RE: Balsa USA 1/4 Sopwith Pup build
Dale is absolutely correct. These smaller ribs are in place to compensate for sheeting (Make sure you center them for top and bottom sheeting.) Also, if the "false" ribs are a bit too small in length (front to back), you may need to shim slightly with a bit of scrap to fit against the leading edge. In addition to this, on my 1/4 scale, I sanded these ribs a bit and adjusted the shape so the sheeting would fit perfectly, making the wing thickness uniform with the sheeting in place. Very easy to do with a sanding block.
Kevin