Definition "lean out"

[planeenglish]

Hi everyone,

I am trying to find a definition for the phrase "lean out" in regards to fuel/air mixtures. If the mixture has to be "leaned out" what must be done?

Thanks in advance,

PE

[cwatters]

"lean-out" means adjusting the fuel air mixture ratio from an incorrect "fuel rich" setting to the optimium ratio.

The expression "lean" is as in "lean times" eg not rich/wealthy.

[planeenglish]

Thanks cwatters,

Just to clarify, it is because the mixture is too rich therefore it should be "leaned out" to rid it of....

Sorry for the ignornace, I'm an English teacher, not yet a pilot.
PE

[Intruder]

To "lean out" means to reduce the proportion of fuel in the fuel/air mixture going to the engine cylinders.

[planeenglish]

OK. I get it now, thanks Intruder.

PE

[captjns]

A carburetor or fuel injector as a part of any engine provides a means of delivering a metered amount of fuel to be mixed with a measured volume of air. This is necessary because combustion can only occur when the air/fuel mixture falls within a given range. The extreme outside limits of this range are approximately 20:1 at the lean end and 8:1 on the rich end. For practical purposes, the operational air/fuel mixture range for most air cooled engines will fall between 16:1 at lean and 10:1 when operating at full rich. Obviously, both the fuel injector and the carburetor are capable of metering within these limits.

With full carburetor heat applied, most float-type carburetors react very sluggishly or inefficiently on a straight-arm throttle technique during a touch-and go landing or an aborted landing. In some cases, the float-type carburetor may refuse to accept the throttle when it is applied in this manner. A gradual, steady application of the throttle is always the best approach.

When carburetor heat air is used at cruise power the mixture should be leaned, otherwise the fuel/air ratio will be to rich. If the heat causes an undesirable power loss at cruise, and additional throttle is available, we can bring the manifold pressure up at least to the power reading before the application of heat; and if additional power is needed and available, no more than a maximum of two inches of MP, or 100 RPM (fixed pitch prop) above the previous power should be added, and then adjust the mixture by leaning it out to obtain the proper fuel to air ratio. It is possible to compensate for the horsepower loss due to heat by means of the latter technique if throttle or RPM are available.

[TruBlu351]

Lean (or less) is for economy cruising or holding.

A rich (more fuel) mixture is for a flight regime where lots of power is required (takeoff, aerobatics etc).

If a mixture is too lean, then it is prone to detonate when the spark plug fires. Kind if a mini explosion instead of a controlled flame front burning in the cylinders. This can really damage the engine.

Another thing to remember is that as you increase your altitude, the atmosphere thins out and becomes less dense. So with reference to maintaining a desired "air fuel ratio", as the cylinders draw in less oxygen you need to decrease the amount of fuel going in to keep that optimum RATIO (you obviously lose power in the process).

[bekolblockage]

The stoichiometric (chemically correct) air/fuel ratio for gasoline is 14.7:1 by weight.
When running at high power settings using rich mixture, the excess fuel assists with cylinder head cooling and avoiding catastrophic detonation.

[planeenglish]

Originally Posted by TruBlu351

Lean (or less) is for economy cruising or holding.
A rich (more fuel) mixture is for a flight regime where lots of power is required (takeoff, aerobatics etc).

Firstly, thank you to all who answered. I am still studying for my PPL and find the intricate responses most informative, helpful and interesting.

Regarding this above statement by TruBlu351, this means that this "leaning out" can happen at any stage/phase of flight and height?

Thanks,
PE

[TruBlu351]

Originally Posted by planeenglish

Firstly, thank you to all who answered. I am still studying for my PPL and find the intricate responses most informative, helpful and interesting.
Regarding this above statement by TruBlu351, this means that this "leaning out" can happen at any stage/phase of flight and height?
Thanks,
PE

You have manual control of the fuel mixture via a lever in the cockpit. You'll takeoff in the full RICH setting for max power. If you left it there as you climbed, it would actually become more rich, so you need to gradually reduce the fuel flow to keep it balanced with the thinner air.

If however, you didn't richen it back up on descent or after cruising and then went full power on the engine, that's where you could get a UNWANTED lean situation.

Intentional lean settings are AOK for economy, but "full power and lean" means melting pistons and spark plugs and then catastrophic engine failure.

AVGAS has an addative called TEL (Tetra Ethyl Lead) which reduces detonation. This provides less tendency to do bad things when in a lean setting. That's what the LL means on the 130LL Avgas (low lead). Low lead versions these days to help the environment

[TruBlu351]

Summary;

Too lean means engine damage at high power.

