Engine temps

[JoshK]

I just meant maximum manifold pressure according to your POH.  I believe with your setup, that requires you to set power at takeoff, and then slowly advance the throttle as you climb to maintain your maximum rated manifold pressure, as it will naturally decrease with altitude.  Later models with the TSIO-360-MB and TSIO-360-SB got a fully automatic wastegate, which is what I fly, and we do in fact go throttle full forward to the firewall, and the wastegate holds it at 36" of MP all the way up.  Maybe some modified TSIO-360-LB and TSIO-360-GB's are the same, I'm not sure.  But the idea is to maintain maximum manifold pressure for best takeoff and climb performance.  Never overboost your engine if it's one that's capable of doing that.
Some pilots used to (and some still do) advocate a "cruise climb" power setting where they reduce power to something like 32" and 2500 RPM, and then pitch for 500 FPM in the climb.  In my plane, that results in 1) higher CHTs due to increased angle of attack, decreased fuel flow, and decreased air flow, 2) longer climbs to altitude, 3) increased total fuel burn for the trip due to lost efficiency, and 4) higher overall trip times due to it taking forever to get to altitude.  So while I started out flying that way, I no longer do.  Full power and full rich mixture to top of climb, then reduce power and lean for cruise. 
If I'm at cruise altitude and have to go up say 2-3 thousand feet for some reason, I might use that cruise climb setting just to avoid drastic changes.  It will quickly spike your CHT's if you watch it.  If a larger altitude change than that is required I will go back to full power, full rich mixture, and cowl flaps open to help keep the engine cool and minimize the time in the climb.  You can regain all that stored energy in the descent.
Never lean in the climb, and never lean for takeoff.  That's a naturally aspirated thing.  Your turbo is always pushing full air, and so you always need full mixture.  If you lean in those conditions, you will spike your temperatures, at best, and not be making full power, or even cause your engine to shutoff, at worst.

I was told to use the reduced power climb to altitude and I typically pull back to 34/2500 but I’m flying a rocket so it’s still 1000+fpm and 125-130kias and lots of fuel. The reason given was the plane has so much power already that even flying at 90% or so power is like flying at 140% power on the original airframe and this allows for better cooling at a cruise climb attitude.

Not being argumentative, just asking, would you advocate the approach of full power climb in the Rocket or a big engine long tail vs the standard M20K’s?


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[Z W]

9 hours ago, JoshK said:

Not being argumentative, just asking, would you advocate the approach of full power climb in the Rocket or a big engine long tail vs the standard M20K’s?
 

I have never flown a Rocket or a big engine long tail, so I have no idea.  Just sharing my experience in a M20K 231 with a TSIO-360-MB installed via STC.  I would probably experiment with different power settings and use the ones that result in lowest temperatures using modern engine instrumentation.  As far as I know, most now agree that high heat is bad for engines, and the cooler you can keep things, the better.

I believe some of the early recommendations from the 80's to decrease power for the climb were based on the idea of "reducing engine wear," "taking it easy on the engine," and "fuel efficiency", and that many of those ideas have been disproven.  Remember these machines left the factory in the 80's with an analog single probe CHT gauge and no fuel flow meter.  They were also designed to just replace a cylinder after it gets fried.

But it's also airframe dependent.  New or worn out baffling could change how your engine responds.  I don't know what cowl flaps your Rocket has.  My 262 has the infinitely adjustable ones controlled by an electric motor that were installed as part of the STC.  231's with different cowl flaps might do better at different power settings.

Some do believe that RPM = wear, and that lowering RPM increases engine life.  The idea is that the fewer revolutions the crankshaft makes, the less all the parts inside rub on each other.  That makes sense to me.  But in my plane, reducing RPM to 2500 for the climb results in significantly higher internal temperatures, so I usually do not do it.

