# Propeller KA 4 70 Geometry

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

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### sURAJNew 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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### jehardimanSenior 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.

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### sURAJNew 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.

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### jehardimanSenior 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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### MarcogenNew Member

Hi everyone, like sURAJ I'm trying to create a 3D geometry for the Ka 4-70.
I'm working in Matlab and for now I've imported in a script the coordinates from the same tables posted by sURAJ.
After a little work on these coordinates I've obtained the results that you can see in the image below.
Now I have some questions for you and I will be very grateful if you can help me.
The points of x=0 in my riferiment system are on the "center line" but I don't understand what it really is.
In this riferiment system the chord isn't horizontal and the origin isn't on the middle of the chord.

Now I want to generate a 3D geometry by importing curves from points in Solidworks but i think I have to convert the coordinates, give to the section the pitch angle and wrap them on an helix, can someone help me ?

The last question is about the thickness at the centre of shaft : I don't know how to use this information.
Sorry but I'm completely new in this sector and I'have already read the carlton section and the PNA

Thank you in advance
Marco

Last edited: Nov 1, 2017
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### sURAJNew Member

You can refer to Carlton's chapter 3. It gives detail information and formulas for generating 3D propeller geometry from 2D airfoil section coordinates. You can refer to section 3.7 for the formulas.

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### MarcogenNew Member

Thank you very much I think I got the geometry

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### Sahil JawaNew Member

can u tell me how to do to convert the coordinates, give to the section the pitch angle and wrap them on an helix, can someone help me ?

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### RomaleNew Member

Could you tell where did you get pitch distribution along the radius?

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### jehardimanSenior Member

Ka series wheels are made for nozzles and do not have changes in pitch radially like open water propellers (i.e. like B series). That is why the root is so shortened and thickened. FWIW, bi-directional Kaplan blades used in thrusters are designed in an entirely different shape and manner.

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### RomaleNew Member

jehardiman, thank you for your reply, the pitch question is clear. Now I'm checking the geometry of sections by tables from Carlton. The reference line for face/back coordinates still not clear for me. I guess (in my picture) Yellow line - reference line for points A and B, distance A-Yellow line - coordinate for the back, B-Yellow line - for the face (in percentage of max. thickness of the section, in some distance from max thick. line - 20, 40, 60...). But when I try to check the shape and thickness close to leading edge the geometry is crashing. (the main idea to use picture of section in scale, then check it by table from Carlton)

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### jehardimanSenior Member

You say the geometry is "crashing", why? Is it that you have a poor splining algorithm? Are you not accounting for nose radius? Remember the root fileting is a whole other issue. There is plenty of space to fair the back and face (though most likely the 0.2R LE is going to be buried in the root filet anyway). I think you might have to look at your table better as it shows the face LE 100% from max thickness as 33.33 but the back LE 90% from max thickness as only 27.40. Either the table is accounting for the root filet or there is an error in the table (noting 23.33 vice 33.33 would not be unrealistic).

Realizing something is wrong and then fixing it are what makes an engineer, everything else is repetition that can be done by anybody.

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### RomaleNew Member

You are right. "Crashing" - wrong word, I meant strange coordinates for face LE 100% - 33 / back LE 95% - 27,40. I did not account nose radius, now I'm checking how to do it correctly. Thank you.

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### RomaleNew Member

jehardiman, could you explain something. I can't find any clear instruction about calculation of Nose/Tail radius. (Neither in Carlton nor in PNA (v2)). I attached table for counting radius of Kaplan blade sections, but drawing from this table doesn't match with drawing from coordinates table (Carlton, PNA).
Em - max thickness of section, Yн - nose circle ordinate, dн - diameter of nose circle (the same for trailing edge (tail) Yx, dx)

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