Old foam wings, obechi sheeting delaminating. Repair/replacement options?

[martin collins 1]

One of the kits i have in my stash is a 1970`s Quest Stomper bipe, was looking it over this evening with a view to building it shortly but the obechi sheeting is delaminating from all the foam parts. The wing sheets are intact but coming off and would need carefully removing completely and re gluing using PVA, if done this way how would i be sure they had glued in all places, obviously i could weight them, would that be sufficient? Alternative thought would be to strip the sheeting off and cover the wings with brown paper and thinned PVA, strong and light. What are peeps thoughts on the best way to make them good?

[stu knowles]

I had a similar situation. I bought some 'glue for the purpose' from the model shop - but it smelled like Copydex and had a green tint.  I found a syringe and pumped the glue under all the loose veneer.  Used a roller to squeeze it into the corners and all the loose bits, Let it go off and then rollered it again. (Copydex is a contact adhesive)

 

I also treated a small flaw on another wing with PVA in a similar fashion, let it dry an then ironed it but this way took a long time to dry.

 

If you can get the veneer off intact, the foaming Polyurothane glue seems to be a good means of gluing then back on although you would probably need the foam blanks to weight it down properly

[martin collins 1]

Thanks for the reply Stu, no blanks in my kit unfortunately, it is loose in a lot of areas so removal may be the best option to ensure it has glue to all areas.

[Graham Bowers]

I re-sheeted a wing that lost it's obechi veneer with balsa sheets, glued together with pva and applied with copydex.

 

[Paul De Tourtoulon]

I tried pva glue and the sheeting warped, there are contact adhesives that will do the job like Copydex but I prefer epoxy resin.

[kc]

If it were my model I would attempt to stick down any loose veneer, then fill any gaps before covering the wings with either  light glass cloth or  'tex  or brown paper to give some strength.

 

Obviously you want to save the wings but in case you end up damaging them make sure you draw around wing profiles tip and root onto paper noting  any washout that can be seen.  Also the basic layout dimensions plus details noting if top and bottom are same..  Then the wings could be replaced if necessary by wing cutters such as Billkits.

 

[gangster]

My money is on Copydex.  It is a latex glue so it won’t eat the foam but will grap like an impact adhesive  I has been around for ever but is still available. 

[dave windymiller]

I had that on an old kit

 

Ended up cutting new foam wings purely for the blanks so i could reskin the original foam with balsa (and have a spare foam wing core).  See link below

 

 

Edited February 8, 2023 by dave windymiller

[Eric Robson]

Did you finish the two Rojair kits Dave?

[JOHN MOSLEY 2]

I used to use copydex  for wing skinning for veneer, but now using Gorilla polyuthane  glue I just thin glue put on balsa sheeting, and then mist foam core with water. Then put in cores and apply a lot of weight. Most important is put thin plastic sheet between  balsa and wing cores. Gorilla can foam through any small gap etc and then permanently

stick outer core to wing. Not saying this is the best but found new veneer is splitting etc. so now using balsa. But balsa is expensive but cost of failure is more costly.

   

[dave windymiller]

The Me109 is "paused" whilst i do my turbine f86 but the komet has been finished and flow successfully. here

[Eric Robson]

Thanks Dave, I missed that one. Looking forward to seeing the 109 fly. Pity the Rojair kits went out of production good subjects and good  kits for their time.

[Roy Thompson]

Been looking for a thread on this topic since I found a nice Magister on eBay. 

 

I wasn’t sure how best to tackle the delaminating/splitting veneer, repair it or strip and redo over and still open to suggestions. So unsure I was I also picked up a part built kit just for the unmade wing. Unfortunately the ctr section veneer is also completely delaminated, but could be a simpler fix.

 

In the mean time I’ve been experimenting with DM Super Phatic and or Aliphatic resin. Have found that Aliphatic takes notably longer to dry out. Started with the lesser damage on the bottom before attempting to touch the top.

 

A couple of questions, where can you buy sheets of obechi wider than 4 inches and is poplar wood an alternative.

[Cuban8]

Many years ago a friend gave me a Sig 65" Zlin kit that he told me had been stored in his loft for ages - I knew the kit came with foam wings so didn't expect them to have survived well at all in such a poor place of storage.......................however, Sig supplied the wings unveneered and although the balsa sheet supplied had gone a tad hard over the years and needed replacing, I managed to veneer them OK with new sheet and the model still flys well today. I used copydex without any problems.