[JoshK]

I have never flown a Rocket or a big engine long tail, so I have no idea.  Just sharing my experience in a M20K 231 with a TSIO-360-MB installed via STC.  I would probably experiment with different power settings and use the ones that result in lowest temperatures using modern engine instrumentation.  As far as I know, most now agree that high heat is bad for engines, and the cooler you can keep things, the better.
I believe some of the early recommendations from the 80's to decrease power for the climb were based on the idea of "reducing engine wear," "taking it easy on the engine," and "fuel efficiency", and that many of those ideas have been disproven.  Remember these machines left the factory in the 80's with an analog single probe CHT gauge and no fuel flow meter.  They were also designed to just replace a cylinder after it gets fried.
But it's also airframe dependent.  New or worn out baffling could change how your engine responds.  I don't know what cowl flaps your Rocket has.  My 262 has the infinitely adjustable ones controlled by an electric motor that were installed as part of the STC.  231's with different cowl flaps might do better at different power settings.
Some do believe that RPM = wear, and that lowering RPM increases engine life.  The idea is that the fewer revolutions the crankshaft makes, the less all the parts inside rub on each other.  That makes sense to me.  But in my plane, reducing RPM to 2500 for the climb results in significantly higher internal temperatures, so I usually do not do it.

Makes sense. My Rocket is a 252 based conversion, and I do exactly what you describe: tune in the cowl flap position to react to temps.

With me and standard fuel load it climbs at 375-380F CHT on the hottest cylinder until the upper teens at a constant rate climb but I’ve started using a constant airspeed climb above 14k to keep things under 380. That turns into hand flying and/or tweaking the programmed climb rate on the old King AP to keep it where the airframe seems to like the airspeed.


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[exM20K]

@Steven B My 231 was equipped with the Merlyn controller as well.  I found that, when hot out, rigging the cowl flaps to trail a finger-width when closed lowered CHT quite a bit without a meaningful speed penalty.

-dan

[Steven B]

Great tip. Thx Dan. I usually have no issue in cruise. But that’s a great tip!

[jlunseth]

On 8/30/2023 at 1:21 PM, Steven B said:

Yeah. I have both the Merlyn black magic fixed wastegate and the intercooler

Those are two different things - a Merlyn and a fixed wastegate. The Merlyn is not a fixed wastegate. The original factory wastegate was a fixed wastegate. It could  be adjusted on the ground by an A&P, but during flight it did not change how much exhaust was wasted. Some exhaust is always wasted by the fixed wastegate. The Merlyn is a differential wastegate controller. It tries to maintain a set difference between pressure at the turbo discharge and the pressure in the induction system. The purpose of that was mainly to control bootstrapping. But also allows for the wastegate to be changed during flight, and best of all it allows the wastegate to fully close, which the factory fixed wastegate could not do. Thus, the CA for the factory fixed wastegate was around 15k and for the Merlyn equipped aircraft around 22.5k.  Merlyn advertised it as an “automatic” wastegate, but the generally accepted meaning of that is a wastegate that will maintain the original MP set by the pilot. So if the pilot sets the MP at, say, 32” the turbo works to maintain 32” as the aircraft ascends or descends. Us pilots have to do the work in the 231. Probably you know all this, just trying to provide information.

[Steven B]

Thank you for all the really informative comments. I’m trying to learn about what I have so I can learn how to care for my engine as best I can. It’s all new to me so I’m asking a lot of dumb questions. Reading about the different setups and how pilots manage their temperatures is a big challenge but I owe it to my mooney and my wallet (and safety) to figure it all out!  I’m not sure what bootstrapping is and what the CA refers to(cruise altitude ?), thank you for all your expertise. Truly appreciated. 

[Steven B]

PS. I think I figured out “critical altitude,” and looked up bootstrapping but I’m not sure I understand it. Ty. 

[jlunseth]

1 hour ago, Steven B said:

PS. I think I figured out “critical altitude,” and looked up bootstrapping but I’m not sure I understand it. Ty. 

The compressor fan in the turbo is driven by the exhaust gases from the engine.  The more exhaust, the more induction pressure the compressor side produces. You can feel this during the takeoff run, you put in some throttle, a little later the turbo kicks in (this is called “turbo lag”), and you can feel the added power and acceleration from the engine. So more power from the engine means more exhaust, which means even more engine power means more exhaust pressure, etc. This is bootstrapping. WIthout a good wastegate it can be difficult for the pilot to manage, and it works on the downside too, in other words if you reduce power you reduce exhaust pressure which further reduces power. The engine and the pilot can wind up chasing each other around trying to arrive at a stable power setting. We don’t feel it much in the Merlyn equipped engine because the Merlyn is there to tamp it down.  A wastegate is an opening or variable valve that lets some of the exhaust gas escape rather than using it to drive the engine to make more power. A fixed wastegate is one where this opening can’t be changed, at least not in flight. A wastegate controller is able to vary how much or little exhaust is wasted. There are several types. CA is indeed critical altitude. I believe there is a technical definition for it, such as the point where the aircraft can no longer maintain a specific climb rate (its either 100 or 300 fpm, I don’t remember). But my definition is more simple. It is the point where the MP stick is full in and the engine can no longer make full rated HP.

