Turbo cool down?
- Thread starter Pilot2087
- Start date
USMCmech
Well-Known Member
Rule #1 about aircraft engines, they don't fundmentally differ from automotive engines. A VW bug engine is virtually identical to the one in your Cessna. After the initial warm up turbochargers in ALL enignes stay at a fairly constant temperature.
The "turbo cool down" time is mostly a myth. Unless you have been running at high power/low airspeed for some time, your turbo is already as "cool" as it's going to get. Sitting still running at idle with minimal airflow through the cowling, your engine is actually heating up, not cooling down.
The engine "cool down" time comes from helos. After hovering for some time, High (max) power/low airspeed the engine will get very hot. Idleing for a short time allows their engine to cool down. Fixed wing airplanes don't really need this.
esa17
Well-Known Member
I have not read the POH for a new fixed wing but I have flown some turbo'd choppers and we still cool the turbo down.
If you have a long taxi I suppose you're alright but it's still better safe than sorry.
2 mins minimum for our UH-1Hs. Agree, since we don't have taxi time, etc. We park and then the engine can come to ground idle, all other times it's in fly. So we can't just shutdown (aside from an emergency shutdown).
R
Roger, Roger
Guest
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.
ppragman
FLIPY FLAPS!
If he told you to jump off a cliff, would you.....
How much is he playing, and how high is the cliff?
I can't say I have ever heard of that. I personally have two cars in the family with turbo's and none of them keep the engine running, that I know of. I would suspect that when a car is not being accelerated the waste gate is left open, keeping the turbo from running. It sure seems like it, since driving down the highway and stopping on the gas has a short lag before I hear the whine of the turbo.
Like others have said though, I would suspect the time the engine is run at low RPM for landing is sufficient for cooling the turbo. I have no experience with it though. Remember, the turbine is powered by exhaust gas, so at 1500 or less RPM that thing isn't really doing much at all.
AviatorGator
Well-Known Member
PGT has it right. My dad installed a turbo timer on his modified F-350 turbo diesel. He also has a boost computer that has among other things, a temperature readout of the TIT. It's quite easy to tell when the temperature has stabilized. Usually taking the truck to the supermarket and back would allow the turbo to cool much more quickly than when we were towing our airboat (much heavier load). With the turbo timer dad removes the key and walks away, and the timer is preset to let the engine run at idle for two minutes (or three minutes during hunting season when we tow the boat a lot) before shutting down.
The fan in mine will keep running for a bit after the key has been shut off (only in hot conditions), but the engine doesn't. The fan is pretty loud, though, so I've had people try to tell me I left the car running when the key is in my pocket.
I remember the DA-42 (diesel version) having a cool-down requirement for the engines: two minutes at idle power before shutdown. Normally, just the taxi-in was enough for take care of it. But if you bumped the throttles even a bit, you had to start the timer all over again. The most likely time for that was on the turn into the parking spot, which was a pain in the ass.
This.
That said, I agree with pprag...if the guy writing the checks says to sit there on the ramp for 5 minutes cooling the engine, you do it...even if you're really (most likely) heating it back up.
FWIW, we idle our engines for 2 minutes after landing because the book says to. The boss-man doesn't. Go figure.
-mini
roundout
VNAV monitor
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.
stratoduck
New Member
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.
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.
If there were only some way to get a bunch of air to flow over the engine and cool everything down at a low power setting prior to the taxi to the ramp......
-mini
///AMG
Well-Known Member
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.
I'd be more interested in hearing what the engineers at the engine/turbo manufacturer have to say about it than the lawyers on payroll at the airframe manufacturer.
-mini
///AMG
Well-Known Member
Fair enough.....if I owned said aircraft I too would probably familiarize myself a bit more with the engineering aspects of operation.
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