Thanks TATTOO ! You are right, it's all there in the instructions...my bad... it just seems logical that the coro direction would run spanwise, providing increased strength to the wing, but subsequent observation on my part has proven my assumption to be incorrect. A good bud made his wing the same way, but avoided the top crease by installing several balsa ribs on the spar, but then we are getting away from the true beauty of these birds, which is of course thier simplicity.