Lean of Peak

[A64Pilot]

36 minutes ago, Marauder said:

Hang in there. My father-in-law dealt with an infection with his knew replacement and overcame it. His biggest aggravation with the situation was being kneeless for the time it takes to heal.


Sent from my iPad using Tapatalk Pro

Now they insert a hinged spacer or so I’m told, so you sort of have a knee, just limited range of motion, I’m told you can walk with this spacer, just not very well.

For both knees I started flying as soon as I could get into the airplane, about three weeks if memory is correct. I hope to not be down long this time, I may have to have someone fly it for me, I don’t want it sitting, my rule is it flies every week, often just once but every week

[Shadrach]

13 hours ago, A64Pilot said:

The chart you posted leaves out something very important, CYL head temp, for instance the point LOP that gives the same HP as full rich, can’t be used because temps get out of control, if it could we would run LOP during takeoff and climb. We takeoff and climb full rich to control temps, if not for temps, full rich would be best power, or maybe that point that’s a tiny bit LOP that gives the same power

High temps will drive detonation, so that chart only shows part of the picture

No, that is not true, and both graphs contradict your statement. CHTs are a proxy for internal cylinder pressure (ICP). All other things being equal, lower ICP equals lower CHT.  Anyone with an engine monitor can see what I have stated and what is in those graphs happen in real time. Incidentally, I have run LOP on take off and in climb just to do it. It's not difficult, but requires more fiddling than I wish to bother with.  It also produces a scenario where distraction from managing the engine during climb could render the mixture in the 40-100ROP zone which is abusive.  Climbing full rich with an NA engine is more conservative because there is little that needs to be managed. In full rich the climb, an unattended engine getting richer means going further ROP. In LOP climb, an unattended engine getting richer means and may go from LOP to an abusive ROP setting.

I'm not sure where your assertion about "out of control CHTs" comes from, but it would be helpful if you offered some evidence to support your claims.  I am sure that you believe what you are saying but it does not comport with what is well understood about combustion.

[Fly Boomer]

1 hour ago, JimB said:

This is basically LOP, they just call it "best economy mixture". 

I think the only way to identify LOP is to first identify peak EGT for each cylinder, and then continue to lean until the last cylinder to peak is a ways to the lean side of peak.  This assures that all cylinders are LOP.  How far on the lean side is “a ways” just means enough to guarantee that you are not fooled by instrument/probe errors.  Then if your CHTs creep up beyond what you are comfortable with, lean further.  Where your engine “gets rough” may have no correlation to where your mixture is vs peak on each cylinder.

[JimB]

34 minutes ago, A64Pilot said:

That’s for carbureted motors and may be LOP, but likely not, most carb motors just won’t do LOP, they get rough first. It’s the way most were taught to lean forever, that is once at cruise very slowly lean until rough, then slow enrichen until just smooth, in other words run as lean as it will run, most likely that puts you close to peak egt

Higher power cruise but still less than 75%, I was taught to lean until peak egt, then enrichen two hash marks cooler than peak, which I believe is 50 ROP

You can do a few things to help, like don’t quite be full throttle, idea is with the throttle partially closed it creates turbulence that may help with mixture distribution, and a little carb heat may help atomize the fuel, and you may be able to go LOP but probably not.

LOP isn’t really possible for a very large portion of the fleet, and you know those motors do fine.

Its actually for Normally Aspirated engines regardless of their fuel delivery system. The only difference in doing this with and without an engine monitor is that with an engine monitor you actually know you how many degrees LOP you are. And yes you are correct, you may not be LOP. Depending on the engine, it might be at peak or a little rich or LOP before it might run a little rough. My point is: If the engine is capable of LOP operation and you lean it until it starts to run a little rough and enrich it just a bit, you will be LOP.

You can add an engine monitor and watch it happen but it still happens. 

Edited October 12, 2022 by JimB

[A64Pilot]

54 minutes ago, Shadrach said:

No, that is not true, and both graphs contradict your statement. CHTs are a proxy for internal cylinder pressure (ICP). All other things being equal, lower ICP equals lower CHT.  Anyone with an engine monitor can see what I have stated and what is in those graphs. Incidentally, I have run LOP in take off in climb just to do it. It's not difficult, but requires more fiddling than I wish to bother with.  It also produces a scenario where distraction from managing the engine during climb could render the mixture in the 40-100ROP zone which is abusive.  Climbing full rich with an NA engine is more conservative because there is little that needs to be managed. In full rich the climb, an unattended engine getting richer means going further ROP. In LOP climb, an unattended engine getting richer means and may go from LOP to an abusive ROP setting.

