The main plane is one of the best examples of construction work to be found among all these models. It is well proportioned and the curve has been skilfully drawn. The plane is made unusually rigid by a series of supports or braces run both horizontally and vertically. Such a plane calls for considerable time and patience, but it will well repay the builder by the long and steady flights it insures for the model. In adding ribs to a large plane of this kind a convenient material may be prepared by splitting up thin wooden plates or dishes, such as you buy at the grocers for a penny. The strips obtained in this way may be easily glued or tied to the edge of the plane and shaped as desired.
A long, straight flight is insured for this model by equipping it with three vertical rudders or guiding-planes. The first rudder is well placed above the front plane. The second performs a good service beneath the main plane, while the third is carried unusually far back behind the propellers. The problem whether a rudder is more effective above or below the planes is very ingeniously solved in this case by placing them in both positions. An interesting principle is involved in placing the rear rudder. By fixing it far behind the center of gravity of the model a considerable leverage is obtained, and a small, light rudder becomes more effective in this position than a much larger plane placed forward. These rudders are built so that they may be easily turned from side to side and fixed rigidly at any angle.
PLATE IV.
One of the Simplest of Aëroplanes to Construct.
Still another interesting feature of this model is the design of the skids. The model is supported at an angle which enables it to rise easily. These skids are besides arranged with shock-absorbers, simply constructed with elastic bands, which enable them to take up the shock on landing and thus protects the machine. This is an interesting field of experiment and a little care in building these skids will save many a smash-up.
It cannot be too often stated, that the supporting power of the planes depends far more upon their shape than their size. A remarkably effective model may be made with planes, which are little more than blades ([Plate 8]). The planes, in this case, are made of white wood, slightly curved. The front or entering edge is very sharp, while, at the rear, a thin strip of shellaced silk is glued, thus forming a good soaring blade. The front plane is a counterpart of the first, except that it is smaller. The only stability plane is a thin, knife-like strip placed vertically just before the rear plane. The model is mounted on skids. It is driven by a small propeller placed far back of the center of gravity. It is probably the easiest as it is the smallest of all models to construct, and will fly for more than three hundred feet.
In building this model it will be found a good plan to bend the strips of wood for the planes by steaming them over a kettle. Allow the steam to play on the under or concave side of the plane. When dry the plane will retain its shape. The front or entering edge should be trimmed away to a sharp line and sand-papered perfectly smooth. The front corners of the planes should be slightly rounded while the rear edges are kept straight. The forward plane should be tilted slightly upward to enable it to rise, but at an angle of less than thirty degrees. The secret of the remarkable flights of this model probably lies in the smoothness of its planes and the absence of irregular parts which offer a resistance to the air.
An interesting field of experiment, as yet almost untouched, lies in the triangular, or narrow-prowed forms of aëroplanes ([Plate 9]). The theory of this model is, that a triangle entering the air end-wise, will meet with less resistance than when presenting a broad, entering edge. The model is, frankly, an experiment, although it has been found to have unexpected stability, and flies well. Its central planes, joined at right angles, is supported by two, lateral, stability-planes, radiating backward from the front of the model. The aëroplane is drawn, not pushed, through the air, by double propellers, and is steered by an angular guiding-plane at the rear. The planes are mounted upon a triangular frame, which runs on wheels, two being set forward and one aft. The planes, taking advantage of the dihedral angle, seem to rest upon the air, which makes for stability. In actual practice, however, the planes in this particular model have been found to be too narrow. The question naturally arises as to the effect of reversing this model and turning the dihedral angle of the central plane, into a tent effect. As a matter of actual experience, the model flies almost equally well upside down.
In many of the early attempts to build aëroplanes the wings or planes were tilted sharply upward from the center thus forming what is known as a dihedral angle. This form served to lower the center of gravity and, it was thought, made for stability. The Wright Brothers found that this plan, although it lowered the center of gravity, caused it to move from side to side like a pendulum, and therefore abandoned it in favor of the flat curved wing which have been so generally imitated. Now this model returns to the old principle of the dihedral model, but treats it in a new way. By building the model with three planes, each with the dihedral angle, the center of gravity has been lowered and, at the same time, the oscillation has been greatly reduced.