Subject: Re: [harryproa] Robs playing with polystyrene...
From: "Rob Denney harryproa@gmail.com [harryproa]" <harryproa@yahoogroups.com.au>
Date: 7/7/2018, 8:18 PM
To: harryproa@yahoogroups.com.au
Reply-to:
harryproa@yahoogroups.com.au

 



On Tue, Jul 3, 2018 at 9:02 PM, '.' eruttan@yahoo.com [harryproa] <harryproa@yahoogroups.com.au> wrote:
 



| PS was good, although I have not jumped on it or hammered it.

Bead foam, right?

​Yes.  Standard density, which is quite soft.  The job should not see any impacts, is lightly stressed and never submerged. This is not the material I wil be testing.   I built a second fairing with just one layer of glass.  Very nearly stiff enough.  The final version may be 2 layers of 400 with no core.    Lightest would be 200 either side of 3-5mm H60 in a mould, but I am trying to build it from a flat panel, which would not work with these materials/methods.


| Remarkably stiff, I had to cut slots in the inner layer of glass to get it to conform to the fairing shape.

How does this compare to other core material you may have made the faring out of? This was wet lay up over solid core, or was the core detailed with resin pockets or something?

​As the core is not highly loaded, it is pretty similar in the required property, which ​is stiffness of a lightly loaded panel.  It would be hopeless for any other use.  No resin pockets or other details.  


| The rudders halves are built, one of them is joined. The ps moulds did not like being filled with sand (alternative to vac bagging) and compressed a little, but once I realised this, they were ok.

So, you were at the limits of the mold strength, and it yeilded some?

​Yeah.  Less sand in the next one and it worked much better.​


| The compression means the leading edge radius was bigger than it should be. Pretty easy fix with some bog and a straight edge. The Foamular or Dow 400 would be better.

I was just thinking of the XPS as a core material. The potential as a mold material I did not think of.

​Good for parallel or linear tapered moulds​, not for elliptical sections, etc.  A 3d printed mould would be cool for these, but I don't have one and the local guys are expensive.

Owly,
Polystyrene at 80 kgs/cu metre (5 lbs per cu foot) would be interesting. Please let us know the cost and, if they have them, the properties.



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Posted by: Rob Denney <harryproa@gmail.com>
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