Cirrus Pilots

[bdhill1979]

http://www.avweb.com/news/maint/182883-1.html

Highlight of the article:

"If shock cooling were a definite hazard, your engine should fall apart when you bring the mixture into idle cutoff at the end of a flight. CHTs fall at a rate of 100°F/min or more in the first seconds of shutdown—triple the rate that starts the typical "shock cooling" annunciator blinking. Does anyone complain that repeated shutdowns are causing head cracking? Of course not.
Then why are we worried about pulling the throttle back?"

I have seen one head cracked and two turbos blown locally (the turbos were by the same guy). While I agree that the whole concept of "shock cooling" is a bit of a boogie man, I'm going to baby the hell out of my engine, its the only one I've got.

 

[TFaudree_ERAU]

Bad example. Once you're below a certain temperature with your CHT's you minimize damage to the engine.

So whats that number that your pile of Amflight data shows? I flew for FLX, another large 540 operator, and they never even touched on the subject of shock cooling. They taught their preferred method of leaning and power settings, but never told us to not fly 140 to a two mile final, pull the power, drop the gear and land.

Can you, without a shadow of a doubt, say that every single Amflight pilot of a 540 powered airplane followed the company SOP to a T? Were they never in a rush to make a schedule and went balls to the wall to the marker, and then slammed the throttle to idle.

I should add that it is my opinion that smooth power reductions are more important than slow power reductions.

 

[bdhill1979]

I was wondering if FADEC would be the answer from a lot of guys. I mean don't get me wrong, the idea of having FADEC to just set power on climb and let the computer take care of the rest is a great one, but you've still gotta watch your cylinder head temps and treat the engine fairly gingerly or you're going to blow it up eventually.

Now somebody is probably going to come in with "SHOCK COOLING IS A MYTH," but Amflight proved time and time again it isn't. They operate more TIO-540's than anybody on the planet, and had operating that engine down REALLY well.

If you were not slowing pulling power back by 30 miles before the FAF, you were already behind the airplane in a very serious way. Sure it slows you down in the terminal environment, and sure it's a pain for ATC (we couldn't maintain any of their speeds, and got resequenced often), but it saved the engine.

The way it was just described is how I flew a turbine engine, not a large piston engine.

Yeah my power reductions start way outside the terminal area. If I am not below 22 inches before the IAF and around 18 inches at the FAF its too late to slow down smoothly, or slow down and maintain a glideslope.

 

[jtrain609]

So whats that number that your pile of Amflight data shows?

If I remember correctly, and it's been a few years, once we got the CHT's below 185 degree's the amount damage you'd get from going to idle was minimal. What you DON'T want to do is go from 350 degree's on your CHT's (or some high number, I don't remember the scale of the gauge anymore) to idle.

Basically what it meant is that we stage cooled until we were at about 18" of power, and then you could go to idle no problem. We had the same issues with takeoff to, BTW, we were not allowed to takeoff until we got our CHT's into a rage that would not damage the engine when you poured on the coals.

Can you, without a shadow of a doubt, say that every single Amflight pilot of a 540 powered airplane followed the company SOP to a T? Were they never in a rush to make a schedule and went balls to the wall to the marker, and then slammed the throttle to idle.

What in the world kind of a question is that? Without a shadow of a doubt? No we don't have FOQA data from the Chieftains, but I'd say that the vast majority if pilots flew within SOP. Every time I was flying with one they did, nor did they attempt to push it. We had our numbers worked out pretty well in that we didn't need to rush much of anything, we just needed to be on time, using the proper procedures. It was drilled into their heads that it might not be their engine that comes apart on them if they abuse them, but it could be their buddy on takeoff who pops a cylinder and crashes. It's happened before with PT6's.

I should add that it is my opinion that smooth power reductions are more important than slow power reductions.

It is not my opinion, but instead my study of the data and anlysis that was put in front of me that says you're wrong.

In the end, do whatever you'd like with your engine. But if you treat your engine poorly for long enough, you're going to do some damage and it'll be costly in one way or another. Either you're going to pop a cylinder or your turbo on climbout while too low to pull your chute, or worse you're going to be in a plane like a 210 where you end up without any good options while low to the ground.

Do what you like, but I've got my data and will continue to discuss it and try to dispell the myths that are out there about engines of this size.

 

[TFaudree_ERAU]

If I remember correctly, and it's been a few years, once we got the CHT's below 185 degree's the amount damage you'd get from going to idle was minimal.

