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Thread: Giant scale prop balancing

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  1. Giant scale prop balancing 
    #1
    Join Date
    08-25-2003
    Location
    Toronto, CANADA
    Posts
    11
    I have a new M\A 18x6 prop that I intend to use. As this is the first project that I've ever done that is this large I am wondering about the prop balance. Do props this large still need to be balanced? It will only be running upwards of 8000 rpm so I wonder if it would be an issue to leave it as is. If it does need a balancing, what is the best way to do this? It is considerably heavier than any other prop I have used before and my balancers simply don't work with a prop of this size. It's either too long or too heavy.

    I suppose I could rig something up that would help me get it close but if it's not needed it's a step I can do without.

    Thanks.

    Bufferoo
     

  2.  
    #2
    Join Date
    10-05-2001
    Location
    Farmville, VA
    Posts
    2,291
    Hi,
    The large props need balancing even more than smaller ones. The mass of those blades, especially a MA plastic, can shake the patooties out of a model when the balance is off even a small amount. I have a metal dowel that is pointed at each end that I slip in the prop and then hold between my fingers, but there are other optios where you could use two parallel metal bars with a metal dowel or tube through the prop hub riding on them. The issue is the mass of the blades, and the distance from the blade cg to the shaft. This dimension is a lot larger than typical for props that you might put on say, a .40. I am fond of wood props because of the considerably lighter blades. Besides, a broken wood prop might mean saving the shaft from bending, while that plastic "lawn mower blade" will put much larger loads on the engine in an impact.
    Cheers, Dave
    Dave Robelen
     

  3. That's what I was afraid of. 
    #3
    Join Date
    08-25-2003
    Location
    Toronto, CANADA
    Posts
    11
    Thanks for the help Dave. I was really hoping that I could get away with it but I'm guess it's just not worth the risk.

    I do have the goodies around to rig up something to balance it...I just didn't want to have to.

    Last thing I need is to replace a crankshaft or bearings.

    I guess the smaller engines do have a definite advantage. I was working on the assumption that with the lower RPMs that the gas engines would run at that the balance wouldn't have such a large effect as with the smaller nitro engines. But as you pointed out with that much extra mass spinning around even a little bit will make a big difference.

    Bufferoo
     

  4.  
    #4
    Hi
    Here is a Video on how to balance large props.http://www.dodvideos.com/don3.wmv


    Good Luck

    Bill
     

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