Turbo Cool Down

[KLRDMD]

There's a good thread on BT about this:

https://www.beechtalk.com/forums/viewtopic.php?f=3&t=136187

[231LV]

Unless you are a member of the forum...you can't view the topic....for my money, I have never believed that allowing the turbo to run on the ramp after landing does anything but heat it up. The turbo cools when descending from altitude. It will never be cooler (when running) than just before touchdown. Taxiing to parking simply runs it a bit hotter IMHO. Of course, the article may show that I have no idea what I am talking about...LOL

[KLRDMD]

Just now, 231LV said:

Unless you are a member of the forum...you can't view the topic....

Registration is free and it is a fantastic forum, even if they are a bit "off" on their choice of airplanes. Lots of good data there.

[Bryan]

Registered yesterday in that forum for another topic I was interested in.  Purchasing a new M20K so this Turbo will be new to me, next week.  My CFI recommends a cool-down period (timer) starting from when you pull the throttle back on short-approach for about 5 minutes before shutting down.  If you add power the timer resets.

After reading the BT thread, it appears that modern insturmentation data shows that after touch-down with the throttle back that the ram-air cooling has done its job enough and more taxing and waiting is just a re-warm-up of the turbo?

What do you Turbo guys think or do? 

[KLRDMD]

Just now, Bryan said:

Registered yesterday in that forum for another topic I was interested in.  Purchasing a new M20K so this Turbo will be new to me, next week.  My CFI recommends a cool-down period (timer) starting from when you pull the throttle back on short-approach for about 5 minutes before shutting down.  If you add power the timer resets.

After reading the BT thread, it appears that modern insturmentation data shows that after touch-down with the throttle back that the ram-air cooling has done its job enough and more taxing and waiting is just a re-warm-up of the turbo?

What do you Turbo guys think or do? 

When you get to the hangar, turn off the engine.

[thinwing]

Upon landing my TIT is at its lowest..say 700 degrees..after taxi to hanger its back up to +900...idling for 2/3 min it drops again to 750 or so.So the question is TIT indicative of turbo temp?

[carusoam]

This is almost like the ROP vs. LOP thread, but...

The discussion leads to sharing knowledge about how the cooling is accomplished in the Turbo.

So much is accomplished by the high flow of oil running through the system. 

The end result is that everyone gets up to speed with how these devices actually work!

A better understanding of the failure modes occurs.  How to better recognize some of the more common failures before they become expensive are shared...

It's a great conversation for those with a Turbo.  Heat is the enemy of metal devices. Air and oil are the primary methods of cooling these devices.

Not overheating them is the most important part of engine ops for the long run.  Cooling them properly helps.

It is a bit surprising that an oilT sensor doesn't get widely adopted to the oil stream exiting the Turbo.  If this temp exceeds a limit, it is probably time to look for a blockage of oil flow.  

Oil coking is bad for exhaust valves and turbos in the same way.  The carbon deposits can block the oil flow resulting in loss of proper lubrication...

The APS guys do a nice service in explaining engine operations independent of the airframe that it is mounted in.

Best regards,

-a-

 

[Shadrach]

15 minutes ago, thinwing said:

Upon landing my TIT is at its lowest..say 700 degrees..after taxi to hanger its back up to +900...idling for 2/3 min it drops again to 750 or so.So the question is TIT indicative of turbo temp?

I would think that oil temp would be a better indicator.

[carusoam]

TIT measures heat generation...

OilT (at the Turbo exit) would directly measures the health of the turbo's lubrication and cooling system.

The engine's OilT will show some detail but can't separate out the turbo's oil from the engine's oil...?

The technology of instrumentation has taken huge leaps in the last five years.  Its expanded use hasn't expanded very far...

Adding another sensor to the oil flow would add some risk for a leak.  Adding one in a well very near the oil flow may be a great compromise.  You only have to look at it if it alarms or if you want to.  Not adding to the work required by the pilot...

PP Thinking out loud.

Best regards,

-a-

 

Edited April 5, 2017 by carusoam

[carqwik]

The turbo cool down is only for the bearings in the turbocharger.  Oil that flows past the bearings wicks away heat allowing the bearings to cool.  It has nothing to do with the temp of the turbo itself, TIT, EGT or anything else.  If you shut off your engine, oil flow stops and the bearings...likely still hot...simply "cook" the oil around them.  It's probably good insurance just to idle for five minutes after runway turnoff...if you have a turbocharger.

Interestingly, the Alfa Romeo 4C sports coupe has an electric pump that flows oil past the turbocharger for five minutes after engine shutdown. 

