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2 Answers

mixture controlling

Asked by: 1967 views Aircraft Systems

Q1. assuming that i am above 3000MSL with level-off. then, i started leaning little by little until RPM is incresed in a moment. i stopped leaning at that time. is it correct for maximum power? 


Q2. we do leaning above 3000'MSL usually. WHY? (is that involved in air density?? what if we do level-off at 2000'MSL or 1500MSL?? do we not have to lean?)


Q3. During Taxiing, less power setting, leaning mixture.

      During Descending or Landing, less power setting, enriching mixture.

      what is the difference?


Q4. why improper mixture controlling makes the spark plugs fouled? how do they connect to each other?

      I can't exactly imagine BIG PICTURE of the engine systems . how these are connected with.

      but trying to make it. i


 so many questions.. 

everytime i thank you people here.


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2 Answers

  1. John D. Collins on Mar 17, 2013

    A1. Leaning for best power for an airplane with a fixed pitch propeller means that the RPM is the highest value for the same throttle position. Lean until the RPM increases and continue leaning until it starts to drop. Once the RPM starts to drop, push the mixture back in again to achieve the higher RPM where it had peaked.

    A2. Leaning at high power settings such as takeoff and climb may overheat the engine. Above 3000 feet, power is reduced because of the lower air pressure, so this is a point where it is normally safe to lean to maximum power. Below these altitudes, you can lean, but you have to reduce the throttle so that you don’t develop power above the limits set for cruise in your POH.

    A3. Normally at low power, the engine is setup to run very rich which helps the engine start and run at idle. Leaning at low power settings prevent partially burned fuel from fouling the engine spark plugs because the temperatures don’t burn the lead and it forms deposits on the plugs. When you are at altitude, leaning is performed to match the fuel flow with the air pressure available. When you descend to lower altitudes you enrichen to readjust the mixture back to the thicker air. Most training airplanes are not equipped with an EGT to determine what a good mixture should be, so for simplicity, students are advised to go to a full rich mixture, usually below 3000 feet. If you have to go around from an aborted landing or for a touch and go, if the mixture is still lean, you may not develop the power you need, or the engine may falter, or it may overheat. So to keep things simple, students are told to go to enrichen as they descend and go to full rich below a certain altitude.

    A4. See A3.

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  2. David Brown on Mar 19, 2013

    If you would like to read some more about this topic, and be a bit more advanced in your understanding can I suggest reading all the John Deakin articles on AV web.

    Click here http://www.advancedpilot.com/tech.html and download the articles. Read them several times so it sinks in.

    If you want to learn more, and you should, click on the course tabs.

    Unfortunately the simple methods taught in flight school are just that. And in my opinion they are far too simple.

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