Leave the fuel tanks full
Not much Benzene in European Mogas these days (tis carcinogenic) Dunno about Oz specs but prolly the same Dunnunda
Benzene's not the most volatile component in any event, butane is, and if that evaporates, you actually get left with a higher octane fuel than before (though less of it of course
)
Benzene's not the most volatile component in any event, butane is, and if that evaporates, you actually get left with a higher octane fuel than before (though less of it of course
)
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FD - one can lead a horse to water (even in a fuel tank), but one can not make it drink.
If the fuel tank is sealed, then the only water that can condense to cause fuel contamination is the water that is in a gaseous state in the tank. Even at 100% relative humidity, on a warm day, the amount of water that can be held is quite small. (Look up "saturated vapour density" on google, and you'll find all the science you need to calculate exactly how much.)
If you leave the tank for days and days, then if it is sealed you can not get more water into it. Each time the temperature cools, some water will condense out. As the temperature increases during the day, it will return to the gaseous state.
100% relative humidity is probably not common inside a fuel tank. Temperature variations greater than 20C are probably very unusual in the UK. And in the typical GA aircraft that most of us fly, you're not likely to have more than 100 litres of empty capacity (although some of you may be lucky enough to have more). The very worst case, therefore is that the 2.1cc of water condenses onto the surface of the tank. If you then fill the tank to the brim, and wait long enough, that water can settle to the bottom of the tank. For various reasons, you won't actually get that much.
At takeoff power, the engine of my aeroplane (O-360) consumes approximately 20cc per second. So, in my very worst case scenario, if all that water condenses out and enters the fuel line, I might get a 1/10th of a second power loss.
I do check my fuel regularly for water, which can come from contaminated supply, or poorly sealed tanks. Everyone should do the same. But even if I have got the science quite badly wrong, the water is not going to come from condensation.
If the fuel tank is sealed, then the only water that can condense to cause fuel contamination is the water that is in a gaseous state in the tank. Even at 100% relative humidity, on a warm day, the amount of water that can be held is quite small. (Look up "saturated vapour density" on google, and you'll find all the science you need to calculate exactly how much.)
If you leave the tank for days and days, then if it is sealed you can not get more water into it. Each time the temperature cools, some water will condense out. As the temperature increases during the day, it will return to the gaseous state.
100% relative humidity is probably not common inside a fuel tank. Temperature variations greater than 20C are probably very unusual in the UK. And in the typical GA aircraft that most of us fly, you're not likely to have more than 100 litres of empty capacity (although some of you may be lucky enough to have more). The very worst case, therefore is that the 2.1cc of water condenses onto the surface of the tank. If you then fill the tank to the brim, and wait long enough, that water can settle to the bottom of the tank. For various reasons, you won't actually get that much.
At takeoff power, the engine of my aeroplane (O-360) consumes approximately 20cc per second. So, in my very worst case scenario, if all that water condenses out and enters the fuel line, I might get a 1/10th of a second power loss.
I do check my fuel regularly for water, which can come from contaminated supply, or poorly sealed tanks. Everyone should do the same. But even if I have got the science quite badly wrong, the water is not going to come from condensation.
I'm not a scientist by a long shot, but here we go:
Left for weeks at a time, fuel tanks do rust from the inside out.
Left for months, it will actually build nice
quarter inch stalagtites of rust in your tank.
That would be one reason for leaving the tanks full.
Rubber bladders dry out and wll crack and leak of not kept wet by fuel.
That's reason #2.
Fuel tanks in aircraft are vented ( exposed to outside air circulation) for obvious reasons.
100% humidity outside will mean 100% humidity inside the tank.
Cycles of heating up and cooling down will draw fresh(moist) air into the tank.
depending on amount of cycles and humidity variations this could mount up to more then 2.1cc's over time.
Water evaporating again when the tank heats up does not mean it will escape the tank through the vent pipe.
Cooling down it will draw in fresh air again. Cycle repeats itself.
reason #3
Engines will draw in fresh(moist) air when cooling down, through the airfilter and through the exhaust.
One reason why engines will rust inside when left over time.
Car exhaust( when cold) will drip water till the pipes heat up and it evaporates.
That's not water in the fuel, that's water condensed overnight.
Check the disc of the brakes on your car after you haven't driven it for a day, that's rust,from moist air.
So unless you live in Arizona......
Left for weeks at a time, fuel tanks do rust from the inside out.
Left for months, it will actually build nice
quarter inch stalagtites of rust in your tank.
