Indoor Autogiro

An experimental model of value to both

The model is distinguished by its simplicity

THE AUTOGIRO is the model builder's drawing. Cement in the ribs, which are likewise 1/32"
orphan child. It has been neglected because it is such sq. and without camber. Make the other blades in the
an inefficient means of flight and because it does not same way and then cover them all with microfilm.
glide, thus making its chances of high duration very Make the hub of 1/32" sheet balsa laminated as
remote. shown, and cement the bearing, which is a washer on
The wingless autogiro, although very either side of the hub, in place. Cement the blades in
successful in full-sized craft has, except in a few place. Raise the outside tip of each vane 1/2" and the
cases, defied model builders. The secret of wingless trailing edge at the third rib from the end 5/32". The
autogiros is patience. Only after many hours of result should be a negative incidence. This is very
experimentation were the kinks of this model ironed important.
out so that it could be termed successful.
The model was designed primarily so that it TAIL AND RUDDER
would stand abuse, as it was realized that it would The tail is made of 3/64" square soft balsa
have many an unfortunate experience before it would which has been pinned to a full sized drawing. The
be adjusted. Weight, therefore, was a minor center rib is flat and the other ribs are slightly
consideration. cambered. Looking toward the propeller the ribs on
the left are conventionally cambered, whereas those
VANES on the right are reverse cambered. This is done to give
The rotor of this model was made three-bladed an even greater rolling moment, to overcome the
for simplicity. A fourth blade may be added. In fact, it torque, than is possible from a flat tail alone. The
would probably be easier to adjust a Model with four rudder is made very simply of 3/64" square balsa and
blades instead of three. So if yon are of an experi- is cemented underneath to keep it out of the way of
mental turn of mind make a fourth blade. the vanes and also to bring the C. G. of the model as
Make a drawing of the outline of the blade and low as possible.
pin 2 strips of 1/32" square medium balsa to the
 MOTOR STICK, LANDING GEAR, thrust bearing and put a loop of 5/64" rubber 13" long
AND VANE BIPOD in place. Now balance the ship without the rotor and
The motor stick is hollow and made in the bipod. The center of the bipod should be located over
conventional way for indoor models. It is 12" long the point of balance. Slice the seam of the motor stick
and made from a blank 1" at the center tapered to 3/4" about 1/2" long just about where each leg of the bipod
at the ends. The blank is 1/32" light sheet balsa. Soak should be. Insert each into its corresponding slit till
the blank in hot water, bend and bind it around a they touch the other side of the motor stick and
former 3/8" by 1/8" at the center, tapered to 1/4" by cement up the slit. Make sure you have the correct
1/8" at the ends, by l2" long. Allow it to dry. incidence in the plane of the vanes (about 5°). If, after
After it is dry cement the seam, angle the front the cement has dried, the bipod is flexible at the point
end, and cement the caps on front and rear. Cement of insertion of the legs, brace it with a strip of 3/64"
the dural thrust bearing and rear hook in place. Make sq. balsa. Now find the approximate vertical position
the landing gear from medium balsa to the size shown of the C. G. (keep the rubber on the motor stick for
on the drawing. Cement the axles in place and put on this test, in order to simulate flying conditions as
the wheels. Keep the wheels on with a drop of cement much as possible.) Then bend the thrust bearing so
at the end of each axle. The bipod is made of medium that the thrust line passes through this point.
balsa 1/8" by 1/16", corners rounded. Then angle one
end of each stick and cement them together, so that
ADJUSTING AND FLYING
First see that the vanes rotate freely. Then,
they form a "V" of the dimensions shown. Make a
holding the model above your head, vines parallel to
shaft, cement it and put on a washer. We are now
the floor, rotate them slowly with your other hand and
ready to make the propeller.
let the model drop. The model should come straight
down or move forward only a short distance. It should
PROPELLER not have rotated with the vanes any more than 1/8 of a
The 7" diameter propeller is carved from a turn in a 6-fool fall. If it did the friction of the vane
light block 7" by 1/2" by 1-1/8". Such a propeller is bearings is too great. Relieve it before going any
used as a low torque is desired. Draw diagonals on the further with the tests.
wide faces of the blank. Cut down to the diagonals, The launching procedure is as follows: Wind
then carve the propeller in the conventional way, the rubber about one of knots. Then, holding the
starting with the concave side of each blade first. model above your head, draw it down vertically and
Finish and sand the concave side before even starting forward so that the vanes rotate and release it. At the
the convex side. After finishing the convex side cut moment of release the plane of the vanes should be
out the template of the blade shape, pin it to the parallel to the ground. The model will probably spiral
blades one at a time, and cut the blades to fit the into the floor because of the torque of the propeller.
template. Finish the propeller To overcome this treat the tail as a wing -- put washin
by sanding; insert the shaft and cement it. The in the left side, washout in the right.
propeller may be 1/32" thick at the tips, as it will take Another trick that might be used is bending
a lot of punishment till the ship is finally adjusted. the rudder to make the model turn against the torque.
This should eventually get the model to fly correctly.
ASSEMBLY If you still cannot get the model to fly well you might,
Cement the tail assembly on the rear end of the motor as a last resort, make a simple auxiliary wing 15" long
stick. The tail should be at a negative angle, as shown and 1-1/2" wide, which call be washed in to overcome
in the drawing. Cement the landing gear in place and the torque.
allow it to dry. Insert the shaft of the propeller in the

Scanned From September, 1943