On Sun, 23 Apr 2006 18:36:42 -0400, Roger
wrote:

On Sun, 23 Apr 2006 00:24:07 -0400, "Peter Dohm"
wrote:

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,

We must live in different climates.
Here in Central Michigan it's not unusual to find the airplane
"dripping" wet with temperature changes.

I have an garage attached to the house. It's not unusual to find the
cars sweating with temperature and humidity changes. I had to work on
the garden tractor today and the engine is wet from the humidity and
temperature changes. (It's been 100% since last night and rained most
of the day.

Current temp is 50F) The weather for the area says 85% but it's
raining with light fog. Of course the briefing I printed out at 3:00
AM says visibility 6, 5000 sct, 10,000 bkn with temp 4 in light rain
and thunderstorms with 5,000 sct.
It's now starting to clear from the west and MOP is showing Vis 10,
1000 sct, 1500 bkn. Most of the afternoon was 1 and 500.

b) an engine covered with plastic and sitting on the ground will
accumulate MASSIVE amounts of water,

We get the same thing in our hangars on the airplanes and engines.
If I went out to the hangar today I'd find the plane dripping. The
temp is dropping slowly. It'll be near the upper 30's tonight.
Opening the cowl would find water droplets on the cylinders and
crankcase.

This is in a well ventilated metal hangar with a concrete floor.

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%.

Also the engine breathes in and out with temperature changes. So
cooling not only raised the relative humidity inside, it brings in
more cool, damp air.

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 it's going to set long it needs to be protected not ground run
according to the engine manufacturers literature.

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

If you are going to ground run it you want to bring it up to operating
temp. It's the short runs that not only don't evaporate much of
anything they put a lot more *stuff* into the oil as the cold engine
isn't running as efficient as a warm one and the byproducts can
condense inside.

Find a good clean spot on the ramp, let the engine warm up normally.
Then stand on the brakes and wind 'er up for a prolonged run. Of
course then makes the neighbors unhappy.

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.

They usually put desiccants in the plugs and plug off the intake,
exhaust and breathers.

Go into Pioneer Airport and look at the antiques that have the engines
preserved. I've forgotten the term, but at any rate each prop has a
note on it that says "Do not turn prop. Engine has been preserved".

3) Yep, I agree that's an old mechanics tales as well. OTOH, any reason
to fly might bew a good reason.

Might be but both Lycombing and Continental subscribe to it.

Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

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

If you feel the need to get the oil moving in a stored engine, crank
it over with the fuel and mags shut off untill full oil pressure is
acheived, then recharge the battery. Do NOT ground run for short
periods without getting the oil temperature up to dry it out.
Particularly important with top-cam engines, as the cams and tappets
are very prone to condensation induced corrosion failures. And worse
with Synthetic oils than standard petro oils.
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