Hi everyone, I wanted to let you know that I haven't been able to fully understand these instruments, one is the EGT and the other is the Fuel Flow.

hey are from the Carenado C337 Skymaster.

The issue is as follows:

1. The checklist repeatedly states:
- Mixture -- Adjust (to a fuel flow of 78 lbs/hr)
- Mixture -- Lean (to a fuel flow of 68 lbs/hr)

Does this mean that the needles on the fuel flow indicator should be around that value?

2. The descent says:
- Mixture -- Adjust (for smoothness, use a rich mixture at minimum power).

Does this mean that:

a.) I raise the lever to maximum and the MP to minimum? or
b.) Every 3000 ft, the mixture is adjusted until reaching 3000 ft and mixture at full rich.

3. The EGT, as I understand it, can be used as Rich of Peak (ROP) or Lean of Peak (LOP). 

ROP: faster, more fuel
LOP: slower, less fuel 

The POH that comes with the fairing does not provide detailed information on the subject, and the checklist only states the following:

- Mixture -- Lean (for cruise fuel flow using the EGT gauge, Cessna power computer, or in accordance with Section II cruise procedures).

And here is a small image of one of the performance charts, which does not detail the use of the EGT very well.

 

So if I use ROP, how do I configure it?
Or if I use LOP, how do I configure it?

I found a 1971 manual for a Cessna C337, and this is all I found:

 

Leaning is a complex topic, and I certainly won't claim to be an expert. (Obviously, don't apply anything I say to real-world operation.)

How you lean can depend on the engine, the engine instrumentation, and personal preference. And the approach to leaning has changed over time -- lean-of-peak (LOP) operation has come into widespread use only relatively recently, isn't possible on all engines, and requires a good engine monitor.

Note also that MSFS doesn't model the engine's response to mixture adjustments particularly well, so what you see in the sim may not be entirely representative of what you would see in real operation.

Here's an article to get you started:

https://www.aopa.org/news-and-media/all-news/2023/february/pilot/technique-no-right-way-to-lean

And here's a video by Mike Busch, one of the gurus of lean-of-peak operation:

Now for some of your specific questions:

3 hours ago, wilivarob said:

1. The checklist repeatedly states:
- Mixture -- Adjust (to a fuel flow of 78 lbs/hr)
- Mixture -- Lean (to a fuel flow of 68 lbs/hr)

Does this mean that the needles on the fuel flow indicator should be around that value?

Yes.

(In which phases of flight does it recommend setting those fuel flows?)

3 hours ago, wilivarob said:

2. The descent says:
- Mixture -- Adjust (for smoothness, use a rich mixture at minimum power).

Does this mean that:

a.) I raise the lever to maximum and the MP to minimum? or
b.) Every 3000 ft, the mixture is adjusted until reaching 3000 ft and mixture at full rich.

I don't know exactly how a descent in a Skymaster is flown, but I'm sure you wouldn't be anywhere close to idle, so I'm not sure what they mean by "minimum power". I expect you'd be at some intermediate, but relatively low power setting (50% or less). At such a low power setting, you can't damage the engine no matter where you set the mixture.

Adjusting the mixture for smoothness means leaning until the engine starts running rough, then enrichening again just enough so the engine runs smoothly. (This will probably not be modeled well in the sim though.) This results in a relatively lean mixture, which makes sense, as it saves fuel, and as noted, at a lower power setting you can't damage the engine by leaning. So I'm not sure why the manual refers to "rich mixture". As you note, you may need to enrichen the mixture as you descend into thicker air.

3 hours ago, wilivarob said:

3. The EGT, as I understand it, can be used as Rich of Peak (ROP) or Lean of Peak (LOP). 

ROP: faster, more fuel
LOP: slower, less fuel 

Essentially, yes, though there's a lot more to go into about when and how to run ROP or LOP (see the references I linked to above).

3 hours ago, wilivarob said:

The POH that comes with the fairing does not provide detailed information on the subject, and the checklist only states the following:

- Mixture -- Lean (for cruise fuel flow using the EGT gauge, Cessna power computer, or in accordance with Section II cruise procedures).

