Fuel Tank Installation - Tips

[jmorrical]

Troy,

Yes I understand that final drill and fit of tank cover is to be completed after wings are covered painted and hung. Sounds like I should just bolt the tank straps together for now at the best guess position. Then be ready to adjust the tanks more accurately to line up with fuel filler port holes when when wings are set.

I'm still wanting to know when I do hang wings where the tank cover is to set on the rib caps. Is it to be flush with the inboard edge of #1 rib cap strip or centered over nut plate holes in #1 & 3 rib cap strips so that edge distances are balanced on both sides of the tank cover?

Could be I'm over thinking this again, but I want a good fit…not sloppy.

Jim Morrical

[TroyBranch]

That is my plan. We will know when we build our second!


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[richphil]

Mitch said to not drill until the wings are on the fuse. If you don't have the wash out quite right, the holes will not line up well when you install the wings on the fuse.
I had to push the tank a fair bit outboard. I plan to slide it if I have to when I install the wings if I don't like where I have it..


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I don't know if anyone else has had the same problem, but I noticed some aluminum chips had worked their way between the fabric and trailing edge of my wing behind my extended tanks. I can only assume they came from drilling the holes in the tank cover after wing installation. Can't believe I didn't take precautions to keep this from happening. I made a small vacuum hose connection to insert through the wing root cover hole and used a suction cup to pull the fabric down to vacuum the chips out. Got some of them the first time but need to do it again to remove the rest of them. I am sure these will eventually wear through my fabric if not completely removed. Got 90 hours and loving my Cub.

[TroyBranch]

IMG_7765.jpg

Since this is kind of related to the tank, here is what I did for the spacer to hold the rib straight from the fabric pulling. I used balsa wood wedges and was able to set the distance easily this way. After shrinking you can add more pressure again by squeezing the wedges together. Once you are happy, just nail them down with a bit it of CA glue (Rib only)

[ceslaw]

Troy,

Yes I understand that final drill and fit of tank cover is to be completed after wings are covered painted and hung. Sounds like I should just bolt the tank straps together for now at the best guess position. Then be ready to adjust the tanks more accurately to line up with fuel filler port holes when when wings are set.

I'm still wanting to know when I do hang wings where the tank cover is to set on the rib caps. Is it to be flush with the inboard edge of #1 rib cap strip or centered over nut plate holes in #1 & 3 rib cap strips so that edge distances are balanced on both sides of the tank cover?

Could be I'm over thinking this again, but I want a good fit…not sloppy.

Jim Morrical

Jim:

I confronted the same issue. My conclusion, noted in a post in May 2014:

Find the fuel tank covers and set them in place. The outboard edge of the fuel tank cover should be even with the outboard cap strap. The fuel filler must be centered within the opening. Only after it is centered should the nuts be tightened.

Don't think you will readjust the alignment of the fuel tanks after they are installed and the wings mounted on the plane. Once tightened down (before fabric is applied) the fuel tanks will be in that location for keeps.

Also note that there is a bit of flexibility in that the insert that goes around the filler neck has a little bit of adjustment.

Chuck

[TroyBranch]

I assume you mean flush with the out board edge of the inboard cap strip at the wing route. I just checked mine and that it what I did. There is no way you could push the tank cover outboard (toward the tip) enough to be flush with the out board edge of the outboard cap strip. It would be hard on the fabric that way too.





Thanks for the help. It would be a pain to fix the rib support wedges if you had to move it after.



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[ceslaw]

They say a picture is worth a thousand words. Hope this helps.


DSC_0463.jpg

[jmorrical]

The first wing was finished two weeks ago. It's been on the wing stand since then. Thanks to ceslaw for the wing stand design!


Last week I noticed a concern about the fuel tank installation that I've not seen any chatter about. I have the extended fuel wing kit and the specific area is on the 12.5 gal tank.

IMG_5470.jpg

The top and bottom of the smaller tank looks great. The top of the larger tank are great also. What caught my eye was the bottom side view around the first tank strap inboard to the #1 doubled rib. The first strap is not entirely resting flush on the tank. I ran my hand down the bottom surface of that tank either side of the strap and out to where the three tank service fittings are welded. I found the tank bottom surface was undulating, pitching and heaving or deformed…how ever you would describe it. The most deformity was at the edge near the fuel tank service fittings. I also ran my hand fwd to aft along the side of the tank (inside that first rib) and it bulges in and out also. I did talk to Mitch about this had he said it was normal. Before the drag wires and tank straps were tightened the tank surfaces were smooth, straight and true.

IMG_5599.JPG

Here's where the first strap in not flush.



IMG_5598.JPG

The deformation is about plus/minus 1/8" I'm estimating.



I'm curious to hear from others about this because I worry I didn't describe it correctly to Mitch. I still have a concern about it.

Jim Morrical

[richphil]

The first wing was finished two weeks ago. It's been on the wing stand since then. Thank ceslaw for the wing stand design! Last week I noticed a concern about the fuel tank installation that I've not seen any chatter about it. I have the extended fuel wing kit and the specific area is on the 12.5 gal tank.

IMG_5470.jpg

The top and bottom of the smaller tank looks great. The top of the larger tank are great also. What caught my eye was the bottom side view around the first tank strap inboard to the #1 doubled rib. The first strap is not entirely resting flush on the tank. I ran my hand down the bottom surface of that tank either side of the strap and out to where the three tank service fittings are welded. I found the tank bottom surface was undulating, pitching and heaving or deformed…how ever you would describe it. The most deformity was at the edge near the fuel tank service fittings. I also ran my hand fwd to aft along the side of the tank (inside that first rib) and it bulges in and out also. I did talk to Mitch about this had he said it was normal.

IMG_5599.JPG

Here's where the first strap in not flush.



IMG_5598.JPG

The deformation is about plus/minus 1/8" I'm estimating.



I'm curious to hear from others about this because I worry I didn't describe it correctly to Mitch. I still have a concern about it.

Jim Morrical

Jim, that's probably just oil canning. Sometimes this occurs from the heating from the welds or just because of stress from rolling and bending the sheeting into position. Like Mitch says, it is industry standard for this to occur. I too have it in my extended tanks. Also, I have worked in the aluminum manufacturing business for over 30 years. Have also seen this in factory tanks out of Cessna and other aircraft we have been asked to repair for friends. No worries!

Richard Phillips

[ceslaw]

Jim

i'm sure that is a non issue.

i had the same thing.

suspect it is related to a lot of welding on relatively thin metal covering a large area resulting in a tiny bit of deformity.

suspect Mitch would tell you the same thing.

Chuck