I'm not sure where your assertion about "out of control CHTs" comes from, but it would be helpful if you offered some evidence to support your claims.  I am sure that you believe what you are saying but it does not comport with what is well understood about combustion.

Take an engine, run it at takeoff power just LOP, see where your CYL head temps go, same engine run it at peak, see where the cyl head temps go, heck run it 100 ROP, see where the CYL head temps go, they will all go to redline or higher.

On edit, pretty sure my EGT is 300 degrees ROP at TO power, full rich

My fuel flow is 19 gallons per hour at takeoff power for one reason, to control CYL head temps, it’s way richer than best power, you would think takeoff power would be best power but it can’t be, because of CYL head temps, so we are so rich we are actually losing power, to control CYL head temps. 

 

[jlunseth]

When I first got my 231 it was obvious the engine had been run on the hot side. It had 646 hours but the turbo needed to be replaced nearly right away and it leaked quite a bit of oil, mainly at the rocker covers. At around 1200 (these are all Hobbs hours) I had to do an emergency descent to a landing from 19k (not due to how the engine might have been run). The problems worsened after that and I had the engine IRAN’d. Determined to find a better way, I went to the APS class in Tulsa and learned a lot. However, the advice from George B., Walter A., et al. was not perfect for me. I got the impression it was mainly based on experience with NA engines, which mine is not, and/or big bore engines, which mine also is not. So armed with the theories they taught, I set about to come up with a way to operate LOP that worked for my engine. I did quite a bit of experimenting and learned quite a few things. First, it is not accurate that LOP results in a power loss compared to ROP. That may be true for NA engines because it is not possible to add more air to lean the mix, MAP is capped at ambient, so your ability to add enough air to run at higher power settings while LOP may be limited. Also, lots of people run at 65% or just under because of the advice that you cannot hurt the engine regardless of where you operate it, LOP or ROP. Sure, if you have been operating ROP at 75% and then because you are afraid of what will happen to the engine if you operate LOP, you always do it at or under 65%, you will have a power loss. However, in my experience with my engine that power loss is in your head, you are the person who has elected to operate at a lower power setting, LOP operations do not require it.

I have a JPI930 which is quite a good monitor and I am able to see quite a bit of information. The theory I came up with was that if you wanted to operate at more standard cruise settings (i.e. >65%) while LOP one way to do it is to add more air. LOP after all is an air/fuel ratio, it is definitely not just a matter of running the engine at less than 65%. The setting I use is 34” MP and 11-11.3 GPH. This gives me right around 71% power and nifty speeds. 71% seemed to be the practical limit in my aircraft, TIT tends to be higher by very roughly 100 dF, and I just do not like to operate with a TIT above 1600 even if the POH allows it. TIT also goes into a long slow climb in my engine if power is higher than 70-71% and especially if OATs are high, and adding more air does not help. If that happens I reduce the fuel flow but 10.9 or 11 is all it usually takes. 

I cannot maintain this in the high altitudes during summer. The TIT starts a slow climb and I just have to reduce fuel flow too much, so above roughly 15-16k I fly ROP. In the winter with cold temps I can go higher and stay LOP. Obviously this is a cooling issue.

I experimented enough to know what MP and fuel flow works. During the experimentation I use the APS advice to operate degrees LOP from the last cylinder to peak (EGT). Now, however, I just watch the TIT and if it climbs up above 1600 I make an adjustment. The control systems on the 231 are not perfect and the fuel flows, and therefore the temps, may move around a little, or fuel flow may increase over a long period of time. Don’t know why. But when that happens I just adjust the fuel flow back to where it was.

Among other things I learned that the aircraft was actually faster this way by quite a bit compared to my previous ROP operations at what were supposed to be the same %power settings. Previously I had been using charts supplied by the intercooler manufacturer, Turboplus, to determine ROP power settings. The charts turned out to be very conservative. Assuming the formula APS puts out that %power equals a constant (13.7 for my engine) times fuel flow in GPH divided by rated HP, I was sure I was operating at 71% HP at my LOP setting, but the plane was faster by at least ten knots than if I set for 71% ROP using the charts. That told me that the ROP setting that I thought was yielding 71% really wasn’t.

Generally, I get about 145 at 3,000 MSL, closing in on 160 at 10k, and in the higher altitudes before I must go ROP I will see speeds in the 165-175 range (all in nm/hr).

