Atlee Dodge tank - brace tube alignment

[Gordon Misch]

Hi all, a question. I'm installing Atlee Dodge 30.5 gal tanks in my 12, and I'm encountering an alignment problem. I'll do my best to describe it, but it's kinda hard. There is a wing brace tube (anti-drag) that runs from the aft, inboard corner of the tank bay diagonally to the forward, outboard corner. At the aft, inboard corner there is a triangular tab, supplied with the tanks, that attaches to the rear spar at the double compression strut at the wint root, and functions as a brace tube to attach point. The brace tube runs through a diagonal passageway in the tank.

Here's the problem: the brace tube is very close to the aft wall of the passageway, about 1/16". That strikes me as too close for comfort; the last thing I want is for anything to possibly vibrate against the tank.

The tab has a bend in it to properly align with the brace tube, and the drawing in the installation manual specifies a certain distance between the mounting holes for the tab, and the bend line in the tab. The actual distance on my tabs is 1/16" to 1/8" greater than that specified distance (hard to measure installed), and the bend line is at least 1/8" away from the edge of the compression strut. That results in the tube being closer to the aft wall of the passageway than if the bend line were at or very close to the edge of the compression strut.

I'm considering a couple different approaches to this near-interference problem.
1. Weld in the mounting holes in the tabs, and re-drill in the correct position. That would move the brace tube closer to the center of the passageway, but not all the way to the center.

2. Shorten the compression strut about 1/4" and install a 1/4" spacer between the rear spar and the tab. That would center the brace tube.

3. Assemble it the way it is, and assume it's alright since nothing is actually touching in the zero vibration, zero load condition.

I plan to call Atlee Dodge and ask them, but the advice or comments from folks here who have done this installation would be very valuable!

Thanks in advance.

 

[Crash]

Gordon, the tabs are always a pain to get lined up. This is the way I install Dodge tanks.

Put the wings on a set of leveled sawhorses. Put a 1 3/8" spacer under the rear spar at the last tank bay rib. Put 4-5 strips of masking tape long the front edge (you will see why I do this later) of the tank, just under the top lip.

Lay the wood wedges and joggle strips in place and shove the tank down into the opening. Put the front edge down first, then the back so you don't disturb the masking tape. Check to see if the tank rocks up and down corner to corner. Shim with .016 shims on the low corner until the tank lays perfectly flat. Drill and cleco the joggle strips in place on the leading edge and rear false spar. Remove the tank and pull off the masking tape. Put the tank back in the mounts and see that is has about 1/16" back and forth movement. You need this. If the tank is too tight in the mounts it will bind and crack.

Drill the rear and front spar flange screw holes using a blind locater to use any existing screw holes in the spar cap.

After you install the diagonal tube ears, drop the tank back in and see that the ears allow enough room to slip the tank in and out and center on the tube carry through tube. You might have to do quite a bit of forming to get the ears to line up with the carry through and the tank to come in and out of the tank bay. Custom cut and drill the carry through tube to match the ears. Best wishes. Crash

P.S. If you do any rigging, loosen up the hold down brackets and with empty tanks, see if they rock up and down at any corner. If they do then you need to re-shim. Also, I used flush rivets to mount the joggle strips to the leading edges so there are no bumps under the fabric.

 

[Gordon Misch]

Thank you, Crash.

When you say "you might have to do quite a bit of forming to get the ears to line up with the carry through and the tank to come in and out of the tank bay", do you mean to re-shape the triangular ear with an offset, as viewed from above? That would align it with the carry-through, but it would also reduce the stiffness of the ear a little - of course maybe not enough to matter. I could do some stress calculations, but if offsetting the ear is common practice and it works, no point in playing with numbers. If an offset is what you mean, how much do you think is acceptable? I think 1/8" - 1/4" would be needed for good alignment in this case.

 

[Yard Dart]

Do you have to have the wash out set before you instal tank?

 

[Gordon Misch]

Yard Dart, that is a clear "yes", from Dodge's installation instructions. The instructions state that the tanks cannot tolerate any twisting. Also, the washout must be set prior to installing the full wrap leading edge material.

 

[Crash]

Yes, you might have to offset them (tube attachment tabs) a little to get the brace tube to center in the tank carry through. Take care. Crash