Red box

[John Pleisse]

Yes...and that other axiom......power below 65%.....do anything you want with the mixture knob.... love it....

[David Brown]

OK folks, this could turn into one of those posts that goes on forever, so brace yourself for a rambling response. I will try to do it justice. First of all much of the material posted above is very good but there is more to clarify.

 

What I see here is people wanting to micro-manage the situation, and not be big picture managers.

 

Question from Aaronk, it is true that the cooler the cylinder the more pressure you can give it, however the more ICP you give it the temperature will rise, these two things go hand in hand. If you get ICP high enough often enough you could do damage, but it is a function of time/cycles, and in normal operation you would not do that. In a N/A engine this is hard to achieve. In a Turbo engine it is much easier. But you have to do some things that would be akin to stabbing your mother to death with a parker pen, cruel and would take a while. I can't see most folk doing that. But let me tell you a story where I think that has been happening.

 

One of the countries best engine shops down here has had a TIO540 from a new 206, it has a couple of trashed cylinders from a 400 hour aircraft, I suspect the owners have been flying it by the old method of 50dF ROP, which might have been fine at 23/2300 but this thing cranks serious MP. Of course with a glass cockpit they can set 50dF ROP with considerable accuracy. Well the engine is showing a couple of cylinders in distress and failure of one with a valve broken, due to severe guide wear and the valve ratting into its seat has fatigued the stem.

 

So is it possible, yes, will it happen overnight, no. But lets think about every engine. Out of six cylinders one will have the worst valve guides, one will have the worst oil flow, one will have the worst rings, one will have broken in the worst, one will have the worst tappet clearance......on you go through every facet. Now what happens when the cylinder that also happens to be the hottest is also coincidental with one or a few of the above mentioned. even if they are all in tolerance? This is now the cylinder that is most likely to live a shorter life. Give it more pressure and more heat and it will expose a weakness far sooner than if you do not.

 

Even the large number of poorly built TCM cylinders that are out there never fail. Why? because one does and the others get ripped off at the same time. But one has to show signs of trouble first. Some IO520/550's go anywhere from 400-1200 hours and out of six there will be maybe three removed, and the others go to TBO, but if there is one thing that will help propagate the damage over time, it is higher CHTs coinciding with ICP. You can heat it to 500dF and 15PSI and it will live forever, but give it lots of cyclcles at a 50dF ROP setting at 32"/2400 and it will likely expose its defects just like the Turbo 206 did.

 

Remember four out of six cylinders were still in one piece, and may have stayed that way for another 2000 hours, or maybe only 200, we will never know.

 

So in closing your question, in theory can a cylinder survive 1100PSI at 330dF, sure it can and it does, when we detonate an engine on the dyno it starts there, and it survives, but the CHT's rapidly rise even with an impressive forced airflow. So you can't have one extreme with another like that. And in an airplane it is not possible to do that.

 

Temperature - Pressure - time/cycles.

 

 

 

TomK, can I clarify a few things, not all POH/engine manuals are well written and are often contradictory to themselves and the science. So do not place good faith in them, you need to critically think them through. We actually spend a bit of time Sunday afternoon on this very topic with several examples to teach folk how to spot them. It is farcical to say the least.

 

#2 You are 100% correct when you say that spending a short period inside the red box will hurt nothing. This is 100% true. Again some people miro manage the science here thinking that during the time it takes to even do a GAMI lean test will hurt things, no it will not. But refer the Turbo 206 example above, we believe spending a long time in a bad place does eventually shorten life.

 

I think I have explained the accumulation effect on the worst combination of tolerances above so hopefully that fits in with the rest of your post.

 

As for spending some time in the red box......heck some times it is fun, or necessary. Let me tell a little story. Last year I had Walter Atkinson and his wife Sonya out here and we were touring around the outback with another friend in a G36. Walter and David were in the G36, Sonya was flying my plane and my wife was asleep in the back. We depart BNE IFR and once out in class G in VMC we were a few miles behind the G36, and we have identical TAS. ATC could not see us any longer outside radar and ADSB, so I said to Sonya, let's sneek up and formate on them. So how do I do that? I wound her up to 2700, we had 24.6" anyway, and this was about 85% power for the day. We were fuel limited, so I could not throw a APS ROP setting at it, so I did what Walter would do....cheat! So we had around 125-150 ROP across all cylinders, this was obviously way better than 75-100, but it did use more fuel. CHT's went up but not above 370ish and it was winter and cool.

