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Fuel Soaked ply

Delamination joint failure

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Phil B08/05/2019 14:50:25
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185 forum posts
174 photos

In my project of renovating an elderly Wots Wot,the main problem is fuel soaking at the nose. Many joints have failed and ply doubles have delaminated. Has anyone succeeded in regluing ply pieces after they become fuel contaminated, maybe after cleaning with acetone or meths?

Nigel R08/05/2019 15:15:02
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3869 forum posts
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I think you're stuck with cutting back to good wood.

Former Member08/05/2019 15:30:43

[This posting has been removed]

Phil B08/05/2019 16:47:26
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185 forum posts
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Yes, thanks, I shall bite the bullet (and the nose off). I don't suppose it's possible to get hold of plans for Wots Wot?

Peter Miller08/05/2019 18:10:21
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11065 forum posts
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I agree,a completely new nose is the only way and then add lots of fuel proofer

Former Member08/05/2019 18:38:48

[This posting has been removed]

Robin Colbourne08/05/2019 18:48:02
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576 forum posts
17 photos

Two part acrylics are supposed to be better than normal epoxy on oil soaked wood, as they dissolve the oil. There are also special epoxies for naturally oily woods:

Oak & Teak glue

3M also do a two part acrylic adhesive intended for oily metal, althought it would probably work on wood as well:

3M Scotchweld DP8407NS

will -008/05/2019 18:52:32
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587 forum posts
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interesting, though for the cost of the special glue I'd rather cut in a new bit of wood. Use the old bits to make a pattern.

The technique I've used in the past to extract the oil is to mix up a paste of meths and talc, spread on the affected area and leave to dry. This wicks the oil into the talc which you can then scrape off. Repeat if necessary. Works well enough for re-covering but I'm not sure I'd trust it for re-gluing structural stuff.

Robin Colbourne08/05/2019 19:09:15
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576 forum posts
17 photos

If ply doublers have delaminated from the balsa, it may be that they were not adequately degreased and keyed in the first place. Birch ply really needs a wipe with a solvent such as acetone and the surface roughened to achieve a really good bond.

Former Member08/05/2019 19:15:41

[This posting has been removed]

Don Fry08/05/2019 20:41:39
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4557 forum posts
54 photos

Trouble is with these special use glues, is the manufacturer will tell you, test to see if it's fit for your particular use. I once many years ago had the joy of watching a motor rip free from an ancient flying dog of a machine.

The motor landed on a big stone, and the dog of an airframe didn't Evan (even) have the decency to wreck itself.

New wood makes sense.

Hate spellcheckers.

Edited By Don Fry on 08/05/2019 20:43:03

Robin Colbourne08/05/2019 23:48:58
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576 forum posts
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Don, you're right. For the sake of a sheet of ply and a sheet of balsa its not worth the risk. The only question is how far Phil will have to go back before he can find dry wood.

Phil B09/05/2019 14:05:31
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185 forum posts
174 photos

Started removing affected parts of nose.

img_20190508_125155.jpg

Removing balsa sides

img_20190509_102951.jpg

Inner ply doublers damaged and joints to formers loose due to fuel seepage.

img_20190509_120531.jpg

Attempting to trace outline of doubles.

img_20190509_123516.jpg

Taking back balsa to sound wood and leaving suitable joining locations for new wood.

img_20190509_133121.jpg

Lots of work. A new fuse is £71... too easy. I paid less than that for the whole airframe with servos and ASP FS80.

Phil B09/05/2019 17:35:07
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185 forum posts
174 photos

Checking paper pattern fits over the affected doubler

img_20190509_155119.jpg

kc09/05/2019 17:57:01
6485 forum posts
173 photos

If it's not too late measure the downthrust and sidethrust used. Making a master template in cheap 3mm ply with both wing seats and cabane and engine bulkhead in correct alignment would help a lot now. Geting the cut outs in doubler is less important. Paper templates especially those with cutouts are too easily distorted, so ply is better than paper or cardboard.

Edited By kc on 09/05/2019 18:00:23

kc09/05/2019 19:20:09
6485 forum posts
173 photos

Perhaps I should explain a bit more about making a master template. I once had a fuselage that had an even worse affliction than oil soakage - it had woodworm! Fortunately only the fuselage was affected and wings and tailplane were OK. Lacking the plan I used a balsa sheet that fitted onto the tailplane and then was located along the top fuselage edge, then the wing seat cut out was carefully drawn onto the balsa and bulkheads positions marked. Then this balsa was shaped to the wing seat and used as a template to produce two identical new fuselage sides. All the old wormy bits were then cut away and new fuselage produced from the template instead of a plan. Replicating the structure was not quite as important as getting the wing acurately located in relation to tailplane. With a biplane getting it also located in relation to the top wing would be important too..

Phil B09/05/2019 19:42:11
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185 forum posts
174 photos

Thanks for that advice. I shall attempt to ensure the wing incidence, down and sidethrust are maintained. At present I am retaining all the important bits on one side while I repair the other, then work on the better side after. I believe I can get away without removing bulkheads or formers. I aim to use additional internal strengthening to make the original structural joints less important if they are less strong than originally.

Phil B09/05/2019 22:41:13
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185 forum posts
174 photos

Template in 3mm ply for the new doubler being sized up

Interestingly, as others pointed out, the new ply also has a waxy feel and will need cleaning and roughing before gluing. I'd be surprised if they do that in the factory with artf construction. I also noticed the charred laser cut edges of formers don't seem to bond well.

img_20190509_220946.jpg

Bruce Collinson10/05/2019 08:34:25
527 forum posts

No, I believe laser cut edges need to be cleaned back to naked timber where glued. Wasn't aware that release agent, the waxy surface, needed the full solvent job, I always abrade it off as it kills both birds with one piece of wet and dry.

BTC

Denis Watkins10/05/2019 09:04:03
4411 forum posts
109 photos

Wow Phil, you are an artist

This job will be stronger than the original, and an abject lesson in repair work

And Yes, laser cut joints need attention, as vaporised wood dust contaminates joints

As you suggest, clean up joint faces to leave micro open pores in the cellulose (wood)

Following you with great interest

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