IO550 vs Cirrus installation

[Jaybird180]

A rather pessimistic SR-22 owner told me that the engine in the SR-22 tends to not make TBO. I don't have any data either way on this matter, but would like some. He says it needs cylinders early. I simply nodded and said, Uh huh, uh huh.

Reading on this forum would indicate that the IO-550 is generally a good engine that doesn't have any "issues" that causes fleet-wide failures to make TBO.

Was this guy pulling my leg, or is there some basis for his claims of the same engine doing poorly in a specific installation, Cirrus specifically?

We were talking about the normally aspirated airplane/engine combo.

 

[Henning]

"I didn't buy this plane to go slow."

 

[Ted]

Henning hit the nail on the head.

The issue with Cirrus engines isn't the engine or the airplane, it's Cirrus marketing and their recommended operating practices, which people follow. LOP is good. 85% power cruise is bad. 85% is not a cruise setting.

 

[poadeleted20]

You can run those engines at 75% power or more to get a lot of speed but the CHT's will be way up there near 400F. Yes, the redline is up at 460F, and the yellow at 420F, but if you run them anywhere over 380F, the cylinders won't last long. Getting the injectors well tuned so you can run 50F LOP will pay off in both dramatically reduced fuel flow compared to the "best power" 75F ROP (about 15% reduction in fuel flow with less than 5% reduction loss of speed), and dramatically reduced CHT's down near 350F rather than over 380F. And that reduced CHT in cruise makes all the difference in the world in engine longevity. It's really astonishing to watch the engine analysis display as you lean like that.

 

[Jaybird180]

Henning hit the nail on the head.

The issue with Cirrus engines isn't the engine or the airplane, it's Cirrus marketing and their recommended operating practices, which people follow. LOP is good. 85% power cruise is bad. 85% is not a cruise setting.

What's the max cruise setting you'd recommend for longevity?

 

[poadeleted20]

What's the max cruise setting you'd recommend for longevity?

65% power, 50 LOP -- just like the Cirrus POH says. In fact, that's what one major operator of SR22's for charter and managed corporate operations directs its pilots to do -- and you know their #1 concern is the bottom line. If it won't run 50 LOP smoothly, find someone who knows better how to tune the injectors and/or get Gamijectors.

 

[Henning]

What's the max cruise setting you'd recommend for longevity?

What does 65% power get you? Fly that speed 20°LOP.

 

[N747JB]

What's the max cruise setting you'd recommend for longevity?

I've never flown a Cirrus, but I always operated big bore Continetal turbos at 65%, that's in 414's and a 421B. I never had a cylinder issue.

 

[Ted]

Yep, 65% LOP. That's what I run.

 

[jsstevens]

Having flown a Cirrus once for ~1/2 hour...

The newer ones only have the single lever control (i.e. mixture is controlled by the computer). How do you run it LOP with that setup? Lower power I get-pull the lever back.

John

 

[Wingsofglass]

Having flown a Cirrus once for ~1/2 hour...

The newer ones only have the single lever control (i.e. mixture is controlled by the computer). How do you run it LOP with that setup? Lower power I get-pull the lever back.

John

A Cirrus has two levers. One works the throttle and prop, the other mixture. You can lean it all you want.

I've been running mine at 75% power. I guess it's time to slow down a bit.
At 75% power, my CHT's are in the 325-350 range depending on OAT and TIT is 1580. It burns about 16gph with a TAS of 180 as long as I'm above 10,000 feet. It's a turbo.

 

[poadeleted20]

I've been running mine at 75% power. I guess it's time to slow down a bit.
At 75% power, my CHT's are in the 325-350 range depending on OAT and TIT is 1580. It burns about 16gph with a TAS of 180 as long as I'm above 10,000 feet. It's a turbo.

Based on the fuel flow and CHT, you're clearly running well lean of peak. The problems occur when folks don't lean enough, so the CHT's are still way up there. Also, some folks are running in the shaded region of the power charts as high as 85% where you can't lean enough to keep the CHT's down, and those folks must be running through cylinders like you-know-what through a goose.

