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Fuel Tank Attach Bracket Issues

F

flyingtaran

Member
Hi All,
Just started looking at my first fuel tank and i've already run into an issue with the 712 Z brackets,
I marked and drilled the 1/8 hole in all 7, then the #12 hole in 6 of the brackets as outlined in the manual, clecoed six of them to the back of the spar and match drilled, then after removing them and attaching the nutplates using my nutplate jig I am having issues bolting the brackets to the spar and even putting bolts in the brackets, it looks as though some of the bolt holes in the brackets are slightly misaligned with the nutplates.
It was pretty tight to get the bolts in the #12 hole before attaching the nutplates.
Should the holes have been match drilled slightly larger than #12?
I have heard mention of the checkoway method, should i research this more and start the brackets again?,
any help is appreciated

cheers

Taran
 
My method is to put a awl into one of the 3 holes to lign up the bracket while I get the other bolts started. Usually works well. Also, I always do the bolts before I screw the tank onto the spar.
 
Jesse said:
My method is to put a awl into one of the 3 holes to lign up the bracket while I get the other bolts started. Usually works well. Also, I always do the bolts before I screw the tank onto the spar.
Click to expand...

I did the same AND did not screw the tank skin to the spar until all the Z brackets were bolted, torqued, and torque sealed.
 
Z-brackets

flyingtaran said:
Hi All,
Just started looking at my first fuel tank and i've already run into an issue with the 712 Z brackets,
I marked and drilled the 1/8 hole in all 7, then the #12 hole in 6 of the brackets as outlined in the manual, clecoed six of them to the back of the spar and match drilled, then after removing them and attaching the nutplates using my nutplate jig I am having issues bolting the brackets to the spar and even putting bolts in the brackets, it looks as though some of the bolt holes in the brackets are slightly misaligned with the nutplates.
It was pretty tight to get the bolts in the #12 hole before attaching the nutplates.
Should the holes have been match drilled slightly larger than #12?
I have heard mention of the checkoway method, should i research this more and start the brackets again?,
any help is appreciated

cheers

Taran
Click to expand...

Ahhh. Z-brackets!. Dan Checkoway prefers not to have his name associated with the method but it does work perfectly. Call it "the revised z-bracket method". Here it is.

First mark a center line on each z-bracket flange but only drill one hole in one flange of the z-brackets matching the hole size in the spar. You can fudge this center line a 64th to make sure the bolt head will clear if necessary. Center worked fine for mine.
I used scrap bolts and nuts next.
Secure the bracket using one bolt. Align center on the other two spar holes.
Another trick is three pieces of brass tubing from a hobby store. ID of the inner one is #40. OD of the outer is the spar hole size. The three pieces slide together to create a drill bushing. Now you can perfectly center drill the holes without messing up the spar holes.
Drill one more hole in the z-bracket. Insert a bolt. Drill the third. Remove and repeat for the others z-brackets.
Once all the z-brackets are done, install the plate nuts on the z-brackets and the plate nuts for the inboard spar z-bracket holes. Mark the other center line on the z-brackets. Install the z-brackets.
Cleko the tank together including the baffle. Use 100% clekos in the baffle to skin and skin to rib holes. Cleko the tank to the wing. 1/8" clekos fit the tank attach nut plates in the wing spar. Use 100%. Cinch it down with straps so the leading edge and tank attatch holes are perfectly lined up. Cleko them also. It should be exactly where it belongs now.
Check center lines in each z-bracket through the baffle holes in the next steps. They should be lined up perfect.
Drill the holes for the inboard baffle to z-bracket. Cleko them.
Remove the leading edge. You have to remove it leaving the tank attach because it won't slide out. You can remove it after.
The outboard end of the tank is now accessible.
Drill the outboard baffle to z-bracket holes. Cleko them.
Disassemble the tank skin from the baffle leaving the baffle clekoed to the two z-brackets.
Drill the remaining z-brackets inserting clekos as you drill.
Now you have a perfectly aligned baffle z-brackets.
It takes a bit longer but it's worth it.
 
Last edited:
wirejock said:
Ahhh. Z-bracket ****. Dan Checkoway prefers not to have his name associated with the method but it does work perfectly. Call it "the revised z-bracket method".
Click to expand...

+1

I used this method on my second set of Z brackets after hitting similar problems and ruining my first set.
 
When I got ready to install my Z brackets after I had drilled them, I too thought that I had somehow drilled in them in misalignment. I did not understand how that could have happened, but the z bracket holes just didn't perfectly line up at final installation time.

I found that if I started all 3 bolts with just a few turns (leaving the bracket loose, i.e. just kind of hanging from the bolts that were barely started in the threads), and continued to snug up the bolts, moving from bolt to bolt after a few turns each, the z brackets all fell right into place. No binding, no eaten threads.
 
Last edited:
I used the "revised" method and the holes came out right on. The manual says to elongate the holes in the spar as required, but that didn't sound like a good idea to me.:confused: IMHO, the manual should be updated.
 
longranger said:
I used the "revised" method and the holes came out right on. The manual says to elongate the holes in the spar as required, but that didn't sound like a good idea to me.:confused: IMHO, the manual should be updated.
Click to expand...

Here's what my RV8 plan has about this, i.e. make the baffle holes bigger.

"skin and leading edge should be perfect. If not, elongate the holes in the baffle inboard or outboard as necessary to
allow the baffle holes to align with the T-701 holes when T-701 is clecoed to the spar."

I tried the Hurlbut method http://www.vansairforce.com/community/showthread.php?t=106499 (back drilling the #12 holes through spar with the tank strapped onto the wing), but while drilling, the pressure apparently flexed the z-bracket and baffle, such that the alignment of the holes was poor, even though the centerline was perfect prior to drilling. While I probably could get the bolts on, I think there would be bending stresses imposed on the baffle, so I'll be trying it the other way, i.e. drilling the bolts first with the bracket bolted to the spar.
 
Revised z-bracket method

Get your z-brackets drilled to the spar first. I used scrap bolts to hold them in alignment along with a center line on the bracket. Drill the center hole on the bench first. Bolt the z-bracket to the spar loose. Center the line, tighten the bolt. Drill one of the ends. Insert another bolt. Drill the third. Once you have all of them done, draw a center line on the other flange and bolt them on. Proceed with revised method. Drill the inboard z-bracket through the baffle holes. Use a drill stop. Cleko. Remove the leading edge and drill the outboard z-bracket. Cleko. Remove the skin and match drill the z-brackets through the baffle holes. Now you have perfectly aligned z-brackets and baffle.
 
Must Read: Z-Bracket

wirejock said:
Ahhh. Z-brackets!. Dan Checkoway prefers not to have his name associated with the method but it does work perfectly. Call it "the revised z-bracket method". Here it is.
Click to expand...

:mad: Dang it, I should have read this post before drilling the Z-brackets. Using the Van's method, if I align the pre-drilled 1/8" hole to the tank baffle, the entire tank will be misaligned by about 1/16". This is to say the pre-drilling of Zbracket flange to the tank baffle is a bad idea. Instead of elongating the holes which will be rather substantial, I will redo the new brackets using the Checkoway method.
 
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