Power setting LOP

[Will.iam]

4 minutes ago, A64Pilot said:

I don’t disagree, if your let’s call it truly LOP you can’t detonate.

The issue as I see it is you have to maintain a pretty narrow EGT range, once you get say -50 or so LOP power falls off of a cliff, it’s safe just slow. 

Then there are engines that will run LOP but just barely, my newly overhauled with new Millenium cylinders IO-540-W1A5D with Gami injectors and new fine wires wouldn’t run any deeper than -10 or maybe -20 LOP before it got rough, so it’s margin was even smaller. It didn’t take a whole lot to put it into a mixture where detonation is possible.

That’s why I preach to run at a power setting that no matter what you can’t get into detonation. Maybe it’s just me, but I occasionally make mistakes, be flying for awhile and realize the boost pump is on, I’ve even found myself trimming out in cruise to discover the flaps were in takeoff position.

As I said all it could take is a slight climb without re-leaning to put yourself into a mixture that you could detonate, and I know if I fly long enough that’s one of those mistakes I’ll eventually make and I’m past the point of gaining experience, I’m at the point where every year in truth I’m not as good as I was the year before, for over 30 years I flew professionally, nearly every day I had Wx. Now I’m doing good to fly twice a week, but I’m determined to fly at least every week.

Running ROP you run the same risk descending and going lean as you do climbing LOP and going lean. Since we learned to manage leaning for takeoff at high density altitude it’s just one of the things you have to train your self to do. If you are going to point out the risk of things. If you fly LOP and get a partial clog in a fuel injector you just get a rough running engine. But i have read of a detonation cylinder because the fuel injector was not delivering enough fuel and it leaned into the red box zone which at take off power was just seconds before damage. Ironically running a 252 turbo with the ability to hold a constant MP as I’m climbing or descending makes engine management in regards to fuel mixture much easier to set it and not mess with it or if i do it’s a quarter turn of the mixture knob to fine tune it. I would climb LOP if it wasn’t for my TIT limit.  By the time i get the TIT below 1600 (my personal limit) I’m back at 70% 

[wombat]

So if my full power fuel flow is 33 GPH, then anything less than 24.75 GPH is less than 75% power.    So is it impossible to hurt my engine (regarding LOP operations, assuming the MAP and RPM are acceptable values) if my fuel flow is less than 24.75 GPH?

[Huckster79]

On 12/28/2023 at 7:23 AM, Mooney in Oz said:

As also recommended by respected former Mooney test pilot Bob Kromer.

What’s the reasoning? Just curious-not challenging.  
 

I was told to reduce it to “reduce stress/wear” but I’ve learned there’s too many OWT in aviation to accept what I was told without question now that you brought up a new view point. 

[AndreiC]

Okay, as the starter of this controversial thread, I’d like to bring the focus back to my situation: is it ok to run 24.9”/2400 at 5000 feet, leaned to 9.4 gph? As I understand it I’m at 70% power and well LOP so should not hurt anything, right?

The reason I am hoping to run like this is that for some reason the difference between 65% and 70%, on my plane, is significant in terms of speed, but not so much in terms of fuel: about 8 knots for about .8 gph more.


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[Shadrach]

32 minutes ago, AndreiC said:

Okay, as the starter of this controversial thread, I’d like to bring the focus back to my situation: is it ok to run 24.9”/2400 at 5000 feet, leaned to 9.4 gph? As I understand it I’m at 70% power and well LOP so should not hurt anything, right?

The reason I am hoping to run like this is that for some reason the difference between 65% and 70%, on my plane, is significant in terms of speed, but not so much in terms of fuel: about 8 knots for about .8 gph more.


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How many times do you want this verified?  By how many people?  Reread the thread and you will see a number of confirmations and the reasoning behind them.  I'm not sure what else can be said.  If you're really uncomfortable, maybe you should seek someone local that you trust or stick to the published POH power settings.  

