LOP operations

[Ted]

True, but if you make your target power airspeed and then lean until speed loss, you'll be plenty lean. There are other ways to play the game.

Again, the Aztec is pretty bad about it. There's a fine line, and without a full-on engine monitor, it simply doesn't work well.

For most airplanes, you're right.

Mechanics are a lot like flight instructors in that regard, they say things even when they don't know what they're talking about because they feel they should.

Agreed.

 

[Henning]

Again, the Aztec is pretty bad about it. There's a fine line, and without a full-on engine monitor, it simply doesn't work well.

For most airplanes, you're right.



Agreed.

Remember, you only need the information once, you don't have to always monitor, you can set up temp test gear at a fraction of the cost and get the information to make an operating table. You then single point to detect gross failure. If you know you are lean enough to avoid the heat condition by using fuel flow. I govern operations by fuel flow vs known parameters and observing the EGT result rather than leaning to EGT. This is why accurate fuel flow is the most critical instrument to running LOP safely. I then watch to see CHT and it's always good. Another nifty not so expensive item is a laser pointer heat gun, those suckers are incredible, at least the Fluke ones I was using. Your CHTs will be reflected in the cowling temp as will major exhaust leaks. I consider them mandatory on the turbo twin Cessnas.

 

[alfadog]

Watch this video and lean on just about everything but full take-off power at sea level.

http://www.eaavideo.org/video.aspx?v=994986557001

Otherwise you will be running your engine "horrendously rich".

 

[Henning]

Watch this video and lean on just about everything but full take-off power at sea level.

http://www.eaavideo.org/video.aspx?v=994986557001

Otherwise you will be running your engine "horrendously rich".

I don't need to watch the video, I don't disagree with any of that in principle and practice. I'll lean 250 ROP full power at sea level as well. I don't stay at full power for 20 seconds, typically less, I don't have to worry about heat, only detonation. My augmentors only show a fine white dust.

 

[Ted]

Remember, you only need the information once, you don't have to always monitor, you can set up temp test gear at a fraction of the cost and get the information to make an operating table. You then single point to detect gross failure. If you know you are lean enough to avoid the heat condition by using fuel flow. I govern operations by fuel flow vs known parameters and observing the EGT result rather than leaning to EGT. This is why accurate fuel flow is the most critical instrument to running LOP safely. I then watch to see CHT and it's always good. Another nifty not so expensive item is a laser pointer heat gun, those suckers are incredible, at least the Fluke ones I was using. Your CHTs will be reflected in the cowling temp as will major exhaust leaks. I consider them mandatory on the turbo twin Cessnas.

An engine monitor is going to be the most cost-effective means for anyone to get this information. Getting it once will help you establish your operating parameters, sure, and on most installations that's sufficient. I agree that fuel flow is what I go by, and really is what you use once you've established what you go by.

That said, on the Aztec, there is a very, very, very fine line between roughness and appropriate CHTs. I have 900 hours in the plane, and I would not try to run the thing LOP without an engine monitor.

The Aztec doesn't have GAMIs, but in my experience the parallel valve IO-540s don't benefit from them much vs. the factory injectors.

Just buy the engine monitor. Even if you don't want to run LOP, it's worth it. I know you agree with that, but it's for the benefit of others.

 

[Dave Siciliano]

The engine monitor has helped me diagnose several problems in the cockpit. I've had the engine run rough before and all I could tell the mechanic was it ran rough. I got to where I could tell which plug needed attention if that was the problem. Could see it affect EGT and CHT might even drop. Just told the mechanic which plug to pull and look at. At first, he just thought I was blowing smoke; then came to realize, that was what was wrong!
I don't look for the amount of mag drop anymore on runup; just what to see all EGTs rise on one mag. It shows all plugs are firing or not.
You will see some things you might not have ever sensed before. When I flew to Merida several year ago over the Gulf, on the way out I saw one cylinder was slightly misfiring. By the time I got near water from Addison, it was behaving properly. Several other things. It's not a cure-all, but can certainly diagnose a lot of things before they get bad, and when they are bad, help you hone in on what the problem is if it's a plug or valve.

Best,

Dave

 

[DouglasBader]

WWII how many planes had multipoint sensors? They all operated LOP, every one of them.

Having flown some of them, I can safely say that's just not true.

