WHAT SQUARE OF THE SPEED MEANS.—In mathematics a figure is squared when it is multiplied by itself. Thus, 4 X 4= 16; 5 X 5 = 25; and so on, so that 16 is the square of 4, and 25 the square of 5. It has been found that a wind moving at the speed of 20 miles an hour has a striking or pushing force of 2 pounds on every square foot of surface.
If the wind travels twice as fast, or 40 miles an hour, the pushing force is not 4 pounds, but 8 pounds. If the speed is 60 miles an hour the pushing force increases to 18 pounds.
ACTION OF A SKIPPER.—When the skipper leaves the hands of the thrower it goes through the air in such a way that its fiat surface is absolutely on a line with the direction in which it is projected.
At first it moves through the air solely by force of the power which impels it, and does not in any way depend on the air to hold it up. See Fig. 1, in which A represents the line of projection, and B the disk in its flight.
Fig. 11. A Skipper in Flight.
After it has traveled a certain distance, and the force decreases, it begins to descend, thus describing the line C, Fig. 1, the disk B, in this case descending, without changing its position, which might be described by saying that it merely settles down to the earth without changing its plane.
The skipper still remains horizontal, so that as it moves toward the earth its flat surface, which is now exposed to the action of the air, meets with a resistance, and this changes the angle of the disk, so that it will not be horizontal. Instead it assumes the position as indicated at D, and this impinging effect against the air causes the skipper to move upwardly along the line E, and having reached a certain limit, as at, say E, it automatically again changes its angle and moves downwardly along the path F, and thus continues to undulate, more or less, dependent on the combined action of the power and weight, or momentum, until it reaches the earth.
It is, therefore, clear that the atmosphere has an action on a plane surface, and that the extent of the action, to sustain it in flight, depends on two things, surface and speed.
Furthermore, the greater the speed the less the necessity for surface, and that for gliding purposes speed may be sacrificed, in a large measure, where there is a large surface.
This very action of the skipper is utilized by the aviator in volplaning,—that is, where the power of the engine is cut off, either by accident, or designedly, and the machine descends to the earth, whether in a long straight glide, or in a great circle.