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Old 10-20-2006, 09:35 PM
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jwblackout
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Default Please help

I'm trying to find any information as to the optimum, minimum, and maximum weight per square inch when laminating balsa to foam. My current project is a 500 sq in panel. I'm using 1/16th in balsa and west systems laminating epoxy. I have 200lbs right now. Is it enough?
Old 10-21-2006, 01:01 AM
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soarrich
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Default RE: Please help

If I understand you correctly thats 2 1/2 pounds per sqare inch, you can probably get 5 times that vacuum bagging it.

I made a 2 Meter wing with balsa, white foam, and epoxy, using weights in the early '80s, I broke the wing up when I got out of soaring, I found that maybe 5% of the foam was glued to the core, yet it had never failed in flight with what in those days where quite hard launches for several years.
Old 10-21-2006, 07:36 AM
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rwlewis
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Default RE: Please help

Me and a friend have been using 4-6 Inches of Mercury. Equates to 8 to 12 Psi at sea level. We use polyurethane glue, 1 lb density foam, and 1/16 contest grade sheeting. Over time we have been leaning toward being closer to 4 or 5...the higher vacuum just does not seem necessary and at 6 inches I think I ahve seen some compression of the foam. Destructive testing of samples shows 100% adhesion at around 4" Hg, no problem.

With 200 lbs, that 200/500 you've got less than 1/2 psi....To get 8 psi with weights, you'd need 4000 lbs...[X(]

That being said, we did several panels with 200 or so pounds of weight and had a similiar experience as stated above by soarrich...No failures, but destructive testing revealed little adhesion over some areas.....

To answer your question, from my experience if you are using 1 lb density Polystyrene foam....1/2 to 1 Psi is minimal......8-10 Psi is optimal....12 Psi maximum.

An additional note on glues...I wet the skin with the polyurethane glue spreading thoroughly, then wipe up any excess with a paper towel, this leave a minimum amount of glue on the surface. I do NOT use any extra water, we are in SE texas (high relative humidty), and by the time you've spread the stuff on, it has been exposed to plenty of atmospheric moisture. I know I am getting plenty of expansion as the glue actually comes up through the wood grain in places, and I have melted away the foam in samples with acetone and see penetration of 1/8" to 1/4" deep into the foam.....

Richard
Old 10-21-2006, 11:00 AM
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jwblackout
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Default RE: Please help

Thanks Richard,

Great information! Seems to me like vacuum bagging is the way to go. This is my first foam wing build, so I wanted to get it together for minimal cost. That being said, I've already invested in the west systems lam epoxy so I'll roll with that. I'm applying the epoxy with a 6" body knife that I have notched every 1/4" (probably more epoxy than I would need if I used more weight or a vac system). I'm using the weight method on this one. As long as this wing doesn't blow apart in the air, I'll be happy.If I do another I'll DEFINATELY use a vacuum bag system. It sounds like with more pressure, I can use less adhesive and build a lighter wing. I'm applying the epoxy with a 6" body knife that I have notched every 1/4".

Anyone else have any input?



Thanks in advance!
Old 10-21-2006, 11:59 AM
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soarrich
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Default RE: Please help

ORIGINAL: jwblackout

I'm applying the epoxy with a 6" body knife that I have notched every 1/4".

Anyone else have any input?
That will give you too much epoxy. After you spread it on, take a credit card from you wife's purse, and use it to try to scrape off the epoxy, the amount you can't get off is enough to hold the skins on. It's a win win, you save weight on the wing and money your wife doesn't spend.[8D]

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