Shock Cooling

USMCmech said:
Thousands of pilots were taught to fear the "downwind turn". Famous authors talked about flying "on the step". Virtually every puppy mill (including the one I went to) teaches that you shouldn't ever run your engine "oversquare". All of these myths are 100% wrong.

"Shock cooling" is just another myth that is based on flimsy evidence. While hard science shows the opposite is actually true.
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Yep. Its the I'd rather learn from flight school rumors than actually do the leg work to find the truth for myself.
I know a few guys that swear by The Step. You ask them to explain it and you get a bunch of Well...Uh's.
I've flown the big Continentals and never had a problem as long as you don't do an idle dive bomb.
 
Hacker15e said:
Well, again, there are certainly truths behind what eventually become WOMs, and this is one of them. It is certainly not an absolute, but it remains a good ROT.

If you read Randy Sohn's "Warbird Notes" entry about reciprocating loads, it will show that there IS an important link between MP and RPM and the overall health of your piston (radial, at least) engine -- and that the 1" per 1,000 RPM is a pretty solid ROT.

http://www.douglasdc3.com/sohn/3.htm
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Very good articles, however the article is clearly written for Wright and Pratt radials. I always want to know the source of operating procedures. Many ROTs do not transfer across equipment. Thanks for the link.
 
jdlilfan said:
Kind of catch 22 with carb engines in the winter. Many POH's call for the power to be set to 1500 for the first minute to allow proper fuel vaporization while the engine warms. I agree with this as well because I have experienced many of 152 engines die soon after starting when the student starts monkeying with the throttle in below freezing temps.
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I am still low time, but I have never seen this 1500 on start that you are speaking of. Would you mind giving an example of an aircraft that requires this? Thanks
 
we do oil changes on hot engine all the time and I always thought that if you do get an oil change you should always let it cool off a bit first. Guess I was wrong but it seems as though this would harm the engine more than 5" every 1 min. Passing cool oil over the crank case is not a big issue as cooling from the jugs I guess. I just changed out a jug in a "P" baron because it was cracked and wondered if this topic was part of the issue.
 
As far as shock cooling, here at UND we have some policies in place but it's mostly instructor preference. We've (and I) have had engines stop due to shock cooling, but that's student pilots with the power at 100%, go to idle, leave it at idle for 30 seconds, then try to go to full power again... and while at -45C (at altitude, the ground was a warm -35C). In the summer, not an issue. How do you recover, allow the engine to cool completely so everything is the same size then airstart it again.

Basically we just watch CHT's to make sure everything is in the green. With the multi-engines we also really watch the CHT's after OEI operations. We have had some issues with rough running or sluggish operations. If we have any cylinder cracks, normally a well used engine at high power... not idle due to cold.

Won't say it won't ever happen, but not here so far.
 
Dang I can't believe the let you fly that cold.
Our operations stop at -18 C...and that is fine with me. :D
 
ProudPilot said:
As far as shock cooling, here at UND we have some policies in place but it's mostly instructor preference. We've (and I) have had engines stop due to shock cooling, but that's student pilots with the power at 100%, go to idle, leave it at idle for 30 seconds, then try to go to full power again... and while at -45C (at altitude, the ground was a warm -35C). In the summer, not an issue. How do you recover, allow the engine to cool completely so everything is the same size then airstart it again.

Basically we just watch CHT's to make sure everything is in the green. With the multi-engines we also really watch the CHT's after OEI operations. We have had some issues with rough running or sluggish operations. If we have any cylinder cracks, normally a well used engine at high power... not idle due to cold.

Won't say it won't ever happen, but not here so far.
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There ya go. Our cutoff for flights was like -40 at the surface or something like that last winter and it got so cold at altitude that I had a tube break in the tire (it was -75F at altitude) and had a flat on touchdown. That can't be good for the cylinders.
 
