Fig. 48. The toy biplane
Ralph explained that the propeller was simply part of a screw thread, and had actually worked its way through the air just as a screw works its way into a piece of wood. Its lifting power had been shown by the way it carried the balancing stick with it up to the ceiling.
"Now," he continued, "when we place a propeller horizontal it will worm its way forward through the air in the same way and carry the aeroplane with it, for the simple reason that it is so placed in the frame it can't get out. As the free space it has to revolve in is only 3 inches, we shall have to cut the blades down to about 23⁄4 inches to give it clearance."
They whittled out a shaft 11⁄2 inches long and fastened the two notched pieces h h to it after placing the propeller in position between the two cross pieces g g which had been previously drilled with 1⁄4-inch holes to act as bearings.
New rubber bands were then passed over the notches, stretched out to the front and rear of the frame, and tied to cross pieces.
By winding up the propeller, these bands were twisted tightly, and when the propeller was released, the bands unwound, causing it to revolve rapidly.
The rudder was now pivoted in position by brads, and the two planes fastened by the same method.
The power derived from the bands was not sufficient to propel the aeroplane fast enough to support it in the air, so it was necessary to experiment with strong thread until the centre of gravity was found. It proved to be near the centre of the planes. Small holes were made with an awl at this point, the thread passed through them and tied. By suspending the aeroplane from a chandelier it took up a horizontal position.