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Weight saving holes in foam core wings.
It's quite common to reduce weight of foam-core wings by removal
of foam. Some people make holes in the foam from top to bottom, and even
cutting out the cores in a honeycomb shape structure. These methods do
save weight, but in my opinion they have too many drawbacks. First of all
the wing becomes very fragile in the areas with balsa sheeting and no foam
underneath, grab a good hold of the wing and your fingers will penetrate the
sheeting. For me the other major drawback is the fact that my usual
vacuum-bag method of applying the sheeting does not work, the foam structure is
weakened so much that it will be crushed by the force of the bag. My method
involve cutting holes in the foam from root to tip of the wing, to maintain the
strength of the cores during sheeting the holes are cut after sheeting the cores
with balsa. To enable this the wire to use for hot-wire cutting needs to
be embedded into the foam before the sheeting is applied. The pictures
below should explain the process steps:
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Use
a straight edge and sharp knife to cut a slit for the wire-
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Push
the wire into the slit
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The wire is in place
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This
picture shows the wing with root-rib in place ready for sheeting. The rib
to be used at tip is shown also.
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The
sheeting is on and the first hole is cut with the previously embedded wire
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The
holes are cut
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The total weight saving for the set of wings used in this example (Integral)
is 42g. That may net be significant, but to get a light model weight must
be saved everywhere.
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