Question When to use Lean of Peak (LOP) Lycoming engines, and maybe others?

[Neal]

I'm curious on when people use lean of peak vs. not. In my last FX-3 I had situations where the engine would hiccup as discussed in another thread below and catch my attention. My new FX-3 has done this the first time about two weeks ago and I think I discovered the trend. I'm typically just enjoying some low power ops and droning around I'd say around 70-80 or better put, between 18 and 20 squared. It seems what I am finding is running LOP at lower power may not be the right thing to do and may be the reason I'm seeing these hiccups - it's too lean for this power setting? So what my plan is going forward is to just run full rich if doing low power cruising around and use LOP for higher power cruise such as anything over 21 squared. I guess I could simply go to lean of peak and then enrichen some amount and probably prevent this but I don't want to end up in that bad area called red fin or whatever it's called where you're not supposed to be.

What is your opinion and or practice as to when to use Lean of Peak and any techniques for what you use for mixture settings and when?

 

[midlifeflyer]

At the low power settings you are talking about, there is no “Red Box” or “Red Fin” (two different depictions of the same concept). It pretty much disappears at about 65% power and below. See, “Red Box, Red Fin,”

I”m not familiar with the FX3. Does it have engine monitoring which gives the EGT & CHT for each individual cylinder? If not, you may be better off leaning the old fashioned way. Leaning to engine roughness and then enrichening to smooth operation is a good LOP approximation. In more than one type, I’ve gotten the same result using either high tech “lean assist” and low tech “rough to smooth.”

 

[Neal]

Does it have engine monitoring which gives the EGT & CHT for each individual cylinder?

Yes it does. Good point on the red fin/box - I forgot that and even attended a great session at EAA AirVenture last year on this. It turns out the Garmin LOP practically aligns with the old way of leaning, so pulling until rough or RPM drop will get you in the same place. I just wonder how lean (of peak) I should be for low power ops.

 

[midlifeflyer]

Yes it does. Good point on the red fin/box - I forgot that and even attended a great session at EAA AirVenture last year on this. It turns out the Garmin LOP practically aligns with the old way of leaning, so pulling until rough or RPM drop will get you in the same place. I just wonder how lean (of peak) I should be for low power ops.

Completely unscientific answer. Just impressions. And bear in mind that I was based for 20 years in Colorado where we never went full rich in a normally aspirated airplane that didn't have some altitude compensation capability.
My sense is that for low power ops, it doesn't matter so long as the engine runs smoothly. Fuel flow is low so you are not getting that much in the way of savings from being 1-2 GPH too lean or rich. At low power you are running cool so not red box - high CHT (and associated cylinder pressures) is just not an issue. Spark plug fouling with a too-rick mixture is probably more significant, although a few GPH plus or minus isn't going to matter that much.

 

[Neal]

Agree, makes sense. My only concern is the spark plug fouling as I even lean during taxi (pull to about a 10-20 RPM increase). I'm at sea level here in VA.