[A64Pilot]

1 hour ago, Will.iam said:

Running ROP you run the same risk descending and going lean as you do climbing LOP and going lean. Since we learned to manage leaning for takeoff at high density altitude it’s just one of the things you have to train your self to do. If you are going to point out the risk of things. If you fly LOP and get a partial clog in a fuel injector you just get a rough running engine. But i have read of a detonation cylinder because the fuel injector was not delivering enough fuel and it leaned into the red box zone which at take off power was just seconds before damage. Ironically running a 252 turbo with the ability to hold a constant MP as I’m climbing or descending makes engine management in regards to fuel mixture much easier to set it and not mess with it or if i do it’s a quarter turn of the mixture knob to fine tune it. I would climb LOP if it wasn’t for my TIT limit.  By the time i get the TIT below 1600 (my personal limit) I’m back at 70% 

If your ROP and descend yes you are getting leaner the more you descend.

However if I’m over 75% power in a descent of 500 FPM or higher my J model will exceed VNE, so it’s unlikely to say the least that many descend at over 75% power I would think, plus obviously the higher airspeed results in much cooler cyl head temps than climbing, so it’s very unlikely your going to get into detonation in a descent

However most climb at the highest power available, that’s the difference

[Ragsf15e]

1 hour ago, AndreiC said:

Okay, as the starter of this controversial thread, I’d like to bring the focus back to my situation: is it ok to run 24.9”/2400 at 5000 feet, leaned to 9.4 gph? As I understand it I’m at 70% power and well LOP so should not hurt anything, right?

The reason I am hoping to run like this is that for some reason the difference between 65% and 70%, on my plane, is significant in terms of speed, but not so much in terms of fuel: about 8 knots for about .8 gph more.


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It’s fine there and that dropoff in knots seems reasonable.  If you’re much leaner than ~40ish lop, power starts to drop off rapidly, thus airspeed decreases rapidly.  Power is fairly constant right near peak, and drops off much more slowly if you’re rich of peak.

[Shadrach]

1 hour ago, wombat said:

So if my full power fuel flow is 33 GPH, then anything less than 24.75 GPH is less than 75% power.    So is it impossible to hurt my engine (regarding LOP operations, assuming the MAP and RPM are acceptable values) if my fuel flow is less than 24.75 GPH?

It’s not that simple. At Max FF of 33gph a significant portion of that fuel is going out the exhaust as unburned hydrocarbons. That surplus fuel is used to slow the combustion event.  For your engine, 75% LOP fuel flow would be ~16.5gph.

I cannot stress enough that a TSIO520 is a power plant that requires a thoughtful and conservative approach.  

[wombat]

34 minutes ago, Shadrach said:

I cannot stress enough that a TSIO520 is a power plant that requires a thoughtful and conservative approach.  

Please don't mis-understand my position here.   I'm not planning on taking any blanket statements and going out and operating my engine this way.    I am gaining academic knowledge which I can perhaps use in a thoughtful manner to expand my engine operations envelope.

But in the continuation of this pursuit....   If we take 305 HP as my 'max', and then anything less than 228.5 HP is < 75%.   So 228.75 HP / 14.9 gives me 15.39 GPH; therefore any time I'm at 15.39, if I can get the engine to run smooth (and the temperatures to be OK, and the MAP & RPM combo is OK) then I'm not hurting the engine, regardless of what position. the levers are in.

@Fly Boomer Continental says 470 is OK.   Nobody here seems to believe it, and I'm not getting anywhere near that temperature on my engine.   But that's why I picked 390 as an "OK" temperature.

[AndreiC]

3 minutes ago, wombat said:

  If we take 305 HP as my 'max', and then anything less than 228.5 HP is < 75%.   So 228.75 HP / 14.9 gives me 15.39 GPH; therefore any time I'm at 15.39, if I can get the engine to run smooth (and the temperatures to be OK, and the MAP & RPM combo is OK) then I'm not hurting the engine, regardless of what position. the levers are in.@Fly Boomer

Isn’t your engine lower compression, so shouldn’t you divide by 13.7?

