Why The Aversion To Leaning Engines?

Geico266 · #1 08-22-2008, 06:45 AM

Why is it some pilots just don't want to lean their engines?

This came up in a "hanger flying" conversation a few weeks ago, and again last night. A buddy has a nice Velocity with a 300 HP Continential. It loves fuel, and he was complainging about operating costs. When I asked him about running LOP he turned white. When I told him how to set it up he got interested and went flying to try it out. His CHT's dropped from 400F to 300F, EGT's dropped from 1450 to 1375. His oil temps dropped from 210F to 185F, his fuel flow dropped from 13 GPH to 10GPH. (He LOVED that part

) and he was still flying at 170knts.

Others I have bought planes from have said they NEVER leaned the engine out. Just "no need to", or "never tried it".
Is this an old habit mislearned from student days? I just don't get it.

What all have you been taught about leaning -vs- how you fly today? Is it instrumentation that allows us to "see" what is going on more? Fear of detonation? Preignition?

We can all do our part to fly GREEN!

<----- Did you notice little green face?

Tomasz · #2 08-22-2008, 07:43 AM

Quote:

Originally Posted by Geico266

Others I have bought planes from have said they NEVER leaned the engine out. Just "no need to", or "never tried it".
Is this an old habit mislearned from student days? I just don't get it.

I sure can't speak for others, but on one of my first lessons my CFII told me to 'lean her a little bit, it's hot out there'. Sure, we didn't do it for fuel efficiency, but I'm no longer red knob shy :-)

Geico266 · #3 08-22-2008, 08:06 AM

Quote:

Originally Posted by Tomasz

Sure, we didn't do it for fuel efficiency, but I'm no longer red knob shy :-)

Red Knob Shy. That's it! Becuase it's a red knob it scares newbies. We should make it GREEN to save fuel!

JDRhodes · #4 08-22-2008, 08:26 AM

I agree. Read Mike Busch's articles on avweb. Big LOP proponent.

I had CFI's in my student days and even advanced CFI's later - after I knew better - that said run FULL RICH below 5000 feet or you'd burn up the engine.

I've also seen that same CFI who cut a lesson short and brought the airplane back because it was running rough at 5,000 feet. Full rich - go figure!

DaX · #5 08-22-2008, 08:38 AM

Forgive my newbness for showing, but LOP = Lean XXX XXX?

airguy · #6 08-22-2008, 08:41 AM

You're exactly right - it's because the don't know how.

In the absence of true knowledge, rumor and hearsay become fact, and there is no shortage of folks willing and eager to tell you that you are going to die instantly if you touch the red knob. We've all the heard the horror stories (and there is a grain of truth in them, to be fair) about trashing engines with poor leaning technique. The instrumentation and knowledge of how to do it takes the boogeyman out of the closet, and makes it very simple to do in a safe manner. A little education and couple of gadgets can go a long way.

JDRhodes · #7 08-22-2008, 08:48 AM

Quote:

Originally Posted by DaX

Forgive my newbness for showing, but LOP = Lean XXX XXX?

Lean of Peak. By leaning the mixture in cruise, the cylinder head temps are brought to peak temperature and then leaning continues until the CHTs come down to a point usually 25-50 degrees below peak, but on the lean side of the curve.

As opposed to ROP - rich of peak - which is probably what your CFI taught you.

Geico266 · #8 08-22-2008, 09:12 AM

Quote:

Originally Posted by DaX

Forgive my newbness for showing, but LOP = Lean XXX XXX?

Don't be afraid of LOP (Lean Of Peak) but certainly study it before you try it. It is more difficult with a carburated engine as the fuel is not even't disbursed into the cylinders, loke fuel injection. There is a science to it, and a lot of history behind it. It was very instrumental in winning WWII. Interesting stuff, to me anyway.

jtrusso · #9 08-22-2008, 09:17 AM

Quote:

Originally Posted by Geico266

Why is it some pilots just don't want to lean their engines?

What all have you been taught about leaning -vs- how you fly today? Is it instrumentation that allows us to "see" what is going on more? Fear of detonation? Preignition?

For me know I'd say the biggest challenge to really leaning it out (has to be ROP though, I'm flying a carb) is the lack of engine instrumentation. The most advanced engine instrumentation I've ever flown with is an EGT gauge, and the planes I'm flying now don't even have that. So for me, knowing what I know from reading this forum, I lean it out till it gets rough and then give it about 1/4 to 1/2 a turn back in. It keeps the oil temp in the green, but the fuel flow seems high with this technique. I'm burning about 9gph in a 150hp C172.

I was taught to leave it full rich below 3000agl, and then when leaning it out quicly turn the knob back in till the RPM's peak after you hit the engine roughness. The CFI would freak out if you didn't start spinning it back in quickly enough, saying that we were "trashing" the engine. To get pack to peak RPM's it usually takes about 1 to 1 and 1/2 spins of the red knob.

scard · #10 08-22-2008, 09:20 AM

Quote:

Originally Posted by JDRhodes

Lean of Peak. By leaning the mixture in cruise, the cylinder head temps are brought to peak temperature and then leaning continues until the CHTs come down to a point usually 25-50 degrees below peak, but on the lean side of the curve.

As opposed to ROP - rich of peak - which is probably what your CFI taught you.

Just to be clear, I'm sure Jeff meant EGTs. Leaning to, and beyond, "peak" is done by reference to exhaust gas temperatures.