The inboard, aft end of the flaps both have an area of loose overlapping skins. The plans don't call for any rivets in this area but I don't like having one of the skins facing forward into the airflow and unattached. To correct this, I made a patch for each flap. This Patch overlays the two skins and is riveted to the inside surface of the flap. I needed the patch because there wasn't enough edge distance with the two skins laying flat on each other. The patch allowed me to place rivets in areas that gave me good edge distant and strengthens the area.
