The model airplane
described here has made flights of from 1000 to 1400 feet in a
"straight away" and remained in the air
three-quarters of a minute.
The first thing to consider in making
this model is what materials are needed. Here they are:
1. Six feet of flat oiled steel wire,
for framework of planes and ribs;
2. One sheet of bamboo fibre paper, for covering planes;
3. Two straight-grained spruce sticks three feet long by
1/4x5/16", for fuselage;
4. Two feet of split bamboo, for cross braces;
5. Three feet of one-sixteenth inch steel wire, for hooks,
etc.;
6. Two seven-inch propeller blanks, for propellers;
7. Forty-two feet of three-thirty-second inch square rubber,
for motors;
8. One egg beater, for winder;
9. One can of glue, for joints;
10. One spool of strong linen thread, for lashing joints;
11. One can of bamboo varnish, for coating planes;
12. One four-inch piece of brass, for bearings;
13. One-half dozen washers, for bearings.
The main frame or fuselage is triangular
in shape and is made of straight-grained spruce, each side or
member being thirty-five inches long by 5/16x1/4". One
end of each stick is tapered off on the inside, to form an
acute angle when fastened together, which is done by gluing
and lashing with thread as shown in Fig. 2. The other
ends are braced six and one-half inches apart by a piece of
bamboo fastened on top of the fuselage by lashing with thread
and gluing one-half inch from the rear end of each member of
the fuselage. The middle cross-brace is also of bamboo and is
fastened in the same way as was the rear brace, on top of the
fuselage midway between the ends as shown in Fig. 1.
Now two blocks are cut to form steps and are glued and lashed
tightly with thread to the top of the fuselage with the flat
sides of the blocks on the sticks, three and one-half inches
from the apex (front end). These blocks are for elevating or
depressing the front plane. The object of this is explained in
the section on Front Plane.
Bore a hole about one-sixteenth inch
through the frame from side to side one-half inch from the
apex. A piece of one-sixteenth-inch wire, 3 inches long, is
inserted and each end bent into a hook to receive the S
hooks of the rubber motors as shown in Fig. 2.
These can be made or bought. To make,
get a piece of three-sixty-fourths-inch brass
five-sixteenths-inch wide and four inches long. This is enough
to make two propeller hangers and should be cut in half and
bent with pliers to form two U-shaped pieces (see drawing Fig.
3). Or use the same amount of flat metal that you will cut
off in making your winder described later on. Now bore a
one-sixteenth-inch hole through the ends so that the propeller
shafts will turn easily. These are glued and lashed to the
rear ends of the fuselage with the ends of the U extending out
from the frame as shown in Fig. 3. For the shafts use
two pieces of wire three and one-half inches long, the same
size as the holes, and with pliers bend a hook at one end of
each wire to support the rubber motors. Push the shafts
through the holes in the brass hangers with the hooked ends
toward the front of the fuselage; place a small bead and
washer on the disengaged end of the wire shaft. Next slip the
propellers on the shafts, with the curved edges of the blades
leading. In revolving they should turn out in opposite
directions. The straight ends of the shafts are bent back over
the propellers to keep them from turning on their shafts. To
cut the propellers refer to section on Propellers.
The frame of the plane F is made
of wire; the best to use is a flat oiled steel, which will
stay bent. A piece 43 inches long is required; it is bent with
pliers to the shape shown in Fig. 1, and the ends
lapped one-half inch and fastened by gluing and lashing them
four and one-half inches from one end of the wire. This four
and one-half inch end is used as a brace or rib; and should
cross the plane frame six inches from one end of the frame. It
is held by gluing and lashing it to the opposite side of the
frame, as shown in Fig. 4. A corresponding rib, five
inches long, with each end bent one-half inch, is fastened in
the same way to each side of the frame or rim six inches from
the other end. After the frame is finished, with pliers bend
the front middle portions of the rib slightly upward (about
one-half inch) as shown in Fig. 4. This is to give what
is known as camber and increases the lifting power and
stability of the flyer considerably. The tips of the plane
frame are also bent up slightly, about 30 degrees, to keep the
model steady in flight.
Use light, strong paper; bamboo fiber
paper is the best. Lay the wire frame upside down on the paper
and cut around the frame, allowing about one-quarter inch for
turning over. The paper is glued along the edges and turned
back over the rim of the plane frame; be sure that it sticks
fast. Care must be taken to get the paper as tight as
possible, as wrinkled surfaces hinder the flying qualities.
The plane is now ready to be painted or sized with a thin
varnish; bamboo varnish is the best, spreading it evenly over
the paper. This tends to shrink and tighten the fiber, and
forms an airtight, strong surface that will give great
sustaining power.
