Engine mixture guidelines

The initial lean should be very quick. It's called the "Big Pull." Fine tune as slow as you need to. You need to avoid the red box, that's why you lean quickly.

I've only heard of a red fox, not a red box. What is that?

In general, I lean to a bit richer than I ought to be, and then after it
stabilizes, I lean from there. But if you overshoot, that's not good.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

What really happens when you go towards peak EGT is you're assuring a
pretty efficient burn inside the cylinders, the exhaust contains little
unburnt fuel and little oxygen. If you play a little with the mixture
when prop and throttle are firewalled you'll probably pick up some RPM,
even at low altitudes. It's especially noticable on hot days.

In cruise with constant speed props the prop pitch changes a little,
taking a healthier bite of the air so as to use the additional power.
CHT is a simple way of measuring what's going on -- it's telling you,
as you go from rich to lean, when you're getting the hottest -- call
that best -- internal temps. Since the fuel (I was taught) helps in
cooling, you want not to overlean so as to save the valves. That
statement probably deserves some research -- why not run schiometric
(I'm sure I mis spelled that) combustion? Does anyone know for sure?

For that matter, if you do get peak power at max EGT, why run on the
rich side? Wouldn't it make sense in terms of fuel economy to run on
the lean side a bit?

I know the dogma, what I'm interested in is the justification. Any
powerplant engineers out there?

For that matter, if you do get peak power at max EGT, why run on the
rich side? Wouldn't it make sense in terms of fuel economy to run on
the lean side a bit?

I know the dogma, what I'm interested in is the justification. Any
powerplant engineers out there?

Google "lean of peak". There is a company out there (whose name escapes
me right now) that makes engine gauges that are supposed to be so good
you can run LOP safely. The issue is that =at= peak, the temperatures
get too hot in the cylinders, and if you don't run cool enough in the
one cylinder that is being measured by the ordinary gauges, you are
likely to be running too hot in at least one of the others.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Jose wrote:



Google "lean of peak". There is a company out there (whose name escapes
me right now) that makes engine gauges that are supposed to be so good
you can run LOP safely.


It's not the gauges, it's the fuel distribution. In order to run LOP
effectively each cylinder must peak at the same, or damned close, fuel
flow and therefore at the same time.

It's not the gauges, it's the fuel distribution. In order to run LOP effectively each cylinder must peak at the same, or damned close, fuel flow and therefore at the same time.

Yep, you're right. And this usually requires an engine mod, since stock
airplane engines are not very uniform. In any case, don't these mods
also come with a gauge for each cylender?

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.

Jose wrote:
It's not the gauges, it's the fuel distribution. In order to run LOP
effectively each cylinder must peak at the same, or damned close, fuel
flow and therefore at the same time.


Yep, you're right. And this usually requires an engine mod, since stock
airplane engines are not very uniform. In any case, don't these mods
also come with a gauge for each cylender?


No, the GAMI's are six injectors that replace the standard six. They
reccomend an engine monitor but it's not necessary. As it happens I can
run real nice LOP without having to buy the GAMI's.

"Newps" wrote in message
. ..


Jose wrote:
It's not the gauges, it's the fuel distribution. In order to run LOP
effectively each cylinder must peak at the same, or damned close, fuel
flow and therefore at the same time.


Yep, you're right. And this usually requires an engine mod, since stock
airplane engines are not very uniform. In any case, don't these mods
also come with a gauge for each cylender?


No, the GAMI's are six injectors that replace the standard six. They
reccomend an engine monitor but it's not necessary. As it happens I can
run real nice LOP without having to buy the GAMI's.

It's been much too long since I've known, and I'm too lazy to look it up on
New Year's Eve, but aren't GAMI injectors usually installed using an engine
monitor to obtain the best match for each injector and cylinder combination?
After the inital shop work with an analyzer/monitor, the use of an engine
monitor by the aircraft operator is recommended, but not required--exactly
as you stated.

BTW, I've always presumed that the advantage of a set of GAMI injectors was
simply that they guaranteed a matched set; but you could also have a
similarly matched set of stock injectors by carefull selection from a
sizeable batch, or simply by fortunate happenstance. Is this your real
world experience, or are you basically using the "hottest cylinder" method,
or both?

Peter

Tony writes:

For that matter, if you do get peak power at max EGT, why run on the
rich side? Wouldn't it make sense in terms of fuel economy to run on
the lean side a bit?

Aside from the most fuel-efficient mixture settings, which settings
are the _safest_? Which settings put the least wear and tear on the
engine?

--
Transpose mxsmanic and gmail to reach me by e-mail.

Jose wrote:

The initial lean should be very quick. It's called the "Big Pull."
Fine tune as slow as you need to. You need to avoid the red box,
that's why you lean quickly.


I've only heard of a red fox, not a red box. What is that?



At and below 60% there is no red box, put the mixture anywhere you want.

At 65% power use richer than 100 ROP or leaner than peak.

At 70% power use richer than 125 ROP or leaner than 25 LOP.

At 75% power use richer than 180 ROP or leaner than 40 LOP.

At 80% power use richer than 200 ROP or leaner than 60 LOP.


As you transition from takeoff power to cruise power if you are going to
be LOP make sure you lean rapidly to the values listed for LOP ops.
Fine tune as necessary.

As you transition from takeoff power to cruise power if you are going to be LOP make sure you lean rapidly to the values listed for LOP ops. Fine tune as necessary.

Ok. My comments were for ROP operations, which is what all the aircraft
I use reccomend. In that case, you should never hit the red box, and
should lean slowly. If you lean quickly and overshoot, you'll be in the
red box.

Jose
--
He who laughs, lasts.
for Email, make the obvious change in the address.