Turbo leaning question - not LOP

[skidoo]

So, I have gone out and putted along at relatively low power at the book numbers for altitude, temp, MP, and RPM. This seems a safe setting when I don't want to spend a lot of time tweaking the mixture. The other day, I had some extra time to think about it, and leaned further to peak TIT. This is where the POH recommends for best economy. I noticed the loss of power when it approaches peak or beyond, but it was still smooth. It does seem to take some time to respond and stabilize the temp indications and I put it back to the numbers shortly thereafter.

I understand that some of you say the worst place to be is like 25 deg ROP due to the highest Internal Pressures. So, this got me to wondering. In the lean process, you would spend some time at that level as you lean. And, if it is the pressure that causes damage, then it would seem that even a little time there could be damaging. Do the max pressures vary significantly with power level like the temperature does? If so, then If I am at low power, what what would be wrong with slowly leaning until I saw a definite peak. If it remains under the max red-line TIT temp along the way, what risk is there for slowly leaning past the 25 ROP area?

 

[denverpilot]

At what altitude? Peak pressure don't mean much if you're already up high and only producing 65% power.

 

[Clark1961]

The experts will be along...

Until then, if you're 65% power of less, the manufacturers say that the engine can't be hurt with the mixture lever.

I look at it this way: at 30" or below, I've got a normally aspirated, low compression (7.5 to 1) engine operating on 100LL. Obviously that's not totally true since the turbo does heat the intake air. The intercooler does change things a bit and may result in more power from the engine for a given MP and RPM at peak TIT. Fuel burn rate comes into the equation at some point and will be the limit for power when LOP. I wish an engine instrument could accurately give a power output number for my engine...

 

[denverpilot]

Heh. Clark, you have the perfect setup for you. A propulsion system only an engineer could love!

 

[Henning]

if you're 65% power of less, the manufacturers say that the engine can't be hurt with the mixture lever.

So, would that be 65% power of the 230hp or 260hp version of the same engine that was derated by reducing max RPM? This is what I love about that statement....

 

[Clark1961]

Heh. Clark, you have the perfect setup for you. A propulsion system only an engineer could love!

It's fun alright...right up to the point I pay for the overhaul!

 

[Clark1961]

So, would that be 65% power of the 230hp or 260hp version of the same engine that was derated by reducing max RPM? This is what I love about that statement....

It seems logical that it's 65% of the max but better to err on the conservative side...

That typed, my engine is the same internally as it's higher HP versions. The only difference was the fuel system. Bolted on the -KB fuel system and intercooler and it was uprated 10%.

 

[gismo]

So, I have gone out and putted along at relatively low power at the book numbers for altitude, temp, MP, and RPM. This seems a safe setting when I don't want to spend a lot of time tweaking the mixture. The other day, I had some extra time to think about it, and leaned further to peak TIT. This is where the POH recommends for best economy. I noticed the loss of power when it approaches peak or beyond, but it was still smooth. It does seem to take some time to respond and stabilize the temp indications and I put it back to the numbers shortly thereafter.

I understand that some of you say the worst place to be is like 25 deg ROP due to the highest Internal Pressures. So, this got me to wondering. In the lean process, you would spend some time at that level as you lean. And, if it is the pressure that causes damage, then it would seem that even a little time there could be damaging. Do the max pressures vary significantly with power level like the temperature does? If so, then If I am at low power, what what would be wrong with slowly leaning until I saw a definite peak. If it remains under the max red-line TIT temp along the way, what risk is there for slowly leaning past the 25 ROP area?

While excessive peak cylinder pressure sounds damaging in itself it's my understanding that the levels reached in the "red box" (mixture/power combinations that yield excessive peak ICP) don't cause immediate damage. Instead this causes significantly higher surface temps inside the cylinder and the secondary effects of that (pre-ignition etc) are the real problem. But since heat is involved the thermal mass of the components will protect things for a "while". GAMI recommends what they call the "Big Mixture Pull" where you go from fairly rich to sufficiently lean of peak quickly so things don't get a chance to heat up. You do need to avoid going higher than the TIT limit for very long as well.

 

[Tom-D]

So, I have gone out and putted along at relatively low power at the book numbers for altitude, temp, MP, and RPM. This seems a safe setting when I don't want to spend a lot of time tweaking the mixture. The other day, I had some extra time to think about it, and leaned further to peak TIT. This is where the POH recommends for best economy. I noticed the loss of power when it approaches peak or beyond, but it was still smooth. It does seem to take some time to respond and stabilize the temp indications and I put it back to the numbers shortly thereafter.