Too lean means your engine stalling. That's how you turn it off by going "mixture FULL lean" or no fuel!!

Too rich means a lot of plug fouling and carbon build up which can also stop your engine in extreme cases. This is called a "Rich Cut".

So, leaning out can happen at any phase of flight, but just follow the guidance in your aircraft manual and you'll have no problem at all.

[Bob Lenahan]

How does this relate to the expression "chill out"?

[TruBlu351]

Originally Posted by Bob Lenahan

How does this relate to the expression "chill out"?

That's Chicago in winter

[shuttlebus]

A few more things...

Just to add my tupence worth...

Rich mixture - burns with a yellowish flame (may be some traces of blue) - incomplete combustion. Will cause fouling of plugs, especially at low revs (and hence why it is a good reason to rev up a piston engine before TO to clear them). Deposits on plugs are black/sooty. Engine response after low speed running can be sluggish at best.

Ideal mixture - burns with a blue flame (reminiscent of the bunsen burners in school). If your mixture is correct a nice chocolate brown deposit ends up on the plugs!

Weak mixture - burns with a blue white or white colour. Hotter than ideal mixture. Plug deposits are a white & chalk like. Continued leam runnign leads to over-heating of the spark plug, thermal failure of the electrode and as mentioned above sharp detonation rather than a nice flame propogation, which can damage the engine.

Regards,

Shuttlebus

[rotated]

Excellent article here explaining some of the basic principles of proper leaning.

[Intruder]

this means that this "leaning out" can happen at any stage/phase of flight and height?

A piston engine is set at the factory to run properly at the highest power certified or normally used. That is attained when the air is at its highest density, at sea level at a low air temperature. With any increase in altitude (and to a lesser extent, temperature or humidity), the mixture will be too rich (i.e., too much fuel for the air that enters the cylinder). Therefore, the mixture control is provided.

A richer-than-normal mixture is used to help prevent detonation and to help keep the cylinder temperatures within normal range. However, this also wastes fuel, since unburned fuel goes out the exhaust. Therefore the engine is leaned to a point determined by some combination of gauge indications of fuel flow at a particular power setting, exhaust gas temperature, and cylinder head temperature. The newest technology engines do this all automatically and electronically using a system called FADEC or Full Authority Digital Engine Control.

[Loose rivets]

Originally Posted by bekolblockage

The stoichiometric (chemically correct) air/fuel ratio for gasoline is 14.7:1 by weight.
When running at high power settings using rich mixture, the excess fuel assists with cylinder head cooling and avoiding catastrophic detonation.

Is the 14.7 a total coincidence?

[planeenglish]

Dear All,

Thank you for these answers (keep them coming). I am still learning so much. Just so you know why I asked this question...

A friend doing the AOPA course for engines and propellers (http://www.aopa.org/asf/online_courses/) came across this phrasal verb. It is no technical dictionary I have and could not find a proper definition.

Thanks so much ,

PE

[Ant]

Excellent articles at avweb.http://www.avweb.com/news/columns/182084-1.html

[NutLoose]

Originally Posted by shuttlebus

Just to add my tupence worth...

Rich mixture - burns with a yellowish flame (may be some traces of blue) - incomplete combustion. Will cause fouling of plugs, especially at low revs (and hence why it is a good reason to rev up a piston engine before TO to clear them). Deposits on plugs are black/sooty. Engine response after low speed running can be sluggish at best.

Ideal mixture - burns with a blue flame (reminiscent of the bunsen burners in school). If your mixture is correct a nice chocolate brown deposit ends up on the plugs!

Weak mixture - burns with a blue white or white colour. Hotter than ideal mixture. Plug deposits are a white & chalk like. Continued leam runnign leads to over-heating of the spark plug, thermal failure of the electrode and as mentioned above sharp detonation rather than a nice flame propogation, which can damage the engine.

Regards,

Shuttlebus

Your ideal is actually slightly on the rich side, this is also to aid cylinder head cooling by using the extra fuel to assist in it.........

When we set the idle mixture on a 152 or indeed any light aircraft we set it to run rich, this is easily seen next time you shut down.......... AT IDLE which will be about 650 rpm pull the mixture closed very slowly you will as the mixture leans (toward the optimum combustion ratio) see the RPM rise about 25 to 50 RPM this is because the engine has been set up on idle mixture to run slightly rich......... leaning it it is getting to the optimum so accelerates slightly before it dies...........

that is how we set it.