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Old Sep 30, 2012, 05:55 PM
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United States, MN, Hermantown
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Foam for cores ? Also tip template placement for washout?

I have this foam, but am not sure what type of foam it is, or if it's suitable for cores.
It was used for insulating roofs.
If useable, wings will have balsa L.E's and T.E., flaps/ailerons, fully sheeted, and 3/4oz glass. CF spars.
TIA
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Last edited by CoolerByTheLake; Nov 01, 2012 at 12:49 AM. Reason: Title change
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Old Sep 30, 2012, 06:00 PM
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It looks like plain beaded foam. Perfect for a balsa sheeted wing.
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Old Sep 30, 2012, 06:15 PM
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It looks a lot more like an extruded (rather than plain expanded) foam, something like Dow Roofmate. It's probably what's commonly called Blue foam (or Pink foam, same stuff, different manufacturer). If so it will be quite a bit heavier than ordinary beaded foam though also somewhat stronger.

It will certainly work well for fully sheeted wings but it's more typically used for unsheeted wings and parts like turtle decks etc. often directly glassed. For the use you want just watch the overall weight.

Steve
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Old Sep 30, 2012, 09:30 PM
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Well it's not beaded foam, although it does resemble it. and it's not polystyrene( like the blue or pink) foams. Much stonger then the beaded, and fairly light. It's not as dense as the Dow or Owens-Ccorning foams.

I got a few of these for free awhile back, and they have a taper to them, from 4" to 3.5" in 4'x4' squares. I just weighed a piece I cut 2'x4' and it weighed 2.1lb.
I figured that is 1152sqin, and my wing panel comes out to be approx 412sqin.

This is for an F-86, so you know what the wing panel shape is. Root cord is 18" tip cord is 9" panel length is 28" Max thickness of root cord is about 1.75"

So if you figure out what each panel wil use, it's very small amount out of each piece. Should not weigh to much at all, for the core, that is.
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Old Sep 30, 2012, 09:55 PM
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Quote:
Originally Posted by CoolerByTheLake View Post
This is for an F-86, so you know what the wing panel shape is. Root cord is 18" tip cord is 9" panel length is 28" Max thickness of root cord is about 1.75"
Which F86 model is it?
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Old Sep 30, 2012, 10:05 PM
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Have been using measurements from this one.
North American F-86F-30-NA "Sabre"
S/N 52-4978 Long , 6-3 wing.

http://www.rcgroups.com/forums/showp...&postcount=173
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Old Oct 02, 2012, 11:07 PM
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In the second picture, there are a lot of white specks. Those looks like "beads" to me! Having cut a lot of Styrofoam these last 30 years, it sure looks like white beaded styro to me.

One thing that I got reminded of recently is that most foams come in different weights. That nice light styro will crumble very easily! Then you take the foam that Omaha steaks are sold in and it's very difficult to get to beads to come off.

Home Depot sells a white beaded foam that makes excellent wing cores and weighs about 2 pounds per cubic foot. But it can be hard at times to find.

I'm not sure as to why, but sometimes building contractors will have sheets custom made with a taper to it for walk in freezers. At least that is what one local supplier told me. He gave me a couple of sheets that were left over from an order that he had. Sure made nice wings!!

Blue Skies...........................Tim
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Old Oct 04, 2012, 11:16 AM
Do it Right, the first time!
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RWCLOUD, It looks pretty ragged because I cut it with a hand saw! Actually, they are not beads, but close up look more like "cells". I got this foam from a roofing contractor. They had cut there own tapers at one time, and I guess now they just buy it that way now. I never pass up anything thats free, if I think I can use it!!
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Old Oct 04, 2012, 09:06 PM
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Just so you know, there's different densities of polystyrene foam (beaded foam).

Obviously you want to have the lightest foam you can find if you're doing sheeted cores.

I know that where I buy my foam from you can buy in "H" grade (heavy), M grade (medium), L grade (light), and SL (superlight). Superlight is around 1lb/ft3 I think.

In my experience, insualtion grade foam is usually H.
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Old Oct 04, 2012, 09:35 PM
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The question

Yes-that is the correct foam for a sheeted wing.
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Old Oct 04, 2012, 09:45 PM
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Ahh, sorry I may have misunderstood when "cores" were mentioned.
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Old Oct 06, 2012, 06:21 AM
Do it Right, the first time!
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Templates and washout

Thanks guys I will give this foam a try. The wings will be sheeted and glassed.

A couple other quick questions. Templates?? I have seen it done two different ways.
1.Separate upper and lower airfoil templates-female
2. single airfoil shaped template-male. Is one more accurate than the other?

Washout--I realize that on build up wings, you would block up the tip of the T.E.
But when cutting foam cores that doesn't seem to practical. My thought was to draw center line threw root and tip of core blank, then center L.E of tip airfoil and raise T.E of tip airfoil the amount of degrees I need for desired washout.
Will this work out the same? I have cut cores but a long time ago, and I don't believe they had any washout.
Thanks for your help.
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Old Oct 06, 2012, 06:34 AM
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preferences.

I prefer a single male template,as smooth as possible on the edges..

A little washout never hurts.

Ha-be sure to reverse the image when cutting the second one.
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Old Oct 06, 2012, 06:44 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
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tip template placement?

Would some one please explain the proper way to locate the tip template on a foam core for washout.

I see how this is done in a built up wing-- http://www.rcgroups.com/forums/showp...0&postcount=18

So how do you go about placing the tip template on a foam core, for lets say 2 washout?
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Old Oct 06, 2012, 04:13 PM
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I draw a centerline on the foam core,and attach the center rib to the core with a couple of long nails through it's center line.

Using a protractor at the tip,draw a center line at 2 degrees,and locate the tip rib there.

I don't always use a degree # though,I just make sure the trailing edge is a bit higher than the leading edge,when the wing is flat on the table.

An accurate measurement to duplicate that on the opposite wing is imperative...

Of course,be sure the templates are securely fastened for cutting.
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