visitor Pat M. wrote to ask that I scan and post this article
for the Yako free flight rubber model. The unique feature of the
Yako is that it is a canard - wing in the back and horizontal stabilizer
up front. It appeared in the December 1971 edition of American
Aircraft Modeler magazine. "For the Tenderfoot" catered to
beginner model builders - mostly kids. They were typically small
free flight or control line jobs that could easily be built without
help from an experienced modeler, although of course seeking assistance
was encouraged. I have been surprised at the number of requests
I have received for models from the "For the Tenderfoot" series
that ran for many years. Could it indicate a resurgence of people
interested in building, trimming, and flying model airplanes rather
than an entire generation settling for ready-to-fly airplanes that
were built in a far-away factory, often by workers who do not earn
enough to buy the models they produce?
By Clarence Mather
When the wing is in back and the stabilizer in front, the plane
is called a canard. They seem to be backward, offer unique appearance
and excellent flyability.
Nice thing about canards-they can carry plenty of wing area
for their size and fly all that much better as a result.
A peppy little tail-first sportster,
Yako provides a lot of fun and performance for a small investment
of time and materials. With perhaps 300 turns cranked into the motor
it will zip up over treetop height and then glide down nicely to
The tail-first or canard configuration has more
stability than the more common tractor and presents a distinctive
appearance. But it needs to be built closely to specifications for
proper flight characteristics.
should be constructed mainly of medium hardness balsa. (If you are
new to balsa wood ask the shop proprietor for guidance.) Measurements
can be made directly from the full-size plans. Parts can be traced
onto sheet balsa by utilizing soft carbon paper. Single-edge razor
blades work well for cutting balsa and a metal straight edge helps
to keep true lines. A piece of fine sandpaper; perhaps No. 250,
wrapped around a wooden block is useful for smoothing balsa edges.
A dozen pins or so are needed to hold pieces at various stages of
construction. A 6 x 18" piece of insulating board or soft wood can
be used as a working surface. Fast-drying plastic model airplane
glues can be used, but the slower-drying white glues are preferable
as they are less likely to warp the surfaces.
Cut the wing
out as a single piece and mark rib locations on underside. Glue
the ribs into position and immediately place the wing on the work
board and pin flat, placing a piece of waxed paper between the wing
and the board to prevent the wet glue from sticking to the board.
If necessary, use pins to hold the wing to the curve of the ribs.
Forcing the surfaces to dry in the flat position helps reduce warps
so repeat the same procedure for the stabilizer.
glue has dried thoroughly, remove the surfaces from the work board
and cut in two down the center. Prop each tip up for the required
dihedral and observe the gaps at the center joint. Take each half
and cut and sand the edge carefully until the joint fits snugly.
If high-shrinkage plastic glues are put into a poor fitting joint
there will probably be warpage. Gaps can be filled with white glues
with little danger.
Glue the longerons to the fuselage side
and add the cabin piece. Plug the front and rear spaces between
the longerons to support the front hook and the prop shaft bearing.
Shape the bottom of the wing center so the wing sets flush on the
fuselage, as in the drawing. Then glue it into place making certain
that the wing is square with the fuselage from the top view. Fit
the stabilizer to the top of the cabin so that the leading edge
is 5/16" higher than the trailing edge! Observe the structure from
the rear and line up the stabilizer with the wing.
pliers will facilitate bending the hooks for the rubber. Use steel
"piano" wire. Bend the front hook and glue securely in position.
Bend the rear hook, but leave other end straight. Cutting burrs
should be removed with a file or a grind stone.
several types of plastic props on the market, but the red, square-tipped
type is recommended because of light weight and high pitch. Obtain
one of seven-in. diameter and cut 1/4," off each tip. The hole in
the prop is too large for the wire, so drill it to 1/16 size and
plug with a piece of 1/16" aluminum tubing. The props come with
a free-wheeling ridge on the wrong end of the hub, so cut and sand
the front flat.
Cut a second piece of tubing for the fuselage
bearing. A razor blade will cut aluminum tubing nicely if it is
pressed firmly into the tubing and rolled back and forth. Nick the
surface of this tube all over so that the glue will grip it securely.
