Shock Cooling
Moderator: drseti
Shock Cooling
How prone or resistant is the Rotax 912 ULS to shock cooling on descent?
Re: Shock Cooling
designrs wrote:How prone or resistant is the Rotax 912 ULS to shock cooling on descent?
There are those who will tell you that "shock cooling" is an old wive's tale, even with more conventional engines.
With respect to the Rotax, the fact that it's water cooled should completely eliminate any fear of "shock cooling" .
Re: Shock Cooling
Say you do a rapid descent of 4,000 feet at 1,200 ft/min with the power pulled back in colder air around 45 F OAT? Not a good idea of course, but can the Rotax with the oil / water cooling take that?
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Re: Shock Cooling
"There are those who will tell you that "shock cooling" is an old wive's tale, even with more conventional engines."
Perhaps that's the perception among some but, once you have full CHT/EGT instrumentation, the cooling rate seen by an engine e.g. during descent becomes observed fact. The issue is whether it's harmful - e.g. leads to cylinder head cracking - or not. With a partially liquid cooled engine, I would expect that consequence - to the extent it exists - is minimized.
Here's a classic article supporting the notion that shock cooling is a myth: http://www.avweb.com/news/maint/182883- ... directed=1
Nevertheless, I refuse to ignore Lycoming's caution - don't allow CHT cooling rate to rise above 50F - because they designed and built my engine, including the cylinders manufactured only a few years ago. What does Rotax say on the subject?
Perhaps that's the perception among some but, once you have full CHT/EGT instrumentation, the cooling rate seen by an engine e.g. during descent becomes observed fact. The issue is whether it's harmful - e.g. leads to cylinder head cracking - or not. With a partially liquid cooled engine, I would expect that consequence - to the extent it exists - is minimized.
Here's a classic article supporting the notion that shock cooling is a myth: http://www.avweb.com/news/maint/182883- ... directed=1
Nevertheless, I refuse to ignore Lycoming's caution - don't allow CHT cooling rate to rise above 50F - because they designed and built my engine, including the cylinders manufactured only a few years ago. What does Rotax say on the subject?
Jack
Flying in/out KBZN, Bozeman MT in a Grumman Tiger
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Flying in/out KBZN, Bozeman MT in a Grumman Tiger
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Re: Shock Cooling
Rotax does not caution against shock cooling.
They do caution about over temps (obviously) and bank angles of 40 degrees (Surprising… I though it would be good to at least 45 degrees bank).
However, from the SportCruiser / PiperSport aircraft POH:
"CAUTION
Rapid engine cooling should be avoided during operation. This happens above all during aircraft descent, taxiing and low engine [rpm] or at engine shutdown immediately after landing.
Under normal conditions the engine temperatures stabilize during descent, taxiing and at values suitable to stop engine by switching the ignition off. If necessary, cool the engine at idle [rpm] to stabilize the temperatures prior to engine shut down."
Of course the bottom line is you have to watch your temps.
I was just looking from some additional input, perhaps also from our Rotax mechanics based on cases that they might have seen.
They do caution about over temps (obviously) and bank angles of 40 degrees (Surprising… I though it would be good to at least 45 degrees bank).
However, from the SportCruiser / PiperSport aircraft POH:
"CAUTION
Rapid engine cooling should be avoided during operation. This happens above all during aircraft descent, taxiing and low engine [rpm] or at engine shutdown immediately after landing.
Under normal conditions the engine temperatures stabilize during descent, taxiing and at values suitable to stop engine by switching the ignition off. If necessary, cool the engine at idle [rpm] to stabilize the temperatures prior to engine shut down."
Of course the bottom line is you have to watch your temps.
I was just looking from some additional input, perhaps also from our Rotax mechanics based on cases that they might have seen.
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Re: Shock Cooling
The 40 degree limit on bank angle is a new one on me. I suspect it's widely ignored in training service while doing steep turns. I've probably done over a hundred in mine, and I'm sure I've gone as far as 55-60 degrees briefly.
PP-ASEL, Flight Design CTSW owner.
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Re: Shock Cooling
Wouldn't that 40 degree bank have to be uncoordinated before the engine 'knows' its banked?
- FastEddieB
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Re: Shock Cooling
This has come up before. It's a weird one. Especially since steep turns are a standard training maneuver.CharlieTango wrote:Wouldn't that 40 degree bank have to be uncoordinated before the engine 'knows' its banked?
It MUST have been a limitation discovered on a test stand.
You're 100% right that as far as the engine goes, in a coordinated turn its still as if in level flight, albeit the engine would be "heavier".
Re: Shock Cooling
As is the oil. . .FastEddieB wrote:. . . 'in a coordinated turn its still as if in level flight, albeit the engine would be "heavier'." . . .
Bill Ince
LSRI
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Re: Shock Cooling
Good point.Wm.Ince wrote:As is the oil. . .FastEddieB wrote:. . . 'in a coordinated turn its still as if in level flight, albeit the engine would be "heavier'." . . .
Is it even remotely possible that the concern is that oil weighing 1.4x it's normal "weight " in a 45° banked turn would be an issue?
I rule nothing out, but that sounds highly improbable. An aircraft engine that cannot be banked to 45° would be sorely limited.
Re: Shock Cooling
You know, as much as POH and manufacturer literature is held as gospel, in some cases you really have to sort out reality from liability paranoia (not saying that is the case here, nor am I suggesting that we become engineers or test pilots)... but do your homework so to speak.
Re: Shock Cooling
I have noticed that my Rotax, which runs on the cool side anyway (thankfully, as I'm in Georgia!) cools down *right quick* in a power off descent from any real altitude. I have seen the temps drop from my normal ~180-220F to 150ish -- quite a difference. I assume that as long as it does not drop below the 140F red line marking the engine is warm enough for takeoff, it's probably okay. I don't do those kinds of descents often, so it's not like I'm running it through brutal heating/cooling cycles all the time.
It's only mid-October, and already my engine rarely gets much above 190F...I am going to have to break out the radiator tape soon.
It's only mid-October, and already my engine rarely gets much above 190F...I am going to have to break out the radiator tape soon.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA
Re: Shock Cooling
We're talking oil temperature, right? Where do you get a 140 redline? The Rotax manual says 50 Celsius minimum, which translates to 122F.MrMorden wrote: I assume that as long as it does not drop below the 140F red line marking the engine is warm enough for takeoff, it's probably okay.
The opinions posted are those of one CFI, and do not necessarily represent the FAA or its lawyers.
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Prof H Paul Shuch
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AvSport LLC, KLHV
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Re: Shock Cooling
My factory oil temp gauge has a red line at around 140F. It might not be exactly on the 140 line, and could be a little lower. I was told that temps above that line are acceptable for takeoff. Maybe Flight Design likes to see higher temps than Rotax?drseti wrote:We're talking oil temperature, right? Where do you get a 140 redline? The Rotax manual says 50 Celsius minimum, which translates to 122F.MrMorden wrote: I assume that as long as it does not drop below the 140F red line marking the engine is warm enough for takeoff, it's probably okay.
Andy Walker
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA
Athens, GA
Sport Pilot ASEL, LSRI
2007 Flight Design CTSW E-LSA
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