You are right, what did I say wrong?
David Johnson said:
Well, I had hoped you might respond in a less sarcastic way so we might get at the issues and leave the rhetoric aside. I offered same as a courtesy. I'll do my best to continue to do so. Again, no disrespect is intended. Cheers,
Dave
Dave you are confusing me, I am just agreeing with you. I think my sense of humor was miss interpreted. Doha!
Your data is irrefutable. Milt's comment, data and referenced article have some great points. I am freely admitting you know more about it than I do, because I never tried it. I was taught not to do it, and that is the way I fly. However I reserve the right to change my mind. To be clear "IT" being big power changes, especially long low power descents.
No sarcasm, in fact I thanked you for being so polite and commented you made good points, several times. What else can I say. I never offended anyone before by saying they where right, well may be except for my ex-wife, but I am sure I was never married to you. (NOW THAT IS sarcasm, bada BOOM bada BANG.
). Lets laugh, OK.
I did point out Lycoming has put a quantitative number to shock cooling and their technical opinion to the subject. However I don't see this countering your conclusion if indeed you do not cooling more than 50F/min. The "ring flutter" is interesting. I take that as don't go below their recommended 15" MAP. I call that don't let the prop push the engine. Another controversy no doubt.
Hey its hard to change years of training, but I respectfully submit you have changed my mind, albeit with some prejudice. I will not change my way of operation but I will look into it further. When I get my plane flying I'll do some experiments myself. However I see no need to stay high and drop in from upon high at "MIN POWER".
The AvWeb article said many things in the start that makes a lot of sense. The math sounds OK and backs Milts data, that CHT does not change much, but the other stuff I don't think makes much impact on the subject.
"To my way of thinking, there is no scientific proof that shock cooling plays a
significant role in cylinder damage in aviation."
It's true and there is no evidence one way or the other. Than it gets into other peripheral or anecdotal evidence that "shock cooling" is a myth and not critical, such as flying in rain (verga). This is kind of weak. Very little water gets to your engine, unless its a typhoon, and wet air is LESS dense and provides less cooling. However if you're in a "verga" the evaporation has occurred and cooled the air. Sure that will help but a very small amount. The author pointed out that its not wise flying into a verga. He is right. (Extreme down drafts occur in verga's and are one sign of possible micro burst.) The RIAN evidence is a non-sequitur.
The cooling at shut down is also weak anecdotal evidence that shock cooling does not exist, in my opinion. The logic is if is OK here it is OK in flight? First the total temp at shut down is much less. Yes there is rapid cooling but from a much lower temp. Cooling from 260F fast is not like going from 400F to 300F fast. Also the engine has to keep running in flight, while going thru this temp transition. The shut down evidence is also non-sequitur, true but logic does not follow conclusion.
So I follow Lycomings recommendations, while still agreeing with you. If you have the full meal deal engine monitor than by all means drop a chop if you maintain Lycs limitations, like:
Minimum in-flight CHT 150F
(I like high 200's or 300F. BELOW 300F lead fouling!)
Max CHT rate of change 50F
Min Oil Temp 165-190F
Min Oil Press 55 psi
Min MAP 15" (my personal rule 19" MAP min until final)
No offense. Besides temp there are reasons as you and I agree to keep it hot. Lead fouling, piston ring flutter and carb heat to name a few.
Cheers George
PS as far as jump planes, the name of the game was to get on the ground. There was no CHT gauge. To get down, put it in a 60-70 degree bank spiral right after the climb and passengers "stepped out". The name of the game was to get on the ground. You tried to keep some power and use the drag from the high "g" steep descending spiral. Some just chopped and dropped. There was no worry of cylinders. It was part of the business.
PSS In fact as a CFI and CFI (ME) I chopped power. Students needed to get simulated power loss demos, multi engine pilots single engine work. However I did things to minimize the danger (of really loosing power) and abuse of the engine. I made sure the engine was in low power cruise or descent before the demo. Therefore it was already cool. The NTSB has so many accident from simulated engine failures they, AOPA, FAA have reports on it. That is why your CFI added power on occasion during a simulated engine failure. GOING TO REAL LOW POWER in descents can be bad. The engine may NOT come back when you need it to.
Carb ICE is a good reason to "keep it hot". Go to idle and you don't have carb heat. When you are ready for power, push the throttle forward and nothing.