Shock Cooling

Douglas

Douglas

Old School KSUX
I have to admit that I don't know much about it.

I was flying a normally aspirated Baron 58 the other day. The company guy I was with really wanted me pull back no more than two inches per two minutes. I was planning on reducing the MP 5". (from 20" to 15" slowly.) Obviously I did just that; he is a very knowledgeable guy that I respect.

Now I did part of my commercial multi-add-on in a Baron 55 (Norm. Asp.) During that training we didn't do the 1"/1 min technique.

I need a quick explanation of what engines shouldn't be pulled back more than 2" at a time and how do I tell, because my old school of thought was that only Turbocharged engines need to be walked by 1"/1 Min. So if that rule of thumb doesn't work, what does?

I also found this article
http://www.avweb.com/news/maint/182883-1.html
Any thoughts?
 
my understanding is pretty limited, but i figure any engine that of any size (200hp or better) should be cooled slow enough to let thick metal cool evenly. In the 206 (io540) we figured about an inch a minute, and i think that is the same engine on a baron... it's dependent on the pilot and conditions, but i figure that you mine as well treat the block as nicely as you can, as the baron is not much of a glider.:D
 
Douglas said:
I need a quick explanation of what engines shouldn't be pulled back more than 2" at a time and how do I tell, because my old school of thought was that only Turbocharged engines need to be walked by 1"/1 Min. So if that rule of thumb doesn't work, what does?
Click to expand...

"Shock Cooling" is something that has gone from a freak event (usually brought on by gross abuse of the engine) to a bogey man that will cause your engine to shatter if you look at it wrong. Many pilots, owners, and CFIs have gone WAY overboard in trying to prevent something that isn't really an issue in the first place. This myth has only been around about 15 years, (which coincides with Contential's drop off in cylinder reliability).

The biggest vairable in cooling an engine is airflow (ie. airspeed), second is power. If you make a modest power reduction (5" or so) and keep a constant airspeed (500FPM) descent, you'll be just fine. Turbocharged airplanes obey the exact same rules, only they run a little hotter all the time.

Also, 30-40% of the total engine cooling is done by way of the oil. The hot oil circulating the engine will keep it warm no matter what you do.

If "shock cooling" was such a hazard, then why do skydiving and areobatic airplanes have engines that run to TBO and beyond? Jump planes spend all day cooking their engines by climbing to alt, then give it a bare 2 mins to cool, followed by a Vne descent. Aerobatic planes use the same engines, power on, power off, hang on the prop, nose dive, all day. If that dosen't cause problems, then your normal flying won't.
 
Honestly... the next time I bring the throttle(s) back from 22" to 15" and establish a descent without a planned out cooling period and someone gives me crap for it due to "shock cooling", can I tell them to shove it and do some research, figuratively speaking?

That was meant to be a serious question, despite the presentation :)
 
c172captain said:
Honestly... the next time I bring the throttle(s) back from 22" to 15" and establish a descent without a planned out cooling period and someone gives me crap for it due to "shock cooling", can I tell them to shove it and do some research, figuratively speaking?

That was meant to be a serious question, despite the presentation :)
Click to expand...
Depends on whether they own the airplane or not. "But some dude on the interwebs said..." isn't likely to be a reasonable justification. Do some more research on the subject; there are some good articles on AvWeb, for starters.
 
aloft said:
Depends on whether they own the airplane or not. "But some dude on the interwebs said..." isn't likely to be a reasonable justification. Do some more research on the subject; there are some good articles on AvWeb, for starters.
Click to expand...

But dudes on the interwebs is where I get all my "official" information! :D
 
USMCmech said:
"Shock Cooling" is something that has gone from a freak event (usually brought on by gross abuse of the engine) to a bogey man that will cause your engine to shatter if you look at it wrong. Many pilots, owners, and CFIs have gone WAY overboard in trying to prevent something that isn't really an issue in the first place. This myth has only been around about 15 years, (which coincides with Contential's drop off in cylinder reliability).

The biggest vairable in cooling an engine is airflow (ie. airspeed), second is power. If you make a modest power reduction (5" or so) and keep a constant airspeed (500FPM) descent, you'll be just fine. Turbocharged airplanes obey the exact same rules, only they run a little hotter all the time.

Also, 30-40% of the total engine cooling is done by way of the oil. The hot oil circulating the engine will keep it warm no matter what you do.

If "shock cooling" was such a hazard, then why don't skydiving and areobatic airplanes have engines that run to TBO and beyond? Jump planes spend all day cooking their engines by climbing to alt, then give it a bare 2 mins to cool, followed by a Vne descent. Aerobatic planes use the same engines, power on, power off, hang on the prop, nose dive, all day. If that dosen't cause problems, then your normal flying won't.
Click to expand...

:yeahthat:

For what it's worth, I've never seen a manufacturer's checklist/POH call for incremental power reductions for shock cooling. This leads me to believe the true experts don't consider it a significant factor.

I've also gone through T206H training at Cessna's factory and the Cessna instructor basically said to be reasonable with power changes, use the cowl flaps appropriately to keep everything in the green, and don't worry about it.

I've also talked to the owner of the dropzone where I fly skydivers and he says in nearly 30 years of operating a C-182 jump plane he's never cracked a cylinder. That's following a profile of mixture rich / cowl flaps closed / RPM and MP at bottom of their green arcs / 160 MPH descents after running the engine at full power for 20 minutes in an 85 MPH climb.