So what about the engine, operating that aggressively at LOP must be tearing it up? Currently it is very smooth, runs clean, CHTs are lower than ROP by quite a bit. The tbo is 1800 and I am at 2355. I wouldn’t ordinarily wait that long just because I am conservative about engines and safety, but it turned out last year when we inquired about a reman, that Conti now has a delivery delay of about 9 months, so we ordered one in April and it will hopefully show up at the end of the year. I intend to abuse it the same way I have the current engine, starting from day 1. The turbo which was overhauled at 645 has not been touched since, and now has about 1700 hours. Since around 1200 hours, the majority of cruise operations have been LOP at my preferred setting.

Fine wires are a must. GAMI’s are a most likely. Regular attention to the magnetos and the spark plug harness are a must. Most issues with a rough running engine, if you have gotten the fuel flows evened out with GAMIs, are going to be related to the spark. 

One nifty thing about the 231 is that it has an interlink between fuel flow and MP. If I set my 34/11.1/2450 and then want to reduce to approach speed of about 120 kts. I can just pull the MP back to 24.5 - 25, it varies a little depending on the day temps. The fuel flow comes with the MP and I will be operating at 9 point something GPH. When I am on final I pull the MP back further and the fuel flow drops with it. So all downward power adjustments will be only with the MP. If I want to increase power for a climb I always go full power, full rich.

Works for me. 

Edited October 13, 2022 by jlunseth

[Andy95W]

That’s a really great write up.  I hope a friend of mine- @T. Peterson - reads it also.

[T. Peterson]

4 hours ago, Andy95W said:

That’s a really great write up.  I hope a friend of mine- @T. Peterson - reads it also.

Yes, it is an excellent write up! Thanks so much for notifying me.

Torrey

[Pinecone]

Thanks.  This is helpful for me to figure out how to run my 252

Doesn't your JPI read % power?

 

[jlunseth]

My experience in the 231 is that the %power reading on the JPI is always wrong and irrelevant. That may be less of an issue with the 252. The difference between the two aircraft is that the 252 has a truly automatic wastegate controller - you set the MP at “x” and the controller holds “x” regardless of what you do with the fuel flow. At least that is how I understand it, I don’t have a 252. The Merlin in a 231 does not do this, it is not a truly automatic wastegate controller, and the factory configuration does not control the wastegate at all.

In the 231 the fuel flow always changes when the MP is changed and vice versa. That creates an issue with the JPI when leaning. What we are taught is to set the MP at a number, let’s say my 34”, with the mixture rich, and then dial the fuel flow back. As you lean across peak over to the lean side, if the engine monitor is set to the Lean function for leaning, it detects when the last cylinder peaks and then determines degrees lean of peak from that.  The JPI then uses the LOP formula to determine %power. But here is the important part, the unit assumes that MP is not changing as you do this. Probably that is what would happen in your 252 with its automatic wastegate controller.

If you try that same thing in the 231 the MP will fall as the fuel flow is reduced, so what you are actually doing is changing the entire power setting. LOP is an air/fuel ratio. But in the 231 when you lean like this, you are not changing that ratio, the engine interlink is doing its best to keep the ratio the same but at reduced power. If you try to use this standard technique in the 231 you will certainly find a peak at some point, but then as you pull the fuel flow out further you think you are leaning but you are not, you are just reducing power at the same air/fuel ratio. That makes the peak that you found completely irrelevant to your new power setting and it renders the %power reading on the JPI completely wrong. In the JPI the reading is based on an algorithm, not an amount of HP detected by any sensor. The assumptions of the algorithm are now wrong, and therefore the result is wrong.

There is a way in the 231 to measure degrees lean of peak with some degree of accuracy. If you try to do it the standard way, putting the unit in Lean mode and leaning over from the rich side, too much changes and the %power reading is just wrong. But you can get a good reading by pulling the mixture over to the lean side with the Big Pull, viz. just pull it lean until you feel a power drop off. Now you put the JPI in Rich of Peak leaning mode. Yes, you read that right, Rich of Peak mode. Lean of Peak mode just detects the last cylinder to peak, Rich of Peak just detects the first cylinder to peak, the unit does not actually detect by sensors whether it is on the rich side or the lean side. In this instance, since you are already on the lean side and your intention is to enrich the mixture until you find peak then lean back, you want to be in first-cylinder-to-peak mode which is ROP mode. Find that peak, then go back lean the desired number of degrees, so now you know you are operating with the cylinder closest to peak being at, say, 30 degrees LOP. There is still a little bit of an issue with the MP changing as the mixture changes but it is much smaller than if you try to lean over from the rich side. When I was doing my experimenting I would actually put in a little MP in order to keep the MP at the same level, while at the same time pulling the mixture back. Not perfect, but close enough.

