Mixture control

[Luke Mc]

Hello
Is the mixture control the equivilent of the choke control on many older cars?
Luke

[Trislander]

Hi Luke,

To answer your question: Well no not really. The choke on older cars is to get the engine to start and warm up quicker for a more stable run. It basically works in a similar way, but for completely different reasons.
The mixture control on piston-engined aicraft varies the ratio of air to fuel that enters the engine cylinders. ie, for the most part, the mixture will be set to rich, the amount of air to fuel is equal, and as you 'lean' the mixture (pull back on the mixture lever), less fuel to air is drawn into the cylinders. This is useful at higher altitudes where the air is much thinner, thus running the mixture at rich would add more fuel to air because the air is not as dense as at sea level, and the engine does not run efficiently. All that is required is for the mixture lever to be leaned back until the RPM level peaks.
On the ground, if the mixture is leaned, less fuel to air is entering the cylinders, causing low RPM.
Basically the fuel to air ratio at all times should be kept equal to gain the most efficiency from the engine, and this is made possible with the mixture lever.

Hope this helps,
Trislander

(EDITED TO GET THE RECIPIENTS NAME RIGHT!)

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http://www.aurigny.com/images.gb%20/trislander.jpg
"Ayline 221 airbourne"

[ 22 September 2001: Message edited by: Trislander ]

[Checkboard]

They both can increase the amount of fuel in the fuel/air ratio going into the engine, but the mixture control does it by indroducing more fuel, while the choke does it by decreasing the amount of air.

Cars also have a mixture control, but it is set by screw driver on the carburretor itself, under the bonnett. As cars usually stay at roughly the same height above sea level, it isn't necessary for them to adjust the mixture while driving.

(From memory! :D )

[ShyTorque]

Or, alternatively,

A choke makes the mixture RICHER to return it towards datum (for starting, when the cold intake manifold causes fuel vapour to condense back into liquid, thus tending to weaken the standard mixture).

A mixture knob makes the mixture WEAKER to return it towards datum (for higher altitude ops where there is less air tending to richen the standard mixture).

ShyT