Engine out practice

Jay Honeck wrote:
The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.

Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.

How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

Matt

Matt Whiting wrote:
When I practiced in my Skylane and also in the club Arrow, I retarded
the throttle smoothly in probably 2-3 seconds. I didn't worry about
shock cooling and never saw any signs of distress in either the O-470 or
the O-360.

I have an 0-320, and we probably take 3-5 seconds to smoothly retard the
throttle to idle during simulated engine failure practice. Thinking back
to the *actual* engine failure due to oil loss, the time elapsed between
seeing no oil pressure on the gauge, the initial obvious signs that the
engine was seizing (bucking and shaking), and the time it quit
completely was probably a total of 10 seconds. So comparing the
simulated engine failure to THAT type of actual engine failure, taking 5
seconds to retard the throttle is NOT out of the realm of realism or
accuracy with regard to simulated practice.

To Jay, do you monitor your engine analyzer when you go from cruise
power into the pattern and then pull the throttle back during your
approach? How gradually do you pull power back there, and how do the
temps on the analyzer compare to what you did in the simulated
engine-out practice?

Shirl

Matt Whiting wrote:
Jay Honeck wrote:
The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.

Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.

How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

It doesn't (in metals) unless the temperature change is very high and
very localized as in welding.


--
Jim Pennino

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Gene Seibel wrote:

I'm not an expert, but it seems to me that the important thing is to
reduce airspeed immediately when reducing power. It's the wind
whistling through an idling engine at 140 knots that's going to do
some serious shock cooling.
--
Gene Seibel
Tales of Flight - http://pad39a.com/gene/tales.html
Because I fly, I envy no one.

Which is what you are supposed to do anyway in an engine out; immediately
reduce airspeed to best glide.

--
Jim Pennino

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wrote:
Matt Whiting wrote:
Jay Honeck wrote:
The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.
Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.

How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

It doesn't (in metals) unless the temperature change is very high and
very localized as in welding.

That's my understanding also, but I wanted to see Jay's information.
Maybe he's found some phenomenon I'm not aware of.

Matt

To Jay, do you monitor your engine analyzer when you go from cruise
power into the pattern and then pull the throttle back during your
approach? How gradually do you pull power back there, and how do the
temps on the analyzer compare to what you did in the simulated
engine-out practice?

Yep. The shock-cooling alarm never goes off during a regular
approach, because of the gradual nature of things. By the time we
enter downwind, we've got the prop and mixture full forward, and are
adjusting manifold pressure (throttle) only slightly to control
airspeed. We're looking for 100 mph/90 knots on downwind.

This wind-down from cruise speed (160 mph/140 knots) usually takes
several minutes, unless we're being asked to keep our speed up at a
controlled field. We generally carry power into the flare (hey, it's
a Cherokee, and a nose-heavy one at that), slowly retarding power as
we touch down.

Apparently this procedure (which we do without thinking about it) is
engine-friendly enough to keep the temperature rate-of-decline outside
of the shock cooling alarm's parameters.

In the future I think we'll practice slow flight (which mimics this
whole engine management procedure) before practicing engine-out
stuff. That should prevent the whole shock-cooling problem,
methinks.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.

Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.

How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

How 'bout this: It's the disparate rates of cooling in some parts of
the engine (versus others) that causes the differential cooling that
induces stress?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

Jay Honeck wrote:
The issue with shock cooling isn't the rate of cooling per se, but
rather stress induced by differential cooling.
Actually, I think it is the rate of cooling *and* the differential
cooling -- if it exists at all. Like you, I am skeptical -- but am I
willing to bet $25K on it? Nope.
How does the rate affect things? I have a masters in structural
engineering and work for a materials company so don't be afraid to get
technical. :-)

How 'bout this: It's the disparate rates of cooling in some parts of
the engine (versus others) that causes the differential cooling that
induces stress?

Yes, that is what I said originally. It is differential cooling that
causes the problem, not the rate of cooling itself. If you could cool
the entire engine uniformly, I don't think it would matter much how fast
you cooled it.

It isn't the rate itself that causes a problem, it is the difference in
rates from one location to another. However, I still think that the
greatest thermally induced stress occurs during the initial heat-up from
a cold start, but I don't have any data to confirm that and I don't have
an instrument airplane with which to collect the data.

Matt

A slow reduction in power setting certainly isn't realistic. I've had a few
power failures in my time (all in twins) and in every case the loss was
fairly sudden. I've never run out of fuel, but I have run a tank almost dry
on purpose, and the associated coughing and sputtering gave me plenty of
warning.

Bob Gardner

"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.

Since the damage (so to speak) had already been done, I continued the
descent toward an Illinois corn field. With the harvest under way, I
had my choice of:

- Freshly harvested corn stubble, not plowed
- Freshly harvested crops, plowed dirt
- Unharvested corn or winter wheat

I opted for the corn stubble, as the stalks would hold the soil
together firmly and not present as much "flip force" to the landing
gear as the plowed or unharvested field. I took it down to 200 AGL
before applying power and heading home, satisfied that we would have
survived and giving the farmer a nice show.

For you aircraft owners who do this regularly, how slowly do you
retard the throttle to prevent shock cooling? (I know -- does shock
cooling really exist? For purposes of this discussion, I'll pretend
that it does.)

Given that the power reduction must be incredibly gradual, do you feel
that this exercise is realistic? There really is no chance to
simulate how you must "suddenly" find best glide speed (after your
engine has presumably just crapped out), since you're gradually
reducing your speed along with your power. Or do you put the plane
into a shallow dive as you reduce power, so as not to lose airspeed?

It's funny -- as renters we practiced this all the time. Now, after 9
years of ownership, we haven't practiced it in ages -- and didn't even
realize this lack until Shirl's comments in Paul's thread. Another
good thing about "belonging" to this newsgroup...

Thoughts?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

In article .com,
Jay Honeck wrote:


In the future I think we'll practice slow flight (which mimics this
whole engine management procedure) before practicing engine-out
stuff. That should prevent the whole shock-cooling problem,
methinks.

Slow flight might increase the problem. You're mushing along with poor
flow through the cowling, low airspeed and using power...perhaps you're
going to increase engine temp. over cruise.

As for the analyzer warning. I had one on my 182 when hauling jumpers.
Just pushing the nose over at the top of the climb *without reducing
power* would result in a "shock cooling" alarm, just the increase in
airspeed created a cooling rate that exceeds the limits. I quickly
learned to ignore the shock cooling warning.

Trainer aircraft are flown hard all the time. Students/renters cram the
power in on takeoff and yank it to idle on downwind time after time.
Those engines last well.

I flew jumpers for 17 years in 182s and 206s. With the exception of one
airplane flown by an idiot (this guy would cram the power in right after
start with no warmup) we didn't have to replace cylinders, engines went
TBO or beyond.

From my experience more damage is done on power increases than
reduction. Be as gentle as you can to your engine but don't go crazy
about the shock cooling thing.