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May 15, 2011, 01:40 AM
Landings are not optional
DeuceTrinal's Avatar
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Discussion

Glue for a T-peg in a bagged wing


I'm going from an arrow shaft through-and-through peg to a nice molded t-blade on my XP-3. I had to adjust the angle of the tang in the wing from what I originally hollowed, so there is a wedge of missing foam area to fill. I'm considering using polyurethane glue (gorilla glue), as it will fill and support the skin really well, and in my experience it's really strong and rigid. The other option is epoxy with microballoons, but it's a fairly large area, and I don't want to have to use a lot of epoxy to fill it, and if I mix in a lot of microballoons to keep the epoxy light, I'm lowering the strength of the epoxy a bunch anyway. I'm out of good epoxy and regular PU glue (I have white gorilla, but I don't think it's as strong) so I have to buy something anyway.

Is there a good reason not to use PU glue? The blade has a 3/8"x2" tang, so lots of area to grab. I usually pre-mix with a drop of water and let it start the foaming process before applying it to limit squeeze-out and mess, I'm confident I can do a good job with the PU, just not sure that it's up to the task.
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May 15, 2011, 12:48 PM
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bluzharp's Avatar
Polyurethane glue is extremely strong on a close fitted joint. The foam that fills in a space is not nearly as strong. I don't know if it is strong enough for your application or not. I think the epoxy splooge would be a lot stronger, especially if you add some glass, carbon, or kevlar fibers to the mixture.
May 15, 2011, 12:51 PM
Kyle Clayton
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Epoxy and microballoons
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May 15, 2011, 01:01 PM
G_T
G_T
Registered User
My tests on polyurethane glue indicate it is one of the weakest choices one can make. I highly recommend against it.

I use laminating resin - West - with the fast hardener (which is not all that fast). Add milled fiberglass and cotton flox. Then add 410 filler to lighten the mix. That works fairly well, as in permanent.

Lacking all that, use the longest cure epoxy you can use. You can thicken with microballoons, but fumed silica would be a better choice, and any sort of fiber filler would be better still. Fresh sand the tongue and do not touch it! You do not want finger oil there.

For some wings, you can use backlighting to see if any voids have been left around the tongue. You do not want voids.

Gerald
May 15, 2011, 02:40 PM
Landings are not optional
DeuceTrinal's Avatar
Thread OP
Ok, epoxy plus filler it is. It looks like I'm going to have to make the drive to the far LHS and pay their high prices on some good glue, all I can find near me is 30 minute Devcon, not exactly high quality glue. I have some old (way old) Z-Poxy laminating resin, testing overnight it hardened nicely but doesn't seems to have much strength.

G_T, what makes fumed silica better than microballoons? I assume fiber thickeners are "better still" because of added strength, right? I don't expect they are going to do very much for reducing weight though.

I'm concerned about the space I have to fill, at the tip it's at least the size of three pennies or even nickels stacked. That seems like a pretty large chuck of epoxy in the wingtip.
May 15, 2011, 08:58 PM
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Last edited by DLGjunkyard; Sep 25, 2018 at 11:16 AM.
May 15, 2011, 09:50 PM
Landings are not optional
DeuceTrinal's Avatar
Thread OP
It's not that kind of blade, Junkyard. It's a T shaped blade, with a long tang or tail that goes into the wing from the outside edge. I originally cut the tip of the wing open and made a slot in the foam with the T aligned perpendicular to the fuse, but the twist in the blade's wings means it's going to be better off with the tail facing a bit aft, aligning the actual finger-hold area of the blade properly. In order to do that, I had to swing the tip of the tang about 5/8" (16mm). This left a wedge of foam to fill. I'll see if I can get a picture showing it.

I may try mixing a double batch of epoxy, one ultra-light that I will fill the empty area with, and another properly mixed fir strength for the blade itself. I think I could apply it with a syringe and get it in the proper areas. We shall see.
May 15, 2011, 10:51 PM
Landings are not optional
DeuceTrinal's Avatar
Thread OP
Ok pics - In the second one you can see the area of foam that is removed (the lighter area below the blade). The hollow goes to just underneath the carbon. The blade is shown in the position it will be glued in.
May 16, 2011, 01:24 AM
Registered User
If your size estimate is right, then even if you use solid epoxy it will be around half a gram. If the hole is so big, balsa sounds like a good idea to take up some of the extra space. Or even foam, if it's just replacing foam. With the microballoon mix to fill in the cracks. Maybe a little fumed silica to keep it from running all out.


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