56 minutes ago, Tom Wright said:

Maybe controversial opinion here but mixture leaning really isn't an exact science. There are tables etc in the POH which give you guideline figures but even amongst the same aircraft type in the real world all engines are different, aging and other external factors can mean that no single setting will give the same outcome on two even 'identical' airframes. We've got a Warrior (160hp) in our fleet which seems to cruise about 10kts faster than all the others at the same RPM setting, and an Archer (180hp) whose performance only just about matches our slowest Warrior. Nobody can figure out why on both counts.

 

There is always explanation  why! For example, low cylinder compression. Different props like cruise via climb via both. One way to find out is to look at maintanance logs 

 

3 hours ago, wilivarob said:

So, if I'm cruising at 12,500 ft with a fuel flow of 95 psi and for whatever reason I want to climb to 13,500 ft, do I add 6 psi to the 95 psi?

(Edited) Not quite. The 95 lb/hr is the total fuel flow, but the 6 lb/hr should be added to the fuel flow for each engine, which in this case is around 47 lb/hr. (Note that the unit for fuel flow should be lb/hr, not psi; the latter is for measuring pressure.)

So you would

• Enrichen the mixture to a fuel flow of 47+6=53 lb/hr
• Pull back on the yoke to achieve a slight climb, at a lower airspeed than cruise, then trim to that lower airspeed.
• Level off when reaching the desired altitude, trim, and lean for cruise as usual.

3 hours ago, wilivarob said:

And I assume that since I'm climbing, I should lean out the fuel, not enrich it.

Yes, if there's a significant altitude difference, you should be leaning as you climb. In this case, as you're climbing only 1,000 feet, it's sufficient to lean once you've leveled off at the new altitude.

3 hours ago, wilivarob said:

That table is the one that comes with the plane by default; I'll leave you the one from the 1971 POH.

Interestingly, this has the same numbers as the previous table labeled "enhanced range mixture". Go figure. In any case, this means you would be using the "normal lean", i.e. 50 ROP. 

Edited November 17, 2025Nov 17 by martinboehme

1 hour ago, martinboehme said:

 

That's how I understand the procedure you quoted earlier. (Note however that the unit for fuel flow should be lb/hr, not psi; the latter is for measuring pressure.)

So you would

• Enrichen the mixture to a fuel flow of 101 lb/hr
• Pull back on the yoke to achieve a slight climb, at a lower airspeed than cruise, then trim to that lower airspeed.
• Level off when reaching the desired altitude, trim, and lean for cruise as usual.

Yes, if there's a significant altitude difference, you should be leaning as you climb. In this case, as you're climbing only 1,000 feet, it's sufficient to lean once you've leveled off at the new altitude.

Interestingly, this has the same numbers as the previous table labeled "enhanced range mixture". Go figure. In any case, this means you would be using the "normal lean", i.e. 50 ROP. 

Thanks, everything's OK.

30 minutes ago, wilivarob said:

Thanks, everything's OK.

Note that I just edited my reply when I noticed that the 95 lb/hr is for both engines total, while the 6 lb/hr should be added to the fuel flow of each individual engine.

6 minutes ago, martinboehme said:

Note that I just edited my reply when I noticed that the 95 lb/hr is for both engines total, while the 6 lb/hr should be added to the fuel flow of each individual engine.

Okay, or instead of adding 6 lb/hr per engine, I add 12 lb/hr to the total fuel flow, so in the example of 95 lb/hr, I add 12 lb/hr.

34 minutes ago, wilivarob said:

Okay, or instead of adding 6 lb/hr per engine, I add 12 lb/hr to the total fuel flow, so in the example of 95 lb/hr, I add 12 lb/hr.

Yup. I think you said that the addon has an engine monitor that shows total fuel flow, so this is presumably what you would be planning to set this? I still think it would be preferable to set fuel flow individually per engine, though, to make sure you're not running one engine richer than the other. (Also, in the real world, 50 ROP might result in different fuel flows per engine...)

Edited November 17, 2025Nov 17 by martinboehme

On 11/17/2025 at 3:35 PM, martinboehme said:

Yup. I think you said that the addon has an engine monitor that shows total fuel flow, so this is presumably what you would be planning to set this? I still think it would be preferable to set fuel flow individually per engine, though, to make sure you're not running one engine richer than the other. (Also, in the real world, 50 ROP might result in different fuel flows per engine...)

Hey buddy, I'm having a strange problem and I'm not sure if it's normal (which I doubt) or if the plane has a bug.

It's been mentioned that when approaching an airport at 8,000 ft takeoff, I should adjust the fuel mixture to 78 lbs/hr, and when starting the climb, I adjust it to 68 lbs/hr.

What's happening with this setting? The plane is having a hard time climbing above 12,000 ft (the target altitude is 15,000 ft).

But when I use the optimal mixture (I call it optimal up to the peak), the plane climbs without any problem to 15,000 ft.

