In another post, there was a question about a plywood reinforced trailing edge. The thread was concerning making a solid wing more durable. This new thread will cover a method I used to easily create a reinforced TE.
I first tried this on a SIG Buster I was flying in Goodyear racing. The plane hunted badly, and was a bit heavy--but it sure did go! The thought was to try to improve things by using a new wing: lighter, thicker airfoil, but hopefully still rugged enough for the rigors of racing. It turned out well, so here are few details.
First, I assembled the wing. This one is a 3/8" balsa plank with higher density wood forward of the spar and lower density wood aft. The stub spar is tapered to reduce weight and also minimize the structural discontinuity you would get with a full section (constant retangular shape). If you notch the rear panel you can epoxy in the spar and then true up the edge before gluing on the aft panel. Next install the tips. One of the purposes here is to use the orientation of the grain to avoid warping (cupping) of the wing. The tip as shown stiffens it up. With the tips installed, now true up the balsa leading edge joining surface. And glue on the "hardwood" leading edge. This one is probably spruce, but I like to use tulipwood as well. It has tight grain, and can be found with pretty low density for its strength. I've also used it for the stub spars and found it perfectly satisfactory.
To get the wingtips to match, I find it easiest to make a template and use it as a sanding gauge.