However, the %power is still no good because now the JPI thinks the engine is operating Rich of Peak, so it is using the POH chart power settings for ROP operations in its algorithm to display %power, but you are flying LOP where a different formula applies.

Even in the 252 you need to understand that about the percent power display. It is an algorithm. From what I can tell, on the rich side it uses the information from the POH charts to determine %power. On the lean side it uses the LOP power formula for that engine. But it is not actually detecting %power. In my engine, when operating LOP, I don’t find it useful at all. It will display something like 90-91% power, but it is assuming I am operating ROP when I am actually operating LOP, where a completely different formula applies to determine %power. The LOP %power display is to difficult to get to with any reasonable degree of accuracy in my aircraft. The POH settings for the 252 make some assumptions, such as just exactly how much cooling of the induction air the intercooler is generating under a particular set of circumstances. That is a number that changes a fair amount from what I can see on my JPI. Probably it is more accurate to simply run the math for %power LOP at a particular fuel flow and use that instead of the display. Remember that when LOP, that formula does not need to consider what the MP is or how dense (how cool) the induction air is, because by definition, Lean of Peak means that there is more air already going in to the mixture than will be consumed in burning the available fuel.

Hope that makes sense. It may seem very complex, but in my aircraft I have reduced to an MP setting that I know works, which is 34”/11.1 GPH/2450 RPM and I just use TIT to manage the fuel flow a little, as I said, if it wants to climb over 1600 I pull off a couple of tenths of a GPH. The rest of it was done just to understand what the best setting is, and what I am doing to the engine.

Edited October 13, 2022 by jlunseth

[A64Pilot]

Not that I’ve seen them all, but I’ve not seen an engine monitor with a percent power be correct, I think they shouldn’t display numbers that are incorrect myself. In other words I think that feature ought to be removed, when you display precise numbers, people tend to believe them of course

At best it’s a SWAG 

[JimB]

1 hour ago, A64Pilot said:

Not that I’ve seen them all, but I’ve not seen an engine monitor with a percent power be correct, I think they shouldn’t display numbers that are incorrect myself. In other words I think that feature ought to be removed, when you display precise numbers, people tend to believe them of course

At best it’s a SWAG 

As part of the installation, you are supposed to program the % of HP. Not sure if it will be consistently correct all the time and at all power settings afterwards but it's a good place to start. I think this is also in the pilot's guide so the owner can adjust it as well if you are finding it off. 

[Shadrach]

8 minutes ago, JimB said:

As part of the installation, you are supposed to program the % of HP. Not sure if it will be consistently correct all the time and at all power settings afterwards but it's a good place to start. I think this is also in the pilot's guide so the owner can adjust it as well if you are finding it off. 

The system essentially uses mass airflow to determine HP. The pilot enters a Horsepower constant which essentially an efficiency calculation that allows the device to calculate the power produced by your engine model based on displacement and thermal efficiency (ie compression ratio) and mass airflow (mp x rpm). That works fine ROP because power tracks mass airflow (more or less). However, it’s useless when running lean of peak, because power tracks fuel flow (more or less)

[A64Pilot]

30 minutes ago, Shadrach said:

The system essentially uses mass airflow to determine HP. The pilot enters a Horsepower constant which essentially an efficiency calculation that allows the device to calculate the power produced by your engine model based on displacement and thermal efficiency (ie compression ratio) and mass airflow (mp x rpm). That works fine ROP because power tracks mass airflow (more or less). However, it’s useless when running lean of peak, because power tracks fuel flow (more or less)

I understand what your saying, but if the instrument doesn’t know PA and temp it can’t know airmass, then throw in as you suggest that it doesn’t know mixture either and we are back to it not being very accurate, it can’t be as it doesn't have enough data. 

My 93 LT-1 didn’t measure airflow, it computed it knowing throttle position and RPM, but it had both an air pressure sensor and air induction temp sensor, so it can be done and done well if you have the data.

[JimB]

 I just thought it is using MAP, RPM and FF to calculate HP. Basically using a digital version of the POH/Lycoming power chart. At 2500 RPM 23.0 inches and 10.5 gal/hr =73 HP

[A64Pilot]

2 minutes ago, JimB said:

 I just thought it is using MAP, RPM and FF to calculate HP. Basically using a digital version of the POH/Lycoming power chart. At 2500 RPM 23.0 inches and 10.5 gal/hr =73 HP

If it did and one would think it would, then it should always match the charts, it’s missing something, perhaps fuel flow?