[Shadrach]

46 minutes ago, wombat said:

Please don't mis-understand my position here.   I'm not planning on taking any blanket statements and going out and operating my engine this way.    I am gaining academic knowledge which I can perhaps use in a thoughtful manner to expand my engine operations envelope.

But in the continuation of this pursuit....   If we take 305 HP as my 'max', and then anything less than 228.5 HP is < 75%.   So 228.75 HP / 14.9 gives me 15.39 GPH; therefore any time I'm at 15.39, if I can get the engine to run smooth (and the temperatures to be OK, and the MAP & RPM combo is OK) then I'm not hurting the engine, regardless of what position. the levers are in.

@Fly Boomer Continental says 470 is OK.   Nobody here seems to believe it, and I'm not getting anywhere near that temperature on my engine.   But that's why I picked 390 as an "OK" temperature.

Your engine has a compression ratio of 7.5:1 which makes it less thermally efficient. For that reason, the multiplier/divisor is 13.7 instead of 14.9.

[Pinecone]

6 hours ago, Shadrach said:

Any idea what caused it? I’ve seen a number of detonation issues over the years. 0% of them were attributable to LOP operations. 

Don't know.  Not deliberate LOP.  Carb engine, only one cylinder detonated.

[BlueDun]

4 hours ago, AndreiC said:

Okay, as the starter of this controversial thread, I’d like to bring the focus back to my situation: is it ok to run 24.9”/2400 at 5000 feet, leaned to 9.4 gph? As I understand it I’m at 70% power and well LOP so should not hurt anything, right?

The reason I am hoping to run like this is that for some reason the difference between 65% and 70%, on my plane, is significant in terms of speed, but not so much in terms of fuel: about 8 knots for about .8 gph more.


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That's right. You are lean of peak at that fuel setting and with that airflow. If your cylinder temps look good -- which you verified -- it's a good plan. It's *roughly* 70%. You then verified the setting with good engine temps. If you had stayed rich, you would have been closer to 75%, I think. It's good to have simple go-to settings. I highly recommend it. 

I took this course and am thoroughly comfortable setting my engine in different ways:

https://www.advancedpilot.com/onlinecourse.html

THAT SAID, no need to over think: 95% of the time i keep it really, really simple and fly. I climb for full power (which may mean some leaning for high altitude), stay wide open throttle and pull mixtures straight back to 13 or 13.5 gph for cruise, and then monitor CHT. (IO550 in an Ovation 3). That gives me 60- 65%, roughly.

Hope this helps you as you learn. 

 

 

[wombat]

4 hours ago, Shadrach said:

Your engine has a compression ratio of 7.5:1 which makes it less thermally efficient. For that reason, the multiplier/divisor is 13.7 instead of 14.9.

Then my 75% LOP power fuel flow is 16.697 GPH.  The ROP numbers in the POH for 75% power are for 20 to 21 GPH.  Quite a difference.

[Shadrach]

32 minutes ago, wombat said:

Then my 75% LOP power fuel flow is 16.697 GPH.  The ROP numbers in the POH for 75% power are for 20 to 21 GPH.  Quite a difference.

Indeed. Do understand that in order to be LOP at 16.5gph you will need to run higher MP than the book 75% ROP MP setting. 

[Mooney in Oz]

9 hours ago, Huckster79 said:

What’s the reasoning? Just curious-not challenging.  
 

I was told to reduce it to “reduce stress/wear” but I’ve learned there’s too many OWT in aviation to accept what I was told without question now that you brought up a new view point. 

See page 2.

Bob Kromer.pdf

[Shadrach]

13 hours ago, wombat said:

Continental says 470 is OK.   Nobody here seems to believe it, and I'm not getting anywhere near that temperature on my engine.   But that's why I picked 390 as an "OK" temperature.

