Uh... What does the Mixture control do?

[tenetarns]

Apologies for the stupid question. I know that mixture adjusts the mixture of fuel and air that's going into the engine. However, what is the purpose of this?

Does it have any correlation to altitude & air density (i.e. at altitude the air is thinner, so you need to increase the amount of air the engine is receiving in order for the fuel to continue to burn efficiently?)

Just speculation - hopefully someone can clear this up for me. I haven't been able to find a straight answer anywhere on the web.

[bill2759]

Of course it's the relationship of altitude. As the air get thinner, the mixture would become too rich. Waste of gas you know. There are other reasons, such as engine temp, etc. But the mixture of air and gas is variable with altitude.

[Cannikin73]

I believe you pretty much hit the nail on the head.

[jcmissionary]

You are essentially correct, however, the mixture control meters the amount of fuel sent to the engine, not the amount of air.

Simply put, the purpose of leaning the mixture is to get maximum performance for a given altitude. For example, my home airport's elevation is 4,500 feet. We need to lean the mixture while on the ground in order to get maximum takeoff performance.

In high performance aircraft, the mixture is also used to control engine temperatures.

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[FITZY]

At higher altitudes and thinner air, the mixture must be leaned by reducing the amount of fuel introduced to the mixture and thereby maximizing combustion efficiency. Supercharging or turbocharging would increase the amount of air available.

Specifics of mixture control are best gotten from the POH for the aircraft and engine, but generally one leans for a maximum exhuast gas temperature, then enrichens a little for smooth engine operation or to achieve a specific reduction in EGT.

A quick Google search turned up this site. See part II in particular:

http://www.cyberair.com/tower/faa/ap...3/0978-13.html

[boboelmo]

I'm no expert on this matter. I have been messing around with mixture, too. Not that I've noticed any airplane performance difference, but I usually "lean" the mixture for the highest RPM. Mostly I only fly the Cessna 172 and the Piper Cub. I pretty much just follow the checklists for climbs and decents and everything without ever really knowing how the mixture was really affecting me. If it's for fuel efficiency, then it wouldn't really matter in Flight Simulator because you're not paying for the fuel, right?

[budreiser]

(If it's for fuel efficiency, then it wouldn't really matter in Flight Simulator because you're not paying for the fuel, right?)

Yeah man! One of the best things about this flight sim. You can total
a 747, no one gets hurt, it don't cost you any more, and State Farm
or whatever other XXXXXXX insurance company don't raise your rates.
Is this a great game or what?

[prowler]

Let's see, XXXXXXX...LOL, bet I know THAT word.

You mean like State Farm (and the rest) did in Florida?

20 years of collecting hurricane insurance policy premiums, with not a single major hurricane and NO claims. Then a big one comes...and they whine like a 6 month old who hasn't been fed in 2 days, and proceed to drop EVERYBODY from coverage?

You want to know who needs to be slapped down? It ain't oil, timber or anybody else.

Insurance companies run this country, it's the biggest rip-off job going. Everybody points the finger elsewhere. Insurance Companies are
into everything from banking to the stock market and mutuals...and they MAKE the insurance "laws" (how much liability coverage you "must" have) What a beautiful scam! All vehicles are unsafe...all activities result in death. And who comes up with these statistics? You guessed it.

OK...off topic rant completed.

prowler

[tenetarns]

Thanks for all the great replies! I feel better now that I wasn't sooo far off. So, basically, you lean when you're at altitude and improve cruise efficiency and engine performance.

Okay, let's say I'm at 5000ft. in my Cessna 172 after climbing from sea level. I reduce power to 75% and then lean the mixture.

[ul]
[li]Keeping the throttle the same at 75%, will the actual power output of the engine reduce when the mixture is leaned? (in other words, will I lose airspeed?)
[li]What gauges will reflect the change?
[/ul]

BTW, FITZY - that link was terrific! Thanks!

[budreiser]

You got that right prowler, and I pretty much told my agent the same
thing but didn't mince words. I told him that the insurance people
could sit back and collect premiums for 2000 years without a disaster
and not reduce rates, but the first time they had to pay out, rates
would go up. He said that wasn't true. I said "prove it to me". He
changed course. My home insurance (State Farm) went up 83% in a little
over a year and I couldn't just sit back and take it anymore. But,
with our other fine species of humans (lawyers), decent hard working
people better have insurance. From the looks of the latest Yellow
Pages, it won't be long before we will need a special Yellow Pages
phone book just to list Attorneys. Did I call them humans? Sorry about
that. This will probably get locked as it has nothing to do with FS9,
but what hey!