Fuel tank fitting problem

[Dgamble]

This seems impossible, so consequently seems like something I must be doing horribly wrong, but I cannot get the two bolts that attach through the center section and into the front of the fuel tank to align.

This is the right bolt (looking aft) and its alignment to the nutplate:




After struggling with it for awhile, I finally decided that the hole spacing might be wrong. I measured the distance between the Vans-provided holes in the center section and the distance between the nutplates on the tank:








They look to be off by about .3cm. I can't see how that could happen at Van's, nor can I see how I could have caused it. Am I missing something really obvious??

 

[Mich48041]

Dave,
Try changing the order of bolt installation. I can not remember the exact sequence, but I think that I put the rear bolt in last.
Joe Gores

 

[Dgamble]

Dave,
Try changing the order of bolt installation. I can not remember the exact sequence, but I think that I put the rear bolt in last.
Joe Gores

I tried all of the possible combinations - no joy. I could get the rear bolt and either of the front bolts to work, but even just the two front bolts was hopeless. I'll be on the phone w/ Van's sometime today, hoping there is an easy solution.

 

[rvbuilder2002]

Dave,
I don't know if this is similar to your problem or not, but when recently doing the tank bracket modification on the Teen Flight RV-12 we had a bolt alignment problem.
Because of bend tolerances, the bolt hole in the bracket added to the left (inboard) side of the tank didn't align with the bolt hole in the lateral mounting plate on the tank. This made the bolt unable to be inserted when it came through the 1/4 inch thick center section C channel. It wasn't discovered until the tank was ready to be reinstalled. We resolved it by removing the nut plate and then match drilling the #12 hole in the thinner bracket using the heavier mounting plate. This ovaled the hole in the bracket very slightly but none of the original design strength was lost because the hole in the mounting plate was undisturbed. A 10-32 floating nut plate was then installed in place of the original K1000, to allow for the slight offset in the nut plate position. The bolt went in easily at reassembly.

 

[Dgamble]

The answer from Van's:

Dave

After looking at your pictures and talking it over with one of the other guys we think your best option is to enlarge the hole in the tank attach bracket. If you take the nut plate off and enlarge the hole to accept the bolt you should be able to rotate the nut plate and drill new holes to attach it.

Sterling

My somewhat ham-fisted efforts to implement the fix:

http://www.schmetterlingaviation.com/2012/06/frikkin-fuel-tank-fitting-fiasco.html

Spoiler: it's still a work-in-progress. I'm still considering going back and replacing the T-1205 tank bracket with a new one, but I'm not convinced that it would turn out much better.

 

[VHRV12]

Dave, I am confused here! Did you ever have the tank bolted up to the center section before installing the reinforcement modification? My T-1205 came pre-drilled and was EXACTLY the same hole spacing as the center section. I have not installed the tank reinforcement mod yet....and just trying to work out if there is a "gotcha" in the mod. The only thing I can see is the hole spacing in the center section or the T-1205 is wrong!

 

[Dgamble]

Dave, I am confused here! Did you ever have the tank bolted up to the center section before installing the reinforcement modification? My T-1205 came pre-drilled and was EXACTLY the same hole spacing as the center section. I have not installed the tank reinforcement mod yet....and just trying to work out if there is a "gotcha" in the mod. The only thing I can see is the hole spacing in the center section or the T-1205 is wrong!

No, I applied the SB on the tank prior to installing it. That said, I am at a complete loss as to how installing the new brackets from the SB could have stretched the T-1205 - that's a mighty thick chunk of aluminum. I can only surmise that the center section was mis-drilled, but I have zero evidence of that and it's pretty counter-intuitive (my assumption being that the center sections are drilled with a jig or by a CNC machine).

It's the only possibility that makes any sense to me, though, and it's why I'm reluctant to tear the tank apart to install a new T-1205, only to find that it still doesn't fit and I have to go about trying to make the same fix and more than likely with similar not-so-great results.

This kind of thing is why I explicitly decided to buy/build a pre-drilled kit: I do my best work when I have someone else do it.

What would be interesting is if you could put a ruler to your center section and see if the measurement of the inboard hole between the two rivet holes is the same as mine. The drawings all indicate that the hole should be centered between the rivets, but the drawings are pretty small and it could just be an illusion.

 

[skydiverlv]

Dave,
Your assumption is correct. The center section is drilled incorrectly. I measured mine and the dimension is the same as your tank bracket.
44.5 cm and the hole in the center section appears to be centered between the rivets

 

[DonFromTX]

Dave:
For what it is worth, I installed my tank before and after the SB, no difference in fit.
Mine is out, I just measured it and the holes in the channel. Both are 44.5 center to center. It would appear you have a mis drilled center channel. Of course I am sure you will want to remove it and replace it with a properly drilled channel, right?

 

[joedallas]

Dave

Could you HeliArc the holes Shut
And then re-drill

Maybe fill the tank with water to keep in Cool

Joe

Dave:
For what it is worth, I installed my tank before and after the SB, no difference in fit.
Mine is out, I just measured it and the holes in the channel. Both are 44.5 center to center. It would appear you have a mis drilled center channel. Of course I am sure you will want to remove it and replace it with a properly drilled channel, right?

 

[Dgamble]

Dave:
For what it is worth, I installed my tank before and after the SB, no difference in fit.
Mine is out, I just measured it and the holes in the channel. Both are 44.5 center to center. It would appear you have a mis drilled center channel. Of course I am sure you will want to remove it and replace it with a properly drilled channel, right?

Yeah, that would be quite a job! It would take six months just to un-do everything that has been done since I started on the center section. I think I'd just quit and buy a -12 already built!

 

[DonFromTX]

For those that have not got to the tank install yet, it would be a good idea to measure the tank mounting holes in the big channel as early as possible. It appears that somehow the CNC machine got bumped a bit and drilled some of them wrong. It will be far easier to work around this mistake now than after you have the tank constructed. Just measure the distance from hole center to center, should come to 44.5. If not, you will need to alter the tank brackets as Dave had to.
What we did NOT determine, is exactly WHICH hole is off! If it is the outboard one, there could be an interference problem with the tank itself, and you may need to move the outboard hole. It may even be BOTH of them that is off.

 

[Dgamble]

What we did NOT determine, is exactly WHICH hole is off! If it is the outboard one, there could be an interference problem with the tank itself, and you may need to move the outboard hole. It may even be BOTH of them that is off.

I'm pretty sure it's the inboard hole. It should be centered between the rivets on either side of it. After drilling the new hole in the tank bracket, everything seems to fit just fine. (Well, almost - I'm going to have to use a floating nut plate as Scott suggested, but that has more to do with the way I had to position the nut plate.)