Fuel Bladders Repair or Replace and Life Expectancy

[Larry Biever]

I'm likely going to be replacing one, if not both of my 180's bladders next month. My left tank has noticeable fuel leakage out the top - near the fuel door when the tank is full, while taking off for the first 15 min. My mechanic said I could possibly have the bladders overhauled, but I'm leaning toward new. Any thoughts on this?

My second concern is during the summer I fly to a grass strip where we camp for weekends and vacation. There is no fuel here and my plane is outside in the sun. Since there is no fuel, my bird sits with less than full tanks. It's usually about 25 to 32C during the day. Over the entire summer my plane would be there a total of about 30 days. Is this going to cause my bladders to fail again in a couple years? Any suggestions on how to minimize damage to the bladders in this circumstance? Unfortunately having full tanks is not possible.

Thanks
Larry

[N3322G]

Hi Larry,

This topic has been discussed several times and the consensus has been - because of the labor of pulling and re-installing and assuming you are going to keep the Comanche for a few more years - folks have been taking the Replace option. Did all 4 bladders on the Twin in 2009 and 2010 from AeroTech and got the ICS discount and have been very happy.

I did read the Service Manual on keeping tanks happy and while it is best to keep them topped, they only recommend remedial action if the tanks will be empty for more than 10 days.

When the Twin was in for 10 week paint job and the tanks were a touch low so they wouldn't inadvertently overflow onto the new paint or prep stuff, I rocked the wings every few days to try to keep the tops of the tanks wet. No scientific evidence to know the impact of that but it made me feel better.

In Texas summer I know even with the bladders full the tops aren't wet and so far so good. 40C is common here and the hangar is hotter than that. We do our best to fly every week - even if it is circles to keep the plane systems happy.

Hope this helps.

[9089P]

Hi Larry,

Pat is correct, if you intend to keep the aircraft awhile, best to go with new as there is a lot of labor in changing the cells out. Don't know how old your cells are but if original they are likely cracked at the top. That said the symptom you note of fuel out the top on take off with full tanks, could be a loose fuel cap. I have had that happen when my caps were old and hardened and consequently not making a good seal. I replaced the caps.

As for keeping the tanks full, we have a 90 gal. plane and keep the mains full but not the aux tanks. This has been the practice since at least 1984 and we have gone through one cycle of cells. We did not notice a significant difference in the longevity of the mains vs aux tanks. The aircraft is always hungered in Northern California with very moderate temps. I would point out that even when full I don't think the tops of the cells are wet. All 4 of our tanks failed on top.

Good luck, Don

[N3322G]

Bill, I should add that all 4 tanks removed were original so got about 40 years. One of the four had been overhauled and it lasted less than 5 years and leaked where it had been patched as well as other locations.

[MULEFLY]

Buy new... you will be a happy camper.. keep them as full as possible... lapses aren't too significant.
Jim

[Larry Biever]

Thanks for the replies. I looked in my log books and the left side bladder was replaced with a new one in 2004 so hopefully we find something simple. The right was 1983 so it might be time for a new one.
Larry

[Zach Grant L1011jock]

Larry,
2005 is a bit new to be having an issue with the tanks, although there were some tanks from one manufacturer that had some issues that were manufactured in that time frame (don't remember which one it was though). If the tank is leaking out of the filler door, there are several possible reasons, and none of them involve the tank directly. As you have seen earlier, the cap could be leaking or you could have the wrong cap for your airplane. If you have the old thermos type, make sure it is non vented. It will be printed on the cap as well as will have a solid bottom. The cap also must fit TIGHTLY. If it is either thermos or plug type, the rubber gets old hard and can crack causing leaks. Short of the cap leaking, the tank flange can leak. There is a cork gasket that can dry out and then it will sepe around the flange. This gasket can be replaced pretty easily without much disturbance to the tank, and then the bolts can be retorqued. Another place to look is in the aft part of the dog dish where the sender is. That gasket can leak as well. I have even seen corrosion in that part of the dog dish that happened from bad access panel seals, and the standing water can sit there for years. This can all be checked very easily by removing the wing access panel. Gasket kits are available from all of the fuel cell manufacturers for about 50 bucks.

As far as sitting in the sun for a few days at a time, that should not be a significant problem. a few months, well, that might be a different story.

-Zach

[Don Ostergard]

Larry-
I don't have my records at hand but A few years ago we discovered the patches in our repaired bladders coming loose to the point of falling right off inside the bladders. My bones still go soft just thinking about it. I wrote an article in the Flyer about it. I will never install repaired bladders again. The labour is the same new or repaired. Maybe even favouring new, as the new ones will likely snap in easier because they have not become deformed. Send me a PM if you have any questions. Don't try to phone me because my Comanche and I are enjoying the good life in Mexico and Central America these days.
Don Ostergard