How safe is it, really?

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 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

"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

In article , Larry Dighera wrote:
On Sun, 5 Dec 2004 07:40:00 -0600, "Dan Luke"
Which is an old wives tale. The amount of water contained in 20-30
gallons of air is insignificant.

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.

I have lived my entire life in humid maritime environments. I have never
lived more than 50 miles from open sal****er despite having lived on two
continents. Where I currently live, it is impossible to be more than 7.5
miles from open water.

However, I have never discovered water condensing in half-full fuel
tanks. It is my practise to make both a visual inspection through the
the filler neck and to sump the tanks before flying whether the plane's
been refuelled or not. In over 1000 hours of light plane flying, the
only time I've found water in the fuel is through leaky fuel caps (the
Beech Musketeer being the worst for this, but also in a Grumman Cheetah)
after a night of rain.

So I'd agree the condensation thing is an OWT, certainly with the fuel
capacities of our planes (the biggest capacity wise that I've regularly
flown are an S-35 Bonanza (74 gal usable) and the Geronimo-mod Apache
(which carried 7 hours of fuel - I don't remember the exact figure in
gallons, but it was a little over 100 gallons capacity in 4 tanks).
With the Geronimo, because it only has 160 hp a side, it's quite
important not to lug around excess fuel.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

On Mon, 06 Dec 2004 14:21:10 -0000, Dylan Smith
wrote:

In article , Larry Dighera wrote:
On Sun, 5 Dec 2004 07:40:00 -0600, "Dan Luke"
Which is an old wives tale. The amount of water contained in 20-30
gallons of air is insignificant.

Just let those tanks inhale and exhale a few times. They do that
every morning and night so there is a *lot* more than 20-30 gallons
involved.


snip

So I'd agree the condensation thing is an OWT, certainly with the fuel


It all depends.


capacities of our planes (the biggest capacity wise that I've regularly
flown are an S-35 Bonanza (74 gal usable) and the Geronimo-mod Apache

I fly a Deb with about the same fuel capacity (not counting the tip
tanks). With half tanks and the plane hangered for two weeks in the
Spring, I drained over two full samplers of water out of one tank and
a half out of the other. None out of the auxiliaries as they were
full.

(which carried 7 hours of fuel - I don't remember the exact figure in
gallons, but it was a little over 100 gallons capacity in 4 tanks).

The Deb will carry 100 when the tip tanks are full.

With the Geronimo, because it only has 160 hp a side, it's quite
important not to lug around excess fuel.

I'm paranoid about fuel, particularly with Michigan weathers tendency
to change rapidly. I might go for a 50 mile jaunt, get a late start
back and end up in Wisconsin, or Kentucky.

I rarely go any where without full tanks, with the exception of the
tip tanks.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

On Mon, 06 Dec 2004 14:21:10 -0000, Dylan Smith
wrote in
::

I have never discovered water condensing in half-full fuel
tanks.

Perhaps the laws of physics have been repealed on the Isle of Man. :-)

"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

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.

Peter,

My
understanding is that having the rubber "wetted" by the fuel helps extend
their lifetime.


"Ah, but my fuel bladders will look pristine to the NTSB guys" , said the
pilot as he crashed into the trees at the end of the runway.

--
Thomas Borchert (EDDH)

"Thomas Borchert" wrote in message
...
Peter,

My
understanding is that having the rubber "wetted" by the fuel helps extend
their lifetime.

"Ah, but my fuel bladders will look pristine to the NTSB guys" , said the
pilot as he crashed into the trees at the end of the runway.

I'm not sure what your point is, but your post seems pretty dumb to me,
especially as a response to my own post. Maybe you'd like to explain
yourself?