Essentially, I think the checklist is leaving it up to you how to lean.

As a starting point, I'd suggest using the "classic" procedure you found in that 1971 POH:

3 hours ago, wilivarob said:

I found a 1971 manual for a Cessna C337, and this is all I found:

This POH describes classic ROP operation. It was written at a time when LOP operation was not "a thing", and indeed it forbids running LOP.

I would suggest using this as a starting point for your flying. Once you're comfortable operating this way, you can explore running LOP, based on the information in the references I posted above. From an internet search, it looks as if the Continental IO-360 in the Skymaster can be operated this way (not all engines can). Not sure if the Carenado model has an engine monitor -- in the real world you'd certainly want to have one for LOP operation -- but this is the sim, so you won't break anything.

Hope this helps, let me know if you have any additional questions.

Edited September 5, 2025Sep 5 by martinboehme

1 hour ago, martinboehme said:

(In which phases of flight does it recommend setting those fuel flows?)

Thank you for responding.

The 78 lbs/hr is for normal ascent.
The 68 lbs/hr is for maximum ascent, although a small table is used here

 

On the other hand, I read the article and there is some truth to the fact that when using LOP, the temperature gauge never reaches 400 degrees CHT, whereas when using ROP, you occasionally see a peak of 400 degrees.

On the other hand, my fuel calculations using ROP are not enough (taking into account that I only use fuel for travel, takeoff, climb, cruise, descent, approach, and landing for now), but if I use LOP, I have some left over, not much, but some.

Now, taking into account that this aircraft, based on the 1971 manual, was not designed to operate on LOP, I don't understand why the fuel calculations don't add up.

8 hours ago, wilivarob said:

Thank you for responding.

The 78 lbs/hr is for normal ascent.
The 68 lbs/hr is for maximum ascent, although a small table is used here

Ah, got it. This table is provided so that you can set climb power directly using fuel flow without having to determine the reference EGT as described in the POH.

8 hours ago, wilivarob said:

On the other hand, I read the article and there is some truth to the fact that when using LOP, the temperature gauge never reaches 400 degrees CHT, whereas when using ROP, you occasionally see a peak of 400 degrees.

That should depend on how far rich or lean of peak you're running. Airspeed is an important factor, too - the slower you are (e.g. in a climb), the less cooling and the higher the CHT.

8 hours ago, wilivarob said:

On the other hand, my fuel calculations using ROP are not enough (taking into account that I only use fuel for travel, takeoff, climb, cruise, descent, approach, and landing for now), but if I use LOP, I have some left over, not much, but some.

Now, taking into account that this aircraft, based on the 1971 manual, was not designed to operate on LOP, I don't understand why the fuel calculations don't add up.

It sounds as if the Carenado model is using more fuel than it should according to the performance tables in the POH. It's hard in MSFS to get all the numbers exactly right. Some developers are better at this than others.

One thing you could do is to develop your own performance tables with the fuel flows you actually observe in the sim.

6 hours ago, martinboehme said:

Ah, got it. This table is provided so that you can set climb power directly using fuel flow without having to determine the reference EGT as described in the POH.....

Thank you, that was really helpful.

Just one last question (see image).

For example:

I am at an airport at 8200 ft, and the checklist for maximum climb shows the following...

So, what configuration should I use, considering that I have both engines running? 

If you noticed, the first image tells me that the RPM should be 2600 RPM, but the checklist (second image) says 2800 RPM; even the 1971 checklist says the same thing.

And (first image) it says that at 8000 ft the fuel flow should be adjusted to 68 Lbs/Hr, but in flight that flow cannot be adjusted exactly, i.e. it shows more or less around 74 Lbs/hr or 54 Lbs/Hr.

Which should I leave it at, always above (74 lbs/hr) or below (54 lbs/hr)?

3 hours ago, wilivarob said:

I am at an airport at 8200 ft, and the checklist for maximum climb shows the following...

