Leave the fuel tanks full
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Leave the fuel tanks full
I was taught, many years ago, when parking an aicraft outdoors to leave the tank(s) full so as to minimise condensation. And, largely, I still do.
But, here's the thing - is there actually foundation in fact of this?
G
But, here's the thing - is there actually foundation in fact of this?
G
Join Date: Jul 2005
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No foundation at all for a typical GA aircraft, if my distant memory of chemistry is correct.
Let's suppose you park your wonderplane with 100 Litres of empty capacity in its tank, on a summer day when the temperature is 30C. Overnight it cools to 10C.
At 30°C, 3.04 grams of water can be held in a 100 litre volume, and at 10°C that falls to 0.94 grams. So, worst case scenario, if the relative humidity is 100%, you could have 2.1 cc of water at the bottom of your tank if all the water vapour condenses onto the surface of the fuel tank and you refuel to the brim while the temperature is still cold.
There would actually be a bit less water than that at the bottom of your tank, as some water can be dissolved in Avgas - I don’t know how much. As your fuel cooled at high altitude, more water could come out of solution.
I don’t know if the saturated vapour density of water will be affected by the presence of other gasses in your fuel tank; we need someone who’s been a scientist more recently than me! If there is an effect, I would anticipate it would be a reduction in the amount of water held.
Conclusion: if your engine fails due to water contamination, it’s not likely to be because water condensed overnight in your fuel tank.
Let's suppose you park your wonderplane with 100 Litres of empty capacity in its tank, on a summer day when the temperature is 30C. Overnight it cools to 10C.
At 30°C, 3.04 grams of water can be held in a 100 litre volume, and at 10°C that falls to 0.94 grams. So, worst case scenario, if the relative humidity is 100%, you could have 2.1 cc of water at the bottom of your tank if all the water vapour condenses onto the surface of the fuel tank and you refuel to the brim while the temperature is still cold.
There would actually be a bit less water than that at the bottom of your tank, as some water can be dissolved in Avgas - I don’t know how much. As your fuel cooled at high altitude, more water could come out of solution.
I don’t know if the saturated vapour density of water will be affected by the presence of other gasses in your fuel tank; we need someone who’s been a scientist more recently than me! If there is an effect, I would anticipate it would be a reduction in the amount of water held.
Conclusion: if your engine fails due to water contamination, it’s not likely to be because water condensed overnight in your fuel tank.
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I was thought to keep the tanks because the fuel vapors are a lot more flammable than the fuel its. The more fuel the less vapors within the tank.
Re minimising condensation; I not too sure. Maybe if the aircraft is out side of a hot day with half full tanks the heat may cause the traces of water with the fuel to evaporate and the condense on the inside walls of the tank, this in turn may lead to water contamination of the fuel.
Please correct me if Im wrong.
Re minimising condensation; I not too sure. Maybe if the aircraft is out side of a hot day with half full tanks the heat may cause the traces of water with the fuel to evaporate and the condense on the inside walls of the tank, this in turn may lead to water contamination of the fuel.
Please correct me if Im wrong.
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there must be something in it, when i was in the u.s training on the warrior, regardless of the plane whichever one wasn't refuelled at the end of the day always had water in the fuel tester in the morning and all the ones that were refuelled had just neat fuel come out!
Better red than ...
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Interesting study done on this last year next door in Rotorheads (http://www.pprune.com/forums/showthr...hlight=gaseous)
Keeping the tanks full to avoid condensation is also a JAA ATPL question in AGK (Airframes & Systems) so one assumes there "must be something in it" (even if it is just Avgas...)
h-r
Keeping the tanks full to avoid condensation is also a JAA ATPL question in AGK (Airframes & Systems) so one assumes there "must be something in it" (even if it is just Avgas...)
h-r
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My understanding -
If there is an excess of air in the tank, condensation can occur in any outside temp. Witness a car windscreen. The water falls through the fuel and collects at the base of the tank. The engine is fed from near the base. Sod's law clearly states that there will be enough "clean" fuel for you to start up, taxi, complete power checks and commence the take-off run. At the most critical point a dollop of water will be sucked up and deprive your ehgine of power for precisely long enough to spoil your day.
Obviously it's avoidable by carefully draining the tanks pre-flight.
Also, I for one HATE getting to an aircraft to find I need to start, taxi to pumps, fuel etc before I can do anything. As a courtesy to the next user I make sure the tanks are reasonably full. Why not full? Short strip, perf-critical I'm afraid.
Oh well!
If there is an excess of air in the tank, condensation can occur in any outside temp. Witness a car windscreen. The water falls through the fuel and collects at the base of the tank. The engine is fed from near the base. Sod's law clearly states that there will be enough "clean" fuel for you to start up, taxi, complete power checks and commence the take-off run. At the most critical point a dollop of water will be sucked up and deprive your ehgine of power for precisely long enough to spoil your day.
Obviously it's avoidable by carefully draining the tanks pre-flight.