That would be one reason for leaving the tanks full.
Rubber bladders dry out and wll crack and leak of not kept wet by fuel.
That's reason #2.
Fuel tanks in aircraft are vented ( exposed to outside air circulation) for obvious reasons.
100% humidity outside will mean 100% humidity inside the tank.
Cycles of heating up and cooling down will draw fresh(moist) air into the tank.
depending on amount of cycles and humidity variations this could mount up to more then 2.1cc's over time.
Water evaporating again when the tank heats up does not mean it will escape the tank through the vent pipe.
Cooling down it will draw in fresh air again. Cycle repeats itself.
reason #3
Engines will draw in fresh(moist) air when cooling down, through the airfilter and through the exhaust.
One reason why engines will rust inside when left over time.
Car exhaust( when cold) will drip water till the pipes heat up and it evaporates.
That's not water in the fuel, that's water condensed overnight.
Check the disc of the brakes on your car after you haven't driven it for a day, that's rust,from moist air.
So unless you live in Arizona......
I'matightbastard
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I have sympathy with the 2 last posts. Yes, it is a real pain having to fill up before flying,
before fill up should be the standard
Some good points above - rusted fuel tanks in an aeroplane is not one of them however - just plain Aluminium.
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I can remember a few years back when we had major bushfires where I lived that the aircraft owners at the local airstrip were reported as having filled their tanks UP to reduce the fire risk - the idea being that fuel vapour, of course, is more flammable than liquid fuel so by filling with liquid fuel there's no vapour left to go BOOM!...
Or something like that.
Or something like that.
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rusted fuel tanks in an aeroplane is not one of them however - just plain Aluminium.
I 've just had another one of those blinding flashes. That's three in a day I'll run out of thunks at this rate.
3) Fuel and water when churned about sufficently will emulsify. However if you leave it over night the water settles out of the fuel and into the drain sumps rather than freezing in the carb jets on take off. which is an aspect of carb icing people often forget about.
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I believe the caution about fuel bladders drying out. On the other hand, since my home airport has been without fuel for 6 months now, there's been numerous times my plane has sat for a week in it's hangar with 2/3rds full tanks, and I've never found a drop of water in either tank. I'm much more suspicious of the fuel I've gotten from unfamiliar pumps while away from home.
A little less conversation,
a little more aviation...
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quarter inch stalagtites of rust in your tank.
just plain Aluminium.
bad news - these are in fact the larval form of the lesser
genus Aetheris Diabolus...the common Gremlin.
Transformation from the larval stage to the adult is
initiated by a strong transient voltage gradient,
combined with a low solar ambient UV... so typically,
they will emerge from the tanks in IMC, just after a
nearby lightning strike - traditionally, all your fuses &
circuit breakers will also have blown. Infestation
at this stage is invariably terminal.
The only known means of disinfection is to fill the tanks
with Gordon's Export Gin (domestic variants are too
diluted), generally obtained from overseas NAAFI outlets.
Best of luck.
Ed.
Last edited by eharding; 14th Dec 2005 at 23:26.
You obviously haven't been near an Auster or Tiger Moth Lately Then.
I actually go out of my way to avoid Austers and had forgotten the Tiger's tank.
This thread will carry on for a looong time..LOL
Not all tanks are aluminum.
And I've never seen corrosion on a Cessna either. Wonder what that bubbly stuff under the paint is......
In any case I have seen tanks removed from a C150 that were filled with brown crunchy ferrous like material, I won't call it rust for now.
I have seen an Aztec parked outside for a couple of months with empy tanks.
You could stick your finger down the filler neck and feel the build-up of, once again,
brown crunchy ferrous like material.
You have more chance of finding water after a nice rain shower, but that doesn't mean that condensation does not occur.
Cheers
http://marinesurvey.com/yacht/fueltank.htm
http://www.stormingmedia.us/79/7915/A791524.html
http://www.brokeboats.com/badtanks.html
http://www.emeraldinsight.com/Insigh...270750507.html
Now don\'t come back saying that this doesn\'t apply \'cause it\'s a boat-tank...
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My tank is carbon fibre. A assume it is immune from most of the problems and will not provide a cold surface for the water to condense out on, so would reduce this as well. Any of our budding physicists care to comment?
Rod1
Rod1
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The worst thing that I've ever seen in a fuel tank was a pencil stub. Someone had tried to dip the tank (C152), dropped the stub in and couldn't get it out. Nor could I.