[gsxrpilot]

3 hours ago, carqwik said:

The turbo cool down is only for the bearings in the turbocharger.  Oil that flows past the bearings wicks away heat allowing the bearings to cool.  It has nothing to do with the temp of the turbo itself, TIT, EGT or anything else.  If you shut off your engine, oil flow stops and the bearings...likely still hot...simply "cook" the oil around them.  It's probably good insurance just to idle for five minutes after runway turnoff...if you have a turbocharger.

Interestingly, the Alfa Romeo 4C sports coupe has an electric pump that flows oil past the turbocharger for five minutes after engine shutdown. 

This is exactly what has been thoroughly debunked as incorrect by the actual research at APS. Idling your turbo for 5 minutes after exiting the runway is actually worse for your turbo than just shutting it down immediately. It's not insurance, it's ignorance of the facts. Of course, it's your airplane, and you do what you like. But it is factually incorrect.

[Dream to fly]

I'd like to contribute to this discussion, and I do realize I am new to the forum and don't want to step on any toes.   We all understand that turbos get hot from the work they do by using hot exhaust gases to spin the turbine and a compressor to compress the air making it hotter to.  This is a vicious cycle that they are built to handle.  There are two main causes of turbo failure and that is dirty air intake and dirty oil cooling.   There are also two times in operation that a turbo is at its critical upset.  The first is start up and the second is rapid deceleration of the engine after a heavy load, both cause an oil deficiency problem.  Start up the oil has to get to the bearings and rapid deceleration causes low oil pressure and a flow issue on the turbo shaft where centrifugal force actually pushes the oil away from the shaft that can be spinning anywhere from 20K - 75K rpms  depending on the geometry and cone characteristics of the compressor design.  Obviously no oil causes wear in either case.  Now if the TIT is used to determine heat load lets say as you land then taxi you will see a drop then a rise in temp,  However your oil temp is still relatively static and oil is what is maintaining the core temp control.  GSXRPILOT is correct 100 percent that idling for minutes after run is bad and here is why.  The temperature of the air is not the factor because as the engine idles it will cool the exhaust output down you are using less fuel and creating less heat. The oil on the other hand is slowing down, pressure and volume decrease and this is bad. The time that you are idling, the oil is actually getting hotter from a condition called superheating this causes the oil to absorb more heat and the bearing actually get hotter even thou there is some flow across them the oil is thin and its working hard.  Now if you just taxi park and shut down everything stops and heat peaks then cools at an expected rise and fall.  The oil trapped in the bearing is not seeing any higher temp then the crankcase bearing or the journals for that matter.  If the engine oil is clean and has not broken down from poor maintenance or oil that is not intended for the design or heat range of the engine it is being used in, its temp will rise and fall with engine core temps and all is good.  The turbo shaft will continue to spin down and will actually pull oil from the supply tube and stay lubricated till shaft stop.  The coking occurs when there is contaminants in the oil that flash or ash, or when it has been subject to heat beyond its specifications That causes it to bake.  That is when coking becomes the problem because that is when no oil can get to the shaft during spin down and metal to metal contact occurs.   If everything is kept clean and filtered a turbo used properly can go thru thousands of heat cycles with little issue.  European performance car manufacturers have know this for years and turbo timers came and went because more damage was done then good.  Now Porsche, Bugatti, Ferrari, even Mercedes are using electric pumps and fans to keep the oil at the higher flow and pressure rates of an engine running at 1500 rpms pushing it thru a cooler with fans removing the heat while the engine is off to cool everything down quicker.  The metals they use are more susceptible to warp because of the alloy mixes they use to save weight.    I hope it helps JOE

[carqwik]

Ok...to each his own...

But I'll stick with the cool down (as recommended by RAM too)...

http://www.ramaircraft.com/Maintenance-Tips/Save-A-Turbo.htm

[gsxrpilot]

The earth is flat, 9/11 was an inside job, the moon landing happened on a hollywood set, and idling for a few minutes after parking "cools" your turbo...

Feel free to abuse your own engine anyway you like... but we cannot allow false and unscientific theories to be spread without challenge.

[jetdriven]

By the time you pull the throttle off as you  drift over the trees and land, and taxi to the hangar, there's your three minutes.  Adding throttle to 1200 rpm or less, intermittently, won't add significant heat to the turbo.

[Greg_D]

7 hours ago, carusoam said:

This is almost like the ROP vs. LOP thread, but...

 

It probably sounds the same because just like in the ROP/LOP threads, one side of the debate is using actual data to form their conclusions and the other side is using anecdotal opinions that sound good to form theirs.

The good folks in Ada actually show a video in their course of a heavily instrumented turbocharged airplane landing.  The coolest points for all the readings (TIT, CHT, and oil temp, both at the oil cooler and in the turbo drain line) is just before the wheels touch the ground.  All parameters increase steadily as the plane is taxied to the hangar.  It only gets worse when the engine is idled for 5 minutes to allow it to "cool".

