On Sat, 23 Oct 2004 23:18:55 -0700, "Peter Duniho"
wrote:


Yes, a week is short enough for corrosion to occur. A few hours is, for
that matter (and that's the literal answer to the original question), and of
course every day you go without flying incurs additional damage.

lets blow away the mystery here. yes corrosion can start in a few
hours ....but why????

But honestly, you obviously don't own an airplane. No owner would seriously
consider pickling the engine for a mere week of downtime. Most owners
wouldn't go to that much trouble for less than a couple of months or more of
downtime. It's just not practical.

my aircraft with an O-200 in it has sat for a year at a time unused on
two occasions. on the first occasion the accessory drive at the back
of the engine disintegrated requiring some major work. on the second
occasion it has now flown 2 years subsequently incident free. why??

Corrosion is a constant process, and the longer you go, the worse it is.

bull**** (and I mean that in the nicest way :-) )

It would be best for an airplane to be flown at least once a day, if not
multiple times a day. A week's not bad, nor are two. Beyond that, you are
likely going to see noticeable long-term effects on maintenance and engine
life.

ok why??? what is the actual process going on here that makes the
running better?

You may be able to minimize the effects
what effects???
by using certain oils (Exxon claims
to have an oil that nearly eliminates corrosion even after long periods of
time), or that might just be marketing hype. I'm not aware of any unbiased
tests that would indicate one way or the other.

of course there are. you just havent read of them. :-) :-)

ok let me answer the questions I posed in tickling peter in the ribs.

moisture in the engine is primarily the bad guy here.
it condenses in the oil as the engine cools after use and will
actually emulsify (well that it what it looks like to me) through the
oil on to the steel surfaces and set off corrosion.
it is worse in winter than in summer and this is probably the one
thing that a hangar offers no protection against.

in my aircraft the first time it sat for a period unloved (the last
owner was sick and grounded for the year) there must have been
moisture/water in the oil. the bearing surfaces in the gear train
within the accessory case all corroded on to the gears. of course as
well as gluing the bits together the corrosion roughens the bearing
surfaces.
crud in the gallery obstructing the oil flow and roughened bearing
faces saw the gear train sieze and part company about half an hour
into the first subsequent flight.
the second time I took precautions to minimise water in the oil and
had no identifiable damage.

there are two methods of making sure the oil and the inside of your
engine is moisture free.
always fly the engine for a minimum of an hour after it has warmed up.
this will assist considerably in boiling off the moisture in the oil
(so thats what the breather tube is for on the engine :-) )
the other technique if you can only make short flghts is to change the
oil regularly. fresh oil is moisture free.
a third technique is to drop the oil into a container. boil it dry on
a stove then put it back into the engine. oil fires are horrific
though and nowhere as much fun as just flying it dry.

if you know that the aircraft is to sit for a long period put fresh
oil into it and run it for a minute or two to get fresh oil in all the
galleries and bearing surfaces then shut it down.
worked for me.

Stealth (there you go a mystery evaporated) Pilot
australia.

btw this matter has been subject of safety advisories in this country.