Word: mache
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Dates: during 1940-1949
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...explosion) moves through air. The actual speed varies considerably with the air's temperature (the colder the slower). To eliminate this variability from their figuring, scientists have given the speed of sound a special name. In aerodynamics, the speed of sound in any air under consideration is called "Mach I,"* no matter what the actual speed...
When an object is moving through air at less than Mach I, compression waves speed out ahead of it. They "warn" the air molecules that a moving body is coming, so the molecules have time to rearrange themselves to flow evenly around it. But above Mach I, the moving body (like the raiding Mongols of the Middle Ages) out-speeds the news of its coming. The air molecules, taken by surprise, are pushed aside sharply...
This is why air designers approach the speed of sound with infinite trepidation. The most troublesome speed begins just below Mach I. When a wing is moving at, say, Mach .80, the air passing over it has to hurry to get around its bulge. If, in doing this, it reaches Mach I, violent things may happen. The smooth airflow breaks into turbulence as hard shock waves jump around on the wing (see cut). The drag increases enormously; the wing's lift drops. The buffeting from the irregular airflow may be strong enough to tear the wing apart. This sometimes...
...transonic" (transition) speed is the worst. After the wing gets moving well above Mach I, the air behaves reasonably again, but in a novel manner. From the leading edge of the wing, two intense sound waves flare off like the bow waves of a boat. Two more flare off from the trailing edge. If the moving object has any irregularities or sharp curves, these are apt to trail their sound waves...
According to the up-to-date method of measuring airplane speeds (in "mach numbers"), the second flight of the Skystreak was no better than the first. During both flights it reached "mach .828." This means that both times it moved at 82.8% of the speed that sound would travel through the same air. While Commander Caldwell was flying the Skystreak, the temperature of the air was only 75° F. But when Major Carl took the controls, it was 94° F. Sound travels faster in hot air, so the speed of sound at the course moved up too, keeping...