By the term "fusellage" or frames, that part of the aeroplane which
serves as the "backbone" and to which all the other members are attached
is implied.
The fusellage above all must be strong. The second requisite is
lightness. The simplest frame for a model aeroplane is a long straight
stick. The cross section of the stick may vary and be either round or
square. A careful workman, however, can build them of "I" section like a
steel girder. Increased lightness and strength is the result.
[Illustration: FIG. 21. A simple "motor base" or fusellage.]
A single skein of elastic when wound up tends very strongly to twist the
framework of the machine out of true. Since the tail and elevator are
usually attached to the ends, the adjustment is thrown out to a marked
degree and the flight of the machine is liable to be erratic.
We have tried building the fusellage of a network of girders such as the
Bleriot and Voisin aeroplanes employ. Nothing could have been prettier
than these carefully designed and constructed frames with their little
struts and guy wires, but we soon found that for plain ordinary everyday
efficiency, the simple stick is the best, provided, of course, that it
is of the proper size to resist the twist of the rubber.
In some cases it is desirable to retain the framework because of the
realistic appearance of the model to the larger machines which it gives.
The only practical method then is to employ a plain stick backbone to
withstand the torque of the rubber and build a false framework around
it. The framework need only be strong enough to support the fabric and
resist the shocks of landing. This method of construction is best suited
to models of the Bleriot and Antoinette types.
The only type of frame consisting of a single member which will resist
the torque of powerful rubber bands successfully is a tube. The rubber
skein is placed inside the tube which may be of wood, paper or aluminum.
[Illustration: FIG. 22. Paper Tube Fusellage. Part of the tube is
cutaway to show the rubber skein inside.]
Paper tubes are excellent for small machines, being exceedingly light
and very strong. They are formed by wrapping tough, unglazed paper
around a rod of the required inside diameter. The paper is well smeared
with glue and wrapped tightly. The rod is afterwards removed. Be sure
that the glue is thoroughly dry before attempting to use the tube.
In larger machines it is preferable to employ some other means of
avoiding the nuisance of a single skein rather than to use a tubular
frame. There are several ways of accomplishing this, the best one
undoubtedly being to balance the torque of one elastic by an equal
torque tending to twist in the opposite direction.
[Illustration: FIG. 23. Two methods of gearing a propeller.]
In Fig. 23, a second skein of elastic is geared to the first with equal
sized gear wheels. The second skein is placed immediately underneath the
first and is equal in length and strength. Placing one skein under the
other and not side by side as might be the first tendency allows the
propeller to be arranged centrally. The lower part of the same figure
illustrates a second method. In this, the propeller is attached to a
long shaft, the other end of which is fitted with a gear wheel. Two
elastic skeins of equal length and strength are attached to a second
gear which meshes with the first. The only disadvantage of this form of
motor is the long propeller shaft required. The objection, however, is
sometimes outweighed by the fact that it is possible to employ a small
gear wheel on the shaft meshing with a large one between the bands so
that the action of the elastic is multiplied and a greater number of
propeller revolutions secured where the length of the bands is limited
and could not be increased in order to bring about the same result.
*Skids.* It requires only very little experience with model aeroplanes
to prove the need of efficient skids on the machine. After the rubber
band motor has run down, the propeller offers considerable resistance to
the forward travel of the machine so that it does not glide properly and
causes it to land on its "nose," often damaging the propeller or front
planes. At the least, the framework of the machine is strained by such a
shock.
[Illustration: FIG. 24.]
Skids of course weigh something and offer a certain amount of
resistance, but the advantages more than outweigh those drawbacks.
Skids are usually made of piano wire, split bamboo or rattan. The skids
should not be made any larger than is necessary to protect the machine.
They do not usually take any special shape but are formed to fit each
individual case.