Message-Id: <3.0.3.32.19981013074941.00ae72d4@olsusa.com>
Date: Tue, 13 Oct 1998 07:49:41 -0400
To: lancair.list@olsusa.com
From: <dechaze@cardell.com> (by way of Marvin Kaye <marvkaye@olsusa.com>)
Subject: Re:Fuel level sensors
Mime-Version: 1.0

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Jim Frantz wrote about float switches not being good because they are affected
by G-loads and turbulence causing the float to probably sink.

Actually that isn't the case.  The same centripetal force acting on the
float as
acting on the surrounding fluid not only canceling any effect but multiplying
the buoyancy of the float by the increase in 'g'.  So if it floats, it'll
float
even better under higher g's. If it sinks, it'll sink harder under g's.  In
fact
the The better way to think of it is simply by comparing densities (which is
unaffected by gravity because it's MASS divided by volume).  

I've got 3 float switches in my tank (Matteson is the mfgr - same as in
Aircraft
Spruce) the lowest (at about the half mark) to turn on pumps, the middle to
turn
off pumps and the highest to signal a light.  I also have a both wing tanks
plumbed through a fuel flow transducer feeding a panel gage so that I will
know
if flow to the header tank isn't nominal.  I'm planning to use the VM-1000
system to warn of low fuel should a pump or relay fail.  The Lancair Avionics
people did the design and put a nice little relay and harness package
together. 
But I didn't think about what I would do if a relay fails and I get the
warning
but I only have a few gallons left.  I'll have to think that failure mode
through.  Thanks for the warnings.

Ed de Chazal
Rochester Michigan