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-   -   Cooling rate (https://vansairforce.net/community/showthread.php?t=126346)

Mike H 07-02-2015 12:55 PM

Just another myth that gets perpetuated and beat to death.

David-aviator 07-03-2015 06:54 AM

Quote:

Originally Posted by Mike H (Post 995331)
Just another myth that gets perpetuated and beat to death.

I agree, don't think it is a big deal unless pulling 60" MP (as I recall) with a P&W 4360.

It had 2 gear driven superchargers and one turbocharger. Cool down rate was very important as the engines only ran about 600 hours at best.

Also true with some Lycomings and Continentals but I don't think anyone is super or turbo charging an RV, yet. :)

chazking 07-03-2015 07:06 AM

Non Issue
 
Caution with the cooling rate, but no need to agonize over it. Myth put to rest.

kenora 07-03-2015 07:32 AM

This is just a FWIW post...

I have been towing gliders with a variety of Scouts (O360) for decades... we climb at 65 mph and regularly see 400 - 430 f cylinder head temps in the summer.
After release we throttle back to 2100 RPM (top of caution zone) and descend at 100 - 110 mph till we see 300 f cyl head temps (after a climb to 4000 agl or more it can be several minutes) but we are targeting 100 f/minute.
as soon as the cyl head temps drop below 300 f its power OFF and maintain 100-110 mph to short final... regularly see 1000 - 1500 fpm descent.
We have NEVER cracked a cylinder using this rather aggressive cooling technique and repeat the cycle 6 times an hour for 8-10 hours a day x July and August.
my 2 cents...... they RARELY break and we regularly get to TBO

dutchroll 07-04-2015 03:35 AM

On my radial (the M14P) the only "cooling" limitation is the bottom end of the CHT range which is 120 deg C.

The Russians specifically mention not allowing it to go below this temp during power off descent, but there is no "shock cooling" limit at all providing it is kept above the minimum operating temperature. Also they require CHT to stabilise < 150 deg C prior to engine shutdown, which makes perfect sense. Given that the engine has been around for several decades, I imagine they would know by now if shock cooling was an issue.

I agree there seems to be more paranoia about this than is really necessary (arguably fed by some of the engine monitor manufacturers).


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