Before you make the cowl, the front end of the fuselage should be complete.
All sheeting must be in place and it should be sanded to shape.
Do not finish sand because the fuselage will need to be sanded after the
cowl is made.
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Join the blocks to make one larger
block that is big enough to make the cowl.
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Sand the back flat.
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Draw centerlines on the top,
sides and front of the cowl to use for reference. A Sharpie fine
point marker works well.
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Place the block against the
firewall and draw the outline of the fuselage on the back of the block.
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Draw the outline of the top
view on top of the cowl aligning it with the outline drawn on the back of
the cowl. Use the coping saw to cut the top view outline leaving it
slightly oversize. Draw new centerlines to replace the ones you just
carved away.
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Now draw the side view on the
side of the cowl. Cut the side view, again leaving it oversize.
Replace the centerlines.
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Cover the entire firewall with
masking tape. I apply the tape so that the edges butt together but
do not overlap.
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Wrap 2-3 layers around the
forward fuselage from the firewall to about 4" behind the firewall.
This tape should overlap itself. It should also overlap the firewall
by about 1/4" to ensure that any resin that gets between the foam and the
firewall doesn't glue the cowl permanently to the fuselage.
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Apply a few good coats of auto
wax to only the masking tape wrapped around the fuselage. Do not
apply wax to the tape on the firewall except for a small bit around the
outer edge.
Keep wax away from bare wood
or it will cause you a lot of headaches when it comes time to apply the
finish. This is why you put tape so far back.
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Wrap newspaper around the
front of the fuselage to keep spray glue from getting on the wood and the
waxed tape.
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Apply spray glue to the
masking tape on the firewall and to the back of the foam block.
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When the spray glue is tacky attach the cowl using firm
pressure. Give it about 15 minutes to set up. Ensure that it
is firmly adhered. If the foam does not feel like it will stay in
place remove it and try again.
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Carve and sand the cowl to
finished shape. The foam will make a huge mess so I suggest you do
this outdoors. Take your shop vac with you so you can vacuum the
dust from you and not carry it all back inside.
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Cut a piece of 2 ounce cloth
to cover the front of the cowl. It should overlap the top and sides
approximately 1".
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Cut a piece of cloth to wrap
around the cowl. It should overlap onto the fuselage about 1" and
the front of the cowl by the same amount.
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Vacuum the cowl and fuselage.
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Mix up the resin according to
the directions. Put the piece of cloth on the front of the cowl and
brush resin into the cloth.
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Immediately apply the piece of
cloth around the cowl using the same batch of resin.
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Allow this to set up until it
can be sanded. Lightly sand the cloth to remove crud and to feather
the overlapping cloth. Do not attempt to sand the cowl smooth at
this point and do not cut into the cloth.
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Continue adding layers of
cloth until the cowl is as strong as it needs to be. I find that 3-6
layers is usually plenty. In fact, I almost never use more than 3
layers. A fiberglass part can be very flexible and still be strong
enough.
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At this point I sand the cowl
as smooth as I can get it and add a final layer of 0.5 ounce cloth.
I think it makes the cowl easier to finish, but it's not absolutely
necessary. You can brush on a final coat of resin instead.
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Allow the part to cure
for another day or two. Longer is better.
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Now the cowl needs to be
broken loose from the fuselage. I grab the front of the cowl and fairly violently
push, pull and tug it until it pops loose.
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While the foam is still
inside, I make the cut-outs in the front of the cowl. I follow this
with more dry sanding and finally a good wet sanding working through
various grits. If you go through the cloth, apply more resin to
those areas and sand some more.
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Now cut the back the of the
cowl so that it overlaps on to the fuselage by however much you want it
to. I normally allow about 1/2" of overlap.
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Gouge the foam from the cowl.
Use coarse sandpaper to remove all the foam adhered to the fiberglass.
Some people use solvent or gasoline, but I think this is a bad idea and it
may damage the cowl. Some solvents can break down epoxy.
If you feel the cowl isn't strong enough after you remove the foam, you
can add more layers of cloth with the cowl detached from the fuselage.
Again, the cowl does not need to be very thick or very stiff. If it
is mounted properly it will last as long as the rest of the model.
At this point you can mount the cowl, make whatever cut-outs are
necessary and finish it as you would any other fiberglass part.
