Lean of Peak

[kortopates]

JPI EDM monitors %Power is based on ROP mixture only. They don't calculate a LOP % power, but it shouldn't necessary as its so straight forward most pilot already know where say 65% power is based on their fuel flow.

[Shadrach]

1 hour ago, DanM20C said:

The percent power is always right on the 17 X FF.  I'm assuming it's using it.   JPI knew the engine when they set up the parameters and I think they programed it then.  I didn't change anything.
 

Cheers,

Dan

13.7 is the multiple for your TSIO360 with 7.5:1 CR.  

[DanM20C]

16 minutes ago, Shadrach said:

13.7 is the multiple for your TSIO360 with 7.5:1 CR.  

I'm confused.  I said 13.7 but for some reason your quote of me is saying 17?

1 hour ago, kortopates said:

JPI EDM monitors %Power is based on ROP mixture only. They don't calculate a LOP % power, but it shouldn't necessary as its so straight forward most pilot already know where say 65% power is based on their fuel flow.

Paul, if you enter the lean find mode and change the setting to LOP, it will display LOP power correctly.  At least my 900 does.  A 830 I flew with a few weeks ago also worked this way.

It doesn't really mater, but it does satisfy my ocd in cruise.

Cheers,

Dan

[kortopates]

Paul, if you enter the lean find mode and change the setting to LOP, it will display LOP power correctly.  At least my 900 does.  A 830 I flew with a few weeks ago also worked this way.
It doesn't really mater, but it does satisfy my ocd in cruise.
Cheers,
Dan

Interesting Dan. According to JPI that would be pure coincidence- are you sure you’re actually see %power change going between LOP peak find and ROP peak find - without making any changes but %power change? they say it’s only based on ROP.


Sent from my iPhone using Tapatalk

[Shadrach]

18 minutes ago, DanM20C said:

I'm confused.  I said 13.7 but for some reason your quote of me is saying 17?

Paul, if you enter the lean find mode and change the setting to LOP, it will display LOP power correctly.  At least my 900 does.  A 830 I flew with a few weeks ago also worked this way.

It doesn't really mater, but it does satisfy my ocd in cruise.

Cheers,

Dan

Hmmm, I read it as 13.7…

All of my Apple products auto correct to make me look as dumb as possible.  Perhaps your quote was caught in the cross fire.

[DanM20C]

17 minutes ago, kortopates said:

Interesting Dan. According to JPI that would be pure coincidence- are you sure you’re actually see %power change going between LOP peak find and ROP peak find - without making any changes but %power change? they say it’s only based on ROP.


Sent from my iPhone using Tapatalk

Yes, I'll set up a 9.5 gph LOP cruise and  the jpi will show 85% power (or something similar).  I'll tap the Lean Find, hit LOP, and then Exit.  Then it will show 62%.   I've never seen in talked about in a manual but I was never looking.  I'll take a look next time I'm at the hangar.

Cheers,

Dan

[jaylw314]

20 minutes ago, DanM20C said:

Yes, I'll set up a 9.5 gph LOP cruise and  the jpi will show 85% power (or something similar).  I'll tap the Lean Find, hit LOP, and then Exit.  Then it will show 62%.   I've never seen in talked about in a manual but I was never looking.  I'll take a look next time I'm at the hangar.

Cheers,

Dan

That's wild, I have an 830 and never noticed that (I never use Lean Find, though).  I've never seen it documented either.  I'll have to test that this weekend.

Edited October 13, 2022 by jaylw314

[jlunseth]

My experience with my JPI930 is that it does switch over to using the LOP formula when you put it in Lean mode. The problem with doing that in my engine is that you now have the EGTs in icicle mode and they are using a wrong peak as a reference. I just ignore the %HP. When I used to operate ROP at cruise quite a bit, it seemed to me it was off by about 8 percentage points. If it said I was at 75% percent I was actually around 67%. The JPI algorithm is proprietary and there is nothing in my manual about it, I can only go from what I have seen on the monitor. 

History: when I first got my 930, which was about 2010, the pilot could modify the HP constant. Then there was a period of several years where JPI gave edit capability to some of their resellers, and the HP constant was then grayed out for the pilot, you needed a code. Now I think you can edit again.

DanM20C I like the way you run your engine. I got to the point where I was closing in on tbo so was going to replace the engine sooner or later so I just went with the 71% HP setting I use. That was a few hundred hours ago now so it seems to work, but nothing at all wrong with your setting.

