Do you prefer a video explanation? See this superb summary from Martin Pauly; it's so clear and so well done that it's added here 15 years after the original article was published. It's 25 minutes, but absolutely worth the time.
Keeping it simple... Sometimes we make aviation techniques
harder than they need to be. So, if you dont have
the JPI data-trapping engine monitor....or even if you
have only the standard factory nozzles... this may help:
The following correspondence came from our in response
to a question from David, a Baron C55 owner (IO-520CB's
285 hp engines with GAMIjectors and a factory single-needle
EGT gauge). His GAMIjectors were installed but not further
adjusted as he has no engine instrumentation with which
to have done so. He was worried about how to try running
on the lean side of best power without a full engine
I said: Hello David, If you are above 8000
feet MSL there is NOTHING you can do with the mixture
levers that will hurt the engine. The altitude alone
will protect the engines as you can not possibly develop
more than 65% power. Remember the information that came
with your GAMIjectors? It says something like:
"CHT must be above 450F AND POWER must be above
65% for detonation to occur. No aeronautical powerplant
engineer differs with that statement."
So - even with the factory single needle EGT instrumentation
- at altitude, get set up for cruise, then pull the
mixtures back till the plane slows just a bit...you
can easily feel it...you HAVE to be LOP at that point
and you don't need any gauges to do that. A
friend of mine did it successfully on his first ride
in my JPI-equipped Baron with his eyes literally closed. He came within 1/2 GPH of being perfect on his first
try, then nailed it the second time. It's easy. Good
From David: Thank you for the FIRST real world
tip on what to do. -David
Later, David was discussing whether his injectors were
properly balanced, (he could not be certain because
he did not have a full engine monitor). He asked:...well,
I don't know that my injectors are properly balanced,
except that the engines run smooth when lean of peak.
Old Bob Siegfried (retired UAL and a Lifetime
Achievement Award winner from the American Bonanza Society)
commented: Good Evening David, If you can lean
it enough to get at least a ten knot drop in airspeed
before they get rough, the fuel/air distribution is
plenty good enough to run lean of peak EGT. That is
how we checked in the days before we had all the fancy
instrumentation!" "Old Bob flew heavy
piston airliners for a living, and has also attended
the in Ada.
If it does run smooth that far lean of peak EGT,
all you need to do is lean it enough to ascertain a
knot or two drop in airspeed and it will be just fine.
Fact is, you don't even have to be able to hold a stable
airspeed. If the air is too rough for that, just lean
one engine at a time. Lean one engine until you just
note that it has lost a little thrust. (The airplane
will then be slightly out of trim). Then lean the other
engine until the aircraft is back in the same trim it
was before you started the leaning process. In the old
days, we called that power leaning.
No need to look at the EGT gauge at all.
Remember, it is a two part process. Leaning for
a ten knot drop in airspeed should be done as an occasional
test to determine whether or not the mixtures are still
well balanced ... to discover any problems such as a
plugged injector. It is not necessary to do the ten
knot test every time you fly. Once you know that [all
is well], there is no reason to run that lean unless
you just prefer to.
In routine flight operations, if you lean until you
can feel a little power loss, you will be on the lean
side of best power. As long as you are above 8000 feet,
you can even run at best power (80F ROP) all day long
with no trouble at all. If you do have good CHT gauges,
it would be best to lean it enough such that the heads
stay below 380 F.
Parenthetically, 6500 MSL is probably OK with
a conforming engine. But if the timing is off or the
ambient temperatures high, 6500 MSL may be marginal.
At 8000 MSL there is no possibility of problems at all.
So, 6500 MSL is the absolute minimum altitude that this
old crude method should be attempted, but at 8000 MSL
or higher, you can do almost anything you want!
The primary advantage of all the fancy engine
monitor instrumentation is for
your education and to help in trouble shooting the
engine if things are not going well. If everything is
working as it should, leaning by feel works fine.
-Happy Skies, Old Bob
From Tom, in a Beech Debonair, who asks: Would
the 10 kts idea be the same for a Debbie also, or is
a smaller airspeed reduction appropriate? -Tom
From Old Bob: Good Evening Tom. Same deal. Remember,
the more engine instrumentation, the better. Without
a full monitor, the ten knot reduction is just a way
to check things. It was all we had fifty years ago,
but if the engine gets rough, we have no way of telling
why. With a full monitor installed, we can quantify
things much closer and we can tell where to look for
the troubles. -Happy Skies, Old Bob
So, where did "Old Bob" Siegfried learn all
this? He said My comments are directed primarily
to procedures used with General Aviation airplanes that
are not as well equipped as the later piston airliners.
I first started running my personal aircraft on the
lean side of best power after I was exposed to such
operation by my early pre-airline training.
This power leaning technique in a twin was first shown
to Old Bob by his boss when he was flying
Bamboo Bombers before he went to work for UAL. After
hiring on at the airline, he learned that it was also
used by the older, prewar, UAL DC-3 captains, but was
not taught by the airline company or generally used
by the WWII trained pilots. These power leaning techniques
were primarily used on engines that were not very well
instrumented and then only by pilots who had a bit of
experience and training well beyond that supplied by
the military or UAL.
Any questions? just give me a call, or click on the e-mail link below