(After Dr. Franz Linke.)
Notice the eddy in the valley to the leeward of the first ridge
A SHELTERED LANDING PLACE MAY BE DANGEROUS
(After Dr. Franz Linke.)
A landing place surrounded by trees is dangerous in windy weather on account of the air waves formed between the moving air above and the calm air below.
AIR WAVES NEAR THE EARTH’S SURFACE
The waves are made visible by smoke
The turbulence of the lower air—a phenomenon that adds so much to the difficulties of starting and landing—extends to various heights, depending especially upon the strength of the wind. A rough rule, evolved by the Zeppelin pilots before the war, was to expect turbulent conditions up to an altitude equal to from ten to twenty times the force of the wind in meters per second. Thus, for a wind of 10 meters per second, the turbulent layer would be from 100 to 200 meters thick. A good picture of the atmospheric ups and downs encountered by the airman when flying low is furnished by the behavior of the smoke from a factory chimney with a moderate wind blowing, forming smoke waves.