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  Simple Lean of Peak According to John Deakin (Even a Caveman Can Do It!)

John Deakin's Simple "Lean of Peak" or "Green of Peak - GOP" Instructions he provided to a Beech Lister:


Keep it simple, folks.


At Fred's 8,000 to 10,000' (good training altitude, you can't hurt the engine with the mixture control there), engine and airplane well-stabilized (so you can see changes), set wide open throttle, high RPM, and do the BMP (Big Mixture Pull) by FEEL. Grab the mixture knob, close your eyes (I am not kidding) and pull, and FEEL the slight deceleration as the HP drops off a little on the lean side.

Important! You have to move the mixture quickly enough to make the change in power obvious, but not so quickly that you overshoot and kill the engine (won't hurt anything if you do, just move it back in a little until power is restored). Five seconds from full rich to the desired point is too long, two three seconds is about right. It's not going to throw you forward into the panel <grin>, but it's pretty distinctive. You ever ride with someone in a car who is constantly jiggling the gas pedal? Those little accelerations and decelerations that eventually drive you nuts? THAT'S the feeling you're looking for.


Most absolutely NAIL it, the first time, and leaning is done. If you're really curious, or you're gathering data, or it's your first few times, then read on.


Let that settle down a bit (five minutes?) and then see how you did by enriching ever so slowly to find peak. No, REALLY slowly, sneak up on it. The EGTs should rise of course, and in the very sensitive NORMALIZE mode, it will be obvious when one column of bars stops rising (peak) and starts falling (meaning you've gone over to the dark side on that cylinder). DO NOT use the "Lean Find" feature, it's much too crude for this. Re-lean until that EGT rises to peak again, and a hair more to see "any drop," and you're there.


Further testing: Note the fuel flow at peak EGT on the first cylinder to reverse (your richest cylinder) and keep going (richer), noting the FF at each peak. Quick and simple GAMI Lean Test, with the advantage that you're starting on the lean, green, cool side, and not leaning through "The Red Box."

Once you know it works, and your cylinders all peak at close to the same fuel flow, on future flights all you need do is the BMP, and done. If you lose a couple of knots, you know it's "right."

Once you have confidence in this technique, you can do it in any airplane, even without a monitor. If normally-aspirated, you should also see a very slight loss in airspeed, perhaps 3 knots.




Excellent Lean of Peak Video by Bonanza Owner Martin P.




HERE is an article by Mike Busch on why NOT to obsess over EGT numbers for leaning.



Here's an engine leaning technique for those without an engine monitor, from Old Bob, Beechcraft Maven and Ancient Aviator. Offered on the Beech List on 9/22/2009:


Old Bob


"Don't be afraid of LOP without engine monitor data. As long as you keep the power below 65% there is no way you can hurt your engine with the mixture control. A quick and easy way to see how well balanced your old injectors are is to set up at seven thousand feet with full throttle and whatever you like to use for cruise. 2300 is always a nice number.


Lean one engine at a time and note the power loss. if you can get a pretty good yaw before the engine gets rough, the distribution is not bad at all.


You may have seen my recommendation at other times as to how to do this with a single engine airplane. As long as you can get a ten knot decrease in speed before the onset of roughness, you can comfortably lean to a five mph drop in speed and be running lean of peak EGT in perfect comfort.


The advantage of having the six cylinder EGT is that you can tell what each cylinder is doing. That IS very important, but don't let the lack of an engine monitor stop you from checking how good your current distribution is working.


Long before our modern instrumentation was available, we always leaned by power loss.

On a twin. we would lean one engine until the airplane was just a bit out of trim then lean the other engine until the airplane was back in trim.


Once again, if the engine or engines get rough before any power change is noted, the distribution is horrible and tells you you need the proper instrumentation so that you can analyze just what is happening. There is no mystery involved and we have been leaning these engines comfortably for as long as engines have powered airplanes."



Bob Siegfried

Ancient Aviator

(630) 985-8502

Stearman N3977A

Brookeridge Air Park LL22