All agree that at great elevations the flying conditions are entirely different from those met with near the surface of the ground, and the history of accidents show that in every case where a mishap was had at high altitude it came about through defect in the machine, and not from gusts or bad air condition.
On the other hand, the uptilting of machines, the accidents due to the so-called "Holes in the air," which have dotted the historic pages with accidents, were brought about at low altitudes.
At from two to five thousand feet the air may be moving at speeds of from twenty to forty miles an hour,—great masses of winds, like the trade stream, which are uniform over vast areas. To the aviator flying in such a field, with the earth hidden from him, there would be no wind to indicate that he was moving in any particular direction.
He would fly in that medium, in any direction, without the slightest sense that he was in a gale. It would not affect the control of the machine, because the air, though moving as a mass, would be the same as flying in still air. It is only when he sees fixed objects that he is conscious of the movement of the wind.
CHAPTER XIII
THE PROPELLER
BY far the most difficult problem connected with aviation is the propeller. It is the one great vital element in the science and art pertaining to this subject which has not advanced in the slightest degree since the first machine was launched.
The engine has come in for a far greater share of expert experimental work, and has advanced most rapidly during the past ten years. But, strange to say, the propeller is, essentially, the same with the exception of a few small changes.
PROPELLER CHANGES.—The changes which have been made pertaining to the form of structure, principally, and in the use of new materials. The kind of wood most suitable has been discovered, but the lines are the same, and nothing has been done to fill the requirement which grows out of the difference in speed when a machine is in the act of launching and when it is in full flight.
PROPELLER SHAPE.—It cannot be possible that the present shape of the propeller will be its ultimate form. It is inconceivable that the propeller is so inefficient that only one sixty-fifth of the power of the engine is available. The improvement in propeller efficiency is a direction which calls for experimental work on the part of inventors everywhere.