Long story short, shock cooling isn't a huge concern of mine.
 
c172captain said:
Honestly... the next time I bring the throttle(s) back from 22" to 15" and establish a descent without a planned out cooling period and someone gives me crap for it due to "shock cooling", can I tell them to shove it and do some research, figuratively speaking?

That was meant to be a serious question, despite the presentation :)
Click to expand...


If it's your plane, yes.

If it's their plane, try to show them some of the articles you found.
 
jrh said:
Long story short, shock cooling isn't a huge concern of mine.
Click to expand...
No offense, but your episode on Sunday suggests that your list of things that concern you might not be as comprehensive as it should..

Methinks I'd reassess my stance on a wide variety of topics after such a wakeup call. Maybe that's just me.
 
Posting a bit angry tonight, are we?
Aloft: Uh, why does it really suck? Because no one's offered you an RJ on a silver platter? Please. With 1100 hrs, you're barely qualified for a Pt 121 job.
Click to expand...

JRH has proven himself here many times.
That is not called for.
 
IMO ignore anything you have ever heard about shock cooling and follow whatever procedure keeps you in the limitations, here:

"4. At all times, caution must be taken not to shock cool the cylinders. The maximum recommended
temperature change should not exceed 50°F. per minute."

Taken from http://www.lycoming.com/support/publications/service-instructions/pdfs/SI1094D.pdf

I have never had to worry about shock cooling except doing aerobatics at -20 C in the Cap 10 doing vertical dive descents, something tells me your typical flight won't involve such maneuvers. The procedure if I remember right was 1800 RPM. In this type of engine I have pegged the VSI on multiple Cessna/Piper aircraft in the winter without ever having shock cooling issues.

I would caution high HP turbo engines as the turbos might be more susceptible to shock cooling, but I haven't had to fly these yet so I wouldn't know. However I would simply consult your manufacturer for a degree per minute change and reference whatever gauges I had to stay within the manufactured recommended limits.
 
aloft said:
No offense, but your episode on Sunday suggests that your list of things that concern you might not be as comprehensive as it should..

Methinks I'd reassess my stance on a wide variety of topics after such a wakeup call. Maybe that's just me.
Click to expand...

wipe the sand out...
 
In all my years of flying any number of recip engines, shock cooling has never been a major concern. That's because although I'm conservative with engine operation, I'm not deathly anal retentive about it. Seriously......1" ever 1 minute? How the hell would you plan a descent.....or even operate in the pattern effectively to land? Yes, I know I'm being facetious, but I'm trying to illustrate a point. And that is, if the engine is so delicate that it can't handle more than 1"/minute power reduction, then it ought not be in the plane.

Even the Continental 520s in the Cessna 404s I used to fly for cargo weren't that delicate, and those were finicky engines to deal with.

Treat the engine with care, operate it within reasonable parameters; but there's no reason to feel you need to treat it like a frail 90 year old person.
 
MikeD said:
In all my years of flying any number of recip engines, shock cooling has never been a major concern. That's because although I'm conservative with engine operation, I'm not deathly anal retentive about it. Seriously......1" ever 1 minute? How the hell would you plan a descent.....or even operate in the pattern effectively to land? Yes, I know I'm being facetious, but I'm trying to illustrate a point. And that is, if the engine is so delicate that it can't handle more than 1"/minute power reduction, then it ought not be in the plane.

Even the Continental 520s in the Cessna 404s I used to fly for cargo weren't that delicate, and those were finicky engines to deal with.

Treat the engine with care, operate it within reasonable parameters; but there's no reason to feel you need to treat it like a frail 90 year old person.
Click to expand...

:yup:
 
Douglas said:
Posting a bit angry tonight, are we?

Aloft: Uh, why does it really suck? Because no one's offered you an RJ on a silver platter? Please. With 1100 hrs, you're barely qualified for a Pt 121 job.
Click to expand...
JRH has proven himself here many times.
That is not called for.
Click to expand...
That post is a) from another thread altogether, and b) wasn't directed at JRH.

Given this, not sure what your point is.
 
shdw said:
IMO ignore anything you have ever heard about shock cooling and follow whatever procedure keeps you in the limitations, here:

"4. At all times, caution must be taken not to shock cool the cylinders. The maximum recommended
temperature change should not exceed 50°F. per minute."
Click to expand...

Retorical question;

Do you know what you have to do to make the CHTs drop 50 deg in 60 seconds?


Unless you are deliberately TRYING to abuse the engine, you have nothing to worry about.
 
aloft said:
No offense, but your episode on Sunday suggests that your list of things that concern you might not be as comprehensive as it should..

Methinks I'd reassess my stance on a wide variety of topics after such a wakeup call. Maybe that's just me.
Click to expand...
Would you rather he did not post that "episode" at all, and have nobody learn from his mistake? He obviously learned from it, and he should not be slammed for it. I have learned a massive amount from JRH from the time I have been on the board and he has already proven that he is a safe pilot.
 
Kind of a sidenote, I had to "fail" a guy on an ICC in his own 182 when I was a CFI because he refused (failed?) to properly fly a non-precision approach from fear of shock cooling his engine.

"Can't shock cool, can't SHOCK COOL!"

"Well, can't reach MDA or fly an ILS less than 120 knots either, can't wreck an airplane to save an engine, sir."

I was a little grumpy that day I guess.
 
I have only encountered the 1" every 1 minute rule of thumb since I started working with big radial engines.
 
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