 

[azure]

With my IO-360, if I try to operate with all cylinders LOP, there is noticeable roughness. I confirmed this with a GAMI lean test last month, as accurately as I could do with an EDM-700 monitor and factory fuel flow meter (analog). The verdict was pretty clear, my cylinders peak over a fairly wide range of fuel flow settings and if two of them are LOP, the other two are still too close to peak to run safely at high power. So basically, at power levels of below 65% (and WOT above 8000 MSL or so), I will run slightly LOP for economy. Higher power than that, I'm 100-125 ROP. I burn away a lot of money that way, but at least I won't damage my cylinders. Somewhere down the line I'm hoping to invest in GAMIjectors.

My point? Lots of people told me that the IO-360 likes to run LOP and that I'd be fine. My advice, worth every penny you paid for it , is to get a decent monitor and run the lean test first before you try to operate LOP at power levels above 65% or so. If I hadn't run the test and just believed everyone, I might have done some damage by now.

Choose wisely as Cap'n Ron says. It's your engine.

 

[alfadog]

With my IO-360, if I try to operate with all cylinders LOP, there is noticeable roughness. I confirmed this with a GAMI lean test last month, as accurately as I could do with an EDM-700 monitor and factory fuel flow meter (analog). The verdict was pretty clear, my cylinders peak over a fairly wide range of fuel flow settings and if two of them are LOP, the other two are still too close to peak to run safely at high power. So basically, at power levels of below 65% (and WOT above 8000 MSL or so), I will run slightly LOP for economy. Higher power than that, I'm 100-125 ROP. I burn away a lot of money that way, but at least I won't damage my cylinders. Somewhere down the line I'm hoping to invest in GAMIjectors.

My point? Lots of people told me that the IO-360 likes to run LOP and that I'd be fine. My advice, worth every penny you paid for it , is to get a decent monitor and run the lean test first before you try to operate LOP at power levels above 65% or so. If I hadn't run the test and just believed everyone, I might have done some damage by now.

Choose wisely as Cap'n Ron says. It's your engine.

I have been running my Arrow slightly ROP but after watching the seminar I linked above, that seems to be the worst place to be (high CHT). I do not cruise over 65% so I should be safe running LOP even with my one-cylinder EGT/CHT.

 

[Henning]

Just buy the engine monitor. Even if you don't want to run LOP, it's worth it. I know you agree with that, but it's for the benefit of others.

Yep, the engine monitor is for FAR more than LOP, in fact for me LOP is a secondary use. The primary is monitoring trends within the cylinders to catch failures while they are still small and cheap to repair.

 

[azure]

I have been running my Arrow slightly ROP but after watching the seminar I linked above, that seems to be the worst place to be (high CHT). I do not cruise over 65% so I should be safe running LOP even with my one-cylinder EGT/CHT.

That's a great webinar and I've learned a lot from Mike Busch's other webinars too, but there are a few things he says that don't make a lot of sense to me. His idea that CHT is a good proxy for intra-cylinder pressure and that as long as CHTs don't go above some reasonable limit you're fine, I tend to take with a very large grain of salt. The single most important factor affecting my CHTs is OAT, the next most important is climb airspeed. But I've never seen any of my CHTs go above 370, and they rarely go above 350 except in the heat of summer. If I see a CHT above 360 I'm lowering my angle of attack to get my airspeed up, or pushing in the red knob if I'm not already full rich. At standard temperature I don't see more than a 15 deg F swing in CHT from max climb after takeoff to cruise. And during my lean test, ALL of my CHTs were around and below 300, even at peak EGT and with the cowl flaps closed (tried closing them just to see how much difference it would make). Maybe my engine just has phenomenally good cooling (though I doubt it, considering the effect of OAT), but regardless, the relationship between CHT and ICP as a function of OAT is a total unknown as far as I'm concerned. So unless I'm misunderstanding his advice, I think I'd be crazy to rely on CHT alone to set my mixture. If I did, I suspect I could be in the red box a lot of the time and blissfully unaware.

 

[alfadog]

That's a great webinar and I've learned a lot from Mike Busch's other webinars too, but there are a few things he says that don't make a lot of sense to me...

