Comprehensive Leaning Guide?

[hazek]

Although you were pointed in many good directions, I would argue the number one things to learn and understand before doing anything is this graph:

 

This graph explains big picture how you can operate your engine, that is the available combustion envelope within which you can operate your engine. After you understand the graph above deeply, then you need to learn how adjusting any of your controls will move you around on the above graph. Then finally you can go look at the sources people linked to understand in which positions of the graph above you should want to operate in. It's all very simple once you understand the above graph.

[Fly Boomer]

19 minutes ago, Rick Junkin said:

13.7 works for a compression ratio of 7.5. The multiplier varies with compression ratio. For instance the multiplier for my TIO-540 with a compression ratio of 8.0 is 14.3

Where did that table come from?

[Rick Junkin]

7 minutes ago, Fly Boomer said:

Where did that table come from?

LOPFFvsHP.xls

[Fly Boomer]

9 minutes ago, Rick Junkin said:

LOPFFvsHP.xls 28 kB · 0 downloads

Any idea where Michael Mahoney got the data?

[Rick Junkin]

15 minutes ago, Fly Boomer said:

Any idea where Michael Mahoney got the data?

There are notes throughout the spreadsheet that discuss his methodology, I think. I don’t have Excel on my Mac and I lose some of the formulas and notes when Apple Numbers imports the file.

I’ve been referencing it for years and the empirical engine data I’ve collected validates the spreadsheet data to an acceptable degree of accuracy. Something less than about 3% deviation.

[Fly Boomer]

19 minutes ago, Rick Junkin said:

There are notes throughout the spreadsheet that discuss his methodology, I think. I don’t have Excel on my Mac and I lose some of the formulas and notes when Apple Numbers imports the file.

I’ve been referencing it for years and the empirical engine data I’ve collected validates the spreadsheet data to an acceptable degree of accuracy. Something less than about 3% deviation.

FWIW the data comports with things posted on BeechTalk several years ago by Walter Atkinson.  Just curious about original source.  Last Modified by Don Kaye, but no way to tell what the modification was.

[Rick Junkin]

10 minutes ago, Fly Boomer said:

FWIW the data comports with things posted on BeechTalk several years ago by Walter Atkinson.  Just curious about original source.  Last Modified by Don Kaye, but no way to tell what the modification was.

Don's modification was most likely just entering the header parameters for his engine.

A search on the file name pointed me to egtrends.com, a site that no longer works. As I recall, I looked there when I originally downloaded the file about 9 years ago (the version I posted in this thread is in the the file section on Mooneyspace, I think), and was able to get into the thermo formulas used to build the spreadsheet. I was satisfied with their veracity at that point, although I can't remember if there were any coefficients used to adjust the theoretical to the empirical. Might have been, based on the accuracy of the output.

[Ragsf15e]

3 hours ago, oisiaa said:

Thanks all!

Here’s some more simplification from a fellow Air Force guy.  Break your “leaning plan” into a few chunks since they have different goals:

Takeoff and climb - full rich, full throttle, full rpm.  Use airspeed higher than Vy to keep CHT temps in limit, maybe ~115mph climb.  As you climb above ~3-5000’msl, you can slowly start to lean using target egt as long as temps are in control, however you can also keep it full rich.  Prop stays full rpm, and full throttle.

Cruise - you likely just need to use rich of peak or peak as you might have trouble getting lean of peak in a C.  You will want to use a key number for 75% power or less (for engine longevity) if youre below about 7000’.  Above that, wide open throttle is below 75% anyway.  Rpm probably 2500 or 2400, whatever feels smoother.  Less rpm equals less power though.  Lean to 100 rich of peak is good - do you know how to do this?  If you’re sure you’ll be 65% or less, maybe try peak egt which basically coincides with lean to rough and then add a little until it’s smooth.

Descending - maybe leave cruise power and enjoy the extra speed.  You might need to slowly get richer as you descend until you are in the pattern and then you probably want full rich, full rpm to be ready for a go around.

[Hank]

On descent in my C, I push for 500 fpm and trim it hands off. As I come down, MP and EGT both increase, so I pull the throttle back to my former cruise setting and push the mixture forward to about my former cruise EGT.

When leveling off, I reduce throttle, then RPM, to match my desired power setting (or airspeed for pattern entry) and lean again.

[jlunseth]

Just to be clear if it is not already, the multiplier (13.7 or 14.9) only applies to LOP ops. The formula does not apply if the engine is operating Rich of Peak. When LOP the power output is determined solely by fuel flow, or so the GAMI people tell us. While ROP it is determined by both MP and FF. Have to go to the POH tables for ROP ops power.

I have a JPI 930. I have well over a thousand hours flying with it. I ignore the % power display, it is based on an algorithm and the algorithm needs a calibration factor called the "K factor." The K factor is supposedly pre-set from the factory for your aircraft.  From many hours of experience with the 930 the display is just not accurate. It is about 7 - 8% off in my aircraft. And how would you as the pilot calibrate the K factor? With what instrumentation? You would need instrumentation that would accurately read out the BHP the engine is producing while in flight.

