Here’s the plan for building the balsa wing.
Ace RC used to produce foam wings which were used in a wide variety of plans published in magazines. The idea was to build a cheap, easy plane without having to cut out ribs. Quite a few of these planes became very popular. Unfortunately the foam wings are no longer available, but you can still build these popular airplanes with a set of balsa ribs to make a wing with the same outline.
With this wing kit, you get a dihedral brace and a pair of root ribs that are trimmed to accommodate it. You can use the brace, or just butt join the two panels and reinforce the joint with glass cloth. There are plenty of ribs to build a 40 inch wing. Use 1/8 x 1/4 spars and 1/4 x 7/16 balsa leading edge. Sheet the leading edge and trailing edge with 1/16″ balsa sheet, and add cap strips on the ribs between the spar and the trailing edge sheet. For greater durability, sheet the entire wing with 1/16″.
If you prefer a wing with ailerons you can build the wing as shown and add flat 1/8 sheet ailerons. Or you can trim the tails of the ribs, add a balsa trailing edge stick, and add a tapered aileron to replace the part you cut off.