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(New Millennium Sleek-Streek... pg. 2)
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Wing Saddle
The wing saddle assembly is built up from a 3/16 sheet
core that is cut to the profile on the plan side view.
The core is designed with a one degree positive incidence
angle-make sure this feature is carefully made in your
assembly. This in turn is sandwiched on either side by
1/16 sheet cheeks, which form a slot that fits on top
of the motor stick. |
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wing saddle (view 1)
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wing saddle (view 2) |
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After the wing is bonded to the saddle, drill 1/16 dia
holes where the toothpick rubber pegs are shown, and press/glue
short toothpick segments (or any thing similar you wish)
into position. |
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The wing assembly
is secured to the fuselage by wrapping small rubber bands (use
of ‘Goodies’ hair rubber bands (black) suggested-check
the beauty supply isle at your local emporium) around the fuselage
and using the pegs as the anchor. The wing can then be shifted
forward and aft to adjust the center of gravity when you begin
to fly the model.
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wing saddle (view 3)
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Stabilizer
and Vertical Fin
Make stabilizer, fin and wing pieces from one sheet of 1/16
x 3" X 36" balsa. For the stabilizer, the pattern
shown is one half the span, so flip the pattern about a center
line drawn on your balsa sheet and trace around for each side.
The one piece stabilizer and the fin can be cut out and sanded
to the pattern profiles with no further consideration if you
wish. A performance refinement is to sand these items to a tapered
cross section (chordwise), which improves the aerodynamic characteristics
of the sheet configuration, as well as lightens the overall
model considerably. You need a sanding block at least 2 inches
by 4 inches with 150 grit on one side and 220 grit on the opposite
side. Carefully sand one side of the stab smooth with the 220
side to start; this will be the lower surface. Flip over, and
carefully sand the stab such that you taper the thickness of
the sheet from about 1/3 of the chord aft to the trailing edge
of the stab. Final size this area using the 220 grit, to get
the trailing edge of the stab almost to a feather edge. If your
wood is soft, do not try to obtain a feather edge, as this will
likely curl as you approach a feather edge, spoiling the piece.
Sand an even radius on the leading edge, and
generally blend everything with the 220 sandpaper. Finish sand
all with 320-400 grit paper to obtain a very soft and smooth
surface, with all the heavy sandscratch removed from the earlier
rough sanding stage. Follow a similar procedure for the fin.
Omit the fuselage notch in the fin until the tapering is completed.
Leave the subfin (bottom) section to nominal material thickness,
as this will be hitting the ground often, and needs the extra
strength.
You can go ahead and install the horizontal stabilizer and vertical
fin at this pointh. I suggest starting with these surfaces being
bonded square to each other and square to the motor stick. Experienced
FF modelers apply stabilizer tilt to influence turn direction
in the glide-if you wish, you may set the stab such that the
right tip is 3/32 higher than the left, which will offer a bias
for a right hand turn. If you wish the opposite, the stab tilt
is opposite. With the stab bonded in place, it will be hard
to adjust stab tilt if things are not just right from the first
flights. Generally speaking, you will want the model to be trimmed
to turn right under power (against torque, which tends to pull
the model to the left), and as the motor runs down, continue
the right hand turning pattern, which will be a larger turning
diameter than under power. This is known as a
“right-right”
pattern (right turn under power, then right turn in the glide).
In practice, you will probably settle for whatever works best
for the model, but in any case, you are after a turning climb,
and turning glide pattern. The Sleek-Streek is
very good at teaching these fundamentals.
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Wing
Construction
The wing panels are cut out of 3 inch wide 1/16 sheet. Align
the patterns to the sheet edges, noting the inboard ends are
at an angle to the sheet edges. Once cut out, book the two panels
together and final sand both to the same profile simultaneously.
Next, sand the bottom surface of each panel with 220 grit and
320-400 grit paper, as this area is difficult to finish sand
after the forming ribs are installed. Then mark the rib center
lines with a light pencil or felt pen. Flip the panels over,
and sand the taper into the sheet as described for the stabilizer
fabrication. It is optional to omit the taper in the wing thickness
if higher performance is not a concern.
Begin forming the wing camber shape by bonding the 1/8"
thick root rib first. Apply medium CA to the leading edge area
for the rib, about 1/4" back from the wing panel LE. Place
the rib against the CA, and press down to obtain the bond and
anchor the sheet to the rib. Next, apply a thin bead of CA under
the rib where it will contact the wing panel. With the wing
panel against the work surface, roll the rib down against the
CA line. The previous bond will pick the sheet up and allow
the skin to wrap against the rib, forming the camber in the
wing panel. Hold in place at the end of the roll (TE in contact
with the work surface) until the CA has kicked and you can release
the pressure. A hint here is to dampen the area of the bond
before applying the CA. Apply the next outboard rib in the same
manner, working from the LE and rolling to the TE. Add the third
and final outboard rib and the wing should have a nice cambered
airfoil section. Repeat the process for the opposite wing panel.
Use your sanding block on the bottoms of the forming ribs to
sand flush to the LE and TE of the wing panel. If your panels
have developed a twist (when set onto your work surface, and
they don’t lay flat at the
forming rib contact areas), you can correct by wetting the upper
surface of the panel with alcohol and then weighting down enough
to hold the panel flat. Allow to sit like this for 24 hours
or so and the twist should be removed. The wing will naturally
sweep up at the trailing edge from the last rib through the
tip. This is desirable, and is known as ‘washout’.
