Comprehensive Leaning Guide?

[oisiaa]

Any recommendations on a comprehensive guide (written or video) on leaning? I recently bought an M20C. I'm an Air Force guy and 99.7% of my hours are in jets or turboprops so the red knob is a bit of a mystery despite reading the POH and other basic guides. It seems almost like an engine self destruct lever if used improperly. 

The POH essentially says full rich when >75% power unless you have an EGT gauge (I do via G3X), but then doesn't say what to do if you do have an EGT gauge. Ideally, I'd like to be able to fly at WOT at altitudes where >75% power can be achieved without burning crazy amounts of fuel at full rich. The lean assist mode of the G3X requires you to find peak EGT which I understand to be the point where detonation is the most likely so at >75% power I don't really think that can be used safely.

My home field is 4,000' so I have questions about leaning for takeoff and climb. 

Thanks for any pointers to good guides or discussions in this thread!

 

[oisiaa]

Also, can I trust the % power readout of the G3X? Is that reliable and accurate just based mathematically on MAP and RPM? If that number can be trusted then I can at least know at a glance when I'm below 75% power. 

[TheAv8r]

Oh man, that's a highly debated question . I'd recommend starting with the Lycoming O-360 Operators Manual, it's about as comprehensive as you can get as to the operation of the engine. Running the engine at > 75% power all the time is a recipe for not hitting TBO FWIW. As far as the relationship between peak EGT, power setting, and where to avoid both detonation margins and get the most life out of your engine, check out this article: https://www.savvyaviation.com/red-box-red-fin/ . The TLDR is: above 75% power, run full rich (this is also what Lycoming who made the engine recommends...). At 75% power, don't go leaner than 150deg ROP. At 65% power, you can basically run the mixture wherever you want. Some nuances to that, but that's a good rule of thumb to get started.

What I would recommend is to find a Mooney CFI in your area and go on a XC flight with them, they can teach you engine management techniques for your airplane in different phases of flight and help answer these questions specific to your equipment. 

[TheAv8r]

4 minutes ago, oisiaa said:

Also, can I trust the % power readout of the G3X? Is that reliable and accurate just based mathematically on MAP and RPM? If that number can be trusted then I can at least know at a glance when I'm below 75% power. 

Not always. It is automatic based on MAP/RPM and Fuel Flow and what has been entered into the configuration. I would compare it against the POH, go to an altitude specified in the POH like 7500ft (checking against density altitude to ensure that's the altitude the engine is really at). Set a 75% power setting, then see what the G3X reads-out. 

[N201MKTurbo]

I doubt you can get an O-360 to detonate no matter what you do. I would quit worrying about that. You will do better thinking about it in terms of your wallet. The worst thing you can do is forget to lean and it will cost you money. If you over lean, it will run rough as soon as you start to lose power. They don’t run LOP very well, so you will be running ROP. Your best bet is to keep an eye on your CHTs and richen up a bit if they get too hot, which probably won’t happen. 

[Ragsf15e]

Just keep your chts below about 400 in climb and maybe 380 in cruise.  After that you can work on fine tuning your technique.  Maybe read about leaning in climb using target egt?

maybe try cruise above ~7000’ and you’ll be faster and below 75% anyway.

[Rick Junkin]

@oisiaa I'm a fan of Mike Busch. Here are two comprehensive videos that should answer most of your questions and also prompt some thinking and more questions.

 

[Fly Boomer]

2 hours ago, oisiaa said:

Thanks for any pointers to good guides or discussions in this thread!

For me, the bottom line is to protect the engine -- in particular, the cylinder heads.  LOP, ROP, red box, EGT, leaning for takeoff are all good discussions, but as you experiment with different settings and techniques, you will probably be okay if you keep all your CHTs below 380 or 390.  And keep in mind that CHT is not an instantaneous reflection of throttle, prop, and mixture -- good idea to make small changes, and give your instruments some time to show a trend or settle into a steady state before further changes.

[47U]

2 hours ago, oisiaa said:

Thanks for any pointers to good guides or discussions in this thread!

Lot’s of good information above… I’m also a fan of Mike Busch.

I had confusion on how best to combine RPM, mixture, and fuel flow when I’m traveling, or just out donk’n around.  The performance charts differ very significantly from the early vintage C/D POH supplement to the latest POH version of the mid-70s.  Influence from marketing, I suspect.

Basic advice from Lycoming in SI 1094D Mixture Leaning Procedures
 

Then from the Lycoming operating manual… which is quite an eye chart…

 

 

So, someone transposed that into a table… a little easier to read… (both of these are easily searched online for non-jpg versions).

 

[PT20J]

You can make this as simple or complicated as you want.

Simple: Full rich above 75% power. Below that, lean until it gets rough and then richen until it is smooth. Richer if CHTs get above 400 F in cruise. During climb, Lycoming allows up to 435 F. Cooler is better, but the few minutes of climb above 400 won't really hurt anything and some M20Cs are difficult to keep below 400 during climb.

[PT20J]

2 minutes ago, 47U said:

Lot’s of good information above… I’m also a fan of Mike Busch.

I had confusion on how best to combine RPM, mixture, and fuel flow when I’m traveling, or just out donk’n around.  The performance charts differ very significantly from the early vintage C/D POH supplement to the latest POH version of the mid-70s.  Influence from marketing, I suspect.