 

[cirrusmx]

75%-79% power, anywhere from 350-380 f on the chts depending on conditions, and bellow 1600f on the tit gives about 180 TAS at 1000ft at 16-7 gph. I believe its a good spot to operate that airplane.

 

[poadeleted20]

75%-79% power, anywhere from 350-380 f on the chts depending on conditions, and bellow 1600f on the tit gives about 180 TAS at 1000ft at 16-7 gph. I believe its a good spot to operate that airplane.

As I said above, a major operator of SR22's tells its pilots to keep CHT's below 350 in cruise, and that includes keeping power under 75%. I realize your operation is within Cirrus' recommendations in the POH, but I'll bet that operator's cylinders last longer than yours. Of course, it's your plane and your money, so do what you like in that regard, but realize there will be a price for it eventually -- and that's what started this thread.

 

[Ted]

75%-79% power, anywhere from 350-380 f on the chts depending on conditions, and bellow 1600f on the tit gives about 180 TAS at 1000ft at 16-7 gph. I believe its a good spot to operate that airplane.

Depends on your definition of "good."

 

[Bill Watson]

"I didn't buy this plane to go slow."

I was just talking to a pilot who had moved to a Cirrus after losing an engine in a Malibu. I talked about LOP ops and speeds, he talked about 'full power' speeds.

I was thinking that perhaps the Cirrus installation is more tolerant of full power operations and that there were the proper tools and operational advice to stay out of the 'hot box'.

He seemed to know what he was doing but going slower was not why he flew a plane.

 

[cirrusmx]

Depends on your definition of "good."

At those settings cost per hour came out to about $330.

 

[poadeleted20]

I was just talking to a pilot who had moved to a Cirrus after losing an engine in a Malibu. I talked about LOP ops and speeds, he talked about 'full power' speeds.

Frustrating, isn't it?

I was thinking that perhaps the Cirrus installation is more tolerant of full power operations and that there were the proper tools and operational advice to stay out of the 'hot box'.

It isn't.

He seemed to know what he was doing but going slower was not why he flew a plane.

Well, you certainly go really fast in a Cirrus if you want, but there is a price you pay for that sooner rather than later, and at Don George Engines, that price is about $27,000.

 

[FastEddieB]

I pretty much always cruised LOP, and these screen shots in my 2003 SR22 were not atypical:

This may have been close to peak, but at these power settings there's no "red box" and 172k on 12.5 gph is nothing to sneeze at, and with CHT's around 300º the engine's just loafing regardless.

 

[Bill Watson]

I pretty much always cruised LOP, and these screen shots in my 2003 SR22 were not atypical:
This may have been close to peak, but at these power settings there's no "red box" and 172k on 12.5 gph is nothing to sneeze at, and with CHT's around 300º the engine's just loafing regardless.

That is sweet!

The only thing I didn't 'get' is the high RPMs. When you setup for say 9,000', are still running it that fast? I guess that's the way to get max %power for high speeds.

I have to get up above 10,000' more often and see what I get.

 

[Ted]

At those settings cost per hour came out to about $330.

Over how many hours? When was the last top overhaul done, and when are you expecting the next? Seems like 2 tops are normal at 85% for each TBO.

Everyone needs to decide how often they're willing to perform maintenance. I have one friend with an SR22T who said one top overhaul was acceptable to him for 85%, and he figured that's what he'd get. Bought his plane at about 600 SMOH with a fresh top, and I figure he'll do another top at 1200.

 

[FastEddieB]

The only thing I didn't 'get' is the high RPMs. When you setup for say 9,000', are still running it that fast? I guess that's the way to get max %power for high speeds.

I am not an engineer, so I'm just parroting stuff I heard.

The rationale is that with no limitation on the 2,700 rpm, the engine will run perfectly happily right up to TBO running at that speed the entire way. And pulling back to a lower rpm does nothing to "save" the engine.

