Turbo Charger Cool Down

[carqwik]

Video explaining the importance of the 5 minute cool down for turbocharged piston engines. 

http://hartzell.aero/article/the-importance-of-cool-down-time-for-your-aircrafts-turbocharger/

This was explained to me back in 1985 when I started flying a T-Arrow IV...the cool down has nothing to with the engine but rather the cooling of the turbocharger bearings which depend only on engine oil for heat dissipation. 

 

[201er]

Wouldn't a turbocharger receive plenty of cooling during the landing pattern? Low power, air cooling, and oil moving? What's five more minutes?

[KSMooniac]

5 more minutes of no cooling air...so it gets warmer.

Sent from my VS985 4G using Tapatalk

[Deb]

17 minutes ago, carqwik said:

Video explaining the importance of the 5 minute cool down for turbocharged piston engines. 

http://hartzell.aero/article/the-importance-of-cool-down-time-for-your-aircrafts-turbocharger/

This was explained to me back in 1985 when I started flying a T-Arrow IV...the cool down has nothing to with the engine but rather the cooling of the turbocharger bearings which depend only on engine oil for heat dissipation. 

 

There is a thread on Beechtalk discussing an opposing view here: https://www.beechtalk.com/forums/viewtopic.php?f=37&t=131819

Edited December 16, 2016 by Deb
You guys are way too fast. Many people who post on Beechtalk have been to the APS course. The thread presents their data.

[carqwik]

Well think about it.  First, this video comes from the manufacturer of turbochargers.  Second, it's not the temperature of the turbocharger which matters, it's the temp of the bearing surfaces which depend solely on oil flow for cooling.  Running the engine at idle does cause the turbocharger to spin (it can't be turned off) but it also allows oil flow past the bearing surfaces which draws away heat. 

The video shows oil coking...that's caused by heat.  My diesel Jeep has a warning in the Manual that talks to an engine cool down for five minutes as well if the engine has been under load for a while...to cool the turbocharger.  I would bet dollars that an auto manufacturer knows more about piston engines and turbochargers than APS...albeit it's a turbo diesel but the same principals apply.  Airplane engines run under heavy loads (say 70% power) and as such generate lots of turbocharger heat in the bearings.  I wouldn't dismiss this as an OWT.

In fact, Cummins also suggests a cool down period for the turbo charger as well. 

https://www.cumminsturbotechnologies.com/Operating Procedures

Again, Cummins is a huge company with lots of $$ for testing and R&D...they would certainly know about how to properly operate a modern diesel engine. 

Edited December 16, 2016 by carqwik

[carusoam]

Ask anyone that has had oil coked in their TC.

 

The cooling aspect may be hard to measure.  There isn't a bearing or oilT thermocouple in that location...  hmmmm? JPI thermocouple mounted on the turbocharger body seems to be a nice idea...?  A TC for the TC as if it didn't have enough already...  TIT, CDT, EGT + one more.

But, the overheating aspect is similar to coked oil in the valve guides.  Equally hard to measure.  And, causes some expensive maintenance issues...

Do whatever it takes to not drive it hard and put it away hot....

Watching TIT values is a good hint to how well the heat source has cooled.  Still won't tell the pilot much about the the temp of the casting...

 

Discussing the topic is a good way to avoid the issues.  Good topic to add to the PPI of a TC'd bird...

 

Great topic...

Best regards,

-a-

[Danb]

The only annoyance is when the line guy directs me to a spot and looks at me while I'm idling like dude turn it off, I have an orange sign that say "turbo cooling" now they look wave and leave me alone. I've religiously have cooled down new I really wonder if it works.

[gsxrpilot]

The guys at GAMI have a much better test facility than Hartzell does and have thoroughly debunked this practice. They actually attached temp probes to the various bearings in the turbo charger its self. They confirmed that the bearings were coolest right at touchdown. They start to warm up during taxi, and while you are sitting there on the ramp idling, they're getting even hotter. So you're actually doing your turbo a disservice by following this practice.

