Engine mixture guidelines

On Sat, 30 Dec 2006 09:27:14 -0800, Mxsmanic wrote
(in article ):

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?



Okay, despite the opinion and experience of many pilots and mechanics, it is
time to point out that most engine and aircraft manufacturers do not
recommend running engines lean of peak. There are some mods out there that
are specifically designed for LOP operation (GAMI injectors, most notably)
and there are a few pilots here who are strong advocates of LOP operation.
Despite the fact that LOP is recommended by some highly respected pilots,
theirs is not the majority opinion, however.

There are even conspiracy theorists who suggest that engine manufacturers
discourage LOP deliberately to shorten engine life and increase sales.
(Apparently they presume that the increased sales outweigh the potential cost
of class-action lawsuits.)

There are equally respected pilots who argue in favor of ROP operation. They
figure that the engineers who built the engine probably know best how to take
care of it. Given that the owner of my flight school agreed with them, I flew
ROP (and probably will again).

The LOP advocates will tell you that running ROP is the reason so many
engines get top overhauls before TBO. I tend to think that the reason for it
is that too many planes don't fly enough, too many pilots don't lean the
mixture at all, and pilots don't inspect the engine for things like damaged
valves which, if not detected, will cause a cracked cylinder.

I have heard very powerful arguments from both sides about it. I do not hold
a strong opinion either way, but since this thread has been dominated by the
LOP crowd I thought I might just mention that not everyone shares their view.
My own practice is to follow the engine's handbook.

Near as I can determine, the biggest problem with LOP operation is that most
engines run pretty rough, especially if the engine is carbureted. They just
don't distribute the mixture evenly to all cylinders and LOP makes it worse.
It is a little easier to be successful at LOP with an injected engine.

Running ROP makes it a little easier to cool the engine if you are getting
pre-ignition or detonation problems. In general, if the engine is starting to
run rough, you want to make the mixture richer, not leaner.

You should also lean the engine aggressively when taxiing. It is real easy to
foul the plugs by taxiing with a rich mixture. I have known some individual
planes that will fail a mag check every time you taxi with the mixture full
rich.

Skydiving planes generally make it to TBO without a top overhaul or any other
major engine work, despite the fact that several times a day, every day, they
take off, climb at full throttle as fast as possible to drop altitude, then
basically coast back to the field with the engine at idle, with pilots who
don't lean at all or who use all different kinds of leaning strategies. Our
instinct is to call that mistreatment of the engine, but in fact it is the
secret to long engine life: run it constantly and keep it out of the red box.

C,

it is
time to point out that most engine and aircraft manufacturers do not
recommend running engines lean of peak.


Not quite. MOst don't say anything about it. The new ones tend to
provide settings for it.

--
Thomas Borchert (EDDH)

On Sun, 7 Jan 2007 02:30:43 -0800, Thomas Borchert wrote
(in article ):

C,

it is
time to point out that most engine and aircraft manufacturers do not
recommend running engines lean of peak.


Not quite. MOst don't say anything about it. The new ones tend to
provide settings for it.



New what? Manufacturers? Engines? Planes? I don't know of any Cessnas, Pipers
or Beeches that provide settings for it. Or Lycomings or Continentals. What
does Cirrus say?

As you know, LOP has been written about quite a lot in recent years. The one
thing I have noticed is that it is a lot easier to get a high performance
engine to run smoothly LOP than it is for the trainer types.

C J Campbell wrote:


New what? Manufacturers? Engines? Planes? I don't know of any Cessnas, Pipers
or Beeches that provide settings for it. Or Lycomings or Continentals.



The Continental IO-550, which is by far the most popular engine now a
days, comes with LOP in the power settings. These come directly from
Continental.

On Sun, 7 Jan 2007 17:07:07 -0800, Newps wrote
(in article ):



C J Campbell wrote:


New what? Manufacturers? Engines? Planes? I don't know of any Cessnas,
Pipers
or Beeches that provide settings for it. Or Lycomings or Continentals.



The Continental IO-550, which is by far the most popular engine now a
days, comes with LOP in the power settings. These come directly from
Continental.



Ah. Thanks. I also did not know that the Continental IO-550 was so popular.
What planes use it?

Newps wrote:
C J Campbell wrote:


New what? Manufacturers? Engines? Planes? I don't know of any Cessnas, Pipers
or Beeches that provide settings for it. Or Lycomings or Continentals.



The Continental IO-550, which is by far the most popular engine now a
days, comes with LOP in the power settings. These come directly from
Continental.


Here's the dope from the people who design, build, suffer the
liability for, and have to pay warranty costs for engines that fail:

http://www.lycoming.textron.com/main...ngEngines.html

An excerpt:

"5. The exhaust gas temperature (EGT) offers little improvement in
leaning the float-type carburetor over the procedures outlined above
because of imperfect mixture distribution. However, if the EGT probe is
installed, lean the mixture to 100oF on the rich side of peak EGT for
best power operation. For best economy cruise, operate at peak EGT. If
roughness is encountered, enrich the mixture slightly for smooth engine
operation."

Another one from the same people:

http://www.lycoming.textron.com/main...erLeaning.html

....and an excerpt from it:

"First we must know that cruise power for Lycoming normally aspirated
engines is generally considered to be 55% to 75% of the maximum power
for which the engine is rated. At these power settings, the engine may
be leaned at any altitude. There has been confusion about the reference
to not leaning below 5000-feet density altitude. Remember that this
reference only applies to those power settings above the cruise range
- those normally used for takeoff and climb. Once cruise power has
been set, leaning to best economy should be standard procedure as
damage to the engine will not occur from leaning at cruise power
settings."

And one about running LOP:

http://www.lycoming.textron.com/supp...ps/SSP700A.pdf

Their website has a huge amount of info available regarding engine
operation.

Dan

C,

What
does Cirrus say?


Cirrus provides settings, as does Diamond (and Piper). They use TCM and
Lyc.

--
Thomas Borchert (EDDH)