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Fuel Tanks

asw20c

Well Known Member
On page 18-03 there is a highlighted note saying that to ensure proper alignment, every 10th hole that attaches the tank baffle to the skin should NOT be countersunk until after the tank is assembled and the initial batch of sealant has cured. First, I've read through this section at least 3 times to try and better understand at what point we are to consider the tank "assembled" and the final countersinking should begin. Would that be after step 5 on page 18-05?
I'm also having trouble visualizing how leaving every 10th hole uncountersunk aids in alignment? Can anyone explain? Also, won't there be tank sealant that oozes up through those holes making later countersinking more difficult?

And lastly, I just discovered that the first comment made by JDA_BTR in the plans Gotchas regarding page 18-04 step 3 and which part gets the #19 dimples is not correct. The plans in fact are correct. The rest of his comments are fine.
 
I want to be clear that I'm not trying to be a jerk regarding pointing out an incorrect entry in the plans Gotchas by another poster here on the forum. I just want to make sure nobody messes up a part because someone else made a mistake in interpreting the plans.
 
I just finished this step on my right fuel tank and I can tell you that those alignment holes are important. Those holes on both sides ensure that the fuel tank is square when you start riveting in that back baffle. Without them the holes are countersunk to a point where the hole in the outer skin is over size which allows some left to right "play" in the hole alignment. I riveted my back baffle in place and then came back the next day and countersunk/riveted those alignment holes.
 
Or consider dimpling the holes in the tank skin and aft baffle flanges. It will be self aligning, less work, stronger, and most of all give you much nicer results aesthetically. See my other posts on this subject...
 
Ok, now I think I get the point. By leaving every tenth hole uncountersunk the clecos in those holes will be "tighter" than in the holes that had already been countersunk. I was thinking it had to do with how the tanks aligned with the wing assembly which was why I wasn't getting the point. Thanks for the feedback.
 
I think the plans describe to not over countersink and as a result you end up with the rivet head slightly proud. I'm hoping that before I paint I'm able to either use 3D primer or skim the rivet heads down to end up with a smoother finish.
 
I'm hoping that before I paint I'm able to either use 3D primer or skim the rivet heads down to end up with a smoother finish.

Yep, rivet shavers and high build primer will help...Did that on my -8A, it was a lot of work and I never was really happy with the end result. So much easier to just dimple, and those rivets came out looking beautiful on my -14 tanks.
 
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