I understand that some of you say the worst place to be is like 25 deg ROP due to the highest Internal Pressures. So, this got me to wondering. In the lean process, you would spend some time at that level as you lean. And, if it is the pressure that causes damage, then it would seem that even a little time there could be damaging. Do the max pressures vary significantly with power level like the temperature does? If so, then If I am at low power, what what would be wrong with slowly leaning until I saw a definite peak. If it remains under the max red-line TIT temp along the way, what risk is there for slowly leaning past the 25 ROP area?

Couple of things to keep in mind, Your cylinders will with stand any pressures you can produce with mixture, and turbo MAP that is set to limit at manufacturers recommendations.
It is the temperatures that will destroy the cylinders if allowed to stay in the red box. So, while you pull thru the red box from too rich to harm your engine to to lean to harm your engine isn't going to hurt anything.

the next issue is the temps and power fall faster on the lean side, and yes the engine will run smoother, because the cylinders will be going putt rather than bang.

 

[Ted]

While excessive peak cylinder pressure sounds damaging in itself it's my understanding that the levels reached in the "red box" (mixture/power combinations that yield excessive peak ICP) don't cause immediate damage. Instead this causes significantly higher surface temps inside the cylinder and the secondary effects of that (pre-ignition etc) are the real problem. But since heat is involved the thermal mass of the components will protect things for a "while". GAMI recommends what they call the "Big Mixture Pull" where you go from fairly rich to sufficiently lean of peak quickly so things don't get a chance to heat up. You do need to avoid going higher than the TIT limit for very long as well.

This is a good summary. On higher power engines (like Navajos) one typically leans to a TIT.

To the OP: what airplane do you fly?

 

[Alexb2000]

On higher power engines (like Navajos) one typically leans to a TIT.

That's the way I've always done it. Simple, consistent, easy.

That said using something like lean assist (ROP or LOP) or just manually finding peak, I just can't see any damage happening for the few seconds it takes you to establish peak. It's not like your CHT's immediately spike with the leaning.

 

[Ted]

That's the way I've always done it. Simple, consistent, easy.

Also can be inefficient. However, if you're running something like a Navajo and don't have an engine monitor, it's going to be your best bet.

That said using something like lean assist (ROP or LOP) or just manually finding peak, I just can't see any damage happening for the few seconds it takes you to establish peak. It's not like your CHT's immediately spike with the leaning.

Again, it depends on what engine you're running and what your power settings are. CHTs won't immediately spike, but your internal pressures and temperatures will. If detonation starts, then you will immediately see that couple micron thick heat boundary between combustion gasses and the piston go away. Sure, you do it a couple of times and it won't hurt anything, but over the 1800 hours of a Navajo's TBO, it wouldn't be a good idea if done every time cruise power is established.

 

[Alexb2000]

Also can be inefficient.

Can you explain how that is inefficient?

 

[skidoo]

To the OP: what airplane do you fly?

T182T. I suppose I should put it in my avatar or profile...

 

[skidoo]

...CHTs won't immediately spike, but your internal pressures and temperatures will. If detonation starts, then you will immediately see that couple micron thick heat boundary between combustion gasses and the piston go away.

That is what I am getting at for this thread. Is it the actual pressures that causes damage or temperature? If it is pressure, then how does the pressure change with power or mixture level. My instrumentation tells me that temperature goes down with lower power levels and mixture constant. So, that leaves more room to fiddle with mixture. But, if damage is caused by pressures, then I have no instrumentation to tell me that. I would like to fiddle with the mixture settings and run at the best economy settings allowed by the POH. But, my concern is misunderstanding something thinking that at low power levels, tweaking the mixture slowly (to ensure good stable readings) will take it through the point of high pressures. If it is not really the pressure that causes damage, then I should be good with monitoring temps, right?

 

[Ted]

Can you explain how that is inefficient?

Well, you're running ROP, which is less efficient than LOP.

That is what I am getting at for this thread. Is it the actual pressures that causes damage or temperature?

Both, but keep in mind that they go hand in hand (more or less). As your pressures rise, your temperatures rise. They will either reach some sort of equilibrium, or, if you have bad detonation, will keep on going until you have a real problem.

If it is pressure, then how does the pressure change with power or mixture level. My instrumentation tells me that temperature goes down with lower power levels and mixture constant. So, that leaves more room to fiddle with mixture. But, if damage is caused by pressures, then I have no instrumentation to tell me that. I would like to fiddle with the mixture settings and run at the best economy settings allowed by the POH. But, my concern is misunderstanding something thinking that at low power levels, tweaking the mixture slowly (to ensure good stable readings) will take it through the point of high pressures. If it is not really the pressure that causes damage, then I should be good with monitoring temps, right?