Rod, surely your carbon fibre would be at ambient temp, just as aluminium would?
My Pioneer's got aluminium tanks, and it lives under cover so no chance of rain ingress. Have only seen water once in the wing tank drains, and that was when the tanks had been left half full for 8 days. On other occasions, no water at all despite slack tanks for similar periods. Depends on climactic conditions probably.
As for all the calcs of possible water quantities done previously by our resident physisists, I would say the calculations are flawed, as they assume only a single atmosphere would be present in the tank ullage space. With diurnal temperature variations, the atmosphere would be changed frequently.
Another suggested reason for keeping your tanks full would be an improved surface/volume ratio for the fuel. The rate of evaporation of the fuel's volatile components depends upon this.
My Pioneer's got aluminium tanks, and it lives under cover so no chance of rain ingress. Have only seen water once in the wing tank drains, and that was when the tanks had been left half full for 8 days. On other occasions, no water at all despite slack tanks for similar periods. Depends on climactic conditions probably.
As for all the calcs of possible water quantities done previously by our resident physisists, I would say the calculations are flawed, as they assume only a single atmosphere would be present in the tank ullage space. With diurnal temperature variations, the atmosphere would be changed frequently.
Another suggested reason for keeping your tanks full would be an improved surface/volume ratio for the fuel. The rate of evaporation of the fuel's volatile components depends upon this.
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My tank is carbon fibre. A assume it is immune from most of the problems
So as long as you stay away from CBs you should be OK!
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At takeoff power, the engine of my aeroplane (O-360) consumes approximately 20cc per second. So, in my very worst case scenario, if all that water condenses out and enters the fuel line, I might get a 1/10th of a second power loss.
If 2 cc of water can enter the fuel line, get swallowed by the engine in 1/10 of a sec with no effect, how come melting carb ice, which is probably a smaller volume over a longer time, has such a major impact on the smooth running of the engine?
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If 2 cc of water can enter the fuel line, get swallowed by the engine in 1/10 of a sec with no effect, how come melting carb ice, which is probably a smaller volume over a longer time, has such a major impact on the smooth running of the engine?
It is not the volume of ice but the obstructing effect it has.
FD
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I'm not sure of the exact science behind it but I can tell you that I used to keep a 150 in an unheated hangar, tanks full after flying almost all the time. No problem with condensation unless the pumps were closed when I'd landed the prior flight and couldn't fill the tanks.
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To answer the question about pre-heating fuel: it is a valid technique used on some gas turbines. Both the Apache and the Wessex (quite an age range then!) use a heat exchanger whereby engine oil is cooled by fuel on its way in.
I once had an engine failure in Yorkshire due to condensation - though thankfully not in an aircraft. Still, scary enough when it is in a narrowboat on the tidal stretch of the Ouse heading for Hull and Rotterdam on an 11 knot ebb tide...
I drained over 10 litres of water from the fuel tank after that little adventure, following years of neglect by the previous owner of the boat. Consensus was that it was almost certainly caused by condensation over a period of years.
Prior to 21 years as an army pilot, I was trained as a refueller, so am better placed that many to understand the problems of water and fuel. Fuel bowsers have very efficient coalescers that extract water from fuel, yet still the annals of aviation are peppered with stories of contam fuel. One such was a Scout AH1 that failed shortly after take-off having just been refuelled. The bowser had been correctly set up for the day, with all the fuel inside flushed through the coalescers. However, the extension hoses which were later used were not flushed. Scout had about a gallon of water in the fuel tank, if memory serves me right.
I once had an engine failure in Yorkshire due to condensation - though thankfully not in an aircraft. Still, scary enough when it is in a narrowboat on the tidal stretch of the Ouse heading for Hull and Rotterdam on an 11 knot ebb tide...
I drained over 10 litres of water from the fuel tank after that little adventure, following years of neglect by the previous owner of the boat. Consensus was that it was almost certainly caused by condensation over a period of years.
Prior to 21 years as an army pilot, I was trained as a refueller, so am better placed that many to understand the problems of water and fuel. Fuel bowsers have very efficient coalescers that extract water from fuel, yet still the annals of aviation are peppered with stories of contam fuel. One such was a Scout AH1 that failed shortly after take-off having just been refuelled. The bowser had been correctly set up for the day, with all the fuel inside flushed through the coalescers. However, the extension hoses which were later used were not flushed. Scout had about a gallon of water in the fuel tank, if memory serves me right.