Cooling Question

AdamZ

AdamZ

Touchdown! Greaser!
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Display name:
Adam Zucker
We all know that shock cooling and over heating is baaaad. So is there a proper procedure when shutting down a single engine or for that matter a twin piston? I recently read Bob Bruneau's post about running the engine on his R22 until CHT reduces to a certain level before shut down.
I was taught and the check list on the rentals tell me pretty much the same things on the Archers and Tigers I fly ...Electronics off, ( already at idle) Mixture to cutoff, and mags, battery/master off...
Does this have the potential to either shock cool the engine or even overheat it due to lack of airflow over the engine? For that matter does the prop wash even give sufficient cooling airflow over the engine when the plane is stationary?
The other day after a 40 min flight from LNS to LOM I had to use the tow bar to push the Archer into its uphill ( UGH) parking space ( no pull throughs all rentals are back in) anyway since I had my hands on the front of the Archers cowl I felt how hot it was. Since I was putting the plane to bed for the night I had to put the cowl plugs in. I thought these cowl plug are probably locking in all that heat. What effect if any does this have on the engine the oil or anything?
 
AdamZ said:
We all know that shock cooling and over heating is baaaad. So is there a proper procedure when shutting down a single engine or for that matter a twin piston? I recently read Bob Bruneau's post about running the engine on his R22 until CHT reduces to a certain level before shut down.
I was taught and the check list on the rentals tell me pretty much the same things on the Archers and Tigers I fly ...Electronics off, ( already at idle) Mixture to cutoff, and mags, battery/master off...
Does this have the potential to either shock cool the engine or even overheat it due to lack of airflow over the engine? For that matter does the prop wash even give sufficient cooling airflow over the engine when the plane is stationary?
The other day after a 40 min flight from LNS to LOM I had to use the tow bar to push the Archer into its uphill ( UGH) parking space ( no pull throughs all rentals are back in) anyway since I had my hands on the front of the Archers cowl I felt how hot it was. Since I was putting the plane to bed for the night I had to put the cowl plugs in. I thought these cowl plug are probably locking in all that heat. What effect if any does this have on the engine the oil or anything?
Click to expand...

Assuming you're not talking turbocharged, you really don't need to do anything special. The cooling rate is usually highest on final approach (especially if you go full rich). Once you are on the ground with cowl flaps open if available, the engines will likely be as cool as they can get while running by the time you taxi in. And in any case the rate of cooling is pretty minimal once you shut down since there is little or no airflow. IME the only thing the cools quickly then is the exhaust pipes.

As to the cowl plugs, as long as you aren't planning to start up again soon (they will exacerbate any hot start issues), put them in unless things are so hot the plugs themselves might melt.
 
I agree with lance...when we use the tannis heater in the winter a thick blanket is thrown over the cowling to avoid heat loss which causes everything to get very warm. Also the airflow on the ground is not very good. I would think CHT's would increase if you let the engine "cool down".
 
One thing to remember is that a helicopter is much different on an approach and landing that an airplane.

For a helicopter the highest power required is in a hover (ignoring IGE and OGE diferences). So the approach, taxi and landing end with the engine developing very high power. While an airplane is at very low power for the approach landing and taxi so cool down from cruise begins much earlier.

This is why the cooldown procedure for a copter is so different.

Joe
 
I went through a major cool down discussion on my turbos with the flight instructor for initial qualification on my P-Baron. The POH says to let them cool for two minutes before shut down and he was strongly on that track.

My position is quite different. Unless I land with a lot of power (drag the plane in on approach), it's as cool as it will get after the approach and some taxi. Taxi to the hanger can actually cause CHTs to rise slightly. My opinion is more harm is done letting it idle fairly rich for two minutes than by shutting it down.

So we monitored CHTs on our JPI. Don't want to crow, but CHTs did not drop measurably from the time we stopped if we idled for two minutes; as a matter of fact, they sometimes rose. I you have an engine monitor, there is no reason to speculate; it clearly shows you what's going on.

