Propeller KA 4 70 Geometry

Discussion in 'Props' started by sURAJ, Jul 8, 2017.

  1. sURAJ
    Joined: Jul 2017
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    Location: usa

    sURAJ New Member

    I am trying to generate CAD model of propeller KA 4 70 in solid works and then later on I am trying to validate open water characteristics of propeller with experimental results using CFD. But I am having some problem with geometry of KA 4 70 propeller.
    First of all I am creating 2D airfoil section and then I am using formulas in Carlton for converting it in 3 Dimensional geometry. I have below question.
    1. I have attached the screenshot of formulas in Carlton. Does these formulas required 2D airfoil section to follow some convention like leading edge should be at (0,0) and trailing edge at (-c,0) where c is chord length ? I have also attached 2D airfoil section. Which airfoil section shall I use for these formulas?

    2. Also, I have attached screenshot of Prop KA 4 70. As can be seen from the picture, generator line is not passing exactly through the center line of chord at each cylindrical section. But, I think that these formulas assumes that generator line and center line are coincident and hence has the term 0.5C in these formulas? How shall I consider this in these formula?

    Thank you in advance.
     

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  2. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    In the 1988 edition of PNA, read Vol II, Chapter 6, Section 6. Geometry of the Screw Propeller. The dashed line shown on the blade development is the line of maximum section, not the 50% cord (though it may be). Additionally, the sections shown have to be laid out on the helical generator line for your specific radius|pitch combination, see the chapter I listed.
     
  3. sURAJ
    Joined: Jul 2017
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    Location: usa

    sURAJ New Member

    Thank you very much. I have gone through the material on propeller screw geometry that is given in PNA Vol II. But, the section does not talk about how to convert 2D section airfoil data in 3D propeller geometry. I am using formulas from Carlton to convert 2D section airfoil to 3D propeller geometry so that 2D airfoil will be laid out on generator line and at particular pitch angle. But I am not sure if these formulas can be directly used for all 2D airfoil or formulas needs to be changed based on airfoil section.
     

  4. jehardiman
    Joined: Aug 2004
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    Location: Port Orchard, Washington, USA

    jehardiman Senior Member

    I see your question now. No, you can't just plug and chug based upon the assumption that c/2 is always on the skew line. As you can see from the KA 4 70 blade section drawing, the center of the section is independent of the skew. FIW, just do it in cylindrical coordinates, there is no need to develop the blade in x,y,z if you use a boring mill not a turret mill.
     
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