Cowl flaps question regarding 182s

woodchucker

woodchucker

Pattern Altitude
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woodchucker
Is there a specific reason they should be closed during landing? I understand why they should be open on takeoff and in cruise as needed, and closed on descent because the extra cooling isn’t needed. I’m talking specifically pattern altitude to landing. Wouldn’t it be better to have them open so there is one less thing to be concerned about in the event of a go around? Or shooting T&Gs. I assume it has something to do with not letting the engine cool further, but I’m not sure. Thanks in advance.
 
I like to leave them closed to not contribute to excessive cooling of the cylinders during the low power descent. Shock cooling is largely a myth (nearly all thermal engine damage comes from OVERheating not OVERcooling), but still no reason to open them.
 
That's the theory. OTOH, since by the time you are on downwind the engine has cooled down substantially I know a number of pilots who reopen cowl flaps on downwind or as part of the power reduction to leave pattern altitude.
 
I have wondered the same myself. FWIW I have been leaving mine open @ landing in case of go around, and to be open after landing in hot weather
 
I leave mine closed to prevent too large of a cooling rate on the cylinders. In the pattern I should be at a relatively low power setting not generating much heat.

In the event of a go-around taking an extra 5 seconds to open the cowl flaps wont hurt anything.
 
flyingron said:
I like to leave them closed to not contribute to excessive cooling of the cylinders during the low power descent. Shock cooling is largely a myth (nearly all thermal engine damage comes from OVERheating not OVERcooling), but still no reason to open them.
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Disagree. Rate of change of temperature is what damages engine components, in addition to high heat. When things heat and expand they do so at different rates causing excess wear. Keeping your engine at as constant of a temperature as possible for as long as possible is ideal. If your engine must cool down then cooling it down as slowly as possible is far more preferable. The less thermal cycling the better and the slower you can do the cycling the better.
 
Mtns2Skies said:
Disagree. Rate of change of temperature is what damages engine components, in addition to high heat. When things heat and expand they do so at different rates causing excess wear. Keeping your engine at as constant of a temperature as possible for as long as possible is ideal. If your engine must cool down then cooling it down as slowly as possible is far more preferable. The less thermal cycling the better and the slower you can do the cycling the better.
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Do you put a blanket on it after shutdown so it doesn’t cool too fast?
 
Salty said:
Do you put a blanket on it after shutdown so it doesn’t cool too fast?
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In the winter, Yes. But also convection cools at a significantly higher rate than conduction, so if there isn't air flowing over the engine (or very little) it's not going to cool as fast as at a low power setting with high speed (descent).
 
Lycoming quotes 50 degrees per minute as a cooling rate they recommend.
 
I used to open them in the pattern for one less thing to do on go-around (same as prop forward for me).

A hangar-mate with a 182 that has gone past TBO suggested I keep them closed. So now I do.

I do worry about lunching the engine during the go around if things get nutty and I forget to open them (poor cockpit flow discipline or delayed checklist use).
 
midlifeflyer said:
That's the theory. OTOH, since by the time you are on downwind the engine has cooled down substantially I know a number of pilots who reopen cowl flaps on downwind or as part of the power reduction to leave pattern altitude.
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That's pretty much my drill unless something particular is going on to change it. I mention cowl flaps during my 'gumpings' which I do many times, usually three at a minimum. I'll say something like "when turning final" and then do it on the final gump. My gump is actually a CGUMP. Sometimes the answer is "no cowl flaps on this plane."
 
it doesn 't matter....do what you like. The most critical phase is the high power climb....and keeping the CHTs below 400 and targeting 370 or less.
 
SToL said:
I just do mine by what ever the book says.

No reason to do otherwise, and this way, I don't have to worry about someone joining up on me in the pattern and telling me I''m flying wrong.
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True that! I do things by the book also but like to know why at the same time. Another example is the Tiger. The book says to start on the left mag. Sure no problem but why? And then I learned about impulse couplers.
 
woodchucker said:
True that! I do things by the book also but like to know why at the same time. Another example is the Tiger. The book says to start on the left mag. Sure no problem but why? And then I learned about impulse couplers.
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SToL said:
I just do mine by what ever the book says.

No reason to do otherwise, and this way, I don't have to worry about someone joining up on me in the pattern and telling me I''m flying wrong.
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Ah but there is a reason to do otherwise - making the go-around simpler - and with no downside.

Beware if too much blind following of the airplane's published manual. There have been advances in our understanding of engines, performance and processes and the associated standard operational procures. The 1972 Cessna 172L manual says zero about leaning for taxi or, for that matter, leaning for takeoff or landing. Full rich all the way, except in cruise. "Following the book" for that at a high density altitude airport will make our day more difficult.

There are manufacturer-published checklist items which are necessary for safe operation. There are others which reflect a technique which may be modified safely and sometimes should be modified. Wisdom is understanding the difference.
 
midlifeflyer said:
Ah but there is a reason to do otherwise - making the go-around simpler - and with no downside.

Beware if too much blind following of the airplane's published manual. There have been advances in our understanding of engines, performance and processes and the associated standard operational procures. The 1972 Cessna 172L manual says zero about leaning for taxi or, for that matter, leaning for takeoff or landing. Full rich all the way, except in cruise. "Following the book" for that at a high density altitude airport will make our day more difficult.

