Ethan's RV-7

2.6 Hours -

I’ve decided to fit the fuel tanks using a method commonly referred to as the Checkoway method rather than using Van’s method.  Dan Checkoway receives credit for this technique (although I don’t think he was the first), but, since he took his website down, I’ve had to use other sources…mainly Brad Oliver’s website (www.rv7factory.com) and http://home.comcast.net/~jwdmac/ZBrackets/zbrackets.html.

Using this method, the z-brackets are fitted to the spar first.  Then, the tank is clamped into place on the wing and used drill the top flange of the inboard and outboard z-bracket.  Finally, the tank is removed, except for the baffle, inboard rib and outboard rib, and the remaining z-bracket top flange holes are drilled using the baffle as a guide.  This method supposedly allows the tank to remain in better alignment than the Van’s method.

The first thing I did was mark the aft flange of each z-bracket (W-712) for the location of the center hole.  It is suggested that this hole be located 1/16” closer to the flange on 6 of the brackets and 1/16” away from the web on the inboard bracket.  This is to give more room for the rivet puller on the outboard brackets and more room for a socket driver or wrench on the inboard bracket.  However, if you don’t make this measurement perfectly, you’ll end up to close to the flange and the nutplates will no longer fit.  I ruined one z-bracket this way before decided to move a little close to center for these holes.

One flange on each bracket is marked. Using this method, the center hole should be nudged toward the web on 6 brackets, and away from the web one bracket (inboard bracket).

Once the location for the center holes were marked, I drilled them with a #12 drill.  The brackets were then bolted to the spar through the center hole.  As soon as I bolted the first one to the spar, I quickly realized I had drilled them off-center, and it was bad enough that it wouldn’t allow one of the outboard nutplates to be attached.  Two more nutplates were ruined before I realized this mistake.  I’m not sure how I did it, but I miss-measured all of the z-brackets.  Fortunately, I hadn’t drilled them all yet.

The center hole is drilled first. After screwing up a couple of these, I moved the hole a little closer to center.

After these mistakes, I had no problems with the remaining z-brackets.

The z-brackets were attached to the spar using a bolt and nut through the center hole.  Then, they were squared to the spar and the remaining two holes on each bracket were back drilled through the spar using the holes in the spar as a guide.

The bracket is bolted to the spar through the center hole and then squared for drilling the two remaining holes.

Squared and secured...time to drill the remaining two holes.

The top and bottom holes are back-drilled using the holes in the spar as a guide. Once drilled, I slipped a bolt through to make sure the bracket stayed square.

Once all three holes were drilled, the brackets were removed from the spar so that nutplates could be attached to the 6 outboard brackets.  The nutplates for the inboard bracket will be attached to the aft side of the spar.

To attach the nutplates, I use a bolt and some washers (the washers keep the bolt from engaging the locking threads of the nutplate making it much easier to remove the bolt) to attach the nutplates to the bracket.  Then, the nutplate was used as a guide to drill the two holes that are used to rivet each nutplate to the bracket.

I secured the nutplates to the bracket using a bolt and washers (the washers keep the bolt from engaging the locking portion of the nutplate). Then drilled the nutplate attach holes using the nutplate as a guide.

I decided to use NAS1097 3-4 “oops” rivets to attach the nutplates.  Since these rivets have a smaller factory head, I hand countersunk the brackets using my swivel deburr tool.  Once countersunk, I squeezed the rivets attaching nutplates and then bolted the brackets back onto the spar.

Finally, the nutplates are riveted to 6 of the 7 brackets. The nutplates for the seventh bracket will be riveted to the spar.

All of the brackets for the left wing are done, but I’ll have to order three new brackets for the right side before I can finish that wing.