Fuel tank skin dimpling - page 18-05

I am trying to solve two mysteries with the fuel tanks. Both are dimpling related.

1. I don't see a step that actually says to dimple the #19 holes around the fuel tank skins. Page 18-03 step 11 says to dimple the skin as shown on page 18-05 figure 1. The figure does not clearly indicate that the #19 holes should be dimpled. It appears that they should be. Am I correct that I should do so at this stage?

2. Two of the #19 holes are marked on page 18-05 figure 1 as "do not dimple." These are the top and bottom of the subassembly, and line up with the MS21051-L08 nutplates. Looking forward in the plans to the wing installation, flush screws are shown in this position, attaching the wing root fairings to the wings. Specifically, it looks like the upper wing root fairing goes here, and on page 41-04 step 12 we are to dimple all of the holes in that part. Any ideas on what I'm missing to understand why these holes are not dimpled or countersunk?

dimple the screw holes

Right above 18-03 step 11, there is a note to dimple the #19 screw holes, in boldface type ... although you are right - the figure on page 18-05 doesn't call them out specifically.

_Alex

AlexC said:

Right above 18-03 step 11, there is a note to dimple the #19 screw holes, in boldface type ... although you are right - the figure on page 18-05 doesn't call them out specifically.

_Alex

Click to expand...

That's the source of my confusion. The bold text tells you how to dimple the screw holes, but the step itself and corresponding diagram don't say to do so. I have had to deal with prematurely dimpled holes before, so I'm probably being overly cautious now.

Any idea what happens with the two un-dimpled #19 holes on the inboard edge?

Those 2 "un-dimpled" #19 holes in the fuel tank skin correspond to the tank attach bracket subassembly (18-04, fig 2) and the two MS21051-L08 nutplates #19 holes, which are part of that.

_Alex

AlexC said:

Those 2 "un-dimpled" #19 holes in the fuel tank skin correspond to the tank attach bracket subassembly (18-04, fig 2) and the two MS21051-L08 nutplates #19 holes, which are part of that.

_Alex

Click to expand...

I noticed that. But if you look ahead to what gets screwed into those MS21051-L08 nutplates through these holes, it looks like AN507 countersunk screws. Granted, I don't actually see a step in the plans to final-install the top wing root fairings, but the cover page of section 41 makes it look that way.

The T-00006 is far to thick to dimple countersink.
The only screw holes that get dimple countersunk are the ones on the T-1005B called out on 18-04. The other screw holes in the T-1005B but common with the T-00006 will eventually get machine countersunk to accommodate the dimples in the wing root fairing.

The ones common to the tank skin (single leg nutplates) will be machine countersunk as well.

In simpler terms, all holes associated with the T-00006 will be machine countersunk because of the material thickness.
The two screw holes where the nutplate rivets to only the T-1005B will be dimple countersunk.