Science: Zone of Quiet

People who were in or near Dayton last April were jolted by loud, explosion-like blasts striking down out of an innocent-looking sky. Most everybody suspected the Air Force, whose nearby Wright-Patterson Field is constantly testing peculiar and violent aircraft. But the Air Force admitted nothing.

Last week Daytonians had another sky-side bombardment. This time they got an explanation; the Air Force had done it on purpose. Before a distinguished audience of scientists and Air Force brass, two test pilots, Captain John C. Newman and Lieut. Harold Collins, climbed their F-86 jet fighters to 43,000 ft. and dived them vertically downward. Pushed by their jets and pulled by gravity, the fighters soon passed the speed of sound. Shock waves trailed in spreading “Vs” from the leading edges of their wings.

At 28,000 ft., the planes pulled out of their dives. The shock waves, increased in force by the turning maneuver, continued straight down to the ground and were heard as explosive bangs. Colonel Franklin Paul, chief of the Air Materiel Command’s Flight Test Division, explained that a speedboat making a sharp turn does somewhat the same thing. Its normal bow wave, increased by the pressure of the turn, grows into a foaming comber.

The Air Force did not reveal the top speed of the diving jets, but it must have exceeded the speed of sound (670 m.p.h. at high altitude) by a wide margin. Some air-wise observers privately calculated that the fighters might have been diving at 1,300 m.p.h. when they made their sudden pullouts.

Pilots Newman and Collins needed no instruments, they said, to tell them at what point their diving fighters had passed the speed of sound. When that time came their cockpits grew quiet; the normal noise of flight abruptly died away. Down they dived in unearthly silence, leaving sound behind, until the slowing effect of the turns brought them back into the sound-filled world.