Malibuflyer wrote:
The pilots are not allowed to know if they fly the planes with or with our shock cooling (to avoid that they make other things differently as well)
Yes, Randomised, controlled, double-blind study (the investigators/engineers must not know either). Best remove any visible engine or oil temperature indicator:)
Shock cooling is not a myth (article):
https://medium.com/@tomvykruta/shock-cooling-is-not-a-myth-df12de9c7af7
Cirrus SR22 Turbo POH recommends 20“ MAP for descent and CHT >250°F.
I adhered to these values and it gives around 170kts for the initial approach. I used a short level segment before the glidepath to decelerate.
Yes; exactly. One keeps some power in for the descent, and makes use of the IAP platform to gradually bleed off any excess speed.
Also the glideslope (whether ILS, LPV or a +V one) is almost never flown on idle.
Well, not on most of our rather draggy piston planes. On a TBM, reportedly, an ILS is flown almost on idle, but that’s a different type motor 
Here is another good thread on this – along with many others.
Very roughly, on a TB20 and some other types, a 3" drop in MP gives a -500fpm rate of descent, which is just right for most scenarios, meets the minimum ATC requirement (one is supposed to advise ATC if unable to achieve 500fpm either up or down; in reality they know light GA often can’t do +500fpm at say FL150) and a 3" drop in MP, from cruise, will probably never create an excessively rapid CHT drop.
Snoopy wrote:
Shock cooling is not a myth (article):
https://medium.com/@tomvykruta/shock-cooling-is-not-a-myth-df12de9c7af7
Nobody – really nobody – questions that temperature of an engine drops very fast when you reduce power to idle in a descent. In that respect – and that is the only thing the author claims – “shock cooling” is obviously not a myth. (Ok, one could argue that “shock” sounds like kind of negative implications and therefore “rapid cooling” might be the better term.
All the debate is not about rapid cooling as such but about the question if such rapid cooling causes engine damage. The author of the article you quoted doesn’t say anything about this.
We now need a hypothesis for how cracks develop, because they do.
So many reasons: High temperatures, mechanical stress, vibrations.
One can find cracks in engines that have never been shock cooled – even never been in an airplane!
Also nobody doubts that engines develop cracks. The only question here is, if rapid cooling of an engine from time to time does contribute to the formation of cracks or not – and that is a question that has so far never answered by use of data and therefore qualifies as open question.
How about flying through a hefty rainshower? I never watched CHT’s in the rain, but I’ll do so as soon as the opportunity presents itself.
One can find cracks in engines that have never been shock cooled – even never been in an airplane!
Never heard of cracks in a new engine. It would be outrageous.
How about flying through a hefty rainshower?
I recall, from somewhere I don’t remember now, a calculation done involving the specific heat capacity of water, the average heavy raindrop size and density, and the resulting mass of water entering the cowling inlets. It may well have been posted here. It should take someone about 10 minutes to work out. I believe @davids likes these puzzles I don’t recall it being significant. Rain has a surprisingly low density of water.
I have flown through plenty of really heavy rain and never got the EDM700 70F/min warning.
Malibuflyer wrote:
So many reasons: High temperatures, mechanical stress, vibrations.
Perhaps. Though the pilot has direct control over the care they take operating the engine, and to some degree, high temperatures. Mechanical stresses and vibrations are much more design and maintenance concerns. The pilot should be aware of obvious changes in maintenance condition of the engine, but short of massive abuse, can’t really affect these factors much.
Malibuflyer wrote:
One can find cracks in engines that have never been shock cooled – even never been in an airplane!
If you’re finding a crack in an engine which has never been in a plane, there are certainly quality control and maintenance concerns about that engine – again, outside a pilot’s control. If it’s not been in a plane, a pilot has not mishandled it!
I’m struggling to understand how it could be asserted that cracks, typical of those caused by shock cooling, could be determined to not be from shock cooling.
Bobo wrote:
How about flying through a hefty rainshower? I never watched CHT’s in the rain,
Generally, the part of the cylinder head vulnerable to cracking is not directly exposed to free flow rain in flight. A half portion of the cylinder barrels, and lower portion of the heads cooling fins are commonly exposed. Though I’m not a thermal expert, I expect that the thermal energy of water drops is very little compared to the heat being radiated by the cylinders – it just boils the water off.
Few things are perfect, and even with care, cylinders may crack. The point is that with engine handling care, cylinder cracking can be greatly reduced, so why not do that?
Peter wrote:
Never heard of cracks in a new engine. It would be outrageous.
Haven’t said that. I was actually referring to engines in boats that have a similar usage profile to aircraft engines (operation under constant high % of power for longer periods of time) but are cooled differently and therefore the aircraft type shock cooling can’t happen.
If it is true that shock cooling is a major driver for such cracks, one would expect that such engines have significantly less of them…