So, what configuration should I use, considering that I have both engines running? 

Full throttle, 2800 rpm, mixture leaned to a fuel flow of 78 lbs/hr.

3 hours ago, wilivarob said:

If you noticed, the first image tells me that the RPM should be 2600 RPM, but the checklist (second image) says 2800 RPM; even the 1971 checklist says the same thing.

2600 rpm is for what the 1971 POH calls a "normal climb". The checklist you quoted above is for a "maximum performance climb".

Let's look at this table again:

3 hours ago, wilivarob said:

This has two rows.

The first row is for takeoff and maximum performance climb. (The extract from the 1971 POH calls this "takeoff and climb".) This is flown at full throttle and 2800 rpm, with the mixture leaned to give the appropriate fuel flow from the first row, for the given altitude.

The second row is for what the 1971 POH calls a "normal climb". This is flown at 24" manifold pressure and 2600 rpm, with the mixture leaned to give the appropriate fuel flow from the second row.

When would you use a "maximum performance climb", and when would you use a "normal climb"?

I don't know how Skymasters are operated in practice, but I think it would be reasonable to stay at the takeoff power setting until you've cleared obstacles, then reduce power to the "normal climb" power setting. This helps with noise abatement and probably also reduces stress on the engine.

3 hours ago, wilivarob said:

And (first image) it says that at 8000 ft the fuel flow should be adjusted to 68 Lbs/Hr, but in flight that flow cannot be adjusted exactly, i.e. it shows more or less around 74 Lbs/hr or 54 Lbs/Hr.

Which should I leave it at, always above (74 lbs/hr) or below (54 lbs/hr)?

Are you saying that the needle in the fuel flow instrument jumps directly from 74 to 54 lbs/hr and cannot be adjusted to an intermediate setting?

This is certainly not what you would see in reality -- fuel flow should change continuously as you adjust the mixture control. This may be a limitation of the model, but I think it could also be a result of the way you're adjusting mixture. What are your control assignments for mixture -- are you adjusting this with the keyboard, by using the mouse to drag the mixture control in the virtual cockpit, or with an axis assignment on your throttle quadrant?

Certainly, if you can only adjust fuel flow in coarse steps of 20 lbs/hr, that will make it hard to lean with any finesse.

19 hours ago, martinboehme said:

Are you saying that the needle in the fuel flow instrument jumps directly from 74 to 54 lbs/hr and cannot be adjusted to an intermediate setting?

This is certainly not what you would see in reality -- fuel flow should change continuously as you adjust the mixture control. This may be a limitation of the model, but I think it could also be a result of the way you're adjusting mixture. What are your control assignments for mixture -- are you adjusting this with the keyboard, by using the mouse to drag the mixture control in the virtual cockpit, or with an axis assignment on your throttle quadrant?

Certainly, if you can only adjust fuel flow in coarse steps of 20 lbs/hr, that will make it hard to lean with any finesse.

First of all, thank you, because thanks to you everything is starting to make sense.

Let me give you some context. Yes, I use the Logitech 3D Pro joystick, and I have it configured as follows:

Keys 9 and 11 for RPM
Keys 10 and 12 for using the mixtures

Now, when you mentioned that you found it strange that moving the mixtures caused changes of 20 lbs/hr, I investigated within the simulator and found an option to use both increase and decrease the mixtures gradually. I had it configured to increase and decrease normally. 

I adjusted it, even the RPM, and I tested it, and the results were surprising. There is still a small difference, but not as much as before.

I take off at 8200 ft, and at approximately 8700 ft, I begin to make the climb adjustments, and the fuel flow reads around 68 lbs/hr (I say around because it reads .5 or .7, meaning 68.5 or 68.7).

At approximately 9000 ft, it reads 70 lbs/hr, and when I go back and adjust it to 68 lbs/hr, it reads 64 lbs/hr, which is quite close to the difference I had before. At 12000 ft, the table is supposed to read 56 lbs/hr, but the closest it gets is 59 lbs/hr.

 

19 hours ago, martinboehme said:

This has two rows.

