...someone had written a while back about a technique of sheeting foam wings without joining the balsa sheets first...
From : Don Stackhouse
Just tape the wood sheets together, masking tape works but Scotch tape works better. Enough epoxy will bleed through the seams to complete the joint. Make sure to put a sheet of waxed paper on both the top and bottom outside surfaces before you put the whole sandwich back in the beds and then in the press, vacuum bag or under weights. Some epoxy will bleed through the porosity in the wood, and without the waxed paper you will end up with chucks of the core beds securely epoxied to the outside of your wing panel.
And Ivan Munninghoff replies:
...I put epoxy on the wood only (not on the foam) and spread it with a serrated edge squeegee.
Doesn't need much epoxy. Then I assemble the whole thing in the shucks and
put the house on it, just like you used to do.
We used essentially this same method to sheet the production wings for our old "Monarch" R/C hand-launched sailplanes, the earlier versions with the balsa-skinned wings. The key is to have enough pressure. It takes an amazing amount of weight to get enough pressure. We ended up building some screw presses out of 2 x 6's and 1/2" plywood, and threaded-rod screws (about 1/2" threads if I remember correctly, I'll take a look at them again next time I'm out in the barn). We could stack a dozen or so cores in their beds in one of these (it helps to use plywood or Masonite separators between each set to keep things flat and distribute the pressure evenly), then crank the top platen down with the screw and cure all of them at once.
If you have enough pressure, you don't need much resin. The wood should look just damp, with no shiny spots. A serrated squeegee is definitely not necessary, and ends up applying more resin than required. If you're not getting good adhesion between the skins and the core, it's because you didn't have enough pressure. Using presses or weights, the leading and trailing edges can be especially troublesome in that regard, you need a (message lost)
Don Stackhouse
DJ Aerotech
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