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WONDERING OUT LOUD

What's this "envelope" people are always said to be "pushing"?

The first time many of us heard the expression "pushing the envelope" was in the movie The Right Stuff, based on Tom Wolfe's 1979 book about the original NASA astronauts. Test pilot Chuck Yeager was said to be "pushing" or "pushing back" the "outside of the envelope" every time he tried to fly a plane at a record speed or altitude.

The expression apparently did originate in the Air Force test pilot program the late 1940s. The envelope in question was the "flight envelope," a term referring to the limits of speed, altitude and other variables at which a plane can fly.

The reason the speed of sound -- which Yeager surpasses near the beginning of the movie -- seemed for so long an impenetrable barrier was because drag increases exponentially on a plane as it approaches the speed of sound. Supersonic flight had to wait for the development of more powerful engines.

Nowadays pushing the envelope refers to any effort to approach or exceed known performance boundaries.

Source: Director Patrick F. Dunn and faculty of the Hessert Aerospace Research Center