Well I got a bunch of good posts about how to buck the aftmost rivets that attach the upper and lower flap skins to the inboard flap rib. Helpful responses were found on both the Matronics list and the Ohio Valley RVators list. Thanks guys! Most of the suggestions described using a chisel or splitting wedge to get in the tight spot. Well I only had one chisel and it proved too wimpy to squash the rivet and I didn't have a splitting wedge, so I decided to go into work and use one of the milling machines to make some custom bucking bars.

Here's #1 in place. You can see how the oval hole in the middle allows clearance for the nutplate.

Now #2 and #3 in action. I really had to pound on the very aftmost rivets (both top and bottom) to get a good shop head. I usually drive 3/32 rivets at 35 or 40 psi, but for these I cranked the regulator up to 60 psi.

As you can see, they came out great.

After (nearly) finishing up the left flap, I needed to install the pop rivets that attach the ribs to the spar. The ones near the top skin are a real bear. I managed to put a slight crimp in the lip of the upper skin doing one of these. After doing the second one I noticed that the rivet's not really straight. Maybe tomorrow I'll go see if I can get a more compact pop rivet tool that'll fit under the lip of the skin better.

In retrospect, I should have put these pop rivets in before riveting the top skin to the spar. The skin would have a lot more flex that way.

Kerin was a huge help tonight. She drove the gun and I bucked. We got the left flap mostly assembled and she also helped support the whole rig while I was doing the aft rivets on both left and right flap inboard ribs. Thanks, sweetie!