During the summer months most of our route was covered during daylight, but as winter approached the hours of night flying increased until darkness set in a few minutes after we left the field at St. Louis.
With night flying and bad weather our troubles began. Our route was not lighted at first and the intermediate airports were small and often in poor condition. Our weather reports were unreliable and we developed the policy of taking off with the mail whenever local weather conditions permitted. We went as far as we could and if the visibility became too bad we landed and entrained the mail.
One of the worst conditions we met with was in flying from daylight into darkness. It was not difficult to fly along with a hundred foot ceiling in the daytime, but to do so at night was an entirely different matter, and after the night set in, if the weather became worse, it was not possible to turn around and return to daylight.
With all of our difficulties, however, the mail went through with surprising regularity. During the first five months of operation we made connections on over ninety-eight per cent of our trips.
There are only two conditions which delay the air mail: fog and sleet. If the fog is light or local, and the sleet not too heavy, the planes continue even then. But when the ground becomes invisible and the fog covers the terminal fields, or when sleet freezes thickly on wings and wires, the planes cannot continue. In such cases the mail is entrained and usually reaches its destination at least as soon as it would have if sent by train in the first place.
Almost every day, in some section of the United States, mail pilots are flying over fog and through storms and rain to bring their ships through on schedule time. The mail plane is seldom delayed and then only by impossible weather conditions. In the future these delays will become fewer as radio navigation and instruments for blind flying improve, until it will be possible for the pilots to keep to their schedules under the worst conditions and in comparative safety.
Another hazard, during certain times of year, is the formation of ice. This will gather on all parts of the plane but mainly on the wires, propeller, and entering edge of the wings. If it forms slowly from a fog or light rain, a plane may be able to continue on its course for some time, but if a heavy sleet storm is encountered the ice may form so rapidly that a ship cannot stay in the air over five minutes before it is so loaded down that the pilot will be unable to keep from losing altitude even with his motor wide open.
The actual weight of ice is not as important as the loss in efficiency of the wing, due to the changed airfoil caused by ice gathering on the entering edge.
Still more loss is caused from the ice forming on the propeller itself. The blades take on a thick coating which continues to increase in depth until the ice from one of the blades is thrown off by centrifugal force. When this happens an excessive vibration sets in and continues until the opposite blade has thrown off its coating.