A few years ago, I showed this video to my hangar neighbor who flies a turbocharged Saratoga. To this day, he still sits there and idles for 5 minutes after every flight, using a timer, because a 300 hour CFI told him that was a good idea.

Edited April 6, 2017 by Greg_D

[carusoam]

It wouldn't take much to add another thermocouple...

Or visit Ada, OK.

Or watch the video a few times.... (highly recommended)

Adding the thermocouple is the best idea because all the theory falls away when reality strikes...  the theory doesn't cover the what ifs like what if a blockage starts to form in the oil recovery system, what if the pump wears down, that kind of thing.

Ordinary people are challenged when it comes to tough topics. This would be a real challenge If your best resource is a 300hr CFI and your contact with the outside world was limited...

The OWTs don't cover reality very well either.

I'm not a big fan of BT.  I reach my daily limit reading about Mooneys here.  But, the APS guys hang out over there and share a bunch of their work there.  And... they let you in, just by asking... somebody has to click a button on their end so it may take some time to be let in...

Since we share the same engines it can be interesting to see what is falling out of the trees over there. Somebody with a broken cam gear on their IO550 posted a few pictures.  Worth seeing if you have an IO550.

Fortunately, if you have to visit over there, you don't have to stay.  

Best regards,

-a-

 

[carqwik]

You can't thermocouple the turbo bearings...that's the only part that matters in this discussion.

[thinwing]

18 hours ago, Greg_D said:

It probably sounds the same because just like in the ROP/LOP threads, one side of the debate is using actual data to form their conclusions and the other side is using anecdotal opinions that sound good to form theirs.

The good folks in Ada actually show a video in their course of a heavily instrumented turbocharged airplane landing.  The coolest points for all the readings (TIT, CHT, and oil temp, both at the oil cooler and in the turbo drain line) is just before the wheels touch the ground.  All parameters increase steadily as the plane is taxied to the hangar.  It only gets worse when the engine is idled for 5 minutes to allow it to "cool".

A few years ago, I showed this video to my hangar neighbor who flies a turbocharged Saratoga. To this day, he still sits there and idles for 5 minutes after every flight, using a timer, because a 300 hour CFI told him that was a good idea.

Actually the turbo cool down recommendation comes from three sources,1 Mooney aircraft intl 2 lycoming 3 kelly aerospace and one of the bigger overhaulers  in the country,Main Turbo systems,Visalia Calif.So you will have to forgive us dumb turbo drivers..we are just following airframe,engine,turbo charger manufacturers recomendations plus a really knowledgeable overhauler who either designed it,installed it,tested it and repaired it.Although I have since modified my shutdown from 5 min to TIT temp drop(usually 1/2 min idle),I have yet to see any real world comparison of turbos lasting less than or greater than tbo using either shut down method.

 

 

[thinwing]

20 hours ago, gsxrpilot said:

The earth is flat, 9/11 was an inside job, the moon landing happened on a hollywood set, and idling for a few minutes after parking "cools" your turbo...

Feel free to abuse your own engine anyway you like... but we cannot allow false and unscientific theories to be spread without challenge.

Who exactly is "we"

[carusoam]

7 hours ago, carqwik said:

You can't thermocouple the turbo bearings...that's the only part that matters in this discussion.

0) are the modern car Turbo systems measuring oil temp or just running a program that works.

1) If the only part that matters is the bearing surface temperature.  Why don't we measure it? (They're deep inside the Turbo)

2) If it is too difficult to measure directly, can we measure it indirectly?

3) the current equipment and procedures seem to work very well.  A simple modification to the cooling procedure comes  from APS using the instrumented turbo out in Ada.

4) we get a few choices from this...

- stay with the aged procedures from the POH.

- adjust the procedures based on facts delivered by APS,  As long as they are appropriate for your machine.

- add some instrumentation to your own hardware.  Probably impossible with out a modification and STC to go with it.

5) can we measure the oilT flowing away from the Turbo bearings?

6) oil that is not flowing very well tends to degrade.  Degradation comes from too high of a temperature over time.

7) if your thermocouple were sensing the oilT where it leaves the Turbo bearings, that would be great.

8) if you can only get a nearby oil temp, or an oil temp that was mixed with cooler oil we would only be getting an indication of something going awry, similar to engine oilT

9) we would like to know the temp of the oil near the exhaust valve. It gets really hot like the oil near the Turbo bearings.

10) how often do the oil lines for the Turbo get flushed out for preventive maintenance?

11) it would be nice to have an alarm from the JPI if an excessive oilT from the Turbo was exceeded.

