Power setting LOP

[AndreiC]

I've been trying for a while to figure out my cruise power settings, a bit unsuccessfully (in part due to a faulty MP gauge which will be overhauled next week). But reading another thread got me thinking about a method that may work better, and I want to ask advice from people here.

My goal is to run LOP and somewhere between 60% and 65% power. The way I've been doing it is to set a MP/RPM setting that should be close to 65%, then do the big pull, and use the EDM700 engine monitor to get to about 20 degrees LOP on all cylinders. Typically this gives me between 8 and 8.5 gph fuel flow at 7000 feet.

But reading about the GAMI information shows that by doing this I run at only 55-58% power: for example, at 8gph, 8*13.7 = 109.6hp, which on a 200hp engine gives only 55% power. To me this means that I could increase the power setting at this point a bit. 

So my plan would be to do the following: when I am stabilized in cruise, do the same thing as before; after the engine settles at, say, 8gph, increase either the MP (if I can get more at that altitude) or the RPM until I get to a fuel burn of 9-9.5gph, while staying LOP. This should give me 60-65% power (so still safe for LOP operations), and I would not give up as much speed as I currently do.

Does this sound reasonable?

[Pinecone]

13.7 is for lower compression engines like turbo engines.

Your number is higher, but I can't recall the exact number.

But otherwise, you method is sound.  But once you know the numbers, you can set MP and RPM and then do the BMP and be pretty much spot on.

[Rick Junkin]

@AndreiC This spreadsheet may help you with some of the details. Enter your engine specifics in the yellow cells and it gives you the FF required for %HP. You’ll need to enter your engine’s rated power and compression ratio.

19 minutes ago, Pinecone said:

But otherwise, you method is sound.  But once you know the numbers, you can set MP and RPM and then do the BMP and be pretty much spot on.

Exactly.

Cheers,
Rick

[jlunseth]

The notion that it is necessary to reduce power to 60-65% to be safe for the engine when running LOP is an apparently widespread OWT. What the GAMI people actually teach is that if you keep the power at or under 65% you can run the engine anywhere you want, whether ROP, LOP or directly at peak. That is because the Internal Cylinder Pressure at 65% is low enough at any power setting that it will not harm the cylinders.

It is no more “unsafe” to run at 70 or 75% LOP than ROP so long as you run LOP enough, or ROP enough. And unless in very cold weather conditions you can generally determine if you are far enough ROP or LOP by cylinder temps, if they are at or under 380 dF you are good. The problem in a normally aspirated engine with trying to run, say, 75% LOP, is generally that you can’t generate sufficient manifold pressure at cruise altitude. The problem in a turbo is that temps, particularly Turbine Inlet Temp, will rise too high in the higher altitudes, because the air is thin and does not cool well and because the turbo is having to work harder to keep the manifold pressure high enough. 

At 70% power the GAMI people suggest running at least 125 ROP or 20 LOP. At 75% at least 175 ROP or 40 LOP, and 40 LOP is about as far as most engines can go without running rough, some less than that. I have used their 70% guidance in my turbo 360 for some time with nothing but good results.

All this assumes that you are following their guidance to use a good engine monitor that reads out the EGTs of each of the multiple cylinders, so that the cylinder closest to peak is the one that is used to measure degrees ROP or LOP. 

Edited December 25, 2023 by jlunseth

[Pinecone]

Yes.

But since I cruise at 63% power, I can be extra conservative by setting that power at full rich when leveling off, then do the BMP to LOP.

GAMI does say you cannot set mixture by CHT, that is a Mike Busch thing.

[Danb]

What would that equate to with a TSIO 550 as in an Acclaim 

[PT20J]

Both Lycoming and Continental recommend setting power with manifold pressure and rpm to some max cruise power (75% for Lycoming, 65% for Continental) before leaning. Why? Because it is absolutely safe. That works acceptably ROP because there isn’t that much power drop off when leaning, but once you lean past peak EGT the power falls off rapidly and the engine will be putting out much less power. You can get the power back by increasing the MAP to increase the fuel flow to a value that gives you the desired power setting. The Big Mixture Pull is just a way to simplify the process.

This works because the BSFC vs BHP curve is approximately linear over a wide range of LOP mixture strengths allowing BHP to be determined primarily as a function of fuel flow. 

The theoretical basis for the multipliers based on compression ratio that APS teaches for calculating HP from LOP fuel flow is that the thermal efficiency of an internal combustion engine increases with compression ratio (the derivation is in every introductory thermodynamics textbook). Thus, at higher compression ratios, the engine extracts more work from the fuel, or alternately, the same power with lower fuel consumption. 