 

Was I catching them....yeah, 11% more speed and 60% more fuel burn. We caught them after 20-25 minutes, which was also not far from the point where the extra burn was going to hurt reserves, so it worked.

 

Did we surprise them...NO. I forgot to turn my transponder off and they were watching us all the time on TCAS!   DOH! DOH!

 

Were we stressing the engine a lot more than before? Yes Sir! 

 

Did it fail? No. And it has not done so since. I am confident that it will make beyond TBO, this is a very healthy engine.

 

So the point here is it is a function of all things. Potential for accelerating the weakest point of failure by continued and prolonged use of high ICP and temperature. We APS believe that if you can minimise these things and still get the same performance desired, you can operate in two ways. One is more likely to yield longer service life. There is no instant trashing of an engine, unless you preignite it for a few minutes.

 

This graphic is derived from real data. Same HP on each curve. Pick your poison! 

 

 

Hope this helps, and if you keep all things in perspective it helps too.

 

 

Quick shameless advert for any Australian viewers, hopefully nobody takes offence.

[Skybrd]

There seems to be lots of experts informing us about the red box. I read the article that Mike Busch wrote and his teaching of the CHT limits and how it relates to the internal combustion pressure. Some of these post seem to go opposite to what he wrote. Who are we to believe.

[KSMooniac]

Hint, not Mike Busch as he relates engine management directly to CHT.  Understand the physics first, and you'll understand why he is wrong on this point.  (He is right on just about everything else.)

[jetdriven]

Yes...and that other axiom......power below 65%.....do anything you want with the mixture knob.... love it....

John, that's probably the only concrete truth to engine management

[aaronk25]

David,

Thanks for the response. Like you said if a person gets into grossly excessive ICP the chts increase and will shoot up beyond normal temps regardless of how much air is going over the cylinder.

I don't want to beat a dead horse and it feels like I am but if I'm cruising along at 330 degrees inside the redbox and chts are stable I may be operating above 700psi but so what? Now 400-420degrees may be destructive at 700psi but if I were to draw a "new redbox" I'd say 1,100psi at 330d (to pick a number) is a heck of a lot better than a 700psi and 400degrees, like on a hot summer day. The 330 degree motor with higher ICP would most likely sail past TBO where the hotter lower ICP engine will likely need cylinders. Heat is key.

I think your "red box" should be based on CHT and ICP not just on ICP.

And KSMooniac...Mike Busch is right about everything.....he is never wrong....he is always right. I mean really he has 4,500 hours on his cylinders and still has 9 of the 12 left and that's cruising at 2100RPM and 31" of MP which creates a lot of pressure, presumably more than 700psi. I mean really, if his theory was flawed he would have been changing a lot more jugs. That proves WITHOUT A DOUBT if your not running in detonation and you keep your chts at or below 380 during normal cruise and keep a firm 400 degree limit ICP WILL NOT CAUSE PREMATURE FAILURE. If your running dangerously high ICP your gonna know it because the CHTs are gonna go though the roof.....so the ICP argument is a mute point. The CHT that you operate at directly corresponds to how long your cylinders are gonna last.

So cooling of our engines is the main factor. If we had liquid cooled heads we could cruise at even harder power settings. The problem is when things get hot it not only weakens metal but more importantly INCREASES the chance of detonation.

I've got 1600hours on my cylinders all with compressions of 74 or better, the only problem I've been having is needing to redo valve guides do to improper alignment with the rocker arms from lycoming. The are wearing the valve guides at the top, not at the bottom, which increases oil consumption and is not related to ICP.

[David Brown]

Aaron, I would bet that at 330dF CHT you are not near or over 700PSI. Tell me your typical cruise method and I can do a guesstimate. But you are almost correct in that CHT plays an important factor, but CHT has nothing to do with the loadings on piston, rods, crank, bearings, gudgeons etc. So the focus on CHT at the expense of all others is like looking for only Zebras when you hear a stampede of hoofs. In the mid-west this could be flawed, they will be horses!

 

I hope you get what I mean.

 

As a rough idea, the strength of the alloy in the head at 380dF is about 78% of the strength at room temperature. At 320dF it is about 90% of the strength. So it is true the same pressure at lower temps is far better, but you rarely get that in practise. The ICP drives the CHT.

