IndoorCanard.pdf

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

instability.

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.

TAIL AND FIN

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

WING

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.

MOTOR STICK AND BOOM

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.

ADJUSTING AND FLYING

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.

PROPELLER

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",

WEIGHTS

Wing

.028 oz.

Tail and Fin

.0035 oz.

Propeller

.018 "

Boom

.003

Motor Stick

.018 "

TOTAL

.0705 oz

Scanned From December, 1937

Air Trails

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