Fuel Bladder Dilemma

[generalaviationguru]

Our new-to-us 1967 F has 64 gallon bladders.  Wonderful for range and most importantly leak-free state of mind.

However, with respect to weight and balance, 64 gallons becomes problematic with more than 2.5 pax with bags.  The bladders were installed in 2023, and we obviously want them to last.  But, topping them off drastically reduces the useful load for the next mission - or wasted time spent burning fuel down for weight.  
 

WWYD?  Do modern bladders tolerate partial fuel better?  Can Wing covers / hangar mitigate under filling?  Or just deal with the MGW problem?

Thanks for the help experts!

 

P.S.:  Also thanks to Mooneyspace Member @Neshi for a great transaction!  We will take great care of this plane!

[RobertGary1]

I would say the plane works for you, not the other way around. Even with sealant keeping the tanks full is probably good for the plane, but who wants to tanker 6 hours of fuel around? Like towing a boat with your Porsche. I don't tanker fuel unless I need to (i.e. in Mexico :))

[Ragsf15e]

46 minutes ago, generalaviationguru said:

Our new-to-us 1967 F has 64 gallon bladders.  Wonderful for range and most importantly leak-free state of mind.

However, with respect to weight and balance, 64 gallons becomes problematic with more than 2.5 pax with bags.  The bladders were installed in 2023, and we obviously want them to last.  But, topping them off drastically reduces the useful load for the next mission - or wasted time spent burning fuel down for weight.  
 

WWYD?  Do modern bladders tolerate partial fuel better?  Can Wing covers / hangar mitigate under filling?  Or just deal with the MGW problem?

Thanks for the help experts!

 

P.S.:  Also thanks to Mooneyspace Member @Neshi for a great transaction!  We will take great care of this plane!

Yeah, tabs (50 gallons) or around 40 is much more flexible. I don’t sweat it on my sealant…

[glbtrottr]

Griggs / O&N recommend that they be kept full for longevity.

When they weren’t kept full in my m20e, I believe the clamps holding the bags together get loose.


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[generalaviationguru]

1 minute ago, glbtrottr said:

Griggs / O&N recommend that they be kept full for longevity.

When they weren’t kept full in my m20e, I believe the clamps holding the bags together get loose.


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How would less fuel (weight) cause the clamps to come loose?

[DXB]

21 minutes ago, glbtrottr said:

Griggs / O&N recommend that they be kept full for longevity.

When they weren’t kept full in my m20e, I believe the clamps holding the bags together get loose.


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Only directive I've heard is never to let them sit dry for more than a couple days. Anyway, it's utterly impractical to keep them topped off all the time, and I strongly suspect @generalaviationguru should not worry about not topping off to 64 gal.   I imagine the fuel vapor (and/or wicking?) is enough to keep the vulcanized neoprene/nylon bladder wall from degenerating in a partly filled tank, but  I honestly have no clue - it there a chemical engineer in the house who can clarify? Regardless, one hears far more about wet wing tank sealant issues than bladder issues - maybe the bladders will all start failing at a particular age but we haven't seen it yet, and I bet very few people keep them topped off all the time.  One does occasionally hear about leaks at the interconnect tubes, but these seem reasonably easy to fix.

 

 

[Mooneymite]

1 minute ago, bluehighwayflyer said:

The language O&N used in the instructions I received after my installation was to keep “some” fuel in them.  I wouldn’t worry about it beyond that. I do think a hangar makes this less critical.  My first 54 gallons have been in service for almost 30 years now.  We added the 10 gallon add-on probably 15 years or so ago now.  So far so good.  

Correct.  "Not empty" does not equate to "full".  As long as they don't sit dry for prolonged periods, they'll be fine.  I think the bladders have been around since before 1990 and there a virtually no reports of deterioration.  Certainly all those owners are not keeping their tanks full all those years.