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"