Each fuel tank attaches to the wings in 3 ways:
All of this is straightforward, except the Z brackets are kinda funky. Nutplates go on the front of one flange, where bolts attach from behind the spar. Then, the other side of the Z bracket has five 1/8" holes where the bracket gets pop-riveted to the fuel tank baffle at a rib location. Pop-rivets are used because the baffle is the last thing to go on each fuel tank...no way to buck or squeeze these rivets since you can't get into the tank.
Now this is all well and good, but you can't just arbitrarily drill the 3/16" bolt holes and the 1/8" rivet holes in the Z brackets (even though that's what Van's instructs you to do). The idea is to position the tank on the wing so that it lines up perfectly, there are no gaps, etc., and then back-drill the Z brackets from behind the spar. That kinda works, but not really. Here's what I did instead...
First I assembled the fuel tank. Skin in the cradle (inner vinyl protection removed).
Attach the ribs. This is WAY more difficult than it sounds. The fuel tank skin is THICK and hard to work with at the very leading edge. It's tough to get the ribs deep enough into the leading edge to get the rivet holes to line up perfectly. Something tells me that the pre-punched kits are actually more difficult in this area! Anyway, you wrestle the tank together. Cleco the baffle in place, but don't cleco it to the ribs. In this picture there's a cleco into each rib, but those have to come out before you do anything else...see below.
Now for the brackets...drill one 3/16" hole in the center of one side of each Z bracket...but don't drill it on-centerline...drill it about 1/16" toward the web. This theoretically will make more space for your pop riveter when the time comes. Trust me. But the inboard bracket needs the bolt holes slightly away from the web...that's so you can get a wrench or socket around the bolt head without the web interfering. Totally convoluted, I know...it gets better.
Ok, so you drilled your one center hole in each Z bracket. Now bolt each bracket to the spar in its respective location. Square the web to the spar. I mean square. Now tighten the nut/bolt (don't worry about torque...just use a "throwaway" AN3-4A nut/bolt and tighten it good so the Z bracket won't rotate). Now back drill the other two holes through the spar (from underneath in this picture).
When you've done this for each Z bracket, it's time to attach nutplates for each of the bolt holes. I found it easiest and most efficient to take three "scrap" nutplates, tap 'em out so the bolts go in nice and easy (which means quick), and then tighten them down onto the Z bracket. Drill out the six rivet holes, and remove the nutplates.
Debur the holes, machine countersink one side for flush AN426AD3 rivets. Then, rivet all the nutplates on. Oh...by the way, don't rivet nutplates on the root Z bracket...the nutplates go on the spar for that one. I'll explain later.
Ok, now bolt all of the Z brackets to the spar. I just used the outer 2 bolts for each of these. No need to go crazy, just have to get the brackets on the spar solid enough to drill the tops.
Now mount the tank on the wing. Man, this picture looks sweet. But in reality, it looks much more impressive than it is. I am so far away from actually having this wing done it's not even funny. Very misleading.
But boy is the setup sweet. There is just no freakin' gap anywhere. Pull the tank down onto the spar so that the baffle rests tightly against the Z brackets, and so the screw holes all align. Make sure you've got no gap between the tank and the leading edge. This picture shows the joint at that joint plate (showing through the holes). We're talkin' miniscule here.
Next, drill the rib-baffle-bracket holes at the wing root. This is the only thing exposed at this point. I used a 12" long drill bit for this so that a little flex in the bit absorbed the offset/angle. Now, after all this freakin' work, and with this beautiful "together" wing before you, take it apart...remove the leading edge, leaving the fuel tank on. I thought I snapped a picture of this, but I must not have. Anyway, it's as simple as it sounds. Take the leading edge off. Here's mine, back in the cradle.
Now you have access to the outboard fuel tank rib. Drill that rib-baffle-bracket joint. Ok, now the baffle is drilled and clecoed to the Z bracket on each end. You're not gonna like this...but take it apart. Remove all the clecos holding the tank skin to the end ribs. Remove the clecos holding the skin to the baffle. Remove the clecos holding the skin to the spar. Lift the tank off.
What you're left with is the baffle and end ribs in place, exactly where they need to be for a perfect tank alignment. Now you have great exposure and stability in order to drill the rest of the baffle-bracket holes from above. Wouldn't you know it...the centerlines on the Z brackets shone right through the holes, dead-on. I didn't even expect it to be that good. I didn't really care so much about alignment of the bracket centerlines, as long as the tank fit perfectly and there were no gaps. Well, centerlines in the holes to boot.
Done. Here you can see clecos in all of the holes.
I'll tell you, that is an awful lot of work just to drill some Z brackets. It took me just about all day to get it done, what with all the bracket and nutplate preparation. But I believe it's well worth it to have a perfect fit and finish. We shall see...