Page:Popular Science Monthly Volume 91.djvu/913

 Popular Science Monthly

��897

���© Underwood and Underwood

Thousands of such machines must be made if we are to win the war in the air. Airplanes must be built on the progressive assembling system adopted in automobile plants. We must be prepared soon to make three thousand five hundred airplanes a month

��kind of mechanical paradox. The frame of the wing is in effect a very carefully de- signed, very carefully constructed bridge. There is probably no other structure in the world that is so light and yet so strong. A pilot who flies at a speed of over a hundred miles an hour, who climbs more than six thousand feet in seven minutes, and who makes a sickening drop two miles in the air in order to escape an adver- sary subjects his wings to terrible strains. Cyclones, which are nothing but winds traveling with air- plane velocity, blow down houses and uproot trees, because the houses and the trees are not stiff enough to withstand such enormous pressures. The modern airplane is a storm machine. It forces itself through the air with cyclone speed; which means that it is subjected to exactly the same pres- sures as if it were lashed firmly to the ground in

���© Brown and Dawson

No iron cross

��for us, but the red, white and blue of Liberty

��the worst Kansas cyclone. Years of re- search and mathematical calculation have taught the airplane builder how to make a wing so strong that it is not likely to snap off like a clay pipestem.

Where Shall We Get Spruce?

To make the wings strong, yet light, spruce is used. If we are to build airplanes at the rate of 3,500 a month we must make deep inroads into our forests. There is none too much spruce of the superior kind re- quired for airplane con- struction. It is hard to find good wood. But the task of building wings is further complicated by the fact that although the spruce is bought by ex- perts, fully two-thirds of it is rejected because of its faulty grain or some other defect.

The building of an air- plane wing is hardly a commercial art. It is

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