I've had no problems with the balsa spars backed with the spruce doubler. The only mod I made to the wing was to add sheer webs out two extra wing bays both front and back spars and also replaced and added 5 ply wing doublers to both front and back top and bottom wing joints instead of the lite ply supplied in the kit. That with a nice two inch strip of fiberglass tape around the wing joint. Never had any problems of weakness in the wing. Even when the wind caught the tail and flipped my Kadet over on the wing, no problems. So I think the integrity of the wing design is just fine, with just a few additions. Also added sheet balsa where mounting the tail and rudder, and added diagonals to the top and bottom of the fuse. Makes for a very strong fuse. The Kadet Senior was my first trainer, and I still have it. I should charge it up and fly again one of these days. Nose wheel has been a drag with the stranded cable, but in general, its ok. If I were to do it again, I'd put in a solid rod straight back to a servo mounted low, keeping it as straight as possible. and I'd probably install at least a strong 46, possibly a 60 instead of the Thunder Tiger 42 I have in it now. Needed nose weight anyway. Otherwise its been a great plane to learn on.