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Thread: GA aircraft engine question

  1. Question GA aircraft engine question

    So I was on the patio and heard a prop fly over head. Could have been your standard issue Cessna. Not sure as I didn't look. But I heard it sputter for a moment and then the engine rev back up. So my question is: Why did it do that? Did the pilot (perhaps a student) not use the right mixture or is there something else here? It's not often I hear that, but on occasion I do.

    Thanks.

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  2. #2
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    Did you see the aircraft? How high was he? Was there a visual cue to what he was doing? How long was the "moment" (one second, half a minute??)? Without at least that, there is no way to tell what the "sputter" was about.

    It's possible they were practicing stalls (aerodynamic, not engine), or they could have switched fuel tanks (not likely in a Cessna), or they could have over-leaned the mixture for cruise flight, or any of several other things, depending on the specific situation.

    So there's no way I can give a definite answer.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

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    I'm sorry. I was sitting on the patio and it has an overhang and I never got up to look past that to see the aircraft in question. I must have heard the sputter for about 5 to 8 seconds or so. There are a lot of Cessna's that fly around here since KFNL is about 3 miles or so East of me. I see them all the time so I'm only taking a wild guess it was a Cessna. Could have even been a Piper. But my money is on a Cessna.

    They may have been in cruise since the plane prop sound fainted away into the distance and not in circles or anything like that.

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  4. #4

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    Quote Originally Posted by CRJ_simpilot View Post
    I'm sorry. I was sitting on the patio and it has an overhang and I never got up to look past that to see the aircraft in question. I must have heard the sputter for about 5 to 8 seconds or so. There are a lot of Cessna's that fly around here since KFNL is about 3 miles or so East of me. I see them all the time so I'm only taking a wild guess it was a Cessna. Could have even been a Piper. But my money is on a Cessna.

    They may have been in cruise since the plane prop sound fainted away into the distance and not in circles or anything like that.
    Since it was only 5 to 8 seconds, I would not say that this is "automatic rough" that comes from descending into denser air. It really sounds like the pilot made the mixture too lean and then went the other way to get it just right. I read one pilot owners handbook that recommended the mixture be enriched to 25 degrees cooler exhaust gas temperature reading than the leanest setting that still runs the engine.

    I've seen a picture of a Cessna fuel tank switch. Uh, I had an FS 2004 British 152 (JustFlight?) that had a selector switch in it, and that aircraft was full of glitches so I wound up only draining one wing's tank after I'd flown it for a while - annoying! I never did figure out how to fix that or why anybody would want it to do that.

    I can't say these are the most likely things, they are just the ones that have given me problems in FS X - which I wish was a lot more accurate.

    Thanks for the good question, Sir, and happy landings, always

    Sean
    'Glichy' controls or switches and don't want to pay for new ones? Read on... You can bring a controller back to life by exercising it through it's full range of motion or from maximum to minimum and back again 50 times. I had a Logitech joystick that gave left rudder without touching it but turning it 50X fixed it.

  5. #5
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    I've seen a picture of a Cessna fuel tank switch.
    The Cessna 150 and 152 have an on/off switch (valve, actually) for fuel. The other Cessna singles have one with left/both/right.

    Obviously you can't select the tank to use on the C-150/2, but on the others running on both is normal, with the left/right mainly used for a short time if the fuel load somehow gets imbalanced between the two tanks. Due to interconnects and venting, if the Cessna is sitting on the ground for a while with one wing low, the low wing will gradually get more fuel, thus imbalanced.

    Since it was only 5 to 8 seconds, I would not say that this is "automatic rough" that comes from descending into denser air.
    Pilots are trained to lean the mixture for cruise, but must then enrichen the mixture as they descend, which from higher altitudes should be a little at a time. However, KFNL is between Loveland and Ft. Collins, CO, about 40+ miles north of Denver, and airport elevation is right near 5,000 feet, so that "automatic rough*" shouldn't play a part.



    * Automatic Rough: That's the first time I've heard the term used for that purpose. Normally, in aviation, the term is used for the apprehension and imagination that can sometimes make a pilot think it might be a little rough when getting into certain situations, such as over the ocean well away from land or over the mountains at night well away from airports, even though the engine is running exactly the same as it was earlier. It's not that there is anything actually wrong, it's just that the worry/concern tends to make small things magnified, thus fueling the pilot's imagination.

    This 1955 article from Sports Illustrated may give you a better idea of its proper usage and what it actually means. I mention the year because Cuba wasn't restricted back then.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  6. #6

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    Quote Originally Posted by CRJ_simpilot View Post
    I'm sorry. I was sitting on the patio and it has an overhang and I never got up to look past that to see the aircraft in question. I must have heard the sputter for about 5 to 8 seconds or so. There are a lot of Cessna's that fly around here since KFNL is about 3 miles or so East of me. I see them all the time so I'm only taking a wild guess it was a Cessna. Could have even been a Piper. But my money is on a Cessna.

    They may have been in cruise since the plane prop sound fainted away into the distance and not in circles or anything like that.
    On the information presented, impossible to conjecture. Was the plane climbing or descending? Had you heard other aircraft from your position on the stoop? Why did you assume a Cessna? Do you even know if it was an Avgas piston?

    It's normal to lean the mixture. It's very common to use the twist function of the vernier but if one is making broad adjustments the vernier is not the way to do it so it is quite common to just use push/pull to get it `in the park` before finessing the mixture with the vernier.
    IF the aircraft was climbing there might have been a sudden power reduction which just sounded to you like sputtering. Or the power reduction might have been followed by mixture adjustment and things may have come back a little too far. Or it could have been tank-switching, or negative-g feed.. upset...

    It could literally be almost anything.

  7. #7

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    Quote Originally Posted by lnuss View Post



    * Automatic Rough: That's the first time I've heard the term used for that purpose. Normally, in aviation, the term is used for the apprehension and imagination that can sometimes make a pilot think it might be a little rough when getting into certain situations, such as over the ocean well away from land or over the mountains at night well away from airports, even though the engine is running exactly the same as it was earlier. It's not that there is anything actually wrong, it's just that the worry/concern tends to make small things magnified, thus fueling the pilot's imagination.
    You're right. I actually read this in one of Richard Bach's books, and that is what he meant. I just misremembered it from the time I took off from El Mirage Adelanto (formerly L69) to go to Southern California Logistics (KVCV). Both about 100' below 3000' MSL. I climbed to, probably 4,000' MSL and leaned the engine, and forgot to go to full rich when I landed. The engine quit about fifty feet about the runway and I didn't have time to build up speed to still make a soft landing. How I learn...

    Here, lomcovak: https://youtu.be/f5haTfIMR-A?t=9

    Although the Soviet team seemed to be able to do them for as long as they wanted to in the Sukhoi at the Paris Airshow.

    Sean
    'Glichy' controls or switches and don't want to pay for new ones? Read on... You can bring a controller back to life by exercising it through it's full range of motion or from maximum to minimum and back again 50 times. I had a Logitech joystick that gave left rudder without touching it but turning it 50X fixed it.

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