I suppose my summary for you is not to worry too much. The T182T is a pretty underpowered, bulletproof engine. I wouldn't try peak/LOP ops at full power, but at any power setting your POH says you can lean to best economy, you're fine. But I'd run it about 40 LOP if the engine will do so smoothly.

 

[gismo]

That is what I am getting at for this thread. Is it the actual pressures that causes damage or temperature? If it is pressure, then how does the pressure change with power or mixture level. My instrumentation tells me that temperature goes down with lower power levels and mixture constant. So, that leaves more room to fiddle with mixture. But, if damage is caused by pressures, then I have no instrumentation to tell me that. I would like to fiddle with the mixture settings and run at the best economy settings allowed by the POH. But, my concern is misunderstanding something thinking that at low power levels, tweaking the mixture slowly (to ensure good stable readings) will take it through the point of high pressures. If it is not really the pressure that causes damage, then I should be good with monitoring temps, right?

At low power (i.e. below 60%) the peak pressure (which drops with power all else being constant) at the worst case mixture (around 20 ROP) isn't as high as it gets with a "safe" mixture at full power so the only things that matter are keeping the CHTs below 400 (380 is even better) and the TIT is reasonably lower than the redline temp. But at a higher power the best method is to lean far enough past peak EGT quickly and then approach peak from the lean side. That way you never get to the highest potential ICP and spend less time in the "red box". In addition if you come at peak from the lean side, the richest cylinder will peak first so the others don't even get to peak let alone beyond.

WRT the damage being caused by pressure vs temperature as Ted explained when the pressure peaks high and early there's more heat transfer to the metal surfaces inside the combustion chamber (valves, cylinder head, piston, and top ring) but due to the thermal masses it takes time for any of those to reach damaging temperatures. Another issue is the potential for pre-ignition (caused by something getting hot enough to ignite the gas before the spark) and once that starts you've got a classic "viscous circle" with the pre-ignition creating higher ICP and higher temps both of which enhance the pre-ignition. But that takes time to cross the damage threshold and shouldn't be a problem if you find the peak from the lean side and do it reasonably quickly.

Excessive peak pressure, especially if it occurs near TDC does create abnormal stresses on the head, wrist pin, con-rod, crank, and associated bearings, but AFaIK you won't come close to that kind of pressure just finding the peak from the lean side and going sufficiently LOP shortly after that.

 

[skidoo]

I have leaned on the ground for max rpm near 1200. And that is with the mixture way far out. It seems like just another 1/4" to 1/2" and it is cut-off. I can't imagine being able to pull it quickly the right amount with little risk of killing the engine first. Is it common to miss that point, kill the engine, and simply get it running again by tweaking the mixture more rich? What is the risk of leaning too far first?

 

[Alexb2000]

Well, you're running ROP, which is less efficient than LOP.

I'm simply saying leaning to a TIT is an easy way to do it. It can be done either ROP or LOP.

On second thought, never mind. I'll bow out of another leaning discussion.

 

[mbundy]

I ran my T182T LOP for a few hundred hours with great success.

Wide open throttle (~32")
2300 RPM
Pull the mixture back to 12.5 gph (don't turn it back, PULL it pack, "the big pull" and then turn to adjust)
That will give ~145 KTAS @ 10,000 feet.
CHT's should be around 365-375

 

[skidoo]

I ran my T182T LOP for a few hundred hours with great success.

Wide open throttle (~32")
2300 RPM
Pull the mixture back to 12.5 gph (don't turn it back, PULL it pack, "the big pull" and then turn to adjust)
That will give ~145 KTAS @ 10,000 feet.
CHT's should be around 365-375

I would like to see this done, but on some one else's T182T first. Maybe someday, I will run into some one to show me.

 

[Ted]

I'm simply saying leaning to a TIT is an easy way to do it. It can be done either ROP or LOP.

This is true, but I find that leaning to a fuel flow is easier.

 

[TMetzinger]

This is true, but I find that leaning to a fuel flow is easier.

Yep, because with EGT/TIT, unless you do it slowly enough you may not know which side of peak you're on.

EGT/TIT measures the fuel/air mixture on the output side of combustion. Fuel flow measures the same fuel/air mixture on the input side of combustion. If the engine is operating normally they'll always track each other. If they don't, or behave differently, than something's changed.