I need to watch it again before I can intelligently respond. I will do that tonight

 

[Ted]

That's a great webinar and I've learned a lot from Mike Busch's other webinars too, but there are a few things he says that don't make a lot of sense to me. His idea that CHT is a good proxy for intra-cylinder pressure and that as long as CHTs don't go above some reasonable limit you're fine, I tend to take with a very large grain of salt. The single most important factor affecting my CHTs is OAT, the next most important is climb airspeed. But I've never seen any of my CHTs go above 370, and they rarely go above 350 except in the heat of summer. If I see a CHT above 360 I'm lowering my angle of attack to get my airspeed up, or pushing in the red knob if I'm not already full rich. At standard temperature I don't see more than a 15 deg F swing in CHT from max climb after takeoff to cruise. And during my lean test, ALL of my CHTs were around and below 300, even at peak EGT and with the cowl flaps closed (tried closing them just to see how much difference it would make). Maybe my engine just has phenomenally good cooling (though I doubt it, considering the effect of OAT), but regardless, the relationship between CHT and ICP as a function of OAT is a total unknown as far as I'm concerned. So unless I'm misunderstanding his advice, I think I'd be crazy to rely on CHT alone to set my mixture. If I did, I suspect I could be in the red box a lot of the time and blissfully unaware.

You're correct about taking that with a grain of salt. I've managed to run engines with CHTs at 320F and still having quite high ICPs.

 

[alfadog]

You're correct about taking that with a grain of salt. I've managed to run engines with CHTs at 320F and still having quite high ICPs.

Do you have ICP sensors?

edit: ICP = internal combustion pressure?

 

[Henning]

You're correct about taking that with a grain of salt. I've managed to run engines with CHTs at 320F and still having quite high ICPs.

Of course LOL, that's the point of LOP. ICP is only indicative of power. CHT is about waste heat. For the same altitude, power setting and airspeed below max attainable; you will be able to achieve that result either LOP or ROP. Maximum performance will always be ROP, about 75*, but then you have to listen. You don't listen for detonation, you listen for the moan that comes before detonation. No lugging moaning load, no detonation; it doesn't happen. There are two ways out of detonation: More Fuel and Less Fuel, I prefer leaning out of risk.

 

[azure]

Of course LOL, that's the point of LOP. ICP is only indicative of power. CHT is about waste heat. For the same altitude, power setting and airspeed below max attainable; you will be able to achieve that result either LOP or ROP. Maximum performance will always be ROP, about 75*, but then you have to listen. You don't listen for detonation, you listen for the moan that comes before detonation. No lugging moaning load, no detonation; it doesn't happen. There are two ways out of detonation: More Fuel and Less Fuel, I prefer leaning out of risk.

This is something that's always bothered me. Say I'm taking off on a hot day from a field that's not too high, but the DA is a little above 5000. Recommended TO technique is to lean for max power. But that's got to be better than 65% rated, maybe 75% because your DA just isn't that high (in the Cardinal, book power WOT at 6000 feet is still 70-75% IIRC). So aren't you pushing your engine into the red box on takeoff??

edit: alfa, ICP is intra-cylinder or internal cylinder pressure.

 

[alfadog]

edit: alfa, ICP is intra-cylinder or internal cylinder pressure.

Thanks. And you have sensors for that?

 

[azure]

Thanks. And you have sensors for that?

Not me. Ted's position is rather, umm... special, I suspect.

 

[Henning]

This is something that's always bothered me. Say I'm taking off on a hot day from a field that's not too high, but the DA is a little above 5000. Recommended TO technique is to lean for max power. But that's got to be better than 65% rated, maybe 75% because your DA just isn't that high (in the Cardinal, book power WOT at 6000 feet is still 70-75% IIRC). So aren't you pushing your engine into the red box on takeoff??

edit: alfa, ICP is intra-cylinder or internal cylinder pressure.

The problem with using 75% power as a reference for this is that number is arbitrarily set by the application, not by any rules of mechanics or physics. You can have the same engine span 70hp at 75% power depending on how it's built and operated for the application.

 

[azure]

The problem with using 75% power as a reference for this is that number is arbitrarily set by the application, not by any rules of mechanics or physics. You can have the same engine span 70hp at 75% power depending on how it's built and operated for the application.

