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Fuel Tank Assembly

October 24, 2011

So the next bit is the fuel tank.  Vans has you complete the fuel tank before moving back to the rest of the wing.  So when I’m finished with the right fuel tank I will be completely finished with it.  As with all things on the plane it starts with assembly.

I know that I preach not to deviate from the instructions, just do what Vans tells you to do, but this is one place where it is universally agreed that Vans instructions can be improved upon.

Vans method of having you do this next part starts with mounting the Z-brackets.  The Z-brackets hold the rear fuel tank baffle to the wing spar.  After this they want you to put the baffle on top of the Z-brackets and drill holes.  The problem with this is that you have to be really careful with the alignment.  If you dont get it right, at best you could be replacing a baffle and all the Z-brackets, at worst you could have a fuel tank that isnt aligned very well.  What follows is refered to as the Checkoway Method, which is the name of the guy who first put it down on his website.  It is considered a far more accurate way to get the baffle drilled to the Z-Brackets.

The summary view looks like this:

  • Mount the Z-brackets per Vans instructions.
  • In the cradle, attach the two end ribs to the fuel tank skin
  • Final drill #19 and dimple the screw holes on the bottom edge of the skin to fit AN509 screws (#8 dimple)
  • Place baffle on top of ribs and cleco around the flange of the baffle
  • Put the fuel tank in place on the spar, screw in 3 screws on either side.  Make sure of snug fit with leading edge assembly
  • Match drill the inboard rib to the Z-bracket.
  • Remove the wing leading edge assembly
  • Match drill the outboard rib.
  • Remove the fuel tank
  • Put the leading edge assembly back in place
  • Remove baffle from the tank and cleco it to Z-brackets.
  • Match drill the rest of the holes in the baffle to the Z-brackets.

Thats the summary.  The end result is that the fuel tank fits perfectly and that is the goal.

The Z-brackets are easy.  You have to find the middle of one flange, and drill a hole.  You then attach the bracket to the spar and drill out the two remaining holes, from the underside of the spar.

You now have to drill the holes for the nut plates.  There will be two smaller holes opposite of the hole that attach the bracket to the spar.  Here’s how I managed this.

Get them lined up and fairly straight.

You then drill #40 holes into the little eyelets to make this.

From here you just have to grab your countersink cage and countersink the holes on the side facing the spar.  You’ll do all but the most inboard rib this way.  With that one you have to put the nut plates on the inside of the spar.  You’ll have as much fun as I did, I’m sure.  🙂

You then countersink the underside of the bracket and you wind up with this.

Now you have to start attaching the nut plates.  This is a relatively common task, and doesn’t cause much problem.  Having my pneumatic squeezer lets me do stuff like this.

This makes the rivets on the nut plates easy.

Then you start pounding rivets.  With the squeezer set in the vice, it makes it way easy to work with.

Watch your fingers.

Get all the nut plates in place and then attach the brackets to the spar.

Now that that is done, get your two outside ribs attached to the skin and then attach the baffle.  I used my pneumatic squeezer to dimple my edge holes for the #8 screws.

#8 dimples around the edge of the skin

I got that idea from another builder, and it was a really good idea.  Now that I am done with this, I can fit it onto the spar.

Perfect fit!

I put the tank in place and it fits perfectly…again I marvel at the accuracy of these kits.  I am glad I did the dimpling too.  Putting in just a few screws around the perimeter pulled everything tight and made the assembly fit like it would when finished.

For some reason I didn’t take any pictures of drilling the ribs to the Z-brackets, but you are only drilling the two ends.  the others come later.  The inboard rib is easy.  Get a really long drill bit and just do a normal match drilling.  The outboard rib requires a bit more effort.

If you take off the leading edge assembly you can easily get to the outboard rib.  It took me all of 3 minutes to get it off, so it really wasn’t a big deal.

After I got the baffle drilled and all the hole prepared I worked on fitting my inner ribs in in the skin.  I had to go back and completely redo the fluting.  I had sort of half-assed it before.  I do have some concerns about my two outer ribs, but I’ll post that on VAF and see what answers I get.   That was my weekend.

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