You can get your CHTs below 185 in flight? The lowest I've ever seen taxiing in is 220. With that logic, you're shock cooling every time you flare to land. Also, I've heard and read that any time CHTs are below 350, heat related stress is virtually a non-issue.

It is not my opinion, but instead my study of the data and anlysis [sic] that was put in front of me that says you're wrong.

My studying of the data and analysis that was put in front of me says that shock cooling is a myth. I'll agree to disagree with your viewpoint.

In the end, do whatever you'd like with your engine. But if you treat your engine poorly for long enough, you're going to do some damage and it'll be costly in one way or another.

I'm not endorsing going from cruise power to idle in 3.2 seconds flat. However, reducing from 20" and 2400 RPM (there is only one power lever in the Cirrus; if you want a specific MP, you take whatever RPM you get) over a period of two or three minutes isn't going to crack a cylinder.

We may not see eye to eye on this also because I'm speaking of normally aspirated engines. Our Cirrus is one of the few that is not turbocharged/normalized. I would be a little more cautious in a turbocharged airplane because I know the amount of cold air pumped in by the turbo is exponentially greater.

 

[bdhill1979]

If I remember correctly, and it's been a few years, once we got the CHT's below 185 degree's the amount damage you'd get from going to idle was minimal. What you DON'T want to do is go from 350 degree's on your CHT's (or some high number, I don't remember the scale of the gauge anymore) to idle.

Our TSIO 520 likes that same range, redline is 460. All of my "data" comes from watching the EDM 800, but at cruise power CHT is around 350-375. With a proper planned power reduction down to that 18 inches MP that goes down to the low 200s. On shutdown I have watched the TIT go from 1500 degrees down to 500 degrees in only two minutes; and I think that is probably the biggest area of damage for these engines, not letting the turbo cool off and slow down, and I see a lot of pilots not doing it. Or thinking that the taxi is enough, right as they crank the engine up to get into their parking space.

 

[jhugz]

Isn't that REALLY mean to the engine?

http://cirrusaircraft.com/turbo/learn/turbotech.aspx

http://cirrusaircraft.com/turbo/learn/wearandtear.aspx

It is practically impossible to shock cool a SR22T.

 

[TFaudree_ERAU]

t-cart.

How often did y'all have cylinders crack in ag operations when you're taking off and landing every 10 minutes? A lot of heating and cooling going on there.

Do tell

 

[jtrain609]

t-cart.

How often did y'all have cylinders crack in ag operations when you're taking off and landing every 10 minutes? A lot of heating and cooling going on there.

Do tell

Ag cats have PT6's eh?

 

[Joe Gremlin]

http://www.avweb.com/news/maint/182883-1.html

Highlight of the article:

"If shock cooling were a definite hazard, your engine should fall apart when you bring the mixture into idle cutoff at the end of a flight. CHTs fall at a rate of 100°F/min or more in the first seconds of shutdown—triple the rate that starts the typical "shock cooling" annunciator blinking. Does anyone complain that repeated shutdowns are causing head cracking? Of course not.
Then why are we worried about pulling the throttle back?"

With all due respect, that statement is very simplistic. I have no idea if shock cooling exists or not. Maybe it does, maybe it doesn't, not for me to say. But I do know pretty much every definition of shock cooling that I'm aware of claims that the issue arises due to the cylinders cooling and therefore shrinking at a faster rate than the pistons moving inside of them which therefore causes undo stress when the now oversized pistons move inside the cylinders. If you shut the engine down, the pistons don't move. Hard to cause much damage when the piston aren't moving, doncha think?

Along this same line of thinking I've often heard the shock cooling is a myth crowd claim that Bob Hoover used to shutdown both engines during every performance and yet he never experienced premature engine failures that could be attributed to shock cooling. Again, he was shutting down engines and going right to feather. Hard to do much damage when nothing is moving.

For my money, I feel that shock cooling is best considered in the same light as Einstien considered God. Or maybe it was Freud. Anyway whomever it was, he said we really can't know whether God exists or not, but its in our best interest to act as though he probably does exist just in case. I don't ask for much beyond idle power from any engine until its at operating temperature. And in air cooled piston aircraft, I try to reduce power from cruise settings in small increments with a good minute or so in between reductions whenever possible. But I also don't lose sleep over it when ATC gives me a slamdunk and I've got to pull off 10" and/or 1000RPM all at once. I just don't make a habit of it.

 

[jhugz]

I also don't run an engine lean of peak or at a MP setting greater then the RPM's. I DO however run everything squared because if not the engine will fall off the hinges.

