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Darren_O

Wing repair help (veneered foam)

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Darren_O

A friend had a little mishap on the Orme today. He's less experienced than me at crashing so I've been volunteered to do the repair. I did give him a duff launch mind so fairs fair. 

I was expecting a built up wing, it's an old epo sheeted type though. Question....is that the spar at the top that's gone? Seems to be one at the bottom too. I take it the foam between stopped them compressing and gave it strength?

Can I splice in, brace and insert foam to repair? Or is there a better way? 

 

Thanks in advance for all the advice from forum members, really appreciate you guys keeping us flying:)

 

 

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Darren_O

It's the top of the wing by the way. Leading edge is obviously gone too...

IMG_20171108_211312627.jpg

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pete beadle

Hi Darren

First things first....What's the name of the 'plane and who makes it?

Regards

Pete

BARCS1702

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Darren_O

ASK18 3m ish manufacturer unknown. Blade type wing joiner, glass fuselage. 

IMG_20171012_125227760.jpg

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oipigface
10 hours ago, Darren_O said:

Question....is that the spar at the top that's gone? Seems to be one at the bottom too. I take it the foam between stopped them compressing and gave it strength?

I'd start by cutting through the smashed 'spar' to see what's inside. That will give you some idea of where the strength comes from. Seems unlikely to be foam, though. Is that plain balsa, or is it faced with some kind of composite?

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isoaritfirst

Consider removing a little more of the skin, exposing clean foam and the spar. Then glue the spar back together and brace if the break doesn’t go back cleanly. 

Insert new foam, sand to shape and then cover over the spar break with new veneer  

Now you should have one break in the middle (spar) two joints in the foam slightly wider apart, and then 2 joints in the veneer ( even further apart). 

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Darren_O

Spar looks to be solid wood. Behind it you can see the bottom of the airbrakes, that's the composite looking thing.

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oipigface
1 minute ago, Darren_O said:

Spar looks to be solid wood. Behind it you can see the bottom of the airbrakes, that's the composite looking thing.

In that case it needs to be replaced by solid wood, preferably from a similar tree. Cut a piece to project well beyond the damage and scarf it in. You'll probably need to remove part of the skin to do this, but you'd be well advised not to have a joint in the skin in the same place as a spar joint. If you want to beef the spar joints up a bit, then some vertical carbon strip facings or some carbon tows would not be out of place, but be careful not to create stress points.

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Darren_O

Stripped it back as advised, it's had a previous repair glassed over. The epoxy is still sticky. No idea how old the repair is, I'm guessing it's ancient. Looks like a full width break.

With the epoxy sticky is the repair sound?  If not, what's the best way forward. I don't want to fix the dink then have this old patch fail.

 

Many thanks.

IMG_20171112_203937735.jpg

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oipigface

Not sure what we are looking at there, Darren. Is that the spar? If the epoxy is still sticky on an 'ancient' repair, it was either pooor quality stuff or poorly mixed. I would use a slow cure laminating epoxy on a job like this.

I would take the whole of the repaired part out, and replace with new wood in the same way as I described before. I would not wrap anything with glass bandage again. Doing that creates stress points at the edge of the bandage, and so weakens the repair. The ends of repairs need to be feathered out to avoid creating these stress points.

Best of luck.

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Darren_O

What looks like spar is actually the bottom of the spoiler/air brake. The spar is in front of that, seems to be balsa strip...

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oipigface

Could you post a photo (or photos) taken from a bit further away, so we can see the damage in context?

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pete beadle

Hi Darren

As OPF says, we need some context here

It appears to me that you are looking at an old model, previously repaired badly by someone who didn't know what he was doing. The blade type joiners were the first clue and the tacky resin was the next.

As you know I fly a lot of old, low-tech gliders and one thing, above all, stands out when removal of the covering after an accident reveals something like this , it's the fact that, if you've removed the covering and revealed the break/repair that you have, there are going to be other potential failure points you can't see yet

Take, for example, the tacky resin/glass repair, if I see a couple of layers of glasscloth applied across a break, it's because the previous owner(s)/repairers didn't appreciate the implications of what they were doing. They probably thought that, by using "modern" materials and modern repair procedures they'd be making the whole airframe better.....that doesn't happen. Usually, repairs like this just add weight and move the next failure point away from the recent/current/repair

The previous repairer should have cut vertical slots extending either side of the break and inserted new sub-spars made of 1/16th "proper" ply, NOT Liteply  to strengthen the  line of the break. He'd then have added much less weight and made a repair that was using the repair principles current at the time of the model's original build and not have left a potential failure point in the structure that would be the very last area to break after anywhere else on the airframe had broken

Pics of the model showing more of the airframe will help us decide whether it's a repair job or a "new pair of wings" job and, not wishing to annoy or depress you (although it probably will) whether the work necessary to do this repair is only going to be the first  in a long line of repairs reducing your precious recreation/family/ personal enjoyment time....here's hoping it isn't....BTW, any repairs on the fuselage?

Regards

Pete

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Darren_O

Nearly finished this repair, had to strip back a lot of the covering to see old repairs. So I decided to recover the wing. Wish I hadn't. Is there an easy way to remove the old film? Whilst some large pieces are coming free clean other bits are delaminating leaving the colour behind on the wing in patches. Its a mess and time consuming..

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oipigface

A heat gun would probably help remove film and colour together. Where the film has been removed leaving colour behind, you could try using a heat gun and a scraper. I'd avoid solvents. You don't want anything soaking through to melt the foam. Last resort would be fine sandpaper. Again needs to be used carefully.

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isoaritfirst

Heat gun or iron, but be careful of getting over keen and putting in too much heat.

The foam will melt beneath the veneer. 

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Darren_O

Can't use a heat gun it's foam under the balsa sheet. Sanding it now, what an awful job this is. Last time I volunteer to fix a model for someone else.

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Steve J

Have you tried packing tape? Or ironing scraps of solartex on the offending bits and then peeling it off?

Steve

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isoaritfirst

Heat gun or filmiron will be ok, you just have to warm it enough to release the glue not burn it off.  As I said earlier just be careful Don’t get it hotter than you can put your hand on. A film gun rather than a paint stripper. 

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