 

By the way Mike would be blushing for sure with your accolades. But it is fair to say he is on the money most of the time except this idea of the 380dF CHT target. He is correct in terms of his engine o his plane. It just cant get bad enough.

 

By the way, there is one famous A&P who learned a massive amount by doing the APS course three (3) times. No names  . He is the only one in history to have done this. He is a clever fellow indeed and does much good work. Join the dots. By the way I admire his work too. But I can't for all the logic and science agree with the target CHT.

[KSMooniac]

And KSMooniac...Mike Busch is right about everything.....he is never wrong....he is always right. I mean really he has 4,500 hours on his cylinders and still has 9 of the 12 left and that's cruising at 2100RPM and 31" of MP which creates a lot of pressure, presumably more than 700psi. I mean really, if his theory was flawed he would have been changing a lot more jugs. That proves WITHOUT A DOUBT if your not running in detonation and you keep your chts at or below 380 during normal cruise and keep a firm 400 degree limit ICP WILL NOT CAUSE PREMATURE FAILURE. If your running dangerously high ICP your gonna know it because the CHTs are gonna go though the roof.....so the ICP argument is a mute point. The CHT that you operate at directly corresponds to how long your cylinders are gonna last.

So cooling of our engines is the main factor. If we had liquid cooled heads we could cruise at even harder power settings. The problem is when things get hot it not only weakens metal but more importantly INCREASES the chance of detonation.

I've got 1600hours on my cylinders all with compressions of 74 or better, the only problem I've been having is needing to redo valve guides do to improper alignment with the rocker arms from lycoming. The are wearing the valve guides at the top, not at the bottom, which increases oil consumption and is not related to ICP.

 

Aaron, I think you're bending over backwards to convince yourself that your operational practices are OK.  You're certainly not letting the laws of physics get in the way of your mission.  The two enemies of structure in our engines are heat AND pressure.  You operating in Minnesota most of the time does wonders to minimize the heat compared to those of us south of you.  Your choice of power setting is drastically increasing the pressure inside the cylinders, and over time this will amount to much higher fatigue loading as I've said before.  It won't crack your cylinders necessarily in a few hundred hours, but try to understand that you are putting a lot more load on your cylinders, pistons, valves, rods, crank, bearings, etc.  The higher ICPs might make your valve geometry problems wear more quickly too... 

 

It is your engine, your choice, your money, and you're certainly free to do it your way.  But before you preach how great your settings are you should fully understand the physics.

 

I've never met a man that is ALWAYS right, and Mike B certainly isn't.  Keep in mind he runs low compression pistons, so his 31" of MP is more like 25 or 26 to us with J engines.  

 

To sum up, CHT control is a NECESSARY parameter for successful engine management, but not SUFFICIENT.  Pressure is also very important.

[DS1980]

MooneyBob,

Did your question get answered?

[MooneyBob]

MooneyBob,

Did your question get answered?

Yes. More then once. I have found out that there is no clear line you can draw. The best thing I can do is to learn as much as possible about the subject and then use my knowledge, judgement and common sense to use it in order to get as much life as possible from the engine and use it as efficient as possible while flying as fast as possible. One thing I will do as soon as I can is to get the modern engine monitor ( I am really leaning towards CGR-30P), new tempest fine wire plugs,and maybe injectors. I believe all this will help me to run the engine smoother and longer eventually.

I am still a very fresh pilot so I have long way to iron all the kinks.

Thanks for advices and comments.

[jetdriven]

Not if you reduce power 1st, then you can LOP/ROP all you want.

Sure but why limit yourself to 65% power or less?

[DS1980]

Bob,

Good conclusions all around. Wrapping your head around the red fin leads you to notice that on the lean side of peak is where engine longevity lives. Your goal should be to get your engine to run about 25-50 degrees lean of peak EGT. Somewhere around this area is where "best economy" is, and is a mixture that will yield about a 30% savings in fuel for a 5% loss in airspeed. Also, going back to the red fin graph, you'll notice this is well outside the red area, so it's easy on the engine. Try this out with your current setup as since you're already injected you may have the fuel distribution to fly LOP without spending any money. The goal is to get to LOP without the engine running rough. If it does run rough, let us know and maybe we can narrow down the cause with more specific info. Just remember that if you're below 60% power (consult the POH), you simply cannot harm anything in your engine experimenting with LOP operations because your engine isn't producing enough power to hurt itself.