PP thoughts only, not a mechanic...

bet regards,

-a-

Edited April 6, 2017 by carusoam

[231LV]

well the guys that prefer to "cool" their turbo while idling may certainly do so. Those who prefer to run their engines 50 degrees ROP are welcome to do that too. I prefer to run LOP and shut down when I get to my hangar. The science from ADA in OK convinced me to do it that way. I suggest that a new turbo driver or a potential one do the research and ask the questions then make their own choice, These forums are great for gathering opinions but they are opinions and guaranteed, they will be diverse!

[gsxrpilot]

There is universal agreement that turbos need to be as cool as possible when shut down. There is also universal consensus that heat is hard on turbos. The only disagreement is how best to achieve the cooling. It's been acknowledged by the engine manufacturers, Mooney and others, that the recommendation on how best to cool a turbo is based solely on measurement of the oil temp and TIT.  

The team at GAMI in Ada are the unquestioned experts when it comes to instrumenting airplane engines. They have spent many years and lots of money developing ways to put temperature probes, pressure probes, and other kinds of measuring devices, deep inside engines and engine components. They also have learned how to record data from these probes in real time many times per second.

They also build and sell turbos for various Bonanza models.

All of this effort and expertise came together as they found a way to measure the temperature of the turbo bearings by installing probes into the housing holding the bearings. Repeated testing on several different turbo'd engines in various aircraft showed unequivocally that the turbo is coolest at touchdown and proceeds to warm up from that point all the way until shut down. The data also showed that sitting and idling for 5 minutes results in a dramatic increase in bearing temps.

This is scientific data, it's not speculation, it's not theory. There are hundreds of pilots who have seen the data first hand. Any of us who took the class in Ada have seen the data live. We've seen the test stand and watched the engines run while probes collect data. Many other pilots have seen the data second hand by reading articles published in various aviation publications, by the team from APS. 

If you agree with Lycombing, Continental, Mooney, Kelly, etc. that heat is damaging to your turbo, then you might be interested in how it's best to shut your engine down with the turbo at it's coolest possible state. And that is unquestionably as soon as you reach the chocks. 

[Shadrach]

11 hours ago, carqwik said:

You can't thermocouple the turbo bearings...that's the only part that matters in this discussion.

I mean no offense, but this is not an argument.  You can indeed measure the oil on the output side of those bearings and indeed those temperature variations will give the best indication of when the turbo is coolest.   APS has done this and just about every other test imaginable on air cooled aircraft engines.  Their advice is entirely data driven.  It is sad, but the same thing cannot be said about a lot of the other recommendations coming from reputable sources.  Your previous statement about "sticking with RAM" is sort of silly. Have you seen data produced by RAM in turbo temps?   Ram makes some great products, but that does not mean that their advice is data driven. If it's contrast to APS's, I would bet that it isn't. Perhaps their stance is liability driven.  If you've been saying the sky is green for last 3 decades and realize that it's actually blue, admitting that put's you in a pickle with all of those who listened to your previous advice and operated as if it were green. 

 

 

[thinwing]

1 hour ago, gsxrpilot said:

There is universal agreement that turbos need to be as cool as possible when shut down. There is also universal consensus that heat is hard on turbos. The only disagreement is how best to achieve the cooling. It's been acknowledged by the engine manufacturers, Mooney and others, that the recommendation on how best to cool a turbo is based solely on measurement of the oil temp and TIT.  

The team at GAMI in Ada are the unquestioned experts when it comes to instrumenting airplane engines. They have spent many years and lots of money developing ways to put temperature probes, pressure probes, and other kinds of measuring devices, deep inside engines and engine components. They also have learned how to record data from these probes in real time many times per second.

They also build and sell turbos for various Bonanza models.

All of this effort and expertise came together as they found a way to measure the temperature of the turbo bearings by installing probes into the housing holding the bearings. Repeated testing on several different turbo'd engines in various aircraft showed unequivocally that the turbo is coolest at touchdown and proceeds to warm up from that point all the way until shut down. The data also showed that sitting and idling for 5 minutes results in a dramatic increase in bearing temps.

This is scientific data, it's not speculation, it's not theory. There are hundreds of pilots who have seen the data first hand. Any of us who took the class in Ada have seen the data live. We've seen the test stand and watched the engines run while probes collect data. Many other pilots have seen the data second hand by reading articles published in various aviation publications, by the team from APS. 

If you agree with Lycombing, Continental, Mooney, Kelly, etc. that heat is damaging to your turbo, then you might be interested in how it's best to shut your engine down with the turbo at it's coolest possible state. And that is unquestionably as soon as you reach the chocks. 

Well than GSX...I guess the boys at ADA will be overhauling your next turbo ,correct?Good luck with that...I think they will say...uh uh..better have main do it...they really know turbos!