MODEL AEROPLANES.
=Self-propelling air devices= must be of the lightest possible weight
and yet they must have strength. There will be no attempt to give a
great variety of model aeroplanes; but a few can be discussed, perhaps
three or four. The first is a little practice model that has been of
great service to me, both for study and for instruction to others. It
is small and will not fly far. I can wind it up and turn it loose in a
schoolroom. It hits rather hard sometimes but nothing has happened to
it beyond a broken propeller, and the rubber bands that are used to tie
the planes to the spine have been broken.
[Illustration: FIG. 220.]
In Fig. 220 the model is shown in two views, the plan and side
elevation. The planes are made of 1/16” birch veneer, but other woods
will do. The small fore plane is bent at quite a sharp angle and was
shaped as shown in Fig. 221. Steam the plane thoroly over the teakettle
and place it under pressure until dry and it will remain so bent. The
plane is also tilted up a little by means of a small wedge.
[Illustration: FIGS. 221, 222.]
[Illustration: FIG. 223.]
The spine is made of spruce and is ¼” × ¼” × 12”. The large plane has
about ⅛” camber and is bent as shown in Fig. 222. Lay a strip as thick
as the desired camber on a board that you can nail brads into. Steam
the veneer for the plane and lay in the ⅛” strip in this case about
one-third the distance back from the front edge, bend down until the
edge touches the board underneath the strip and drive brads in slanting
so as to hold it down. The brads can be bent down a little after they
are driven in. By using brads on both sides the veneer can be held down
until dry. The outline can be cut away before or after the bending.
The decoration of course is not essential, but it is interesting to
beautify it a little. The anchor block for the propeller shaft is of
wood ¼” × 1” × 1” and is glued and nailed with brads to the rear end of
the spine. A piece of tin ⅜” wide is bent about the top of the anchor
block, _f_, Fig. 223. The hole in the wood should be larger than the
propeller shaft while the hole in the tin should make a good fit. In
this way the bearing is on the tin instead of the wood, and reduces the
friction to a minimum. After the tin is on, the block should be wound
with linen thread and coated with glue or shellac.
[Illustration: FIGS. 224, 225.]
The propeller shaft is made from a bicycle spoke, Fig. 223; two of
these can be purchased for a nickel. The long nut, shown at _b_, is
cut with a metal saw in two places, giving small nuts _c_ and _d_; _c_
is used on the inside and _d_ on the outside of the propeller. The
spoke is then cut off long enough to pass thru the propeller, a glass
bead as a washer, and the anchor block, with room for a good hook on
the end for the attachment of the rubber motor. The propeller will be
discussed further in the next chapter; the only thing to be mentioned
here is the size of the blank from which it is made, which is ½” × 1” ×
4”. Another piece of the spoke is bent as in Fig. 224, and is inserted
in the fore end of the spine and bent still further into shape like
Fig. 225. This gives the other anchor hook for the rubber motor. One
other piece is the small keel shown in the side view. A groove is made
in the under side of the spine and the keel set in with glue.
I am using four rounds of 1/16” rubber string for the motor. That
makes eight strands. Six do very well. This is a very useful little
model but it will not fly over fifty feet, or mine has not, but the
fact that it does not fly far, gives you opportunity to study its
start, its landing, and its flight. The long distance models are out
of observation range so soon that we miss the chance to diagnose their
crazy symptoms, if they have any, and most of them have some.
[Illustration: FIG. 226.]
At the beginning of model aeroplane making, everyone seemed to try
to see how much surface could be exposed in the planes, now the best
models are those with as narrow planes as it is possible to use and
still support the air craft. The reason is obvious--there is so much
skin friction on broad surfaces. At the beginning, many were inclined
to scoff at the rubber band motor, but since flights have been made
considerably over a half mile, with this same power, it seems good
enough for anybody. Most of the long distance flyers have long
framework so as to accommodate long strands of rubber, which allow much
increase in the winding up of the motor.
[Illustration: FIGS. 227, 228.]
=A Good Model.= A simple and effective model is shown in Fig. 226. Lay
out a light framework, as shown in Fig. 227. It is the combination of
a tailless kite and a triangular box-kite. Three long sticks, _a_,
_b_, _c_, are used for the triangular portion and three cross-sticks,
_d_, _e_, _f_, are for the wing supports. A vertical post, _g_, about
¼” × ⅜” × 8” is used in the center of the rear (the wide part), to
stiffen the frame and give an anchorage for the propeller shaft. Four
light braces, _h_, _i_, _j_, and _k_, make it possible to use lighter
material than one would suspect for the entire framework. In a model
3’ long, _a_, _b_, and _c_, need not be larger than 3/16” square, but
there must be no split or uneven places in a stick so small. The braces
⅛” × 3/16” would be plenty large. The two upper pieces, _b_, _c_,
should be flattened on the inside of the front end so as to make them
join together, terminating in a point. The lower spine, _a_, should
be flattened on the upper side for the same reason. All three should
be glued and lashed together with linen thread. A triangular block,
_l_, should be placed about 4” back from the front end with a strong
cup-hook screwed in the side toward the rear, on which the ring of
the rubber motor is attached. The block, _l_, must be well secured to
the triangular framework with glue and thread. The cross-piece, _d_,
is 30” long and is bowed upward as is shown by Fig. 228. Piece _e_ is
24” long, 5” in front of _d_, and both are 3/16” × ¼”. ⅛” × 3/16” will
be heavy enough for _f_, and this should be bowed much more than _d_,
and _e_. It will be necessary to steam this piece a little. Chinese
rice tissue will be good for covering. Cover the underside of the two
planes, and the underside of the triangular framework which is similar
to the hull of a boat, and acts as a keel. Test out well as a glider.