There was very little perform change on my plane going from 2,700 down to 2,500 rpm. Mine had a "sweet spot" at about 2,650 rpm, where it seemed just a tad smoother, so I ended up running it there most of the time.

Somewhere I have a screenshot of a spreadsheet I made when I was playing around with different power settings. I'll see if I can find it.

 

[FastEddieB]

I think this shows how little difference rpm made once you set a given fuel flow:

At the time, 2,690 rpm was generally my max setting.

 

[NoHeat]

A rather pessimistic SR-22 owner told me that the engine in the SR-22 tends to not make TBO. I don't have any data either way on this matter, but would like some.

At COPA, some original owners of the early SR22s (circa 2001) are approaching 3000 hours now, well beyond the 2000 hour TBO mentioned by Continental.

They stay out of the "red box" of high power and high EGT, and fly lean of peak at a moderate power such as the 65% that was mentioned here.

Turbocharged Cirri OTOH often don't last as long as the normally aspirated ones.

In either case, it is widely recommended on COPA to get to LOP from ROP by doing the so-called "big pull," which is a fairly rapid mixture pull until a slight deceleration is felt (not using the too-slow lean-assist feature provided on the MFD by Cirrus). This minimizes the time spent at the most damaging conditions, in the red box.

For normally aspirated SR22s operated conservatively at about 65% power and at least 50 degrees LOP, performance is typically around 168 TAS at about 12.5 GPH.

 

[Henning]

I am not an engineer, so I'm just parroting stuff I heard.

The rationale is that with no limitation on the 2,700 rpm, the engine will run perfectly happily right up to TBO running at that speed the entire way. And pulling back to a lower rpm does nothing to "save" the engine.

There was very little perform change on my plane going from 2,700 down to 2,500 rpm. Mine had a "sweet spot" at about 2,650 rpm, where it seemed just a tad smoother, so I ended up running it there most of the time.

Somewhere I have a screenshot of a spreadsheet I made when I was playing around with different power settings. I'll see if I can find it.

When I talk with the industrial/marine engine guys these days, they no longer talk about time and duty rating. They now rate engine longevity in fuel volume, as in "This is a million gallon engine. Run it anyway you like, once you run a million gallons through it, it'll be done."

 

[Ted]

When I talk with the industrial/marine engine guys these days, they no longer talk about time and duty rating. They now rate engine longevity in fuel volume, as in "This is a million gallon engine. Run it anyway you like, once you run a million gallons through it, it'll be done."

They also have a much larger cooling system.

 

[Henning]

They also have a much larger cooling system.

No doubt, but the number itself is not critical, the methodology still works since fuel=heat and it rises exponentially with speed. The real benefit the modern engines have is precise fuel metering to prevent heavy carbon deposits, which is also one of the prime benefits of running LOP. Those carbon deposits are the basis of most cylinder problems. This is also a direct function of fuel vs time. Heat is not the only, nor of the greatest detriment to engine longevity.

 

[Jaybird180]

I am not an engineer, so I'm just parroting stuff I heard.

The rationale is that with no limitation on the 2,700 rpm, the engine will run perfectly happily right up to TBO running at that speed the entire way. And pulling back to a lower rpm does nothing to "save" the engine.

There was very little perform change on my plane going from 2,700 down to 2,500 rpm. Mine had a "sweet spot" at about 2,650 rpm, where it seemed just a tad smoother, so I ended up running it there most of the time.

Somewhere I have a screenshot of a spreadsheet I made when I was playing around with different power settings. I'll see if I can find it.

Seems this makes a good case for the blue knob STC

 

[FastEddieB]

Seems this makes a good case for the blue knob STC

Funny...

...with so little performance difference at different rpm settings, and the ability to already change rpm over a reasonable range without a prop control (and still maintain WOT)...

...I'd say that's a case against the blue knob STC.

 

[Bill Watson]

I think this shows how little difference rpm made once you set a given fuel flow:

At the time, 2,690 rpm was generally my max setting.

