October 14 marks a historic date in aviation history, as it was on this day in 1947 that Chuck Yeager broke the sound barrier for the first time.
The sound barrier?
Breaking the sound barrier means exceeding the speed of sound in air, i.e. 340 metres per second or 1,224 km/h in air at 15° (when heat varies, speed varies). The breaking of the sound barrier is accompanied by an explosion sound (supersonic bang) that lasts as long as the aircraft is at supersonic speed. So, contrary to popular belief, the “supersonic bang” doesn’t mean that a plane has broken the sound barrier, but that it’s moving faster than that speed. The noise therefore accompanies the plane as long as it is at supersonic speed, but for someone on the ground hearing the noise, the plane is moving away so fast that it sounds like a sudden and single sound.
The origin of the term “sound barrier” comes from the idea that it was an impassable limit. When, during the Second World War, the first pilots began to approach it, they noticed such extreme phenomena on their aircraft that they thought it was a physical limit that could not be exceeded.
The quest for the sound barrier
As human beings are constantly striving to push their limits, the very fact that the sound barrier is presented as an insurmountable limit has prompted engineers and pilots to find a way of breaking through it.
Although it wasn’t the first aircraft to break the sound barrier, nor was it designed to do so, it was the Messerschmitt Me 163 Komet that served as the model for conquering the sound barrier. It entered service shortly before the end of WW2, in 1944, and its capabilities impressed Allied pilots, who later used captured aircraft to attempt to break the sound barrier. To no avail. But it was the aircraft that suggested that the goal was finally attainable.
It served as a model for the De Havilland DH 108 Swallow, which was designed for transonic flight. Again in vain, as it disintegrated in flight as it approached the sound barrier, killing its pilot, Mr. de Havilland’s son Geoffrey de Havilland Junior. A second test pilot, John Derry, is killed aboard a second prototype.
But American engineers didn’t give up, and built an aircraft in the shape of a rocket ball with wings: the Bell X1, designed to be dropped at high altitude by a B-29A Superfortress bomber. This project was part of a joint program between the USAAF (United States Army Forces) and the NACA (National Advisory Committee for Aeronotics), forerunner of NASA.
It was aboard this aircraft that Chuck Yeager was the first to break the sound barrier.
Chuck Yeager
A former U.S. Air Force pilot during the Second World War, where he earned “Ace of Aviation” status (after winning 5 combat victories), he remained active after the war, becoming successively an instructor pilot and then a test pilot.
Assigned to Edwards Air Force Base (known as Muroc Field), he was the first man to break the sound barrier on October 14, 1947, aboard the Bell X-1.
For the record, Yeager shouldn’t have been the first man to break the sound barrier, or at least not that day. Victim of a riding accident the day before, he fractured two ribs. But not wanting to pass up the opportunity or leave the honor to someone else, he concealed his injury and so flew with this handicap.
His feat remained a secret for some time, as the US military was reluctant to make public some of the technological advances implemented on the X-1 as a result of the Cold War.
He later commanded American bases in Germany and France (Toul Rosières).
In 1963, he lost control of a Lockheed NF-104A at an altitude of 33,000m (an airliner flies at around 10,000m) and, after a 30,000m drop, miraculously managed to eject. He survived the accident with severe burns.
This did not prevent him from taking command of a base during the Vietnam War, where he carried out a number of victorious missions (127).
He retired in 1975, remaining a frequently consulted reference in the world of aeronautics (notably during the space shuttle explosion), and passed away in 2020 at the age of 97.
The controversy
Yeager may have been the first to “officially” break the sound barrier, but others may have done so before him.
A German pilot involuntarily blocked the speedometer of his Messerschmitt at 1,100 km/h after a dive of over 10,000m. So we don’t know whether he went further or not.
It is also said that supersonic bangs were heard during F-86 Sabre tests, which would lend credence to the idea of breaking the sound barrier, but nothing has been made official.
Chuck Yeager’s legacy
While today only military aircraft fly beyond the sound barrier, commercial aviation would never have known Concorde without its feat, and we may well see supersonic commercial flights again in the years to come, thanks to Boom Supersonic’s Overture.
The quest for the sound barrier was immortalized in the book “The right stuff” and the movie of the same name.
It was also on October 14, but in 2012, that Felix Baumgartner broke the sound barrier, but in freefall, having jumped from an altitude of 36,529m.
Finally, it wasn’t until 1953 that a woman broke the sound barrier: Jacqueline Cochran.
Photo : Chuck Yeager’s bell X-1 by crbellette via Shutterstock