Pinecone, as most of the guys on here know, the constant is dependent on the compression ratio of the particular engine. There is a different constant for NAs which are a higher compression engine, and someone once wrote about some aircraft TCd engines with a different compression ratio than mine, so there are a couple of other constants in use out there, but I think you are right, most of the true TCd engines would use the 13.7 constant. True TNd engines would have a different constant.

 

Edited October 14, 2022 by jlunseth

[carusoam]

One thing the JPI does…. When switching modes LOP/ROP…

it correctly uses first to peak, or last to peak, depending on which mode you are using…

 

Note for A64… check your LT1’s details… I’m pretty sure there is a hot wire hidden in the intake system for measuring MAF…. I don’t have a ‘93… but I have one on either side….   look for a bunch of wires attached in the middle of the intake hose… a short section of about 4” long… screens protecting it on both ends…

 

Note for JL…. Great description of M20K LOPs again!  Thanks for sharing the details….  
 

Best regards,

-a-

[A64Pilot]

8 hours ago, carusoam said:

One thing the JPI does…. When switching modes LOP/ROP…

it correctly uses first to peak, or last to peak, depending on which mode you are using…

 

Note for A64… check your LT1’s details… I’m pretty sure there is a hot wire hidden in the intake system for measuring MAF…. I don’t have a ‘93… but I have one on either side….   look for a bunch of wires attached in the middle of the intake hose… a short section of about 4” long… screens protecting it on both ends…

 

Note for JL…. Great description of M20K LOPs again!  Thanks for sharing the details….  
 

Best regards,

-a-

The 93 didn’t have it, it was a speed/ density system is what they called it. Haven’t had that car since 2010 it went in as a clunker in the cash for clunkers thing.

https://www.ls1lt1.com/threads/93-z28-speed-density-injection.41633/

The mass airflow sensor came out in 94. I assume emissions is why

What confused me was that my Duramax Diesel had a hot wire mass airflow system, what could a Diesel do with it, it can’t adjust fuel / air mixture? I assume it kept fuel flow down until boost built thereby avoiding smoke, but that’s a guess.

[Tom 4536]

20 hours ago, DanM20C said:

Yes, I'll set up a 9.5 gph LOP cruise and  the jpi will show 85% power (or something similar).  I'll tap the Lean Find, hit LOP, and then Exit.  Then it will show 62%.   I've never seen in talked about in a manual but I was never looking.  I'll take a look next time I'm at the hangar.

Cheers,

Dan

My 930 acts the same and it gives the same readings as you posted.

Edited October 14, 2022 by Tom 4536

[kortopates]

19 hours ago, DanM20C said:

Yes, I'll set up a 9.5 gph LOP cruise and  the jpi will show 85% power (or something similar).  I'll tap the Lean Find, hit LOP, and then Exit.  Then it will show 62%.   I've never seen in talked about in a manual but I was never looking.  I'll take a look next time I'm at the hangar.

Cheers,

Dan

Thanks keep me posted. Its definitely not documented and JPI Technical support says they only support ROP % Power. There would also have to be a constant for the LOP power multiplier with ability to update it to provide correct  %power LOP - that would be a clear sign that this undocumented feature exist. But we may not see all the params in a approved for primary versions.  I'll have to review the settings on mine again - its been awhile since I actually looked on the monitor versus what's documented. Hope you're right.

[Pinecone]

1 hour ago, kortopates said:

 There would also have to be a constant for the LOP power multiplier with ability to update it to provide correct  %power LOP - that would be a clear sign that this undocumented feature exist. But we may not see all the params in a approved for primary versions.  I'll have to review the settings on mine again - its been awhile since I actually looked on the monitor versus what's documented. Hope you're right.

There is a setting for this in the 830

Page 58, Engine Constant 

https://www.jpinstruments.com/wp-content/uploads/2012/07/PG-EDM-730_830_851_740-Rev-F-TB2.pdf

They show a default setting of 14.9, which is in the ball park for many NA engines.

 

There is also a setting for Horsepower Constant on Page 50.  That seems to be for ROP

[DanM20C]

2 hours ago, kortopates said:

Thanks keep me posted. Its definitely not documented and JPI Technical support says they only support ROP % Power. There would also have to be a constant for the LOP power multiplier with ability to update it to provide correct  %power LOP - that would be a clear sign that this undocumented feature exist. But we may not see all the params in a approved for primary versions.  I'll have to review the settings on mine again - its been awhile since I actually looked on the monitor versus what's documented. Hope you're right.

@Pineconebeat me to it.  I just looked through the 900 manual and didn't find anything about seeing a change in % power from ROP to LOP.  But on Page 47 they show the engine constant setting and mention 13.7 for turbo or 14.9 for normally aspirated.  That must be for LOP power calculation.