Slip the prop shaft through this tube, the glass bead, and then
the propeller. Bend the wire shaft over at a right angle.
the first Yako the shaft was bent over past a right angle so that
it would catch on a blade. During the glide, the prop would stop
and the model would wander about depending upon the rudder effect
of the particular prop position. This model was lost in a thermal.
The second Yako has a free-wheeling prop (sketched on plan) which
reduces drag and allows a constant glide circle. The small piece
of tubing is glued to the prop and lashed with thread. The ratchet
is bent so that it flips free when the prop turns clockwise by the
slipstream, but catches the bent-over shaft when turned by the rubber.
Attach the prop assembly to the fuselage by gluing the nicked tubing
to the rear balsa plug and wrapping with fine thread a few times.
Take care not to get any glue into the shaft-tubing joint. Angle
the prop as shown in the side and top views - the right tip of the
prop should be about 1/4" closer to the wing than the left side.
These angles help keep Yako in a smooth climb.
landing gear and secure in position, lining it up so that the model
sets level. Wheels can be built up or purchased - plastic wheels
are heavier but they work well.
Purchase enough rubber for several motors, as they break, wear out,
etc. To make a secure knot, first tie it loosely then work saliva
into the knot by chewing. Now pull the knot tight-right to the breaking
point of the rubber. Rub some castor oil, glycerin, or commercial
lubricant into the rubber so that it appears moist. Slip the rubber
into the hooks with the knot at the front.
Just because it looks backward, doesn't make it tough to
build or fly. Climb is straight ahead with a slow right-turning
Observe the model
from the rear to check for warped wings or stabilizer. The trailing
edges should be parallel to the leading edges of each surface. Small
warps will probably be tolerable, but large ones should be reduced
or removed. Hold the wood between the thumb and forefinger, then
pinch and bend opposite the warp. Apply the process over an area
rather than in one spot. If a warp is persistent, one of the regular,
fast-drying model airplane glues can help remove it. To bend the
wood down, rub a thin layer of glue under the area. If the wood
needs to be bent up, rub the glue above the area. Hold the wood
in the bent position while the glue sets. The rear part of the fin
should be bent to the right about 1/32" to produce a right turning
This will counteract the left turning effect of
Test fly Yako over the softest
area you can find. At our San Diego flying site that means picking
the spot where the rocks are smallest! Select a time when the air
is near calm such as early morning or late evening. Wind the motor
by turning the prop counterclockwise about 100 times. Launch Yako
with flying speed slightly nose up and just to the right of any
wind. The model should climb at a shallow angle with little or no
Learning the correct launch speed may require some
practice. If launched too fast Yako may zoom up and stall; if launched
too slow it will dive. If either condition persists small adjustments
can be made on the stabilizer. (It is assumed that the wing and
stabilizer angles and the model balance point were checked during
construction.) The outer part of the stabilizer can be bent down
to correct dives or up to correct stalls by the methods described
to remove warps. Any sharp turning tendencies should be countered
by bending the rudder opposite the turn.
When the flight
pattern is satisfactory, put more turns into the rudder and observe
closely as models often require additional trimming under the higher
torques. The number of turns that can be put into the rubber depends
upon its quality. Most motors will take 300 hand turns. When fully
wound our Yako climbs steeply, then rolls into a climbing turn to
the left. As the torque lessens, the model flies nearly straight
- then glides in a large right circle. Occasionally we use a long
motor - perhaps 18" - and stretch it out and wind it with a winder.
With such power this model has climbed to surprising heights. If
Yako seems sluggish, it may be due to low torque rubber - try a
larger size. Keep the prop shaft and bearing well-oiled.
for larger image>
The AMA Plans Service offers a full-size
version of many of the plans show here at a very reasonable cost. They will scale the plans any size for you. It is always
best to buy printed plans because my scanner versions often have distortions that can cause parts to fit poorly. Purchasing
plans also help to support the operation of the Academy of Model
Aeronautics - the #1 advocate for model aviation throughout the world. If the AMA no longer has this plan on file, I
will be glad to send you my higher resolution version.
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Posted February 22, 2014