Matt Whiting wrote in news:foeQi.309$2n4.18956
@news1.epix.net:

Stefan wrote:
Matt Whiting schrieb:

And Lycoming benefits if your engine lasts fewer hours.

So avoiding shock cooling actually lowers its life span? Wow.

You have no evidence that following Lycoming's recommendations avoids
the mythical shock cooling demon or that it lengthens engine life. My
experience is that the engines that are run the hardest also last the
longest. I'm basing this on everything from chainsaws to lawnmowers
to
motorcycles to cars to trucks to off-road heavy equipment (dozers,
skidders, etc.) to airplanes (trainers, air taxi operations, cargo).

I'm personally not convinced that Lycoming's recommendations lengthen
engine life.

Matt



Shock cooling isn't mythical. It's a fact. It's a physical law.

Any component subject to heating is subject to this law. If you take a
piece of metal and heat it rapidly on one side, that side will expand
more rapidly than the other. This gradient of temp will cause a
difference in physical size one side to the other. The elastic stress
induced by this is cyclically compounded and the resultant locked stress
points that build up in the material, particularly if it's a brittle
material like cast iron, will eventually fail, given time.
The speed at which these stresses are imposed are critical. Speed
because if you introduce the heat gradually (decrease the speed of the
overall temp change), it's given a chance to get to the other side and
expand the other side at a rate not quite so dramatically different as
the side the heat is applied to. Simple eh?
The quicker you insert heat on one side of the material, the greater the
load on the opposite side and the more likely minor damage events
(cracks on a near molecular leve) are occuring. These tiny bits of
damage will become stress risers for the next time th ematerial is
loaded and the cracks will continue to expand until a failure of the
component occurs.


I think Lycoming probably figured most of this out in the 1920s,
Continental even earlier.

However, if it's anectodal evidence that is required...
I've worked for recip operators where this was a daily problem. In
glider tugs, for instance, jug failures were common. Operations had to
be tailered to minimise the strain, and these adopted procedures worked.
I've also flown big recips and they also required careful management to
avoid blowing the top of a jug off. The emphasis is always on minimising
the speed at which th etemps change.
Jets are no different. Blades ae subject ot enoromous thermal stresses,
and all of the procedures laid down by the manufacturers are designed to
extend engine life as much as possible. Everything from engine startup,
through warmup times to takeoff (admittedly not all manufacturers have
done this over the years and there are other reasons for this) to
reduced power for climb to care in reduction of power at top of descent
are all used to this end.


Other bugbears of the punished engine are micro-seizures and excessive
friction due to reduced or even sometimes increased, clearances due to
rapid temp changes.

If the aircraft is being manuevered violently along with rapid power
changes, you can add precession to the damage being caused.In
aerobatics, obviously.
That is why, even though the pilot must be prompt with his power
changes to maintain control of his speed, it is accepted that it is best
practice to make these changes as smoothly and deliberately as possible
whilst still meeting the demands of aircraft control.
But even relatively mild manuevering combined with rapid throttle
changes will induce the same stresses to a lesser degree and are
therefore undesirable.

None of this is new info , of course. I have engine operating manuals
from the 1930s that address all of these issues and modern manuals
remain pretty much the same. These principles were understood long
before that. Interestingly though, I have a workshop manual for a 1933
Le Blond that talks about corrosion on the inside of a hollow crank,
it's causes and prevention, all of which could directly apply to that
debacle with lycomings. Seems some lessons have been forgotten!
The manufaturers have no interest in misleading anyone into screwing
their engines up to increase their profits. They rely on their
reputations as builders of reliable engines to increase their sales.
An engine that never makes it to TBO would be a liability to them..
Want to increase your engine life and reliability? Don't bash your
throttle around.

For real improvement in addition to these suggestions, install a pre-
oiler and oil heater. Your bottom end will last forever and the top will
be much improved as well. If you're operating on condition you might get
double the TBO overall or more! A really good filter is essential for
longevity as well.Get an STC for one if there's not one readily
available for your airplane..



Bertie