Engine mixture guidelines

Mxsmanic wrote:
Up to now when flying in simulation, I've had the simulator take care
of engine mixture adjustments. However, since I'd have to do this
myself in real life, I've decided to make some modest attempts at
managing mixture myself. Unfortunately, the POH and the other sources
I've consulted are rather vague on how mixture should be adjusted.
Can anyone offer general guidelines on when to enrich or lean the
mixture? It seems that max rich is used when maximum power is
required (?), such as at take-off, but I'm not clear when the mixture
should be leaned in particular. And what are the potential
consequences of an incorrect mixture?

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As altitude increases the air gets thinner so you need less fuel to
maintain the proper air to fuel ratio. Running too rich (too much fuel)
causes incomplete combustion resulting in spark plug fouling. Running
too lean (not enough fuel) causes overheating especially the exaust
valves.
The most efficient way to determine the correct mixture is with a EGT
(Exaust Gas Temperature) gauge. As you turn the mixture control out the
EGT will increase to a point and then begin to decrease as the mixture
gets too lean. Lean the mixture until it peaks and then enrichen it
(turn it back in) until it drops 50°C.
Though not as accurate, you can also note a increase in RPM's as you
lean it. Lean to peak RPM then turn it in a full turn.
Remember FULL rich for takeoffs and landings unless your flying at
Leadville, CO or some other really high altitude airport.
Steve

Running too rich (too much fuel)
causes incomplete combustion resulting in spark plug fouling. Running
too lean (not enough fuel) causes overheating especially the exaust
valves.

I suspect most MSFS simulated aircraft do not simulate engine damage
from improper leaning. They will simulate the fan quitting at idle
cutoff though.

The most efficient way to determine the correct mixture is with a EGT
(Exaust Gas Temperature) gauge. As you turn the mixture control out the
EGT will increase to a point and then begin to decrease as the mixture
gets too lean.

In real airplanes there is a lag. Lean it out slowly. A Cessna 182
manual I remember reading said that it should take about two minutes to
find the peak. This may also not be adequately simulated in
"entertainment level" simulators.

Lean to peak RPM then turn it in a full turn.

I've never heard "a full turn", though I have heard the less helpful
phrase "a bit". Not all airplanes have vernier controls, and I don't
think MSFS aircraft do either.

Jose
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wrote:


Remember FULL rich for takeoffs and landings unless your flying at
Leadville, CO or some other really high altitude airport.

No. Lean above 5000 as a general rule. Some aircraft, like my Bonanza,
has a scale on the fuel flow instrument that tells you where to lean to
for every takeoff regardless of altitude.

Jose wrote:




In real airplanes there is a lag. Lean it out slowly.

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.

Jose writes:

I suspect most MSFS simulated aircraft do not simulate engine damage
from improper leaning. They will simulate the fan quitting at idle
cutoff though.

Yes. Most types of damage are not simulated in MSFS aircraft, nor is
cumulative damage simulated (as far as I know).

Leaning the mixture beyond a certain point does indeed stall the
engines in the Dreamfleet Baron model I fly in simulation.

In real airplanes there is a lag. Lean it out slowly. A Cessna 182
manual I remember reading said that it should take about two minutes to
find the peak. This may also not be adequately simulated in
"entertainment level" simulators.

I see a lag in the simulator, also.

I've never heard "a full turn", though I have heard the less helpful
phrase "a bit". Not all airplanes have vernier controls, and I don't
think MSFS aircraft do either.

The Baron has controls similar to the real aircraft, that is, two
levers for mixture.

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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
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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
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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
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