I've only done the "big pull" on engines with a fuel-flow meter.

 

[Ted]

Yep, because with EGT/TIT, unless you do it slowly enough you may not know which side of peak you're on.

I actually once ended up LOP with the Navajo this way. But since the owner of the plane warned me that he would castrate me if I ran it LOP, I promptly changed back to ROP. Fortunately, he forgave me for my indiscretion.

When asked why I'd follow the owner's instructions, well, it's his plane, and I'd expect him to follow my instructions if flying my plane. As he put it "If you want to go run a Navajo LOP then you can buy your own one and put $100,000 worth of engines on it like I did."

 

[skidoo]

Help! I went out today and set power for the normal POH numbers at 8000 ft, 2000 rpm, and 20" mp. Then, pulled back MP to 14" and putted around a bit. So, I thought I am at very low power, lets see what how it feels if I try to see a peak. So, I slowly dialed back the mixture some more. The TIT temps were fine, but I did not like where the EGT's were going. At normal power levels the EGTs were always lower than TIT. As you can see in the photo, all EGT's were maxed out in the indicator. I could not really find a peak before the engine began running rough. I did not like that either, so mixture just above rough and I snapped a photo, then back to normal mixture setting.

In the Lycoming leaning procedure it states

"(b) Lean slowly in small steps, while monitoring instrumentation, to peak TIT or maximum allowable TIT whichever occurs first."

and then earlier it says

"For best economy cruise, operate at peak EGT. If roughness is encountered, enrich the mixture slightly for smooth engine operation."


What I don't understand is if it reaches peak and becomes rough, and then enrichen slightly, and say the leaves it at 25F ROP, there are those who say that is the worst place to be. I could not find any such warning in the Lycoming leaning procedure nor the POH.

What are your thoughts on this and the settings in the photos.

Also, I see a redline for TIT, but don't see any for EGT. Anyone know why not?

 

[Clark1961]

Also, I see a redline for TIT, but don't see any for EGT. Anyone know why not?

With EGT there is nothing to worry about melting. With TIT, gotta worry about failure of the turbocharger.

As for the rest, sounds like some sort of problem with fuel balance or ignition. Dunno, sounds flakey. Even my TSIO-360 will go lean-of-peak and the engine is a bit of a conundrum for the GAMI folks.

 

[texpilot]

I occasionally fly (tailwind or just killing time) my T182T LOP. No problems after 750 hours on the tach. CHT's stay nice and cool. I pull the MP back to 28" and prop to 2300 and do the big pull to about 11.5 GPH then add MP. Usually 30" /2300 12.5GPH 145TAS @7500 so I lose about 4-5 knots from my ROP crusie of 2200/28 15.5 GPH.

Couple of hints:
Keep in mind that below 65% you can set the mixture anywhere without hurting anything. Passing through the red box will not hurt anything. Just don't leave it there for any length of time. There is not a max EGT only a max TIT. You are only producing around 50% power at your power settings so you can set the mixture anywhere (including 25rop) without hurting anything. The T182T's AJ1A is de-rated so it's pretty tough and runs just fine at higher power settings.

Bob

 

[skidoo]

Can anyone else confirm there is no max EGT? What concerns me most is that I think I was running near only 35% power and the EGTs went off the chart. Maybe I have a misperception here, but I had assumed that with all else the same, and increase in MP would result in an increase in EGT. But, if that were true, where would those temps be if I increased MP to 20 or even up to 28"?

Could it have been rough simply because, when leaning, the power was so low, or maybe the rpms were at minimum?

 

[Clark1961]

EGT off scale means unburnt fuel in the exhaust system - not a good thing. That or the scale was too low to begin with...

 

[texpilot]

So what is off scale? There is no maximum EGT. I would think variations in EGT would be a better indication of a problem. I have always thought of "off scale" as one EGT much higher or lower than the rest. The EGT's in the pic provided show realtively uniform EGT's with the hottest being the number 1 @ 1585. Looks normal to me.

Bob

 

[Clark1961]

So what is off scale? There is no maximum EGT. I would think variations in EGT would be a better indication of a problem. I have always thought of "off scale" as one EGT much higher or lower than the rest. The EGT's in the pic provided show realtively uniform EGT's with the hottest being the number 1 @ 1585. Looks normal to me.

Bob

Yup, no problem with 1585. Max TIT for me is 1650...

 

[gismo]

Can anyone else confirm there is no max EGT? What concerns me most is that I think I was running near only 35% power and the EGTs went off the chart. Maybe I have a misperception here, but I had assumed that with all else the same, and increase in MP would result in an increase in EGT. But, if that were true, where would those temps be if I increased MP to 20 or even up to 28"?

