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Scram

Rear spar separated from wing skin

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Scram

As title, quite a lot of my Crossover wing rear spar has separated.

Which is better to use to re-attach, thin cyano or thin laminating epoxy?  Both seem to be brittle when cured.

For strong joints I favour adding some micro fibre to the epoxy but not much as it would make it too thick to run into the joint.

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pete beadle

Hi Scram

Hmmmmm adhesives that are brittle are usually cellulose-based, epoxy glues usually feel slightly flexible, cyano tends to feel different depending on it's viscosity and/or gap-filling properties. Personally I'd prefer the two-part epoxy but it seems to be a personal choice more than anything

Regards

Pete

BARCS1702

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satinet

thin CA

 

2 part epoxy is okay but you cannot wick it in to the gap without pulling the whole thing apart. 

Re the strength of CA you can build a woodie with only using it nowadays.  I tested it by gluing the main spar back to the wing on a busted plane and i couldn't pull it off again without destroying the lamination. 

 

clamp the drag spar back down (claps/vice with suitable cushioning) and wick in very thin CA. e.g pacer zap.  thinner the better. 

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isoaritfirst

Some of the problem you now have is possibly because the rear spar has been reglued before with epoxy.

Tack the spar in place with cyano. work small areas at a time to ensure you are holding it while it tacks. Then flood with cyano.

If you want to add more reinforcement,

Mix up a quantity of epoxy and Microballoons, to a nice mix that will flow, warm it slightly.

Then try to get it behind the spar.

You could do this by drilling a large hole in the root rib then feeding in a tube and injecting the mix along the inside of the spar.

Then stand the wing on its end so that the mix runs and forms a fillet along the spar/wing. Might need to do twice to fillet top and bottom edges.

 

Plug the root hole with soft balsa, ideally set as crossgrain. 

 

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isoaritfirst

epoxy is also very susceptible to not being mixed correctly. Get it wrong or not use some heat during the drying process and its likely to fail.

Cyano it all back together - and fly it.

More flying will (eventually) improve the time that your repairs last.

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isoaritfirst

You should also consider whats breaking it.  

It may not be crashing, it may be badly set servos forcing the spar away, or applying brakes during high speed flight.

Linkages can also put significant pressure on hinges if they are not designed well. That hinge pressure may also cause spar separation, if the joint is poor.

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Scram

Thanks all, Mike in particular,  all sound  advice.  It will be done.

I think it is likely the unplanned arrivals is mostly to blame!!  😣

I don't know what it is with cyano. Many times I use it, it won't go off without activator.  But if I get it on my fingers they instantly stick together!!  I don't like to apply activator first in case it seals the edge, preventing the cyano getting into the joint.

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pete beadle

Hi Scram

The usual reason for cyano not to harden quickly is if you're working in a warm dry room - it works better when damp

Your fingers supply the damp

Regards

Pete

BARCS1702

 

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isoaritfirst

buy some fresh zap pink cyano.

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Scram

I done it with my pink Zap. Seems to have it solid  👍

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satinet

Your fingers have moisture on them which helps the activation. 

The forces on the drag spar are tensile (pulling apart), which is what super glue is good at. 

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Kyri

I have used 24hr araldite for this type of thing. If you are able to separate the surfaces along the section properly with some bits of balsa, then you can apply the araldite to the surfaces. If you heat it first, it will be runnier, and you will still have plenty of time to apply it. Compressing the relevant areas with something soft like towel and some weights on top will ensure your trailing edge is not thicker than it was originally as the glue cures.

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Skip

I use laminating epoxy, 2 pieces of right-angle Aluminium, a syringe, some sort of plastic tape and clamps. 

I find I have to redo CA after relatively minor bumps as I think it is a more brittle repair.

This might be a bit of a suck eggs situation, but make sure the wipers are free from getting glued!

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Scram

Thanks for further answers.  I suspect you may prove right Skip.

It is done with pink Zap now but I'm going to reinforce with micro-balloon filled epoxy, along the outer side as I can't get inside enough because the servo frames are glued in.  With a bit of care this will be OK.  I also reinforce the wiper attachment as it is very fragile.

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Scram

Reinforcement of rear spar completed top and bottom using micro balloon filled laminating epoxy.

IMG_4145.JPG.78f170fd3bdefe81408be40a3f06a0ba.JPG

I always find it difficult to judge how much epoxy I need to mix and hate both being short (though not such a problem with slow setting laminating epoxy) and mixing too much and wasting a lot.

Well I mixed up a batch and soon decided I had apparently mixed far too much  :blink:   Also, as the mix had to be fairly runny to go through the "syringe" and injecting pipe, I would only be able to do the bottom joint after the top one was hard i.e. next day or later.  So how to avoid wasting half the batch was solved by pouring half of the mix into a milk bottle top, covering with cling film and popping it into the freezer.  Freezing stops the curing process.

20181202_105651s.jpg.a40dd663a024671da0e6755bb2cb370e.jpg

After I finished applying the mix to the top joint I also put the "syringe" and the mixing pot (yogurt tub) into the freezer too.  2 days later I pulled it all out, left it on the table for an hour or so and the epoxy was runny again.  A little too thick to suck up into the "syringe" so I just warmed it a bit in a bowl of hot water.  BINGO.

Wing left leaning at about 45 degrees ensures mix stays where I need it.  I write "syringe" because the item I'm using is actually a measuring tool for measuring the correct dose of anti arthritis medicine for applying to Slopedawg's dinner.  I've collected quite a few. A short length of broken off aerial tube is inserted into the syringe nozzle to be able to apply the epoxy mix into the aperture.   The syringes also make measuring the correct mix of epoxy to hardener very easy having checked the weight ratios and transferred this to the volumes needed.

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