On Sun, 5 Dec 2004 07:40:00 -0600, "Dan Luke"
wrote in
::


"Larry Dighera" wrote in message
.. .
On Sun, 5 Dec 2004 06:42:51 -0600, "Dan Luke"
wrote in
::

... so that [they] always have full tanks," which is a silly
practice unless one ALWAYS knows the next flight will require full
tanks.

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.

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.

However, PA28-235 can carry its empty weight (~1,400 lbs) in useful
load, so weight management through fuel offloading is seldom
necessary.

Personally, I prefer that water never be present in the aircraft fuel
system, especially in aircraft with fuel tank bladders....