Could it have been rough simply because, when leaning, the power was so low, or maybe the rpms were at minimum?

Chances are the fuel was burning slowly enough that the fire was still going when the exhaust valves opened. At the low power you were running that's not going to hurt a thing as long as the TIT is within acceptable limits. There are no absolute limits on EGT because there are too many things that affect them. In your case one such thing is the likely possibility that your wastegate was fully closed raising the back pressure as well as the amount of time the exhaust gases spend in the vicinity of the EGT probe.

 

[skidoo]

Chances are the fuel was burning slowly enough that the fire was still going when the exhaust valves opened. At the low power you were running that's not going to hurt a thing as long as the TIT is within acceptable limits. There are no absolute limits on EGT because there are too many things that affect them. In your case one such thing is the likely possibility that your wastegate was fully closed raising the back pressure as well as the amount of time the exhaust gases spend in the vicinity of the EGT probe.

That is an interesting theory... I went back through some other photos and found some normal readings. Normally, what I see is EGT about 100F cooler than TIT. But, it appears that as MP is reduced, they get closer together. I guess I was surprised by the TIT being cooler than EGT at the very low power setting.

 

[skidoo]

So what is off scale? There is no maximum EGT. I would think variations in EGT would be a better indication of a problem. I have always thought of "off scale" as one EGT much higher or lower than the rest. The EGT's in the pic provided show realtively uniform EGT's with the hottest being the number 1 @ 1585. Looks normal to me.

Bob

By off the scale, I mean that the last LED in the bar graph was reached. Any higher temp, there were no more bars to display... Because they are all but one at the last bar, they just appear equal. There is now no way to see how well they are balanced above that level. I am normally fine with a TIT of 1585, but have not seen EGT that hot before... Nothing wrong with the engine, Just trying to understand what is going on.

 

[texpilot]

Ski,

I highly recommend attending the Advanced Pilot Seminar (APS) in Ada, OK. They also have an online course that is just as informative. Absolutely wonderful and "eye opening". Totally changed the way I operate aircraft engines.
BTW, I'm flying tomorrow and I'm going to see if I can duplicate your low power EGT's. I'll post a pic.
Adios,
Bob

 

[Ted]

14" is really too low. When you get down into that range, the burn rate goes down significantly.

Try operating at the 23"/2300 RPM range. That ought to work better.

But really you would benefit from taking an advanced engine management course. The APS course is a good one, and I offer engine management training one-on-one in your plane as well.

 

[denverpilot]

But really you would benefit from taking an advanced engine management course. The APS course is a good one, and I offer engine management training one-on-one in your plane as well.

Heh heh... do you offer the $20 O-470 course too?

"Push throttle forward. Leave it there. Open cowl flaps. Don't climb at Vx for extended periods. Pull prop back at cruise or whenever else you feel like it. Lean to manufacturer's recommendation ROP, or if at 65% power or less, peak if you feel like it. It won't run worth a damn anywhere else. Let's land and get lunch."

 

[Ted]

Heh heh... do you offer the $20 O-470 course too?

"Push throttle forward. Leave it there. Open cowl flaps. Don't climb at Vx for extended periods. Pull prop back at cruise or whenever else you feel like it. Lean to manufacturer's recommendation ROP, or if at 65% power or less, peak if you feel like it. It won't run worth a damn anywhere else. Let's land and get lunch."

If you came to me with an O-470, I'd say "Well, I can give you the course, and if you have an engine monitor I can teach you how to use it more fully. But otherwise, there's really not much value."

I'm more aimed towards people with higher power engines that benefit from education in engine operation. Turbocharged engines as well as the higher power naturally aspirated ones.

 

[denverpilot]

If you came to me with an O-470, I'd say "Well, I can give you the course, and if you have an engine monitor I can teach you how to use it more fully. But otherwise, there's really not much value."

I'm more aimed towards people with higher power engines that benefit from education in engine operation. Turbocharged engines as well as the higher power naturally aspirated ones.

Understood. Thus the ribbing and the smileys.

 

[Henning]

I would like to see this done, but on some one else's T182T first. Maybe someday, I will run into some one to show me.

Why the f- should someone bother to demonstrate to your lame mind how to save yourself money? If you can't work it out, and you can't understand when it's explained to you, what makes you think you deserve more effort than that? Waste your money down the toilet for all anyone else cares, you aren't costing me money and stressing my plane.