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Posted: 1/5/2020 1:57:20 PM EDT
[#1]
Lycoming seems to think it’s an issue, but what do they know?
https://www.lycoming.com/content/how-avoid-sudden-cooling-your-engine |
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Posted: 1/5/2020 4:47:43 PM EDT
[#2]
I shock my Pratt’s all the time...wait, wat?
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Posted: 1/5/2020 5:03:45 PM EDT
[#3]
Pulling the power to idle cools the engine faster than pointing the nose downhill. Can't remember what degrees/minute I used when I had my Bonanza (Continental IO-470 powered) but yes it can happen and be hard on a motor. But you really gotta wail on it to happen.
Bet these old timers say that lean of peak is a myth too. Go read these articles, all of them. That'll square things away. https://www.avweb.com/flight-safety/pelicans-perch-index/ |
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Posted: 1/5/2020 5:10:15 PM EDT
[#4]
Shock cooling has nothing to do with flying in rain. It’s when you chop the power quickly. Reduce the Heat on the Inside of the cylinder.
Don’t listen to old FBO bastards. Hangar flying is GD in real life. |
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Posted: 1/5/2020 5:19:22 PM EDT
[#5]
Glider operations are familiar with shock cooling. Maximum power for 5 to 10 minutes, then chop the throttle and spiral down at low power to pick up the next tow. It's a thing.
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Posted: 1/5/2020 6:18:52 PM EDT
[#6]
Quote HistoryQuoted:
Pulling the power to idle cools the engine faster than pointing the nose downhill. Can't remember what degrees/minute I used when I had my Bonanza (Continental IO-470 powered) but yes it can happen and be hard on a motor. But you really gotta wail on it to happen. Bet these old timers say that lean of peak is a myth too. Go read these articles, all of them. That'll square things away. https://www.avweb.com/flight-safety/pelicans-perch-index/ ETA: none of the links in that index work. |
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Posted: 1/5/2020 6:20:54 PM EDT
[#7]
Quote HistoryQuoted:
Don’t listen to old FBO bastards. |
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Posted: 1/5/2020 9:08:29 PM EDT
[#8]
The guys at Superior Cylinder are not worried too much about it. 14:30 in to the video.
 Cylinder Compression Failure - InTheHangar Ep 64 |
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Posted: 1/5/2020 10:47:32 PM EDT
[#9]
Absolute truth. Flight schools here decided Sundowners were the perfect trainer. Any second run cylinders would crack through the exhaust port and we had 2 or 3 that were over 50% on the way to head separation. Touch & goes would kill Lycoming cylinders.
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Posted: 1/6/2020 4:42:36 AM EDT
[#10]
Quote HistoryQuoted: Cool link, thanks! ETA: none of the links in that index work. |
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Posted: 1/6/2020 2:14:31 PM EDT
[#11]
I mostly had to worry about it in turbo-normalized engines like on Cessna 414s and Navajo Chieftons. My company in Alaska had the policy of pulling off no more than 1" of manifold pressure every minute. I was typically too busy to pay that close attention to it so I usually cheated and just did 2" every 2 minutes. But it really made you plan your descents. Then we had to sit on the ramp to wait for engine temps to get below some predetermined temp before shutting down. Can't remember what that temp was now.
I never worried too much about shock cooling in normally aspirated engines. My 172 endured a lot of power chopping yet always made it to tbo. Same for the Comanche 250. |
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Posted: 1/6/2020 3:38:26 PM EDT
[#12]
The IO540's in my old Aztec made it to TBO with no issues and my partner routinely made power-off descents.
Since he was an IA of long experience, I didn't question it. |
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Posted: 1/6/2020 4:19:12 PM EDT
[#13]
Link to John Deakin’s AvWeb articles.
https://www.flywire.online/post/links-to-guys-smarter-than-i-am |
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Posted: 1/6/2020 5:46:23 PM EDT
[#14]
Here's a link to one of John's articles, little google-fu and you should be able to find the rest. https://www.avweb.com/features_old/pelicans-perch-18mixture-magic/
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Posted: 1/6/2020 6:28:09 PM EDT
[#15]
Quote HistoryQuoted:
The guys at Superior Cylinder are not worried too much about it. 14:30 in to the video.  https://www.youtube.com/watch?v=nX__4D_m1RQThey had a good alternative explanation as to how engines could be damaged where people think it is shock cooling but really something else in similar scenarios as well. |
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Posted: 1/6/2020 6:50:12 PM EDT
[#16]
Quote HistoryQuoted:
Absolute truth. Flight schools here decided Sundowners were the perfect trainer. Any second run cylinders would crack through the exhaust port and we had 2 or 3 that were over 50% on the way to head separation. Touch & goes would kill Lycoming cylinders. |
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Posted: 1/6/2020 7:24:43 PM EDT
[#17]
Don’t know if it will induce failures, but it will accelerate wear.
