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  1. #1

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    Prop balancing

    Can someone explain how to do this? This is what I am understanding: The prop is reamed oversized. What keeps it centered on the shaft. Is some kind of bushing required?

    "The prop hub aft surface and aft hole are precisely defined during molding. However, post-molding shaft hole drilling may induce minor angular mis-alignment of the prop with the engine shaft. This hole mis-alignment is avoided by use of a tapered reamer to slightly enlarge the prop hole forward of the aft surface. This causes the prop to precisely register with the engine shaft at the aft surface and hole."
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  2. #2

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    RE: Prop balancing

    Are you asking about balancing a propeller or reaming the hole so it will fit the prop shaft of your engine?
    Plane crazy!

  3. #3

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    RE: Prop balancing

    To me, it seems if the hole was perfectly centered, the APC props I am using would be much better balanced from the factory. My question is why APC states what I quoted, and how to do it. Somewhere else I saw a online store selling bushings for use with APC props, that "eliminated the need for balancing". I dont believe the claim, but is there a way to minimize the amount of material added or removed from the prop.

  4. #4
    ChuckW's Avatar
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    RE: Prop balancing

    I always use a stepped reamer. This generally assures a perfectly centered hole (at least matching the original hole). Just ream to match the size of the engine shaft. I often check balance after reaming but I rarely find them out by much if any. The reamers are available in both standard and metric.

    http://www3.towerhobbies.com/cgi-bin...&I=LXK248&P=ML

    http://www3.towerhobbies.com/cgi-bin...&I=LXEGH6&P=ML

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  5. #5

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    RE: Prop balancing

    Thanks. I'm still trying to figure out what APC means by there statement.

    A quote from another website.

    " One of the most important things most competitive flyers have done for years is to make sure their props are properly aligned with the crankshaft of their engine.

    Some flyers have recently run across APC props with engine shaft holes that appeared less than perfectly straight. Upon close examination they discover the hole in the front of the prop hub is sometimes slightly off, but the hole on the backside is right-on.

    This challenge can be taken care of in a fairly straightforward way by using a tapered reamer. Whereas regular drilling only adds to the problem, a tapered reamer, when used properly, can ensure that the engine shaft hole is both straight and properly centered.

    The big plus when reaming APC props is the precision engineering that goes into the design and molding. Because the propeller hole position is created during the molding process, the position of the hole is extremely precise on the backside of the hub. Simply use the tapered reamer to bore from the front side of the hub to enlarge the hole (see the illustration below).

    This is actually the most accurate way to insure proper alignment of any prop, even if the hole appears to be centered. When the prop washer and prop nut are installed and tightened, the molded hole in the back of the hub centers the prop and allows the back of the hub to serve as the reference to seat flat against the drive washer or spinner back plate.

    This simple operation will provide one of the most accurate methods of making sure the prop is perpendicular to the crankshaft. Now the β€œtip tracking” will be as perfect as you can get. Most contest flyers have been doing this for years."

  6. #6
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    RE: Prop balancing

    A misaligned cylindrical hole will cause the prop to sit cockeyed, but a misaligned tapered hole will allow the prop to sit flush with the thrust plate.
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    Mike B. AMA# 42400 www.gettingairborne.com
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  7. #7

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    RE: Prop balancing

    The machining process of drilling a hole, is not always a precise process. Drill bits generally have two flutes. This can allow the drill to dig in and be pressed to one side or the other at the start of the drilling process, thereby causing some asymmetry to the first hole As Chuck recommends above, buy a stepped reamer. The only bushings I've ever seen are for putting on a spinner backplate, when the hole in the backplate started out to big. Also, like Chuck says, I balance every prop, some need it, most are close enough.
    Plane crazy!

  8. #8
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    RE: Prop balancing

    ORIGINAL: tsperry88

    Thanks. I'm still trying to figure out what APC means by there statement.
    There are three forms of misalignment:

    1) Radial and parallel to the shaft axis
    2) Frontal and non- parallel to the shaft axis
    3) Both combined

    The manufacturer is stating and guaranteeing that:
    1) The aft hole is concentric with the rotating axis of the body of the propeller
    2) The aft surface of the hub is parallel with the rotating plane of the propeller.
    3) If you don’t mess with those surfaces, the propeller will spin concentrically and within one unique plane.
    4) The above has nothing to do with balance of the mass of the propeller (that is fine work left to you).

    Just like unbalance, geometric misalignments will cause vibrations.

