We'll begin this post with my three legged dog Roxy. No particular reason other than she has been present for much of the work on this airplane and deserves some recognition. [applause] Just kidding about the three legs.
The first step in assembling the fuel tanks is to prepare the Z-brackets. It seems that there are two camps when it comes to this step: the Van's way, or the Dan Checkoway method. Everyone seems to agree that Dan's method is superior, but there are plenty of sage advisers online to offer the tried and true: "follow the manual and you won't be sorry" or the somewhat less helpful "I did it the Van's way and it worked out fine."
So what is a Z bracket? It's an aluminum extrusion whose cross section is in the shape of a "Z." These extrusions are about 4.5" in length and are fastened vertically along the front face of the main spar and form an interface between the fuel tank and the spar. The Z bracket will be riveted to the tank on one side and have nut plates to capture bolts coming through from the other side of the spar. Removal of the fuel tanks for inspection or repair is facilitated via these bolts.
I decided to investigate Dan's method but I ran into a road block right away -- his website is no longer available. To learn about this now mysterious method, I would have to gather the information second hand from those who claim to have followed it. Right away I find that the method is not really documented as thoroughly as I would like. More like just a mention here or there and some pictures.
Here is I summary of what I believe the much bally-hooed Dan Checkoway method to be:
1. For six of the seven Z brackets, mark a line lengthwise along one flange 1/16" offset from the center, away from the web. The offset should be such that additional clearance to the web for a socket or wrench is achieved.
2. Find the center of the Z bracket along the line and drill a #12 hole.
3. Temporarily install on the spar and tighten down with AN3-4A bolt. Make sure the bracket is square to the spar. Check the line through the other two holes in the spar and clamp the bracket securely.
4. Match drill the other two holes through the spar and bracket.
5. Install the nut plates on the brackets.
6. Install the brackets on the spar.
7. Assemble the fuel tank with clecos and install on the spar.
8. Position the 7th Z bracket optimally in the inboard location under the inboard fuel tank rib. This will be the bracket that did not get the nut plates. Clamp the bracket securely and then match drill the screw holes through the spar.
9. From either end of the tank, match drill the tank's rear baffle to the Z bracket and rib. Then secure with clecos.
10. Remove the fuel tank skin and the tank's inside ribs.
11. Match drill the inside Z brackets through the rear baffle.
Lastly, and this is very important, Sit down and have a beer!
Armed with a semblance of the Dan Checkoway Z bracket alignment method, I went to work on marking, drilling, and nut plating the Z brackets for both wings.
After the brackets are drilled for the bolts they are then prepared for nut plates. Using the nut plate itself, the ears are drilled through. The last step is to counter sink the other side so the rivets holding the nut plates on will sit flush. This allows the Z bracket to sit flat against the spar.
With the nut plates complete, the next step is to mount them on the spar. Since they will get mounted and removed several times before the fuel tanks are complete, I'm only putting two of the three bolts on for now.
The Z brackets are on the spar and I've clecoed the left fuel tank together.
I placed the tank on the left wing and match drilled the W-423 splice plate the attaches the outboard end of the fuel tank to the matching leading edge section. Note the strap to hold the tank down tight before drilling.
The final step for the Z brackets is to match drill through the back of the fuel tank and in to the forward flange on the bracket. The tank skin must first come off to permit access. The inboard end rib is match drilled through to the Z bracket. Here it is shown after I removed the rib and was in the process of removing the tank skin.
At this point I finally had to face the consequences of not following the build manual's order of construction regarding the leading edge section and fuel tanks. After I had finished the leading edge sections I, impulsively it seems, decided to rivet them on to the spar.
Unfortunately, with the leading edge section in place, it is not possible to match drill the outboard end rib through to the Z bracket below because the end rib's flange faces outboard leaving no room between it and the leading edge section to access the rib flange from that side. Crap! While it certainly would be preferred to lock down the far end of the tank's rear baffle before match drilling the interior rib-Z bracket connections, there is another way for us scofflaws. (People who don't follow the manual.)
Step one on getting myself out of this predicament was to release one side of the tank skin leaving the other firmly attached to the spar. Then reach up inside and match drill the next rib in from the outboard end to locate the tank's rear baffle to the Z bracket. With that rib's Z bracket clecoed down, the rear baffle is now set firmly from end to almost end. OK, so far, but what about the inaccessible outboard Z bracket?
Well, I can see it up in there just laughing at me, but what to do about it? Here is a closer view. The bracket is just barely visible in the middle at right, between the rear baffle (above) and the spar (gold).
My solution was to spray some primer through the gap at the Z bracket and baffle. This will mark the bracket's exact location relative to the baffle. When I remove the tank I can reposition the bracket up to the paint line then do the proper match drilling. Whew! Disaster averted. Now on to the next calamity.
The final step on the Z bracket odyssey is to complete the tear down of the fuel tank, removing the skin and ribs to expose the rear baffle. Now the interior Z brackets can be match drilled.
With the rear baffle exposed, the remaining Z brackets are easily match drilled. So now I remove the baffle to reveal my primer paint trick. Fortunately, the line is very sharp which will facilitate the re-positioning nicely.
And so the last Z bracket is clamped to the baffle and match drilled. Now that I been through this once, I should be able to complete the right wing Z brackets with a minimum of drama.
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