I worked at an FBO in college. There was a skydiving club with a 206. All that thing did was full-climb, then spiral down. Over and over and over. That engine aged faster than a trailer park queen on meth. |
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Posted: 1/7/2020 10:32:15 PM EDT
[#18]
Quote HistoryQuoted:
I mostly had to worry about it in turbo-normalized engines like on Cessna 414s and Navajo Chieftons. My company in Alaska had the policy of pulling off no more than 1" of manifold pressure every minute. I was typically too busy to pay that close attention to it so I usually cheated and just did 2" every 2 minutes. But it really made you plan your descents. Then we had to sit on the ramp to wait for engine temps to get below some predetermined temp before shutting down. Can't remember what that temp was now. I never worried too much about shock cooling in normally aspirated engines. My 172 endured a lot of power chopping yet always made it to tbo. Same for the Comanche 250. |
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Posted: 1/8/2020 6:47:40 AM EDT
[#19]
What about the thermal stress on an engine when you take off once the oil is in the green at 100 degrees and apply 38" and 2700 RPM? I generally try to keep cooling less than 40deg/min in the descent, but that's an arbitrary rate. Mooney Rockets often go 400 hours past TBO on their TSIO520-NBs to the bewilderment of the 414 guys. The theory is that overall cooling may be better. On another note, I run full power to altitude in both planes. I made it past TBO on my IO360 running it like that and the book from Continental doesn't have a 5 minute limitation on the NB like many other 520 variants, so I maintain full power up to FL240, provided all the temps look good. Another thing to note is a lot of pilots talk about keeping cylinder temps in the IO360 below 400; the Lycoming bulletin advises 415 is fine in cruise with up to 435 in climb.
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Posted: 1/8/2020 7:37:15 AM EDT
[#20]
Quote HistoryQuoted:
What about the thermal stress on an engine when you take off once the oil is in the green at 100 degrees and apply 38" and 2700 RPM? I generally try to keep cooling less than 40deg/min in the descent, but that's an arbitrary rate. Mooney Rockets often go 400 hours past TBO on their TSIO520-NBs to the bewilderment of the 414 guys. The theory is that overall cooling may be better. On another note, I run full power to altitude in both planes. I made it past TBO on my IO360 running it like that and the book from Continental doesn't have a 5 minute limitation on the NB like many other 520 variants, so I maintain full power up to FL240, provided all the temps look good. Another thing to note is a lot of pilots talk about keeping cylinder temps in the IO360 below 400; the Lycoming bulletin advises 415 is fine in cruise with up to 435 in climb. It's funny because it's true 
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Posted: 1/16/2020 5:31:51 PM EDT
[#21]
Don't know if this is relevant but on Jan. 14, 1944 a P-38 crashed near Sterling, OK. Stated cause was engine failure due to shock cooling after a max-performance climb to 20,000 feet.
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Posted: 1/16/2020 6:25:17 PM EDT
[#22]
Quote HistoryQuoted:
What about the thermal stress on an engine when you take off once the oil is in the green at 100 degrees and apply 38" and 2700 RPM? I generally try to keep cooling less than 40deg/min in the descent, but that's an arbitrary rate. Mooney Rockets often go 400 hours past TBO on their TSIO520-NBs to the bewilderment of the 414 guys. The theory is that overall cooling may be better. On another note, I run full power to altitude in both planes. I made it past TBO on my IO360 running it like that and the book from Continental doesn't have a 5 minute limitation on the NB like many other 520 variants, so I maintain full power up to FL240, provided all the temps look good. Another thing to note is a lot of pilots talk about keeping cylinder temps in the IO360 below 400; the Lycoming bulletin advises 415 is fine in cruise with up to 435 in climb. Out of 5 414's we have 2 that are 7's and can't be de-rammed because it modified the engine beams at install. We build probably 5 engines a year in house because of TBO and 135 not because they done. I haven't looked at the pile in a few months but I probably have over a dozen cylinders with cracks in the head that will pass compression check all day long. The cracks are in the induction plenum between the cooling fins. It shows up as a blue stain running down the intake runner. |
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Posted: 1/17/2020 4:14:42 AM EDT
[#23]
Part of the com multi checkride requires the applicant to do an emergency descent. Which means our planes are doing quite a few for practice. Our procedure is power to idle, prop full, mix full, and pitch for Va, usually 4k fpm. Probably, oh I dont know, 5-10 times a week.
