Lean of Peak

[Gutenberg]

For us piston drivers out there. A Lancair factory instructor was teaching one of my students to run aggressively lean of peak (100 degrees lean of peak at 85 percent power) with only a single needle-type gauge for CHT. I was under the impression that this can be a dangerous practice without using tuned injectors and a JPI style engine monitoring system.

At 85 percent, I would think that while passing through peak EGT, there might be some serious detonation going on.

Your thoughts...

 

[Dangerkitty]

For us piston drivers out there. A Lancair factory instructor was teaching one of my students to run aggressively lean of peak (100 degrees lean of peak at 85 percent power) with only a single needle-type gauge for CHT. I was under the impression that this can be a dangerous practice without using tuned injectors and a JPI style engine monitoring system.

At 85 percent, I would think that while passing through peak EGT, there might be some serious detonation going on.

Your thoughts...

I do know that the Cirrus folks (especially the ones with the glass cockpits) are BIG into running their engines Lean of Peak. They state that the engine actually runs much cooler and it is better for the engine. I never fully understood the concept but I didn't read into it all that much.

I do know that there is a group of Mechanics and Piston Engine Experts that run a class in Ada, Oklahoma. The Cirrus pilots highly reccommend it. Evidently these guys will change the whole way you think about and operate high perfomance piston engines.

I forgot the name of the class but I do know that they have a website. If you go to www.cirruspilots.org and ask on the public side of the site I am sure they can direct you in the right direction.

 

[mtrv]

Evidently these guys will change the whole way you think about and operate high perfomance piston engines.

This falls into the catagory of what causes lift, and the power/pitch debates. Lycoming is NOT a fan of leaning past peak, and as previously mentioned, fuel injection is required over a carb setup for more even temps; in addition to needing EGT readings for each cylinder. You could still have just one gauge, if there is a rotory type switch to select between single cylinders.

I personally think the pro's & con's of leaning past peak will go on forever. Because that's exactly what it is, a bunch of pro's & con's.

 

[GravityHater]

I believe the restriction is more like you have to be <65-70%HP; LOP and 85%HP can result in engine damage.
The other important thing you need is not individual egt, so much as individual CHT - because you also cannot do LOP if any one cylinder is going to run outside the max operating range. Many are limited by mfg at 450F but I wouldn't go LOP if any cylinder was >375F.
The thing to read is articles by a guy named Deakin on Avweb.com.

 

[Gutenberg]

yea deakin, been through them all about three times.

 

[mar]

Leaning and CHTs

They state that the engine actually runs much cooler and it is better for the engine. I never fully understood the concept but I didn't read into it all that much.

Obviously a richer mixture cools CHTs. And CHTs will rise while leaning to peak EGT. But if you continue to lean the engine will, let's say, "loose power" and actually result in lower CHTs.

It won't necessarily result in detonation but obviously enrichening the mixture before an application of power is pretty important.

I probably follow the Rep's advice, they usually know best.

 

[Dangerkitty]

Like I said I really dont understand it but I have been flying piston's very very very rarely the past 10 or so years.

I prefer turbine.

 

[Bryan D]

Lop Or Pol

I believe the restriction is more like you have to be <65-70%HP; LOP and 85%HP can result in engine damage.
The other important thing you need is not individual egt, so much as individual CHT - because you also cannot do LOP if any one cylinder is going to run outside the max operating range. Many are limited by mfg at 450F but I wouldn't go LOP if any cylinder was >375F.
The thing to read is articles by a guy named Deakin on Avweb.com.

Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.

 

[PeteCO]

Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.

Not if you have precise enough fuel control. By definition, lean of peak EGT is also cooler than peak EGT, yes?

 

[GravityHater]

Do you mean "lean of peak" or "peak of lean"? If you lean after peak ("lean of peak") you could burn a piston or valve.

That's the myth these folks have been busting for the last 5-10 years... lean of peak (LOP) in SOME circumstances, if done correctly, IS safe for your engine and will NOT result in burned valves if you follow all the caveats.
In fact they say it is a better way to run some engines.

I used to violently resist this philosophy too until I did some learning about it! It seems it is less of an opinion now.... they have developed some pretty good science to back it up.