Engine out practice

Stefan,

Evidently, Lycoming knows how to build engines


Oh? The AD record seems to indicate otherwise.

--
Thomas Borchert (EDDH)

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

Stefan wrote in
:

Matt Barrow schrieb:

Thomas offers data and evidence, Lycoming offers anecdote and
legend.
Lycoming offers running engines. Thomas offers words.

Try something other than "Argument from Authority", such as EVIDENCE.

Evidently, Lycoming knows how to build engines. Evidently, Lycoming
has a lot of experience by looking at used engines while overhawling
them. I don't know how many engines Thomas has built or overhauled. I
don't even know where his data comes from and how it was collected.

Or, if you can show that Lycoming HAS NOT been shown to frequently be
FOS,

No idea what a FOS should be. Please write in a language I understand.

then you can make their case.

I'm not making anyone's case. In fact, I couldn't care less, as I'm
happy enough to operate a liquid cooled engine with 21th century
technology.



Actually, that engine is 19th century technology with some cute and badly
thought out curliecues added.


Bertie

Stefan,

And two more thoughts:

Evidently, Lycoming knows how to build engines.

Which doesn't directly mean anything with regard to operating them.

Evidently, Lycoming has
a lot of experience by looking at used engines while overhawling them.

Which, again, doesn't directly say much about why they need overhauling.
That cracked cylinder head doesn't come with a sign next to the crack
reading "I was caused by shock cooling".

--
Thomas Borchert (EDDH)

Bertie the Bunyip wrote:
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.

A physical law, eh? I've had 8 years of engineering school and haven't
seen this law. Can you provide a reference to the law of shock cooling?
I searched for the "law of shock cooling" in Google and came up empty...


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.

Yes, I'm well aware of thermal expansion and its affects. When an
engine is pulled to idle, the cylinders and heads are getting cooled
from both sides, the outside via airflow and the inside via airflow
through the engine. The far greater differential is under full throttle
during the first take-off when the engine has not yet reached thermal
equilibrium and you are heating it intensely on the inside and cooling
it on the outside.

If people wanted to talk about shock heating, then I'd be much more
willing to believe them and this fits the physics a lot better in my
opinion. Shock cooling is much less an issue from both a physics
perspective and an experience perspective.

Matt

Matt Whiting wrote in
:

Bertie the Bunyip wrote:
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.

A physical law, eh? I've had 8 years of engineering school and
haven't seen this law. Can you provide a reference to the law of
shock cooling?
I searched for the "law of shock cooling" in Google and came up
empty...


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.

Yes, I'm well aware of thermal expansion and its affects. When an
engine is pulled to idle, the cylinders and heads are getting cooled
from both sides, the outside via airflow and the inside via airflow
through the engine. The far greater differential is under full
throttle during the first take-off when the engine has not yet reached
thermal equilibrium and you are heating it intensely on the inside and
cooling it on the outside.

If people wanted to talk about shock heating, then I'd be much more
willing to believe them and this fits the physics a lot better in my
opinion. Shock cooling is much less an issue from both a physics
perspective and an experience perspective.


It's the same either way. Cooling and heating are two sides of th esame
coin. It takes time to disapate heat and it's not so much the passage of
heat from one area to another (or the disappation, it's irrelevant) but
the speed at which the cooling or heating is taking place and thus the
gradient across the material.
In short, you take a frozen lump of metal and apply a torch to one side
you have a problem.
Take a cherry red pice of metal and put some ice on side and you have
the same problem (more or less, and disregading crystalisation)


Bertie

On Oct 13, 8:55 pm, Matt Whiting wrote:

It seems to me that upon engine start the pistons would heat up much
faster than the cylinders causing the same net affect as cooling down
the cylinders faster once hot. Either way the pistons are hotter than
the cylinders.

Matt

At idle or low power settings there is little heat generated. So
little, in fact, that it can take forever to get the CHT warm enough
to carry out the runup when the temps here are -15 or 20°C. The
cylinder has plenty of time to warm up. It's the sudden removal of the
heat source when the atmosphere is really cold that problems might
arise. In Canada we have to think about it a little more than the
pilot in Arizona. Pistons are aluminum and expand at twice the rate of
the steel cylinders, clearances get small during operational temps,
and shrinking a cylinder quickly around a hot piston is asking for
scuffing or seizure.
We run six Lycs in flight training ops. They usually reach TBO
in good condition. They get a lot of rapid throttle movement, even
though I constantly make noises about not abusing the engines. In my
opinion, opening the throttle too fast can do more damage than closing
it too quickly. Cylinder pressures can get high enough with rapid
throttle movement to cause detonation, however briefly, and cracking
of various parts might occur. A pilot who bangs the throttle open is
applying high manifold pressures to an engine at very low RPM, the
definitive extreme oversquare situation.
Closing it quickly in flight will cause afterfiring (lean
mixtures that often don't fire in the cylinder, igniting instead in
the hot muffler). Cracking of exhaust components is a risk there, and
we find that often enough.
Our students get plenty of forced-approach practice. The engine
is throttled back in two or three or four seconds. Transport Canada
tells us that some practice forced landings (PFLs) end in the real
thing when the carb ices up during the glide. The syllabus calls for
an application of power for a few seconds every 1000' of altitude loss
to clear the engine, but since the exhaust system is cool in the
glide, it can take much more than a few seconds to clear any ice
accretion and the engine might not respond when necessary.
For those lucky ones with injection, carb ice is not a problem,
but most of us are stuck with carbs and need to be thinking, when we
check the weather before the flight, about what the atmosphere is up
to. We wouldn't dive into unknown waters without making sure there
weren't hidden rocks or sharks around, and we shouldn't launch without
knowing the temp and dewpoint spread, right?

Dan

Newps schrieb:

The engine manufacturers are about the last place I'd look for engine
management techniques.

Interesting point of view. Please explain.

Newps schrieb:

Lycoming and Continental offer no science whatsoever to back up their
recommendations. There are several companies that can show you hard
scientific data to disprove what the engine manufacturers claim.

Which are those companies and where do I find those data?

Stefan writes:

Interesting point of view. Please explain.

There is a potential conflict of interest in that an engine that lasts a long
time delays a replacement sale. However, other factors come into play, such
as liability, reputation and customer goodwill, and so on, so it's not clear
that a manufacturer wouldn't provide good advice.