What are typical CHTs using book ROP power settings?  You should enjoy lower CHTs at equal power when LOP. TIT may be a challenge to attaining the desired LOP power setting.

[Shadrach]

@AndreiC, what cylinder are you using as a reference for LOP cruise?

[A64Pilot]

The max CHT’s are just that, Max. The engine manufacturer has to demonstrate that the engine won’t destroy itself at those numbers, not that it won’t suffer from significantly increased wear / stress etc.

Lycoming in several places has printed for max longevity to run 400F or LOWER CHT. and I think the max on Lycoming is 500 F, so they want you running at least 100F cooler than Max for long life. Remember Cyl temp is an indicator of stress the engine is under it’s not just cyl head temp, it’s other components as well and of course hot heads is one of those things that significantly reduces detonation margin, unless you find yourself in a box canyon or something and have to climb at Vx or similar to clear terrain there is no need to operate at high cyl head temps. Get into the habit of cruise climbing, that is at much higher speeds than Vy and you can keep cyl head temp in the middle of the green most days.

The generally accepted percent power where you can’t hurt a Continental with mixture is 65%, Lycoming it seems has a greater margin of 75%.

65% and 75% does not mean that if you operate higher than those numbers LOP that you will detonate, those numbers just mean if you operate below them and make a mistake and allow the engine to enrichen that your mistake shouldn’t be a costly one.

[A64Pilot]

14 hours ago, Pinecone said:

Don't know.  Not deliberate LOP.  Carb engine, only one cylinder detonated.

It’s difficult to near impossible to get an O-470 LOP, some have said if they run short of WOT that the partially closed throttle plate causes enough turbulence to atomize the fuel enough to do so, and some have said if you run some carb heat that helps too, that they can barely get LOP. I’ve never tried myself.

But you can pretty easily operate one just rich of peak without any tricks

Sometimes we just never know, my guess is it was likely pre-ignition and of course many argue that pre-ignition is always the precursor to detonation, but does it matter who’s on first? From an owners perspective you still end up with a big bill, so does it matter who shot John?

What matters of course is how to prevent it in the future, there are many ways to get into detonation, it can be as easy as forgetting to go rich before going full throttle to climb etc.

 

[Pinecone]

1 hour ago, A64Pilot said:

65% and 75% does not mean that if you operate higher than those numbers LOP that you will detonate, those numbers just mean if you operate below them and make a mistake and allow the engine to enrichen that your mistake shouldn’t be a costly one.

Exactly.

Those limits are for safe operation at ANY mixture setting.  Once LOP, you can run any power setting. 

[A64Pilot]

10 minutes ago, Pinecone said:

Exactly.

Those limits are for safe operation at ANY mixture setting.  Once LOP, you can run any power setting. 

I know that and thought I had explained that adinfanitum 

Point I try apparently unsuccessfully to make is if you stay within those numbers you are protected if you make a mistake is all, because as you say those numbers are safe for ANY setting. I guess too just ignore that Lycoming says for max engine life to fly at or below 65% power too?

Anyone is free to do as they please, years ago I was taught during a risk analysis class the most conservative response rule, that is when faced with more than one possibility, choose the one that’s less likely to get you into trouble.

It’s in everything, some push fuel, argue that you don’t have to land with the reserve just have planned to have it. Most conservative response is land and re-fuel.

Those that are arrogant enough to believe they are better,  that they know what they are doing, that they don’t make mistakes can of course operate as they please.

[Shadrach]

58 minutes ago, A64Pilot said:

It’s difficult to near impossible to get an O-470 LOP, some have said if they run short of WOT that the partially closed throttle plate causes enough turbulence to atomize the fuel enough to do so, and some have said if you run some carb heat that helps too, that they can barely get LOP. I’ve never tried myself.

