Flipped the assembly over and clecoed it together, using weights on top and placing the aileron over a flat work surface (kitchen table). Blind (pop) riveted the counterbalance pipe to the leading edge skin. While checking that the aileron remains flat, riveted the bottom side of the nose rib to the skin. Then, riveted the bottom side of the main ribs to the aft skin, and finally blind (pop) riveted the leading edge and aft sking to the spar.