Sequoia Aircraft Corporation F.8L Falco, Construction Manual

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F.8L Falco Construction Manual 8–9 Revision 4, March 1, 2002
The West System epoxies are low viscosity resins, designed primarily as a moisture protection
coating that is adapted for use as a wood glue. They have little resistance to glue starvation
caused by clamping, and Gougeon recommends the addition of Microfibers (cotton flox) to the
resin to prevent glue starvation and for greater gap-filling capabilities.
The West System epoxies require a five-to-one mixing ratio, but this is not a problem since
Gougeon sells dispensing pumps which provide the necessary ratios of resin and hardener. We
highly recommend the West System for use as a moisture protection coating, both as an interior
varnish and when covering the outside of the airplane with fiberglass cloth and epoxy. If it
weren't for our concerns about the temperature performance of epoxies, we would recommend the
West System without reservation for gluing wood.
And what does Gougeon Brothers say about our position on epoxy? The head of the testing
department says that our position is exactly the same as theirs: that concerns about the
temperature performance of room temperature cure epoxies are valid even though they are not
aware of anyone having problems with white-painted epoxy-built wood aircraft. They know from
tests that the temperature performance of West System is better than high viscosity flexible
epoxies (such as T-88). They have not run enough tests at elevated temperatures to chart the
performance of their epoxy system. They are hard at work developing an epoxy system with better
temperature performance, but it is a difficult task. The reactive diluents which are needed to thin
the epoxy for good penetration into the wood fibers lower the temperature performance, and the
additives that raise the temperature performance have undesirable characteristics.
Figure 5
Test Blocks
All wood aircraft manufacturers test each batch of glue by gluing two blocks of maple wood
together. When pulled apart, the wood must fail before the glue. Maple is used since it is stronger
than spruce, so if the glue will hold until the maple breaks, then it will have plenty of strength
with spruce. This technique of using test blocks is an excellent one, and something you should