Shock cooling on descent

[trey2398]

After 3 months of putting around local airports, I finally took my new-to-me 201 out to see what she had.  I went from Bulverde, TX to KNEW to KSHV, then back home.  Flying at 11,500, I planned on coming down at 500fpm to 1,500 into KNEW.  Doing 3 mile/min over the ground and needing 20 minutes to get down, I asked for lower about 70 miles out.  I had been set at 21"/2500RPM (180mph TAS and just under 10 gal/hr....love that!!!) at cruise and was advised to only pull about 1"/2-3 minutes to avoid shock cooling.  My CHTs had all been 320-350.  When I pulled out that first inch, I didn't get much of a descent rate so I decided to bring back the RPM as well.  After a couple of minutes, I pulled more throttle but when I started to get a good descent rate I noticed that the #1 cylinder jumping between 290 and 320 so I added power to keep it above 300.  I know that I could have just pushed the nose down, but I'm trying to learn the engine better.  So I guess my question would be...how is shock cooling defined?

[bnicolette]

Correct me if I am wrong, but I think the idea is to keep it less than 50 degrees per minute of cooling on the CHT's?  I have my JPI 830 set to alarm me if I exceed this limit of 50 degrees cold (CLD) and I really haven't come close with the way I have been operating the airplane.  During descent I don't touch my throttle at all, just mixture and RPM.

Why pull any manifold pressure out at all?  I have just been pushing the nose over and letting her eat, assuming it is smooth out of course!!  Most times when I am traveling, I have not touched the throttle from at the start of my takeoff run till a couple miles out before landing?

How about the other guys with 201's?  Perhaps, I am doing something wrong and I could be totally off base.  I am new to the Mooney and have only been flying it since February of this year.

[jetdriven]

i push the nose over, l;eave it firewalled and leaned,  and take the 20 knots extra and dexcend around 750 FPM.  this gives a 3 degree desent or 300 Feet per mile.  So use your altitude to calculate when to start down.,      at 25" MP (around 4000 feet) I limit the MP to 25", and 3-5 minutes out begin working the power down to 18" on downwind. If you level off at pattern altitude a couple miles from the airport at 18", you will be at the right speed on downwind.

Lycoming says no more than 50 degrees per minute.  Ours in the few hours we have flown it in the spring, changes maybe 30 degrees total.  Keep power in it, keep it lean, leep it warm.

 

Zef from mooneyland says if the MP is above 18", the engine is driving the prop and there will be no shock cooling.  I pretty much agree.

 

YMMV but this works for me.

[Parker_Woodruff]

Quote: Bnicolette

Correct me if I am wrong, but I think the idea is to keep it less than 50 degrees per minute of cooling on the CHT's?  I have my JPI 830 set to alarm me if I exceed this limit of 50 degrees cold (CLD) and I really haven't come close with the way I have been operating the airplane.  During descent I don't touch my throttle at all, just mixture and RPM.

Why pull any manifold pressure out at all?  I have just been pushing the nose over and letting her eat, assuming it is smooth out of course!!  Most times when I am traveling, I have not touched the throttle from at the start of my takeoff run till a couple miles out before landing?

How about the other guys with 201's?  Perhaps, I am doing something wrong and I could be totally off base.  I am new to the Mooney and have only been flying it since February of this year.

[WardHolbrook]

Check out some of article on engine operation by John Deakin and others on avweb.com.

 

http://www.avweb.com/news/maint/182883-1.html

http://www.avweb.com/news/pelican/183094-1.html

Not saying or implying anything, just some food for thought.

 

[jlunseth]

That's about what I do in my 231.  I take off and climb to altitude at WOT (being normally aspirated you might want to lean during climb), then I lean at cruise.  When it comes time to descend I just push the nose over.  During the descent I usually need to adjust the throttle every few thousand feet to make sure it does not creep up too far with the change in altitude.  The cylinders stay nice and warm.  I use the VNAV feature of the Garmin 430 to determine when I need to start down to maintain an approximate 500 fpm descent.

[jetdriven]

Quote: WardHolbrook

Check out some of article on engine operation by John Deakin and others on avweb.com.

 

http://www.avweb.com/news/maint/182883-1.html

http://www.avweb.com/news/pelican/183094-1.html

Not saying or implying anything, just some food for thought.

 

[trey2398]

Thanks for all of the info. I guess the last part of the first article sums it up. Never thought of it this way....