 

[TFaudree_ERAU]

Ag cats have PT6's eh?

Air Tractor AT-300
Air Tractor AT-501
Thrush S-2R

 

[jtrain609]

I also don't run an engine lean of peak or at a MP setting greater then the RPM's. I DO however run everything squared because if not the engine will fall off the hinges.

You know the whole square thing is an old wives tale, right?

We climbed our Chieftains at 38" of manifold pressure, 2,400 RPM and 36 gallons per hour per side.

 

[jhugz]

You know the whole square thing is an old wives tale, right?

We climbed our Chieftains at 38" of manifold pressure, 2,400 RPM and 36 gallons per hour per side.

Dudeee I rlly need a sarcasm tag on that...i thought the very last statement covered it.

 

[jtrain609]

Dudeee I rlly need a sarcasm tag on that...i thought the very last statement covered it.

You'd be surprised the things people believe. Truth be told, the Chieftain, with you being set between a pair of TIO-540's, sounded like a very angry person was trying to rip the world in two.

It didn't help that Amflight removed every single piece of sound proofing they could manage to rip out of that airplane.

 

[TFaudree_ERAU]

If you shut the engine down, the pistons don't move. Hard to cause much damage when the piston aren't moving, doncha think?

Excellent point, and one I hadn't considered.

And in air cooled piston aircraft, I try to reduce power from cruise settings in small increments with a good minute or so in between reductions whenever possible. But I also don't lose sleep over it when ATC gives me a slamdunk and I've got to pull off 10" and/or 1000RPM all at once. I just don't make a habit of it.

I totally agree with you. I usually reduce in about 3 or 4 stages depending on my altitude. Descent, initial approach, final approach and of course landing. If I'm on a short hop, obviously the descent is not necessary. This whole 1" per 1000' is nonsense, as are the time constraints in which the CHT can only reduce a certain number of degrees. If you make smooth power reductions and your CHTs aren't going from 380 to 200 in two minutes, I honestly don't believe you have anything to worry about. 380 at TOD, 320 in the terminal area, down to 270 over the marker, to 230-240 at landing, followed by further cooling to 200 during the taxi is going to do just fine for a long time.

 

[jtrain609]

Excellent point, and one I hadn't considered.



I totally agree with you. I usually reduce in about 3 or 4 stages depending on my altitude. Descent, initial approach, final approach and of course landing. If I'm on a short hop, obviously the descent is not necessary. This whole 1" per 1000' is nonsense, as are the time constraints in which the CHT can only reduce a certain number of degrees. If you make smooth power reductions and your CHTs aren't going from 380 to 200 in two minutes, I honestly don't believe you have anything to worry about. 380 at TOD, 320 in the terminal area, down to 270 over the marker, to 230-240 at landing, followed by further cooling to 200 during the taxi is going to do just fine for a long time.

What you just described is stage cooling.

Cooling, quite literally, in stages.

 

[TFaudree_ERAU]

What you just described is stage cooling.

Cooling, quite literally, in stages.

I understand that, but all too often I hear that if you don't do the 1" per 1000' or if you reduce CHT by more than 50 degrees every 5 minutes, you're going to die on the 22nd time you don't it. That was the myth I was trying to disprove.

I also still maintain my opinion that if you have to rush or are late with the power reduction and don't hit those numbers precisely, you won't do any damage to the engine aside from the normal wear and tear.

 

[jtrain609]

Who in the world uses 1" per thousand feet? That's what you lose as you climb eh? Anybody that is recommending that doesn't know their rear end from a hole in the ground, and it certainly isn't stage cooling. Heck if you lose 1" for every thousand feet you descend, you'll never actually reduce power because you'll gain that inch back as you come down another 1,000'.

Amflight's stage cooling schedule was 2" of manifold pressure every two minutes, no matter what altitude you were at. By DOING 2" of manifold pressure every two minutes, you would bring your CHT's from the 350 range down to under 200 by the time you got to the marker.

The CHT's were what mattered, not the amount of manifold pressure you're taking out. All you were trying to do is remove the energy (heat) from the engine at a calculated rate, and 2" every 2 minutes would give us that desired rate.

Never heard 50 degrees every 5 minutes either, because it cools faster than that. If you're moving at 3 miles per minute, and you need 30 miles to go from cruise to the FAF (as far as your reductions in manifold pressure are concerned) then you're losing 150 degree's in 10 minutes, so about 15 degree's a minute.

 

[trafficinsight]

everybody knows engines are made of glass and piston rings of cane sugar... if you taxi too hard past one it'll shatter...