Removing an extended range fuel tank

[Mark Albery]

I have a leak from one of the connecting tubes between my extended range fuel.

There isn't enough room to remove and replace that tube without removing a tank. I don't think they can be slid sideways against the ribs sufficiently for access.

So that would mean removing the trammelling rods that go through the tanks.

Can this be done safely without removing the wing? I presume new inspection hatches will be needed to access the outboard ends of the trammelling rods and I presume that they can be re-tensioned to the same length of exposed thread at each end.

I guess this is a fairly rare task so would appreciate if anyone has any experience or alternative suggestions.

The maintenance manual has no mention of tank removal.

[jmorrical]

I've finished the Carbon Cub EX(1) and have an Airworthiness Certificate. I've taxied it twice for various things. The last taxi I fueled it to nearly full for first flights. Since doing that when I open up the cockpit I've noticed a faint smell of fuel. I spent some time looking for a leak and the last place I looked was the tanks. When I took off the right side extended range tank cover I found a seep at a weld on the inboard tank.

Kit support offered a replacement tank, but that's a six month production delay. Another solution was to use ProSeal to patch over the seep. That was the course I initially decided on then CubCrafters Kit Support offered to repair the tanks with a quick turn around. They would leak check again also of course. So with great disappointment that is the course I've decided on.

I've seen the Service Instruction SI0020 Rev. C that has useful information. Does anyone have experience with extended fuel tank removal that would add something here? I am also trying to decide how I should box up the tanks with adequate protection for shipment. Any experience or ideas how I should make or find a box large and strong enough for the job?

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After clean up and less than one hour this is what I see.

[Andy]

Well that's ugly and I'm sure a huge disappointment when so close to first flight. I hope you caught it and got the tank drained before the fuel damaged the wing paint.

If it happened to me I think I'd accept the CubCrafters offer of a new tank and remove the leaking tank for interim repair by a local welder.

Thanks for the link to the related SI.

[aeroaddict]

Sorry to hear of this!

For the leaking tank weld, as much as this should NOT have happened (a QC escape!), I think I'd go with the ProSeal fix. And yea, I'd request a new tank from CC.

I have no idea on how the remove a tank. But CC should.

[aeroaddict]

Any updates?

Any process on how to remove a fuel tank?

Thanks

[Andy]

Previously referenced SI0020 is written for the CC11 but I would think the removal of the FX/EX drag wires would be similar.

Once the drag wires are out of the way wouldn't removal be a relatively easy drain, disconnect, and lift out? I say "relatively easy" because removal of the drag wires looks like no fun at all with the wing covered and installed.

[Andy]

The drawings of the CC11 wing in SI0020 seem to show that the lower surface of the leading edge skin does not extend back to the front spar in the area that the access hole has to be cut.

The photos of my FX-3 wing build seem to show that the lower surface of the leading edge skin does go all the way back to the front spar from the root until well outboard of the fuel tanks.

If that's correct then it seems that the hole required to access the front end of the drag wire must be cut through the leading edge skin not just through fabric.

Is that correct?

[aeroaddict]

Hence my question.

If I recall correctly, you can access the front inboard threaded portion of tank trammel wire via the gap between fus and wing.

Removing the wire/rod would require removing the flap and false spar from the rear to access the wire??

Was just curious if there were any new information.

[jmorrical]

First for clarity I've built an EX(1). Here is the executive summary of my tank removal decision.

It has been hard to make. I’ve spent a good bit of time researching and seeking advice from Kit Support, the CubCrafters Forum and builder’s FaceBook, other builders and A&P AIs, etc. There are two choices: Remove the tanks and repair or make some expedient repair. If I had a more significant leak I would be compelled to remove the tanks. So far there is no damage to fabric or paint. I’ve decided on a less invasive course. If the expedient repair does not work I’ll move on to remove the tank.

Kit Support (KS) initially offered a new tank, but supply chain time line is six months. Also in first discussion the suggestion was to use JB Weld or ProSeal which I considered. Then KS said if I sent my tank they would repair and leak check in quick order and get it back to me.

Reason not to remove tanks:

• Expedient repair could be the fix and I’m flying first flights soon.
• Kit Support says they remove very few tanks. So experience is limited.
• Each drag wire lock nut was secured with Loctite 271 (Red). It’s a permanent install requiring heat to free…so it says. I know it’s a small nut, but torque to remove is unknown to me. And, can I hold the wires somehow to torque the nuts off over the long cured Loctite? I know torque required to loosen increases as Loctite nuts are removed. I remember the damaged two drag wires trying to learn in the build how to hold them while tightening the nuts. Found I could use a small tab of scrap aluminum as a sacrificial metal between the wire and vice grip.
• The plastic anti-chafe tube over each drag wires thru tanks was secured to drag wires with friction tape on both ends. I’m not sure how I would remove it and be able to pull the wires thru the block they are mounted thru. I am sure I couldn't just pull the wire over the friction tape. Kit Support says they would pull drag wires thru the cockpit.

Van’s RV builders build wet wings. Some notice rare fuel seeps from time to time. One solution they share on Vans Forums is to use Loctite 290 (Threadlocker Green). Loctite says in an alternate application the low viscosity and capillary action of this medium-high strength thread sealer wicks into porosities in welds, castings and powdered metal parts and cures to prevent leakage. It is resistant to fuels also.

I have decided to apply Loctite 290 then when that cures I’ll put down some JB Weld Original Cold-Weld over the area.

When I see results I will update the experience here.

[Ak Paul]

Thanks for sharing this with us. Look forward to hearing your results. Good luck