[N201MKTurbo]

I read somewhere once that the dual sleeve bearing used in the RaJay turbo is immune to the evil effects of cooked bearings while the Garrett turbo is not.

I just wait till the TIT gets below 700 to shut down. It is usually there on touchdown, but goes up taxiing in. I have had just about every turbo failure ($$) except bearing problems. But that is just one data point. 

[aviatoreb]

I am COMPLETELY sold that the turbo is as cool as it will get upon touch down, and starts to heat up a bit during taxi.  BUT, could it be that the practice of turning it off without "cool down" leads to coking but not for the reasons they say.  Maybe it is not heat but somehow insufficient flow or some such.  Maybe they have the wrong reason, cooling down, but they are identifying nonetheless a good practice?

That said, I don't buy it.  I land, taxi in, which is usually about 2 minutes after touch down anyway before I shut down, and then I just shut down as soon as practical based on the positioning of the airplane.  It is one of these things where one needs to make a decision which theory to put your practice in, and I put mine in the coolest-at-touch-down theory.

Separately, TiT and CDT are the only temp measurements we get for turbos, but those are gas temps.  How do those relate to turbo body temps?  It is funny there is no temp probe in the turbo like there is in cylinders where we get both CHT and EGT.  I would think this would be useful?

Also, yes 70% is a large fraction of engine percentage, at 100% but if an airplane were a car engine, then that 100% would be uprated to 200% (or something bigger) since in cars, engines are not expected to run very more than a few seconds at high power versus airplanes where they are expected to run at high percentages for hours on end.

But I really don't know what is the turbo body temp but I would guess it is related to the only things we can measure, CDT and TiT and those can be high depending on how you lean, somewhat independently of percent power, right?

[jackn]

Here's some data. On landing TiT is low, but turbo temp is probably still high. When you turn off the runway, TiT goes back up and stays up until you do the cool down. I'm going to continue to do my usual cool down. 

[KSMooniac]

APS put thermocouples ON the turbo housing, and proved that the turbo is at minimum temp at touchdown after low power approach and landing with lots of cooling air. It gets warmer as you sit there because cooling air is almost nil. TIT and CDT are gas temps as previously mentioned and don't correlate to actual turbo temps since cooling air is a huge input to the equation. This is unique to our planes since they're air-cooled, while automotive turbo engines (& diesels) are liquid-cooled and thus have the capacity to cool down while stopped due to radiator fans and coolant circulating thru the system.

Sent from my VS985 4G using Tapatalk

[ArtVandelay]

I'll bet anyone doing training in a turbo plane does more damage...

Short field takeoff, engine out, slow flight, touch and gos...probably all are harder on an engine then shutting down a few minutes after landing.

[carqwik]

The temp of the turbo housing is irrelevant to this discussion...it's the bearings that only get oil for cooling that matter.  I don't know how APS could measure the temperature of the bearings. 

Garrett published an interesting paper about turbocharger cooling...although it addresses water-supplied cooling systems for a turbo, it makes the point about cooling the bearings and bearing shaft.  In a water system, a properly designed system continues to draw water over these parts through thermal differences...but since our planes don't have a water cooling system, the takeaway has to be to continue running oil over these parts.

https://turbobygarrett.com/turbobygarrett/sites/default/files/Garrett_White_Paper_01_Water_Cooling.pdf

 

[goterminal120]

It has more to do with oil supply than cooling. Once the engine is shut down no oil is going to the spinning turbo shaft. The shut down procedure is to allow the turbin to slow down from its operating 30-40k rpm. After a long taxi it would not be necessary,but jumping off the runway to parking it couldn't hurt anything.

