[Leonard_Smith_nz]

All,

I've been following the discussions on LOP operation and it's been very enjoyable and educational reading. What I'd like to consider for a moment is leaning for 'carbureted', single CHT/EGT setups. In my case I own a RV6 with a new TMX O-360, assembled by the kind folks at Mattituck, NY. (Free beer to New Zealand, Mahlon!)

During initial flight training I was taught: Above 3000ft lean to roughness and then enrich the mixture by 3 turns. A more senior instructor later told me to lean to peak EGT and then enrich by 50 degrees.

I'd like to get some thoughts on the safe leaning for my motor. I'm not concerned in running LOP, just want to verify what I've been taught. I'm aware that some bright minds have researched these areas extensively, but I cannot find that much information related to the basic setup I have.

Any advice and opinion appreciated.

Please limit comments to the setup that I currently have. It's not going to change in the next few months. Right now I want to FLY!

 

[vlittle]

Leonard, you will probably get a hundred opinions.

Start with this one:

Lycoming Reprint

Vern Little

 

[Ted Farmin]

Leaning

I was told by a major engine rebuilder that with the gas that we have
today you should lean to peak and then richen 100 degrees egt. He has
seen a lot more of cracked cyls. from people leaning to peak that he
has quiz'd on how they opperate thier engine.



Ted
___________
wiring the Dynon

 

[gmcjetpilot]

From Lyc

All,

I've been following the discussions on LOP operation and it's been very enjoyable and educational reading. What I'd like to consider for a moment is leaning for 'carbureted', single CHT/EGT setups.

What an elegant and diplomatically stated thread.

What Jug is the EGT on, and how did you determine it? (#3 followed by #4 is popular, sometimes #2?)

After you figure out your EGT is correct you can just lean to peak and enrichen to 100F ROP or what ever you want. I personally go with a schedule:

75% power 100 ROP
65% power 75 ROP
55% power 50 ROP
50% power peak

At 55% power you probably are at higher altitudes and need all the pwr you can get, so lean for best power (max RPM/airspeed or 100F ROP). Key is lean below 75% power and smoothness.



IS YOUR EGT ON THE LEANEST CYL?
There's an assumption your EGT is really on the "First to peak" cylinder; until you have done a flight test and determined this you are guessing a little. Of course with NO EGT you are guessing, but that has also worked for many decades. The 1st to peak changes for differnet altitutudes / power. Certainly with a Carb, the 1st to peak cylinder changes with throttle position, therefore making it very difficult, or perhaps impossible, to choose a best cylinder for probe installation. We'll assume we are always talking WOT below 75% power.

Lycoming recommendations, without a EGT, described in the Ref below, aka the roughness method, is lean to roughness and slowly push the mixture in for smoothness for Econ. For best power use the tachometer or airspeed indicator to determine best power. Lycoming says you can refine these methods if you have an EGT gauge, as you do:

"if the EGT probe is installed, lean the mixture to 100oF on the rich side of peak EGT for best power operation. For best economy cruise, operate at peak EGT. If roughness is encountered, enrich the mixture slightly for smooth engine operation."​

NOTE: Lycoming assumes your single EGT instrumented to the first to peak cylinder. Also they don't mention 50F ROP. Look at the graph shown in the Ref below you can see 25 ROP gives the highest CHT. 50F is a little too sporty for me, unless I am lower power.



During flight test consider using the roughness method, lean to rough and slowly enrichen to smoothness. Note EGT at peak, rough and than back at smooth. After noting peak, lean further to see the drop on the LOP side to roughness and note that change. Then enrichen to smoothness and again note the change in EGT. Always wait for the EGT gauge to stabilize. Take your time.

If you get roughness well before the EGT peaks you probably don't have the 1st to peak cylinder instrumented. Consider switching EGT gauge. This is what flight test is all about.

NOTE: Pick ONE flight condition every time, such as WOT AND BELOW 75% POWER; You'll need to fly at least to 8,500-9,500 density altitude. I assume you have both RPM & MAP to determine your approx % power. If you don't have MAP consider getting one, even with a fixed prop.


Here are some references: Lycoming leaning, EGT gauge

PS: Some will adamantly tell you, YOU can fly LOP even with this single EGT gauge configuration. That may be true with cracking the throttle, carb heat and so on, in theory. If you are down in the 65% or less range you can't really hurt it, but for this discussion we stuck to the traditional (Lycoming base line) method of leaning.