    The manufacturer is asking the consumer not to modify the mentioned surfaces, if the hole diameter needs to be modified, since he knows that a manual work will lead to misalignment.
    This introduced misalignment will be compensated by the adjustment of the mentioned surfaces against the shaft and the back plate.

    MinnFlyer schematics posted above explain this perfectly.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  9. #9

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    RE: Prop balancing

    i have a prop thats balanced perfectly on a dubro balancer even balanced the hub as i saw done on utube, the prop will sit at any angle, but on the plane it shakes like crazy. when i bought the prop i drilled the hub to the needed size put it on the balancer and had 1 blade heavy so i started sanding the back of the heavy blade, then switched to spraying clear enamal on the lite blade, it took about 5 heavy coats to get it right. it shakes so bad there must be a differance between static and spinning balance points. i'm wondering if this prop can be saved?
    I don\'\'\'\'t always crash, but when I do!

  10. #10
    MinnFlyer's Avatar
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    RE: Prop balancing

    Try removing the clear enamel and put the heavy side opposite the piston at Top Dead Center
    Mike B. AMA# 42400 www.gettingairborne.com
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  11. #11
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    RE: Prop balancing

    Do as MinnFlyer says, but discard the propeller if it continues vibrating so much.

    The damage those vibrations may cause to the engine bearings and frame are much more expensive than a new propeller, I believe.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  12. #12
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    RE: Prop balancing

    This may be happening to your assembly of propeller-engine, which is common for holes that are modified by hand and get misaligned.
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    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  13. #13

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    RE: Prop balancing

    i took minnflyer's advice, sanded alot of the clear enamel off, put the heavy blade opposite top dead center. started the engine and watched the prop as the throtle was increased.at just above a high idle it shakes and the tips go off track then come back in. the worst vibration is at half throtle ( the slave struts vibrate so bad there life span would be in minutes). the rest of the way to full throtle it's not good but alot smoother than half throtle. so, another prop is likely needed.
    I don\'\'\'\'t always crash, but when I do!

  14. #14
    Moderator da Rock's Avatar
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    RE: Prop balancing

    Buy yourself a prop reamer. They do a much better job of enlarging the hole accurately. Enlarging that hole can often ruin a prop that was good to begin with if your proceedure isn't accurate. Reamers are more accurate from the gitgo.
    Good flying wit ya today

  15. #15

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    RE: Prop balancing

    a prop reamer is now on the list.
    thanks for the help
    I don\'\'\'\'t always crash, but when I do!

  16. #16

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    RE: Prop balancing

    Has anybody used the Vess Balance Ring ? The shaft on the Dubro Balancer seems fairly short. I have not found a accurate way to ensure the shaft is level and true within the towers to ensure I get a accurate balance ?

    Also is it better to balance the spinner and prop at the same time or do them seperately ?

    This is my first time messing with gas props I used to just used the cheap fingertip balancer.


    Thanks Scott

  17. #17

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    RE: Prop balancing

    Hi!
    What brand?
    Jan Karlsson - Supplier MVVS Products

  18. #18
    LesUyeda's Avatar
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    RE: Prop balancing

    " The prop is reamed oversized. What keeps it centered on the shaft. Is some kind of bushing required? "

    Yes. APCs come with a variety of plastic bushings on a "tree". You select the bushing that fits your crankshaft, and install it into the recess in the end of the prop.

    Les

  19. #19

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    RE: Prop balancing

    Small APC's have the bushings, but the bigger ones have to be reamed.

    to straitnickel: You mentioned that your blade tracking is off, which will cause vibration even with a perfectly balanced prop. To fix that, you can sand the back of your hub flat, making sure to get the blade tips the exact same distance to the flat table you're working on. Then you'll need to use a tapered reamer like the thread has talked about to let the hub sit flat. It may not be worth the effort to you to save a $4 prop, but that's likely the issue.
    No kid, I said break ground and fly into the wind!

  20. #20

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    RE: Prop balancing


    ORIGINAL: MinnFlyer

    A misaligned cylindrical hole will cause the prop to sit cockeyed, but a misaligned tapered hole will allow the prop to sit flush with the thrust plate.
    Thank you for the picture Mike, that dummied it down enough so even I could understand it.
    I can't recall even getting an APC prop that wouldn't balance but I'm sure it happens. I think the biggest APC I have ever used was a 17 inch. Once you get past the 12 inch the prices do go up quite a bit but still, if I had one that wouldn't balance I would pull it and buy another. I mite even send it back to APC so they could evaluate it and find the problem. I'm guessing but I bet they would make good on the bad prop too?
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