Put more and less curve to bows, and experiment for poise of model. A
small piece of tin on each side of the support will give a good bearing
for the propeller shaft. The hole in the wood should be a trifle larger
than the shaft. String is run from both ends of _d_ and _e_ to the
front end of the framework but is not attached to _f_.
[Illustration: FIG. 229.]
When long models are made with single spine, they need some simple
wire supports to prevent springing up or down, and from left to right.
Fig. 229 is 4’ long and the spine is only ¼” × ¼” at the small end ¼”
× ⅜” at the larger end. A little 1/16” oak veneer cut in strips 3/16”
wide would be very serviceable for the purpose of support in trussing
the long spine. It should stand 2” above and below the spine, and the
same amount for the right and left brace, Fig. 230. The wires for these
should extend about a foot on each side of these posts, and be attached
to the spine with little tin anchors, as shown in Fig. 230, _a_.
[Illustration: FIGS. 230, 231, 232.]
The propeller shaft bearing is of metal and is lashed to the
cross-piece, called the base, Fig. 231. It is not necessary to have
two points of bearing for the shaft. The metal is about 1/16” × ¼” ×
1”, bent as in Fig. 232, and lashed to the under side of the base. The
planes are similar to those in the next model. 1” × 1½” × 7½” propeller
blanks are used. Try about fourteen strands of 1/16” string rubber for
each motor, seven rounds.
[Illustration: FIG. 233.]
=My favorite model aeroplane= is shown in Fig. 233. It had made some
very pretty flights when it took a notion to glide into a young man’s
bicycle as he was riding by. Well, there was no improvement on the
aeroplane when the chain and spokes of the bicycle were thru with it.
[Illustration: FIGS. 234, 235, 236, 237.]
The framework is light and is spread well at the rear. The two spines
are 3/16” × ¼” × 33” and they come together at the forward end, the
vertical section being ¼”. Nine inches back from the front end is a
cross-piece that is just under ⅛” in thickness, ¼” wide and 2½” long.
The cross-piece is on the upper side of the spines, and is fastened by
a small ¼” brad, is lashed with thread and coated with glue or shellac.
The other cross-piece is 1” forward from the rear end, is of the same
dimensions in cross-section as the forward piece, but is 8” long and is
secured in the same manner as the other, see Fig. 234. The framework
is further stiffened by two fine wires that run diagonally from the
ends of one cross-piece to the ends of the other. They are secured to
the inside vertical face of the spines by means of small pieces of tin
that have two small holes, one at each end, the one receives a ¼” brad
that is driven into the spine, while the wire is attached to the other
hole. The little pieces of tin are about 3/16” × ½” and are lashed to
the spine in addition to the fastening by the small brad. This kind of
fastening prevents slipping, also the cutting into the wood, either of
which would destroy the efficiency of the wire. In order to increase
the tension of the wire, a small turn-buckle is inserted, Fig. 235.
[Illustration: FIG. 238.]
[Illustration: FIGS. 239, 240.]
[Illustration: FIG. 241.]
The bearings for the propeller shafts are lashed to the outside face of
the rear end of each spine, Fig. 236. The bearing is a piece of brass
1/16” × ¼” × 1”, and is bent to a right angle at the middle. A small
hole is drilled for a brad into the side of the spine and the other
hole is drilled to receive the propeller shaft, which is 1/16” steel
wire. The shaft is bent into a hook after it passes thru the bearing.
To prevent the rubber of the motor from touching the steel wire, which
is injurious to the rubber, a small rubber hose is slipped over the
hook. In this model, the propellers are pieces of veneer steamed and
pressed into the spiral shape. The propeller shaft then is bent around
the center of the propeller, has two little washers between this and
the bearing, after which comes the covered hook, see Fig. 237. A piece
of tin ½” wide and 1¼” long is folded about the propeller before the
shaft is bent around. The shaft is soldered to the tin, the tin being
secured by two small brads and shellac. A small tin rudder with a small
fold in its upper portion may be slipped over the back cross-piece,
Fig. 238. The fore plane is made of very thin spruce, shaped like Fig.
239, and is bent up almost like a butterfly’s wings, Fig. 240. The
wood is less than 1/16” thick. A double hook as anchors for the double
motors, is bent and secured about the fore end of the framework. The
hooks are covered with the rubber hose, the same as the propeller
shaft, Fig. 241.
[Illustration: FIG. 242.]
The large plane is 4½” in the widest place and is 20” long. It is the
shape of Fig. 242 in outline, the straight side being to the rear. The
outline of the plane is a steel or brass spring wire 1/16” diameter
and is spliced at the center of the long sides, being soldered at
this point. The ends of the wire lap over an inch or more. There are
but two ribs which are 5½” from the outer ends. The ribs have a slight
curve upward, most of it being near the free edge of the plane, Fig.
243. The ends of the ribs are bent at a right angle and are soldered
to the outside framework of wire. The cover of the plane is made of
prepared silk and is made ¼” larger all around than the size of the
outline of the wire frame. A ¼” hem is then turned which gives strength
to the edge. The cover is now over cast with needle and thread to the
framework, stretching fairly tight.
[Illustration: FIG. 243.]
The framework of the large plane is not secured directly to the wooden
framework of the model, but is soldered to wire loops that in turn lie
flat on top of the spines of the frame, Fig. 242, _a_, _a_. This gives
opportunity to tie with string so as to try out the model. If it is too
far forward, it can be slipped back and vice versa; when the correct
position is located, it is permanently wired to the wooden framework.
The fore plane is attached by means of rubber string. This is known as
the Mann monoplane, and is a commercial product.
The propellers will be further discussed in the next chapter.