Hello,

I already watched some videos on how to understand rich of peak EGT and lean of peak EGT and whats the reasoning behind it.
But how do I lean the 172s correctly (like in real life) for a given speed ?

Lets say Im cruising at 10.000 feet with 122 ktas rich of peak egt and now I want to go down to 95 ktas lean of peak egt, how would a real 172s pilot do that ?
I managed to do it with a lot of "dead reckoning and adjusting" (which was fun😅) and of course help from the autolean display in the G1000nxi, but that took me like 10 to 15 minutes...

I mean I could adjust the throttle get 95 ktas, but then I have to readjust the fuel mix to find peak egt again and then from there lower it to -50 degree F for lean of peak egt, but that will lower my knots under 95 ktas and if I now readjust the throttle, I would also have the readjust the leaning afterwards and so on and so on...

So how to do it correctly ?

And one bonus question:

I know that cylinder/engine damage is not modelled in the MSFS2020 C172s, but are there some numbers I should watch out for ?
Should I just watch out to not go over -100F of peak or is the overall EGT number (like 1500F EGT or 1200F EGT) more important ? 

Edited July 8, 20223 yr by Rucki

In real life, I never flew a C 172 with an EGT gauge.  I just leaned it out, until the engine sounded rough or rpm slightly dropped, and turned it towards rich until it smoothed out. 

2 hours ago, Rucki said:

Lets say Im cruising at 10.000 feet with 122 ktas rich of peak egt and now I want to go down to 95 ktas lean of peak egt, how would a real 172s pilot do that

POH is giving us performance (and this is important to understand) for "RECOMMENDED LEAN". Which is -50F rich of peak. Also the table is for a max loaded airplane at 2550 lbs. Any time you are not flying at MTOW, your values and POH will differ (but that's OK since differential is on the "safe" side of fuelburn)

There is no table/chart for RPM/TAS under PEAK EGT conditions, at least not on the plane I fly. When I learned the 172S, instructor said that PEAK EGT would reduce TAS by around 4-5kts, but we always flew per the POH.
RPM might rise(?) 10-20RPM when I am done leaning, which doesn't have much impact (start at 2350, end up at 2370)
And default "Lean Assist" in NXI has its flaws, not like the real plane behaves. (biggest gripe is how qickly any change is sensed on the display. Using lean assist is a chore that takes around 30secs when I do it, due to the time it takes for the system to reflect any change in mixture)

MFD "Lean Assist"-page  in a light loaded 172SP, roughly 60% power (TAS 111) at 6.500ft,  ISA  -9C.

Edited July 8, 20223 yr by SAS443

1 hour ago, Bobsk8 said:

In real life, I never flew a C 172 with an EGT gauge.  I just leaned it out, until the engine sounded rough or rpm slightly dropped, and turned it towards rich until it smoothed out. 

I learned to fly on a Piper warrior and this is how I was as taught as well.  I'd say this method is basically a best power setting, or sometimes known as "big mixture pull" method.

There are definitely other methods (and I'm not too familiar with them).  

For example for Lean of Peak, you'd find the hottest cylinder (as you pull out the mixture), and then continue leaning about 50 degrees beyond the hottest.  75-100 might be more appropriate.

Rich of peak or ROP is sort of the opposite.  When you find the hottest cylinder (or EGT if you don't have an engine monitor), you richen the mixture till the temp changes another 50-100 degrees.

2 minutes ago, ryanbatc said:

I learned to fly on a Piper warrior and this is how I was as taught as well.  I'd say this method is basically a best power setting, or sometimes known as "big mixture pull" method.

There are definitely other methods (and I'm not too familiar with them).  

For example for Lean of Peak, you'd find the hottest cylinder (as you pull out the mixture), and then continue leaning about 50 degrees beyond the hottest.  75-100 might be more appropriate.

Rich of peak or ROP is sort of the opposite.  When you find the hottest cylinder (or EGT if you don't have an engine monitor), you richen the mixture till the temp changes another 50-100 degrees.

I always liked the idea of rich of peak, figuring it was less stress on the engine. 

5 minutes ago, Bobsk8 said:

I always liked the idea of rich of peak, figuring it was less stress on the engine. 

And it may be - but probably engine dependent.  There are more advanced methods of course but typically those require a nice engine monitor - like the one on the upcoming A2A PA24.  There are also some areas you definitely don't want your engine running.  Like the "red box" as described by this person

https://www.jpinstruments.com/news-events/2013/05/the-red-box-advanced-leaning-tips-by-mike-bush/

 

54 minutes ago, ryanbatc said:

I learned to fly on a Piper warrior and this is how I was as taught as well.  I'd say this method is basically a best power setting, or sometimes known as "big mixture pull" method.

There are definitely other methods (and I'm not too familiar with them).  

For example for Lean of Peak, you'd find the hottest cylinder (as you pull out the mixture), and then continue leaning about 50 degrees beyond the hottest.  75-100 might be more appropriate.

Rich of peak or ROP is sort of the opposite.  When you find the hottest cylinder (or EGT if you don't have an engine monitor), you richen the mixture till the temp changes another 50-100 degrees.

In the video I watched to learn about how to do it on the G1000nxi he told the opposite, lean of peak from the coldest cylinder and rich of peak from the hottest (although he showed it on the Bonanza G36, but I guess the engine logic will be the same). (The video was: https://www.youtube.com/watch?v=Q4w7jkJakQM&t=289s )

Is the correct procedure not described in any POH or other something other like company manuals or such ?

 

2 hours ago, Bobsk8 said:

In real life, I never flew a C 172 with an EGT gauge.  I just leaned it out, until the engine sounded rough or rpm slightly dropped, and turned it towards rich until it smoothed out. 

So the danger to damage the cylinders because of wrong temperatures isnt that high ?

That's probably correct.  Like I said I'm not expert and it's something I haven't really mastered.  Anytime I fly it's basically big mixture pull but I need to learn how to really make the engine efficient.

15 minutes ago, Rucki said:

So the danger to damage the cylinders because of wrong temperatures isnt that high ?

Biggest potential for damage is shock cooling the engine on rapid descents.

22 minutes ago, Rucki said:

So the danger to damage the cylinders because of wrong temperatures isnt that high ?

I own 172 for many years. We lean aggressively even during taxi.  Most 172 I get to fly and instruct don't have EGT gauges and using method described by Bobs8 is widely used. I can recall a case when it  damage O320. However, exceeding max RPM (which happens with certain kind of props)  does overstress and damage cylinders. I had to deal with that kind of thing, and eventually after engine overhaul change propeller  to prevent it from happening again (average renter usually doesn't care about airplanes or engines ) 

Here’s some interesting info https://airplaneacademy.com/engine-leaning-using-egt-rich-of-peak-vs-lean-of-peak/

3 hours ago, sd_flyer said:

I own 172 for many years. We lean aggressively even during taxi.  Most 172 I get to fly and instruct don't have EGT gauges and using method described by Bobs8 is widely used. I can recall a case when it  damage O320. However, exceeding max RPM (which happens with certain kind of props)  does overstress and damage cylinders. I had to deal with that kind of thing, and eventually after engine overhaul change propeller  to prevent it from happening again (average renter usually doesn't care about airplanes or engines ) 

When I flew a C 172, which was on lease back by a dentist, I flew it like it was my own. I loved flying that aircraft.