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Reply-To: "David Carter" <dcarter@datarecall.net>
From: "David Carter" <dcarter@datarecall.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
References: <list-752625@logan.com>
Subject: Re: [FlyRotary] Re: Vapor Lock
Date: Mon, 21 Feb 2005 11:41:21 -0600
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Excellent and accurate posting by Ernest.  The collection of moisture in
bottom of tanks by "natural, unavoidable action" is exactly why we have fuel
"quick drains" at low spots in tanks and fuel systems.  Only if the water is
getting mixed vigorously and reliably and adequately by a fuel injection
system would a person want to ignore the presence of that accumulated water.

David

----- Original Message ----- 
From: "Ernest Christley" <echristl@cisco.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, February 21, 2005 9:18 AM
Subject: [FlyRotary] Re: Vapor Lock


> Wendell Voto wrote:
>
> > I find it interesting that you get water in the sump on a Velocity. A
> > previous owner of one told me that since the tanks are
> > composite/sandwich structure that water does not condense in the tanks
> > and never got any moisture in the fuel.  Where are you getting fuel?
> > Could it have water in it? (they put water in everything now days to
> > "enhance it" or make you pay $4 a pound for it).
> > Wendell
>
>
> Please, everyone, please understand that ANY closed tank with a small
> orifice opening (a vented fuel tank, for example) can become a very
> effective water pump.  The process:
>
> -You spend Saturday flying, and park the plane on the ramp in
> anticipation of Sunday's flight.  The hot sun keeps the fuel in the half
> full tank warm for the rest of the evening.
> -As the sun sets, your tanks begin to cool.  Cool gasses occupy less
> volume, tank sucks air in through the vent (exactly as it was designed
> to do).  Unfortunately, it's sucking air at exactly the same time as
> water is dropping out of the air mixture.  This may be more of a problem
> in North Carolina than other locals, but evenings here can be downright
> sticky in the summer.  The air that the tank is sucking will be VERY wet.
> -When the tank warms in the morning, the gases will expand and it will
> push out the air above the fluid.  The water that was in the air is now
> below the fuel, so it doesn't get pushed out.
> -You can't make it to the airport Sunday, so the plane sits on the ramp
> all week.  Each day, the tank will heat and cool, sucking in a gulp of
> wet air every night.
>
> The end result is a pumping action.  A very insidious and unavoidable
> one.  It doesn't matter what they tank is made of.  A full day's heat
> soak, followed by a full night's cooling will make the pump work.  The
> only way to stop is to:
> 1)Live in a place without water vapor problems.  Either a very dry
> environment, or one so cold that all the water sits frozen on the ground.
> 2)Seal the tank perfectly completely.  At which point it won't work well
> as a vehicular fuel tank, but at least won't have to worry about water
> in the fuel.
>
> >>  Homepage:  http://www.flyrotary.com/
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>
>