Fuel tank mystery hole

This afternoon we were in the garage final drilling, well, a BUNCH of holes. (So, what's new, right?) But there is one hole (on each tank skin) that seems out of place. It's in the line of holes where the tank skin attaches to the the lower baffle flange, right in line with the middle rib. All of the other holes are evenly spaced, but this oddball evenly splits the "normal" spacing. There is no corresponding hole in the baffle flange.

Reading ahead, I can't find any reference to it, and though it appears depicted in the rivet diagram on page 18-5, it doesn't look like a rivet is called for.

I've left it undrilled for now. If anyone can clue me in on why it's there, I'd be most appreciative.

Thanks.

Jeff

A photo might help.

By any chance is it where an access panel will end up? Trying to remember stuff, and taking a shot in the dark here..........

I think it's so you can keep your rear tank baffle oriented correctly from top to bottom. Match drill the hole into the baffle and then you have orientation.

Jesse said:

so you can keep your rear tank baffle oriented correctly from top to bottom

Click to expand...

I thought that's what a Sharpie was for.

The clecos are attaching the tank skin to the middle rib. The holes running left to right are in the skin and are where the skin attaches to the tank baffle lower flange. The four holes on either side of the rib are evenly spaced, then there's that one odd hole in line with the rib that has me ... ok, I'll say it ... baffled.

I think Jesse's guess is as good as any. Jeff, kudos for your attention to detail. I never noticed, but you're right - if you look closely, there is not a rivet symbol over that hole in the plans. That being said, both of my tanks are done with a 3.5 riveted in that hole

That hole is there to make sure you don't put the baffle in upside down. There actually is a matching hole in the baffle flange...on the bottom only. Look again, I think you will find you have the baffles spun around 180.
Cheers.
Evan

If you look at page 18-4 rev. 0 figure 2 part number T-1002 the tank baffle. In the middle bottom you will see the three holes that correspond with the holes in the skin in your picture.
If you already have the tank zees in and pro-sealed and you have the baffle upside down you could match drill the top skin to the hole in the baffle and the bottom baffle to the skin. I'm pretty sure the remainder is the same. Just find some other way to keep things oriented properly.
I ended up sealing my zees incorrectly after having everything well thought out and marked very well, but then I had a brain fart and rotated the baffle for a second for something and got distracted and never turned it back. Returned after lunch and started pro-sealing. It's only after dropping the baffle down into the wet pro-seal and clecoing everything in place, I made a last check on orientation before riveting the baffle to the skins. I was pissed and worked very late that evening cleaning the pro-seal , drilling the offending rivets , cleaning all the rivet drilling chips thoroughly , new pro-seal and final riveting.
Goes to show me that no matter how careful I am I still screw up.

Evan wins the prize!

Sure enough, I had the baffle in "upside-down."

Ron, I looked at the diagram, and sure enough, just as you described. Though, if Van's wanted to be completely accurate, they would have had matching holes illustrated on the skin. Not that I probably would have noticed it.

Now then, the question becomes--are the baffles symmetrical, except for this one hole? I final drilled the whole thing, so do I leave the baffle as is and match drill the one hole? I'll be sending off an email to the Mother Ship.

Fortunately, I only did this on one tank. We hadn't installed the second baffle.

Thanks for solving the mystery.

Jeff

Just a guess, but look to see if the location of the z-bracket mounting holes changes when you rotate the baffle. I am guessing they will, and that is why it is indexed.

I would have to do some checking on Monday to be sure, but I think teh bend angle on the baffle flanges is slightly different between the top and bottom (it's not a symmetrical airfoil).

Any resolution?

Any resolution? Would be helpful for the next guy who makes the same mistake (me). I just assumed the parts were symmetrical, and got lucky (50/50 chance!) on the left wing. Not so lucky on the right wing. I'd simply assumed they were symmetrical and drilled through both on the top and the bottom to preserve my match drilling, as I'd already match drilled most of it when I realized the problem. If they're not symmetrical, would be good to know that now rather than after I rivet it in

It is not symmetrical. The -14 plans called out this tooling hole that identifies which flange is the top, and has a note telling you to not drill and rivet the skin in this location. Can't remember if the -10 plans called it out, but I do recall the -10 plans were slightly different and contained less deatil.

The hole in the skin would be easy to plug, or you could just add the additional fastener. Have you tried installing the baffle right side up to see if the skin to baffle rivet holes align correctly?

What's asymmetrical about it? The flange angles? All the holes (except that center hole) line up. I haven't swapped it, but since they all line up with it in backwards, I'm sure they line up with it the other way, too. But since it's all match drilled, it seemed better to leave it backwards.

The extra hole isn't mentioned at all. I drilled it, and planned to rivet it because the directions say, "Final-Drill all tank skin to baffle flange holes to #40" and this is clearly a tank skin to baffle flange hole. The hole does not show a rivet being installed, but it doesn't make sense to just leave the hole open?

The flange angles are definately slightly different. I did cleco one of mine in upside down when I initially fit it prior to match drilling despite reading the note and knowing better, the skin to baffle holes did line up. I cannot remember if the holes common to the aft flange of the ribs and baffle will line up correctly if it is installed upside down.

So what do you do with the extra holes? Fill them when it's time for paint?

Van's got back to me with confirmation that the flanges are indeed at different angles. I can't really see it, but I believe them. It's otherwise symmetrical, so I swapped it to the correction orientation and all the holes still line up, so I'm just going to press ahead, and not worry about the fact that all the holes were match drilled in the wrong place, since they line up.