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Old Jan 13, 2013, 08:37 PM
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Help!
Bagged wing core foam choice

I'm interested in bagging a wing for a full spar, 5+m scratch scale sailplane, using a Feathercut and Phil B. method. It's my 1st large bagging attempt. I'll also use the foam for a fuse plug. I plan to use either the Dow blue, or Owens pink 2" styrofoam for the cores . Both are available locally. Are they equal in use, characteristics and results, or is one preferred over the other? Thanks for your help in making the best choice. Bob.
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Old Jan 13, 2013, 08:55 PM
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They are so close for the same given density that either would be fine. The pink seems to make fewer hairs, but the difference isn't drastic.
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Last edited by Cory; Jan 13, 2013 at 09:17 PM.
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Old Jan 14, 2013, 12:55 AM
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What you really want to be looking at is the compression strength of the foam. Its rated in PSI

Dow blue foam highload 40 is 40 psi
highload 60 is 60 psi
highload 100 yep, you guessed it 100 psi
SM is common at 30 psi
dow specs http://building.dow.com/na/en/produc.../rigidfoam.htm

pink foam 250 =25 psi
300 = 30 psi
^^ foamular
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Old Jan 14, 2013, 10:38 AM
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Dow Surfboard Blanks

I use the surfboard blanks. My understanding is that the foam has a vertical grain and is a bit stronger than the insulation foam commonly used.
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Old Jan 14, 2013, 05:59 PM
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The pink foam and spyder foam (surfboard) are a bit easier to work with and sand better in my opinion ! The spyder foam cuts very nicely as well !
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Old Jan 15, 2013, 04:59 PM
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Foam Choices 2"x4x8

Thanks guys for the replies & information. Since this is my 1st attempt, I'll stick with the low d stuff--It's cheaper, and available locally at the box stores. My choices for local purchase are Owens pink #15, ($28), Dow blue #20 ($35) or Dow blue 25 ($45). Guess I'll check them out tomorrow, and make a choice. Thanks again for the help. All suggestions welcome. Bob.
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Old Jan 15, 2013, 06:32 PM
I DS slower than I build!
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Personally I would go with the blue 25 psi foam. I would be concerned that the cheepo 15 psi stuff is not strong enough. I'm only guessing on this but since you are building a 5 meter wing there will be larger forces involved. The 60" DLG guys typically use 60 psi foam, and occasionally 40 psi.
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Old Jan 15, 2013, 06:51 PM
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If I used kevlar skin I will use DOW SM [30 psi] because the compression strength is more than suitable and the kevlar offers better dent resistance. 30 psi is great . The thing I dislike about the 30 psi compared to 60 psi is when you get to cutting the gap for the hinges. The denser foam cuts are clean whereas the soft foam tend to want to ball up in front of the blade and pull out from under the foam. Its important to hold your [new] blade on a sharp angle or the hingeline becomes as mess. I sure wouldnt let price dictate which foam I use.Far to much work goes into the wings to worry about a few dollars IMO
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Old Jan 15, 2013, 07:48 PM
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I agree, I need to go with the higher d#, probably at least 25#. This will actually be a 6.6m scale sailplane wing, each side having a 6' and 5' panel. One dealer has blue foam that is printed "Blue Dow Board 250". I'm not sure if it is 25#, so I'll check it out in person tomorrow, along with other higher density options. I never realized there were so many kinds of blue and pink foam. Definitly need to do more research before buying. Thanks for giving me a head start, and saving some future problems. Bob
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Old Feb 03, 2013, 04:03 PM
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If you build a stout spar system, I would not worry as much about the density of the foam.
If your spar is going to be less "over built" in quest of saving weight, you might be better off springing for the denser foam.
Its easy math that a big project time wise doesn't really warrant saving a few dollars on the raw materials.
Got me feet wet in Scale Aero-Tow yesterday, it was awesome!

Good luck with your project!

The designation Square Edge or Square Board 250 is almost certainly 25PSI foam, they are very simple about their labeling.
It may be a good idea to use Hi-Load 60 on your inboard panels to add a little strength and crush resistance there (plugging into mono-blocks in the fuse?).

R,
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Old Feb 03, 2013, 09:17 PM
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If you are using the Phil Barnes method that means you will be gluing carbon tubes into the cores as a spar/joiner interface with carbon uni bagged over the surfaces.

The uni-carbon is the actual spar in this set up, the carbon tubes are for the most part just along for the ride but they are very handy for holding the joiners and they do add a small margin.

One critical component in this type of wing build is the foam because it acts as a shear web between compressive and tensile forces acting on the wing (between the two layers of uni-carbon, the spar) these carbon tube/uni wings are susceptible to buckling failures and when that happens it is usually catastrophic...the denser foam helps prevent this. If you use light foam your wing will probably be great for a while but in my experience all the wings I built in this fashion with light foam failed long before the ones I built with denser foam.

So you want Hi-Load-60 minimum...at least on the root sections. You are building a multi-panel wing so if you want to use lighter (cheaper) foam use it out near the tips but use the best you can get in any case.

I don't mean to preach but it sounds like you will be putting many hours of effort and a lot of heart into this glider, don't start the whole project with a potential disappointment factor built in.


Tony
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Old Feb 04, 2013, 08:57 PM
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Where are you guys buying spyder and rohacell? Who usually has the best pricing?
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Old Feb 04, 2013, 10:53 PM
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foam

Thanks Tony, R and others for the suggestions. I did find out the hard way that some of the 4'x8' pink and blue foam comes scored about .5-.75" deep on both surfaces so it can be snapped to fit 16 & 24" studs. Since this is for big wings, with up to 1 1/4" rib heights, I had to take them back, but I did find some 2x8' square cut blue, which is 25#, and not scored Since this wing will have a full, cf cap and solid web spar system, I might just use the 25# if I can't find denser locally. I'll keep looking . Not sure where to get the 40-60# foam without breaking the bank. Thanks again, Bob.
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Last edited by flyingfever; Feb 04, 2013 at 10:55 PM. Reason: add info
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Old Feb 04, 2013, 11:03 PM
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I actually found highload 60 at 30 per sheet rather than 34 for SM at Rona home center. If you find highload 60 the price isnt necessarily more E-mail DOW and ask them where their closest dealer is to you. thats what I did
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Old Feb 05, 2013, 09:10 AM
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I used to buy HL 60 from a place called WhiteCap supply, I think. The 2' wide sheets were about $18 a sheet if I recall correctly.

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