Corning Foamular 250 for Winglets

[Byang]

Hello! 

First time poster here! Currently working on a Long EZ, and was wondering if Corning Foamular 250 pink insulation board can be used as a substitute for the XPS PIB that ACS sells. Been doing some research online and haven't found any info in terms of aircraft construction, but know a few groups in college that laminates over the stuff for cars and RC planes. There's probably a good reason why this isn't being done, but the tech data seems pretty similar between foamular and the ACS stuff. Is it something worth looking into and testing? Would really appreciate some thoughts and ideas. Thanks! 

[Marc Zeitlin]

9 hours ago, Byang said:

Hello! 

First time poster here! Currently working on a Long EZ, and was wondering if Corning Foamular 250 pink insulation board can be used as a substitute for the XPS PIB that ACS sells...

The answer is "no". Insulation board is not appropriate. Stiffness is too low. See:

https://www.aircraftspruce.com/catalog/cmpages/styrofoam.php

which is effectively the same thing, and which I evaluated for ACS and made sure that they put a note on the page explicitly saying it's NOT appropriate.

Why not just use the correct material?

[Jon Matcho]

The top chart is the Styrofoam foam, and the bottom is the Foamular pink board. Compressive strength is higher with the pink Foamular board. Flex strength is not shown for the Styrofoam foam. Having worked with both, I suspect the pink board is actually "stiffer" than the plans material.

Regardless, the cells are MUCH smaller in the pink foam and would make bonding difficult (and the results questionable). The "Large Cell" in the Styrofoam product name is important because it easily allows the epoxy to form a strong mechanical bond between the foam and the fiberglass.

1 hour ago, Marc Zeitlin said:

Why not just use the correct material?

Absolutely! Spare no expense when building airfoils to plans.

[zolotiyeruki]

3 hours ago, Marc Zeitlin said:

Why not just use the correct material?

I understand that Dow no longer manufactures the blue styrofoam, and replaced it with a new formulation that doesn't adhere as well to epoxy, so long-term availability is a concern.  Did I hear wrong?

[Kent Ashton]

On the topic of foam:  It appears that Dow has recently changed the formulation of the blue polystyrene foams (tradename Sytrofoam) we use to make wings (see clip from Dow's website below). 

https://www.dupont.com/building/styrofoam.html

I do not see the large polystyrene blocks listed in the Spruce catalog.  No idea if the Low-GWP foam would be suitable and anyway, I do not see it in the size we need.  I see a few dock-builder suppliers that say they stock blue floatation billets.  Here is one, maybe they still stock them.

https://www.dockbuilders.com/shop-by-category/floating-docks/dock-flotation/dow-styrofoam-billets.html?gad_source=5&gclid=EAIaIQobChMIpdXCku_jiAMV6GRHAR3GzgChEAAYASAAEgI3UPD_BwE

Edited September 27 by Kent Ashton

[zolotiyeruki]

16 hours ago, Kent Ashton said:

I do not see the large polystyrene blocks listed in the Spruce catalog.  No idea if the Low-GWP foam would be suitable and anyway, I do not see it in the size we need.

 

I'm unaware of any empirical testing of either the pink hardware store foam or the new Low-GWP foam.  Thus far, all I've seen is a comment here or there.

[Marc Zeitlin]

18 hours ago, Kent Ashton said:

I do not see the large polystyrene blocks listed in the Spruce catalog....

You mean this stuff?

https://www.aircraftspruce.com/catalog/cmpages/polystyrene.php

[Byang]

23 hours ago, Marc Zeitlin said:

Why not just use the correct material?

Oh I will, just wondering why people don't use the stuff considering its cheaper and much more readily available. I now have my answer! I managed to find a supplier for foam in Kansas City, checked the TDS and its the exact same thing that ACS sells. Just gotta drive out and get it. Thanks for the help!

[Marc Zeitlin]

2 hours ago, zolotiyeruki said:

I'm unaware of any empirical testing of either the pink hardware store foam or the new Low-GWP foam.  Thus far, all I've seen is a comment here or there.

I've had the stuff that the OP posited in my shop. I've handled it and attempted to bond to it. It is not acceptable.

I have not yet tested the new formulation of the XPS - I'll buy a piece to test, although I suspect that there will be zero difference. The bond between the foam and the glass laminate comes from a mechanical bond between the micro and the pores in the foam, not from surface finish of the foam, although if the foam were made of teflon, that would be problematic. At any rate, by the middle of next week, I'll have an answer.

While it does not come in the same sizes as the original foam, it can easily be built up to work - it's not like the plane was carved out of a solid piece of foam in the first place.

[zolotiyeruki]

On 9/28/2024 at 9:49 AM, Marc Zeitlin said:

I've had the stuff that the OP posited in my shop. I've handled it and attempted to bond to it. It is not acceptable.

I look forward to seeing your results with the grey styrofoam.

Out of curiosity, how did the pink XPS fail your tests?  I know the faces are pretty smooth, and might not bond with epoxy without at least a little sanding.  Was that it? Or is it structurally (shear, compression, etc) inadequate?

[Marc Zeitlin]

5 hours ago, zolotiyeruki said:

I look forward to seeing your results with the grey styrofoam.

Me too. I'll have some tomorrow - should be able to test it by the end of the week.

5 hours ago, zolotiyeruki said:

Out of curiosity, how did the pink XPS fail your tests?  I know the faces are pretty smooth, and might not bond with epoxy without at least a little sanding.  Was that it? Or is it structurally (shear, compression, etc) inadequate?

It's too smooth and doesn't bond worth a crap. It doesn't sand - it just tears. It's too flexible - the modulus is far too low, and it's not stiff enough to provide buckling resistance to layups.

Other than that, Mrs. Lincoln, how was the play?

[zolotiyeruki]

Any updates on the testing?

[Marc Zeitlin]

2 hours ago, zolotiyeruki said:

Any updates on the testing?

Got the foam yesterday. Busy for the next week or so, but I've got a few layups to do so I can probably just tack on a small layup to the new stuff to see how it works.

First impressions are that other than the color, it feels, looks and acts exactly like the original blue stuff. Unless it's got some additive in it that keeps the epoxy from sticking to it, I don't imagine there'll be any difference whatsoever, but we'll see.