Originally Posted by DRBuilder
For Mitch Locke... Why are 1100-08 plate nuts (countersunk) used here instead of 1000-08 plate nuts? The spar flange is countersunk to accommodate the dimpled fuel tank skin with 8-32 flat head screws. The 1100-08 plate nut creates a void between the flange and the plate nut threads.... not good. Not to mention, the 3-3.5 rivets are too short to create a good head on the 1100-08 due to the thickness of the plate nut. I installed the 1000-08 plate nuts in 2 of the locations and they work perfect, with no void between the spar flange and the plate nut threads. Can you comment?
I'm not Mitch but I know the answer.
This is the exact same thing that has been done ever since the new spar design began being used (RV-8), and the void you are concerned about is not an issue. The majority of the strength is from the dimple acting in shear on the countersink.
The nutplate is used to guide the pilot of your countersink cutter when doing the countersinking.
If you use K1000 nutplates, the cutter will begin cutting into the nutplate before you get to the full depth required for the countersink.
Couple of other comments...
The rivets that are used to install nutplates provide zero strength to the fastener joint. They only hold the nutplate in position and prevent it from rotating while installing the fastener.
Sometimes a rivet a bit on the short side is spec.ed because the next longer would be maybe a bit on the long side and more difficult to set straight.
Everything about the RV14 kit was done for a reason, and the way the kit is supplied is a copy of how the wings were built when the structural testing was done.
So my advice would be a recommendation that builders not make changes without knowing the specifics of why something was done a particular way.
But, as always, this is experimental aircraft and you are free to do it differently if you choose.
BTW, the countersinks in your photos are not deep enough. The countersink depth needs to except the skin dimple, not the screw head, which requires a deeper counter sink than the screw does.