Edited December 16, 2016 by goterminal120
Added word

[Marcopolo]

In all the videos and all the write-ups, it is not the turbo housing that is of concern, it is the bearing and oil temperature over that bearing that we are concerned with.  I agree that TIT and CDT are at minimums upon landing, but I do need to taxi, at least off the runway, so shutting down immediately upon landing doesn't seem like a good idea, nor do I think that the bearing and oil temperatures have reached minimum yet (at least by looking at my oil temperature gauge).  While taxiing to my hanger there may be several times when the RPMs are taken above 900 or so causing TIT to rise a bit which will slow down the oil cooling curve that I was on.  So I think that adding a minute or two of idle time (900 rpm) when I get to my hanger or tie down will only help and in my opinion can in no way hurt the turbo bearing and shaft, not concerned about the housing at this point.

 

Opinions-R-us

 

Ron

[Emmet]

Well think about it.  First, this video comes from the manufacturer of turbochargers.  Second, it's not the temperature of the turbocharger which matters, it's the temp of the bearing surfaces which depend solely on oil flow for cooling.  Running the engine at idle does cause the turbocharger to spin (it can't be turned off) but it also allows oil flow past the bearing surfaces which draws away heat. 
The video shows oil coking...that's caused by heat.  My diesel Jeep has a warning in the Manual that talks to an engine cool down for five minutes as well if the engine has been under load for a while...to cool the turbocharger.  I would bet dollars that an auto manufacturer knows more about piston engines and turbochargers than APS...albeit it's a turbo diesel but the same principals apply.  Airplane engines run under heavy loads (say 70% power) and as such generate lots of turbocharger heat in the bearings.  I wouldn't dismiss this as an OWT.
In fact, Cummins also suggests a cool down period for the turbo charger as well. 
https://www.cumminsturbotechnologies.com/Operating Procedures
Again, Cummins is a huge company with lots of $$ for testing and R&D...they would certainly know about how to properly operate a modern diesel engine. 

There are lots of turbo diesels from different auto manufacturers which are equipped with a start stop system in Europe. This system shuts down the engine all the time when the car stops for more than a few seconds even if it has been run hard for the last minutes or hours (and they are run hard with high power when driving 135mph). Obviuosly they don't see a problem ...

[DVA]

TiT has nothing to do with the temperature of the turbine casing, the bearings, the oil in the scavenger, etc. Recall that TiT is just a probe in the exhaust flow. When you are landing you have the power way back or at idle - of course TiT and EGT will drop fast and deep. As you taxi, you need more power and as a result TiT and EGT will go up. But that doesn’t necessarily equate to the temp (increase or decrease) of the turbo itself. 

Recall that the turbo is a big hunk of metal and as such it will take a lot longer to begin to increase its mass heat or decrease it. Don’t let the TiT gauge be your indictor of the temperature of the turbo for the sake of this discussion.

 

[Marcopolo]

8 minutes ago, Emmet said:

There are lots of turbo diesels from different auto manufacturers which are equipped with a start stop system in Europe. This system shuts down the engine all the time when the car stops for more than a few seconds even if it has been run hard for the last minutes or hours (and they are run hard with high power when driving 135mph). Obviuosly they don't see a problem ...

These vehicles (much newer than our planes) have water and oil cooling for the turbo bearings, this combination will rarely see oil coking due to the ability to keep the turbo oil and bearing temps at or below the coking level, and they have the ability to lower these temperatures much faster with the oil water combination., leaving them the ability to shut off while idle, 

 

Ron

[jlunseth]

Let me provide some reality from the roughly 1100 hours I have on my TSIO360LB and its turbo.  The turbo had to be rebuilt right after I bought the plane but it would be impossible to pinpoint the reason.  The prior owner and the pilots he loaned the plane to had run the engine pretty hard.  My point is the turbo was rebuilt at about 650 hours and I now have more than 1100 hours on it (around 1750 total), who knows what the rebuild cause was.  

