Scimitar Propeller Blades - angle or pitch change

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  • substandard
    Lieutenant, Junior Grade
    • Jun 2020
    • 34

    Scimitar Propeller Blades - angle or pitch change

    Are there any rules of thumb or observations for blade angle change or prop pitch change (perhaps expressed as a pitch factor) as we go from blade root to tip?
    I am crafting a 7 bladed scimitar style prop and wondering how much to bend the blades along their length to reduce turbulence and produce a more laminar flow out of the prop.
    Thanks for any reply; I know just enough to be dangerous on propellers.
  • substandard
    Lieutenant, Junior Grade
    • Jun 2020
    • 34

    #2
    Got it I think.
    Best laminar flow happens when pitch across the span of the blade is same at each radius point. Pitch=2*pi*R*tan of blade angle (I think). So we're twisting the blade to change its angle witch will maintain the same pitch value at each radius point on the blade. Seems simple enough. Please correct me if I'm wrong in any of this.

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    • Subculture
      Admiral
      • Feb 2009
      • 2119

      #3
      The formula is correct. Optimum prop pitch for scale subs tend to be from around 0.7-1.5 times the diameter. Higher pitch tends to be better for higher speed, but torque roll can be a problem on a boat with lower stability and a single screw. The larger the prop is in relation to the craft the more it's affected by propeller pitch, other factors include the boats overall weight, power at screw etc. 1:1 pitch to prop diameter-known as a 'square prop'-is often a good compromise, but often some empirical testing is the only answer.

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      • substandard
        Lieutenant, Junior Grade
        • Jun 2020
        • 34

        #4
        Originally posted by Subculture
        The formula is correct. Optimum prop pitch for scale subs tend to be from around 0.7-1.5 times the diameter. Higher pitch tends to be better for higher speed, but torque roll can be a problem on a boat with lower stability and a single screw. The larger the prop is in relation to the craft the more it's affected by propeller pitch, other factors include the boats overall weight, power at screw etc. 1:1 pitch to prop diameter-known as a 'square prop'-is often a good compromise, but often some empirical testing is the only answer.
        Question on that. Given that the blade angle changes quire a bit, for example it may change from about 35 degrees at root to maybe 7 degrees at tip; what blade angle do I use for calculating the nominal pitch of the prop?

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        • Subculture
          Admiral
          • Feb 2009
          • 2119

          #5
          Pitch is taken at 0.7x radius

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