Not sure what you're getting at Henning. Sure there will be differences in hp between individual engines of the same model, that's a given. By "application" do you mean aviation vs something else, or how the engine is operated in flight (fuel flow, MP, RPM)?

My question was, how can it be safer to run an engine WOT i.e. max MP and RPM, leaned for max power at takeoff, vs in cruise at the same DA? Both situations, you're operating the engine at or close to peak power for the altitude. If anything, it should be worse at takeoff and climbout because you don't have as much cooling.

 

[alfadog]

Not sure what you're getting at Henning. Sure there will be differences in hp between individual engines of the same model, that's a given. By "application" do you mean aviation vs something else, or how the engine is operated in flight (fuel flow, MP, RPM)?

My question was, how can it be safer to run an engine WOT i.e. max MP and RPM, leaned for max power at takeoff, vs in cruise at the same DA? Both situations, you're operating the engine at or close to peak power for the altitude. If anything, it should be worse at takeoff and climbout because you don't have as much cooling.

My understanding, very much FWIW, is that you lean ROP for takeoff at high DA. But I understand that conflicts with the webinar about that ROP area.

 

[Ted]

Do you have ICP sensors?

edit: ICP = internal combustion pressure?

Not on the plane, used to on the stand all the time.

Of course LOL, that's the point of LOP. ICP is only indicative of power. CHT is about waste heat. For the same altitude, power setting and airspeed below max attainable; you will be able to achieve that result either LOP or ROP. Maximum performance will always be ROP, about 75*, but then you have to listen. You don't listen for detonation, you listen for the moan that comes before detonation. No lugging moaning load, no detonation; it doesn't happen. There are two ways out of detonation: More Fuel and Less Fuel, I prefer leaning out of risk.

If you can hear detonation in an airplane, then you're better than, well, everyone I've met on the subject. Which includes a lot of people who've done that their whole careers on these engines.

 

[Henning]

If you can hear detonation in an airplane, then you're better than, well, everyone I've met on the subject. Which includes a lot of people who've done that their whole careers on these engines.

As I said, I don't listen for detonation, I listen to the engine load condition which indicates the the conditions that support detonation are present. Just because you're in 'the red box' does not mean you're in detonation, it means you're operating in a realm where if other conditions all align you can get detonation. I compare all the incoming data streams to keep things working properly.

 

[Ted]

As I said, I don't listen for detonation, I listen to the engine load condition which indicates the the conditions that support detonation are present. Just because you're in 'the red box' does not mean you're in detonation, it means you're operating in a realm where if other conditions all align you can get detonation. I compare all the incoming data streams to keep things working properly.

That is all.

 

[Henning]

??? You don't listen to your engines?

 

[Ted]

??? You don't listen to your engines?

Of course I do, and many things can be determined from that. But to think that you can listen for detonation or tell in many cases that it's unhappy or you're operating in, or will soon be operating in detonation? I call BS. Lots of people make that claim, and not a single one has ever been able to show me that they can do it consistently like you can with something that actually measures ICPs, or at least an engine monitor.

Like I said, if you can, you're better than me and people I know who did that their whole careers on piston aircraft engines both on dynos and in flight.

 

[Tom-D]

??? You don't listen to your engines?

Yes we could hear them very well, but it was difficult to tell wither it was 1-2-3- or 4.

want to know when it was detonating ? watch the torque meter.

 

[Tom-D]

I certainly would concede that on Superior or ECI cylinders it may not be necessary, however the factory cylinders on a Lycoming are typically going to benefit. Keep in mind the factory Lycomings are nitrided and are harder than the Superior and ECI cylinders, which are not made out of the same metal using the same processes. How difficult it is to seat rings is mostly a function of hardness of the components. Use components that aren't as hard, and they'll seat easier.

I don't buy that Ted, break in is more a function of the finish left by the finish hone than hardness, because a ECI cylinder such as shown is nearly polished smooth, and they show no cross hatching as does a new Lycoming cylinder.

 

[Henning]

Of course I do, and many things can be determined from that. But to think that you can listen for detonation or tell in many cases that it's unhappy or you're operating in, or will soon be operating in detonation? I call BS. Lots of people make that claim, and not a single one has ever been able to show me that they can do it consistently like you can with something that actually measures ICPs, or at least an engine monitor.

