An aëroplane to be considered shipshape must be even more perfect in every detail than the finest racing yacht. Go over your model, scrutinize every detail; if after taking every precaution, your planes do not fit like the sails of a racing yacht, cover them with a thin solution of paraffin. On hardening, this will hold the material perfectly smooth, so that the planes will offer a perfect lifting surface.
The amateur aëronaut must be prepared for disappointments. An aëroplane is one of the crankiest crafts in the world to manage. It may twist and turn, plunge in and out, up and down, apparently without the least excuse. There is always, however, a good reason somewhere for its behavior. As you learn its ways, which, after all, are very simple, the flights will be longer, swiftier, and steadier. There is no toy in the world which so quickly repays one for patience and perseverance.
CHAPTER V
FINE POINTS OF CONSTRUCTION
A GREAT many experiments have been made to find whether the flat or curved wings give the best support, and how sharply the curve should be drawn. The wings of birds are curved slightly upward, and in the end, after all the experiments, it has been found that this curve is just the right one. All forms of aëroplanes will fly more swiftly and steadily if the planes be slightly bowed or flexed. After you have built your aëroplane with flat wings it will repay you to replace them with flexed planes, and you will find that the experience in building models will make this construction very simple.
The lighter and more flexible materials, such as bamboo or cane, are best for the curved planes. After you have decided upon the dimensions of the wings cut the pieces for the ends slightly longer than the width of your planes. These pieces may then be bent by steaming them over a kettle of boiling water and bending to the desired curve. When dry they will hold their shape remarkably well. Another plan is to use a flexible strip and pull the ends together by a strong thread or wire until the wood is bowed to just the right curve. A corset steel or whalebone may readily be curved in the same way. It is a common mistake to curve the plane too sharply, when the resistance offered to the air will be greater than that with the flat plane.
A plane two or three feet in width cannot be held in shape merely by curving the end pieces. A series of ribs must be added at equal distances, each having, of course, exactly the same upward curve. The ribs may be fastened to the sides of the planes with small brads or simply with glue or wire. The covering should then be drawn down. A very smooth covering may be made of rice-paper. Cut the sheets the proper size and lay them for a few minutes between moistened cloths. Now stretch the paper carefully over the frame and glue in position. When dry the paper will contract and leave a smooth, taut surface like the head of a drum.
Much depends upon the curve of the plane. A wing whose curve is not a perfect arc of a circle, but which is rounded just back of the front edge and flattened at the rear, will be found to offer the least resistance to the air. The best plan is to study the curves in the aëroplanes or models and imitate them. Different models require different planes. It is a problem which each young aëronaut must work out for himself.
A Model Aëroplane Built from the Drawing ([Plate C], Chap. IV).