Cooling engines at different altitudes

[save]

Does altitude freeze effects count in when you try to cool your engine as fast as possible in AH  ?

Generally 100 meter (300 feet ) higher altitude  temperature  will cool off by 0.7 C degrees. I also hear my friends flying air cooled engines, they worry about chock cooling by simply go idle at wintertime / flying high. Since I fly liquid engine VLA's temperatures are less factor.


Since my favourite ride is the the air cooled engined FW a-series , I struggle to keep temperature because in MA your are easy outpaced by many  hot rods. At 20k air temperature should be really low, but I can see little or no difference in cooling effect.

[Lusche]

Does altitude freeze effects count in when you try to cool your engine as fast as possible in AH  ?

No.

The "cooldown" times of WEP are fixed and can not be influenced by the player in any way.

[icepac]

Less dense air transfers less heat.

[colmbo]

Since my favourite ride is the the air cooled engined FW a-series , I struggle to keep temperature because in MA your are easy outpaced by many  hot rods. At 20k air temperature should be really low, but I can see little or no difference in cooling effect.

In the real world the air is also very thin at high altitude which reduces it's cooling capacity --  less air, less heat carried away.

[B4Buster]

save, shock cooling piston-driven aircraft is something you need to keep in mind in the real world, particularly when flying high performance aircraft. There is a bit of controversy regarding this though.

I don't recall reading anything about shock cooling aircraft in WWII but surely it must have been an issue. Anyone?

[Widewing]

save, shock cooling piston-driven aircraft is something you need to keep in mind in the real world, particularly when flying high performance aircraft. There is a bit of controversy regarding this though.

I don't recall reading anything about shock cooling aircraft in WWII but surely it must have been an issue. Anyone?

When first introduced in the ETO, some P-38J pilots claimed to have suffered from excessive oil cooling at high altitude. Ground crews were blocking off portions of the heat exchangers to keep heat in the oil. Later investigation revealed that the issue was not really too much cooling, but pilots who used the manual over-ride switch to set the cooler flaps fully open, and then forgot to move the switch to the automatic position. Once they began following procedures, always using the automatic setting, the issue disappeared.

[Captain Virgil Hilts]

Oil could get cool enough in the P-38 to congeal in the boost control system that was regulated by oil pressure. It would allow the turbocharger to run away, not only producing too much boost, but eventually exceeding the safe RPM, at which point the turbine could literally explode. The armored ring around the turbocharger was there as much to contain a possible turbine failure as it was to protect against damage by enemy fire.

The same turbocharger, used on the P-47 and some bombers, could over speed and over boost there as well, but for other reasons. The P-47 actually had a light that glowed brighter as the turbocharger reached excessive RPM.

I suppose, in theory, it might be possible to "shock" an aircraft engine. But it would require that a heavily loaded and very hot engine be suddenly exposed to much colder air found at a much higher altitude, while the load that created the heat was lowered substantially. I'm not even sure that running at WEP until you got up to over 400 MPH level speed, pulling a steep "zoom climb" then slamming the throttles closed during, at the end of, or after a steep zoom climb could do it. It would probably be even more difficult with a liquid cooled engine, and you'd have to cool the coolant in the radiator instantly, and have it surge into the water jacket of the engine.

You'd be trying to duplicate the effects boiling most or all of the coolant out of your car, then pumping it full of chilled water, but in an aircraft, in flight. You can crack a head or a block, or blow a head gasket, in a car or truck, doing that.

I'm not sure you could do it even if you forced the oil cooler and radiator "doors" on a P-38 shot for speed at WEP, then slammed the throttles to idle and the doors open when you got 10K feet higher. Maybe.

[Midway]

That brings up a question I've always had.  If I cut my engine at high speed and just coast with it off to cool it and the temp gauge drops way down... why is it that when I start the engine again, the temperature heats way faster than when I started my sortie?

