In preparation for riveting, I have been looking at a few places on the fuselage skins. In each case where three layers of skin come together there is or will be a slight gap once riveted. The shop manual says nothing about these joints and they won't be obvious since they are on the bottom of the structure. Even so, I wonder if they should be sealed with a bit of tank or firewall sealant.
I happened to be working at the NMUSAF this evening (special aircraft opening for a test pilot association) so I took a close look at the fuselage skin on a C-123 and found the same issue. The only difference I noted was the rivets were universal head and the spacing was a little closer which reduced the gap just a bit. I couldn't see any sealant in the seams. Nevertheless, I may send a message out to the local builders group to see if there are any comments.
