Left Tank 1

There are a couple of methods of aligning and installing fuel tanks.  Vans instructions have you basically drilling one of the holes in the z-bracket initial fitting, then elongating them to get the lateral alignment correct.  I did not like this idea of intentionally elongating holes, so I used a different approach developed by Dan Checkoway that many people have had success with.

First step in this procedure is to assemble the tank assembly in the cradle. 

Given the thickness of the tank skins, this is very hard.  Like the leading edge process, be sure and start from the leading edge and work backwards (skipping every other hole).  The tools I used to accomplish this were a 6d finishing nail and a nail set.  I used the nail to initially get the hole in position, then pull it in line and hold it with the nail set (while I placed the cleco).

You then go about locating the holes in the z brackets that attach between the main spar and baffle.  Find the centerline of each of the attach faces and draw a straight line.  You then drill a hole for the AN3 screw in the lengthwise middle of the z-bracket on one side only.  I am told that it is best to offset it slightly toward the web on the six outboard brackets, as this should provide better access to the pop rivets in the baffle.  Do not offset this much (no more than 1/16), as the nutplate would then interfere with the web. On the inboard most bracket, offset the hole slightly away from the web.

 Once the brackets are all drilled, you can then temporarily fasten them to the spar.  Using an AN3-4A bolt and 1065 nut, attach the brackets through the center bracket attach hole in the spar web.  Use a square to get them aligned real well (perpendicular) and tighten the bolts securely.

With the brackets all firmly attached to the spar, backdrill the two outer attach holes from the underside through the spar.  You can then remove all of the brackets and drill the nutplate rivet attach holes.  You do not want to drill rivet holes on the inboard-most bracket, as the nutplates get attached to the spar.  To drill the nutplates you can use a scrap nuteplate (attached with an AN3 bolt) as a guide.  I have found it is much quicker and easier to use a nutplate drill jig.  They are available for $17 at Yardstore.com.

Once the nutplate attach holes are all drilled, go ahead and attach the nutplates to the bracket.  Although the instructions don't mention it, I went ahead and primed the brackets before attaching the nutplates.  You can also go ahead and attach the nutplates to the inner-most bracket spar location at this time.  With the nutplates all attached, bolt them to the spar (using just two outer-most screws).