Next time you're at your airplane check with the lean find, then push the LOP and see if it changes your % power. 

Cheers,

Dan

[jlunseth]

What I remember is that once you switch to LOP you then can’t switch back to ROP unless you shut the engine monitor down, so you are basically stuck with the LOP mode for the rest of a flight. Maybe that has changed. At any rate it never occurred to me to make the switch in flight. I just noticed that in Lean mode the %power number always matched the formula for LOP ops.

[natdm]

31 minutes ago, jlunseth said:

What I remember is that once you switch to LOP you then can’t switch back to ROP unless you shut the engine monitor down, so you are basically stuck with the LOP mode for the rest of a flight. Maybe that has changed. At any rate it never occurred to me to make the switch in flight. I just noticed that in Lean mode the %power number always matched the formula for LOP ops.

If it's anything like the 830, you can toggle between LOP and ROP the same way you get in to the LOP configuration. 

[Will.iam]

3 hours ago, jlunseth said:

What I remember is that once you switch to LOP you then can’t switch back to ROP unless you shut the engine monitor down, so you are basically stuck with the LOP mode for the rest of a flight. Maybe that has changed. At any rate it never occurred to me to make the switch in flight. I just noticed that in Lean mode the %power number always matched the formula for LOP ops.

All of what jlunseth has stated about 252 is correct and I’ve confirmed you set MP and it stays which makes sweeping with mixture control easy to do. I do as Don does running 9.5 as that keeps my TIT below 1550. At 11.1 i think would push me to 1600. @jlunseth are you running that 11.1 with cowl flaps closed or open?  

Also running at 9.5 i also use just 25” MP this puts me at 15 to 25 degrees LOP depending on OAT. I could run 34”MP at 9.5 but my LOP would be closer to 80 to 100 degrees LOP and my CHT will drop below 330 and the flame front would be so slow it might not finish before the exhaust stroke started thus dumping some flame out the exhaust. I could reduce the RPM to compensatebut then i lose a little speed in the process. Especially at higher altitudes. Adding more fuel would speed the flame front fast enough to finish but i think the extra heat would drive my TIT above 1550.

I also realize those LOP readings are a proxy for peak EGT difference change. As an interesting experiment when at peak just change your RPM while in lean find mode and it will say i just went 60 or 70 LOP when i did not change the air/fuel mixture ratio at all but my EGT comes way down because that’s all the lean of peak find algorithm checks is how much the egt changes from when it was the hottest. 

[jlunseth]

Normally I run with cowl flaps closed. If the temps start creeping up and I can't control TIT enough with just a few tenths adjustment in the fuel flow then I open the cowl flaps one notch. The 231 has a mechanical cowl flap system, one notch and full open. I haven't ever gone to cowl flaps full open. Its a little hard to do, too much resistance in flight at cruise. The couple times I have tried it for whatever reason it concerns me that I might bend the mechanism. One notch is easy though. I don't have to use one notch very often, just very hot summer days. The speed loss is small compared to the benefits of running LOP, less than five knots.

My plane has been in the shop for some new avionics but I get to fly tomorrow, I will try switching LOP and ROP but I am pretty sure the manual says no. My JPI is now over ten years old so maybe that has changed in newer versions.

On the issue of higher TIT, I had some email discussions with Walter Atkinson several years ago and some other discussions with turbo/supercharger engineers about the durability of turbos. They were clear that as long as you stayed under the redline you were safe and the turbo would not prematurely fail. My POH redline is 1650. I just don't feel comfortable operating it that high, for one thing, the fuel flows move around in my aircraft a little, not the best control system I guess. Not much, but if you are operating right at 1650 and the fuel flow change .5 GPH you are going to exceed the redline. Even then, the momentary limit is 1725 so it probably would do no harm, I just don't want to go there. 

As I said, I have operated this way quite alot, had the turbo OHd about 1700 hours ago. Initially it concerned me that the turbo would be working harder with the MP at 34, so I have it borescoped at annual every year.  Haven't had a problem. Your mileage may vary. 

Another initial concern that was raised by Bruce Jaeger about LOP was that EGTs are about 100 dF higher, so would that cause early valve failure because the valves are in a higher temp environment. Haven't seen that either. I get those borescoped regularly also.

