BUILDING THE MOTOR
A WELL-CONSTRUCTED glider alone makes a fascinating toy, but once the motor has been installed it seems almost alive. Your little craft will now be ready for new conquests. It will imitate the flights of the famous aviators, contending with the same problems, perhaps meeting similar accidents.
The motor is the most interesting, as it is the most important, detail of the aëroplane. Although it is possible to buy the propellers for the motor, it is advisable that every boy should work out this problem for himself. An effective motor is easy to build, and costs practically nothing. The length of your propeller-blades should be equal to about one third the width of your largest plane. For this you will need six strips of some light wood, such as pine or ash, although a cigar-box wood, if the grain be straight, will answer. Cut the strips to measure about half an inch in width and one eighth of an inch thick. (See Plate B.)
THE PROPELLER BEFORE CUTTING DOWN.
Plate B.
The strips should be covered with a thin glue and laid one on top of another, and a very thin nail be carefully driven through the little pile at the exact center between the two ends. While the glue is still soft, turn the sticks on the axis formed by the nail, so that they make a double fan, spacing the outer edges about one quarter of an inch apart. Be certain that the fan is regular, and then give the nail a final rap to tighten its hold and keep all the glued surfaces together, and set away to dry. If you can prop up the ends it will be better to put a flat-iron or other weight on each end to make the strips glue together tighter.
The thrust or propelling power depends as much upon the curves of the propeller as upon the force with which the motor is driven. If the propeller be too flat, it will not take hold of the air, while if the pitch or angle of the curve be too sharp, it will simply bore holes in the air and create a vacuum which is useless. The pitch should be about one in twelve; that is, if the propeller-blade be twelve inches long, the curve should be one inch high.
When the glue is thoroughly dry and hard the projecting step-like edges may be cut away. A flat chisel or an ordinary pen-knife will do the work. Be careful to keep the ends uniform, since much depends upon the balance. Cut away the wood until the blades are one eighth of an inch or less in thickness, and round off the corners. The propeller should then be sandpapered perfectly smooth and varnished. You will be delighted to find how professional and shipshape the finished propeller will be.
Now carefully remove the nail fastening the pieces, and you will find, of course, that it marks the exact center and forms a perfect axis. Should you need to enlarge this hole, do not attempt to bore it, since this may split the wood, but burn it out, using a nail heated over a gas-flame. Now insert a stiff wire in this hole—a hat-pin will answer—and fasten it by clenching it at the back tight to the propeller, and fill up the hole with glue. The photographs of the propellers of various models will give you an excellent idea of the proper curve.
Aviators differ as to the proper position for the propellers in toy aëroplanes. Here is a problem you must work out for yourself. Some believe that the propeller placed in front of the planes gets a firmer grip on the air, since when the propeller is at the stern the planes make many disturbing currents, just as a steamship churns the water in its wake. Others argue that by placing this propelling force at the rear of the planes the craft is made more steady. At any rate, excellent flights may be made with either arrangement.