I just watched a program about the huge Oresund bridge between Denmark
and Sweden, and there was a segment about how the corrosion problem for

the bridge was dealt with. Instead of painting, they use sealed
compartments that have the air humidity kept below 60%. This they said
eliminates corrosion. This started me thinking about the corrosion we
aircraft owners are told to guard against, since I have personally been

told by an overhaul shop, that half of all the engines he sees that
need work, need it because of corrosion. There are several "facts" that

I am beginning to question as to their validity. The ones that come to
mind a

1) You have to get the oil up to 180 deg F or the water in the oil
won't evaporate.


2) Starting and ground running the engine for a minute or so is the
"worst" thing you can possibly do.


3) Flying for an hour will "clean" the oil (or at least evaporate the
water, preventing acid formation) so that it doesn't turn to acid and
dissolve the engine while sitting idle.


----------------snip-----------

Blue Skies
Rusty

1) In automobiles years ago, the standard assertion was that you had to
get the engine temp up to 160 degrees for the water to evaporate from the
oil. As it happened, that was actually measuring water temp. 160 degrees
was simply the most common coolant thermostat temperature in those days. So
if the same jack asses are still breathing in and out, they are probably
claiming that 205 degrees is mandatory today.
About all I know for sure about water water condensing into much of
anything is:
a) it almost never happens inside a garage or hangar,
b) an engine covered with plastic and sitting on the ground will
accumulate MASSIVE amounts of water,
c) a small light object such as a medicine vial with a snap type lid will
accumulate water outdoors in the shade--such as under a patio roof.
As to evaporation, warmer is faster; but if the ambient humidity is
100%, a surprisingly small temperature rise (10 or 20 degrees IIRC) above
ambient will bring the relative humidity inside the engine below 50%.
2) I am not an aircraft and engine mechanic. However, I am confident
that running a Lycoming engine to circulate the oil is FAR BETTER than
letting it stand; both for the cylinders and the famous cam and tappets.
If I owned it and was not flying at least weekly, you're damned
right I'd ground run it! Not very long, but enough to circulate the oil and
at least get the temp needle off the peg. If, for any reason I was unable
to run the engine frequently, I would certainly place dessicant packages in
the intake(s), exhaust(s), and crankcase breather.
3) Yep, I agree that's an old mechanics tales as well. OTOH, any reason
to fly might bew a good reason.

As to the bridge, apparently the Danes and Sweedes haven't shelled one
another across the straights for so long they've forgotten about that. ;-)
In any case, small amounts of surface rust are trivial for a structure like
a bridge; but seriously debilitating inside an engine!

Peter