Page:Popular Science Monthly Volume 92.djvu/738

 Wind, Weather and the Airman

The Invisible Perils of the Whirlpools, Gusts, and Eddies of the Ocean in which Men Fly

��AIR navigation, in its relation to AA weather, is repeating the history of marine navigation. The slow sailing-ships of early days were the sport of wind and waves; the great ocean liner of today pursues the even tenor of its way regardless of the elements. Under the urge of necessity the military aviator now flies in all kinds of weather, and his high- powered machine negotiates atmospheric difficulties that would have been insupera- ble a few years ago. Nevertheless, even the biggest oceanlin- ers sometimes come to grief, and the day is still distant when the aviator will not need to keep his weather-eye wide open.

Airships and air- planes are the sub- marines of the at- mosphere, but the element in which they ply is far more fickle than the ocean. The cur- rents of the latter are comparatively feeble and regular; those of the former are often immense- ly powerful and capricious.

���Flow of Air Over a Ridge

Notice that the crest of the air wave lies a little beyond the crest of the ridge. This does not apply to isolated hills, which the air easily passes around

���Flow of Air Over Two Ridges

Notice the eddy in the valley to the leeward of the first ridge. In this case the crest of the air wave still lies beyond the crest of the ridge, as seen above

���There Are Winds and Winds

An aviator study- ing the atmosphere learns much of inter- eat. The structure of the atmosphere with respect to wind is a subject concerning which a great fund of knowledge has re- cently been acquir- ed through the

��A 'Sheltered" Landing-Place May Be Dangerous

A landing-place surrounded by trees is dangerous in windy weather on account of the air waves between the moving air above and the calm air below

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��Waves and Gusts in the Air

The iihutratinn shows how these an- niadt by smoke. The reader will bo able to

��this phenomenon for himself almost any windy day

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��practical experience of aeronauts on the one hand, and the scientific investigations of meteorologists on the other. The mariner dreads a strong wind; the aero- naut an unsteady one. Mere strength of wind is harmless to the aviator, except in starting and landing, and, indirectly, owing to its ability to drive the airplane far out of its intended course. If the stronge3t hurricane that ever blew were perfectly steady, the airman might well be as indifferent to its speed as the average mortal is to the speed with which our terrestri- al globe rotates on its axis. But un- fortunately the wind is hardly ever steady, either in force or direction. It is full of gusts and eddies, up-cur- rents and down- currents, and it is these eccentricities which gradually de- velop in the aviator a sort of sixth sense, a "feel" for atmos- pheric fluctuations, that enables him to adjust his machine instinctively to the forces tending to disturb its equi- librium. He also learns by experi- ence the conditions under which irregu- larities of a pro- nounced character may be expected. He becomes well acquainted with the great mound of air that drives the air- plane upward in passing over a hill or mountain; with

��visible observe

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