 | |  | |  | |  |
At the AMA Nationals in 2005 I had two airplanes to fly the ten rounds. In
one heat I was in five mid air collisions. The airplane survived those
collisions but I could feel the foam beneath the covering flexing and knew
that eventually I would have to strip off the covering tape and repair the
cracks that ran through the wing.
In the top picture on the right (click on it to see larger view) a Sharpie felt
tipped marker has been used to trace over the cracks in the wing. Do this
on both the top and bottom of the wing. In some cases you will not be able
to see the breaks in the foam until you forcibly flex the wing. Mark the
cracks and get ready to start the repairs.
The second photo shows holes drilled every half inch along the cracks. In
most cases these holes are 3/16" and do not go all the way through the
wing. These holes will be filled with Elmer Ultimate Polyurethane glue. The
PolyU glue is itself a foam and will bond completely with the surrounding
foam and become an integral part of the structure and eventually be
stronger than the surrounding foam.
In the third photo you can see the glue being forced into the holes. It is
messy as it flows out, but force it into the holes thoroughly. Messy is bad,
but getting a lot of glue into the hole and into the crack is a really good
thing.
Wipe the excess glue off the wing surface. As PolyU glue dries it will
expand into the hole, the crack and out of the hole and make a big ugly
glue blob mess on top of the wing. Wipe off the ooze that is now still liquid
and then apply masking tape over the glue. It won't prevent the glue blob
from foaming but it will help minimize it.
Once the glue has hardened, usually about 24 hours, you can cut off the
blobs and sand out the glue. I have found the Great Planes Power planer
to be the best tool to cut down the expanded glue. A Master Airscrew razor
plane will also make quick work of cutting down the glue.
The two wings I have repaired in this manner were completed much faster
than building an entirely new wing and certainly a lot less costly. They fly
identically to the way the wings flew when new.