I e-mailed George Braley at GAMI and asked him about this. He stated that in all the years he's been installing and repairing turbos, he's never seen a failure attributable to a turbo not being allowed to cool down. He does suggest cooling if one does a long, drag in approach as mentioned above. Otherwise, between the approach at lower power and taxi to the hanger, the turbo has plenty of time to cool.

If you really want to see 'shock cooling' watch what happens on the engine monitor when you put the mixture(s) full rich while coming in on final (another thing I do not do).

Best,

Dave
 
Dave,

My take is that it's not just cooling the turbos, it's also letting the oil temp come down too. On my turbo, the oil cooling is critical to longevity.

I find that at most airports, the time to taxi to parking, plus a little groundskeeping inside the cockpit will give me 5-7 minutes of cooling time, enough to let temperatures come down a bit.

YMMV.
 
what happened to oil 'coking' in the bearings? I don't fly a turbo so this is not an opinion; just a q about what others have told me. Is it a problem or no?
 
As Lance said, there's nothing to be gained by running a non-turbocharged airplane engine longer on the ground. Without the cooling flow of flying speed through the engine, the cylinders will not cool at a harmful rate on shutdown. However, opening up the cowl as much as possible after shutdown is good for things like hoses and wiring, because without that cooling flow, the air temp in the engine compartment goes way up after shutdown -- like 240F or so according to a friend who instrumented the engine compartment of his Tiger. Leaving it opened up for as long as possible (or until the metal cools) is better for the longevity of that stuff, but not particularly harmful if you don't.
 
Let'sgoflying! said:
what happened to oil 'coking' in the bearings? I don't fly a turbo so this is not an opinion; just a q about what others have told me. Is it a problem or no?
Click to expand...

Dave, that's why the recommendation on my plane for 9-10 minutes of cool-down. OWT? Dunno.
 
Bill:

You are, of course, correct. I've not found that to be an issue either unless, as stated, I do a long approach with high power and drag the plane in.

Think about the power settings one runs as compared to cruise. I normally cruise at 30" of MP, 2,200 RPM and 13.5 to 14 gph. In the A-36 it was 16 GPH. As I approach, I bring MP back to 25" about 10 miles out. 21" as I approach the pattern and 17" is the final approach setting for an instrument approach or close in when visual. So, I've been running reduced power for over 5 minutes plus pattern time, and been in a gradual descent with good airflow over the engine. I've not seen any benefit in my plane to taxiing in and sitting and letting the engine run at idle for a couple minutes in oil temp, TIT or CHTs.

If one did a slam dunk approach, taxied right off and immediately shut down, I could see an issue. If one did a long, slow approach with high power, I would also suggest a cool down period.

Now, this is a beechcraft with a graphic engine equalizer where I can clearly see all those readings. I don't have any time in a Tiger or your plane. Things could certainly be different there.

Dave
 
Bill:

I don't want to beat up POHs too much as we have a lot of folks that don't own their own plane, haven't attend engine management courses, or done testing on the plane they fly.

The POH in the P-Baron was written in 1982. In talking with the factory guys that were there at the time, the engineers didn't dictate everything--there was this thing called marketing--also legal. Many things were changed to emphasise things that would sell and/or to disclaim things that could create liability----I really don't care about those things (other than to learn from the accident/incident).

Instrumentation has changed. The graphic engine equalizer provides insight that simply wasn't available when the plane was manufacturered. A lot of empirical imformation has been obtained on engine test stands. The disclaimers have increased for things that have been done that have nothing to do with the aircraft; all pilot techniques--errors.

Anyway, there is a lot of third party info available to me on the TN Bonanza and P-Baron which is TC. There must be a resourse available to you on your plane that can confirm what being touted or update it. Who manufactured your Turbo? That's where I'd begin.

Dave
 
Dave Siciliano said:
Bill:

I don't want to beat up POHs too much as we have a lot of folks that don't own their own plane, haven't attend engine management courses, or done testing on the plane they fly.

