Wing joining
 

Hi,

I received my LA RACER 40 from The World Models.

When I put the wings together, I can see a little (0.8mm) gap in the middle of the wing.
Can I leave it like that when I glue with epoxy or should I try so sand the surfaces until I have a tied fit?

Also, the covering is overlapping the wing joint surface by 2mm, should I cut this away? I am afraid that doing so, the covering might come loose, but than again, the gap will be even bigger.

Any advise would be welcome.

Thanks,

Filip

RE: Wing joining
 

I would just slather the epoxy on the ribs and wing joiner and put it together.

Notes:
Most wing joiners are angled for a slight dihedral make sur you DON"T fotget the wing joiner and you put the wing joiner in PROPERLY!!!

Have some isoprpyl alchohol ready for epoxy clean up as epoxy will ooze from the joined sections.

Clamp it the best you can and allow it to fully cure.

MR G

RE: Wing joining
 

Thanks.

Yes, there is some dihedral and the wing joiner is installed properly. It is just that the glue surface, when you look over the length, is a little hollow, which creates the gap. I am just worried that the epoxy in this area gets brittle. Maybe I should ad some shredded glass fiber to make it more stronger. Instead of messing around with sand paper an run the risk of changing the dihedral.
I am sure this is not the only kit with this problem and I am curious how more experienced builders cope with this.

Rg,

Filip

RE: Wing joining
 

Couple of options - if you can't sand it out, I would:
1. Mix microballoons in with your epoxy to make a light, strong "filler" to fill the gap whilst joining the wings, and
2. Consider stripping the covering back a couple of inches either side and 'glassing the join - if you're REALLY careful it's sometimes possible to peel back the covering, join/glass, then iron the covering back on.

(I once glued the tailplanes in upside-down in an ARF - stripped the covering off, and used it to recover them right-way-up:))

Cam

RE: Wing joining
 

I normally cut the 2mm covering overlap on the joint surfaces of the wing. After the epoxy has set just tape up the wing joint line with clear tape. Has always worked for me.

RE: Wing joining
 

Any gap can be a problem. You want to make sure that the wing joiner is well-glued in its pocket, and that the ends of the wings that butt together fit with zero gap! If you have a gap, then that means that the wings are not well-glued. The wing joiner does not usually carry 100%of the loads across the joint, but needs good gluing of the spar-ends as well. Also, if the wing has a gap in the center, then there can be some movement between the wing panels that can cause the center joint to fail. People who have this happen usually think it's a problem in the quality of the design or construction when it's really their assembly job.

If the wing panels have a gap, then sand the ends of the joiner to fit. If there's a gap on one side and not the other, sand the ends until you have a perfect fit. The better fit you have, the stronger the wing will be.

RE: Wing joining
 

Sand the gap out! Remove the covering. I prefer to use 30 minute epoxy in this area, and if possible rap the joint with glass. The flatter and truer the two contact surfaces are the better the bond will be.

RE: Wing joining
 

I also would sand the joint for a well mated surface.

When you have some time on your hands, try this. Mix a small amount of epoxy (5, 30, or whatever) and just let it harden on a plastic lid overnight. Also glue two pieced of light ply together with the same stuff. Next day, try and get the light ply apart. You won't. Now try and break the spot of epoxy. See how easy it is to break when by itself.

Point is, the strength of the joint comes from a tight fit of the two surfaces with the epoxy reaching into the fiber of the wood and kind of welding the pieces together. Gaps weaken the joint, because all that is holding it is the brittle epoxy. Over time, this joint will develop cracks, unless backed with a layer of glass, as mentioned above. I little sanding to make a machine like fit, and then glued properly with epoxy, will make a strong, lightweight joint. Always make sure you are gluing wood to wood also. Always remove any covering in the way of the joint. Otherwise, the joint is as strong as the bond of the covering to the wood. Not very.

RE: Wing joining
 

Thank you all for the replies.

I also figured that sanding would be the best option, so I already started yesterday. It looks a lot better and is actually not such a difficult job.
I still have a tiny gap on one side in the middle and am not sure how far I can go with removing material. On some spots I can already see the next layer of material, mind you, it is a very thin layer. It is not the strength I am worried about after removing material, but the front of the wing has a sort of dowel pen that fits in a slot of the fuselage. If it gets too thin it might get some play. But I guess I can also fix that so figure it is best to keep sanding until I have a perfect fit.

Rg,

Filip

RE: Wing joining
 

I would use milled fiberglass not micro balloons if you add anything to the epoxy.

RE: Wing joining
 

Agreed - even better.