Popular Science Monthly 



895 



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 



