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Posted by cliffo | Dec 20, 2011 @ 10:35 AM | 3,650 Views
The Brown Hue

This blog entry will include my ongoing experiments with vacuum bagging EPP. Most knowledgeable builders using EPP foam have recommended NOT vacuum bagging EPP foam. These experts are referring to the typical manner of vacuum bagging using epoxy, fiberglass a blue or white foam wrapped in 14 mil mylar sandwich. This is then stuffed into a bag with all the air sucked out by a compressor at from 5Hg-27Hg.
Some of the reasons "bagging" EPP is not recommended is that epoxy does not stick well to EPP foam, also the fiberglass tends to get pushed into the natural openings and crevices of the EPP making for an unattractive finish.

The Process:
I have found a different manner that seems to work well in the limited experimentation I have done. The method requires that you iron laminate to the fiberglass, kevlar, etc.. Laminate is a plastic film with, generally, glue on one side. We are used to seeing it as the plastic that encases our drivers license but it has many uses and has become popular as a covering because it is inexpensive. Gluing the fiberglass to the laminate means you heat the laminate with an iron onto the fiberglass. Typically I have been doing this with 1/64" ply between the mylar and the iron in an attempt to keep the laminate smooth. Lately I have been just ironing it straight on. For the glue I have been using brown Gorilla glue carefully screeded onto the fiberglass. Wetted with water and layed onto the EPP...Continue Reading
Posted by cliffo | Nov 03, 2011 @ 07:16 PM | 3,224 Views
EPP foam is like a sponge cake. Easy to compress but very hard to damage. When using mylar covering on EPP it is easy to put in a warp because of the shrinking characteristics of the mylar. Laminate, because it doesn't shrink, seems to be the perfect covering for EPP and it's cheap. Many of the glues do not seem to work on EPP foam especially Epoxy. CY glue works but it is so stiff and the foam is so soft sometimes there are difficulties. Laminate we use has glue that is activated with heat from our hobby irons. It seemingly does a good job on EPP but the adhesion is not very good over time or after some bumps. Extreme filament tape has glue that sticks to EPP better but overtime it too has difficulties and especially if moisture is introduced.

What is available as a substrate cover that helps the adhesion is 3M90 spray adhesive. The best way I can describe 3M90 is spray contact cement. When you spray from the can it comes out thick and stringy, yuck. The best way I have found to spread this is to have a latex gloved hand ready to smear the glue onto the EPP foam after it is sprayed on.

After you get the 3M90 covered wing done it is ready for the Tape and laminate. Extreme tape is very susceptible to UV light and I like to add some 2" colored packing tape over the Extreme tape. After taping the wing sometimes I will add even more 3M90 for the laminate part of the covering.

When heating and gluing the laminate I have found having my iron as hot as I dare and not melt the foam or tape works best for a very good adhesion. From testing I have found the higher heat re-melts the glue of the 3M90 for an even better adhesion of the laminate and tape.

Test for yourself and let me know how your wings come out.

Posted by cliffo | Nov 03, 2011 @ 05:59 PM | 2,886 Views
Melting the trough for the spars:

I have a modified cheap soldering iron that I have ground the tip on. Actually the very tip I have ground round. Above this round tip I have ground a blade shape to go through the top of the wing. Where the blade shape stops is where the soldering iron glides along a metal ruler as I am melting the foam for the spar. Can you imagine it in your head? I may post pictures.

The bottom of the tip is melting the foam for the spar. The blade portion above is melting foam but much less and so the round spar pops into the wing with foam holding it on top. Your then not melting a ditch for the spar but a circle below the top of the wing with a small opening that the blade portion made.

Glueing the spar:

Most hot melt glue gun glue from Home Depot and etc is low temperature. This is what you want. The high temp glue will melt the foam. Before laying the glue down make sure you can pop the spar in to where it sits flush in place. Sometimes you have to dig out partially melted foam and other junk. Use some needle noses here for cleaning out.
Laying down the glue then I stick the tip of the glue gun into the trough through the opening the blade portion of my soldering iron made and quickly run a bead of hot glue. The glue hardens in about 40 seconds if your gun is at the correct operating temperature. Pop in your pre-cut spar and viola. I can install all 6 spars in about 15 minutes using this method.

Why not use Gorilla Glue? The hot melt has a harder hold on the spar. I have experienced the white Gorilla Glue letting go of the foam. This method is much faster.

Based on recent tests of the white vs brown Gorilla Glue, from very limited testing, the brown Gorilla Glue does not foam as much however the brown glue appears to be twice as hard as the white glue which to me would make for a better spar installation.

If memory serves none of my wings using hot glue have experienced flutter or flapping but they have using the white Gorilla Glue.