The one way I found to approximately calibrate it is to learn to operate LOP, then make a LOP power setting while flying the aircraft in level flight.  The LOP formula can then be used to determine percent HP and note the airspeed. Then get out of LOP operations and, while still in level flight, operate the engine ROP, allow the airspeed to stabilize (t takes a little bit in a Mooney) and determine what ROP combination of MP and FF is required to produce that airspeed. Then look at the percent HP display and note how far off it is from the percent power you obtained using the LOP formula while in LOP operations. Adjust the K factor so the percent HP display is correct for that ROP power setting. I never did this in my own aircraft, it seemed like alot of screwing around to get the display to read approximately correctly. I just ignore the % power display, it is not required equipment.

[hazek]

31 minutes ago, jlunseth said:

While ROP it is determined by both MP and FF.

MP and RPM.

[Matthew P]

Don't overcomplicate it...set your prop, twist mixture till rough, add a couple turns till roughness goes away and you are good...come out to be about the same as reaching peak EGT and adjusting to ROP since you are not an IO360

[Pinecone]

On 9/22/2025 at 3:38 PM, hazek said:

MP and RPM.

MP, RPM AND Fuel Flow

[Hank]

32 minutes ago, Pinecone said:

MP, RPM AND Fuel Flow

Fuel flow determines power when LOP.

When ROP, it's the Performance Tables, which assume leaning to some point (RTFM), specific throttle and RPM settings, and particular altitudes. The Tables for my C are given at Sea Level, then in 2500' increments up to 12,500 msl.

Interestingly enough, the % Power for a given MP / RPM combination increases as altitude increases, until that MP can no longer be developed due to reduced atmospheric pressure. Hadn't noticed that until just now.

[hazek]

7 hours ago, Pinecone said:

MP, RPM AND Fuel Flow

Okay, to clarify precisely:

Power equals torque times angular velocity.
Angular velocity is proportional to RPM (specifically, it’s 2π times RPM divided by 60 to convert revolutions per minute to radians per second).

Therefore power is proportional to torque * RPM.

Torque is proportional to manifold absolute pressure under ROP conditions with constant mixture and timing, since manifold absolute pressure drives mean effective pressure.

Therefore, power is proportional to MAP × RPM when ROP at constant mixture/timing.

The suggestion of power = MAP × RPM × FF is incorrect for ROP, where power is air-limited (excess fuel), not fuel-limited. FF correlates with power ROP but isn’t a direct multiplier in the formula like it is LOP, where at lean mixture power is proportional to FF due to excess air.

Varying mixture ROP introduces an efficiency factor: power ≈ η × MAP × RPM, with η peaking at best power (~50-100°F ROP) and dropping at full rich or leaner due to incomplete combustion.

[Pinecone]

8 hours ago, Hank said:

Fuel flow determines power when LOP.

When ROP, it's the Performance Tables, which assume leaning to some point (RTFM), specific throttle and RPM settings, and particular altitudes. The Tables for my C are given at Sea Level, then in 2500' increments up to 12,500 msl.

Interestingly enough, the % Power for a given MP / RPM combination increases as altitude increases, until that MP can no longer be developed due to reduced atmospheric pressure. Hadn't noticed that until just now.

Fuel Flow IS a factor.  It is not the primary factor.

LOP, Fuel Flow is the primary factor.   There are slight effects of RPM (burn time versus dwell time) since we do not have variable timing (in most cases).

[Pinecone]

2 hours ago, hazek said:

Okay, to clarify precisely:

Power equals torque times angular velocity.
Angular velocity is proportional to RPM (specifically, it’s 2π times RPM divided by 60 to convert revolutions per minute to radians per second).

Therefore power is proportional to torque * RPM.

Torque is proportional to manifold absolute pressure under ROP conditions with constant mixture and timing, since manifold absolute pressure drives mean effective pressure.

Therefore, power is proportional to MAP × RPM when ROP at constant mixture/timing.

The suggestion of power = MAP × RPM × FF is incorrect for ROP, where power is air-limited (excess fuel), not fuel-limited. FF correlates with power ROP but isn’t a direct multiplier in the formula like it is LOP, where at lean mixture power is proportional to FF due to excess air.

Varying mixture ROP introduces an efficiency factor: power ≈ η × MAP × RPM, with η peaking at best power (~50-100°F ROP) and dropping at full rich or leaner due to incomplete combustion.

So FF IS a factor.  Again, it is not the primary or major factor like LOP, but there is an effect.

Look at the chart posted earlier.  % power varies from 100% at peak power mixture to about 95% at full rich mixture on that chart.

[hazek]

25 minutes ago, Pinecone said:

So FF IS a factor.

Oh yeah definitely! When you want to be totally precise and determine whether or not you are at 65% power or 68% then yeah you should mention FF. 

EDIT: And only to determine the mixture as that is really what is a factor, not the absolute FF value.

[EricJ]

So we don't have friction losses any more? 

[PT20J]

The only way to accurately measure power is with a torquemeter. Everything else is an approximation.

The single multiplier of fuel flow for LOP operations works as a good approximation because BSFC is nearly constant over a wide range of mixtures when LOP. You can use the same technique when ROP, but you have to calculate a multiplier for each operating point. Using the IO-360 Part Throttle Fuel Consumption chart from the Lycoming Operator's Handbook, we can calculate that the multiplier for 65% power at 2500 rpm is 11.5 at best power mixture and 13.6 at peak EGT. (pick a BHP point and rpm and use the chart to determine the fuel flow in lb/hour. Divide the fuel flow by 6 to convert to gal/hour and then divide the BHP by this number).

There is also a method the Lycoming developed many years ago for calculating power from fuel flow (attached).

Power_from_fuel_flow.pdf