 

"If shock cooling were a definite hazard, your engine should fall apart when you bring the mixture into idle cutoff at the end of a flight. CHTs fall at a rate of 100°F/min or more in the first seconds of shutdown—triple the rate that starts the typical "shock cooling" annunciator blinking. Does anyone complain that repeated shutdowns are causing head cracking? Of course not.

Then why are we worried about pulling the throttle back?"

[jetdriven]

lots of OWT's abound.  I like the one from the engine shop (Ney, I think) that re-bores cylinder barrels straight with no choke, then recommends the factory mixture setting plus one gallon per hour. 

 

For one thing, rebuilt cylinders can be a disaster, but no choke?      Then the 1 GPH extra, thats  11.5 GPH in a mooney 201.  The valve guides fill with lead necessitating a top overhaul. Not to mention an extra 10K in fuel costs over the life of the engine.  The oil analysis must be full of lead.     OWT..

[rogerl]

There seem to be some good points, both common sense observations as well as references from other researchers in this discussion.  The fact remains, however, that Lycoming themselves recommend guarding against "shock cooling".

My reference is "Lycoming Flyer Key Reprints" part "Avoid Sudden Cooling of Your Engine" that begins with:

"Sudden cooling is detrimental to the good health of the piston aircraft engine.  Textron Lycoming Service Instruction 1094D recommends a maximum temperature change of 50° F per minute to avoid shock cooling of the cylinders."

The article continues on to describe the various engine conditions that may result from exceeding these guidelines, procedures to avoid etc.

I'll keep a copy of the reprints for a few days here

 

[WardHolbrook]

Quote: rogerl

There seem to be some good points, both common sense observations as well as references from other researchers in this discussion.  The fact remains, however, that Lycoming themselves recommend guarding against "shock cooling".

My reference is "Lycoming Flyer Key Reprints" part "Avoid Sudden Cooling of Your Engine" that begins with:

"Sudden cooling is detrimental to the good health of the piston aircraft engine.  Textron Lycoming Service Instruction 1094D recommends a maximum temperature change of 50° F per minute to avoid shock cooling of the cylinders."

The article continues on to describe the various engine conditions that may result from exceeding these guidelines, procedures to avoid etc.

I'll keep a copy of the reprints for a few days here

 

[rogerl]

As with supernatural beings, you choose what you want to believe.  I think the thousands of engines experience, design -level knowlege of the metallurgical minutiae, and conservative attitude slightly outweigh opinions of such mechanics who may have owned a few lycomings, seen perhaps scores of them through periods greater than five years, and maybe even have worked on hundreds in passing.

Personally, I choose to take greater stock in the former with regards to the one lycoming I depend upon and maintain.

 Wives' tales indeed!

[Shadrach]

Quote: rogerl

There seem to be some good points, both common sense observations as well as references from other researchers in this discussion.  The fact remains, however, that Lycoming themselves recommend guarding against "shock cooling".

[WardHolbrook]

Quote: rogerl

As with supernatural beings, you choose what you want to believe.  I think the thousands of engines experience, design -level knowlege of the metallurgical minutiae, and conservative attitude slightly outweigh opinions of such mechanics who may have owned a few lycomings, seen perhaps scores of them through periods greater than five years, and maybe even have worked on hundreds in passing.

Personally, I choose to take greater stock in the former with regards to the one lycoming I depend upon and maintain.

 Wives' tales indeed!

[jetdriven]

fiunny how Lycoming has all the cam, cylinder and crank shaft problems (AD's, etc) yet they maintinain that "Only Lycoming can build you engine as good as we can".   sure.  My engine was built at an A&P hangar in Tulsa. 

[Shadrach]

Quote: rogerl

As with supernatural beings, you choose what you want to believe.  I think the thousands of engines experience, design -level knowlege of the metallurgical minutiae, and conservative attitude slightly outweigh opinions of such mechanics who may have owned a few lycomings, seen perhaps scores of them through periods greater than five years, and maybe even have worked on hundreds in passing.

Personally, I choose to take greater stock in the former with regards to the one lycoming I depend upon and maintain.

 Wives' tales indeed!

[scottfromiowa]

Not saying right or wrong, but I keep throttle fire-walled and RPM at 2500 during decent.  I trim for 500fpm decent and keep airspeed below 180mph indicated by reducing pitch if needed.  I will increase mixture as I come down.  I have not experienced any significant cylinder temp fluctuation and I like the free speed downhill (making up for the climb).  I don't worry about shock cooling my engine...and have seen no signs on my multi-probe that this is occuring.

