Mach 1: Assaulting the Barrier

In 1947, no airplane had ever gone faster than the speed of sound.

The Douglas D-558-2 Skyrocket (shown here at Edwards Air Force Base circa May 1949) pushed past Mach 2 on November 20, 1953, beating an advanced X-1 to the record. (US Navy via National Air and Space Museum. Photo SI A-5168-C.)
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This all came to a tragic end in September 1952, when de Havilland test pilot John Derry pulled apart a D.H. 110—the prototype Sea Vixen—trying to make a yet-bigger boom. One of the 100’s two engines somersaulted lazily into the Farnborough crowd, killing 28 and injuring 63, forever making anathema at Farnborough, and throughout the United States as well, the act of flying directly toward an airshow crowd.

Air Force pilots boomed for the fun of it during the ’50s. “We used to hear sonic booms all the time when I was teaching at Texas A&M,” reminisces Howard Wolko, a curator at the National Air and Space Museum. “Whenever a graduate joined the Air Force and finished training, he’d come back and buzz the campus supersonically. You’d hear it and just think, Oh, yeah, another Aggie got his wings.”

That tradition ended when one fighter job centerpunched his own field with a particularly powerful shock wave created by a dive to 8,000 feet. He broke windows, loosened doorframes, and cracked ceilings all over the base, ending the era of casual sound-barrier breaking, although isolated incidents continued to cause damage and injuries.

Strain gauges installed in houses that have been subjected to sonic booms show that the increase in pressure distorts a small building by a fraction of an inch. Two shock waves travel with an airplane flying faster than sound, one at the nose and one at the tail. The passage of the first almost instantly raises the air pressure slightly. In the 0.3 seconds or so before the second shock, the pressure rebounds to slightly less than ambient. The arrival of the second shock restabilizes it. This doubly whammy not only breaks windows but creates that characteristic boom-boom of a low-altitude supersonic flight.

The intensity of sonic booms is measured by the increase of pressure, or “overpressure,” and it can be doubled and tripled by maneuvers such as pull-ups and steep banks. Since the shock wave trails from the airplane at an angle, it’s thought that the ultimate sonic booms are produced by dives just steep enough to cause the entire “face” of the shock wave to arrive on the ground at once.

The all-time Glass-Makers’ Appreciation Award, however, should go to the U.S. Air Force F-104 pilot who in November 1959 buzzed an uncompleted terminal at Ottawa’s Uplands Airport at 500 feet and did $300,000 worth of damage to windows and the roof.

Little more was known about sonic booms until the mid-1960s when the Federal Aviation Administration, assigned to determine the social acceptability of supersonic transports, did what it claimed was more research on noise than had been done in the whole of human history.

During 1964 the FAA had the Air Force wallop Oklahoma City with eight sonic booms every flyable day for six months, using the area’s 700,000-odd inhabitants as unwitting and unwilling subjects in an experiment to determine society’s threshold of auditory pain. Century-series fighters and B-58 Hustlers played the city like a drum, which doubtless is why the project was code-named Operation Bongo.

The effects of the booms ranged from the inevitable to the incredible. One victim claimed that her bra strap snapped whenever the Air Force lowered a particularly loud boom. (“The engineers had a strain gauge all fixed up for her, but she wouldn’t give her name,” said one FAA spokesman.) Another Sooner said the daily 7:00 a.m. blast scooted her bed across the floor. A third claimed her furniture was shrinking. But some effects were serious. A high school student was beaned by a light fixture jogged loose during history class. An Oklahoman with hypertension was ordered by his doctor to leave the city for the duration of the tests, for the sound of the booms made him so furious that he quite literally could have died.

In all, the FAA got 15,116 complaints during the Oke City tests, sometimes as many as 500 a day. Many of them were simple noise gripes, but legitimate suits for property damage ended up costing the government $123,070 in the five years following the experiment.

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