I never really thought much about shock cooling until I saw two Seneca's in 30 days come into our maintenance facility with a cylinder completely blown off (happened during flight). Lucky no one died... One was caused by a group of students and their instructor decending form altitude at idle and then bringing the power up too quickly (probably had full rich mixture the whole time as well).

The second incident occured on a checkride with the examiner after an engine shutdown.

Always remember to close those cowl flaps and keep the engine warm while operating single engine. When you restart, bring the power up to sim feather (12" or so) until you are well into the green on the CHT. The cylinder starts to cool around those hot pistons and if you bring the power up too quick, KA-BOOM! (especially if you leave it full rich for a while).

When you start flying larger twins, the more engine temperature management becomes an issue. You really need to start thinking about decent planning (3 miles per thousand ft) and pull back MP about an inch per thousand throughout your decent.
 
SoCalFlyer2 said:
When you start flying larger twins, the more engine temperature management becomes an issue. You really need to start thinking about decent planning (3 miles per thousand ft) and pull back MP about an inch per thousand throughout your decent.
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Hey who asked where these rumors come from earlier this thread? or was that another thread? Anyways I found the culprit capan where u want em?

Just messing with you but this 1 inch per thousand is a myth and likely was true for one airplane but is certainly not true or even close to true for most others.
 
SoCalFlyer2 said:
When you start flying larger twins, the more engine temperature management becomes an issue. You really need to start thinking about decent planning (3 miles per thousand ft) and pull back MP about an inch per thousand throughout your decent.
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Can you explain why, or where you heard that? And the exact reasoning?

Be careful with your answer though.....cuz you're gonna be wrong ;).
 
BrewMaster said:
Can you explain why, or where you heard that? And the exact reasoning?

Be careful with your answer though.....cuz you're gonna be wrong ;).
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Simple.... you lose about 1" per thousand feet of manifold pressure as you ascend so it makes perfect sense to pull it back an 1" per thousand as you decend to maintain a constant power/airspeed rate of decent. If you plan for about 3 miles per thousand feet you can make a gradual decent and never have to pull it to idle and dive bomb. Now if you have a turbo that goes out the window... :)
 
SoCalFlyer2 said:
Simple.... you lose about 1" per thousand feet of manifold pressure as you ascend so it makes perfect sense to pull it back an 1" per thousand as you decend to maintain a constant power/airspeed rate of decent. If you plan for about 3 miles per thousand feet you can make a gradual decent and never have to pull it to idle and dive bomb. Now if you have a turbo that goes out the window... :)
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Edit: Wording

By that logic you will take out 1" than gain 1" back slowly (in the descent) and take 1" back out again. To take this further, 1" is equal to approximately 100 FPM descent which would slow to level flight as you descend and from the increasing MP and then increase back to 100 FPM again and repeat. I don't want to do the math but I would bet this would take a Mooney from 25,000 feet a REALLY long time to descend. You might have to initiate your descent into NYC over Chicago...

Hey, what does a turbo charged engine that doesn't loose/gain manifold pressure do?


I forgot, "power/airspeed rate of decent"
 
SoCalFlyer2 said:
Simple.... you lose about 1" per thousand feet of manifold pressure as you ascend so it makes perfect sense to pull it back an 1" per thousand as you decend to maintain a constant power/airspeed rate of decent. If you plan for about 3 miles per thousand feet you can make a gradual decent and never have to pull it to idle and dive bomb.
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Sorry, but that makes NO sense. Just because the MP decreases by itself as you go up, that doesn't mean you decrease it manually as you go down.

Nor does that give you a "constant power/airspeed" rate of descent. You may get a constant airspeed, but you won't get constant power doing it that way. You're reducing the power as you descend. Constant MP does not = constant power.

Don't believe me? Check out your performance charts for cruise. Look at the difference between 23" at x thousand vs y thousand as a % of rated power (using the same RPM, of course).

