Leaning..

ccsmith51 · #1 03-12-2011, 07:04 PM

Recently there was a discussion on leaning for slow flight. A question was posed about leaning until the engine stutters, then going rich until smooth operation.

What is actually happening when the stutter happens? Is it detonation from a very lean condition in one or more cylinders? Or it it just one or more cylinders not firing because it (the) are so lean it (they) cannot support combustion, therefore a "rough" running engine?

BTW, I made my second flight in my RV-4 today. What a dream machine!! At least until it is time to land. I have a LOT of work to do to learn how to keep her strait after touchdown...

Chris

Ironflight · #2 03-12-2011, 08:29 PM

Quote:

Originally Posted by ccsmith51

........ Or it it just one or more cylinders not firing because it (the) are so lean it (they) cannot support combustion, therefore a "rough" running engine?

That's what I have always found it to be. I flew for decades with no EGT or CHT instrumentation (we all did back then...) and leaned this way - pull until it's rough, then smooth it out. I now have all sorts of instrumentaiton and EGT graphing in realtime - and I get to the exact same fuel flow if I do it by ear and feel or by watching the data. Engines are still engines....

Paul

John Clark · #3 03-12-2011, 09:43 PM

Quote:

Originally Posted by Ironflight

That's what I have always found it to be. I flew for decades with no EGT or CHT instrumentation (we all did back then...) and leaned this way - pull until it's rough, then smooth it out. I now have all sorts of instrumentaiton and EGT graphing in realtime - and I get to the exact same fuel flow if I do it by ear and feel or by watching the data. Engines are still engines....

Paul

Engines are, indeed, still engines. Although, after spending the time to carefully balance the injectors in my IO-360, I seem to have created an interesting situation. Leaning in cruise it never really gets rough, it just starts to smoothly lose power when the mixture is pulled too far.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

gasman · #4 03-12-2011, 10:32 PM

Quote:

Originally Posted by John Clark

Engines are, indeed, still engines. Although, after spending the time to carefully balance the injectors in my IO-360, I seem to have created an interesting situation. Leaning in cruise it never really gets rough, it just starts to smoothly lose power when the mixture is pulled too far.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

And this is what I don't understand......... This is exactly what happens when I lean my O320...... except I have a carb............

pierre smith · #5 03-13-2011, 05:18 AM

...in my -10, since we balanced the injectors.

The engine is just not making the power that it does when ROP, according to a power chart that someone had on here several weeks ago....the ICP (internal cylinder pressures) drop off, after peak during leaning and continue to do so until 50 deg LOP.

My -10 loses around 8-10 MPH from 50 ROP to 50 LOP but my fuel consumption also goes from 14.5 GPH down to 11.4 GPH.....or $15/hour savings. Do the math for an engine that'll run 2,000 hours.....$30,000 saved, more or less.

Best,

DanH · #6 03-13-2011, 08:09 AM

Quote:

Originally Posted by ccsmith51

What is actually happening when the stutter happens? Is it detonation from a very lean condition in one or more cylinders? Or it it just one or more cylinders not firing because it (the) are so lean it (they) cannot support combustion, therefore a "rough" running engine?

Probably not "cannot support combustion" but rather "cannot reliably ignite" a lean mixture. Pilot reports seem to suggest smoother LOP operations with any electronic ignition able to run wider plug gaps and/or deliver a longer duration spark. They also seem to be able to lean much further than 50 LOP.

nucleus · #7 03-14-2011, 09:15 PM

Have dual Pmags with the Iridium NGK Plugs, haven't balanced my injectors, the leanest cylinders will run smoothly 80-90 degrees lean of peak, which is about 15-20 degrees leaner than with the regular NGKs.

Hans

java · #8 03-15-2011, 12:37 AM

When I bought my 6, it had a simple, non-vernier mixture cable. I found it impossible to fine tune the mixture. I had it changed out on a recent annual for a vernier cable, and in a couple of flights since then have found my fuel burn to be down by almost a gallon an hour. That red knob does have it's uses!