.
i.
Scrape the seam on the outside of the cowl to take out any rough spots or flaws. Low spots in the seam can be filled with
Sig Epoxolite putty. Don't put on too much Epoxolite and expect to sand away the excess later. Epoxolite dries very hard
and must be worked into its final desired shape before it hardens. Use your finger or a single-edge razor blade, dipped in
water, to smooth the Epoxolite into the low spots along the seam. Let dry overnight, then sand the entire cowl smooth and
scratch free with fine sandpaper.
j.
With a Dremel tool or X-Acto knife, cut an opening in the front of the cowl large enough for the engine's prop shaft and
drive washer to fit through. Locate this hole according to the thrust line mark that you made on the cowl at the start of this
section.
k.
Cut out the two small air intake openings in the front of the cowl. Refer to the
Fuselage Front View plan for the exact size and location.
l.
A piece of 1/2"x1/2"x6" basswood is provided for making six equal 1" long Cowl
Mount Blocks. After cutting them to length, epoxy the blocks in place on the front
of the firewall, letting them stick out past the edge of the nose planking slightly.
Mount the engine on the firewall. Slip the cowl over the engine and up to the
Cowl Mount Blocks. Now you should be able to see where the blocks need to be
taken down in order to fit properly inside the cowl. Use a sanding block to bevel
and reshape the blocks as necessary until the cowl will slide back over the blocks
and onto the fuselage.
m.
Tape the cowl in correct alignment on the fuselage. Drill pilot holes for the Cowl Mount Screws (#4 sheet metal type,
furnished) through the cowl and into the Cowl Mount Blocks at the same time. Take the cowl off and open up the holes in it
large enough to pass the mounting screws. Then put the cowl back on and thread the mounting screws into the blocks.
n.
Trim out the molded plastic Air Cleaner Cover to fit on the chin of the cowl. Leave a small flange around the edges for
gluing. Hold the Cover in position on the cowl and draw around the outside of it with a pencil. Cut out the cowl plastic about
1/8" inside of the lines, so that cooling air will be able to flow through the Air Cleaner Cover and into the engine
compartment. After this is done, glue the Cover in place and then cut open the front of it (within the framed area) with an X-
Acto knife. This opening can be left wide open, or if you want a more scale appearance you can glue in a piece of plastic
window screen (wait until after all painting is done).
o.
Trim out the Right and Left Dummy Engine Cylinder moldings along the lines shown in the photo. Leave a small flange,
about 1/16" to 1/8" wide, along the back of the part where it will match the curvature of the cowl. The best procedure for
trimming is to rough out the part with a heavy-duty scissors or shears, and' then finish the edges with a sanding block or
Dremel tool. Next, carefully position the Right and Left Cylinders on the cowl using the plans and photos as a guide. Mark
their location on the cowl with a pencil. Then carefully bond the cylinder moldings in place with dope thinner, MEK, or
cyanoacrylate adhesive. Again, avoid getting adhesive on your fingers and making finger prints on the plastic.
p.
Trim out the Right and Left Top Shrouds
according to the trim lines molded into
them. The trim lines are not very
prominent. Holding the parts up to a light
will make the lines more visible. You can
trial fit the Top Shrouds onto the
Cylinders at this time in order to fine-
tune the fit of the trimmed edges, but it is
best if they are not glued on permanently
until after the Cylinders and Cowl are
completely painted. The Top Shrouds
can be painted after they are in place.
Engine Cooling Notes
The most important factor in cooling a fully cowled model engine is to keep
a constant stream of fresh, cool air moving through the cowling. Large
volumes of air aren't necessary, just a steady flow of new air. This is
accomplished by having more exit area for the air than incoming area.
Inadequate exit space can cause heated air to be trapped in the cowl, and
this is what causes overheating and engine failure.
Consequently, on our prototype models, we provided for additional exit
space by
1. opening up the bottom of the cowl at the rear, and
2. cutting away the cowl plastic that is inside the dummy engine
cylinders and then opening up the back of the cylinders themselves.
As an extra precaution, we also installed a baffle (made of sheet balsa) in
the bottom of the cowl. It directs all of the air that comes in through the Air
Cleaner Cover upward towards the engine cylinder before it can exit out
the bottom opening in the cowl. With the setup described here, we have
never experienced any overheating problems with glow engines from .60
to .90 cu. in. You may need to use a little ingenuity with some similar tricks
to insure that your engine installation runs cool.