duck.pdf

THE DUCK

BY LOUIS GARAMI

A rubber-powered amphibian.

The Duck takes off easily from water. The

landing gear folds upward for water flying, is

locked in place by rubber band.

Right-The ship is light but strong.

Assembly is easy.

The hull, tail, and engine nacelle are cut

from sheet balsa. Consequently,

performance is better then would be

expected.

With the exception of the multimotored

ships, an amphibian is regarded as one of the

toughest to adapt for rubber power. The

numerous problems in designing which pop up

here and there are all out of the ordinary and

even the necessary flying adjustments seem to

go against one's previous experiences.

The main problems are to secure a

normal length of concealed rubber line, safe prop

clearance with a normal size prop, and an easily

retractable landing gear for water take-offs.

In the past few years I have made several

attempts to produce a good flying amphibian, but

for some reason they all wound up far too

complicated to attract the average builder. The

first models had a regular crankshaft

transmission with the propeller constantly

shaving the imaginary pilot's head in the open

cockpit. Later on a single universal joint would

do, but at the same time it would scare away the

interested builder.

And then came the "Duck."

There are no mechanical gadgets to coax

into action here, which, while taking most of the

romance out of it, places this amphibian within

the ability of the average sport modeler.

The unusual features are the

tissue-covered sheet balsa body and tail for

waterproofing, the built-in upthrust to overcome

the tendency of diving, and a very simple

retractable landing gear.

And now you may ask the often-heard

question: But how does it fly, mister?

sides and trimmed after. The whole top can be

made easily out of one piece, but the front end of

the bottom requires four pieces. Two pieces

between formers FC and FB, and from FB to the

very nose, two other pieces, with the grain

running right-angle to them, are required.

Trim and sandpaper the edges smooth.

Now dope a strip of tissue along each corner to

cover up and strengthen the joints. Proceed to

cut out all the openings. Cutting the window

shapes out of a different color tissue and doping

in their places on the body makes the

razor-blade work easier and neater. Next the

landing-gear struts are bent. Do not forget to slip

the aluminum tubings on first. They are glued on

FB (several coats) through the side windows.

Now you can cover the windows with

celluloid, fasten small hooks for the landing-gear

rubber bands, also the two straight wires through

the top which hold the rubber bands for the

nacelle.

The wheels and water rudder are made of

light balsa and waterproofed by several coats of

dope.

The slight bulge of the nacelle sides is the

result of an extra coat of dope on the uncovered

insides. First the top seam is pinned and

cemented, then the bottom former FE and the

solid balsa front piece are added. Two wire pins

fix the nacelle to the body. Place the nacelle in

position on top of the body and press lightly to

mark the position of the pins. Now enlarge the

two holes and glue a square piece of sheet

aluminum, also punctured, to coincide with the

holes.

The two-piece nose plug is fitted and

carved to shape. The bearing is a copper washer

and small bushing in the front and rear of the

nose plug. Cut the propeller out of medium-hard

balsa. Waterproof with a couple of coats of dope,

colored or otherwise. Fit in the same bearings as

on the nose plug, and make sure that it is

equipped with your choicest freewheeling.

Use six strands of 1/8" flat rubber for

motive power. It is important to lubricate the

rubber, because going through the body it

sometimes rubs slightly on the wood. For this

reason the rubber should be put in the body and

the prop tried for smooth run. If too much

Excellent, my dear chappie. But definitely.

BODY AND NACELLE

The body and nacelle are made of 1/32"

soft sheet balsa. First cut out two of No. 1 and

No. 3 blanks and one of No. 2 blank. Now cover

these with Jap tissue on one side. Make sure

that a left and right blank is obtained of each

twin. In addition to these cover a whole sheet of

1/32 x 2" the same way to provide for the top

and bottom of the body. The best way to cover

with tissue is to brush dope on the whole

surface, lay an oversize tissue on top and

smooth out with the palm of the hand. To

counteract the strong warping tendency a coat of

dope should follow on the other side, and when

both sides are dry the tissue is trimmed with a

razor blade.

Now prepare the four formers (FA, FB,

FC, FD). FA is a triangular block of wood forming

the nose of the body. Cement the rear hook on

FD before assembling the two sides. First pin

and cement the two sides to FA. When the glue

has set put the other formers in one by one and

lastly pull the top of the tail together and cement.

Bottom blank No. 3 is fitted in between the two

sides, thereby shaping the bottom of the boat

from the step on.

All the other pieces needed for the body

are just oversize pieces of wood glued on to the

vibration results the cause may lie in too small a

hole on top of the body or bottom of the nacelle.

Or a too-large hook on prop shaft striking the

sides of the nacelle will cause uneven run.

With the tail surfaces fixed in place, the

center of gravity should fall to a spot five inches

from the nose. Set the wing so that this spot

coincides with the wing spar, not forgetting the

proper incidence and dihedral.

WING AND TAIL

Cut out ten ribs, two of which are 1/4"

thick. These are placed first as wing roots, and

later on carved to fit the side of the nacelle. The

wing is made in two halves. Fix the two end ribs

of each wing to the leading and trailing edges

and set the remainder and the spar in after.

Bend a 1/4" wide bamboo into the shape of the

tip above the gas range and slice two 1/16"-thick

pieces off with a knife. Upon finishing the wing

frames, cover them with tissue, spray with water

and dope once.

The tail surfaces are of 1/32" sheet balsa.

Cut out the exact shape and smooth the surface

with fine sandpaper. Cover both sides with tissue

the same way as the body has been.

FLYING

A rough adjustment can be accomplished

indoors, in the cellar, or even a large-size room

with pillows placed at the probable landing spot.

Ten feet of gliding is ample distance to show a

stalling or diving tendency. Warp the elevator

flippers to correct anything but a flat glide. Do not

rush outdoors regardless of the weather; wait for

a calm hour and save yourself a lot of trouble.

For outdoor adjustment I recommend 1/16" right

rudder and an equal amount of right thrust on the

nose plug. Wound to capacity, which is four

hundred turns, it will take off from water or land

alike.

BILL OF MATERIALS

(Soft balsa throughout)

2 sheets 1/32 x 3 x 36"

1 sheet 1/16 x 2 x 36"

1 prop block 6 x 1 x 3/4"

1 length bamboo 1/4 x 15"

Small blocks for nose plug, nose of hull, bottom of

nacelle Wire bushings, aluminum tubing and washers

Scanned From August 1939

Air Trails

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