Skip

[MikeOH]

When going on a cross-country flight this is my procedure:

1) Take off at WOT, Full rich, max rpm (unless at high DA, then lean for sea-level EGT at full power)

2) At 1000-2000 AGL, pull rpm back to 2600-2650 for the climb

3) During climb lean to maintain sea-level EGT and monitor CHTs < 380

4) Level off at 8000-10000 and leave WOT, pull rpm back to 2500-2550

5) Big mixture pull to 8.5 to 9.0 gph.  (65% x 200 HP = 130 HP; 15 x 8.5=128 HP, 15 x 9.0=135 HP) and monitor CHTs (typically 310-350)

[Ragsf15e]

52 minutes ago, MikeOH said:

When going on a cross-country flight this is my procedure:

1) Take off at WOT, Full rich, max rpm (unless at high DA, then lean for sea-level EGT at full power)

2) At 1000-2000 AGL, pull rpm back to 2600-2650 for the climb

3) During climb lean to maintain sea-level EGT and monitor CHTs < 380

4) Level off at 8000-10000 and leave WOT, pull rpm back to 2500-2550

5) Big mixture pull to 8.5 to 9.0 gph.  (65% x 200 HP = 130 HP; 15 x 8.5=128 HP, 15 x 9.0=135 HP) and monitor CHTs (typically 310-350)

I know this is blasphemous, but I do everything like @MikeOH, but I don’t do the bmp.  I use the lean find function and slowly decrease the mixture so I can get it just barely lean of peak on the last cylinder and see where each one peaks.  There’s enough variation in the setting based on exact cruise altitude, temperature, altimeter setting, etc, that I kind of like to see it.  At the 8-10,000’ (with an na engine) mike mentioned, you are low enough power that you aren’t going to hurt anything leaning slowly, and power drops off rapidly if 9 gph happens to be farther lean of peak than you intended.  The bmp is for higher power settings (low alt or a turbo) so that you don’t dwell in the “red box” at high power.

[MikeOH]

@Ragsf15e

Sometimes, I will do the same as you and slowly lean while watching for each cylinder to peak...used to do that every time but kind of got bored when I ended up in the same place each time!  Another sacrilegious practice that I follow is to just richen the mixture if I want to go faster!  As you say, at 8-10,000 feet you can't hurt anything; I just keep an eye on CHTs but have never had an issue.  I'll even run at peak EGT if I have enough of a headwind...OH, THE HORROR!!  (I'm too cheap to ever run 100 ROP in cruise)

[carusoam]

Let’s see if I can add something without adding a mistake….

1) The big pull… a step used for people using a turbo charger… where leaning slowly can leave the turbo running at incredibly high temps for longer than necessary…

2) the big pull for a NA engine… will get you in the window of the final setting quicker… which is OK too…

3) peak occurs in a slightly different place depending on a bunch of variables… but, on that one current flight…. You set your MP, and RPM and then lean as slowly as you are comfortable… wait for the EGTs to respond, lean again… wait again, lean some more…

if you over shoot… Enrichen slowly… wait longer…  

going up or down… the peak is in the same place.  It will appear to move if you don’t wait long enough for the TCs to completely settle.

4) Some thermo couples react faster than others… see how long yours takes during the run-up… each time you click a mag off and on…

5) Expect if you are hunting up and down with the mixture knob, and can’t figure out why the EGT doesn’t settle smoothly in the same place… even fast EGT sensors take about 15 seconds to settle on the final value…

6) I like being at 10k’ for leaning experiments… or setting the MP at 20”…

7) Running at peak… or a few degrees LOP guaranties that all of the Dino juice has been converted to noise, while producing maximum power for speed… with an MP that is safe, and CHTs below 380°F….

8) Near impossible to set %bhp with an MP gauge that isn’t working properly…. But, at 10k’, running wide open throttle (WOT)… you can’t hurt the engine while experimenting with your leaning procedure…

9) It is also important to have your CHTs reading properly… this way you will know that your cylinder cooling is getting done as expected…

Message for my friend @Danb… the %hp calculation always uses the Compression Ratio (CR)… the TN’d IO550 is a lower compression than the NA engines, but not as low as the typical TC’d engines…  the POH will have the CR for the engine listed shouldn’t be too hard to find… 

PP thoughts only, not a mechanic… or CFI… or instrument guru…

Best regards,

-a-

[Shadrach]

On 12/25/2023 at 12:50 PM, jlunseth said:

The notion that it is necessary to reduce power to 60-65% to be safe for the engine when running LOP is an apparently widespread OWT. What the GAMI people actually teach is that if you keep the power at or under 65% you can run the engine anywhere you want, whether ROP, LOP or directly at peak. 