But you can pretty easily operate one just rich of peak without any tricks

Sometimes we just never know, my guess is it was likely pre-ignition and of course many argue that pre-ignition is always the precursor to detonation, but does it matter who’s on first? From an owners perspective you still end up with a big bill, so does it matter who shot John?

What matters of course is how to prevent it in the future, there are many ways to get into detonation, it can be as easy as forgetting to go rich before going full throttle to climb etc.

 

A more correct statement would be that it’s hard to get an O470 to run smoothly with all cylinders LOP.
It is not hard to get it to run smoothly with some cylinders LOP and some cylinders ROP.
This engine was likely leaned at a high power setting and ended up with an uninstrumented cylinder operating at an abusive, ROP, mixture setting for an extended period of time. It heated up, then began detonating and self destructed.

Any time a carbureted engine is leaned to rough and enriched to smooth (standard practice) there will likely be cylinders all over the mixture spectrum. That is why it’s a bad idea to lean a carbed engine above 65% power.  It can be done with a well instrumented engine, doing so with a single cylinder CHT/EGT is asking for trouble.

[Shadrach]

8 hours ago, A64Pilot said:

I know that and thought I had explained that adinfanitum 

Point I try apparently unsuccessfully to make is if you stay within those numbers you are protected if you make a mistake is all, because as you say those numbers are safe for ANY setting. I guess too just ignore that Lycoming says for max engine life to fly at or below 65% power too?

Anyone is free to do as they please, years ago I was taught during a risk analysis class the most conservative response rule, that is when faced with more than one possibility, choose the one that’s less likely to get you into trouble.

It’s in everything, some push fuel, argue that you don’t have to land with the reserve just have planned to have it. Most conservative response is land and re-fuel.

Those that are arrogant enough to believe they are better,  that they know what they are doing, that they don’t make mistakes can of course operate as they please.

Some of Lycoming’s recommendations are factually lousy. Read the bolded section below of SI1094. There is no better way to put a cylinders at peak pressure/CHT.  

• The exhaust gas temperature (EGT) offers little improvement in leaning the float-type carburetor over the procedures outlined above because of imperfect mixture distribution. However, if the EGT probe is installed, lean the mixture to 100˚ F on the rich side of peak EGT for best power operation. For best economy cruise, operate at peak EGT. If roughness is encountered, enrich the mixture slightly for smooth engine operation.

Lycoming limits power because it’s one way to protect the ham fisted and the ignorant from harming an engine. However, their recommendations are far from optimal.  What’s optimal is to know which cylinder is richest and which cylinder is leanest and ensure that the rest are set more conservatively  set than whichever of those cylinders is being referenced for setting power.  Lycoming and the industry in general has been selling poorly instrumented engines to ignorant pilots for so long that it seems that its never occurred to them that there might be a better way. Or perhaps it’s the legal department that wishes to minimize inconsistencies in recommendations. It’s hard to defend inconsistencies in court…

I am grateful that APS, along with JPI, EI, Et al…came along to fill the void. The thing you fail to grasp is that those of us that know that each cylinder is operating in the desired place on the mixture spectrum with healthy CHTs are operating under the “most conservative response rule”.  Of course there will always be those that wish to operate like it’s 1960…

By the way, Lycoming does not recommend LOP operations, yet you operate your engine LOP. All of your hemming and hawing about how other folks operate sort of reminds me of a person that breaks the speed limit by 10mph and then calls someone that passes at 20mph over a maniac.

 

[Pinecone]

7 hours ago, Shadrach said:

A more correct statement would be that it’s hard to get an O470 to run smoothly with all cylinders LOP.
It is not hard to get it to run smoothly with some cylinders LOP and some cylinders ROP.
This engine was likely leaned at a high power setting and ended up with an uninstrumented cylinder operating at an abusive, ROP, mixture setting for an extended period of time. It heated up, then began detonating and self destructed.

 

If you are talking about the one I posted pictures of, it was not leaned at the time that occurred.  It was full rich.