Engine out practice

"Jay Honeck" wrote in message
ups.com...
As previously noted (in the thread about Paul's wife getting scared),
Mary and I had virtually stopped doing this kind of flying for fear of
harming our (very expensive) engine. A lively debate ensued as to
whether or not repeated high-to-low-to-high power applications would
wear out your engine any faster than would normal operations.


Jay, the cylinder barrels on your engine are steel with air-cooling fins
attached. Your pistons and cylinder heads are aluminum alloy. The two
metals will expand and contract at different rates when heated or cooled.
Think about the way the thermostat in your house works. A bi-metal strip
(strip of metal composed of one type of metal on one side and another type
on the other), when heated or cooled bends because of the different
expansion rates of the two metals. When I think of shock cooling I think of
the sudden removal of the heat source (abrupt power reduction) along with
the different metals contraction rate (steel with air blowing over it's
cooling fins versus aluminum inside the barrel with hot oil being sprayed on
it). It is easy for me to visualize the scuffing that can occur because of
the reduced clearances as the barrel contracts onto the piston. The same in
reverse would hold true for shock heating.

Whether any of this is true I don't know, but I am with you that gradual
increase or reduction of power seems less likely to cause damage to an
aircooled engine.

--
*H. Allen Smith*
WACO - We are all here, because we are not all there.

"Jay Honeck" wrote in message
ups.com...
As previously noted (in the thread about Paul's wife getting scared),
Mary and I had virtually stopped doing this kind of flying for fear of
harming our (very expensive) engine. A lively debate ensued as to
whether or not repeated high-to-low-to-high power applications would
wear out your engine any faster than would normal operations.

I eventually agreed that gradual power changes would not unduly harm
an air-cooled engine, and vowed that I would endeavor to practice this
most-important skill on our next flight. And we did.

We were on a flight back from Galesburg, IL when I started the
procedure, and very gradually began a power reduction whilst in cruise
flight at 3500 feet. I took a full minute to reduce the power to
idle, watching our (newly reinstalled) JPI EDM-700 engine analyzer for
signs of stress.

As RPMs dropped below 1000, the "shock-cooling alarm" suddenly went
off, flashing its dire warnings that EGTs had dropped beyond (and
faster) than recommended limits. (I can't remember what the threshold
is for that alarm -- it's preset.)

This despite my most careful power reduction, which (obviously) wasn't
slow enough.
....

Thoughts?

You're worrying about virtually nothing!
http://www.avweb.com/news/maint/182883-1.html

Shock Cooling: Myth or Reality?

Powerplant management guru Kas Thomas of TBO ADVISOR examines the physics
and metallurgy of "shock cooling" and concludes that, contrary to the
conventional wisdom, it is not a major contributor to cylinder head
cracking.

Matt Barrow schrieb:

You're worrying about virtually nothing!
http://www.avweb.com/news/maint/182883-1.html

Shock Cooling: Myth or Reality?

Powerplant management guru Kas Thomas of TBO ADVISOR examines the physics
and metallurgy of "shock cooling" and concludes that, contrary to the
conventional wisdom, it is not a major contributor to cylinder head
cracking.

Lycoming says otherwise:
http://www.lycoming.textron.com/supp...Operations.pdf

Lycoming
Sudden cooling is detrimental to the good health of the piston aircraft
engine. Lycoming Service Instruction 1094D recommends a maximum
temperature change of 50° F per minute to avoid shock-cooling of the
cylinders.

Operations that tend to induce rapid engine cooldown are
often associated with a fast letdown and return to the field after
dropping parachutists or a glider tow. There are occasions when Air
Traffic Control also calls for fast descents that may lead to sudden
cooling.

The engine problems that may be expected when pilots consistently
make fast letdowns with little or no power include:

1. Excessively worn ring grooves accompanied by broken rings.
2. Cracked cylinder heads.
3. Warped exhaust valves.
4. Bent pushrods.
5. Spark plug fouling.
/Lycoming


Be aware that "powerplant management guru Kas Thomas" won't buy you a
new engine if you happen do damage yours by following his recomendations.

It's every operator's choice whether he prefers to believe the engine
manufactorer or some guru.

Stefan

"Stefan" wrote in message
...
Matt Barrow schrieb:

You're worrying about virtually nothing!
http://www.avweb.com/news/maint/182883-1.html

Shock Cooling: Myth or Reality?

Powerplant management guru Kas Thomas of TBO ADVISOR examines the physics
and metallurgy of "shock cooling" and concludes that, contrary to the
conventional wisdom, it is not a major contributor to cylinder head
cracking.

Lycoming says otherwise:
http://www.lycoming.textron.com/supp...Operations.pdf

Lycoming
Sudden cooling is detrimental to the good health of the piston aircraft
engine. Lycoming Service Instruction 1094D recommends a maximum
temperature change of 50° F per minute to avoid shock-cooling of the
cylinders.

Thomas offers data and evidence, Lycoming offers anecdote and legend.

Takes yer picks.

Matt Barrow schrieb:

Thomas offers data and evidence, Lycoming offers anecdote and legend.

Lycoming offers running engines. Thomas offers words.

"Stefan" wrote in message
.. .
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.

Or, if you can show that Lycoming HAS NOT been shown to frequently be FOS,
then you can make their case.

Stefan wrote:
Matt Barrow schrieb:

Thomas offers data and evidence, Lycoming offers anecdote and legend.

Lycoming offers running engines. Thomas offers words.

And Lycoming benefits if your engine lasts fewer hours.

Matt

Stefan wrote:
Matt Barrow schrieb:

Thomas offers data and evidence, Lycoming offers anecdote and legend.

Lycoming offers running engines. Thomas offers words.


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.

Stefan wrote:

Lycoming says otherwise:


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

Newps schrieb:

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

Interesting point of view. Please explain.