There are manufacturer-published checklist items which are necessary for safe operation. There are others which reflect a technique which may be modified safely and sometimes should be modified. Wisdom is understanding the difference.
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Which is why I have asked also. It seems the thread so far is about 50/50 on that.
 
midlifeflyer said:
The 1972 Cessna 172L manual says zero about leaning for taxi or, for that matter, leaning for takeoff or landing. Full rich all the way, except in cruise. "Following the book" for that at a high density altitude airport will make our day more difficult.
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Agreed 100%, however when I posted I thought we were talking about cowl flaps. Now ya gone done n' changed it on me.
 
SToL said:
Agreed 100%, however when I posted I thought we were talking about cowl flaps. Now ya gone done n' changed it on me.
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I was only challenging the "follow the manual" statement and pointing out that it is not necessarily the end-all and be-all answer.
 
If the OAT is below 30c or so, I don't think leaving the cowl flaps closed on a 182 would make too much difference in a full power go-around.

A fifteen minute climb to cruise altitude, on the other hand should dictate open flaps.

I've seen 5KIAS difference in cruise speed because of forgotten open flaps.

I would worry about it more in a Mooney or a Navajo...
 
IK04 said:
If the OAT is below 30c or so, I don't think leaving the cowl flaps closed on a 182 would make too much difference in a full power go-around.

A fifteen minute climb to cruise altitude, on the other hand should dictate open flaps.

I've seen 5KIAS difference in cruise speed because of forgotten open flaps.

I would worry about it more in a Mooney or a Navajo...
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My question is more about leaving them open for landing. Does the extra cooling have an adverse effect on engine life.
 
Mtns2Skies said:
I leave mine closed to prevent too large of a cooling rate on the cylinders. In the pattern I should be at a relatively low power setting not generating much heat.

In the event of a go-around taking an extra 5 seconds to open the cowl flaps wont hurt anything.
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Yep. My A&P told me to leave them closed
 
woodchucker said:
My question is more about leaving them open for landing. Does the extra cooling have an adverse effect on engine life.
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no....mine get opened on down wind. Not that it's "needed" but...it's about getting ready for the next phase of flight/taxi. If I need to go-around....we're good for that too.

You will not over cool....or shock cool....your cylinders. ;)
 
flyingron said:
I like to leave them closed to not contribute to excessive cooling of the cylinders during the low power descent. Shock cooling is largely a myth (nearly all thermal engine damage comes from OVERheating not OVERcooling), but still no reason to open them.
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Overcooling can stall an engine...kaput. Overheating can cause pre-ignition causing power loss or failure. Don't think you want that. Pay close attention to the eng temp/cyl temp gauge. In time you'll get to know the airplane's characteristics.
 
flyingron said:
I like to leave them closed to not contribute to excessive cooling of the cylinders during the low power descent. Shock cooling is largely a myth (nearly all thermal engine damage comes from OVERheating not OVERcooling), but still no reason to open them.
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Most times shock cooling will slip up on a pilot in a long drawn-out descent from altitude. Even during Summer. That's mainly when I watch the gauge closely and adjust cowl flaps as needed to maintain the temp I want.
 
The way I look at cowl flap operation is "monitor engine temp just like you do any other instrument." Mostly depends if you're operating in wintertime Alaska or summertime Imperial Valley.
 
flyingron said:
I like to leave them closed to not contribute to excessive cooling of the cylinders during the low power descent. Shock cooling is largely a myth (nearly all thermal engine damage comes from OVERheating not OVERcooling), but still no reason to open them.
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I've heard that shock cooling is a myth, but never seen any documented evidence for it. Thermal cycling is a standard protocol for accelerated life testing of most products. I am not clear why it doesn't apply to aircraft engines.
 
Would someone with a 182 and engine monitor mind flying the pattern once with closed and once with open and dump the data for us to see.

All I know is if they are closed on final and you go around or you are doing touch and go's I will wait to open them until all the other more important stuff like mixture, carb heat and flaps are resolved. It's easy, if just for an instant, to have the eyes looking down to close them and not on the runway and horizon.
 
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Watch an engine monitor while in the pattern and after landing and you’ll dismiss the shock cooling BS.

A go around isn’t SOP. Deal with full power heat when you utilize full power.
 
Sinistar said:
Would someone with a 182 and engine monitor mind flying the pattern once with closed and once with closed and dump the data for us to see.

All I know is if they are closed on final and you go around or you are doing touch and go's I will wait to open them until all the other more important stuff like mixture, carb heat and flaps are resolved. It's easy, if just for an instant, to have the eyes looking down to close them and not on the runway and horizon.
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So do it twice with closed?
 
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Cowl flaps? It's definitely part of the GUMPS mnemonic. I'm sure it's in there somewhere. Must be the S.
 
sarangan said:
I've heard that shock cooling is a myth, but never seen any documented evidence for it. Thermal cycling is a standard protocol for accelerated life testing of most products. I am not clear why it doesn't apply to aircraft engines.
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We hear about shock cooling, but no one ever talks about shock heating on the take off roll.
 
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