I fly by what APS says, which is that cool down is a myth and unnecessary.  My turbo is fine, in fact better than fine, after 1100 hours no cool down.  In that number of hours I have done many types of flights, but probably the most hours in total have been cruises to a distant destination at a cruise setting.  I have been running the last probably 400 hours mostly at about 70% HP LOP, which I accomplish by setting the MP at 34".  The TIT is up around 1600.  The moral of the story is that the turbo is running hard and as hot as it is ever going to get for a few hours.  My typical descent from cruise is to simply point the nose over and pull of about an inch of MP because the extra speed is going to cause the MP to gain about that much, in other words I am keeping the MP pretty much stable.  The TIT will go down because the engine is not working as hard, lets say into the 14-1500 range.  That descent can be a few minutes, or from the flight levels, 45 minutes.  When I am approaching the airport I normally go to 24+", which produces about 120 kts.  I rarely look at the TIT because I have other things going on, but it is down further, in the 12-1400 range.  I might fly like that for 10-20 minutes.  By now, the turbo, which was glowing cherry red at cruise, or at least the collector and the lower deck were, has cooled down a fair amount.  Downwind will be at around that 24" setting but the airspeed will be around 90 because the gear is now down.  Abeam the numbers, and for the next probably five minutes, power goes to 17" and then to 14-15 on short final, which is nearly an idle setting on my engine.  At the end of the runway it goes as low as it can go, but the RPM's don't drop that much because the CS prop is on the stops now, and the plane's forward speed is assisting the prop.  At the end of the landing runout the temps are all at the lowest levels they will reach until shutdown.  The taxi in will warm things but just a little.  So I have a nice, cool turbo at that point.

Now comes the interesting part.  The video put up by the OP from Hartzell says the engine must be run at 900 for 5 minutes, and if it goes above 1200 the 5 minute cool down cycle must be started again from scratch.  But in the TSIO360LB (and the GB as well), as any owner will tell you, the gear ratio on the alternator coupler is such that if I drop the RPM's under 1100 the amps go negative and the buss voltage starts to drop, in fact even if you don't have an accurate monitor as I do, the red annunciator light saying LOW VOLTS will get your attention.  You can run the engine at 900, yes, but every second you are doing that you are drawing current from the battery.  One of the MAPA instructors I once flew with said, "Do you ride the brakes or put up with the red light?"  I knew exactly what he meant.  You either taxi that engine at a good clip, and use the brakes to slow down as necessary, or you tolerate the low voltage warning light.

So there ain't no way I am running my turbo at 900 RPM for five minutes before I put the plane away, and I have never done that.  Living in Minnesota and doing many cold starts, I need my battery to be as healthy as it can be, and that means full charge when I put the plane away.  Yet my turbo is just fine and happy.  

On the issue of who you should believe, APS or the manufacturer, we have engine settings in our POH's that nobody should ever go near.  Those come from "the factory."  We are told by the same factory that wants us to run the engine "Best Power," right at peak, that we should never run LOP, which is much easier on the engine.  I have been to APS, I have watched an engine run on the test stand and seen the real time readouts on ICP and all the temps.  And they haven't just run "an engine" on that stand, that have run scores if not hundreds, of all types and all power settings.  They have run engines so hard on that stand that they have had plugs blow out of the engine.  The instrumentation on their stand is so good that if the engine or any part of it even breathes hard, they see it.  

I pretty much know who I trust on this, and my turbo does too.

[Emmet]

Let me provide some reality from the roughly 1100 hours I have on my TSIO360LB and its turbo.  The turbo had to be rebuilt right after I bought the plane but it would be impossible to pinpoint the reason.  The prior owner and the pilots he loaned the plane to had run the engine pretty hard.  My point is the turbo was rebuilt at about 650 hours and I now have more than 1100 hours on it (around 1750 total), who knows what the rebuild cause was.  

