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Old Aug 30, 2012, 03:49 AM
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Here's an idea for you. I've had good luck with polyurethane glues and molds. I brushed a thin layer in the painted mold and when tacky, placed polyurethane wetted cloth. Works. I noticed a few voids where I didnt brush it even, but that's easy to prevent with good eyes.

I've also mixed microballoons and polyurethane glue into a shaving cream consistency and used it as a filler. It doesnt expand much. I've often thought it might be capable of a wing, if the right density mix could be found. I have a lost foam pod where I used it as a filler for the wing saddle and there was a lot to fill.
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Old Aug 30, 2012, 04:36 AM
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Derbyshire, UK
Joined Aug 2008
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In the past, I've done the 'half cores into moulds' method and found that works very well but never had much luck with poured polyurethane cores. However, recently refurbishing an elderly Robbe ASW19, I noticed the cores for those were PU but with veneer skins (and in parts, had gone a little crumbly).

Anyone know how they're done? I thinking the cores need to moulded first then put into another mould with the veneer skins and pressure applied to bond the whole lot together...?
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Old Aug 30, 2012, 08:04 AM
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gold coast australia
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In my PU wing I did suffer from crumbling aswell.
Also did have problems with moisture and warping.
I guess ??? Moisture in the wing when wing gets hot expands and warped wings.
This only happens on thin lay up's.

I like the concept of molded cores for light wings.

Another tip...
For every 10'c of temp PU expands twice as fast.
Cooling it Does help...put it in the fridge before you mix it. At a cost of high density..

Tim
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Old Aug 30, 2012, 05:27 PM
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Tim, when you put foam into both halves and trimmed later with a wood saw, how did your mould flanges go? I wouldnt mind giving this a go but cant work out the best way of trimming the foam nice and flush without wrecking the mould flanges.
I use a router to trim my spar caps flush with the flange, and thought this might work but the caps are right in the middle of the mould. Routing near the edges of the mould fills me with fear!
I love the sound of foam filled wing moulds (PU and Ampreg) but both seem to come with so many uncertainties and variables. You and Andrew do great actually trying out all these ideas- I always think yeah!...and then no, what if this or that happens.
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Old Aug 30, 2012, 06:24 PM
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Nothing...

It's not like you are sawing through a tree. You cut across the wing in a few slices. Cuts like butter.
BUT , I did start off putting tape around the flange.
Doings it this way there are NOT many variables. You don't have to do it all in one piece. In a larger wing do it in 3 or 4 parts. Makes it very easy. If you need a bit more, or you have a hole etc. Just add more.
And in warm conditions , you have all the time in the world to work as you do not have to close the mold.
Also most PU's expand properly above room temp, so you get better expansion lighter wings.

I where to do one again now. I would do it open mold...cut it off , add spars ( carbon sock).. Dig a channel around the LE about 10 to 15mm wide fill with ampreg and close the mold.

You would end up with a wing similar weight to a light v- bagged wing but with better molded Finnish , with a bullet prof LE.

And it would be repeatable every time, variables to a minimum..
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Old Aug 30, 2012, 06:42 PM
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razortoe's Avatar
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Quote:
Originally Posted by josh18 View Post
Tim, when you put foam into both halves and trimmed later with a wood saw, how did your mould flanges go? I wouldnt mind giving this a go but cant work out the best way of trimming the foam nice and flush without wrecking the mould flanges.

After watching the video and considering the alternatives / opinions above, I think the free-rise foam in separate halfs with post-trim joining is the way to go. Much more control, more consistent density, zero voids, and more importantly - less stress

What about making a crappy mold/jig only used to help guide the foam trimming. The mold could be made from high-density, no-skin, flexible foam. It just needs to hold the wing half in alignment and help you cut.