Edited September 1, 2023 by jlunseth

[Steven B]

Makes total sense. Thank you for turbos for dummies, exactly what I need. It’s all very technical especially for us basic minded pilots!  But I can understand the way you explained it!  

[JoshK]

3 hours ago, jlunseth said:

The compressor fan in the turbo is driven by the exhaust gases from the engine.  The more exhaust, the more induction pressure the compressor side produces. You can feel this during the takeoff run, you put in some throttle, a little later the turbo kicks in (this is called “turbo lag”), and you can feel the added power and acceleration from the engine. So more power from the engine means more exhaust, which means even more engine power means more exhaust pressure, etc. This is bootstrapping. WIthout a good wastegate it can be difficult for the pilot to manage, and it works on the downside too, in other words if you reduce power you reduce exhaust pressure which further reduces power. The engine and the pilot can wind up chasing each other around trying to arrive at a stable power setting. We don’t feel it much in the Merlyn equipped engine because the Merlyn is there to tamp it down.  A wastegate is an opening or variable valve that lets some of the exhaust gas escape rather than using it to drive the engine to make more power. A fixed wastegate is one where this opening can’t be changed, at least not in flight. A wastegate controller is able to vary how much or little exhaust is wasted. There are several types. CA is indeed critical altitude. I believe there is a technical definition for it, such as the point where the aircraft can no longer maintain a specific climb rate (its either 100 or 300 fpm, I don’t remember). But my definition is more simple. It is the point where the MP stick is full in and the engine can no longer make full rated HP.

CA is that point at which the turbo can no longer maintain sea level rated power at the given altitude at full throttle. 

Service Ceiling is where the plane can no longer maintain 100fpm climb rate. 

I am not too familiar with the spec on the original 231's however as I looked hard for a Turbo Arrow 3 for a while I can tell you that turbo Arrows were originally made with a fixed waste gate and no intercooler, giving them a critical altitude of 12,000ft MSL and a functional service ceiling in the low 20's, around 21,000 IIRC.  Bootstrapping was a major concern for them just like people talk about the early 231's. 

Someone, I believe Merlyn, made an intercooler and automatic wastegate STC for it that brought the CA to 19k and solved the overboosting problem which gave the early tArrow's a huge bump in capability as well as easier engine management for less experienced (and tired) pilots.  Personally having flown 2 people and 50gal on board (72 total allowed) to 21,000 at a 800fpm climb rate all the way to FL180 I was blown away at the performance compared to my N/A Arrow 3 under the same kind of loading.  This solidified wanting a turbo-something for my next airframe. I just happened to find a Rocket first... I'm not disappointed 

[Steven B]

That’s all great information and honestly new to m. But I want to learn as much as I can. I rarely fly above 12/13K feet but probably should. Sounds like that’s what this machine is built for. I know service ceiling is 24K. No idea what CA is. Have to check the POH. THX AGAIN. you’re definitely a welcome wealth of knowledge. 

[JoshK]

3 minutes ago, Steven B said:

That’s all great information and honestly new to m. But I want to learn as much as I can. I rarely fly above 12/13K feet but probably should. Sounds like that’s what this machine is built for. I know service ceiling is 24K. No idea what CA is. Have to check the POH. THX AGAIN. you’re definitely a welcome wealth of knowledge. 

Is your Rocket a 231 conversion?  The 252 Conversions are 28k SC's

Both of them are guaranteed to have CA's at 23k per the Rocket manual, which gives pretty incredible performance at FL240.  Recently I took mine from GRB to MQS at FL230 and a 40kt push in well a little over 2.5 hours.  It loves to be up high.

 

[Steven B]

I dont have a rocket…unfortunately. 81, 231. 

[Steven B]

Rocket is Super impressive 

[JoshK]

I dont have a rocket…unfortunately. 81, 231. 

Oh for some reason I had it mind that you did. Either way the 231 is pretty damn fast on its own.

A good friend has one with the various updates and mods for speed and altitude. He said 200-210 are his best altitudes. He has gone to 230 but with the extra heat generated he wasn’t going as fast due to more drag from the cowl flaps and extra AOA.