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Posted: 1/17/2020 4:39:09 AM EDT
[#24]
Never seemed to be a problem on my old Chevy Corvair.
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Posted: 1/17/2020 6:23:31 AM EDT
[#25]
Quote HistoryQuoted: A 414 with ram 7 tsio520's is pretty close to clapped out by TBO even if you do the oil changes at 25hrs like you're supposed to. A ram 4 or non ram 414 will go way past TBO if the pilot does his part. Out of 5 414's we have 2 that are 7's and can't be de-rammed because it modified the engine beams at install. We build probably 5 engines a year in house because of TBO and 135 not because they done. I haven't looked at the pile in a few months but I probably have over a dozen cylinders with cracks in the head that will pass compression check all day long. The cracks are in the induction plenum between the cooling fins. It shows up as a blue stain running down the intake runner. I’m in annual right now. Cylinder #1 was 70 and #4 was 68. He figures the ring wasn’t seated right during the compression test as he opened the oil cap and could hear the air. All others were 75. This is good, considering I haven’t had a paycheck since July. The question is whether the fine wire plugs are worth doing this year and if I can get my fuel burn down to something comparable to my other plane. When I had a steady paycheck, I didn’t worry about fuel burn, but it would still be useful for increasing range, especially with pax and being able to keep enough fuel in the plane so as not to have to refuel every short trip would be nice too. |
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Posted: 1/17/2020 2:05:31 PM EDT
[#26]
Quote HistoryQuoted: I’m a bit curious how you operate your engines. I tend to run 100% to FL240 and then back down to cruise power, keeping TIT <1550 in the climb and CHTs <400. CHTs might lose 40 degrees over the course of a couple of minutes when transitioning to cruise at 70-76% power, but it’s tough to get fuel burn to under 18gph. There are guys who have spent a lot of time getting GAMI spreads right and have installed fine wires and are able to run LOP. They claim 16GPH and 35” of mp, keeping TIT under 1600, and have made it collectively thousands of hours without cooking their engines. I’m in annual right now. Cylinder #1 was 70 and #4 was 68. He figures the ring wasn’t seated right during the compression test as he opened the oil cap and could hear the air. All others were 75. This is good, considering I haven’t had a paycheck since July. The question is whether the fine wire plugs are worth doing this year and if I can get my fuel burn down to something comparable to my other plane. When I had a steady paycheck, I didn’t worry about fuel burn, but it would still be useful for increasing range, especially with pax and being able to keep enough fuel in the plane so as not to have to refuel every short trip would be nice too. We don't have edm or anything like that, just factory CHT/EGT and a shaddin fuel flow, flown very conservatively. |
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Posted: 1/18/2020 11:32:33 PM EDT
[#27]
I conduct ME Checkrides in Duchess and DA-42Ls in the Midwest. The ACS requires that we shut down an engine during the checkride. As a high time piston pilot and A&P it pains me to do that in the winter but to the best of my knowledge we've not cracked any cylinders. I do ensure we cool it down and warm it up gently, but the cylinder temperature cools quickly when off.
I"m sure it's possible to crack them especially in turbo'd engines but seemingly it's also possible to not if you take care to not abuse them. |
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Posted: 1/19/2020 1:06:32 AM EDT
[#28]
I brought this up to my IA who worked at a flight school early in his career. I mentioned the jury still being out on shock cooling and he responded like I was nuts. He said he replaced many cracked cylinders on their Cessna 310s that he believed was due to shock cooling. The way we discussed it made a lot of sense. If you're on approach and ease the power out, you're already fairly low and don't have nearly as much airflow through the cowling as you do if pull power at altitude and are trying to stay under Vne and ramming tons of cold air around cylinders.
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Posted: 1/19/2020 2:57:33 AM EDT
[#29]
I’m not an aviation recip expert by any means, but I don’t buy much of it except for a few specific engines that are known for being sensitive in general.
I never worried about it with any of the common recips. That said, I know most guys don’t understand how the mixture works. |
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