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Installing wing joiners in foam-veneered panels

General discussion on any topic which doesn't have a natural home on any of the other boards.
Pete Marsden
Posts: 20
Joined: 17 Mar 2018, 08:45
Location: Southampton

Installing wing joiners in foam-veneered panels

Post by Pete Marsden »

Since the Wanischek days I've always installed wing joiners by filling a void in the foam panel with slow set epoxy and fitting the root rib complete with pre-mounted blade to said panel, standing the panel on its tip and leaving to set.
Once many years ago, a mate of mine managed to fill his airbrake with resin using this method but we found the bowden cable outer passed into this void - so no surprise.
However, recently I had a similar issue but no bowden cable; therefore no route to the air-brake. Fortunately this was on one of my less important models so no real problem.
BUT, I decided to run some tests (poor pickie enclosed) and was stunned to find that all three resin types I use pass through both medium and high density white foams and unbelievably through blue foam as well.
I tried lining the cavities with balsa sheet but to no avail - it was as if vapours were causing the issue of the foam melting away.
I finally found that if I installed a 2mm balsa box, brushed in a thin coat of gel and allowed that to fully cure before continuing, the issue went away.
I've also recently had the opportunity to section a (broken) wing I built in ~'88 and the un-lined box is perfect.
At the moment it does seem I've developed the 'Sidam' touch!
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Slide1.JPG
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VinceC
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Re: Installing wing joiners in foam-veneered panels

Post by VinceC »

That is a fascinating test and one I will certainly keep in mind. Thanks for posting
MDev
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Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Installing wing joiners in foam-veneered panels

Post by MDev »

Apart from the viscosity of your resin and it finding its way through, your problem might be caused by the heat of the epoxy curing and causing the foam to buckle? Any quantity of epoxy will tend to give off heat when curing and the foam will insulate the heat and keep it within the bounds of the void thus getting almost to a position where the heat becomes a ‘runaway’ issue, heat from the warmed epoxy may well cause the internal air pressure to rise and resin could be forced out or find the path of least resistance. It wouldn’t take much change for this to happen. Just a thought?
MDev
Posts: 160
Joined: 07 Oct 2018, 19:17
Location: WEYMOUTH

Re: Installing wing joiners in foam-veneered panels

Post by MDev »

I should add that once the resin has been lost from your intended place the temperature drops enough to relieve the issue, my thoughts are still with an exo-therm issue though.
Pete Marsden
Posts: 20
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: Installing wing joiners in foam-veneered panels

Post by Pete Marsden »

I should have mentioned that further tests were carried out at 5'C, i.e. in the fridge (pleased the 'boss'!). i was convinced it was exothermic especially as the first problem occurred during the hot spell (anyone remember that?) but subsequent tests seem to suggest otherwise.
These tests included various forms of ballast from none, through micro-balloons to micro-fibres.
Also I tried 'open' tests as seen in the pickie and 'enclosed' tests using 10" long sections of scrap wing. I got similar results for both.
Interestingly, when I tried with 30 minute epoxy (expensive test!!!) - no problems occurred.
As I say, this has never happened to me before (and I've made a few - not just gliders) but I intend to carry out further experiments. I just wish I still had some of the older epoxy to compare because I cannot help thinking something may have changed in the formula.
roo Hawkins
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Location: Northamptonshire

Re: Installing wing joiners in foam-veneered panels

Post by roo Hawkins »

I think the problem is that you are using just epoxy. I use a mix of epoxy and carbon fibre or glass. For my joiners. Cut up carbon or glass in very small bits and mix with epoxy in to a putty. Less resin to get hot and much stronger with carbon or glass.
Pete Marsden
Posts: 20
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: Installing wing joiners in foam-veneered panels

Post by Pete Marsden »

As mentioned above: -
''These tests included various forms of ballast from none, through micro-balloons to micro-fibres.''

I've just sourced some 'original' epoxy - I'll keep you posted.
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Simon WS
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Joined: 18 Mar 2015, 11:39
Location: Kent, UK

Re: Installing wing joiners in foam-veneered panels

Post by Simon WS »

I suspect it's the hardener - the fast setting epoxy will have more aggressive hardener. What happens if you just put a bit of the hardener on the foam?
Pete Marsden
Posts: 20
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: Installing wing joiners in foam-veneered panels

Post by Pete Marsden »

Hi Simon,
I'm suspecting you could be right.
I'm just waiting for a contact of mine on the Continent to send me a sample of epoxy/hardener which he believes to be from the Wanischek supplier to see if it helps.
What I'm really struggling with is the fact that I've made 8 sets of fitted wings in the last 18 months with no issues whatsoever until this recent problem.
I have recently changed the brand of epoxy 'cos I couldn't find the old stuff - so maybe that has something to do with it.
The polystyrene is the same since I bought several cubic metres 5 years ago and haven't used it all yet!

On another related topic, I tried 6 mm (long) chopped glass strands with the resin but they all sank to the bottom as the mix cured.

Many thanks to all for the feed back. As I say I intend to carry out a set of more disciplined experiments once my current project is out of the way and will keep you all informed.
Pete Marsden
Posts: 20
Joined: 17 Mar 2018, 08:45
Location: Southampton

Re: Installing wing joiners in foam-veneered panels

Post by Pete Marsden »

OK, I'll try and keep this brief!
I've redone the tests on HD white foam using three types of epoxy, West Systems, SP and ZAP.
With the first two I used both micro fibres and micro balloons with 'slow' hardener (pot life ~ 3 hours).
The SP reacted almost immediately with the micro fibres - this doesn't surprise me - I've had 5 min epoxy set quickly with 'fibres, I'm told it's something to do with surface area(?)
Anyway, as can be seen from the pickie, very disappointing.
However the ZAP PT 40 was absolutely fine.
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Final test.jpg
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