Practical Construction: Planes
There is little difference of opinion regarding the construction of
the planes of a model aeroplane, and the methods of making can be
classified under three headings—cane, wood, and wire.
There are advocates for each form of construction, and it is difficult
to state definitely which is the best practice, each having equally
good results. The wire plane, especially when steel wire of the music
or piano variety is used, is much stronger, offers less resistance
to the air, and has a neater appearance than the others, but it is
slightly the heavier. A wooden plane can also be made extremely neat
and light, although it is a little weak. Birch is the best wood to use
for this purpose, as it is extremely tough and not too heavy. Where
cane is used for the frame, pinning and gluing is out of the question,
hence binding and gluing must be resorted to. A plane so made is very
strong and flexible, and will withstand a great amount of rough usage.
It is, however, not neat in appearance and hardly to be recommended,
although many prizes have been won by models possessing such planes.
Yet another form which can be considered good practice consists of a
combination of umbrella ribbing and piano wire. This gives a very rigid
and almost unbreakable plane, but its weight for small machines is
prohibitive. It should chiefly be used for power-driven machines, power
in this instance meaning any form of motive power other than elastic.
[Illustration: Fig. 58.—Wooden Planes]
=The Wooden Plane.=—In constructing wooden planes it is usual to adopt
the method shown by Fig. 58. The spars are set out to their correct
positions but left overlapping, so that the pinning operation does
not split the ends out. The pins should be driven through to secure
the frame to bench, so that it remains true until the glue has set.
Whereupon it may be prised up with a pocket-knife, and the pins
clinched over as shown in the joint analysis A. The centre rib should
be trimmed up as shown at B, to provide a means of attachment of the
completed plane to the fuselage or body of the machine. Two spars are
sufficient for models up to 36-in. span, but over that three spars
should be used, as in the part plan (Fig. 59), or two spars spaced
closer together, as in Fig. 60, may be used, with a thread trailing
edge. This gives a neat appearance to the finished plane and greater
rigidity.
[Illustration: Fig. 59.—Three Spar Plane]
[Illustration: Fig. 60.—Two Spar Plane]
[Illustration: Fig. 61.—Cane Plane]
[Illustration: Fig. 62.—Umbrella Ribbing Plane]
=The Cane Plane.=—Another form of construction that is very light
is that shown by Fig. 61. Here a length of thin cane is bent to the
form of the outline, the ribs being bent to align with the leading
and trailing edges. Gluing and binding is used here. Such a plane can
be made light, but it always has an appearance anything but neat. It
cannot be advocated for machines over 30 in. in span.
=The Umbrella-ribbing Plane.=—Umbrella ribbing can be utilised, in
conjunction with piano wire, for plane construction as shown by Fig.
62. The channel of the ribbing should be thoroughly cleaned with emery
cloth, so that the leading ends of the ribs can be soldered therein.
Three spars should be used for spans over 30 in.
For the planes of model flying machines steel wire offers exceptional
advantages, as it is practically unbreakable and can be bent to
any desired shape. Another advantage is that it offers a minimum
resistance when travelling in the air. To the uninitiated, the making
of steel-wire planes is a difficult undertaking; but if the following
instructions are carefully carried out the planes will prove very
satisfactory.
First procure a piece of wood about ½ in. thick and slightly larger
than the plane to be made, and draw on it a plan of the plane as
shown in Fig. 63. For example, it will be assumed that a plane 30
in. span and 5 in. wide, having four ribs, is to be made. For planes
approximately this size, No. 17 S.W.G. steel wire is employed. Before
beginning the work the wire should be straightened as much as
possible. Then lay the wire over the plan, beginning at =A= (Fig. 63)
and passing round to =B=. As the wire is bent to the shape of the plan,
it must be fastened down to the board by means of small staples. Then
cut four pieces of wire for the ribs =C=, =D=, =E=, and =F=, allowing ½
in. each end for turning at right angles as in Fig. 63.
[Illustration: Fig. 63]
[Illustration: Fig. 64
Figs. 63 and 64.—Making Wire Planes]
The framework is now ready for soldering together. It is essential that
the wire and soldering bit must be perfectly clean. Apply a little
killed spirits of salt to the parts to be soldered, and then place a
piece of solder in position and touch with the hot soldering bit. Care
must be taken to see that the wires lie close together.
When the plane is soldered together remove all the staples and clean up
all the joints with a file. The joints must now be bound round tightly
with fine iron wire, which must be perfectly clean. The plane must now
be fastened to the board again, and all joints soldered again. When
the soldering is completed the plane is once more removed from the
board, straightened, the dihedral angle given, and the ribs bent to the
desired camber. If the soldering has been carefully accomplished there
is no fear of the joints giving way.
[Illustration: Fig. 65.—Swept-Back Wing]
For covering planes it is far better to purchase a waterproof silk
especially manufactured for the purpose than to attempt to use ordinary
silk. The silk varies in weight from 1 oz. to 1½ oz. per square yard.
When cutting the silk about ½ in. must be allowed for turning over for
fastening. At the curved ends of the plane slits about ½ in. apart
must be cut in the edge of the silk, as shown in Fig. 64. Apply a
thin coating of glue to the silk (use seccotine) to be turned back,
and allow sufficient time for the glue to get tacky. Then stick over
the plane, beginning at =A= (Fig. 64) and finishing at =B=. Allow time
for the glue to set, then fasten the opposite end in the same manner.
Care must be taken to stretch the silk tightly, so that it is free from
wrinkles. Then fasten first one side of the plane and lastly the other.
Another method of covering steel-wire planes is to lace the silk to the
framework. The silk must be cut about ¼ in. larger than the framework,
and the edges hemmed with a sewing machine. The silk cover when hemmed
should be slightly smaller than the framework. First sew the silk
roughly in position, and then carefully sew it, beginning at one end,
following with the other end, and lastly the sides. The stitches should
first be passed through the silk, and then round the wire at intervals
of about ¼ in.
Fig. 65 is the plan of a swept-back wire plane. The plan should
be drawn full-size on a board by means of squares, the contour of
the plane being contiguous in relation to the squares as that in
the illustration and the method outlined above followed. The ribs
should also be fitted up to the outline, being bound and soldered
to the piano-wire frame. For machines above 30-in. span a third
strengthening spar should be fixed in the position of the dotted line
to obtain rigidity. Two central ribs should be fitted to provide a
spar-attachment. The tips require to be set at a slight negative angle
as at =C=.