Engine out practice

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

Remove .spam.sux to reply.

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

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

"Matt Whiting" wrote in message
news
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

By implication, a fast cooling rate would cause *more* differential cooling,
since the cylinders cool from the fins inward. The faster the cooling, the
higher the delta-T between the internal and external surfaces of the
cylinders. The higher the delta, the more internal stresses on the cylinders
due to the different growth between the hot and cold surfaces.

But you already knew that and were just being difficult, eh?

KB

Kyle Boatright wrote:
"Matt Whiting" wrote in message
news
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

By implication, a fast cooling rate would cause *more* differential cooling,
since the cylinders cool from the fins inward. The faster the cooling, the
higher the delta-T between the internal and external surfaces of the
cylinders. The higher the delta, the more internal stresses on the cylinders
due to the different growth between the hot and cold surfaces.

But you already knew that and were just being difficult, eh?

It is a subtle point maybe, but an important one. It isn't the rate of
cooling that matters. It is a difference in rate between two locations.
Faster cooling doesn't necessarily a greater differential, it all
depends on how the cooling is done.

In some materials and at some temperatures, the rate of cooling can
change the fundamental material properties. That is a different issue
than what is involved with engines.

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

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"

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.

Jay:
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.

Dale:
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.

That was my first thought, that slow flight would increase temp and,
therefore, how would it prevent the shock-cooling problem (if indeed it
is one)?