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Spray Foam in W715 Wing Tip?

CD.

Active Member
I have a 7A with the old style W715 batwing tips. The paint has cracked a few inches in from the trailing edge tip. I think it may be because of some flexing due to a thin fiberglass area. I have the wingtip off working on my lights. The area is too restricted for access to add another layer of fiberglass. I have another similar finish crack behind the light pocket that I am going to add a fiberglass strip while the wingtip is off.

My question is.. can I just spray some of expanding foam down in that trailing edge tip to provide some internal support? Any reason why I shouldn't do that?

Thanks!
 
Everyone I know who has used spray foam in that type application has indicated it is/not a stable product and led to more problems down the line - bulges and the like. I know a couple of those folks have dug the spray foam out after the problems became apparent.

Is there any way you could use tools (popsicle sticks, paint stirrers) to add a layer of fiberglass in the tight area(s)?
 
We do this often in the composites shop in similar scenarios with good results. Make sure that the foam has a large area to escape. If you do not, it will bulge.
 
Something to think about

Consider styrofoam bean bag balls from hobby lobby. Stir in some West 105 like you are making carmel corn. Feed it down into the crevice with a ruler, aluminum strip etc. this should be much lighter than glass bead micro.
 
I tried two-part urethane foam to stabilize wingtips so I could block sand them nice and flat. They were beautiful...until altitude changes made the foam shrink and swell. Same thing happened with one small section applied for shape, and left inside a non-structural layup. Won't do that again. Pour foams are not like block foam, and I can't imagine spray foam is any better.
 
Flox

I wanted some sandable structural edge. They needed a little cut off.
The wingtips were hung from the garage frame. Taped the open edge to form a dam. Some flox was mixed and applied with a popsicle stick taped to a dowel. It flows so the aft edge needs to be level. Worked great. If you want it lighter, mix in some of the foam beads mentioned. Should make for a really strong light filler.
 
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