The old 3M 77 contact cement is back!

[Earl Haury]

FWIW, I conducted an experiment with adhesives for skinning wings a few years ago. 

I glued two pieces 1" X 3" X 1/4" balsa to opposite sides of a 1" sq. block of 1# density foam using a variety of adhesives. The foam was placed at one end of the balsa "skins." After the adhesive cured a 1" dowel was placed next to the foam (placing the center at the center of the balsa) and the assembly placed on a digital scale. With the scale tarred to 0, pressure was then applied to the end opposite the foam until the balsa separated from the foam. The force at which the separation occurred was noted. (Pretty much a perpendicular pull on the glue joint / foam.)

Adhesives included 3M77, Sorghum, ProBond, and several epoxies with and without "hairspray" treatment of the wood.

The 3M77 assembly separated at 16# with no foam staying with the wood (adhesive failed), the Sorghum let go at about 8# and some foam beads still being glued to the wood. The ProBond and all of the epoxy assemblies all failed at 18# (nominal) with the foam blocks separating.

Conclusion: Under the best conditions the contact cements aren't as good for wing skin attachment as epoxy or ProBond. (But then that's pretty well known.) 

Unknown: Behavior in shear - which is, at least, equally important.

Earl
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