14 minutes ago, wilivarob said:

Hey buddy, I'm having a strange problem and I'm not sure if it's normal (which I doubt) or if the plane has a bug.

It's been mentioned that when approaching an airport at 8,000 ft takeoff, I should adjust the fuel mixture to 78 lbs/hr, and when starting the climb, I adjust it to 68 lbs/hr.

What's happening with this setting? The plane is having a hard time climbing above 12,000 ft (the target altitude is 15,000 ft).

But when I use the optimal mixture (I call it optimal up to the peak), the plane climbs without any problem to 15,000 ft.

It's certainly possible that the engine performance isn't modeled very accurately. (Carenado is not known for being particularly rigorous in this department.)

How do you set what you call the "optimal mixture"? Which fuel flow do you get when you set the mixture in this way?

31 minutes ago, martinboehme said:

It's certainly possible that the engine performance isn't modeled very accurately. (Carenado is not known for being particularly rigorous in this department.)

How do you set what you call the "optimal mixture"? Which fuel flow do you get when you set the mixture in this way?

Here's how I do it:
1. During the "Before take-off" checks for magneto testing, I need to have 1800 RPM. After completing the checklist and before putting the throttle to idle, I start adjusting the mixture to slightly increase the RPM (up to a peak).

2. When I line up on the runway, with the brakes applied, I can adjust it a bit more. At this point, I have the RPM at maximum and the throttle at maximum. I release the brakes, and the mixture gradually increases until it stops moving on the digital gauge. Then it starts to decrease and then increases again slightly, reaching approximately 120 lbs/hr.

3. When I finish retracting the landing gear and flaps, I begin reducing the RPM to 2600 and start adjusting the mixture to 78 lbs/hr (although the closest I get here is 77 lbs/hr - 70 lbs/hr).

10 minutes ago, wilivarob said:

3. When I finish retracting the landing gear and flaps, I begin reducing the RPM to 2600 and start adjusting the mixture to 78 lbs/hr (although the closest I get here is 77 lbs/hr - 70 lbs/hr).

So do I understand correctly that you set the mixture to 78 lbs/hr for the climb (instead of 68 lbs/hr as given in the table), and this allowed you to successfully climb to 15,000 feet?

Did you lean the mixture further during the climb (you would usually do this in real life) or did you leave it set to give a fuel flow of 78 lbs/hr all the way?

What did you do differently when you had trouble climbing above 12,000 feet?

 

47 minutes ago, martinboehme said:

So do I understand correctly that you set the mixture to 78 lbs/hr for the climb (instead of 68 lbs/hr as given in the table), and this allowed you to successfully climb to 15,000 feet?

Did you lean the mixture further during the climb (you would usually do this in real life) or did you leave it set to give a fuel flow of 78 lbs/hr all the way?

What did you do differently when you had trouble climbing above 12,000 feet?

I think I made a mistake. When I fly adjusting the mixture to the values on the nameplate, the plane struggles to climb above 12,000 ft.

 

When I use the optimal mixture, it climbs well. Throughout the entire process—takeoff and climb—I maintain the optimal mixture, gradually reducing it until there's a peak (digital indicator). So, if the indicator peaks at 120 lbs/hr during takeoff, as I climb I begin reducing the mixture until there's another peak, and so on. The relative value is between 100 lbs/hr and 90 lbs/hr.

 

This is the digital indicator I'm referring to.

The image shows gallons/hour, mine is set to pounds/hour

Edited November 21, 2025Nov 21 by wilivarob

Remember guys,  "leaning" figures always corresponding to particular power settings like manifold pressure and rpm. If you are running higher power settings then specified gph numbers will be different from one in the tables. 

The discussion about the proper way to "lean" is like the discussion about what controls speed and what controls sinkrate - pitch or power? 🤣

Everything becomes more easy when you understand the underlying physical principles (in both cases), but unfortunately this eludes even many pilots, we call them "rote-learning pilots". They will study the numbers in the handbook and follow them religiously (which isn´t wrong per se, but they lack the knowledge of why).

When a reciprocating engine generates a force to move the cylinder, it burns a mixture of fuel and air. The composition of this mixture determines HOW it burns. 

If there is too much air or too much fuel, the mixture will not burn and the engine does not deliver power.

There is a mixture that has "just the correct mix" and it is called the "chemically correct mixture (CCM)", is usually around 1:15 and will burn without any fuel or air left after the process. It will also burn the hottest.

Then there is a mixture that is "the most explosive", i.e. it will burn the fastest, giving out the most power, this is called the "best power point (BPP)" and is usually around 1:12.5. This will not burn as hot (since some unburnt fuel will be left in the exhaust).

When you climb, air gets thinner (less), so you need to reduce the amount of fuel to keep the "same" mixture ratio.

When the engine is running too hot, you want to add more fuel (so the exhaust gets colder) - this comes at the expensive of both power and fuel economy.

When you want to get the best fuel economy, you want to hit the CCM, but this comes at the expense of engine heat.

