Fuel Soaked ply

[Edgeflyer]

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 R]

I think you're stuck with cutting back to good wood.

[Former Member]

[This posting has been removed]

[Edgeflyer]

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 Miller]

I agree,a completely new nose is the only way and then add lots of fuel proofer

[Former Member]

[This posting has been removed]

[Robin Colbourne]

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 -0]

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 Colbourne]

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 Member]

[This posting has been removed]

[Don Fry]

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 Colbourne]

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.

[Edgeflyer]

Started removing affected parts of nose.

Removing balsa sides

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

Attempting to trace outline of doubles.

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

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

[Edgeflyer]

Checking paper pattern fits over the affected doubler

[kc]

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

[kc]

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..

[Edgeflyer]

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.

[Edgeflyer]

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.

[Bruce Collinson]

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 Watkins]

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

[kc]

That's a very neat bit of work! Of course keep a template in case of any further 'incidence' is a good idea. Same as when starting a kit - drawing around every component onto paper and noting material is a good insurance.

I looked up the component shapes ( actual photo copies ) of a Wots Wot kit and its very different to Phil's model which must have been a later kit or a Ready Built model.

Ply manufacturers deny that there is any release agent used but it's the heat glazed the surface.   I have never had a problem with ply doubler to balsa joints, but then I always used Thixofix or sometimes Glue Film.  Perhaps that's why instructions usually say use contact adhesive rather than PVA etc for doublers  -the rubbery type of contact adhesives sticks well to ply without any preparation.

Edited By kc on 10/05/2019 11:24:46

[onetenor]

I didn't know Thixofix was still about Glue Film never heard of it. The point is these adhesives contain their own solvent so deal with the waxy surfaces automatically so to speak. I think it is actually oils etc in the wood drawn to the surface and baked into the waxy film we find.on the surface. So yer pays yer pennies an' makes yer choice. Contact types or thinners etc and wood glues. I got a few samples of ply from Enricio Iglesias (Julio's cousin) via this forum but can't find the thread now.. He sent me some useable samples of quite a dark 3 ply about 1/8th thick. Very rigid but no apparent oils/waxes on the surface. Not had a chance to use it yet He was offering it for sale BTW

[kc]

Thixofix is still available but now says its improved.

Glue film is used in marquetry and veneering and is a thin film of heat sensitive glue on a backing sheet.

[Edgeflyer]

Not much time today. Cut out lightening holes in the doubler.

Checked fit before removing last bits of damaged doubler.

These parts were well glued.

Drew round for second doubler. Now need final fit of first doubler.

Doing the tab cut outs without Cad is patient work, hopefully, worth it to retain joint strength.

[Edgeflyer]

Where I'm cutting through sound joints some seem to be cyano, which leaves a crisp residue, whilst the better ones have a flexible residue such as PVA might leave. I worked for Dunlop Research in the days when we invented Thixofix. We all knew it was rubbish, less strong than Evostick, but the thixotropic idea was a brilliant marketing idea and it sold well. You couldnt really build like this from scratch without laser cutting as the intricate ply jigsaw pieces are very time consuming.

I experimented with gluing some of the old bits back together. The worst of the contaminated parts I put back together with Pu glue, clamped overnight, no preparation such as cleaning or scraping! Resulting joint when set was pretty good, you could break it apart, but with some structural care and cleaning prep I think it will be OK. Interestingly I put 2 ply offcuts, sanded and cleaned, together with medium cyano, overnight. Next morning joint failed dismally. I don't think cyano is any good for ply.