A very satisfactory monoplane can be made from the plans shown in Fig.
49.
The material for the frame should be quarter-inch white pine or spruce.
The six long strips are 30 inches in length, and for fastening, holes
should be drilled and the connection made by passing fine soft wire
through them and binding fast.
The top frame, formed of four of these long strips, should be made
first, with particular attention to the measurements, so that both
sides shall be exactly the same size and weight.
At the rear end the two long strips may be wired together temporarily.
The propeller shown in the drawing can be made at any time from a piece
of white pine 7/8 inch thick and 12 inches long by 1-3/4 inches wide.
It is a good piece of whittling work.
[Illustration: Fig. 49]
[Illustration: Fig. 49 (a). The toy monoplane.]
The 3/8-inch hole for the shaft should be bored first, and the
propeller blades reduced to a thickness of 1/8 inch at the centre of
the blade, and 1/16 inch or less at the edges.
The shaft needs to be strong, and should be made of a piece of 3/8-inch
dowel rod. Make a saw cut with back saw in the end, which is to be
fastened in the propeller.
When ready to assemble, push this end into the 3/8-inch hole in the
propeller, drive in a soft pine wedge with a little glue, and a rigid
fastening will result.
The groove in the rear end of the shaft is to take the thrust of the
propeller, and hold it in the machine. This groove may be readily cut
out with the knife, and smoothed with sand-paper. Two bearings are
necessary to hold the shaft in alignment. The forward one is a strip
of pine 1/4 by 3/4, with a 3/8-inch hole bored at the centre. This
hole should be sand-papered until the shaft turns in it freely. The
rear bearing is a strip 5/8 by 3/8 inch, laid out as shown at _a_. The
quarter-inch hole must be bored first. Next, drill two small holes with
a fine drill on either side of the hole for the wires which are to hold
the two pieces together. Next saw on the pencil line shown, removing
the small piece _x_. Test the bearing by placing the small grooved
section of the shaft in the quarter-inch hole to see if it turns
freely. When this has been accomplished, the propeller and its bearings
are ready for the monoplane.
Looking at the front view, the two uprights are 9 × 3/4 × 1/4 inches.
At the top ends they are rabbeted as shown, and wired to the top frame.
At the bottom they are wired to the long strips which form the long
sides of the bottom frame.
Before putting these uprights on, a 1/4-inch hole should be drilled
1-1/2 inches from the bottom of each. These are to receive the 1/4-inch
dowel rod which acts as the axle for the spool _s_. This rod should
be 10 inches or more in length, so that brads or wire may be passed
through the ends outside the uprights to keep the axle in place.
The small spool which acts as a pulley must be perfectly free to turn
on this rod, and be kept in place by two brads driven through drilled
holes on either side of it.
The front and lower parts of the frame are now ready to be assembled.
The four long strips constituting the body of the frame are all wired
together at the back, temporarily. To finish the forward part, saw out
a strip 3/8 × 1/4 inch, and form on each end a rounded bearing, as in
the automobile, for two wheels 1-3/4 inches in diameter. Saw the wheels
out of 3/16-inch basswood, drill a hole at each centre, place on the
bearing, and fasten in place with a flat-head wire nail and a small
washer next to the wheel. Sand-paper the wheels smooth, and see that
they turn freely. Tack the strip, or wire it to the uprights, as low
down as possible.
The rear end of the monoplane is a nice little problem. Cut out a block
of pine from 1 inch to 1-1/8 inches square. In the side facing the
front place a screw eye for fastening the spring or rubber bands.
The rudder is shown in the drawing. Drill two holes, as shown, and
drive in brads or flat-head wire nails, as large as the hole, so that
the rudder may be turned by hand, but not free enough to turn with the
wind.
Next drill a hole clear through the block for the axle of the tilting
planes.
It is not necessary that the axle be at the exact centre of the cube.
It should extend quite through both planes as well as the cube, and be
bent around the edges, so as to make them rigid. They should be snug
enough to turn by hand, but not loose enough for the wind to shift.
The four sides of the frame are now whittled down to fit the block, and
wired to it.
Last comes the question of motive power.
This is _the_ great problem. The writer is opposed to encouraging
boys to believe that these toy aeroplanes can be made to fly great
distances. The propeller would have to be made to revolve at high speed
for several minutes in order to accomplish this, and the tension of
rubber bands is not equal to it. The machines can be made to fly short
distances only. The problem of aviation is now a question of motors,
and the smallest gasolene motor, with its tank, etc., requires a fairly
large aeroplane to lift it. No doubt, the problem will be solved within
a short time, but it has not been done at the time of writing.
For this size of toy monoplane several large rubber bands may be tied
together, fastened at the screw eye on one end and to a piece of strong
linen kite cord at the other.
Pass this cord forward under the spool and up to the propeller shaft.
Drill a small hole in the shaft, draw the cord taut, and fasten it
through this hole.
While the model has no planes as yet, it is wise to get the propeller
working before putting them on, as the space for working is freer.
Wind up the propeller until the bands have been stretched to their
limit, then let go. It may be necessary to place wheels at the rear,
the same as in front. On a smooth floor, the machine should be drawn
forward several feet by the action of the propeller.
It is entirely practicable, on a plane of this size, to use the works
of an ordinary alarm clock in place of rubber bands.
Remove the outer casing of an old clock; loosen the four brass nuts
that hold the frame together, and take out all the wheels, except the
axle on which the mainspring is fastened. Put the frame together again
with the four nuts.
The axle for the mainspring extends outside of the frame, and is
threaded to receive the handle for winding. Take this handle off. Drill
a hole in the end of the propeller shaft, slightly smaller than the
mainspring axle, and screw the latter into the propeller shaft.
You now have the clock-works on the end of your shaft, and it is
necessary to fasten a strip of pine 1/2 in. by 1/4 in. to the upper
sticks of the frame in order to wire the works fast, as they must not
be allowed to turn. By turning the propeller you wind up the clock, and
as soon as you release it, as there is no escapement now to regulate
the spring, it tries to unwind at once, and the propeller starts at
terrific speed. Look out for your hands, as the propeller blades have
no conscience.
This action, although strenuous, is short lived, but much more powerful
than rubber bands. The spring of an ordinary alarm clock is powerful
enough to drive a wooden two-bladed propeller 12 inches in diameter
with blades two inches wide at the outside. It will draw a monoplane of
this size along the floor several feet.
Having finally decided the question of power, it remains to attach the
planes.
The remaining long strip is wired to the top pieces, 12 inches from
the front, and the plane, made of silk, oiled paper, or very thin
card-board, attached.
In many toy aeroplanes the bands of rubber are not stretched, but
twisted. The shaft in this case is a wire which, after being fastened
to the propeller, passes through a glass bead and then the frame,
ending in a hook to which the rubber bands are attached. There must be
a perfectly clear space from front to back of the frame. The glass bead
between the propeller and frame is to relieve the friction.
X