Mixture Control

[kkrummy1]

What is the current concensus on proper leaning? I was taught to lean to peak EGT and then richen about 10 degrees. Now my friend tells me that's wrong and that leaning to peak and leaving it there is better. I have heard some say lean to 10 degrees lean of peak on the EGT.  So! what's the correct answer if there is one?

[Baradium]

It depends on what aircraft you are flying,  which engine it has, and what kind of operation you are doing.

Not all engines have procedures published for lean of peak operation.  Lean of peak also is harder on the engine.


If you are doing a high power cruise you would likely want rich of peak operation for power output and ease on the engine.

If you are trying for long range cruise you are more likely to want to use closer to peak EGT.  But you will want to check the POH for your aircraft for the recommendation as well.

Some newer aircraft recommend lean of peak operation.  This does reduce fuel consumption, but as I said before is harder on the engines and some engines do not handle it as well as others.

So in other words, all three can be "proper"  although I'm not completely sold on the whole lean of peak thing.  I like to baby my engines.  The idea is that by the time you have to do an earlier overhaul you saved enough in fuel to more than make up the difference.


I have been away from the piston world for a while, but I'm sure someone will chime in if I got anything off.

[Turbomallard]

Some of that depends on what brand of engine you are flying... in articles I've read it seems like Continentals like lean of peak, Lycomings don't. But, overall, having read a bunch of articles on this over the last few years, I'd say that the consensus is that... there's no consensus.   

TM

[Rooster Cruiser]

TurboDuck is correct:  There is no consensus.  Recommended engine operation varies from engine to engine, and installation to installation.  The first place to go to for guidance would be the AFM or POH for the airplane.  If there have been aftermarket additions, like turbochargers, GAMIngectors, etc, then consult with the modifier's operations practices that have been added into the POH.  An even better reference would be the mechanic that works on the airplane and gives it annuals and oil changes.

Under no circumstance should you simply operate according to whatever "Joe Schmoe" said to you over a cup of coffee at the airport cafe!  If their advice is incorrect and you destroy an engine in flight, the FAA will probably blame you (i.e.:  Pilot Error) instead of mechanical failure.  That can lead to enforcement action against your pilot certificate(s) and a possible denial of insurance claim for not following manufacturer's recommended operating practices.

Happy Flying!

RC

[Mike]

It's been a while for me with the pistons but:
It can't be bad for the engine to run fat, right?
Too lean and you're dealing with heat/lubrication/and so forth but if you want to be on the safe side you can't go wrong with not leaning (at the expense of performance of course but strictly looking at engine health)....

[Fabo]

You could "drown" the engine if the mixture is way too rich....

[Baradium]

It's been a while for me with the pistons but:
It can't be bad for the engine to run fat, right?
Too lean and you're dealing with heat/lubrication/and so forth but if you want to be on the safe side you can't go wrong with not leaning (at the expense of performance of course but strictly looking at engine health)....

Too rich can almost be as bad as too lean.

You'll burn more fuel and more importantly foul your spark plugs.     You'll get less power and the fouled plugs will decrease it further.   A bad thing whether you're on a cross country or doing touch and goes. 

You should always lean some, the question is how much.  Conservatively rich of peak would be the way to go.

[chuckar101]

It's been awhile for me as well.  But what I remember is like everyone says.  Check the aircraft AFM.  I do know on the large Lycomings that I flew the most, we operated just rich of peak.  This gave us the best cruise and helped keep the turbochargers clean.  I know when operated to rich you would foul not only the spark plugs but could jam up the waste gate.

[Mike]

AHA! Looks like I learned something as well.
Thanks guys. Makes a lot of sense.

In the piston helicopters we flew we rarely leaned them because of the clutch. You're risking the engine just quitting rather than running rough if you didn't lean right although we leaned a little by feel. And fouled plugs are quite common in helicopters. So there you go.....