The POH in the P-Baron was written in 1982. In talking with the factory guys that were there at the time, the engineers didn't dictate everything--there was this thing called marketing--also legal. Many things were changed to emphasise things that would sell and/or to disclaim things that could create liability----I really don't care about those things (other than to learn from the accident/incident).

Instrumentation has changed. The graphic engine equalizer provides insight that simply wasn't available when the plane was manufacturered. A lot of empirical imformation has been obtained on engine test stands. The disclaimers have increased for things that have been done that have nothing to do with the aircraft; all pilot techniques--errors.

Anyway, there is a lot of third party info available to me on the TN Bonanza and P-Baron which is TC. There must be a resourse available to you on your plane that can confirm what being touted or update it. Who manufactured your Turbo? That's where I'd begin.

Dave
Click to expand...

Dave, do you have the OAT probe on your JPI? If not I think you could add a probe that measures the actual temp of the turbo housing (best to measure the exhaust turbine side). That way you could actually monitor the temp when deciding when to shut down. I think the goal would be to have the turbo temp down to around 220 F or wherever you think is cool enough that the oil won't be harmed. Turbo coking of engine oil was definitely a problem on cars before they all went to water cooled turbo bearings which pretty much eliminated the problem. Synthetic oil is also far more resistant to coking than mineral based.

If I had turbos on an airplane I'd definitely want to have a temp gauge for them. Alternatively you could hop out after shutdown and measure the temp with an IR sensing thermometer to see if you were doing OK and then modify your shutdown procedure until it looks fine.
 
If I had turbos on an airplane I'd definitely want to have a temp gauge for them. Alternatively you could hop out after shutdown and measure the temp with an IR sensing thermometer to see if you were doing OK and then modify your shutdown procedure until it looks fine.[/QUOTE]

Actually Lance, I asked the GAMI guys about this. They have the STC on my turbo system and of course have been installing their own for several years. They said this wasn't an issue. Maybe on some of the other systems, but not theirs (which has been designed more recently than some). They didn't feel there was a good way to measure more than what's been discussed. Shortcomings of one sort or the other. The have an operating manual that comes with their turbo--no cool down.

Another very good reason for you to come down and for us to fly over there and visit with them :D . Then, instead of talking to a middle man like me, you can kick it around with the engineers directly!!

Dave
 
Dave Siciliano said:
Bill:

I don't want to beat up POHs too much as we have a lot of folks that don't own their own plane, haven't attend engine management courses, or done testing on the plane they fly.

Anyway, there is a lot of third party info available to me on the TN Bonanza and P-Baron which is TC. There must be a resourse available to you on your plane that can confirm what being touted or update it. Who manufactured your Turbo? That's where I'd begin.

Dave
Click to expand...

Hey, Dave, do what's best for your machine.

I do have a JPI, plus a digital TIT. No sensor on the outside of the turbo frame, though. Turbo is a Rayjay.

How much cool down I do is a function of the approach. If I can keep it slow enough to open the cowl flaps in the pattern, so much the better.

I find that the turbo gets about 800-900 hours between overhauls. The last one (which, other than the turbo that went in with engine OH, is the only one I'v done) was necessitated due to bearing problems & slight oil leakage at the bearing seals. However, the problem was found when we had the turbo off after discovering an exhaust crack on the back side of the wastegate where it would have blown on the turbo.

The 800-900 hours is typical based on my discussions with other owners and a review of the logbook.

It may not be cause for concern, and I don't doubt the GAMI guys too much (other than a little discussion over on AvSig where one of them INSISTED that I ought to be able to run LOP with this b^$tard turbocharged/carburated engine). My experience has been bearing issues, ergo, I take a little more time to cool.

Again, might work fine on your plane, but I find that the POH (and other owner) recommendation is probably appropriate for mine.

I like Lance's suggestion - I just need to find a way to temperature-sample the turbo before shutdown...

best,

bill
 
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