I fly by what APS says, which is that cool down is a myth and unnecessary.  My turbo is fine, in fact better than fine, after 1100 hours no cool down.  In that number of hours I have done many types of flights, but probably the most hours in total have been cruises to a distant destination at a cruise setting.  I have been running the last probably 400 hours mostly at about 70% HP LOP, which I accomplish by setting the MP at 34".  The TIT is up around 1600.  The moral of the story is that the turbo is running hard and as hot as it is ever going to get for a few hours.  My typical descent from cruise is to simply point the nose over and pull of about an inch of MP because the extra speed is going to cause the MP to gain about that much, in other words I am keeping the MP pretty much stable.  The TIT will go down because the engine is not working as hard, lets say into the 14-1500 range.  That descent can be a few minutes, or from the flight levels, 45 minutes.  When I am approaching the airport I normally go to 24+", which produces about 120 kts.  I rarely look at the TIT because I have other things going on, but it is down further, in the 12-1400 range.  I might fly like that for 10-20 minutes.  By now, the turbo, which was glowing cherry red at cruise, or at least the collector and the lower deck were, has cooled down a fair amount.  Downwind will be at around that 24" setting but the airspeed will be around 90 because the gear is now down.  Abeam the numbers, and for the next probably five minutes, power goes to 17" and then to 14-15 on short final, which is nearly an idle setting on my engine.  At the end of the runway it goes as low as it can go, but the RPM's don't drop that much because the CS prop is on the stops now, and the plane's forward speed is assisting the prop.  At the end of the landing runout the temps are all at the lowest levels they will reach until shutdown.  The taxi in will warm things but just a little.  So I have a nice, cool turbo at that point.

Now comes the interesting part.  The video put up by the OP from Hartzell says the engine must be run at 900 for 5 minutes, and if it goes above 1200 the 5 minute cool down cycle must be started again from scratch.  But in the TSIO360LB (and the GB as well), as any owner will tell you, the gear ratio on the alternator coupler is such that if I drop the RPM's under 1100 the amps go negative and the buss voltage starts to drop, in fact even if you don't have an accurate monitor as I do, the red annunciator light saying LOW VOLTS will get your attention.  You can run the engine at 900, yes, but every second you are doing that you are drawing current from the battery.  One of the MAPA instructors I once flew with said, "Do you ride the brakes or put up with the red light?"  I knew exactly what he meant.  You either taxi that engine at a good clip, and use the brakes to slow down as necessary, or you tolerate the low voltage warning light.

So there ain't no way I am running my turbo at 900 RPM for five minutes before I put the plane away, and I have never done that.  Living in Minnesota and doing many cold starts, I need my battery to be as healthy as it can be, and that means full charge when I put the plane away.  Yet my turbo is just fine and happy.  

On the issue of who you should believe, APS or the manufacturer, we have engine settings in our POH's that nobody should ever go near.  Those come from "the factory."  We are told by the same factory that wants us to run the engine "Best Power," right at peak, that we should never run LOP, which is much easier on the engine.  I have been to APS, I have watched an engine run on the test stand and seen the real time readouts on ICP and all the temps.  And they haven't just run "an engine" on that stand, that have run scores if not hundreds, of all types and all power settings.  They have run engines so hard on that stand that they have had plugs blow out of the engine.  The instrumentation on their stand is so good that if the engine or any part of it even breathes hard, they see it.  

I pretty much know who I trust on this, and my turbo does too.

My experiences are quite similar to yours. A few thoughts about the infallability of the manufacturers:

Were they able to design a balanced intake system?

Did they even recognize how important that is ?

How many tries did it take them to build a good turbo installation ?

Have they ever published any data?

I personally believe in what is most reasonable according to the available data, but that is everybody's own choice.

One more thought about the coking: if the pressure of the hot oil drops below the turbo chargers check valve pressure of 15psi while running at low rpm - could this probably cause what you intend to avoid ...?

[Joe Zuffoletto]

I've put 1000+ hours combined on a K and a TN and I have never done a turbo cool-down, and I never had problems with either turbo.

[gsxrpilot]

8 hours ago, jackn said:

Here's some data. On landing TiT is low, but turbo temp is probably still high. 