The first row is for takeoff and maximum performance climb. (The extract from the 1971 POH calls this "takeoff and climb".) This is flown at full throttle and 2800 rpm, with the mixture leaned to give the appropriate fuel flow from the first row, for the given altitude.

The second row is for what the 1971 POH calls a "normal climb". This is flown at 24" manifold pressure and 2600 rpm, with the mixture leaned to give the appropriate fuel flow from the second row.

When would you use a "maximum performance climb", and when would you use a "normal climb"?

I don't know how Skymasters are operated in practice, but I think it would be reasonable to stay at the takeoff power setting until you've cleared obstacles, then reduce power to the "normal climb" power setting. This helps with noise abatement and probably also reduces stress on the engine.

 

 

Please note that the first line refers to a single engine and the second line refers to both engines.

So, based on what we have learned, it would be as follows:

Normal climb:

RPM 2600 MP 24" and mixtures at 78 lbs/hr (with both engines).

Maximum climb:

RPM 2600 MP 24" and mixtures at 68 lbs/hr (according to the image, taking off at 8200 ft and with both engines).

 

2 hours ago, wilivarob said:

Now, when you mentioned that you found it strange that moving the mixtures caused changes of 20 lbs/hr, I investigated within the simulator and found an option to use both increase and decrease the mixtures gradually. I had it configured to increase and decrease normally. 

I adjusted it, even the RPM, and I tested it, and the results were surprising. There is still a small difference, but not as much as before.

Great to hear you now have better control over mixture!

2 hours ago, wilivarob said:

Please note that the first line refers to a single engine and the second line refers to both engines.

I see that.

The first row (for takeoff, which would obviously be on two engines, or for single-engine climb) is also the power setting (2800 rpm, full throttle) that you would use for the "maximum performance climb" from the checklist you quoted earlier. It's easiest really to think of this row as "full power". The table labels it "takeoff or single-engine climb" since full power is what you want for takeoff or if an engine has failed - and also for a maximum performance climb. The second row is normal climb power.

2 hours ago, wilivarob said:

So, based on what we have learned, it would be as follows:

Normal climb:

RPM 2600 MP 24" and mixtures at 78 lbs/hr (with both engines).

Not quite. The normal climb would use the fuel flow from the second row, so 68 lbs/hr at 8000 feet. (Note also that the second row states "2600 rpm".)

2 hours ago, wilivarob said:

Maximum climb:

RPM 2600 MP 24" and mixtures at 68 lbs/hr (according to the image, taking off at 8200 ft and with both engines).

Again, not quite.

Maximum climb uses the "full power" setting, i.e. full throttle and 2800 rpm. So you'd use the fuel flow from the first row (again, it's easiest to think of this as "full power"), so 78 lbs/hr at 8000 feet.

I think the "single engine" versus "twin engine" labeling in the table may be confusing things here.

The first row is simply "full power", but it's instead labeled according to the situations in which you might want full power, namely takeoff or a single-engine climb (where you desperately need all the power you can get). But you can also set full power if you want a maximum performance climb -- it's just not mentioned in the table.

The second row is a reduced power setting that gives you an adequate amount of climb power in the normal case where both engines are working and you don't need the absolute maximum climb performance you can get. "Normal climb" might be a more appropriate label, but the table chooses to call it a "twin-engine climb". The intent is the same though: This is the power setting you would use for a climb in normal operation.

22 hours ago, martinboehme said:

..... The second row is a reduced power setting that gives you an adequate amount of climb power in the normal case where both engines are working and you don't need the absolute maximum climb performance you can get. "Normal climb" might be a more appropriate label, but the table chooses to call it a "twin-engine climb". The intent is the same though: This is the power setting you would use for a climb in normal operation.

All clear now, thank you.

Finally, could you send me an email address via private message so I can contact you if I have any questions in the future?

Glad to hear it's now all clear!

You can DM me if you like, but I'd suggest asking here on the forums, as there are often others who have the same issues.

Have fun with the Skymaster and happy landings!