How safe is it, really?

On Sun, 05 Dec 2004 18:28:38 +0100, Stefan
wrote in ::

Larry Dighera wrote:

I submit, that water in an aircraft fuel system has the potential for
disaster. To argue otherwise seems absurd.

Nobody argues otherwise.

Those who dismiss condensation as a source for water in an aircraft
fuel system have done so.

But claiming that condensation caused by
halfways empty tanks is a noteworthy source for that water is equally
absurd.

How much water does it take to clog an aircraft fuel line when it
freezes? Take a guess?

If there is water in your tanks, chances are you buyed it at
fuel price. Another important source is a leaking seal while the plane
is parked in the rain.

That is borne out by:
http://www.ntsb.gov/ntsb/brief.asp?e...08X08676&key=1

But you're correct in one way: If you always fill the tanks after each
flight, there won't be water in the tanks. No, not because there is no
condensation, but because you will have to drain a couple of gallons
before the each flight.

Unfortunately, just draining the tanks without making an effort to
position the aircraft so that water trapped in the folds of a rubber
fuel bladder is able to reach the sump will not remove it.

Water in an aircraft fuel system has the potential for disaster.

Larry,

rests on the
notion that air contains a certain amount of moisture, and that the
water will condense out of the air contained in partially emptied
tanks and contaminate the aircraft's fuel system.


which has never been proven, AFAIK.

--
Thomas Borchert (EDDH)

Larry,

moisture to condense out of the 40 gallons of air contained in them,
will result in enough water in the fuel system to interfere with
operation of the aircraft's power plant.


Says who? Please elaborate your calculation, which I cannot at all
follow.

AFAIK, Cessna once tried real hard in a climate chamber to produce a
noticable amount of water in an aircraft tank. Didn't happen.

--
Thomas Borchert (EDDH)

Larry,

I submit, that water in an aircraft fuel system has the potential for
disaster. To argue otherwise seems absurd.


Yes, but isn't introduced by condensation. It is either already in the
fuel at the time of refueling, or it comes in during rain through leaky
fuel caps.

--
Thomas Borchert (EDDH)

Larry,

Those who dismiss condensation as a source for water in an aircraft
fuel system have done so.


Huh? How so?

--
Thomas Borchert (EDDH)

"Dan Luke" wrote in message
...
The practice of topping the fuel tanks after each flight rests on the
notion that air contains a certain amount of moisture, and that the
water will condense out of the air contained in partially emptied
tanks and contaminate the aircraft's fuel system.

Which is an old wives tale. The amount of water contained in 20-30
gallons of air is insignificant.

I would agree that condensation is practically never an issue, but like
Larry I would not say that it could NEVER be an issue. Most of the time,
even when the air is very humid, the likelihood of the temperature changing
enough to cause any significant amount of the water vapor to condense is
incredibly small, and the total amount of water is also small. But to say
that it simply cannot ever be a source of water in a fuel tank seems
short-sighted to me. A tiny amount of water, in the wrong place at the
wrong time, can cause all sorts of trouble.

That said, there's another reason to try to keep the tanks topped off if you
can, when the airplane is equipped with rubber fuel bladders. My
understanding is that having the rubber "wetted" by the fuel helps extend
their lifetime. In my plane, I'm "fortunate" enough to have just one fuel
tank with a rubber bladder, with the other four being sealed aluminum
structures. So I always top of the one rubber bladder tank, and leave the
others partially or entirely empty.

Pete

"Larry Dighera" wrote:
A Piper PA28-235 can have 84 gallons of fuel in 4 tanks, so leaving
them half empty, for instance in a humid maritime environment,
overnight where the temperature drops sufficiently to cause the
moisture to condense out of the 40 gallons of air contained in them,
will result in enough water in the fuel system to interfere with
operation of the aircraft's power plant.

How much water is there in 40 gallons of air, Larry? Assume that when
the airplane was parked, the temperature was 20 C and the air was
saturated (which would be extremely wet conditions, BTW).
--
Dan
C172RG at BFM

Peter Duniho wrote:


That said, there's another reason to try to keep the tanks topped off if you
can, when the airplane is equipped with rubber fuel bladders. My
understanding is that having the rubber "wetted" by the fuel helps extend
their lifetime. In my plane, I'm "fortunate" enough to have just one fuel
tank with a rubber bladder, with the other four being sealed aluminum
structures. So I always top of the one rubber bladder tank, and leave the
others partially or entirely empty.

Where you live and where you keep your plane are major factors. I have
bladders in my 182 and never have them full except the night before a
long trip. I normally keep mine at approx half full. My plane is
hangared and our climate is moderate. Worst case is to leave your plane
outside in the baking sun and constantly changing temps. In the winter
my hangar stays in a realtively narrow 10 degree temperature band.

"Dan Luke" writes:

How much water is there in 40 gallons of air, Larry? Assume that when
the airplane was parked, the temperature was 20 C and the air was
saturated (which would be extremely wet conditions, BTW).

An opportunity to disturb high school chemistry knowledge cobwebs!
Water has a 20mb vapour pressure at 20degC, so water would form 2% of
the sea level atmosphere at full saturation. The ideal gas law
indicates there would be about 0.12mol in there, which has a mass of
around 2.2g, which could condense to around 2mL. Not much, but if it
decides to freeze and get sucked in and collected, could it plug up a
fuel line?

- FChE

"Frank Ch. Eigler" wrote in message
...

"Dan Luke" writes:

How much water is there in 40 gallons of air, Larry? Assume that
when
the airplane was parked, the temperature was 20 C and the air was
saturated (which would be extremely wet conditions, BTW).

An opportunity to disturb high school chemistry knowledge cobwebs!
Water has a 20mb vapour pressure at 20degC, so water would form 2% of
the sea level atmosphere at full saturation. The ideal gas law
indicates there would be about 0.12mol in there, which has a mass of
around 2.2g, which could condense to around 2mL. Not much, but if it
decides to freeze and get sucked in and collected, could it plug up a
fuel line?

Remember that in Larry's example the water is distributed among four
tanks. 2mL split four ways ain't enough to worry about.

If it freezes will it float in avgas or stay on the bottom?
--
Dan
C172RG at BFM