 

4 hours ago, Marcopolo said:

nor do I think that the bearing and oil temperatures have reached minimum yet (at least by looking at my oil temperature gauge).  So I think that adding a minute or two of idle time (900 rpm) when I get to my hanger or tie down will only help and in my opinion can in no way hurt the turbo bearing and shaft, 

 

6 hours ago, carqwik said:

The temp of the turbo housing is irrelevant to this discussion...it's the bearings that only get oil for cooling that matter.  I don't know how APS could measure the temperature of the bearings. 

I think it's interesting that all of the voices against the research done by APS are based on "probably", "I think", "in my opinion", and "I don't know".  This is exactly the point of the RESEARCH done in Ada, OK by the guys at GAMI and APS. They specialize in debunking old wives tales, and random made up and passed down theories with good old fashioned science and math.  Obviously everyone agrees that turbo bearings are the issue. APS spent quite a bit of time and effort working out a way to actually measure the temperature of the turbo bearings. Then they had to find a way to do the measurements in flight on a working airplane. With this done, it's time to look at the math. The results show unequivocally that letting the engine run for 5 minutes after parking, to let the "turbo cool down", actually hurts the turbo bearings more than shutting down immediately upon reaching a full stop.

I know science, math, and even facts are kinda out of fashion right now, but for us engineer types, facts still matter, science is the way to find facts, and math is the exact science.

But don't take our word for it. Sign up and go to Ada, OK and see for yourself. It might be the best $1 AMU you'll spend on your airplane.

[Marcopolo]

GSXR,

 

 Since you quoted me above I'd like to reply.  I used "think" and "in my opinion" because I don't have the equipment to measure such things and as of yet the conversation hadn't proven otherwise.  There was a point made that somebody had placed a thermocouple on a turbo housing and deduced that it was at minimum temperature upon landing, I have yet to read in this thread that someone had measured the temperature of the oil at the turbo shaft bearing at that point in time.  As I stated, I can only look at the tools that I have and make reasonably educated deductions.  My oil temperature gauge does not stabilize on the lower temperature until 1 1/2-2 minutes after I land, I am usually at my hanger by then and I let the engine idle at 900rpm while I write fuel totals and flight times down.  My alternator is still charging at 900 but it will cut out if idling much lower.  I did read your statement about the temperatures creeping upward while you idle after landing and that possibly doing a diservice to the turbo but you weren't referencing any GAMI or APS data at that point i didn't think.  Again, the oil temperature stabilizing at it's lowest point is what I'm referencing to tell myself that temperatures throughout the engine have stabilized,  I do have sufficient pressure at 900rpm to displace the check valves to ensure oil flow.

 

  I've run several turbo engines in my race cars and now the one in my K, very different animals to be sure.  The ones in the race cars are rebuilt or at least IRANd too often to let build-up occur but I still allow a cool down period based on oil temps on those also, I know that the pattern is our cool down period, but i don't "think" allowing another minute, or five, or ten is going to create an issue.  Most turbo issues in the early passenger cars were traced to inadequate cooling down prior to shut down, hence a device called a turbo timer.  The newer vehicles have added additional cooling mechanisms to help with this but they stil suggest a cool down period in many of the owners manuals.  Again, I understand that the "cool down period" isn't the question here, its the 5 minute mandate

 

  I am not asking anyone to change what they are doing, I am only stating what I do and why I "think" or "thought" it was correct.  I've been at this airplane thing for a lot less time than most of you and will continue to question things I don't fully grasp or understand, my apologies ahead of time!

 

Ron

[gsxrpilot]

Ron,

Everything in my post including the admonition that the 5 minute "cool down" after parking is actually harming the turbo, comes from GAMI and APS. That is exactly what we were told in the course, with all the relevant data to back it up.

And as those who have taken the course will know, the course manual has an appendix with excerpts from various POH's that have been thoroughly debunked by the research and science done at APS.  

So my point was really in agreement with you, that since none of us has the equipment, or possibly the engineering degrees/experience to use it anyway, maybe we should accept actual data from engineers and scientists who do have the equipment and know how to use it.  Rather than our own guesses and opinions.  But then you might have to go take the course yourself?