I am in the process of building the wing for the Penknife and I have a question about the trailing edge. The instructions say "When determining rib orientation, notice the angle of the trailing edge of each rib.The trailing edge is cut to 90-degrees to one side of the rib . This side of the rib is placed down on the plans(so the trailoing edge of each rib is perpendicular to the building surface.)" Does this mean that the trailing edge will be slightly angled upward or downward? Thanks for any help.