Such a form of construction is shown in Fig. 84. This outline has some advantages from one standpoint, namely, that it utilizes that part of the blade near the hub, to produce a pull, and does not relegate all the duty to the extreme ends or tips.
Fig. 84. A Suggested Form.
To understand this more fully, let us take a propeller six feet in diameter, and measure the pull or thrust at the tips, and also at a point half way between the tip and the hub.
In such a propeller, if the blade is the same width and pitch at the two points named, the pull at the tips will be four times greater than at the intermediate point.
CHAPTER XIV
EXPERIMENTAL GLIDERS AND MODEL AEROPLANES
AN amusing and very instructive pastime is afforded by constructing and flying gliding machines, and operating model aeroplanes, the latter being equipped with their own power.
Abroad this work has been very successful as a means of interesting boys, and, indeed, men who have taken up the science of aviation are giving this sport serious thought and study.
When a machine of small dimensions is made the boy wonders why a large machine does not bear the same relation in weight as a small machine. This is one of the first lessons to learn.
THE RELATION OF MODELS TO FLYING MACHINES. —A model aeroplane, say two feet in length, which has, we will assume, 50 square inches of supporting surface, seems to be a very rigid structure, in proportion to its weight. It may be dropped from a considerable height without injuring it, since the weight is only between two and three ounces.