[colmbo]

I suppose, in theory, it might be possible to "shock" an aircraft engine. But it would require that a heavily loaded and very hot engine be suddenly exposed to much colder air found at a much higher altitude, while the load that created the heat was lowered substantially.

You don't have to go high to cool the engine too quickly..remember the higher you go the less dense the air.  High airspeed at low power settings is what cools the engine quickly.

I'm not a big believer in some of the "shock cooling" horror stories that are prevalent in aviation, but it makes sense that thermal cycles do take a toll on the metal in the engine.

[Oldman731]

You don't have to go high to cool the engine too quickly..remember the higher you go the less dense the air.  High airspeed at low power settings is what cools the engine quickly.

I'm not a big believer in some of the "shock cooling" horror stories that are prevalent in aviation, but it makes sense that thermal cycles do take a toll on the metal in the engine.

"Repeated thermal shock can cause a number of engine problems. In its Key Reprints, Lycoming warns, "Unless the pilot takes certain precautions, fast descents carrying high cruise rpm and low manifold pressure (MP) cause broken piston rings from ring flutter, and also cause cracked cylinders at the spark plug and valve ports, and warped exhaust valves due to sudden cooling."

Lycoming further warns that sudden cooling can result in fouled spark plugs and sticking exhaust valves, which can lead to bent push rods. This sort of damage is not only expensive to fix, it can lead to a power loss or engine failure."

http://www.aopa.org/members/ftmag/article.cfm?article=2534

- oldman

[colmbo]

Lycoming warns

Lycoming also said that cooling faster then 30 degrees F per minute is shock cooling.  In my 182 (Continental powered) simply leveling from the climb and accelerating would start the front cylinders cooling faster then that according to my 14 channel engine monitor.  From practical experience I don't believe the shock cooling is as critical as many would have you believe.

[Oldman731]

Lycoming also said that cooling faster then 30 degrees F per minute is shock cooling.  In my 182 (Continental powered) simply leveling from the climb and accelerating would start the front cylinders cooling faster then that according to my 14 channel engine monitor.  From practical experience I don't believe the shock cooling is as critical as many would have you believe.

Could be.  But they're the ones who build the motors.

- oldman

[BaDkaRmA158Th]

That brings up a question I've always had.  If I cut my engine at high speed and just coast with it off to cool it and the temp gauge drops way down... why is it that when I start the engine again, the temperature heats way faster than when I started my sortie?

I don't know, but i do know it helps drop the wep temp lower,faster. I also noted that putting a engine on close to idle (30-40%) and hitting my - key on the keypad (3-4 TIMES) a bit also helps the cool down timer. I do suppose it is because your engine is not running idle nor on full, and the blades are not "digging" so hard through the air. Its like telling the engine to relax and cool down,but under flight and controlable speeds. Simply cutting the engine is not the best thing to do in alot of cases, and remember with higher alt also comes less air, air to remove heat. I also think it simply comes down to the coolant and oil temps dropping as well.

so, its F: all of the above.

[Midway]

I don't know, but i do know it helps drop the wep temp lower,faster. I also noted that putting a engine on close to idle (30-40%) and hitting my - key on the keypad (3-4 TIMES) a bit also helps the cool down timer. I do suppose it is because your engine is not running idle nor on full, and the blades are not "digging" so hard through the air. Its like telling the engine to relax and cool down,but under flight and controlable speeds. Simply cutting the engine is not the best thing to do in alot of cases, and remember with higher alt also comes less air, air to remove heat. I also think it simply comes down to the coolant and oil temps dropping as well.

so, its F: all of the above.

Thanks.  That all makes sense to me.

[MK-84]

Could be.  But they're the ones who build the motors.

- oldman

     Is it also possible they say this because it is a known condition that could potentially, theoretically, possibly, maybe cause damage and they want to distance themselves from blame if there ever is an issue?  (i.e. we told you so)
     Other then the concept of the idea I don't really understand shock cooling, however maybe this is really only an issue of ultra high performance engines, even beyond what a typical ww2 aircraft were using?