Basic advice from Lycoming in SI 1094D Mixture Leaning Procedures
 

Then from the Lycoming operating manual… which is quite an eye chart…

 

 

So, someone transposed that into a table… a little easier to read… (both of these are easily searched online for non-jpg versions).

 

Just keep in mind that the data in the Lycoming manual is for an engine on a test stand. The installed numbers are somewhat different because the airplane manufacturer designs the induction and exhaust systems, both of which reduce power output. This is why the numbers in the POH are generally different. POH's didn't exist before the mid 1970s when the General Aviation Manufacturers Association came up with a consensus standard. Prior to that, each manufacturer created some sort of owners manual that often had scant information and there was no consistency between manufacturers.

If you want to play with the Lycoming data, there is an app: AircraftPower that makes it easy to try different combinations of variables.

[N201MKTurbo]

Probably the only way to make an O-360 detonate; start at a sea level airport or lower. During your run up lean to peak EGT. As soon as you get the gear up, close the cowl flaps and roll the prop back to 1900 RPM. When the CHTs get smoking hot, it might detonate.

So, if you are worried about detonation, avoid doing the above.

[Hank]

My best recommendation is to check the Downloads section for an M20-C Owners Manual. What year is yours? There are several Manuals to choose from; I know I uploaded my 1970 book, and downloaded a 1977 one for comparison (the last year the Cs were made).

I use my CHT gage to lean by; whenever I'm at or above 8000 msl, I run between Peak EGT and 25° Rich of Peak, which usually gives me 8.4 - 8.7 gallons per hour when calculated at the fuel pump; indicated airspeed is usually in the mid-140s mph. 

Our carbureted engine does better if the first thing you do after leveling off and accelerating is pull the throttle back just enough to make the MP needle start to move--I call this WOT-, and the angled throttle plate inside the carb hopefully creates turbulent airflow inside, leading to improved full atomization and more even mixing. Our fuel-injected friends don't have to worry about this, as mixing happens inside the cylinders, but ours happens prior to flow splitting, and poor atomization or poor mixing will lead to uneven fuel distribution and unequal power generation in the cylinders. 

As mentioned above, quick and dirty leaning is simply lean until the engine gets rough, then enrichen until is smooths out. My wife often announces Rough about the same time I spot Peak temperature on the EGT. 

Have fun with your Mooney, and recognize that the Red knob is not instant death or destruction. In fact, it takes several seconds to stabilize after moving the Red knob, and may take several adjustments to get it where you want it.

FWIW, the only time my engine has been 150° ROP in the 1000 hours I've flown it has been during takeoff and climb; I generally cruise under 100°Rich. 

Fly safe out there!

[Jim Peace]

I know EGT's really don't have a red line but in the O-360 in a C what would be highest number you would want to see even if CHTs are at or under 400?

[hammdo]

My C @ 9000 WOT (~21 MAP, 2400 RPM ) or key # 45

 

[Jim Peace]

did you have carb heat on? I like your 0 FF,,did you have your CARB heat on?

Here is mine the other day at either 8 or 9000 feet...

[hammdo]

That was before I added FF. I averaged 7.2 GPH in that flight with a touch of carb heat…

~148 knots true in cruise...

-Don

[47U]

12 minutes ago, hammdo said:

~148 knots true in cruise...

And… how many knots is that fancy @Sabremech cowl worth???  

[oisiaa]

14 minutes ago, hammdo said:

That was before I added FF. I averaged 7.2 GPH in that flight with a touch of carb heat…

~148 knots true in cruise...

-Don

What's the idea with partial carb heat? 148 KTAS is great! 

[hammdo]

5 minutes ago, 47U said:

And… how many knots is that fancy @Sabremech cowl worth???  

A lot!

-Don

[hammdo]

6 minutes ago, oisiaa said:

What's the idea with partial carb heat? 148 KTAS is great! 

Fuel distribution along with a slight throttle reduction helps…

-Don

[Pinecone]

Here is where Mike Busch learned about leaning - https://www.advancedpilot.com/

They have not had an in person for a number of years (and two of the main presenters have passed away), but the online works well.   These are the guys that pushed LOP operation over the cries and anguish of many, including some of the current gurus or LOP (I won't mention any names ).

No, the G3X % power numbers are not accurate.  And LOP is easy, for turbo engines the HP is 13.7 times the fuel flow.  So my normal cruise fuel flow of 10.1 GPH is 138 HP.  Divide that by 220 (max) and I am at 63% power.  My old JPI 830 got this right.

George Braly developed an algorithm for ROP operation, I think Cirrus wanted it, and it may be in the Cirrus G1000 implementation.

[Hank]

The Performance Tables in the Owners Manual shows % Power. I keep them on my knee board for easy reference. 

Over time, you'll probably find yourself using the same power settings at similar altitudes, and that will make power setting even easier.

The MAPA PPP course advocates Key Numbers. The Key Number for an M20-C is 46. So use any throttle and prop setting where MP + RPM/100 = 46. For example, 22" / 2400 is good; 22" / 2500 is not so good; the Key Numbers provide a safe place to run the engine, and you can pretty much put the mixture wherever you want.

Happy flying!

[oisiaa]

Thanks all!

[Rick Junkin]

2 hours ago, Pinecone said:

And LOP is easy, for turbo engines the HP is 13.7 times the fuel flow.

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.

EDIT: The Lycoming O-360-A1D in the OP's M20C has a compression ratio of 8.5 and a LOP fuel flow multiplier of 14.9. @oisiaa