That OWT is spread here on a regular basis. Theoretically it is safe to run at an power level on the lean side, provided there is sufficient air available to maintain an adequately lean FA ratio at the FF needed for 100% power (just as its safe to run 100% ROP provided there’s an adequate surplus of fuel). It’s not practically possible for a number of reasons, but some TN applications can get close. I run in excess of 80% LOP when cruising at low altitudes. 
 

Another OWT is that “peak” is an abusive mixture setting. I have determined through testing that for my power plant, peak EGT (richest cylinder) produces about the same or slightly cooler CHTs than 100ROP, all other things being equal. Peak is the intersection of max power and max BSFC and is an excellent choice for cruising at DA’s between ~5,000 and 12,000. Peak makes for the best heater output in winter, but only by a small margin.

[wombat]

Here is a question for folks about running a turbocharged engine....

If

Cylinder temps are "OK" (Let's say 390, and redline is 470 on a Continental TSIO-520-NB)

AND

Turbine inlet temperature is "OK" (Let's say 1,600, and redline is 1,700 for 1 minute max, 1,650 max continuous)

AND

The manifold pressure and engine RPM combination is found as an acceptable power setting in the manual. (Let's say 32" and 2,400 RPM)

 

Then: Am I running my engine safely regardless of where I am in relation to peak EGT or 'the red box', and what manifold pressure, RPM, and fuel flow I'm using? 

 

Asked another way, are the absolute value of those temperatures the sole measure I need to determine if I'm running my engine in an 'healthy' way? (TIT in order to make sure the turbine is safe, and CHT to make sure the rest of the engine is safe)

[A64Pilot]

An issue using CHT as a means of determining detonation is that there is a not insignificant lag between what could be going on in the combustion chamber and the time required to heat the mass of the head until it registers as too hot.

Excessive combustion temps and or detonation damage is cumulative, you can get into “light detonation” several times with no apparent issue then one day a hole appears in your piston dome. It’s pretty much like all redlines on an engine, you can exceed most redlines by a significant amount with no apparent damage, but often damage is accumulating, you think you didn’t hurt anything but you might have.

You see it often in turbines, people over temp them on takeoffs and since nothing happened they think it’s not harmful, but the compressor turbine is stretching and cracks are beginning unknown to the operator, then one day it lets go, and often when it breaks they aren’t exceeding the redline.

Follow what @PT20J is saying and you and your engine will have a long and happy experience, just because you can do something if your really paying attention doesn’t mean that you should or there is much advantage in doing so, accept .1 or .2 GPH higher fuel burn or 1 or 2 kts cruise for the additional safety it provides, your engine will thank you.

 

[wombat]

@A64Pilot Let's say these are steady state temperatures and I achieve these temperatures by slowly approaching them from the 'cold' side of the curve, regardless of which side I'm on.  (if I'm LOP, I approach it slowly from being too lean, and if I'm ROP I approach it slowly from being too rich)   So there is no risk of anything from the lag between the actual in-cylinder or in-exhaust temperature and the measured temperature from the probe.

If I do this, am I potentially damaging my engine despite the RPM& MP combo being an approved one and the CHTs and TIT are 'OK'?

[A64Pilot]

Just now, wombat said:

@A64Pilot Let's say these are steady state temperatures and I achieve these temperatures by slowly approaching them from the 'cold' side of the curve, regardless of which side I'm on.  (if I'm LOP, I approach it slowly from being too lean, and if I'm ROP I approach it slowly from being too rich)   So there is no risk of anything from the lag between the actual in-cylinder or in-exhaust temperature and the measured temperature from the probe.

If I do this, am I potentially damaging my engine despite the RPM& MP combo being an approved one and the CHTs and TIT are 'OK'?

From what I’m understanding of your question your last sentence is key.

No as long as your operating within OEM specs you shouldn’t be hurting anything.

I have zero turbo experience but it’s my limited understanding that it would be very difficult to be at a harmful mixture setting detonation wise that wont have you exceeding TIT, perhaps turbo operators will chime in. It’s my limited understanding that TIT is your limiting number mixture wise.

But again surely those with turbo experience will chime in.

 

[Pinecone]

If you are under 65%, you can run anywhere in the mixture range from full rich and so lean it is misfiring.  Over 75% you can run power settings that will damage your engine.

GAMI says to not set mixture by CHT.  And you can have a TIT within limits, but the engine is running in the red box/fin.

As for POH settings, remember that the early TLS/Bravo POH had power settings that gave cylinder life of a few hundred hours.

Best, take the APS course in person (when the restart).  For now, take their online course.

