Harper's Outdoor Book for Boys

by Joseph H. Adams

It only remains now to make the screw and attach the rubber band. For the hub of the wheel you will need a small cork. This cork must be kept from turning on the end of the shaft. If the sharpened end of the shaft carrying the hook for the rudder was simply stuck into the cork, it would soon wear loose and turn easily. To make a firm hold for the shaft, bore a hole through the cork about a quarter-inch from the large end, and drive a plug of soft wood into this hole. The flat-pointed end of the shaft can now pass into the cork and be forced into the wood, being careful to have the end of the point parallel to the grain of the wood. This will give a firm hold and prevent the screw slipping.

The blades of the screw are made of thin paper gummed on to short pieces of bamboo. Lay one of the bamboo spokes on a piece of thin, stiff paper, and then gum over it a small strip of the thin Japanese paper before referred to. When this is dry, cut it down to the proper shape and sharpen the end of the spoke. Force these spokes into the cork so that all the blades will turn the same way, as shown in the picture—i. e., so that when the screw is turned the blades will all strike the air in the same manner and tend to force the machine forward, not so that some try to push it forward and some backward.

Select a rubber band of the proper size—such a one as will stretch the length of the backbone easily and not be so strong that, when stretched, the backbone is bent into a bow. Tie this band to the forward support with a string, and then draw it back and slip it over the hook on the shaft.

To wind up the machine, hold it by the backbone and turn the screw the wrong way until the rubber is twisted tight. Then hold the machine up, let go the screw, and when it is revolving rapidly, give it a gentle push forward. If it pitches head-first, draw down the wings; if tail-first, let up the wings or turn the screw the other way. If the wheel does not revolve rapidly cut off part of the blades or use a stronger rubber. Some little adjustment of the kind is usually required before the thing moves properly.

A contrivance of this sort should be very light. The one before me has wings two feet from tip to tip, and it weighs when complete—backbone, wings, rubber, screw, etc.—only one-third of an ounce.

Self-acting Aërial Car

Here is an idea for a mechanical toy to be used either on a kite-string or a cord stretched from a flag-pole in the yard or a handy tree. The only condition is that the lower end of the cord is directly against the wind. The elevation at which the car can run will depend on the strength of the wind and sail area of the machine. The only wood used is the lightest and driest pine that can be procured. The carriage is made entirely of one-half by one-quarter inch wood, and is composed of two strips, fourteen inches long, placed one inch apart. The two guiders are two inches from each end, and have a small screw-eye on the lower extremity, through which the cord is passed. On the upper side of the carriage, exactly in the centre, are screwed two eyes, which should measure a little over a half-inch in diameter of the inside of their circle. Through these is passed the spar of the sail, allowing enough space to insure easy turning, as the spar acts as an axis on which the sail turns when on its downward trip. This spar is at right angles with the carriage. Two upright sticks measuring twenty inches, and the same dimensions as the material used for the construction of the carriage, are next added. These should be slightly pointed at both ends, and a cross-bar at the top of these uprights securely fastened gives additional strength. The balancing-bar is made of three-eighths by three-eighths inch pine, tapering at the lower end, and is ten inches in length, and fastened to the carriage by two strips of wood—five by one-quarter by one-eighth inch. The wheels are formed as follows: Take a piece of one-eighth inch pine, which should be at least three inches wide. On this place a strip of wood, we will say, for instance, ten by one-quarter by one-half inch. By driving a small wire nail through both pieces of wood, and inserting a sharp knife-blade through the upper piece of wood, and turning (the upper piece) slowly from left to right, you will find you can cut a perfect circle in the lower piece of wood. The wheels are formed by this process. It takes four pieces of stiff card-board and two of wood to make the wheels for the carriage. The diameter of the wooden wheel is one and one-half inches, while the card-board disks are two and one-quarter inches. The wheels in the draught are a trifle smaller, but by experiments it is found that the above-sized wheel makes faster time. You will see that after cutting out your disks the hole made by the wire nail is exactly in the centre. Run a small wire nail through the three disks, placing the wooden disk in the centre and the card-board ones on each side (this makes three disks for each wheel). Put some glue on touching surface, and clinch the three together with pins or wire brads. The place where these nails go is shown by the spots on side draught of the wheel. The axle-tree is made of oak, and at the extremities a piece of stout wire is inserted, which extends one-eighth of an inch beyond the wood of the axle-tree. The hardest axle-tree is one made from the shafts of an old clock. Take particular care that the wheels run very true, as the success of the machine depends to a great extent upon this.

From the lower extremity of the balancing-rod hangs a weight. The easiest way to make this weight is to take a small bag, and fill it with sand until the machine balances (the sail in horizontal position). Having progressed thus far in the construction of the machine, turn the sail in a horizontal position, and attach a cord from one side of the cross-bar to a small grooved wheel at the aft end of the carriage. From the screw-eye at lower extremity of the balancing-bar is attached a small rubber band; when stretched it will reach within three-quarters of an inch of the small wheel at the aft end of the carriage. It will be found, after the cord and rubber band have been joined, that upon letting go the perpendicular bars the sail will turn in a horizontal position. At the forward end of the carriage is a catch, to which is fastened a ring. The catch comes in contact with a block (previously placed three-quarters up the string). The detail drawings show the formation and working of the catch. Fig. 4.