The CGR-30P is great if you have the eyesight and for panels that lack real estate. Hard to go wrong with EI.

[DS1980]

Sure but why limit yourself to 65% power or less?

Baby steps. Best to stay low on power while a new pilot is feeling out operating at mixtures they are unfamiliar with. Not everybody is a Byron or a Ross....yet.

[MooneyBob]

Bob,

Good conclusions all around. Wrapping your head around the red fin leads you to notice that on the lean side of peak is where engine longevity lives. Your goal should be to get your engine to run about 25-50 degrees lean of peak EGT. Somewhere around this area is where "best economy" is, and is a mixture that will yield about a 30% savings in fuel for a 5% loss in airspeed. Also, going back to the red fin graph, you'll notice this is well outside the red area, so it's easy on the engine. Try this out with your current setup as since you're already injected you may have the fuel distribution to fly LOP without spending any money. The goal is to get to LOP without the engine running rough. If it does run rough, let us know and maybe we can narrow down the cause with more specific info. Just remember that if you're below 60% power (consult the POH), you simply cannot harm anything in your engine experimenting with LOP operations because your engine isn't producing enough power to hurt itself.

The CGR-30P is great if you have the eyesight and for panels that lack real estate. Hard to go wrong with EI.

Thank you so much. My eyesight is excellent ( with my reading glasses) :-) . What I like about the CGR-30 is that it is primary, the size ( I can put it righ in front of me next to the AI) and the price is right.

[DS1980]

To sum up, CHT control is a NECESSARY parameter for successful engine management, but not SUFFICIENT.  Pressure is also very important.

Only curious, and not trying to prove a point, although it will come off as such. Have you encountered a situation where ICPs are acceptable but the pressures inside the engine are not? Unless there is some external source of artificial cooling, CHT will be a direct indicator of ICP.

What we really need is an FAA certified ICP gauge.

[jetdriven]

Bob,

Good conclusions all around. Wrapping your head around the red fin leads you to notice that on the lean side of peak is where engine longevity lives. Your goal should be to get your engine to run about 25-50 degrees lean of peak EGT. Somewhere around this area is where "best economy" is, and is a mixture that will yield about a 30% savings in fuel for a 5% loss in airspeed. Also, going back to the red fin graph, you'll notice this is well outside the red area, so it's easy on the engine. Try this out with your current setup as since you're already injected you may have the fuel distribution to fly LOP without spending any money. The goal is to get to LOP without the engine running rough. If it does run rough, let us know and maybe we can narrow down the cause with more specific info. Just remember that if you're below 60% power (consult the POH), you simply cannot harm anything in your engine experimenting with LOP operations because your engine isn't producing enough power to hurt itself.

The CGR-30P is great if you have the eyesight and for panels that lack real estate. Hard to go wrong with EI.

Per Lycoming you can operate at peak EGT at 75% power or less. That's why I dont understand all the POH beaters who say operate per the manufacturer. for EGT I use 15-25 LOP and consider CHT. Above 8-10K DA peak EGT and higher, ROP. I can say that best efficiency can be found at 50 LOP on a IO-360 lycoming but most of it is because of the massive loss of speed (10-20 knots TAS). Anything leaner than 25 LOP should only be for CHT control.

[KSMooniac]

Only curious, and not trying to prove a point, although it will come off as such. Have you encountered a situation where ICPs are acceptable but the pressures inside the engine are not? Unless there is some external source of artificial cooling, CHT will be a direct indicator of ICP.

What we really need is an FAA certified ICP gauge.

ICP = pressure inside the cylinders... not sure what you got transposed in this question.  Perhaps you meant acceptable CHT?

 

"external source of artificial cooling" in my opinion could be flying along in the dead of winter with very cold OAT.  Very dense air  --> greater mass airflow into the engine ---> greater ICP but relatively cool CHT due to the very cold OAT.  That can generate a very high ICP easily.

 

yes, we could use an ICP sensor... GAMI has developed one, but it is cost-prohibitive for production use.  It feeds their experimental PRISM system that offers a lot of benefits at first glance, but of course not available in the certified world at this point.

