When you slip the top skin over the bottom skin/rib combo, you need to take a careful measurement of the distance from the rear of the assembled flap to the foreward most point on the bottom skin. The bottom skin/rib combo can actually slide forward and backward inside the top skin. You need the distance to be 11.25 inches precisely. That gives you the plan measurement of 10.50 inches from trailing edge to the flap spar, measured parrallel to or through the tooling holes. Any further and the location of the match drilled holes in the top skin-to flap spar will not be correct, causing problems when you countersink the spar. You might have the holes in the spar too far aft and that makes for poor countersinking or very very difficult dimpling, if you choose to dimple. That would be because the holes in the spar would be too close to the curve of the spar web for easy dimpling. Take your time and double check this 11 1/4 inch measurement all along the spar before you drill it. POSTSCRIPT 2/21/2011-- Don't use the 11.25 inch measurement. To build the flap correctly, just be sure you have 10 1/2 inches from outside trailing edge, through the tooling holes to the FRONT of the flap spar. I built these two flaps 3/16 too long by using the 11.25 inch measurement. Don't do it.
That is the top skin upside down. The bottom skin/ribs are to the right..
You slip the top skin over the bottom and drill it into place.
Make this measurement check several places on the bottom bfore clamping it in place for drilling.
