Aero-Tips!
A good pilot is always learning -- how many times have you heard
this old standard throughout your flying career? There is no truer
statement in all of flying (well, with the possible exception of
"there are no old, bold pilots.")
Aero-News has called upon the expertise of Thomas P. Turner,
master CFI and all-around-good-guy, to bring our readers -- and us
-- daily tips to improve our skills as aviators. Some of them, you
may have heard before... but for each of us, there will also be
something we might never have considered before, or something that
didn't "stick" the way it should have the first time we memorized
it for the practical test.
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Aero-Tips 09.25.06
Should you routinely top off the
airplane's fuel tanks after the last flight of the day? Generally
the answer is "yes," but it depends on several factors.
The main reason it's a good idea to top off all fuel tanks
before the plane sits overnight is to prevent condensation in the
fuel. Air inside a fuel tank will cool as the overnight air
cools. If the air is moist and the temperature cools to the
dew point, liquid water will condense from the air space in
less-than-full tanks and drop into the fuel. Filling the tanks
minimizes air space in the fuel system (it will never completely
eliminate it), making water accumulation overnight less likely. Of
course water in aviation fuel will degrade engine performance and
may cause a total engine failure.
Filling up right after landing also ensures you'll be there to
supervise fueling, and makes it less tempting to "fire up and fly
away" in a low fuel state if time pressures, a line at the fuel
pump or a broken-down fuel truck affect your next planned
departure.
Top it off?
There are some times, however, when you may not want to fully
fuel the airplane before it sits overnight. Most airplanes can
carry a full cabin load or a full fuel load, but not both. If you
think you may need to carry a full load on the next trip, or you
can't predict the cabin load (example: charter flying), you may
need to hold off on the final fuel load until just before taking
off. In that case, it's best to partially fill the tanks
(minimizing air space) and drain the sumps before completing the
just-before-takeoff fuel load (to remove overnight condensation
before it mixes with the new fuel).
You might also avoid completely filling the tanks if the air is
cool and is expected to heat up significantly any time before you
fly again. Fuel expands with heating, often enough to flow outward
through the tanks' air inlet vent lines. In some designs there is
no check valve to prevent fuel from draining overboard through the
vents; once started fuel may siphon overboard, partially or even
completely draining the tanks.
Aero-tip of the day: Fill the fuel tanks as
much as possible before parking the airplane overnight, but fill it
completely only if it makes sense to do so.