Also, I for one HATE getting to an aircraft to find I need to start, taxi to pumps, fuel etc before I can do anything. As a courtesy to the next user I make sure the tanks are reasonably full. Why not full? Short strip, perf-critical I'm afraid.
Oh well!
I for one HATE getting to an aircraft to find I need to start, taxi to pumps, fuel etc before I can do anything.
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I have sympathy with the 2 last posts. Yes, it is a real pain having to fill up before flying, which I have to do nearly every time even if I'm just doing a short local. Inevitably there will be a queue at the pumps, or they're shut for some reason or other. It all eats into your precious time that the plane is booked for, and is a right fag if you have non-flying friends with you who have to hang around.
Not to mention the fact that some planes I've flown have been reluctant to start again after a stop at the pumps.
On the other hand, arrive with four of you for a PA28 that has been filled to the top - you've had it.
Not to mention the fact that some planes I've flown have been reluctant to start again after a stop at the pumps.
On the other hand, arrive with four of you for a PA28 that has been filled to the top - you've had it.
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And that, I'm afraid, is the inevitable collision between sensibilitiy & practicality.
Being sensible means filling them after flight to minimise the risk of condensation.
Being practical means leaving them half empty for the next person to decide how much fuel they need.
Pre-flight, I used to shake the wings to move any water droplets down into the sump and then drain the fuel, by which time the nice chappie with the fuel bowser had arrived.
As a matter of interest, how many pilots have had water in their fuel testers? Is the problem more due to badly fitting fuel caps than condensation?
The Koliber had a very effective rubber bung sealing the filler neck and a metal flap over the top of it. We never had water in the fuel.
Being sensible means filling them after flight to minimise the risk of condensation.
Being practical means leaving them half empty for the next person to decide how much fuel they need.
Pre-flight, I used to shake the wings to move any water droplets down into the sump and then drain the fuel, by which time the nice chappie with the fuel bowser had arrived.
As a matter of interest, how many pilots have had water in their fuel testers? Is the problem more due to badly fitting fuel caps than condensation?
The Koliber had a very effective rubber bung sealing the filler neck and a metal flap over the top of it. We never had water in the fuel.
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Typical old wives aviation tale.
Adrian has it right. The rest of you seems to prefer to indulge in keeping the old tales going.
Few questions:
Q: How often does your car engine stop due to water contamination as a result of condensation in a non full tank?
A: Never.
Q: Can I fill up an empty metal container with water by leaving it in a hangar for a few days and nights?
a. Yes of course, that is how we fill them anyway!
b. No, are you stupid?
Water in fuel tanks in aeroplanes is a result of dodgy seals or contaminated fuel being put into those tanks.
Nothing more, nothing less.
Adrian has it right. The rest of you seems to prefer to indulge in keeping the old tales going.
Few questions:
Q: How often does your car engine stop due to water contamination as a result of condensation in a non full tank?
A: Never.
Q: Can I fill up an empty metal container with water by leaving it in a hangar for a few days and nights?
a. Yes of course, that is how we fill them anyway!
b. No, are you stupid?
Water in fuel tanks in aeroplanes is a result of dodgy seals or contaminated fuel being put into those tanks.
Nothing more, nothing less.
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The same advice is given to boat owners regarding keeping tanks full, and I have seen the evidence of condensation my self but that is with gas oil and in a more humid marine enviroment, not sure how that translates to aircraft.
That said, all modern marine engines are fitted with water seperators so unless there is gallons of water there is never a problem. couldn't these be fitted to aircraft fuel systems as a backup to draining the tanks before flight?
That said, all modern marine engines are fitted with water seperators so unless there is gallons of water there is never a problem. couldn't these be fitted to aircraft fuel systems as a backup to draining the tanks before flight?
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Chemistry apart, on many a/c, full tanks gives a chance to positively check fuel levels against gauge readings before engine start ( no chance of (a dipstick) misreading a dipstick).
Personally, I prefer to top up fuel and other fluids as part of the 'post flight / wind down / rosy glow', rather than as an additional 'pre flight wind up'.
Anyway, the Chipmunk only carries 9 gal per side, has better '2 up' CG margins with full fuel, and it's kinder on the flexible tanks to keep them full.
The fuel and oil uplift is also logged directly against the last sortie and a quick mental check of flying time/type against consumption is no bad thing (this especially applies to oil consumption on the Gipsy Major!!).
Personally, I prefer to top up fuel and other fluids as part of the 'post flight / wind down / rosy glow', rather than as an additional 'pre flight wind up'.
Anyway, the Chipmunk only carries 9 gal per side, has better '2 up' CG margins with full fuel, and it's kinder on the flexible tanks to keep them full.
The fuel and oil uplift is also logged directly against the last sortie and a quick mental check of flying time/type against consumption is no bad thing (this especially applies to oil consumption on the Gipsy Major!!).