Yeah, the Rocket is thoroughly amazing to me. I couldn’t be happier with it


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[Pinecone]

5 hours ago, Steven B said:

That’s all great information and honestly new to m. But I want to learn as much as I can. I rarely fly above 12/13K feet but probably should. Sounds like that’s what this machine is built for. I know service ceiling is 24K. No idea what CA is. Have to check the POH. THX AGAIN. you’re definitely a welcome wealth of knowledge. 

I wrote an article for Mooney Flyer on why a turbo may be the answer.

https://themooneyflyer.com/issues/2023-AugTMF.pdf

 

[Steven B]

Thank you!

[Steven B]

Great article. Take home message to me. Fly higher, use oxygen, take advantage of the turbo!

[Pinecone]

8 minutes ago, Steven B said:

Great article. Take home message to me. Fly higher, use oxygen, take advantage of the turbo!

Thanks.

Yes, use it the way it is meant to be used.

Definitely get a Mountain High O2D2 to use a LOT less O2.

[Steven B]

Will do. I tried the boomula, but sent it back bc I couldn’t get it to swing close enough to my nose. Seems it need another swivel joint to bring it closer. Any other companies make that besides Aerox?

[JoshK]

Will do. I tried the boomula, but sent it back bc I couldn’t get it to swing close enough to my nose. Seems it need another swivel joint to bring it closer. Any other companies make that besides Aerox?

https://preciseflight.com/product/a5-boom-cannula/

https://www.mhoxygen.com/product-category/cannulasface-masks/cannulasface-masks-e-z-breathe/

https://aithreaviation.com/products/aithre-boom-cannula-preorder


I decided to go with a mask from Aerox. Even for use below 180 I found it more comfortable than the way the cannula felt and it gives me the option to go to 250 if I needed to without descending, switching Oxygen hardware, then climbing back up.

I have Cannulas (cannulae?) on board for all 4 seats but only my older son has any interest in wearing oxygen. If all 4 of us are onboard then I keep it below 10k as my wife is not comfortable with using supplemental oxygen.

@pinecone good article, well done


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[Z W]

I use a Mountain High oxygen boom, paired with one of their O2D2 systems.  Works great.  Added a transfill setup in the hangar this year to have the option to fill the tank myself and always have O2.  Should have done that years ago.

My preferred altitudes are 15-17k.  High enough for all the benefits of the turbo (speed, smooth air, above most weather, no traffic, no ATC restrictions, terrain clearance, glide distance for an engine failure), but plenty of useful time of consciousness if you or a passenger has an oxygen delivery problem.  No need for a mask, and no requirement to be IFR, although I often am.

This is the only real reason I don't go higher, except maybe for a short bit to cross the Rockies:

In reality, seems like I get to the high teen altitudes about 1/3 of the time.  Headwinds.  Clouds.  Flight too short to climb that high. 

On headwind flights, I'll climb until I'm out of the bumps, then stay as low as I can stand to minimize the headwind.  I try to get up to at least 7k.  Below 10k, once you're used to being higher, it feels like there's something wrong with the plane because you're going so slow and because the ground looks so close.

Nice article, @Pinecone.  I'm with you.  They can pry the turbo from my cold, dead hands.

[Pinecone]

32 minutes ago, Z W said:

I use a Mountain High oxygen boom, paired with one of their O2D2 systems.  Works great.  Added a transfill setup in the hangar this year to have the option to fill the tank myself and always have O2.  Should have done that years ago.

My preferred altitudes are 15-17k.  High enough for all the benefits of the turbo (speed, smooth air, above most weather, no traffic, no ATC restrictions, terrain clearance, glide distance for an engine failure), but plenty of useful time of consciousness if you or a passenger has an oxygen delivery problem.  No need for a mask, and no requirement to be IFR, although I often am.

Nice article, @Pinecone.  I'm with you.  They can pry the turbo from my cold, dead hands.

I have not done a transfil setup, as I picked up the airplane with about 1500 in the tank.  It was filled at annual in Dec.  Still have 1250 in the tank. So not filling often

Thanks, glad you liked the article.

[Steven B]

All valuable information. Thanks to all the Mooney experts!  I’ve not flown to 18K of above. So a cannula or boom is inadequate at higher altitudes, you have to use the mask?  Also is the O2D2 system worth it at $1200? Thats a lotta oxygen fills. Thanks everyone!