Additional Fuelproofing; Balance The Airplane Laterally; Final Sanding; Covering - GREAT PLANES Piper j-3 cub Instruction Manual

combinations will determine where the screws should be
installed. In any case, keep the screws approximately 3/8"
forward of the aft edge of the cowl. Tape the cowl in place so
it does not move and drill a 1/16" hole for each screw.
5. Remove the cowl and enlarge the holes in the cowl only
to 3/32". Glue a 1/8" x 1/2" x 3/4" ply Cowl Screw Block
(CUB4F22) to the inside of the fuselage at each screw
location. Extend the 1/16" holes through the ply screw blocks.
6. OPTIONAL STEP - To help extend the life of your cowl,
roughen the inside surface of the cowl (around the cowl
mounting holes) with coarse sandpaper. Apply a layer of
lightweight fiberglass cloth over each hole using epoxy or
CA. Do not use polyester resin as it will melt the plastic. Let
the epoxy thoroughly cure, then re-drill the mounting holes.
7. Sand the entire outside surface of the cowl lightly with
400 grit sandpaper. Spray on a coat of primer, then sand
smooth with 400 grit sandpaper. Paint the cowl with fuelproof
paint. We used Top Flite Cub Yellow LustreKote.
HINT: Access to the fuel lines can be a problem in a cowled
engine; therefore, we suggest that you install a Great Planes
Easy Fueler (GPMQ4160) valve. This makes it much easier
to fill and empty your tank.

Additional Fuelproofing

If you have not already done so, make sure the entire engine
compartment is completely fuelproof. Also fuelproof any
wood that will not be covered and which may be exposed to
glow fuel residue. Use epoxy thinned with alcohol, polyester
finishing resin or fuelproof paint.

Balance the Airplane Laterally

NOTE: Do not confuse this procedure with "checking
the C.G." or "balancing the airplane fore and aft". That
very important step will be covered later in the manual.
Now that you have the basic airframe nearly completed, this
is a good time to balance the airplane laterally (side-to-side).
1. Temporarily attach the wing and engine (with muffler)
to the fuselage.
2. With the wing level, lift the model by the engine
propeller shaft and the bottom of the fuselage near the aft
end (this may require two people). Do this several times.
3. If one wing always drops when you lift, it means that side
is heavy. Balance the airplane by gluing weight to the other
wing tip. NOTE: An airplane that has been laterally
balanced will track better in loops and other maneuvers.

Final Sanding

Check over the entire structure carefully, inspecting for any
poorly glued joints, gaps and "dings". Apply additional glue
and/or balsa filler as necessary, then sand the entire structure
smooth using progressively finer grades of sandpaper.
Because it is assumed that you have had some previous
model building experience, we won't go into detail in regard to
the covering procedure. Follow the instructions included
with your covering material.
NOTE: When covering the fin and stab, begin by
applying 1/2" wide strips of covering in the corners
between the fin and stab, and (on the bottom of the
stab) between the stab and the fuse sides. Next, cover
the stab and fin with pre-cut pieces that have a straight
edge to overlap (1/8"+ overlap) the strips you
previously applied. DO NOT, under any circumstances,
attempt to cut the covering material after it has been
applied to the fin and stab, except around the leading
and trailing edges and the tip. Modelers who do this
often cut through the covering and part-way into the
balsa stab. This can weaken the stab to the point where
it may fail in flight! Also note that when the sided are
covered, the covering material should be ironed only to
the bottom of the window cut-outs to the top of the
fuselage side. This will give the appearance of the open
tube fuselage structure found on the full size Cub.
Recommended Covering Sequence:
1. Strips as described in above note
2. Rudder left side
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Covering