I have tried a couple of different kinds of adhesive, and I recommend only Uhu brand glue stick. I tried heat activated adhesives, other brands of glue stick, thinned white glue, and a couple of other things, but from my experience Uhu works the best.
Carbon: So far, all the carbon structures I have covered start out flat, so I tape the covering down to a flat surface. I pull it tight, but not so tight that it stretches. I then go over the carbon rods that are to be covered with the glue stick. I put it on somewhat thickly, but then go back a smear it, and leave only a very thin coat. The thinner the better, as it will dry more quickly, but make sure it is completely covered. Now put the glue covered carbon onto the Reynolds. Then with a very sharp X-acto knife cut around the carbon, leaving enough covering to wrap around the rod, the more of the rod that the covering wraps around, the better it will stay attached. Start wrapping the extra covering around the rods. It is best to do a spot here and there, and then go back and do the whole thing, that way you are less likely to pull it off one side as you wrap it around the other. I usually go over it lightly, and then once it is all wrapped, I go back and press it on more firmly.
Now let it dry for at least an hour, I usually let it dry over night to be on the safe side. Next shape the wing (add dihedral, etc), tail or whatever you are making in to the shape you want. Then go over it with a not so hot covering iron to get out the wrinkles. (Make sure your iron is not too hot, since it will melt the covering and/or snap the carbon rods.) I use a TopFlight covering iron and set it at no more than 1/3.
For example, to make a Kolibri wing:
Balsa: For balsa I use similar techniques, usually though, I am not covering something that is flat, in that case I do not tape the covering down. First put a couple of light coats of dope on the balsa structure where ever the Reynolds will be stuck onto it. After the dope is fully dry, put on a thin layer of Uhu, the same as described above for carbon. Then put the covering onto it little by little keeping it as tight as you can (but do not stretch it). Let the glue dry a little, and trim off any extra Reynolds. Let it dry over night. Go over it with a not so hot covering iron to get the wrinkles out. (Make sure your iron is not too hot, since it will melt the covering and/or snap the carbon rods.) I use a TopFlight covering iron and set it at no more than 1/3.
I hope to add pictures at some point, let me know if you think they would help, or if you have any questions. I take no responsibility for how your wings turn out... unless they turn out well.
I tried a couple of different methods when covering with mylar. The first thing I tried was applying thinned Elmers glue, let it dry, and then put the mylar on with an iron. This method did not work very well, it was relatively difficult and once it was on it did not stick well. For my next attempt it tried another heat activated glue, it also did not work very well.
At about that time I then heard a number of people using a regular old glue stick. I had one, so I figured I would give it a try. First I put a thin coat of dope over the structure where the mylar attached and let it dry. I then rubbed on the glue stick and applied the mylar pulling it tight to get as many wrinkles out as possible. I let it dry a day and the glue was still not dry. I let it dry some more, but even when it as dry the mylar pulled off easily. At this point I was just about ready to give up, but then someone suggested using Uhu glue stick. I did, and this worked much better then any thing else I had tried.
Now, on to the actual technique. First find a flat surface and lay the covering down on it. Stretch (do not actually stretch the covering, just make it tight) the covering out and tape it down so it is nice a flat and there are no wrinkles in it. Rub the glue stick over the carbon rod that will be attached to the covering, the trick here is not to use too much glue, I spread it on, and then wipe over it with my fingers, so what remains on the carbon is a very thin layer. Next lay the carbon onto the mylar and push down all the way around to make a nice bond. Take the tape off (which was holding it tight) and wrap the covering around the carbon a little ways to get a better bond. Let it dry about an hour or so, and then trim off the excess with a hot soldering iron. For wings, do not shrink the covering until you have put the threads on that give the wing its dihedral. The wing cross section should get some curvature as you shrink the covering.
I had some trouble the first couple of times I tried to cover wings with mylar. I tried a couple of different methods, and the above worked the best. The first couple of times I covered wings the covering started to pull off. The first time I think there was too much glue and it never really dried that well. The covering started to pull off about a week after I put it on. The next time (described above) I made sure there was just enough glue, a very thin layer. This looked like it would be the answer, but eventually it started to come off again. Now when I cover wings, I leave the threads on that shape the wing (not the ones that give it dihedral, but the ones that form it into an oval). The first couple of times I covered it, I cut them off after I shrunk the wing. I guess the carbon is too stiff and wants to go back to the circle shape and pulls so much that eventually it will pull to covering off. Leaving the threads on fixed the problem.
Here is a summary for balsa structures:
© 2001-2004, Matthew J Litke