[Shadrach]

19 minutes ago, A64Pilot said:

I understand what your saying, but if the instrument doesn’t know PA and temp it can’t know airmass, then throw in as you suggest that it doesn’t know mixture either and we are back to it not being very accurate, it can’t be as it doesn't have enough data. 

My 93 LT-1 didn’t measure airflow, it computed it knowing throttle position and RPM, but it had both an air pressure sensor and air induction temp sensor, so it can be done and done well if you have the data.

Agreed, it’s a fuzzy measurement as are the POH numbers which are all given on the standard day.

[JimB]

11 minutes ago, A64Pilot said:

If it did and one would think it would, then it should always match the charts, it’s missing something, perhaps fuel flow?

Probably density altitude or the OAT isn't 100% accurate ....

[PT20J]

George Braly has stated that most engine monitors %HP calculations are not accurate. He told me that he developed a proprietary algorithm for Cirrus when they still used Avidyne that made it’s way to Garmin when Cirrus switched to Garmin. I think it is in my G3X which seems pretty accurate at all mixtures. The algorithm is proprietary, but it is possible to make some educated guesses.

The G3X EIS setup parameters are: Lycoming or Continental, turbo or normally aspirated, and max power@rpm. This implies that it probably uses a table lookup for some data.

From Heywood, internal Combustion Engine Fundamentals, eq. (15.3)

mep = (volumetric efficiency * air density * fuel/air ratio) / sfc

This could be calculated from MAP, rpm, OAT, pressure altitude, and fuel flow with some help from a lookup table.

Skip

 

 

[ArtVandelay]

 I just thought it is using MAP, RPM and FF to calculate HP. Basically using a digital version of the POH/Lycoming power chart. At 2500 RPM 23.0 inches and 10.5 gal/hr =73 HP

But that only works when ROP, LOP it’s some number x fuel flow.
For my IO360 the engine constant is 14.9

[jaylw314]

2 hours ago, Shadrach said:

The system essentially uses mass airflow to determine HP. The pilot enters a Horsepower constant which essentially an efficiency calculation that allows the device to calculate the power produced by your engine model based on displacement and thermal efficiency (ie compression ratio) and mass airflow (mp x rpm). That works fine ROP because power tracks mass airflow (more or less). However, it’s useless when running lean of peak, because power tracks fuel flow (more or less)

In the EDM 700 manual, it specifically states HP% is directly proportional to fuel flow and is intended to be 100% at full rich only.  I've never seen it documented on other JPI devices how or if some other calculation is used for HP%, and it's annoying the 900 doesn't specify that.

FWIW, in the 700 manual, it uses the same procedure, to use MP and RPM to set 70% power, not because it measures and uses MP/RPM in the HP% calculation, but ostensibly so you don't have to fly level at 100% power.  There's not really a setting for that in cruise anyway.

I've never gotten a clear answer as to how other JPI devices calculate HP%, but I wouldn't put it past them to simply use what the 700 uses and call it a day  

[DanM20C]

5 hours ago, jlunseth said:

It will display something like 90-91% power, but it is assuming I am operating ROP when I am actually operating LOP, where a completely different formula applies to determine %power. The LOP %power display is to difficult to get to with any reasonable degree of accuracy in my aircraft.

I have the JPI900 but I think the 930 behaves the same.  I enter the lean find mode, then push LOP, then exit the menu.  That tells the JPI you are LOP and it uses 13.7+FF to get the % power.  I don't use lean find to lean at all, I just switch the mode so my %power is correct.  Otherwise, like you, I just keep MP up 33-34" and Lean to 9.5-10gph.  A little more conservative than you but I like to keep my TIT below 1550.    

Cheers,

Dan

[Shadrach]

3 minutes ago, DanM20C said:

I have the JPI900 but I think the 930 behaves the same.  I enter the lean find mode, then push LOP, then exit the menu.  That tells the JPI you are LOP and it uses 13.7+FF to get the % power.  I don't use lean find to lean at all, I just switch the mode so my %power is correct.  Otherwise, like you, I just keep MP up 33-34" and Lean to 9.5-10gph.  A little more conservative than you but I like to keep my TIT below 1550.    

Cheers,

Dan

How did the JPI get the 13.7 number to make the calculation? Did you enter that ref? In my airplane the multiple would be 15.1.

[DanM20C]

23 minutes ago, Shadrach said:

How did the JPI get the 13.7 number to make the calculation? Did you enter that ref? In my airplane the multiple would be 15.1.

The percent power is always right on the 13.7 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

[Pinecone]

It seems that 13.7 is the number for most turbo engines.

If you want to be a bit more precise, I have seen it stated as 13.75

There is a place in the JPI 830 to set this.