Like I said, if you can, you're better than me and people I know who did that their whole careers on piston aircraft engines both on dynos and in flight.

Yes, I am saying that there is a recognizable note a gas recip engine gives off that is always there prior to detonation, it is the indicator that those levels of pressure required to support it have been reached. If that note is not detectable, I do not worry about detonation. The more RPM you run at pressure the greater your margin from detonation. It's what to listen for when you pull the prop back.

 

[Ted]

I don't buy that Ted, break in is more a function of the finish left by the finish hone than hardness, because a ECI cylinder such as shown is nearly polished smooth, and they show no cross hatching as does a new Lycoming cylinder.

There's a bit of both, though. Certainly the finish impacts it, but depending on the hardness of materials, the establishing of wear patterns will happen faster or slower.

How many hours it takes I'd expect to vary depending on a number of factors, and certainly if one allows the CHTs to get too hot in the process of attempting to break in the engine then that's going to be detrimental. I'd say even for hard cylinders that 50 hours is a bit on the high side (the 5-10 rule is probably about right in most cases), but that's probably painting with a broad brush for people who aren't doing things properly.

Yes, I am saying that there is a recognizable note a gas recip engine gives off that is always there prior to detonation, it is the indicator that those levels of pressure required to support it have been reached. If that note is not detectable, I do not worry about detonation.

I'd say you're fooling yourself if you think you can tell from that sound in an airplane. But go on believing what you want.

The more RPM you run at pressure the greater your margin from detonation. It's what to listen for when you pull the prop back.

Not always true in these engines. I've seen a number of cases where at lower RPMs detonation goes away with all other conditions the same, simply because the engine is producing less power. There are more factors at work.

 

[Tom-D]

There's a bit of both, though. Certainly the finish impacts it, but depending on the hardness of materials, the establishing of wear patterns will happen faster or slower.

How many Rockwell hardness points will there be between an ECI and any other nitrided cylinder?

Not much I suspect.

 

[Henning]

I'd say you're fooling yourself if you think you can tell from that sound in an airplane. But go on believing what you want.

Not always true in these engines. I've seen a number of cases where at lower RPMs detonation goes away with all other conditions the same, simply because the engine is producing less power. There are more factors at work.

You can escape detonation in any of the 6 directions quite safely, the question is which produces the power result you want most safely. Consider that detonation events become more likely as load increases with torque requirements of reduced RPM pitches, when operating at higher power settings you provide a greater margin from detonation using the high RPM/low MP option for a power setting.

 

[DouglasBader]

Yes, I am saying that there is a recognizable note a gas recip engine gives off that is always there prior to detonation, it is the indicator that those levels of pressure required to support it have been reached. If that note is not detectable, I do not worry about detonation.

You may have accomplished what no other can do or has been able to do. You've apparently got better hearing than a teenager, too.

 

[denverpilot]

This is something that's always bothered me. Say I'm taking off on a hot day from a field that's not too high, but the DA is a little above 5000. Recommended TO technique is to lean for max power. But that's got to be better than 65% rated, maybe 75% because your DA just isn't that high (in the Cardinal, book power WOT at 6000 feet is still 70-75% IIRC). So aren't you pushing your engine into the red box on takeoff??

Remember there's typically an extra enrichment that happens at full throttle in most aviation carbs. Fuel injected, different story.

At the high-midway DAs, like here in DEN and slightly East, where you might be at 75% power if it's cold out, most of us are taught to lean to peak power at run-up RPM not at full throttle, then add two half twists of mixture richer from there on a vernier or some pre-detrmined distance forward on a throttle cluster style. That gives a plenty rich mixture for takeoff.

Head up to airports above 6000 or have a hotter than standard day, it won't matter for detonation, and you'll want a brief static full-power run-up to quickly set it, but it will matter for CHT in the climb. Too hot for the dry high air up here to carry away heat.

We have to give our O-470 some extra fuel in the initial climb to keep it cooled until we can level off. Cowl flaps open the whole time of course. On the hottest summer days, we may not even close them or close them halfway in cruise.

 

[Tom-D]

At the high-midway DAs, like here in DEN and slightly East, where you might be at 75% power if it's cold out,

Some body tell me what the DAs are at 7000' at -15 degrees?

 

[Henning]

You may have accomplished what no other can do or has been able to do. You've apparently got better hearing than a teenager, too.