This helps stabilize the model and tame stalling characteristics.
Add some twist such as this once you start flying the model,
if it appears to be roller coasting during the climb, or during
the glide phase.
3” dihedral is required at each wing tip. This is developed
by propping the wing tip up 3" using a block of wood, book,
etc, and the root end of the wing panel flush to the edge of
your workbench. Using your sanding block held lightly against
the vertical side of your workbench, lightly sand the root end
of the wing panel until it is flush with the vertical edge of
your workbench. Repeat the process for the opposite panel.
On a piece of wax paper, prop one wing tip up 6", or each
wing tip up 3" as done for the center joint sanding. Dry
fit for a tight gap at the center joint. Weight the wings down
to keep the root ribs against the work surface. When satisfied
with the joint fit, apply medium CA or carpenter glue to the
joint and position the panels back together and allow to cure.
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Final
rigging
Next step is to bond the wing saddle to the wing assembly. This
can be done with respect to the rest of the model by installing
the saddle onto the motor stick, and blocking the motor stick
to be square to your work surface. Block sand the wing root
ribs such that the bottom of this joint is flat and flush from
LE to TE. Position the wing assembly onto the saddle, and block
up either wing tip until you have both tips the same distance
from your work surface. Apply a weight at the wing center to
keep things stable while performing this dry fit. With the wing
square to the fuselage and tail elements, apply a shot of thin
CA to tack the wing to the saddle. Remove the wing and saddle
assembly from the motor stick, and apply more CA to firmly bond
the saddle in place. Install the wing rubber hold down pegs
as noted earlier.
Install the prop hanger and rear motor hook after the wing and
empennage rig have been established. Glue the prop hanger assembly
onto the front of the motor stick with medium CA to anchor in
place for the thread wrap. Position the landing gear and tack
in place with medium CA. Use of upholstery thread (fabric shop
item) is recommended for the thread wrap, as you can pull quite
tightly without breaking it. Begin the thread wrap by anchoring
in place at the front or aft end of the prop hanger block using
medium CA. Once this is done, begin wrapping the thread around
the front of the motor stick, capturing the landing gear wire
and the prop hanger, maintaining a fairly tight (not crushing)
tension in the thread as you wrap. After ten or so wraps, smear
the thread with medium CA, or if you prefer, cellulose cement.
Continue wrapping neatly until the prop hanger is completely
wrapped and secured against the prop hanger block. Apply a thick
coat of medium CA, and with your finger tip wrapped in a plastic
bag or plastic wrap, smear the adhesive into threads to completely
saturate and cure-the plastic on your fingertip will help accelerate
the bond in the CA.
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the .032 rear motor hook approximately as shown, using
the round nose pliers. You need a loop 5/32-5/32 dia;
leave the tail on the loop pointing up, as this prevents
the motor from coming free in flight as it runs down.
Make some thread wraps around this as done for the prop
hanger to secure the hook in place. |
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 rear
motor hook |
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Drill a 3/32 dia
hole through the keel near the rear hook. When winding the model,
it is pinned through this hole while upside down on your stooge,
and the motor removed from the prop shaft hook for the winder.
Add wheels-balsa ply built-up or plastic work fine. Your Sleek
Streek is nearly complete at this point!
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Finishing
The model can be flown with no finish applied if desired. Some
moisture proofing is desirable, and this is best accomplished
using polyurethane varnish that is wiped on lightly using toilet
paper or cheese cloth. Dab a folded piece of TP with varnish,
and wipe onto all the exterior surfaces of the model. Apply
a light coat, and allow to dry 24 hours. Sand the surfaces with
400 grit paper to remove any fuzz that may have appeared from
the application of the varnish. One coat should be enough to
moisture proof the model. Decoration can be added as desired,
just don’t add any weight! Typical finish is to spritz
a splash of bright, high visibility color onto the wing tips,
tail with Design Master floral paint,
as sold in aerosol cans at art supply stores. Use blue or black
on the wing bottom to give high contrast against the sky as
you follow your model for retrievals. The use of dope to seal
the model is strongly cautioned against, as warping can be problematic.
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Propeller
Plastic propellers work well. Select an 8" Peck, or other
commercially available propellor of about 8" diameter.
Higher performance can be had by cutting down a larger diameter
commercial prop to approximately 8" diameter. This gives
more pitch than the stock 8" prop. Install the prop with
a Teflon thrust washer between the prop hub and thrust bearing.
Teflon thrust washers are available from FAI Model Supply, or
Cambell’s Custom Models. Small brass washers sold by Peck
Polymer also work to minimize friction-install two between the
prop hub and prop hanger bearing.
Set the loop of the prop shaft to be behind the prop hanger
block as shown to prevent the rubber motor from bunching up
under the prop hanger and locking the prop in flight. Apply
3-in-1 oil to the prop shaft and work this forward and aft to
lubricate the bearing and prop hub for smooth operation.
Carved balsa wood propellers offer higher performance and lighter
weight. Use the Sleek-Streek to explore the
skill of carving a propellor yourself.
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