Page:Popular Science Monthly Volume 91.djvu/911

 Popular Science Monthly

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��of many a plant; but the best airplane plant in the country now produces only five engines a day.

The difference between an automobile and a Liberty engine is as the difference between a cheap alarm clock and the finest chronometer. The excess metal on as many as eighteen automobile-engine cast- ings is sliced off at once like so much butter by huge automatic machines. A single

��into the cylinder or into a bearing, the engine must suffer. If even the head of a screw is slightly mutilated in driving it home or a pipe is ever so slightly indented that screw and that pipe must be rejected. And so it is with every part. Every third man in the engine plant is an inspector — usually a Government inspector. Fully sixty per cent, sometimes eighty and even ninety per cent of the parts produced are

���I'ruas iUus. Serv.

Wrapping fabric around the body of a fuselage. Note how the strips are held during the application. Each strip has been carefully tested, and so has every piece of wood

��machine-tool will bore out or ream as many as half a dozen automobile-engine cylinders to receive their pistons. Automatic ma- chines are also found in airplane-engine plants; but the airplane-engine is essentially the product of the craftsman rather than of the machine. The magnifying glass is not rn essential tool in the making of an auto- mobile engine; it is never missing in the airplane-engine factory. And why is it used ? Simply to examine steel for minute flaws. It is unnecessary to worry much about the interior of pipes or crankcases in making automobile engines; if an automo- bile should stop in the middle of the road for no apparent reason no one is endangered. But if a Liberty motor should suddenly stop in midair a brave man may lose his life. That is why the maker of Liberty motors scrapes the interiors of pipes and crank- cases. Little grains of sand imbedded in the metal are picked out by hand, because if the minutest particle should find its way

��rejected. Is it any wonder that Liberty motors are worth five and six thousand dollars apiece, and that there is less profit in selling them at that high price than in selling automobile engines of equivalent horsepower ?

Climbing and What It Means

Yet despite all this care the engine is not perfect. When you want it to do its best it does its worst, which means that at high altitudes it is least instead of most efficient. A mountaineer who must first climb two miles before he can fight is in the same posi- tion as a fast fighting airplane. He has had all the hard work of climbing and must then puff very hard in order to inspire enough air in a rarefied atmosphere. An airplane must climb five, ten, fifteen, even twenty thousand feet, and the higher it climbs the less power is delivered by the engine. The engine cannot breathe as much air as it re- quires, and air is as essential to an engine as

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