Thanks for that.

I was running at lower RPMs on my '10 for lower GPH but also for comfort. It gets a lot quieter down at 2300 and 2400 but I'll take it up to 2500 for a few extra knots.

I'm going to try the higher rpms and see how it feels and performs.

I spent so much time flying my Maule around at 113 TAS that I'm happy at any TAS at or above 150 knots and will quietly fly it there if downwind and I can make my destination. I generally fly it at 155 knots or better if upwind.

I'm scheduled to go to a class at Airflow for injector tuning and LOP ops. I tuned my selfup over a year ago and been pretty happy with the results. It should be interesting to see what the manufacturer knows.

 

[poadeleted20]

That is sweet!

The only thing I didn't 'get' is the high RPMs. When you setup for say 9,000', are still running it that fast? I guess that's the way to get max %power for high speeds.

I have to get up above 10,000' more often and see what I get.

In a Cirrus, manifold pressure and RPM are not independent values. The single power control lever is hooked to a cam/follower assembly which varies the propeller control governor according to a fixed schedule of RPM versus lever angle. This schedule is such that with the throttle at full or typical climb power demand, the engine RPM will be 2700 RPM. As the throttle comes back from the climb range to the the cruise range, RPM is scheduled back to 2500 RPM where it stays until demanded power is reduced below the governed range. At 9000 feet, that means you'll have 2700 RPM at full throttle (just below 21" MP), but it will schedule back to 2500 RPM fairly quickly as you come off full forward, and be at 2500 RPM from there all the way back to a very low power setting well below 50%.

Even at 2000 feet, you will see about 27.4" MP and 2700 RPM at full forward power lever, but as you pull the lever back, it will stay at 27.4" MP while RPM drops to 2500 until you get below 93% power, then it will stay at 2500 RPM while MP drops to about 24" at 75% power and MP will continue to drop further with RPM constant at 2500 until a very low power setting.

For these reasons, the Cirrus is generally flown using the %HP indications rather than MP/RPM. For example, in a SR22, I'd pull it back to 50% power for descent, 40% power on downwind, 30% power on base, and 15-20% power on final -- without looking at MP or RPM. And that's how it's taught in the Cirrus Standardized Instruction Program (CSIP).

 

[Bill Watson]

In a Cirrus, manifold pressure and RPM are not independent values. The single power control lever is hooked to a cam/follower assembly which varies the propeller control governor according to a fixed schedule of RPM versus lever angle. This schedule is such that with the throttle at full or typical climb power demand, the engine RPM will be 2700 RPM. As the throttle comes back from the climb range to the the cruise range, RPM is scheduled back to 2500 RPM where it stays until demanded power is reduced below the governed range. At 9000 feet, that means you'll have 2700 RPM at full throttle (just below 21" MP), but it will schedule back to 2500 RPM fairly quickly as you come off full forward, and be at 2500 RPM from there all the way back to a very low power setting well below 50%.

Even at 2000 feet, you will see about 27.4" MP and 2700 RPM at full forward power lever, but as you pull the lever back, it will stay at 27.4" MP while RPM drops to 2500 until you get below 93% power, then it will stay at 2500 RPM while MP drops to about 24" at 75% power and MP will continue to drop further with RPM constant at 2500 until a very low power setting.

For these reasons, the Cirrus is generally flown using the %HP indications rather than MP/RPM. For example, in a SR22, I'd pull it back to 50% power for descent, 40% power on downwind, 30% power on base, and 15-20% power on final -- without looking at MP or RPM. And that's how it's taught in the Cirrus Standardized Instruction Program (CSIP).

Very interesting since I have zero Cirrus experience.

I've been trying to move to per cent power settings for my approach work. I think I'll try to incorporate some this into my flying and see how it works.

 

[poadeleted20]

Very interesting since I have zero Cirrus experience.

Their IM's are available on line for perusal.
http://www.cirruslink.com/mycirrus/onlinepoh.aspx

I've been trying to move to per cent power settings for my approach work. I think I'll try to incorporate some this into my flying and see how it works.

