yeager enlisted as a private in the U.S. Army Air Corps at the age of 18 and served in World War II, where he flew 64 combat missions.

In 1945, he was assigned as a maintenance officer to the Flight Test Division at Wright Field, Ohio, flight-testing the planes. Col. Albert Boyd, in charge of the test program for the Air Force, invited him to become a test pilot, and Yeager accepted, transferring to Muroc to enroll in the Flight Performance School. It was there that Yeager was selected to be the first person to attempt to exceed the speed of sound.

The flight

Yeager's first test launch of the Glamorous Glennis took place on Aug. 29, 1947, with subsequent attempts increasing speed by two hundredths of a Mach number. Mach is a unit of measuring the speed of sound in a given medium; a plane traveling at .2 Mach moves at only two-tenths the speed of sound, while Mach 1 is equal to it. (The speed of sound is about 758 miles (1,220 kilometers) per hour at sea level, and decreases with altitude.)

Reaching .86 Mach on the sixth flight, the X-1 began to experience turbulence from the shock wave formed by the compression of the air. On the seventh flight, at Mach .94, Yeager lost the ability to control the plane's elevator, a problem since the shock waves caused the nose to pitch up and down. He cut the engines, dumped the fuel, and landed safely in the desert. Another pilot suggested using the horizontal stabilizer to correct the problem, and on-the-ground tests seemed to suggest the alternate method of control would work.

Two days before his historic flight, Yeager was thrown from a horse while riding with his wife and broke two ribs. Knowing that he would never be allowed to fly, he traveled to a doctor off base and had them taped up. Unable to close and latch the side door by hand, he utilized a broom handle at the suggestion of a fellow pilot.

On Oct. 14, 1947, Yeager and the X-1 were dropped from the B-29, and quickly accelerated away. When the controls locked up, he successfully used the horizontal stabilizer to keep the plane stable. As the plane accelerated to Mach 1.06, controllers on the ground heard the first sonic boom. (The end of a bullwhip moves faster than the speed of sound. Some say the "crack" is a small sonic boom.)

After exceeding the speed of sound, the buffeting decreased, creating a smooth short flight. The plane remained supersonic for approximately 20 seconds before Yeager turned off two of the four engines and slowly decelerated.

The follow-up

Chuck Yeager
Chuck Yeager continued to act as a flight consultant for the air force until his last flight on October 14, 1997.
Credit: Air Force Test Center History Office

Yeager continued to fly experimental aircraft for the Air Force, and was appointed director of the Space School, NASA's precursor, where he trained astronauts to prepare for launch. He flew more than 120 combat missions in Vietnam. After 34 years in the military, he retired in 1975 at the rank of brigadier general, though he continued to serve as a consultant. His last flight as a military consultant occurred 50 years to the day after he broke the sound barrier.

In 1979, Tom Wolfe's best-selling nonfiction book, The Right Stuff, and the subsequent 1983 movie popularized Yeager's exploits to a generation too young to remember them.

Yeager and his wife, Glennis, had four children before her death in 1990. He remarried in 2003.

—Nola Taylor Redd

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The Greatest Moments in Flight

The Most Amazing Flying Machines Ever

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