Full or Empty tanks?

Store with full tanks or empty tanks?

  • Total voters
    46
  • Poll closed .
D

Darwin60

Line Up and Wait
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Darwin60
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Seeking the collective wisdom.
C182 hangered in S Fla for the next 9 weeks while I am away.
Fuel tanks currently have about 15 gals each.
Would you fill them now or wait to fill them before the first flight in November?

Thank you
 
Aside from the anti-condensation benefits above, 100LL has been slowly creeping back up in price, so you may save a few bucks filling up now...
 
If you have the rubber bladders they can dry out if not kept wet.
 
I never bought into bladders drying up. But what the hell, fill them. That way you'll have a bigger mess to clean up when they leak. ;)
 
If your bladders crack they are way to old anyway.
 
9 weeks doesn't feel like a long amount of time, but I'd fill it it up for storage.

Of course, you could always just send me the keys and I'll make sure the aircraft stays properly exercised instead of in storage?
 
Just think of how happy you'll be in 9 weeks when it's time to fly and you don't have to go to the pumps.
 
I think condensation is largely a red herring. Almost all the signs of water in the fuel come from leaking caps. Still, there's no reason NOT to fill them. As pointed out 100LL is by design pretty stable.
 
Question..
Are the large fueling tanks insulated? I'd think if anything was going to condensate when partially full, they would.
 
Skyrys62 said:
Question..
Are the large fueling tanks insulated? I'd think if anything was going to condensate when partially full, they would.
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Also, the science has been reviewed here several times over the years.

The capability of a tank to condense any significant quantity of water in a closed space is not there. Water in fuel is almost always introduced through other means, such as leaky fuel caps and rain.
 
Tabs or some lower limit. Why fill them up if that then limits the payload? Or with an excellent fuel flow meter, leave it wherever it is and then add what you need for the next flight just before that flight.

With over 5.5 hours of cruise time with full tanks why do I need them full?
 
Stewartb said:
I never bought into bladders drying up. But what the hell, fill them. That way you'll have a bigger mess to clean up when they leak. ;)
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We've still had to replace ours periodically despite a club policy of topping off after every flight. Maybe due to thermal cycling from being outside?
 
Looks like the "fill up" vote wins. But in general, especially since you are in Florida, I would keep the tanks full. Will help keep moisture out
 
Tantalum said:
Looks like the "fill up" vote wins. But in general, especially since you are in Florida, I would keep the tanks full. Will help keep moisture out
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Pot stirrer here. :)

What is the total moisture that can condense out of a GA fuel tank sized volume of air at even 100% humidity, vs a leaky cap on the wing or at the fuel farm?

And does a full tank prevent the latter?

The sweating glass of cold ice tea on a humid day is exposed to a virtually infinite volume of air that it condenses, by comparison

(just one of those engineer types who likes to do the math ;) )
 
ElPaso Pilot said:
Pot stirrer here. :)

What is the total moisture that can condense out of a GA fuel tank sized volume of air at even 100% humidity, vs a leaky cap on the wing or at the fuel farm?

And does a full tank prevent the latter?

The sweating glass of cold ice tea on a humid day is exposed to a virtually infinite volume of air that it condenses, by comparison

(just one of those engineer types who likes to do the math ;) )
Click to expand...
It's a reasonable question, and one I have wondered myself. However, since the fuel tank is vented it is also exposed to a theoretical infinite volume of air also

Now, if we assume a tank full of gas, then even if the cap is very leaky the water would have to displace the gas first.. which I guess it could do since water is heavier
 
ElPaso Pilot said:
Pot stirrer here. :)

What is the total moisture that can condense out of a GA fuel tank sized volume of air at even 100% humidity, vs a leaky cap on the wing or at the fuel farm?

And does a full tank prevent the latter?

The sweating glass of cold ice tea on a humid day is exposed to a virtually infinite volume of air that it condenses, by comparison

(just one of those engineer types who likes to do the math ;) )
Click to expand...

The answer is: Not enough to worry about it!
 
Perhaps not directly applicable but motorcycles stored indoors can and do accumulate condensate in partially filled tanks.
 
ElPaso Pilot said:
Pot stirrer here. :)

What is the total moisture that can condense out of a GA fuel tank sized volume of air at even 100% humidity, vs a leaky cap on the wing or at the fuel farm?

And does a full tank prevent the latter?

The sweating glass of cold ice tea on a humid day is exposed to a virtually infinite volume of air that it condenses, by comparison

(just one of those engineer types who likes to do the math ;) )
Click to expand...
The tanks aren't hermetically sealed, so you're not limited to the mass of water in the air that's currently in the tanks.
 
Lindberg said:
The tanks aren't hermetically sealed, so you're not limited to the mass of water in the air that's currently in the tanks.
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Yup. But to balance my contrived simplification, that slightly vented volume of air in the tank will never drop from 100% to 0% humidity, either, and air exchanges are going to be low through the vent tube. It takes a lot of air to generate a very small amount of liquid condensation.

If this was a real issue, other than a theoretical few fractions of an ounce, we would be sumping water all the time in every tank on an airport with similar weather conditions.

More often, my experience is most pilots generally go years or decades without finding any water at all (unless their caps leak in the rain), then find a bunch. That's special cause, not condensation.
 
