Turbo cool down?

stratoduck said:
modern automotive turbo chargers typically are water jacketed - they are cooled by the coolant system. the old turbochargers from the 1980's and older lacked this, and were only cooled by the oil. one must let the car idle a minute or two for the turbo cool down. otherwise, the trapped oil in the bearing would congeal, and eventually plug the passageway, and the turbo would seize. the water jacket keeps the temperatures in check. synthetic motor oils can be heated about 200 degrees F higher (than conventional oils) before they start congealing, so this and the water jacket have eliminated the idling cool down. you may recall turbocharged cars from that era needing a replacement turbocharger after 35-70k miles, because few people adhered to the cool down time. if the car was allowed to idle down, the turbo would outlast the life of the engine.

naturally the aircraft engines would be lacking in providing a water jacket cooling system, with the exception of the DA-42 and the liquid cooled continentals.

turbos should also be given a proper warm up time. when the oil is cold, there really is inadequate oil flow to the bearing. this isn't a factor so much in aircraft engines as the taxi out and run-up gets a least a little heat in the oil. this is more a factor for the cars, and throttle applications should be minimal to keep the turbo from spinning up as much as possible for the first few minutes.
Click to expand...

Not all modern turbocharged cars are cooled this way. The 3 of my cars which are turbocharged are all oil cooled. However, you bring up a good point about synthetic oils - we can get away with this in cars by using synthetic oils. There are no synthetic oils available to purchase for airplane engines. I don't buy the argument about 1930s technology not needing advanced oils - this here is a perfect argument in favor of synthetics. My guess as to why there aren't any is cost. Too much cost to get it approved and not enough market to recoup the money spent for design and approval.

Bottom line is that the powerplant vendors and manufacturers are going to have to do something sooner rather than later if avgas's days are numbered.
 
stratoduck said:
naturally the aircraft engines would be lacking in providing a water jacket cooling system, with the exception of the DA-42 and the liquid cooled continentals.
Click to expand...
DA42 turbo is only oil cooled. At least on the Thielert motor, I'm not sure about the Austro.
 
minitour said:
I wasn't trying to be a male fun-stick...just making a statement. Sorry, I realize now that it came off that way.

-mini
Click to expand...

Oh no offense taken my friend, I didn't think you intended it that way either.....and it was a good point anyway
 
The cool down period remains a suggested operating practice in both Continential and Lycoming engine manuals (in addition to POHs). Therefore, it's something I practice.

The risk/reward analysis tells me that a five minute cool down period isn't going to cost much or prove any damage so simply put - no harm, no foul.
 
///AMG said:
Not really on production cars, but lots of aftermarket cars running high boost (like 15 psi or more) will have this installed. These engines are working hard, in many cases almost too hard, and they need the extra help cooling down. An aircraft engine typically does not run anywhere close to this level of boost, but in any case, I'd follow what is written in the POH of course.
Click to expand...

Where the problem lies is if someone drives the car hard, then shuts it down shortly thereafter. If it is run at normal speeds for a few minutes usually that is enough to keep the oil from coking in the center section bearings. Shutdown timers were/are installed as some extra insurance but aren't really necessary, in my opinion, as long as one doesn't shut the engine down within 3-4 minutes of the engine being run at full boost for a prolonged period of time.
 
roundout said:
I don't know about the 400 or Cirrus but the Acclaim POH calls for 5 minutes at idle. I noticed that after about 90 seconds to 2 minutes on the ground that the TITs and CHTs would start rising back up. The chief pilot and head of mx said the same thing so we started using 2 minutes.
Click to expand...

The owner of a Seneca V I flew wanted basically the same thing. We'd leave them all the way at idle until the TITs got below 800 and then pull the mixture. Usually only took a minute or so. We never let them run past that, so I don't know how long it took for them to start warming back up.

From an engineering standpoint, I understand the not enough airflow sitting parked at idle school of thought.
 
Roger said:
Don't many turbo'd cars have an automatic function that runs the engine at idle for a few minutes after the key has been shut off to ensure turbo cooling?

Back in the day I had a "turbo timer" on my car that would leave it running for a couple minutes to cool it down.
Click to expand...
 
I want to say the 402 requires 2 minutes at taxi power. I personally try to keep the power below 1000 RPM, but if we're above about 6500 pounds on landing I can't get it to creep below 1200-1300 RPM. I'm not going to sit there idling on a tight ramp with rampers/passengers around just to cool the turbos further. They're fine.
 
Roger said:
Don't many turbo'd cars have an automatic function that runs the engine at idle for a few minutes after the key has been shut off to ensure turbo cooling?

Knowing the difference between idling TIT (~800-1000 F) and full power TIT (usually 1600-1700 F) I would guesstimate that you might actually be able to help the turbo cool down a little by running at idle. Whether it's enough to really prevent coking on the turbo bearing, I have no idea. Also, I'd guess that after an approach, landing, and taxi (all at relatively low TITs) you probably are as cool as you're going to get.
Click to expand...


It's a turbo timer, and it's to keep the oil flowing so it doesn't cake up in the galleys of the turbo from a brutally hot turbo that was just run the snot out of, got hot as hell and shut down. When an airplane lands, it's been at a reduced power setting for at least a few minutes, then at a reduced power setting for taxi, etc. I'm no airplane mech. but I do know turbo's, and if you run a good oil in a car (i.e. syn. oil), it's a waste of gas. In an airplane, it's a waste of hobbs hours.
 
The bossman tells us we have to wait 5 minutes for our Turbo 210's.

Sort of a pain in the butt to sit there on the ramp idling while the ramp guys glare at you.

Either way the boss says do it that way, so I comply.

If anyone can find some actual material on this please post, I can't find a thing.
 
Our general rule is after descent and getting off the runway, don't exceed 1300 RPM and it will still count as turbo cool down. If you exceed 1300 RPM, let the turbo rest for 30 seconds to a minute. Problem with the turbos on our Bonanzas and Cirrus' is that once the engine is shut down, very little oil is moved anywhere, thus oil caking on the turbo bearings, but if you don't exceed 1300 RPM, there shouldn't be too much heat in there after a nice long descent
 
I was always under the impression that it was to allow oil back to the bearings more than just cooling. The bottom line is once you are in the pattern or low enough where your MP is below ambiant then the waste gate is open and the cooling begins because the turbo isn't really being used. Cars are a bad analogy because it uses boost for such a short period of time(during acceloration) you can't compare it to an airplane other than function. Same form, but different function.
 
Roger said:
Dude, we're still using FREAKING MAGNETOS.
Click to expand...


Yeah, but for a redundancy reason. Ballbearing (oil less) are so simple. My brothers race car uses them. Twin 84mm (IIRC). No lines going to the turbos at all. And th ball bearings are ceramic to deal with the heat.
 
You must log in or register to reply here.
Back
Top