Problem with doing that in your Maule is that the %HP you get at any given MP/RPM combination varies with density altitude. The Cirrus takes care of that with a digital computer that automatically determines %HP based on MP, RPM, pressure altitude, and temperature.

But for your approach work, you can definitely come up with standard power settings for particular configurations (e.g., MP/RPM/pitch attitude to get 80 knots and 400 ft/min with one notch of flaps for ILS final). Read Chapter 3 of Peter Dogan's The Instrument Flight Training Manual, widely available in the internet, for more on that subject.

And if you really want a %HP display in your Maule, you can get that with most of the JPI EDM-series engine analyzers.

 

[Henning]

Their IM's are available on line for perusal.
http://www.cirruslink.com/mycirrus/onlinepoh.aspx

Problem with doing that in your Maule is that the %HP you get at any given MP/RPM combination varies with density altitude. The Cirrus takes care of that with a digital computer that automatically determines %HP based on MP, RPM, pressure altitude, and temperature.

But for your approach work, you can definitely come up with standard power settings for particular configurations (e.g., MP/RPM/pitch attitude to get 80 knots and 400 ft/min with one notch of flaps for ILS final). Read Chapter 3 of Peter Dogan's The Instrument Flight Training Manual, widely available in the internet, for more on that subject.

And if you really want a %HP display in your Maule, you can get that with most of the JPI EDM-series engine analyzers.

Well then it only works ROP. The only accurate way to gauge %power is with TAS.

 

[poadeleted20]

Well then it only works ROP.

Why do you say that? MP/RPM/temp/PA are the only inputs into the power charts in the engine manuals. Figuring HP off fuel flow, yes, mixture setting matters, but not otherwise.

The only accurate way to gauge %power is with TAS.

Not so. The TAS/HP relationship depends a good deal on configuration, gross weight and even cg location.

 

[Henning]

Why do you say that? MP/RPM/temp/PA are the only inputs into the power charts in the engine manuals. Figuring HP off fuel flow, yes, mixture setting matters, but not otherwise.

Not so. The TAS/HP relationship depends a good deal on configuration, gross weight and even cg location.

Because I can can keep all those factors the same and reduce power by reducing fuel once LOP.

 

[poadeleted20]

Because I can can keep all those factors the same and reduce power by reducing fuel once LOP.

No, you can't. If you reduce HP with that c/s prop system by leaning the mixture, you'll see MP go down during part-throttle operations. Maybe not much, but if power changes, so will MP. It's basic physics, thermodynamics, and the HP equation.

 

[Clark1961]

No, you can't.

He can in a turbocharged aircraft - I do it on most every flight.

 

[Ted]

No doubt, but the number itself is not critical, the methodology still works since fuel=heat and it rises exponentially with speed. The real benefit the modern engines have is precise fuel metering to prevent heavy carbon deposits, which is also one of the prime benefits of running LOP. Those carbon deposits are the basis of most cylinder problems. This is also a direct function of fuel vs time. Heat is not the only, nor of the greatest detriment to engine longevity.

My point was that you said the modern marine engines are sold as "run however you want, they're good for X amount of fuel." In an air cooled piston, I could run it exceedingly poorly and I could get way less life out of it, at least out of the cylinders. So I don't think the analogy works quite the same. If we had a radiator the size of the Atlantic Ocean (literally) then it would be different. But for us it's more complex, as you know.

 

[Clark1961]

My point was that you said the modern marine engines are sold as "run however you want, they're good for X amount of fuel." In an air cooled piston, I could run it exceedingly poorly and I could get way less life out of it, at least out of the cylinders. So I don't think the analogy works quite the same. If we had a radiator the size of the Atlantic Ocean (literally) then it would be different. But for us it's more complex, as you know.

We have a radiator the size of the sky...but it's just not very efficient. (and to the nit pickers: I was just following Ted's lead in using the Atlantic as a heat reservoir and calling it a radiator)