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sheeting foam wing ?

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Old 10-20-2006, 09:47 PM
  #1  
jwblackout
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Default sheeting foam wing ?

I'm sheeting a 500 sq in wing panel with 1/16th in balsa skins and west systems laminating epoxy. I have 200 lbs to put on my saddle/core sandwich. Is that enough? What are minimum/maximum/optimum loadings per sq in when doing this?
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Old 10-20-2006, 10:01 PM
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Default RE: sheeting foam wing ?

Double or triple your 200 pounds would be better.

At 500 squares and only 200 pounds--your less than 1/2 pound per square inch of wing.

You really can't get too much weight on it. Even 500 pounds would only be 1 pound per square inch.

You can make some pretty heavy sandbags out of an old car innertube. Remember the old rubber tire innertube? Cut it and then tie the end closed. Fill the other end with sand. Tie it closed. More wight than you'll want to lift up and put on the bench. Cheap.
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Old 10-20-2006, 10:08 PM
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jwblackout
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Default RE: sheeting foam wing ?

Thanks RCPilet,

Any suggestions on getting that much weight on an 18 x 36 sheet of particle board? Seems like vacuum bagging is the way to go, but my resources are limited!
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Old 10-21-2006, 06:17 AM
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Default RE: sheeting foam wing ?

There are a bunch of reasons that almost everyone who continues to sheet foam wings eventually migrates to vacuum bagging. And there are two reasons they don't change after that.

It's really worth the effort to find yourself a bag. That's about the only hard part, and it's a lot easier than all the effort and difficulty to gather up weights and junk. And the vacuum bag puts tons of pressure on the sheeting uniformly. The weights don't, and they slide off, and you've got to have a strong level area for the stack (floors ain't always level) and etc etc etc

Plastic drop cloths often come in adequate thickness, and are cheap.
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Old 10-21-2006, 09:43 AM
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Default RE: sheeting foam wing ?

Check out ACP Composite's cheapest vacuum bagging complete set up. I found that the $100 spent on it was well worth the cost, and it comes with a great video to get you going and show you what you can do with vacuum bagging. http://www.acp-composites.com/
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Old 10-21-2006, 11:14 AM
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jwblackout
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Default RE: sheeting foam wing ?

Thanks fellas!

The apc system looks great! I really want to get this build under my belt before I invest in a vacuum system. I, like most us here, am afflicted with rcaholism so I know I'll build another one. I just don't want this wing to fail on me. I'm pretty sure that on my next build I'll use vac and poly glue to adhere skins. It seems like the lightest, strongest way to go. With that said, on THIS build I'll be using west systems epoxy applied with a body knife that I have knotched every 1/4" and WEIGHT. Designer recommended AT LEAST 1/4 lb per sq in, so I doubled that. Sounds like the more weight I can round up the better off I'll be.

Any other advice?

Thanks in advance!
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Old 10-21-2006, 04:47 PM
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Default RE: sheeting foam wing ?

Any other advice?
Do not, repeat not, use that putty knife. Anything that has notches in it will give you way too much epoxy and way, way too much weight without any benefit to the strength.

Designer recommended AT LEAST 1/4 lb per sq in
That's a total of 125# versus the vacuum bagging system giving you about 7 pounds per square inch or total weight equivalent of 3500 pounds. Which do you think will give you the better bond and stronger wing?

I really want to get this build under my belt before I invest in a vacuum system.
If it's time that's an issue, the ACP system can be there in two days.

No, I don't work for ACP, but after my experience I wouldn't waste my time doing it the way that you are planning, especially since you state
I just don't want this wing to fail on me.
One more thing - Use 1/32" balsa instead of the 1/16" you mentioned. It will give you more than enough strength. It's not the thickness of the balsa that gives strength, it's the completeness of the bond of the foam to the balsa.
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Old 10-21-2006, 07:15 PM
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Default RE: sheeting foam wing ?

Everything Newc said plus..........

The vacuum system will help retain the sheeting in the right orientation to the core. Loading bricks or sacks of corn or whatever you've found to pile onto your wing is not going to keep things lined up, it's going to contribute to shifting the sheeting around from where you placed it.

It's really not easy to set up two sheets of balsa that're slick with epoxy onto an almost weightless foam shape and then place that result so it'll keep its orientation as you start to load on your weights.

You aren't going to be able to see if the skins are aligned as you slowly stack your weights. And the building load being erratically placed is going to make the skins want to shift on the core. And you won't know it's happening.

However, once you've collected whatever it is you plan to use for weights, they'll be readily available for a 2nd try as soon as you open up the surprise package when it's cured. How do I know? Ain't saying, but I promise that I will never again try that.
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Old 10-21-2006, 08:18 PM
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Default RE: sheeting foam wing ?

One more thing - Use 1/32" balsa instead of the 1/16" you mentioned. It will give you more than enough strength. It's not the thickness of the balsa that gives strength, it's the completeness of the bond of the foam to the balsa.
That depends what you are building and loads it is expected to withstand. A good bond with foam will help prevent the skin from buckling under compressive loads, but it is the thickness of the balsa and it's density that withstands compressive loading.
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Old 10-21-2006, 10:41 PM
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jwblackout
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Default RE: sheeting foam wing ?

Thanks for all the great advice everyone!

Sounds like I need to get myself a vacuum bag setup before I go after the wing project. I've already laid up the flying surfaces for the empannage (I had a couple extra rudders to practice on), but at this point I could always pickup the vac system and re-do the rudder and horizontal stab in the interest of saving weight.
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Old 10-22-2006, 08:19 AM
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Default RE: sheeting foam wing ?

but at this point I could always pickup the vac system and re-do the rudder and horizontal stab in the interest of saving weight.
If I were you, I'd make a 2nd set for no other reason than to get an idea of what you get with the different techniques. If you're cutting your own cores, the cost to do extras is almost zip.
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Old 10-22-2006, 10:05 AM
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Default RE: sheeting foam wing ?

I like the way you think darock.
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