After the folding there are still gaps between different layers of folded paper (tearoff edge). These and the kinks transversal to the airflow may have a detrimental effect on aerodynamics, especially on the upper side of the wing. In some models the surfaces are not aligned to the direction of flow acting as airbrakes. Typically the center of mass is at 1/81 and the center of area is at 1/2 of the plane lengths. Two methods exist to shift the center of mass to the front. One rolls up the leading edge which then stays unswept. The other uses a swept wing or axial folding to produce something like a fuselage extending out of leading edge of the wing.