[DS1980]

Per Lycoming you can operate at peak EGT at 75% power or less. That's why I dont understand all the POH beaters who say operate per the manufacturer. for EGT I use 15-25 LOP and consider CHT. Above 8-10K DA peak EGT and higher, ROP. I can say that best efficiency can be found at 50 LOP on a IO-360 lycoming but most of it is because of the massive loss of speed (10-20 knots TAS). Anything leaner than 25 LOP should only be for CHT control.

I believe that Lycoming knows how to mechanically build a strong engine, but never learned the way to operate them. I referred Bob to the POH to determine %HP, not mixture settings.

I agree with everything in your statement, except that I am a POH beater. Is this so bad? I think that an airplane should be flown according to it's certification, and I allow myself to deviate from such things when smart research proves otherwise. But following the POH to a T is up for debate, hence the "flaps on takeoff" thread. What a disaster.

[Bob - S50]

Yes. More then once. I have found out that there is no clear line you can draw. The best thing I can do is to learn as much as possible about the subject and then use my knowledge, judgement and common sense to use it in order to get as much life as possible from the engine and use it as efficient as possible while flying as fast as possible. One thing I will do as soon as I can is to get the modern engine monitor ( I am really leaning towards CGR-30P), new tempest fine wire plugs,and maybe injectors. I believe all this will help me to run the engine smoother and longer eventually.

I am still a very fresh pilot so I have long way to iron all the kinks.

Thanks for advices and comments.

Bob,

 

Be sure to do a GAMI test before you buy new injectors.  Our stock injectors gave me a spread of 0.1 GPH last time I checked.  No sense buying new ones if the ones you have are good.  On the other hand, if it turns out they aren't, GAMI injectors will probably pay for themselves in a few years.

 

Best of luck,

 

Bob

[DS1980]

ICP = pressure inside the cylinders... not sure what you got transposed in this question.  Perhaps you meant acceptable CHT?

 

"external source of artificial cooling" in my opinion could be flying along in the dead of winter with very cold OAT.  Very dense air  --> greater mass airflow into the engine ---> greater ICP but relatively cool CHT due to the very cold OAT.  That can generate a very high ICP easily.

 

yes, we could use an ICP sensor... GAMI has developed one, but it is cost-prohibitive for production use.  It feeds their experimental PRISM system that offers a lot of benefits at first glance, but of course not available in the certified world at this point.

Yes, CHT. Wrong abbreviation. I'd like to know if flying in cold air really does lower CHTs to the point that they would not correlate with ICPs. This is where the direct indication would be nice. I don't think there are any studies or any way to prove at what temperatures CHT no longer provides an indication of pressures both on the high and low side. 

[ArtVandelay]

Per Lycoming you can operate at peak EGT at 75% power or less. That's why I dont understand all the POH beaters who say operate per the manufacturer. for EGT I use 15-25 LOP and consider CHT. Above 8-10K DA peak EGT and higher, ROP. I can say that best efficiency can be found at 50 LOP on a IO-360 lycoming but most of it is because of the massive loss of speed (10-20 knots TAS). Anything leaner than 25 LOP should only be for CHT control.

But they recommend 65%, which for my J I am going to be at anyway at cruising altitude,so no big deal

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[MooneyBob]

Bob,

 

Be sure to do a GAMI test before you buy new injectors.  Our stock injectors gave me a spread of 0.1 GPH last time I checked.  No sense buying new ones if the ones you have are good.  On the other hand, if it turns out they aren't, GAMI injectors will probably pay for themselves in a few years.

 

Best of luck,

 

Bob

What is the best way to perform the GAMI test? I probably need the engine monitor first, right?

[Cruiser]

The GAMI test measures the fuel flow value at which each cylinder reaches peak EGT as the mixture is leaned. 

You need a FF readout and EGT probe on each cylinder. 

It is easiest to do when these values are recorded on some monitor device.

Now You have to decide on which engine monitor to get.

[Marauder]

The GAMI test measures the fuel flow value at which each cylinder reaches peak EGT as the mixture is leaned.

You need a FF readout and EGT probe on each cylinder.

It is easiest to do when these values are recorded on some monitor device.

Now You have to decide on which engine monitor to get.

I think Bob is looking for a step by step process to do the test. Is it documented somewhere?

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[ArtVandelay]

I think Bob is looking for a step by step process to do the test. Is it documented somewhere?

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http://www.gami.com/gamijectors/leantest.php