Tracking on My props

Discussion in 'Cinestar 8' started by Pavlos Antoniou, Nov 1, 2012.

  1. Pavlos Antoniou

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    Hello guys all my APC 14x4.7 have tracking problems..!

    What can i do for this?!
     
  2. Gary Haynes

    Gary Haynes Administrator
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    Can you be more specific? Photos, etc?
     
  3. Pavlos Antoniou

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    Hmmm tracking is tracking...! i cannot say it in other words..!

    Here you can see what is tracking :)

     
  4. Gary Haynes

    Gary Haynes Administrator
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    I would send them back to where you bought them and get replacements. The only other thing to check would be that you inserted the hub insert so that it didn't get a bit of an angle on it. Maybe remove it, see if the blade tracks without it in place. If it is good then the insert was placed at an angle. If it doesn't track without the insert then the blade is definitely flawed.
     
  5. Pavlos Antoniou

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    I baught the from quadrocopters.us
     
  6. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I agree with Gary -- if the two blades fail to transcribe the same plane, the propeller is distorted. However, what I do NOT know is whether a propeller whose blades fail to track, if properly balanced, will fail to operate correctly.

    Andy.
     
  7. William Johnston

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  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Thanks, William. I agree that the physics would be the same for smaller aircraft. I'm still pondering why one blade spinning in one circular disk and another blade spinning in another circular disk, presuming that the prop is balanced, would cause vibration? One blade is going to be getting "cleaner" air ahead of the other, while the other is going to getting "dirtier" air from the leading blade....

    Ah well, one more topic about which I know absolutely nothing....

    Andy.
     
  9. Pavlos Antoniou

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    For sure these props will cause Vibrations..>! And for sure the props have problem from factory because the tracking is 5mm++

    On helicopters tracking is causing very bad vibes..!
     
  10. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I don't doubt that it is true -- what I was trying to figure out was why. What causes the vibrations?

    Andy.
     
  11. Janne Hoglund

    Janne Hoglund Member

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    Hi Andy.

    A prop out of track gets a shift in center of gravity every turn and that way it causes vibrations.

    Regards.

    /Janne
     
  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Janne:
    Well, actually my little brain teaser was: "why one blade spinning in one circular disk and another blade spinning in another circular disk, presuming that the prop is balanced, would cause vibration?"

    So your idea doesn't quite work, because if the prop is correctly balanced the C of G, by definition, would not shift, would it?

    Don't get me wrong -- I'm not trying to be smart-ass -- it's just the way my mind works: to ponder if you balance a prop correctly does tracking matter?

    I can see a glimmer of an argument to the effect that we balance props statically and the dynamic balance might be a different story, but it's not a "oh, yeah, that must it" kind of argument (yet).

    Andy.
     
  13. Joe Azzarelli

    Joe Azzarelli Active Member

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    Andy
    I am with you on this. I think tracking blades are more efficient because they have, presumably, the same pitch and are providing the same amount of lift on each side of the motor. A severely out of track blade could produce much more lift from one side and you can see ( in your mind's eye ) how this would create a cyclical vibration.

    If I get an APC that is noticeably out of kilter, I will not use it. But a small amount is acceptable. I found that every APC prop that I have purchased ( 16 - don't ask ) are heavy on the side that has the size and pitch embossed near the hub. A perfectly balanced prop is much more important than perfectly tracking blades.

    For real helicopters tracking is quite critical. I used to own a MD-500D and tracking 5 blades was very much an art...

    Joe
     
  14. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Joe:
    Yeah, I was pondering "center of lift" kind of thinking at lunch today and wondering what the vector diagram of the forces would look like. I suspect that is a better explanation than mass/balance.

    Ah well, I find it's good to think these things through....but then I may have a sick mind.... :)

    Andy.
     
  15. Pavlos Antoniou

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    At the end i think i cannot do something...! i will have to go with wood props that are a lot better :) :)
     
  16. Janne Hoglund

    Janne Hoglund Member

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    No worries mate :)

    But I think that if one ¨circular disk¨ is not parallell to the other your prop may be balanced when sitting still, but when in motion not balanced because of difference in centifugal force.

    My Thinking;
    If you have a prop with one, one meter blade and the weight of one kilo, and the other blade two m but the weight of 1/2 kilo.
    Sitting still this prop would be balanced, but in motion certainly not?

    Is my thinking here balanced or not ;-)
    Myself now I am not sure.

    Hopefylly somebody can chim in and tell us how things work.

    Best Regards.

    /Janne
     
  17. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Janne:
    Yeah....I think you've seen the question: the difference between static balancing (not spinning) and dynamic balancing (spinning).

    Here's a thought experiment of an extreme case: Imagine a propeller with just one blade -- on the other side where the blade is missing is a mass balance -- just a weight carefully chosen to statically balance the prop. blade.

    Will it cause vibration?

    The correct answer is no.
    See http://en.wikipedia.org/wiki/Single-blade_propeller

    So now imagine a two bladed propeller, with one blade in the normal position, and the other blade badly out of track (say at an angle of 10 degrees forward from the other). But the propeller is properly balanced.

    The "normal" blade will be developing X amount of lift, and the "abnormal" blade will be developing Y amount of lift. Will X = Y? If not, why not?

    If this was on a light aircraft, I think X may not equal Y because the relative wind of the forward motion would mean that the abnormal blade is being presented at an angle to the relative wind, so the normal side would pull forward with greater force than the abnormal side.

    But with a copter there is not that much relative wind (in a hover, there's none). Perhaps the normal blade would create a partial vacuum that would deprive the abnormal blade of some iift? I don't know.

    But if a one bladed prop doesn't vibrate (and that's an extreme case of one blade flat and one blade at 90 degrees (pointing straight up on a copter)) .... well you see the problem....

    Ah well, enough of this pondering. Got to do some useful work on the next DVD.... :)

    Andy.
     
  18. Janne Hoglund

    Janne Hoglund Member

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    Thanks Andy for your words of wisdom. I´ll have to read more about this subject!

    But I do know that both on my 450 and 700 heli, Blades with bad tracking do kreate vibrations.

    Looking forward to the next DVD, Heavylifter is it?

    /Janne
    And thanks Tabb for a great Forum!
     
  19. Pavlos Antoniou

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    its different in helis because its not Fixed pitch..!
     
  20. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    On your heli's I wonder whether the vibration is caused not so much by the tracking, but that they blades were in balance when tracking correctly, and become out of balance when the tracking error occurs and that it's this lack of balance that causes vibrations, not the actual tracking (which is just a collateral symptom of the lack of balance). Thus leading me full circle to ponder whether an APC prop that is tracking badly might be usable if it is balanced properly.

    Edit: Good point, PaNt. That might compound the problem too.

    DVD? A Rather Good (Beginner's) Guide to MK Tool, MK_GPX and MP_GPXTool.
    It will answer questions facing the Fourth Age of Humankind such as: "What's a virtual COM Port then, eh?" :rolleyes:

    And, yeah, kudos to Tabb.

    Andy.
     

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