Principle of the Helicopter
A helicopter differs from every other sort of flying machine because it takes off vertically, the airscrew being on top instead of at the front. Here is a device that will illustrate the way a helicopter works, and if it is properly made it will rise to quite remarkable heights. It is easy to make, and will provide you with hours of enjoyment as you try to beat each record height obtained.
Get a circle of very thin tinned iron. Now draw on it, in pencil, the outline of three propeller blades. Then shape them with scissors, as shown in diagram A. Now, take some stout wire that will not easily bend, force it into a circle, slightly smaller than the original circle of tinned iron, and solder the ends. The next thing is to place the propeller blades centrally on the ring of wire, turn the projecting ends over the wire, and solder them neatly. This done, make cuts in the blades, then bend them at an angle and pierce the center with three holes. Diagram B shows exactly what you must aim at.
Three more little articles must now be contrived. For the first, take an empty cotton spool, and put in it two pegs at such a distance apart that they will fit into the two outer holes in the propeller blades. These pegs can be made easily by cutting inch lengths from the stout part of two large French nails. (Diagram C.) The second article is a holder. For this procure the wooden handle of an old screw-driver, and, instead of the ordinary piece of metal, insert a rod of iron, six to eight inches long. See that it holds firmly in the handle, and is of a suitable gauge for running through the centre hole of the propeller blades (Diagram D.) The last requirement is a length of cord.
Now for the way this little contrivance works. Hold the handle of the screwdriver in the left hand, drop the spool on to the rod, and place the helicopter on to the top of it. Now wind the string tightly round the reel and then pull firmly. The metal wheel will rise off its seating rod and soar up into the air. By winding the cord just tight enough, and pulling with sufficient strength, the blades will rise to a great height. Note that the contrivance should not be held quite vertical, but tilted slightly away from your person, in order that it may not dash against you. See also that nobody is standing in front of you. Keep your onlookers at your side, or well in the rear. Only use the apparatus in big open space.