That depends, My "Cheap Thrill", December 1998 Model Aviation, weighs in at 11 -12 oz with TD 049. It has a 36 in wing. I think with your wing your airplane should come out under10 oz. Less if you are running an engine less powerful than a TD 049. In your wing, I would suggest putting in a vertical cross piece, 1/8 x 1/16, between the spars at each rib. Particularly if you want to cut out a good bit in the center of the rib.