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Cooling rate

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brian257

Well Known Member
I have my GRT EIS/EFIS set up to alarm at 50 degree per minute CHT cooling which is the standard rate I have seen published. Pretty much every time I pull power on downwind I get cooling rate alarms from downwind all the way to final. Obviously these alarms are distracting, but I do tent to pay attention to what is alarming and acknowledge them in case it is something more urgent that is alarming. To make it worse, the GRT alarms for each cylinder so I wind up acknowledging three or four alarms while on base when I should be paying more attention to what is outside.

I get these alarms on my downwind power reduction even when I reduce to under 1/2 throttle in my slow descent to the airport and have all the CHT temps under 375 degrees before downwind so I don't think at that point I am really in danger of shock cooling (and many articles on the subject suggest shock cooling damage is mostly a myth anyway).

So I am wondering if everyone else with engine monitors with cooling rate alarms is getting the same alarms as me or do the rest of you have this alarm turned off or set to a higher cooling rate than I do? Or, as I suspect, does the GRT alarm at just a momentary cooling rate of what is set where other monitors don't alarm unless that rate is sustained for a longer time?
 
Since I pretty much have to pull power off in order to land, and I don't want to fly a jet-sized pattern, I don't worry about too rapid of cooling rates, and have never set any alarms for them.

There ARE engines that are sensitive to lots of different things, but the basic Lycosaurus is pretty tolerant of mild abuse - and before the days of engine monitors, when we didn't know what was happening to them, they tolerated pilots pretty well too.

Paul
 
I do not use the cooling rate alarms.

I only use alarms to note real problems, not potential problems or near the edge of the "green" conditions. That's a philosophical choice and probably worthy of a lengthy debate on the internet. ;-)
 
FWIW, I have the GRT alarm set for 50F p/min, but it never trips. The initial CHT isn't very high (~350 ballpark), and descent is made with the cowl door closed, at anywhere from 500 to 1000 FPM, 200 kts. I'll be 300~320 at downwind.

I get these alarms on my downwind power reduction even when I reduce to under 1/2 throttle in my slow descent to the airport and have all the CHT temps under 375 degrees before downwind
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You must be cruising with CHTs at 400+. I'm not getting into that particular primer war, but with 375 on downwind I can see how you would get an alarm. You're probably at or below 300 when crossing the threshold?
 
Dan, I was kind of guestimating my temps. I will pay more attention to them this weekend and get real numbers. This is on a Mustang 2, not an RV and I have fairly big cooling inlets in the cowl and I am moving pretty fast from downwind to touchdown. Even though I have the big cooling inlets I still get a little over 400 on the rear cylinders on the top of a climb so I need to make a plenum and cowl flaps and get my cooling situation a little better. For now I was wondering if I really have a rapid cooling issue or not.
 
I experience same nuisance warnings ...

When I set up my GRTs, I set the cooling rate alarm point at 35 degrees, per recommendation from Mike Busch in a webinar. That resulted in constant alarms. Since then I've reset it to 40 and 45 sequentially, and I STILL get alarms if I pull power by more than 200 RPM. I attributed the alarms to the efficiency of my cooling plenum, but on reading the OP here it seems it is not a "plenum thing."
Given the posts I read above, I'll likely just kill those alarms for the future. If nothing else, it will save wear and tear on my "alarm acknowledge" button! :D
 
I guess the consensus is that nobody is using this alarm with success. I guess I will up the temp to 65 or 75 and see if that kills the false alarms or just turn them off.
 
i use 70

I use 70 and rarely have alarm but always plan my descent well ahead and frequently fly IFR so almost always straight IN approach. With 50 I was ok but it was distracting me sometime In the cloud on the approach with other better things to do than silencing alarm . 70 is fine for me. I don't care too much if it come up but it remember me to be gentle with the engine. ( Anything to save these $$$ engine)
 
Mike H said:
Just another myth that gets perpetuated and beat to death.
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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. :)
 
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
 
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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