Edited October 15, 2022 by jlunseth

[Will.iam]

1 hour ago, jlunseth said:

Normally I run with cowl flaps closed. If the temps start creeping up and I can't control TIT enough with just a few tenths adjustment in the fuel flow then I open the cowl flaps one notch. The 231 has a mechanical cowl flap system, one notch and full open. I haven't ever gone to cowl flaps full open. Its a little hard to do, too much resistance in flight at cruise. The couple times I have tried it for whatever reason it concerns me that I might bend the mechanism. One notch is easy though. I don't have to use one notch very often, just very hot summer days. The speed loss is small compared to the benefits of running LOP, less than five knots.

My plane has been in the shop for some new avionics but I get to fly tomorrow, I will try switching LOP and ROP but I am pretty sure the manual says no. My JPI is now over ten years old so maybe that has changed in newer versions.

On the issue of higher TIT, I had some email discussions with Walter Atkinson several years ago and some other discussions with turbo/supercharger engineers about the durability of turbos. They were clear that as long as you stayed under the redline you were safe and the turbo would not prematurely fail. My POH redline is 1650. I just don't feel comfortable operating it that high, for one thing, the fuel flows move around in my aircraft a little, not the best control system I guess. Not much, but if you are operating right at 1650 and the fuel flow change .5 GPH you are going to exceed the redline. Even then, the momentary limit is 1725 so it probably would do no harm, I just don't want to go there. 

As I said, I have operated this way quite alot, had the turbo OHd about 1700 hours ago. Initially it concerned me that the turbo would be working harder with the MP at 34, so I have it borescoped at annual every year.  Haven't had a problem. Your mileage may vary. 

Another initial concern that was raised by Bruce Jaeger about LOP was that EGTs are about 100 dF higher, so would that cause early valve failure because the valves are in a higher temp environment. Haven't seen that either. I get those borescoped regularly also.

Thanks. Nice to see at least in your personal experience that running the turbo from 1550 to 1600 has not shortened your turbo life or seemed to cause extra wear. I have heard Mike Busch also say the exhaust valve can easily handle the higher egt temps for NA and for us turbo guys we hit TIT limits before egt’s get high. 
I’ll try 34” and 11.1 next time I’m up and see where my TIT settles at as your right just a .1 difference changes my TIT by about 1 degree or so if MP is held constant. 
 

I will also match 2450, as slowing down the RPM helps with the heat not being as high going to the TIT. I normally use 2500rpm as that was easy to remember and i had heard my prop was designed with 2500 being the most efficient speed for the prop. 

[jlunseth]

2500 will probably work fine. 2450 is just a superstition of mine. I doubt there will be a difference, let me know if there is.

[A64Pilot]

Just about everything will last longer if operated significantly below redline as opposed to those that are operated at redline.

Many things that cost way more and are more intensively studied will have different limits, often based on time. Turbines often have shorter time limits as temps increase, often it’s because get any metal hot enough it softens, spin it fast enough and long enough it can stretch and may contact the housing or at least form cracks.

So I think you guys who won’t run at redline continuously are smart to do so and will enjoy a more trouble free and longer lasting engine, not just the turbo, the whole thing.

Besides how often is your ITT system calibrated? Good to leave a cushion.

[kortopates]

If you're flying LOP, the slower the RPM the deeper you'll be able to go LOP without roughness. The higher MAP also adds some efficiency. Concern for Prop efficiency is a distant third IMO. 

[Pinecone]

On 10/14/2022 at 7:07 PM, Will.iam said:

I also realize those LOP readings are a proxy for peak EGT difference change. As an interesting experiment when at peak just change your RPM while in lean find mode and it will say i just went 60 or 70 LOP when i did not change the air/fuel mixture ratio at all but my EGT comes way down because that’s all the lean of peak find algorithm checks is how much the egt changes from when it was the hottest. 

When you change the RPM you change the amount of air moving through the engine.  More RPM, more air.

[Will.iam]

18 minutes ago, Pinecone said:

When you change the RPM you change the amount of air moving through the engine.  More RPM, more air.

But you also change the amount of fuel in the same ratio as the air so your lean of peak or rich of peak doesn’t change and good that it doesn’t as can you imagine you are 100 rich of peak and you increased the RPM and now you are at peak burning up your engine all because you increased tour RPM from 2200 to 2700 to start a climb for an example. People would be damaging engines way more than they do now if that was the case. 

[Fly Boomer]

On 10/14/2022 at 7:33 PM, jlunseth said:

As I said, I have operated this way quite alot, had the turbo OHd about 1700 hours ago. Initially it concerned me that the turbo would be working harder with the MP at 34, so I have it borescoped at annual every year. 

How is that done?  Can you get a scope up the exhaust far enough to see something?  Can you get a view of the inside of the turbine?  I assume not much to be gained looking inside the compressor?