[Shadrach]

On 12/27/2023 at 2:35 PM, A64Pilot said:

Follow what @PT20J is saying and you and your engine will have a long and happy experience, just because you can do something if your really paying attention doesn’t mean that you should or there is much advantage in doing so, accept .1 or .2 GPH higher fuel burn or 1 or 2 kts cruise for the additional safety it provides, your engine will thank you.

 

It looks like you are referring to me without actually referencing me.
Nothing I do with my engine requires that I am “really paying attention” anymore than I would be “really paying attention” operating any other way. I try to pay attention to my engine on every flight, especially in critical phases. I think that if one operates with a minimal amount of instrumentation, one would naturally wish to operate very conservatively.  I too operate very conservatively. I just use temperature instead %power of as a proxy for internal cylinder pressure and engine health.  If you can outline a scenario in which my engine is stressed when the highest CHT is <340…during a mid Atlantic August…I’m all ears.

It also seems there is some confusion  about how detonation typicall manifests with regards to mixture (to be clear, detonation is nearly impossible to induce in a NA Lycoming). The order of operations for mixture induced detonation typically starts with pressure from a rapidly propagating combustion event that occurs close to TDC. This makes for excessive peak internal cylinder pressure (ICP). As a result, CHT’s begin to elevate.  If nothing is done to reduce ICP, CHT will continue an ever more rapid increase. Detonation will begin at some combination of elevated CHT and high internal pressure. The severity of the detonation and how long it is allowed to continue will determine if permanent and/or catastrophic failure will occur .  Yes there are scenarios where detonation can be induced by pressure alone, but none that realistically apply to a normally aspirated Lycoming. 

Another thing that should be made clear. It would require idiotic levels of abuse to get a normally aspirated Lycoming to detonate even while in the “red box”… to get it to detonate with all cylinders on the lean side of peak would be damn near impossible. Operating on the lean side of peak above 65% is not dangerous, it’s not cavalier and it’s certainly not difficult…nor does it require special attention. It simply requires that one verify they are operating a well conforming engine (which is almost all stock, 4 cyl Lycs) and that one has a way to discern that the mixture on all cylinders is beyond peak. I could do this in my plane with the mixture knob and the airspeed indicator and be adequately precise. However, it’s much nicer to have engine data, especially when you’re learning.

LOP operations are not riskier than ROP operations, nor are the margins thinner.  If you look at Lycoming’s own graph, it shows CHT at peak EGT being roughly equal to CHT at ~130ROP. While the graph is conceptual, my real world experience after flying a well instrumented Lycoming for 20 years is that it’s a realistic representation of what can be duplicated in the field. If anything, peak (on richest cylinder) is more conservative than 130ROP (leanest cylinder).  Detonation is just not the risk that it’s being portrayed as on the lean side of peak. Indeed there is almost no scenario where CHTS climb after peak, much less detonate.

Many Pilots want to know more about their power plants and how they perform. They install engine monitors so they have access to real time data to use in pursuit of maximizing efficiency, speed and longevity. I’m pretty sure almost none of them instrumented their engines so that they could just set it at 60%. It’s fine advice for someone who doesn’t know what they don’t know. People don’t take cooking classes to learn how to pour cereal into a bowl. These threads are about optimal operation not just adequate. Moreover, the genesis of this thread centered on NA Lycoming ops. For TSIO engines, there are additional operational factors, considerations and risks as there are for TN’d engines. While the concepts, physics and chemistry are the same, I think blending NA and Turbo engine operations into one thread is suboptimal.

For those of you that wish to learn something interesting about your engine. Record your CHTs at a full rich power setting in level flight and then (all other things remaining equal) pull to the lean side and see what LOP setting approximates the same CHTs as full rich. Those of you that have never tried this will likely be surprised at how close to peak on the lean side the engine will be to produce the same CHT as full rich. 

[Will.iam]

I agree with this. The main problem is balanced fuel flow. As flying rich hides the imbalance much better than flying LOP. Ot allows the engine manufacturers to be sloppy on fuel flow balancing if you only run ROP. When i first got my 252 it would not run very far lop before getting rough running. After gami balanced my fuel flow it runs LOP well. I have a neighbor that would like to run LOP but doesn’t like the rough running from his engines. I keep telling him get the fuel flows balanced and he will like LOP. 

[AndreiC]

Here is one new data point, from a flight I took yesterday. 6000 ft, 24”/2400, 15 degrees LOP, 9.2 GPH, OAT around 40 dF. Three CHTs were around 280, one around 310. 
 

The plane seemed to be very happy at this setting, cruising along at about 145 kts. My question is if this is a good setting for the engine, or if I’m harming anything there. My calculations are that this should be fine (evidenced also by the low CHTs). In fact I am a bit worried my CHTs were so low, could it be my engine monitor is not showing correctly? 