#1 most definitely not true... Dude, I was taught it when I was 11. In the days before computer control engines, this was the art to operating and racing; there is a reason it was named 'tuning' an engine, you worked by ear. I started doing this stuff in 1976 with some guys down the street that took me in like a little brother.

#2 to my great surprise is true as it proved in the box just a couple of years ago. It really amazed me considering my cumulative lifetime exposure to industrial levels of noise.

 

[denverpilot]

Some body tell me what the DAs are at 7000' at -15 degrees?

You can just barely make 77% on a Standard day at a Pressure Altitude of 6000 in my aircraft. Hotter it falls off. Colder you drop 1" MP.

It's also quite a ways above 3C around here this time of year.

PA at the airport as I type this is 5914.
DA is 7319.
It's 15C at 03:00 local.
It will be 28.3C by 1PM this afternoon.

Thus, my comment that to get 75% around here you need it to be colder.

Truthfully you can just barely make it. Wouldn't count on an older engine and prop doing it though.

At 8000' PA you won't make 75% even at -23C.

So like I said, we just barely make 75% power most of the year unless it's cold.

Go downhill to KS and you got it made.

 

[Ted]

How many Rockwell hardness points will there be between an ECI and any other nitrided cylinder?

Not much I suspect.

Good question, that's one number I've never seen. I'd suspect that they are lower, though, simply as a function of their typically shorter life vs. factory, not to mention the lack of nitriding.

You can escape detonation in any of the 6 directions quite safely, the question is which produces the power result you want most safely. Consider that detonation events become more likely as load increases with torque requirements of reduced RPM pitches, when operating at higher power settings you provide a greater margin from detonation using the high RPM/low MP option for a power setting.

Ok, you did not state increase RPM and decrease manifold pressure (which will work). Yes, escpaing detonation is simple enough to do, I agree there.

That doesn't change the fact that I think you're fooling yourself if you think you can tell this stuff by sound on an aircraft engine. Sure, people have done it on cars, but the noise that exists on cars is much lower, and a lot more of it comes from the engine rather than from the propeller and wind noise. Even if you personally can predict the onset of detonation from sound on a car, to think you can translate it to a plane is silly. Again, in your 310 it's irrelevant since you'd have to try really hard to get detonation anyway. In a Navajo or a 421, that advice would be significantly worse.

 

[Dr. O]

For an old engine test cell supervisor, watching this thread has been a hoot...

First consider that a diesel engine is ALWAYS running LOP except under one very specific condition (full throttle and maximum load) Yet these engines routinely run a million miles down the highway without burning pistons, detonating, or blowing up..

Second, notice that the Gami people do not tell you to take your injected engine out and just run it LOP willy nilly... The injector fuel flows need to be balanced so that you do not have one cylinder running too rich (not too lean) and burn a piston or exhaust valve under high throttle, LOP operation... This is what GAMI sells, the hardware to make LOP at higher power settings feasible...

Third, on a carburetted engine the spread between the richest and leanest cylinder at any given throttle setting, is normally/always too great to safely allow LOP at engine powers of approx. 75% and greater... For 70% and under you can,and I have for 50+ years, run them LOP (at least most of the cylinders Yes, I have a single cylinder EGT on each engine - but, old habits are hard to break... Lean until rough, go rich just enough to smooth it out... My engines routinely go beyond TBO (way beyond)

The guys running those turbo engines, which are usually right on the ragged edge of either detonation or melting the cylinder head, are the ones between a rock and a hard place... Henning says he knows what he is doing and I don't dispute him... What I do note, is that a blown engine has a very tight margin between performance and melting down and needs an alert pilot to make it to the TBO...

 

[Ted]

First consider that a diesel engine is ALWAYS running LOP except under one very specific condition (full throttle and maximum load) Yet these engines routinely run a million miles down the highway without burning pistons, detonating, or blowing up..

And turbine engines run LOP all the time as well.

Funny though, diesels weigh a great deal more with huge pressure pulses not seen in gas engines. It's really not a good comparison - LOP in a gas engine actually lowers peak pressure and smooths out the pressure curves, diesels operate entirely differently.

Kinda like saying that an elephant and a mosquito are both animals, so a mosquito should therefore be much like an elephant.