Since you can not measure the mixture directly, you need to help yourself with other indicators, good ones are RPM (unless a governor messes with it) or the Exhaust gas temperature (Cylinder Head Temperature will lag behind and is also influenced by cooling airflow).

So in situations where you need the best power - lean for BPP. This is SOMETIMES achieved by simply putting the mixture "full rich", but if you really want the max output, you need to run up your engine, put it in in a situation where it can not reach it´s maximum RPM, and then slowly lean the mixture until the RPM is "the highest it can get". 
So in a fixed speed prop, set the RPM to maximum, add throttle until you reach maybe 75% of that, then lean until the RPM maxes out.
The same thing would theoretically work before approach, go full RPM, reduce throttle until your RPM drops below that, then lean/rich to max RPM.

For the cruise flight, when you want best fuel economy, lean until the EGT maxes out. 

Always bear in mind that engines MAY not be able to handle the heat generated and often the manual mandates to run more "fuel rich" than BPP or CCM.

Also keep in mind that with every change in altitude, you will need to readjust the mixture - if you lean to CCM at 10,000 feet and then descend to sea level without touching the mixture, your engine may sputter and falter as mixture gets too thin (more air, same fuel) to burn.

Edited November 22, 2025Nov 22 by Litjan

8 hours ago, sd_flyer said:

Remember guys,  "leaning" figures always corresponding to particular power settings like manifold pressure and rpm. If you are running higher power settings then specified gph numbers will be different from one in the tables. 

That's understood. I think we've already established above that @wilivarob is setting full throttle and 2,600 rpm, as assumed in the placarded power setting table.

10 hours ago, wilivarob said:

This is the digital indicator I'm referring to.

The image shows gallons/hour, mine is set to pounds/hour

OK, I think we've found the issue. The number you're seeing here is total fuel flow for both engines, while the table you're referencing gives fuel flow for an individual engine. (I think we've discussed this distinction before?) If you're setting a fuel flow of 78 lb/hr here, you'll get only 39 lb/hr for each engine, which is way too low. (BTW, 78/hr would be 13 gal/hr, not 8.2 gal/hr as in the picture, but IIUC that screenshot isn't even from the Skymaster you're flying?).

This total fuel flow display on the Garmin isn't really intended to be used for leaning. Instead, you would use it to check, for example, that your actual fuel flow matches what you assumed in your flight planning, or to determine your endurance (though the Garmin helpfully computes that for you).

Instead, set your fuel flow for each engine Individually on the analog fuel flow gauge. If you like, you can then cross-check on the Garmin. If you set 78 lb/hr for each engine, you should see around 156 lb/hr total fuel flow on the Garmin (or around 26 gal/hr, depending on the units your Garmin is set to).

Or you can just ignore the table and continue to do what has worked for you, namely leaning by reference to EGT. This is the more common procedure in the real world too.

5 hours ago, martinboehme said:

OK, I think we've found the issue. The number you're seeing here is total fuel flow for both engines, while the table you're referencing gives fuel flow for an individual engine. (I think we've discussed this distinction before?) If you're setting a fuel flow of 78 lb/hr here, you'll get only 39 lb/hr for each engine, which is way too low. (BTW, 78/hr would be 13 gal/hr, not 8.2 gal/hr as in the picture, but IIUC that screenshot isn't even from the Skymaster you're flying?).

That's the GTN 750, and it's not the one it comes with by default. Also, the image is just for reference since I didn't have the simulator running at the time to take a real screenshot, so that 8 Gallons isn't my configuration.

 

5 hours ago, martinboehme said:

Instead, set your fuel flow for each engine Individually on the analog fuel flow gauge. If you like, you can then cross-check on the Garmin. If you set 78 lb/hr for each engine, you should see around 156 lb/hr total fuel flow on the Garmin (or around 26 gal/hr, depending on the units your Garmin is set to).

Or you can just ignore the table and continue to do what has worked for you, namely leaning by reference to EGT. This is the more common procedure in the real world too.

I performed these tests:

1. When using 156 lbs/hr (78 per engine) for takeoff, this is what the GTN 750 gauge shows; it doesn't go beyond that. If I lean the mixture, it goes down; if I richen it, it goes down. This is what I call the optimal mixture.

Takeoff

Climb

And this is the speed that this configuration generates.

 

Now when I adjust to what was previously discussed, maintaining 78 Lbs/Hr on takeoff (39 per engine) and 68 Lbs/Hr on climb (34 per engine), this is what is obtained.

Takeoff

Climb

And this is the speed that generates these adjustments.

 

I add the following, although the values are not those in the table, they are the closest.

 

I'd like to add something else, in case it's helpful: these climb tests were performed at 2600 RPM, 21 MP (it doesn't climb higher due to the altitude), an approximate climb rate of 600 bpm, and a weight of 4530 lbs.

And one more small detail: when I climb at 2800 RPM (full throttle), I gain a little more speed.

Edited November 22, 2025Nov 22 by wilivarob