Most, if not all, of the water I have drained from various C-152s and C-172s
has been the direct result of leaks through the filler gaskets, following
rain or aircraft washing. All of these aircraft are maintained by an FBO
with a very conservative approach (that borders on the fanatical) to
aircraft maintenance and operation. The filler design might as well be a
funnel considering how it collects water.
There are two other possible sources, both from condensation. The overnight
temperature cycle as mentioned, and from the reduced pressure at altitude
causing ingestion of moisture laden air when returning to the ground. Think
about what happens to the plastic bottle of water last used for quenching
thirst at altitude, when back on the ground; the same thing happens to the
vented gas tank, except of course it doesn't collapse - the vent solves one
problem while causing another.
All of this may be of academic interest most of the time but we all know
that the possible consequences of water in the fuel are likely to be more
severe in an airplane than an automobile, so it isn't paranoia to go after
every drop of water during every pre-flight. Installing both a gascolator
and fuel drains is prudent.
"Drygas" is for keeping frozen water from clogging the lines. It is a
substance that is mutually miscible with water and gasoline so there are no
longer two liquid phases in the fuel system.
Best regards,
Rob Housman
A070
-----Original Message-----
On Behalf Of Fred Fillinger
Sent: Thursday, October 12, 2000 7:38 AM
Subject: Re: [gascolators and drains...]
Theories: In the old days, people in winter climates often added
"drygas." But maybe the prime source of water then was leaking
underground storage tanks, all now replaced in the U.S. Auto fuel
tanks now do not vent directly to outside air, but through the
charcoal canister, which is purged by manifold vacuum on startup.
It's possible the phenomenon isn't really a hazard in aircraft. Of
44,000+ NTSB reports online, only 2 contained any form of the word
"condense" in reference to the fuel tank. One quoted the A/C
operating handbook, and another FAA advice, both referring to the
"possibility" of such moisture condensation. But in neither case did
the NTSB say the water contamination was likely from that source.
That's 0/44,000, and you'll get 5 hits looking for "mice" or "mouse"
as a contributing factor in the accident.
The only real distinction I see is the location of the filler caps.
Regards,
Fred F., A063, N3EU
Chris Beck wrote:
>
> This always has me wondering. Why don't our automobiles have gascolators
and
> more trouble with water in the fuel? I surely don't drain the tank of my
> Saturn before every commute to work, and change the fuel filter every
30,000
> miles. In 127,000 miles, I've never had so much as a burp to to a fuel
> problem, and I regularly run the tank to empty before filling up. Why are
> aircraft so susceptible to water problems?
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