This small plane is sometimes called the
elevating plane, as by raising or lowering it regulates the
upward and downward movement of the model in flight. It is
made of the same material and like the main plane, with the
exception that it is bent up at the ends to form a dihedral
angle of about 45 degrees, as shown in Fig. 2. This
plane has only one rib and is covered with the paper on the
underside instead of on the top. The wire for the rim and
single rib is twenty-four inches long and bent, and the rib
formed in the way described.
The small plane is fastened on top of
the fuselage three inches from the apex, with its straight
front edge over the blocks, by wrapping with a strip of rubber
tightly around the plane and frame, first over the plane and
then under the fuselage as shown in Fig. 2. The main
(rear) plane is fastened on top of the fuselage in a similar
way, with its straight front edge eight inches from the rear
brace of the fuselage.
Make four S hooks from a piece of
one-sixteenth-inch wire and hook them on the front rubber
anchorage and propeller shafts to hold the rubber. About
forty-two feet of three-thirty-seconds-inch square rubber are
needed; twenty-one feet for each motor. Make a loop in both
ends of each portion of rubber and hook one over the front S
hook, then pass the rubber around through the S hook at
the rear, back and forth, until the second loop is slipped on
a hook. Do the same with the other rubber motor.
There are two propellers for this flyer,
one a right-hand and the other a left-hand propeller. A
right-hand propeller is one of which the uppermost blade turns
toward the right as the propeller revolves in traveling
forward. Of course, a left-hand propeller turns in the
opposite direction.
In making a propeller the best way is to
buy what is known as "blanks," which can be had from
almost any supply dealer. It is then cut into shape with a
knife, which would be a good deal easier than cutting the
blank first out of a block of wood.
In making a right-hand propeller, draw a
curved diagonal line at each end of the blank at opposite
angles as shown in A, Fig. 6. To carve, hold the
blank in the left hand, cut the portion B out, starting
at the dotted line C, as shown in Fig. 6, so
that the blades will be concave, i.e., curved in as shown in D,
Fig. 7. The blank is then turned over and the portion E,
Fig. 7, is cut to follow the other side. Care must be
taken, however, not to get the blade so thin as to weaken it.
Observe carefully in the drawing how the propeller is shaped
at the middle for a hub. It is at this point the full
thickness of the blank. The same process is used for the other
blade of the propeller. The leading edge is always the curved
edge.
When the four sides are finished,
sandpaper the surfaces until they are perfectly smooth. The
propeller should now look like Fig. 8.
To make a left-hand propeller, the
curved diagonal line at the beginning is drawn at an opposite
angle, and the opposite cutting operation is carried out.
It would take altogether too long to
wind up the rubber motors by turning the propellers. One of
the best ways to accomplish the winding is to make a winder
from an egg beater, which is shown in Fig. 5, although
a better one can be made from a hand drill. The two beaters,
of flat metal, are each clipped three inches from the gear
wheels on one side and one and three-quarters inch on the
other. Then slip in the gear wheels with the attached pieces
of metal down on the heavy wire on which they revolve and cut
the wire off three-quarters inch from the cast iron bracket to
which the ends of the wire are bound.
Now put the gear wheels and the attached
metal extensions back on these three-quarters-inch wire stubs,
and hold them there by soldering on a piece of brass tubing
that will just fit on the wire stub or axle, moderately close
to the gear wheels. Now bend the flat extensions on a line
with the wire stubs, so that the tips of the extensions will
meet; the extra one-quarter inch of flat metal on one side is
turned over on the other shorter end, and through these three
thicknesses of metal a one-sixteenth-inch hole is bored. Make
two S hooks out of a three-inch piece of
one-sixteenth-inch wire (same as used for the S hooks
of the rubber motors). Insert a hook of the S in the
one-sixteenth-inch hole and pinch it together with pliers, to
keep the hook tightly in place. The winder now looks like Fig.
5. Both rubbers can be wound up at the same time by
hooking them on the hooks of the winder; one turn of the large
wheel means five turns of the rubber.
Put a little oil on the bearings so that
the propellers will turn easily.
Have some one hold the model at the rear
by the propellers and fuselage. Unhook the S hooks with
the attached rubber from the front rubber anchorage and hook
them on the winder, step back until you have stretched the
rubber about twice the length of the machine, and wind it up
about 100 turns of the winder for a trial flight. Then hook it
back on the front rubber anchorage.
Grasp the rear cross-brace with the
right hand in such a way as to prevent the propellers from
unwinding, supporting the flyer by the middle cross-brace with
the left hand. Push the flyer forward through the air, letting
go with both hands at the same time.
Longer flights can be made by winding
the rubber up a greater number of turns: 250 turns of the
winder is the limit.
Be patient if things don't go just
right; keep trying; you will succeed.
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