Page:Popular Science Monthly Volume 91.djvu/926

 Testing Airplanes in a Man-Made Storm

At the Washington Navy Yard a seventy-five-miles-an hour wind is shot against warships and airplanes to determine their air resistance

���Because the tunnel is so large the models are made big enough to represent the actual machines faithfully in every particular. The wind attains a velocity of seventy-five-miles an hour

��WHAT the model basin for towing small models of ships is to the naval architect, the windtunnel is to the aeronautica 1 engineer. In the past, ships developed good shapes through centuries of service only. A faulty design might prove slow, but rarely unsafe. On the other hand, faulty airplanes are death- traps, incapable of that continuous service from which experience grows.

The invention of the airplane is due to the windtunnel. Models of wings were exposed to an artificial current of air and the force and direction of its pressure weighed. When the Wright Brothers found that they could not rely oh previous ex- periments made on the airpressure of wings (the German pioneer, Lilienthal, had ex- posed them only to the irregular natural wind), they resorted to a primitive wind- tunnel. All early windtunnels were too small.. They could .not produce air currents fast enough; they were merely ventilating fans that forced fresh air continuously into a small passage. Nevertheless, we owe to them, such as they were, the modern

��fast and stable airplanes and the racing Zeppelin.

Nothing has so retarded aeronautic progress in America as the fact that work with Professor Zahm's pioneer windtunnel of 1903, at the Catholic University, Wash- ington, D. C, was discontinued. For a decade, while Europe was waking up to the full importance of the subject, our country lacked this most necessary instrument.

The new windtunnel of the United States Navy is a model for the world. It is end- less, forming a complete circle, or rather a circuit flattened into the shape of a chain- link. As there is no resistance against the motion of the air contained within a closed circuit, except its friction against the walls, and as the blower does not overcome the inertia of continuously renewed quantities of air, this arrangement gives the artificial wind a cross-section of eight feet and a ve- locity of seventy-five miles an hour. The artificial storm is produced by a blower of five hundred horsepower.

Because the tunnel is so large the models are made big enough to reproduce the actual

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