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Coming at this from a slightly different perspective I've always been told that it's best to leave any vehicle with full tanks and over many years tinkering with cars, both fuel tanks I've had to replace were corroded from the inside out. Both vehicles were used by the previous owners as second cars and only part filled as they only did short runs.
Another thought occurs to me that bladder tanks lose flexibility if allowed to dry out, as you don't know how long it will be before the A/C is used again it would seem to be a sensible precaution to leave the tanks full.
Yet another thought occurs that the old natural rubber seals on riveted tanks would dry out if the tanks were not full.
So lots of reasons why it was good practice and may well still be. Perhaps another example of doing the right thing for the wrong reasons.
P S I don't have many cans in my shed overflowing with condensation. However I do have a whole buch that are really rusty!
Another thought occurs to me that bladder tanks lose flexibility if allowed to dry out, as you don't know how long it will be before the A/C is used again it would seem to be a sensible precaution to leave the tanks full.
Yet another thought occurs that the old natural rubber seals on riveted tanks would dry out if the tanks were not full.
So lots of reasons why it was good practice and may well still be. Perhaps another example of doing the right thing for the wrong reasons.
P S I don't have many cans in my shed overflowing with condensation. However I do have a whole buch that are really rusty!
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A really really good reason to fill up straight after a flight is because it enables a quick departure later.
Once one is airborne, one has to land anyway (sounds stupid I know). Whereas a departure depends on all sorts of stuff, starting with the weather and, in many places abroad, involving the filling in of a pile of forms. The last thing one wants to do is mess about with all that and then not go because they can't find the avgas bowser or nobody can (or wants to) speak English.
In the same vein, all large airports want to get the occupants off airside really quick. You land and usually within minutes a van or bus turns up to get you out of there. This is a brilliant time to fill up. Just politely refuse to leave the aircraft until you have fuel. It's amazing how quickly they "find" the fuel then
Once one is airborne, one has to land anyway (sounds stupid I know). Whereas a departure depends on all sorts of stuff, starting with the weather and, in many places abroad, involving the filling in of a pile of forms. The last thing one wants to do is mess about with all that and then not go because they can't find the avgas bowser or nobody can (or wants to) speak English.
In the same vein, all large airports want to get the occupants off airside really quick. You land and usually within minutes a van or bus turns up to get you out of there. This is a brilliant time to fill up. Just politely refuse to leave the aircraft until you have fuel. It's amazing how quickly they "find" the fuel then
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Mogas users think of this
The issue of tanks full or empty will always err on the side of fill them up, however if you leave a plane in humid conditions for a period of a month or more the condenstion becomes more significant.
Now for the MOGAS users and in Europe this is more common than here in OZ, the bigger problem is Premium ULP is enhanced with octane boosting products like Benzene, which easily evapourates, before you know it, you are back to regular ULP, so fresh is best with PULP.
Just a thought....
J
Now for the MOGAS users and in Europe this is more common than here in OZ, the bigger problem is Premium ULP is enhanced with octane boosting products like Benzene, which easily evapourates, before you know it, you are back to regular ULP, so fresh is best with PULP.
Just a thought....
J
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I cant leave my tanks full. My 152 leaks fuel from the breather pipe check valve (despite being replaced a couple of months) faster than it burns it. This is a common problem on all 152's.
I would be very unpopular if I burnt the hangar down from a fuel leak!!
I would be very unpopular if I burnt the hangar down from a fuel leak!!
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From Flyin Dutch
firstly car engines dont stop due to water contamination probably because they generally have water seperators in them nowadays as said by yorks. This is an innovation which has sadly not been adapted to GA engines in general.
Secondly you will never fill a metal container with condensation by leaving it in a hangar because it is not a sealed environment like a fuel tank, the water is able to evaporate out of it once the temperature rises again. A fuel tank not only traps the water inside once it condenses, but due to the fact that it is vented and not air tight extra moisture is able to get in over time.
Overnight the amount of moisture you are likely to encounter is minimal although it still warrants draining. But if the plane isnt used over a period of time then you would be surprised at the amount of water you can find.
just my two cents..
Zepth
Few questions:
Q: How often does your car engine stop due to water contamination as a result of condensation in a non full tank?
A: Never.
Q: Can I fill up an empty metal container with water by leaving it in a hangar for a few days and nights?
Q: How often does your car engine stop due to water contamination as a result of condensation in a non full tank?
A: Never.
Q: Can I fill up an empty metal container with water by leaving it in a hangar for a few days and nights?
Secondly you will never fill a metal container with condensation by leaving it in a hangar because it is not a sealed environment like a fuel tank, the water is able to evaporate out of it once the temperature rises again. A fuel tank not only traps the water inside once it condenses, but due to the fact that it is vented and not air tight extra moisture is able to get in over time.
Overnight the amount of moisture you are likely to encounter is minimal although it still warrants draining. But if the plane isnt used over a period of time then you would be surprised at the amount of water you can find.
just my two cents..
Zepth