[Shadrach]

On 12/27/2023 at 8:00 PM, Will.iam said:

I agree with this. The main problem is balanced fuel flow. As flying rich hides the imbalance much better than flying LOP. Ot allows the engine manufacturers to be sloppy on fuel flow balancing if you only run ROP. When i first got my 252 it would not run very far lop before getting rough running. After gami balanced my fuel flow it runs LOP well. I have a neighbor that would like to run LOP but doesn’t like the rough running from his engines. I keep telling him get the fuel flows balanced and he will like LOP. 

For the op of this thread, this is not an issue as injected, Lycoming, 4 cylinders typically have excellent fuel/air distribution out of the box. Regarding  the K model, the stock injectors in your TSIO360 MB1 likely flowed very evenly and precisely. The intake manifold is the problem and necessitates uneven injector flow to create even fuel air ratios. The “three holed flute” design of the intake allows fuel to migrate from one cylinder to the next, causing a progressively richer mixture. The reason most Lycomings run LOP well in stock configuration is because fuel cannot migrate from one intake tube to another like it does with the Continental.

 

EDIT: it looks like my assumptions about the TSIO360-MB1 intake design were incorrect. However it stands true for the TSIO360-LB and GB suffix engines.

[Shadrach]

12 hours ago, AndreiC said:

Here is one new data point, from a flight I took yesterday. 6000 ft, 24”/2400, 15 degrees LOP, 9.2 GPH, OAT around 40 dF. Three CHTs were around 280, one around 310. 
 

The plane seemed to be very happy at this setting, cruising along at about 145 kts. My question is if this is a good setting for the engine, or if I’m harming anything there. My calculations are that this should be fine (evidenced also by the low CHTs). In fact I am a bit worried my CHTs were so low, could it be my engine monitor is not showing correctly? 

That is a conservative setting (just under 70%). If your CHTs are only 240° Higher than the OAT of 40°, your engine is not stressed.

[0TreeLemur]

2 hours ago, AndreiC said:

Here is one new data point, from a flight I took yesterday. 6000 ft, 24”/2400, 15 degrees LOP, 9.2 GPH, OAT around 40 dF. Three CHTs were around 280, one around 310. 
 

The plane seemed to be very happy at this setting, cruising along at about 145 kts. My question is if this is a good setting for the engine, or if I’m harming anything there. My calculations are that this should be fine (evidenced also by the low CHTs). In fact I am a bit worried my CHTs were so low, could it be my engine monitor is not showing correctly? 

According to the attached figure (from the Lycoming engine operator's manual, which assumes ROP ops), at 6000 ft and 24"/2400 rpm you are running at about 73% power.  Based on my experience, I think at 9.2 gph you are running richer than you need to, possibly near to or in the dreaded "red box".  Here's why I say that:

At TOC, I level out, reduce to 2400 rpm and mp to where I want, close the cowl flaps, and let it speed up.  Above 5000 ft, WOT, else 24" MP typ.  At or below about 7000 ft, I quickly pull the mixture back to a ff of about 7.5 gph, then richen to 8.3 gph.   That's a good place to start the LF function LOP.  Richen to peak, then lean it back to about -15F LOP on the richest cylinder.  It will typically be right at about 8.2-8.5 gph.  That minimizes time spent in the "red box".   Higher than 7,000 you can lean a bit more than 7.5 gph, and start LF from there.

How well this works depends on your GAMI spread.

[Ragsf15e]

2 hours ago, AndreiC said:

Here is one new data point, from a flight I took yesterday. 6000 ft, 24”/2400, 15 degrees LOP, 9.2 GPH, OAT around 40 dF. Three CHTs were around 280, one around 310. 
 

The plane seemed to be very happy at this setting, cruising along at about 145 kts. My question is if this is a good setting for the engine, or if I’m harming anything there. My calculations are that this should be fine (evidenced also by the low CHTs). In fact I am a bit worried my CHTs were so low, could it be my engine monitor is not showing correctly? 

Yeah, absolutely nothing wrong with that.  My cylinders would be at similar temps there.  Your monitor is probably correct there.  Increase mixture to ~11gph for ~100 rich of peak and i bet you see all the chts climb to ~330+. You’ll likely gain 5kts, but your original setting is more efficient and cooler.  It’s where I fly.

 

 

[Mooney in Oz]

On 12/27/2023 at 9:04 AM, bluehighwayflyer said:

I would leave the RPMs all the way up at 2700 until the top of the climb, then pull it back to your preferred cruise setting.

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