What I did find from my research is that if you choose to countersink, there is no need to countersink extra deep to allow for a thin layer of proseal between the rivet and the skin (unlike using tank dimple dies for the rib/skin connection) This lead me to a debate on the forums just having the rivet set flush with the skin. Seems that a flush 3/32 rivet will result in a knife edge condition in the slightly thinner 0.032" material. According to the forums this knife edge condition is not wise. I was surprised to read that Vans technical support is not keen on the knife edge condition in this area. The instructions call to machine countersink the rivet, with no red flag on making sure to avoid a knife edge condition.
Oh well....that why there's forums called plans "Gottcha's"
According to the information in the forums leaving a flush rivet slightly proud will help avoid the knife edge condition. I have chosen to follow this method. The question of the day...is what is the correct dimensions to proceed.
According to the forums and rivet Mil-Spec MIL-R-47196A. The maximum head protrusion for rivet shaving is 0.006" and a minimum head diameter of 0.161". Therefore if my goal is to countersink to a diameter of 0.162" this will meet the minimum specification for maintaining rivet strength if the rivet is shaved or sanded down flush. Although, my goal will be to leave the rivets proud in this area to maximize strength. Maybe the gap left is a fillet of proseal? That would be ideal!
Here is the countersink diameter on my test piece.
Here is how the rivet sits proud with that diameter. Really minor!
I had posted on Vans Airforce my findings and let it sit for a bit before I took action , just in case someone had chimed in that it was not a good idea. So while I waited I devinyled the left wing skin.
After an hour I checked back on the post, and all was good. I also double checked with my buddy mike who is an aircraft mechanic and air accident investigator to see what his thoughts were. After consulting with him, I decided that my findings were correct and I completed the riveting on the right wing skin.
The rivet sits slightly proud.
I then removed the baffle and decided to fit up and match drill the fuel cap. I took my time to make sure it was centered and everything looked good. I marked the holes. Clamped it to the skin and re-checked.
All was good so I drilled. I'm very happy with how it turned out.
Once that was done, I disassembled the right tank, and cleco'd the left tank. Holy crap those two outside (blank ribs) are awful to get aligned and cleco'd in. I managed to make it work....finally, but the holes are taking a beating. Once the tank was cleco'd I set it on the Left wing and the fit was perfect.
I repeated the same steps as the right tank. Used straps and clecos. Everything fell into place. So I match drilled the joint plate. First to #30 then to #19. I match drilled the inboard z-bracket.
Disassembled the left leading edge to gain access to the outboard leading edge.
I started to match drill the baffle, but it's getting quite late and I've put in a huge day. So that's it for tonight.
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