Wing root fairing and tank skin edge distance.

Hi All,
I'm about to install my wing root fairings (F-799), and was just checking edge distances on the tank skins (T-701). It appears I have 15.5/32" of tank skin to play with before it butts up against the tank rib, but if a k1100-08 nut plate is 13/32" wide, then that means my hole centerline only has a 9/32 edge distance. In addition, this short distance (13/64) between the hole centerline and the tank flange means the make die will riding up on the tank rib flange, giving me an ugly dimple. There seems to be little addressing this in people's websites or the forum. How are people dealing with this? Are you guys making a shim the same thickness as the tank rib flange for the dimple die to ride up on, then just putting up with this lousy edge distance, or are you switching over to NAS514P-6 screws and just using twice as many so this edge distance is ok? Or something else? Words can not explain how frustrated I am with the edge distances in this kit. If they are that mad keen on saving weight, make me cut another lightening hole somewhere, but quit giving me lousy edge distances to work with.
Tom.

Gday Tom
Is the issue the #8 screw dimple?
Most of my larger female dimple dies have been ground down on one edge to accommodate issues such as this. If that is still too close to the tank rib flange then the shim trick should solve your problem. I don't specifically recall a major issue there.
For the -3 and -4 rivets a set of narrow diameter females is very useful too.
Cheers

Thanks Richard. Yes, the #8 dimple is part of it. Because the web of that last tank rib is on the outboard side of the flange, the doubler solution should work. If it doesn't, I guess I'll have to grind my female die down on one side. The other real issue is that the edge distance is less than adequate, which really irritates me as I built these exactly to spec. I really don't like dimpling when I have less than adequate edge distances, especially on a fuel tank I spent way too much time constructing. I'm working on another issue right now where I do not have adequate edge distance, and have found that substituting two high strength #6 NAS514P screws for every #8 AN509 works as an adequate replacement from a load perspective. I'm just not looking forward to taking off twice as many screws every annual at this location.
Tom.

Tom,
The wing root fairing is just that, a fairing. It does not have any high loads applied to it. In fact it is just cantilevered off the inboard end of the wing.
Edge distance is not critical for these screws. That is probably why a search in the forums doesn't find much on the subject from anyone else.

Thanks Scott. You are right, I think everyone is just sucking it up and living with it. It appears that from other posts I can find that people are just putting the hole centerline 1/4" in from the edge. I just didn't want to be stretching any metal near the seals on the tank. A leak is the last thing I need right now. I'll have to add a wider flange at this location to my Christmas list, and maybe it'll be a bit wider on the next -7 I build.
Tom.

Countersunk skin thickness

Disregard. Reading the plan the wrong way.