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The Canard
An indoor pusher of advanced
design and simple construction - an
ideal project to in augurate the
indoor season
The indoor pusher is a vagrant; its
flight course can never be foretold
By Lawrence N. Smithline
THE INDOOR PUSHER is almost as extinct
as the Dodo bird. Six or seven years ago at least one
pusher could be seen at the regular Saturday sessions
at the armory. Not so to-day. Their extinction may be
attributed to the conviction of most model builders
that the limitations of a pusher as regards endurance
are more numerous than those of a tractor. Still, in its
defense, it may be said that pushers, besides
providing a great deal of fun, have much to teach the
model builder.
Pushers are really tandem planes for both the
wing and "tail" surfaces do the lifting at all times.
This is plainly evident when one notes the location of
the center of gravity of the plane in relation to the
wing and tail. Another outstanding characteristic of
pushers is that the fin is ahead of the center of gravity.
The reason for this is that most pushers require their
directional centers farther forward to prevent spiral
The building of a pusher brings up no
absolutely new problems, so that we can get right
down to work. There is, though, a minor
constructional difference dictated by convenience
rather than by necessity; that is the carving of a left-
handed propeller instead of a right-hand propeller.
This will facilitate winding the motor, because it can
be wound in the conventional way and still push
rather than pull.
The wing is built up in three sections. The
spars are made of light balsa 5/32 x 1/16" tapered to
1/16" square at the tips. Round all the corners; sand
them smooth with #10-0 sandpaper; pin them to the
drawing and wet them with water. Cut out the ribs
from 1/32" "C" stock balsa. ("C" stock balsa has a
speckled appearance. It is very stiff but light.) After
the water put on the spars has evaporated, cement in
the ribs. As you work out toward the tip it will be
necessary to shorten the ribs. Do this by cutting off
one third the excess length from the front end and two
thirds the excess from the rear. This will tend to keep
a more uniform wing section. Make a cardboard
template of the tip and bend two strips of 1/32" square
balsa, soaked in water, around it. After they have
dried, cement them to the tip sections. Cover the three
sections separately with microfilm and then cement
the sections together with 1-1/2" of dihedral under
each tip. Make wire clips to fit the fuselage and
cement them to balsa stilts each two inches long. The
pusher wing should have no angle of incidence, so
after the stilts have been cemented to the wing make
sure that the distance from the lower edge of the wire
clips to the front and rear spar, are the same. This
completely finishes the wing.
The tail of a pusher is built in the, same way
as that of a tractor, except that the two halves of the
tail are cemented together only lightly before
covering, in order that the dihedral angle ought be put
in later. Make a template of one half the tail from
cardboard, bend two 1/32" square soft strips which
have been soaked in water around the template and
allow them to dry After they have dried pin them to a
drawing of the tail shape, cut ribs from 1/32" "C"
stock and cement them in place in the same manner as
the wing ribs were installed. Put a drop of cement at
The wing is what is known as the "swept-
forward" ellipse. It is an ellipse distorted so that the
one-third points of the ribs lie on the same straight
line. The wing is exactly the same as was used on the
Class "C" Tractor described in the January 1937 issue
of Air Trails. You can save yourself considerable time
if you still have the draving of the wing. If not, you
will have to take time out to make a new drawing.
the joint of both bent strips. Use no more cement than
is absolutely necessary to hold them together.
Make a template of the fin shape and bend a
strip of 1/32" square balsa around it in the same
manner as the tail. Cement the rib in place and cover
both tail and fin. After the tail is covered put in the
proper amount of dihedral by cracking the cement
joint at the center, raising the tips and recementing it.
After the cement has dried, heat-treat the film at the
dihedral in order to remove any wrinkles in the film.
Heat-treating is merely passing a hot wire under the
film at a distance of about 1/2". Wrinkles call be seen
to dissolve with the application of heat.
The motor stick and boom for a pusher are
made in exactly the same way as that of tractor.
However, the pusher boom is somewhat shorter than
the tractor boom. Make a motor stick former of hard
balsa 5/32 x 3/8" at the center, tapered to 3/32 x 1/4"
at the ends and I5" long. Round the corners and
smooth the former The blank is made of 1/32" sheet
1-1/8" at the center, tapered to 3/4" at the ends and
15'' long. (The wood should be light but as stiff as
possible.) Soak the blank in hot water, bend it around
the former, and bind it with 1/2" wide bandage. Allow
the water to dry out, remove the bandage, and then
sand it with #10-0 sandpaper. Then yon may cement
the sean, caps thrust bearing, and rear hook in place,
after you have taken the formal blank off the former.
Make the boom former of hard balsa, 3/32 x
3/16" tapered to 1/16 x 3/32" and 9" long. Round the
edges and smooth the stick. Make a blank of 1/64"
light sheet balsa 5/8" tapered to 3/8 x 9" long.
Proceed with it as was done with the motor stick --
soak, bind, sand, and cement the seam. After it is
finished cement it to the motor stick with the front
end raised 3/16".
or from a semicarved 16" propeller of pitch-diameter
ratio 1.6. Finishing a semicarved propeller will save
you about two hours, as well as give you a more
perfect pitch propeller. In both cases carve the
concave sides first and completely finish them before
proceeding to the convex sides. Smooth the blades
with #10-0 sandpaper. Make a template of the blade
shape and cut the blades to fit. Make a shaft of .016
wire and insert it into the propeller in what would
ordinarily be backward for a tractor. Coat the hub
with cement.
Cement the fin onto the boom in the position
indicated in the drawing and then cement the tail in
place. Put the wing on the motor stick, remembering
that the tying goes on in reverse from the ordinary
way; that is, with the trailing edge toward the
propeller. Insert the propeller shaft into the thrust
bearing and put a loop of 7/64 x 1/30 x 17" brown
rubber in place. Glide the model. If it stalls, move the
wing forward; if it dives, move it backward. Note that
you do the opposite to a pusher to correct dives and
stalls, but the same treatment is used for both pushers
and tractors in cases of washing in or out.
After a good glide has been obtained, wind the
motor about 500 turns.
The method of launching pushers is somewhat
different from tractors. It is done as follows: Hold the
model with one hand only. Grasp the propeller hub
and thrust bearing with your thumb and index finger.
The middle finger supports the motor stick. Raise the
model to eye level and holding it at a slightly positive
angle, thrust the model forward at approximately fling
speed, and release it. The model should fly it circles
about 40 feet in diameter. If the Model tends to dive,
or stall, correct it as explained previously. More full
winding may tend to dive the plane. Correct this by
moving the wing forward.The model under full winds
and good conditions shouId break 20 minutes. To
date, the highest time known to be done with pushers
is 16 minutes. Let's see what you call do about it.
The propeller of the pusher is left-handed, as
explained previously, for the convenience of winding.
It is carved from a block of 4-lb. balsa 1-3/4 x 1 x 6",
.028 oz.
Tail and Fin
.0035 oz.
.018 "
Motor Stick
.018 "
.0705 oz
Scanned From December, 1937
Air Trails
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