[Shadrach]

Quote: scottfromiowa

Not saying right or wrong, but I keep throttle fire-walled and RPM at 2500 during decent.  I trim for 500fpm decent and keep airspeed below 180mph indicated by reducing pitch if needed.  I will increase mixture as I come down.  I have not experienced any significant cylinder temp fluctuation and I like the free speed downhill (making up for the climb).  I don't worry about shock cooling my engine...and have seen no signs on my multi-probe that this is occuring.

[Kwixdraw]

I notice that Superior and ECI Never have any recalls or ADs on their stuff.  I guess they really know how to build a Lycoming huh?  Seriously folks. There is something to making life as easy as you can on your engine. With all the scanners and monitors we have now, individual operators probably have more data at hand than the engineers did when they designed the engine and the OWTs came about back in those dark ages. Was chatting with Gerry at Lycon the other day, about some work I want done and how best to proceed with an overhaul. I mentioned that I was thinking about a cylinder and head rebuild using a brand X cylinder because I thought it would give me certain advantages, using my heads and new cylinders with the latest greatest coating in them. Well I got a detailed explanation of how he would do it and a lot of reasons to just go with the Lycoming cylinders. Especially on the IO-360 in a 201. They build their Reno race engines with them and he had darned good reasons for doing it.  They get upwards of 245 HP out of the 0-360 in mild tune and converted to injection. That's on a prop dyno not just a figure out of the air. Of course that's not a certificated engine either. Standard Georgia warranty; "If it breaks in half , both halves belong to you." That's racing.

[rogerl]

Quote: WardHolbrook

I would point out again, that neither Continental nor Lycoming seem to have this metallurigical thing quite figured out yet as evidenced by their all to frequent cylinder, cam, crankshaft and case recalls. I guess solid research and the laws of thermodynamics are not to be used to refute OWTs.

Just a question... How come most jump planes and glider tow planes seem to make it to TBO just fine? You'd think that those engines would be eating cylinders at prodigious rates. They don't. I suggest that money spent taking an online course on powerplant management at AdvancedPilot.com would be well spent. 

[danb35]

If we leave aside all the Lycoming-bashing (mostly well-deserved) and discussion of whether "shock cooling" is an OWT or not, we reach a more basic issue: Lycoming says to avoid cooling the engine more than 50 deg F / minute.  In normal operations, can you exceed that cooling rate anyway?  I can't.

My "shock cooling" alarm on my engine monitor goes off if the cooling rate exceeds 30 deg/min.  The only way I've been able to make it happen is by taking off and climbing to ~3k at full power, then pulling back to 20"/2500/7 gph or so--and even then it goes out on its own in a few seconds.  I don't think I could get to 50/min with anything less than an inflight engine shutdown.

On the other issue: GAMI/APS says, "Here's the theory, and the science behind that theory.  Here's the data that supports that theory.  Come to our course, and you can watch an engine behave exactly as that theory predicts."  Lycoming says, "We designed the engine, so we know best.  Do it our way because we say so."  I know which one I find more persuasive.

[jetdriven]

either way i think that 50 degrees a minute is quite a large value.  Our engine runs at about 350 CHT so thats 6 minutes to room temperature.   Ours changes 30 degrees over 10-12 minutes.  If that.  If you are cooling the plane to below 200 degrees CHT I dont think thats good either.

[PTK]

Quote: Shadrach

Uhh... guys, Lycoming manufactures the engine and Lycoming honors the warranty. I would listen to Lycoming!!  Anyone can say whtever they want but they are not responsible or liable.  Use common sense and LISTEN to Lycoming.  Do not discount the voice of experience over some "wannabes" out there who talk without any substance.  

[rogerl]

Quote: allsmiles

Uhh... guys, Lycoming manufactures the engine and Lycoming honors the warranty. I would listen to Lycoming!!  Anyone can say whtever they want but they are not responsible or liable.  Use common sense and LISTEN to Lycoming.  Do not discount the voice of experience over some "wannabes" out there who talk without any substance.  

[PTK]

What do you want Lycoming to come up with?  They developed and gave us a bulletproof engine for our Mooneys!! If we follow some of their simple directions and give it half a chance it will go well beyond TBO!!   What did the other talking heads and "engine experts" come up with? Did they come up with something that I missed?