pitch angle

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

1. Joined: Apr 2013
Posts: 4
Likes: 0, Points: 0, Legacy Rep: 10
Location: Plymouth

Chris MatthewsNew 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. Joined: May 2008
Posts: 2,337
Likes: 199, Points: 63, Legacy Rep: 1082
Location: Beaufort, SC and H'ville, NC

philSweetSenior 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. Joined: Mar 2005
Posts: 139
Likes: 27, Points: 28, Legacy Rep: 209
Location: Durham, NH USA

DMacPhersonSenior 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. Joined: Aug 2007
Posts: 5,852
Likes: 290, Points: 83, Legacy Rep: 1749
Location: Tasmania,Australia

rwatsonSenior Member

Last edited: Aug 29, 2013
5. Joined: Aug 2007
Posts: 5,852
Likes: 290, Points: 83, Legacy Rep: 1749
Location: Tasmania,Australia

rwatsonSenior Member

6. Joined: Jun 2009
Posts: 1,173
Likes: 137, Points: 63, Legacy Rep: 1165
Location: Sweden

baeckmoHydrodynamics

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. Joined: Nov 2007
Posts: 2,913
Likes: 62, Points: 48, Legacy Rep: 719
Location: Melbourne/Singapore/Italy

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. Joined: Nov 2011
Posts: 242
Likes: 12, Points: 18, Legacy Rep: 117
Location: New England

johneckSenior 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.

Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.