The top skin mating to the flap frame was a tricky part of the flap construction. After using the -03 skin assembly instructions and carefully marking and drilling the lower skins to each flap frame, I discovered an odd alignment issue on the top surface.
I posted the issue on the GlastarNet forums and, though I received some good feedback, most of it suggested I had done something incorrectly in either measuring or drilling the flap to this point. I was having a hard time getting a consistent span-wise alignment of the skin rivet holes over the rivet line markings on the upper spar flange. On the ends they were off by as much as 1/8" and about 2/32" in the center. In order to get them to line up, I found I needed to push the skin forward, creating a sort of dimpled effect on the leading edge arc. Not good. Time to step back....
Fortunately, Stacy and I had a short trip planned to Cleveland and that gave me an opportunity to read and reread the assembly instructions while en route. Once back in the shop, I confirmed all markings and drilling thus far was dead nuts on. So still...why the discrepancy??
So I looked closer at my 1"x4"x10' jig pieces. Turns out the flap track guide arms were ever so slightly lifting the spar off the 1x4, forcing a sort of uniform "twist" at each end. So I remeasured the positioning, and notched the 1x4 under the flap track guide arms and BINGO!, everything came together. I still need to force the trailing edge down to even up the upper and lower trailing edges, but this helped the skin sit flat on the spar and eased the force on the forward-most nose rib flange (which doesn't receive a rivet anyway). Now the spar line is perfect and the rest of the drilling went very well. I still need to drill the nose ribs and trailing edges, as well as size up the ribs to #30 for the blind rivets, but the main mystery was solved so I am really happy with the outcome for this portion of the build.
Finished match drilling the left top skin to the frame and then set up the trailing edge joggle alignment jig. This is just the same 1x4 pairs used in the earlier part of the flap construction, but I cut the intermediate board down to 3.25 and used those scrap strips to prop up the back end under the trailing edge joggles. Pitched the intermediate board to sit flap against the rear ribs and all was lined up nicely.
I used the rivet fence to the 1.5" spacing in the manual and carried that exact spacing from factory hole to factory hole, straight down the rivet line. I maintained the lower skin cusp all the way back and managed to have about 1/32" overhang from the top skin to the bottom. This actually went better than expected and the trailing edge is nice and straight!