-mini
 
Re: flying on "the step". For a given power setting there are 2 different speeds you can fly (at least), depending on which side of the power curve you are on, right? in that case, it would make sense that if you climb at a steep angle of attack you may attain a lower airspeed in cruise than if you were to shallow out your angle of attack or maintain climb power until you get established at cruise speed.
 
SpiraMirabilis said:
Re: flying on "the step". For a given power setting there are 2 different speeds you can fly (at least), depending on which side of the power curve you are on, right? in that case, it would make sense that if you climb at a steep angle of attack you may attain a lower airspeed in cruise than if you were to shallow out your angle of attack or maintain climb power until you get established at cruise speed.
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Why? When you stop climbing you're going to change the pitch angle to level off...unless you level off strictly with power. In which case, you'll probably be using less than cruse thrust anyway. Why would you want to do that?

When you change the pitch angle (lower), the thrust "vector" lowers also, dragging the airplane with it (Faster).

We have no problem maintaining the same cruise speed whether we climb at max climb or cruise climb.

-mini
 
shdw said:
Edit: Wording

By that logic you will take out 1" than gain 1" back slowly (in the descent) and take 1" back out again. To take this further, 1" is equal to approximately 100 FPM descent which would slow to level flight as you descend and from the increasing MP and then increase back to 100 FPM again and repeat. I don't want to do the math but I would bet this would take a Mooney from 25,000 feet a REALLY long time to descend. You might have to initiate your descent into NYC over Chicago...

Hey, what does a turbo charged engine that doesn't loose/gain manifold pressure do?


I forgot, "power/airspeed rate of decent"
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In the turbo cirrus, which is normalized, you do nothing. Just start your descent and if you need to pull back a few % power to keep the speed down out of the red you do. But at 85% power you can make a 500 fpm descent without changing anything. You are way over tubulence penetration speed though, so if it is rough or IMC I do not do this. If it is rough I will pull it back to about 65-70% and make the descent. That is the beauty of the cirrus normalized system, I can descend from 25,000 feet and not once touch the mixture or the throttle until on approach. The same goes for the climb, mixture full till level off, you lean the mixture to 17GPH fuel flow, and it is set, no matter what altitude you climb to. You just make minor changes(+/-1 GPH) based on CHT.
 
minitour said:
Why? When you stop climbing you're going to change the pitch angle to level off...unless you level off strictly with power. In which case, you'll probably be using less than cruse thrust anyway. Why would you want to do that?

When you change the pitch angle (lower), the thrust "vector" lowers also, dragging the airplane with it (Faster).

We have no problem maintaining the same cruise speed whether we climb at max climb or cruise climb.

-mini
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Yeah, that makes sense, of course. I was just trying to be contrary :p Thats the only argument I've heard that was even somewhat half believable about "the step"
 
I do think shock cooling is a bit overrated. But there also no harm in taking extra care of the engine if conditions allow.

Back in my 135 days we always used the 1 inch a minute rule of thumb for the C310/402 and 421's. The 310's and 402's normally made the TBO without a problem.

For whatever reason the 421's never seemed to make TBO. They were always jug problems. I remember one flight we commented on that one engine may actually make TBO...Nope, it started pouring out oil 2 hrs short of TBO.
 
Bandit_Driver said:
I do think shock cooling is a bit overrated. But there also no harm in taking extra care of the engine if conditions allow.

Back in my 135 days we always used the 1 inch a minute rule of thumb for the C310/402 and 421's. The 310's and 402's normally made the TBO without a problem.

For whatever reason the 421's never seemed to make TBO. They were always jug problems. I remember one flight we commented on that one engine may actually make TBO...Nope, it started pouring out oil 2 hrs short of TBO.
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The Continental 520s on the 404 and 421 were touchy, but didn't need to be too babied. Agree that shock cooling has been far overblown by some, and there's no harm in taking care of the engine. But treating it like a frail elderly person is going a bit overboard, IMO.
 
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