pitch angle

Discussion in 'Props' started by Chris Matthews, Aug 24, 2013.

  1. Chris Matthews
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    Chris Matthews New Member

    how do you calculate the pitch angle of a blade on a propeller of P/D = 1.4 at the tip and at the root (r/R = 0.15).
     
  2. philSweet
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    philSweet Senior Member

    Pitch ratio isn't measured at the tip. It is measured at some arbitrary distance from the center - 70% out is somewhat standard. The pitch is the distance that a section will screw itself forward with no slip. It usually isn't constant across the span of the blade. So there isn't any real way to calculate it with any confidence. You either measure from an existing prop, or design one to suit your needs.

    About all you can say from the posted info is that 2 * Pi * r * tan(phi) might equal 1.4* D at some place along the span. See the hydro dictionary thread at the top of the subforum All Things Boats and Boating. There is a link to it in the first post. It has the definitions of propeller terms, although pitch itself is not explained very well for some reason.
     
  3. DMacPherson
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    DMacPherson Senior Member

    Pitch angle at any radial position (r/R) is defined as: ATN([P/D]/(PI*[r/R]))

    Remember that P/D must use the pitch value measured at the radial position - not some average overall pitch for the propeller. (Of course, a constant pitch propeller has the same P/D for all radii.)

    Don MacPherson
    HydroComp
     
  4. rwatson
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    rwatson Senior Member

    Last edited: Aug 29, 2013
  5. rwatson
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    rwatson Senior Member

  6. baeckmo
    Joined: Jun 2009
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    baeckmo Hydrodynamics

    If you cite the text correctly it says "there is no pitch shown on Volvo Duoprops" (my underlining though...). Volvo does not publish dia or pitch on the Duoprop or IPS equipment, but refer to a "size number", like A4, where the letter shows propeller series, and the number is referring to, but not showing the actual pitch.

    Generally, the configuration at the station r=0.7 x R (where R is max propeller radius) is used, since it represents the "mid area", but in some cases the load distribution over the radius is changed, and then the pitch may be taken at another (more representative) radius.
     
  7. powerabout
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    powerabout Senior Member

    Is there a standard for where to measure pitch as you would need 2 dimensions radius and leading to lagging edge on the blade for cambered blades
     

  8. johneck
    Joined: Nov 2011
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    johneck Senior Member

    Don M has provided the method to calculate the pitch angle. So if you can measure the angle, the inverse will give you the pitch. The pitch is for the nose-tail line, so for cambered sections it is not so easy to measure directly, but you can certainly measure and find the pitch with sufficient accuracy for most purposes.

    Many propellers are constant pitch, but if they are not, then take several measurements and use some sort of weighted average.
     
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