In place of flanges, you could mold in PU-resin guide-rails. PU stands up well to abrasion, and the rails could be made to be replaceable. Their job would be purely to help support and guide a long flush-cut saw blade (no tooth-set) for final trimming.
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Old Aug 30, 2012, 07:44 PM
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Thanks guys- all these ideas are starting to sound VERY apealing! I layed up some tail skins last night. I will do the fill and join today.
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Old Aug 30, 2012, 09:54 PM
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Wow that video is excellent! Very very well done and great info. It answered a few questions (eg the bit about side drag against the container, and the bits about orienting vent holes ... ) Thanks heaps Troy.

A lot of questions ran thru my mind while watching it.

1) The effect of humidity ... we get a lot of variation, from over 90% in summer to down to 23% in westerly winds. Hmm, I wonder whether that's a big problem? And if so, how to manage it?

2) Colouring of the foam sounds interesting ... a white foam colour under a glass skin would provide a good light coloured backing so that you could use less yellow/ white paint.

3) Most importantly, from your experience Troy, if you were doing this, how would you do it? Basically I want to be able to lay up the wing skins in the mould ... I guess it's best to cure them first ... add the various hardware, and then add foam to fill the thing and close the mould and have it fully expand. A few bubbles etc aren't going to be a big deal ... the foam is there to support the skins and to absorb impacts. Are there better types of foam? Are there foams with longer working times??? I'd really appreciate any advice. I guess it's possible that there are no PU foams that will provide the answers, and maybe I'll go back to vac bagging blue foam half-cores in place etc. But I'd like to check out all the options. I'm after simple methods that can be done in the back shed, that provide durability ... and a 98% result rather than perfection.
I think I would use a higher density foam, do an open rise on each half, and trim to the flanges. I actually have some skins in a wing mold that are waiting for me to do this. I have tried to inject foam with the molds closed but I didn't have enough working time. It would work much better if I had one of our meter-mix dispense equipment set up with foam. But I also want to see how it can be done without equipment.
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Old Aug 30, 2012, 10:46 PM
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Bellingen NSW Australia
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Crumbling problems.

Quote:
Originally Posted by Troy View Post
I think I would use a higher density foam, ............
Is the higher density foam likely to crumble less as has been reported several times here Troy? Do you know?

That is the only thing that concerns me at all with the method. I am tempted to give it a go myself. Maybe the hot wire cut blue foam cores method first.

Jim.
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Old Aug 31, 2012, 04:50 AM
Arrarrar!
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Hey, I did an open pour this arvo and cut it off with a hacksaw- no worries. I joined them with PU and now Im just waiting for it to dry. Looks pretty promising!
My foam is a pretty high density- 96kg/cubic metre (does that sound right?) Anyway it sets very hard, not like Ampreg sounds, but heaps harder and stiffer than blue foam. It doesnt seem that brittle either.
So I'll see what happens when I crack it open!
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Old Aug 31, 2012, 05:07 AM
AvB
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I've been thinking I can't judge much about my wing till the control surfaces are cut. I just did them now. There are no bubbles along the cut edges, none at all. I am really surprised ... I thought most likely there would be the odd void, but the foam is really very homogeneous all along. And it seems to have lost very little in bend and torsional rigidity after cutting the hingelines. This is a good wing.

Great work Josh. You're covering a lot of ground fast!
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Old Aug 31, 2012, 05:45 AM
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Thanks Andrew, I popped it just before and Im happy to say Im VERY happy with it! It seems very tough and is really stiff. Its heavy, but Its made with 879gsm quadraxial glass which Ive also been playing around with. I dont know why I didnt try foam filled wings long ago- its so easy and seems to come out so good! I reckon Im gonna get the scorcher wing mould ready to make a wing this way tomorrow.
Heres a pic
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Old Aug 31, 2012, 05:57 AM
AvB
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879gm!! That's insane!
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Old Aug 31, 2012, 06:57 AM
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gold coast australia
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Sweet josh well done.
96kg is what I used to use. And I agree, it doesn't crumble nearly as much. Hurry up and make a PUorcher ..

Tim
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Old Aug 31, 2012, 09:26 AM
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Cool stuff Josh.
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