A few weeks ago, I needed a 1/48 Cougar in BA colors, so I upsize the little 'regular size" redraw I did a few years back. When I started to build it, I ran into the same difficulty with the wings as I did n the past. I must be getting old--my minds still like a trap--a rusty trap, though, now--
It took a few minutes of contemplation (and a second set of wings) to get me back to when I was working with this nice little model and building a dozen or so to verify my recolors.
Anyway--here's the straight scoop on getting nice wings on either of those planes: Score both the top and bottom of the wing at the wingfold line. Glue the wing up, and then, with a very sharp exacto, carefully cut the upper wing's score line almost from leading edge to trailing edge--to maybe within a sixteenth or so. Glue the top and bottom to the fuselage--make sure everything's aligned well. Afer the glue's set--put a bit of glue along the cut line, gently tuck the upper outer wing section inside the inner part, set a zero dihedral for the Cougar or positive one for the Panther, and let dry thoroughly.
(the other plane is Kancho's F11F that I recolored for this display--I highly recommend this kit for any Grumman fans out there)