Sig's instructions called for the cores to be rolled onto the skins on a flat surface, but given the slight undercamber and quite thin section, that seemed a sure recipe to create an instant twisted wing.

I used the cores packaging  as a jig placed on a flat surface and wound up with two nicely skinned cores that were dead straight given I could really weight them down to conform to the desired shape. I think I'm right in saying that American kits tended to come with foam wings that were unskinned.

 

[Nick Cripps]

Roy, have a look at the poplar veneer available at Balsa Cabin

 

 

[Roy Thompson]

7 hours ago, Nick Cripps said:

Roy, have a look at the poplar veneer available at Balsa Cabin

 

 

Hi Nick, thats where i saw the popular veneer originally. My question is, is it a good alternative for obechi. The website give no information on that, so I assuming it’s maybe but what’s different is it better or worse.

[Jim Hearnden 1]

I used to make my own wings in the early 90's always used watered down white PVA (50/50) and used to leave them for around  a week in most weathers & never had a problem.

[Outrunner]

I'm sure I've read before of covering the foam cores in brown paper and watered down PVA, I'd try it myself if I had some foam cores....

[Cuban8]

32 minutes ago, Outrunner said:

I'm sure I've read before of covering the foam cores in brown paper and watered down PVA, I'd try it myself if I had some foam cores....

I know that method has been used on smallish, thick sectioned flying wings and deltas, but on longer and more high aspect ratio types I'm not so sure - at least not without an underlying veneer or inlet spars - I think even Christmas and birthday paper has been used to good effect in the past.

I'm sure someone will be expert in it.

[PatMc]

Chris Gold designed & built quite a number of scale, mainly multi engined & edf, models using foam & brown paper. They weren't small models. 

A club mate, sadly no longer with us, also specialised in the method of construction on both small & average size scale models. His models included a Sunderland, Junkers 52 among many others. The Junkers had a central Laser engine with 2 freewheeling outers, span was around 6 ft. The corrugations of the full size were replicated using recycled corrugated cardboard boxes courtesy of the staff at a local Morrisons.

Edited June 11, 2023 by PatMc

[Nick Cripps]

20 hours ago, Roy Thompson said:

My question is, is it a good alternative for obechi

I hope so, I've just bought some for veneering a set of floats for a waterplane.

From a bit of reading, poplar is of a similar density to obeche and also slightly stronger, but is softer and more porous so will most likely soak up more paint/glue.

I've had a good search around on the internet and it looks like Hobson's choice unless you go for balsa or brown paper as mentioned by others.

[Jim Hearnden 1]

12 hours ago, Cuban8 said:

I know that method has been used on smallish, thick sectioned flying wings and deltas, but on longer and more high aspect ratio types I'm not so sure - at least not without an underlying veneer or inlet spars - I think even Christmas and birthday paper has been used to good effect in the past.

I'm sure someone will be expert in it.

Mick Reeves Disco which was basically a 1" disc 24" diameter was to be covered in wrapping paper. Worked quite well. I also covered a 36" home cut wing with solarfilm. It had a single LE & TE & flew with an SC 12, never broke it.

 

[Geoff Copping]

On 10/06/2023 at 16:00, Nick Cripps said:

Roy, have a look at the poplar veneer available at Balsa Cabin

 

 

I have an Art Hobby Odyssey 2.7m glider and I can confirm that poplar is a very good sheeting wood.

It is foam core laminate as, I believe, are all Art Hobby gliders. Some up to 3.4m.

The Odyssey takes a full on bungee launch with 'luggage rack' bungee and I've had it for a few years now. Just a few coats of sanding sealer and it's still perfect.

[Jon H]

This may have been covered before but if not its worth noting that foam veneer wings are essentially stressed skin. All of the strength of the wing is in the skins as there are no spars. Smaller models may be ok with paper over the foam but i would not be using that as a replacement for the wood on a larger model. 

 

I just took on a Spitfire with a completely delaminated wing and am weighing my options on the repairs. 

[Roy Thompson]

Thanks for the info guy's, it helped a lot in making a plan.

So I'm thinking to strip the old veneer from the unmade CTR section and replace with poplar, then coat with watered down PVA to seal before finishing.

 

Old wing, I've been experimenting, and it seems to be working OK.

1 open up the crack, 2 wick in glue, 3 clean up, 4 pull the split together with tape, 5 lay bar on top to add pressure to split area, 6 use what's at hand to apply wight, 7 leave it a day.

To finish I think I'll sand back to the veneer then glass.

 

Time-consuming but seems to be working even on the larger ones.

Edited June 12, 2023 by Roy Thompson