Blade profiles definition - PropellerBlade function

[Mr. Daniel Floden 0]

Hi,

 

In order to understand your definition of pitch, skew and rake I have a couple of questions.

 

In the documentation there is a profile and a picture showing the definitions, although its slightly confusing since the (by the look of it) the pitch definition is defined as the blade profile is  rotating around max thickness when picth is altered.

 

If that is the case then rake would be influenced and this is not the case when you model the blade by the curves in CAESES. 

 

Can you point out what the tho points in that picture represents, one should be the generator line and the other max thickness, but which is which?

 

BR

Daniel

 

 

[Jörg 29]

Hi Daniel,

 

Sorry for the confusion - here are more details: The x-, y-  and z-coordinates are given by.

 

Here is a figure which explains the transformation:

 

Does this help?

 

Cheers

Joerg

 

PS: The pictures are taken from a paper which can be downloaded from our website (Rechnererzeugte Propellergeometrien; Stefan Harries, Bernd-Leopold Käth; Institut für Schiffs- und Meerestechnik der Technischen Universität Berlin, 1997).

[Mr. Daniel Floden 0]

Hi Joerg,

 

According to the definition of the Teta-angle in the picture of the profile above, the rotation (pitch) of the blade is done at the "1/2" point, which by definition alters the rake (ZR). This is not the case when modelling in CAESES. Thats the reason for our confusion.

 

I guess the blade profile is rotated around where the mid choord crosses the z-axis, in order to alter rake, skew and pitch independantly?

 

BR

Daniel

[Jörg 29]

Hi Daniel,

 

Just to make it clearer again, the procedure can be understood as follows (based on a centered profile, mid chord position on z-axis):

 

1. Apply rake
2. Rotate around mid chord position (center) using pitch angle
3. Apply skew along the new (local) x-direction of the profile

 

The result is shown in the second picture above.

 

Cheers

Joerg