I decided to go ahead and assemble the upper forward fuselage, since I had enough cleco’s, I needed a larger priming batch, and it gets a bunch of drilling / countersinking out of the way. It turns out there is a problem with two of the ribs in this assembly, as noted in this VAF posting, and I have the same problem. Either the holes in the front of the F-1045 ribs are incorrectly punched, or the corresponding holes in the firewall are wrong. During assembly, the ribs are first riveted to the top skin. If this is done, then the holes in the front flange will not line up with the firewall.
If the front flange holes are cleco’d to the firewall, there is a 1/8″ gap between the top flange and the top edge of the firewall. I can’t adjust the firewall flange – then the cowl would not fit. I tried cleco’ing down the top skin, and it sortof goes down OK, but the forward most cleco doesn’t actually close the gap between the flange and the top skin. The rest of the skin is “pulled down” to the flange, resulting in the skin curving inward. The front flange holes can’t be re-drilled, the correct position would overlap (just) with the existing holes.
The fix recommended by Van’s is to put a new flange on the front of the F-1045 left and right ribs. I bent up some 0.032″ Alclad to use as replacement front flanges. The pictures show the modification to the F-1045L (left side) rib. I removed the rib and made up a simple frame on the bench that the rib fitted into snugly. This allows installing and match drilling the new flange in the exact same forward position on the rib. I carefully cut the old front flange off, de-burred the resulting edge, and using the bench frame match drilled the new flange into place, finally trimming the bottom of the flange to match the front of the rib.
The rib with replacement flange can then be cleco’d back in place, with a reference line drawn on the flange so it can be sighted through the firewall holes and lined up properly. The front flange is a bit tight because the holes in the firewall are already dimpled. There are seven holes that now have to be carefully match drilled. The rib was removed again, all holes were de-burred, and the front flange holes were dimpled.
Finally, the rib was re-installed, and with the front flange holes now in the right place, the top skin sits flat on the top flange of the rib, and a straight edge held on the skin shows no gap.
With the two F-1045 ribs fixed up, the entire upper forward fuselage assembly can now be match drilled.