ElPaso Pilot said:
Yup. But to balance my contrived simplification, that slightly vented volume of air in the tank will never drop from 100% to 0% humidity, either, and air exchanges are going to be low through the vent tube. It takes a lot of air to generate a very small amount of liquid condensation.

If this was a real issue, other than a theoretical few fractions of an ounce, we would be sumping water all the time in every tank on an airport with similar weather conditions.

More often, my experience is most pilots generally go years or decades without finding any water at all (unless their caps leak in the rain), then find a bunch. That's special cause, not condensation.
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According to some random googling and probably bad math, 100 gallons of air at 80* and 100% rh will have contain somewhere in the neighborhood of 10 ml of water. Over nine weeks there's going to be temperature and pressure changes, which would mean air moving in an out of the tanks. Now, I don't know what's going to happen, but I don't think it's as simple as saying there's not much water in "that much" air. For the record, the only time I got a significant amount of water out of my tanks, the plane had spent a couple of days on the ramp and was likely rained on.
 
I fill, but mostly for convenience, so I don't have to stop at the fuel farm before departing.

As long as the aircraft is cooled below the dew point, any available moisture will continuously condense. Once the first load of moisture inside the tank is condensed, further condensation will depend on the rate of air exchange, which is probably relatively slow depending on the size of the fuel vents. If above the dew point, no condensation will ever occur.

Condensation is the worst when the plane is cold soaked overnight and then the hangar heats up during the day and the air inside gains moisture load, which could be enhanced from, say, snow melt or rain runoff leaking under the door. I've frequently seen the exterior of the aircraft completely soaked after a cold night in the hangar. The air in the hangar warms up much faster than the aircraft and provides the moisture. Outdoors the aircraft will warm faster in the sun. Ive never found water in the tanks when stored inside, even when partially full and the aircraft exterior was wet from condensation.

Having said all that, unless there are frequent warm-cold cycles, it is unlikely to be able to build up a significant amount of water in the tanks through condensation unless you leave the plane alone long enough for many such cycles.
 
frfly172 said:
If you have the rubber bladders they can dry out if not kept wet.
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I have bladders and filling the tanks makes no difference. If there is any liquid fuel in the tanks the tanks will fill with vapor regardless but "full" tanks do not wet the top of the bladders inside since the slightest evaporation will soon leave a gap. What you do need to be concerned about is external abrasion on the top of the tanks so make sure to heavily tape the tops where the upper surface can move against the structure.
 
flyingron said:
I think condensation is largely a red herring. Almost all the signs of water in the fuel come from leaking caps. Still, there's no reason NOT to fill them. As pointed out 100LL is by design pretty stable.
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I agree that leaking caps are a big contributor, especially on something like a J-3 with the rod through the cap fuel gauge, a vented cap where rain can be blown in the vent, or a flush fitting cap where the fill neck can be recessed - one bad seal and you're taking on water.

In the past, when I lived out west where a humid day was maybe 30%, I would have agreed with you about condensation being a non issue. However living in eastern NC, where 90% humidity is pretty common and 60% is a pretty 'dry' day, I disagree.

It's less of an issue if the aircraft is in a hangar where the day to nigh temperature extremes are less. But if the plane lives out on the ramp the temperature changes are much greater and the expansion and contraction of the air in the tank creates a lot more airflow in and out of the tank, brining a potentially unlimited amount of moisture with it.

If fact, I'll suggest that some of the water getting into tanks of aircraft left out on the ramp isn't getting there by leaking through the cap at all.
 
Darwin60 said:
Seeking the collective wisdom.
C182 hangered in S Fla for the next 9 weeks while I am away.
Fuel tanks currently have about 15 gals each.
Would you fill them now or wait to fill them before the first flight in November?

Thank you
Click to expand...

Water getting into the fuel is the least of your problems. Nine weeks sitting unflown in FL will mean at least six weeks with no oil on the cam or lifters - in Florida, the salt air and humidity capital of the nation.

Either arrange to have someone fly it an hour every 2-3 weeks, or pickle engine with:
1) Storage oil,
2) A desiccant plug in each cylinder,
3) Desiccant plugs in each exhaust, and
4) A bag of desiccant in the air intake, before sealing the intake with duct tape, etc.

Water in the fuel would mean draining the sumps. Rust on the cam and subsequent spalling of the cam lobes and cam replacement will cost you about $10K.
 
Larry Vrooman said:
Water getting into the fuel is the least of your problems. Nine weeks sitting unflown in FL will mean at least six weeks with no oil on the cam or lifters - in Florida, the salt air and humidity capital of the nation.

Either arrange to have someone fly it an hour every 2-3 weeks, or pickle engine with:
1) Storage oil,
2) A desiccant plug in each cylinder,
3) Desiccant plugs in each exhaust, and
4) A bag of desiccant in the air intake, before sealing the intake with duct tape, etc.

Water in the fuel would mean draining the sumps. Rust on the cam and subsequent spalling of the cam lobes and cam replacement will cost you about $10K.
Click to expand...

I think this is an urban myth...here is a picture of my old camshaft, been sitting in my hangar in SE Florida, only a few miles from the Atlantic Ocean, no oil it, for 3 years...
4e882bfbb65df02e290689aff7645f06.jpg


According to your theory this should be a pile of rust by now.


If you change the oil frequently and especially before any long layoffs it will prevent acids from forming and I think this is what causes corrosion, not moisture in the air.
 
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