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I recently saw this .gif on wikimedia commons.enter image description here
I have now decided to try 3d modelling the Savonius VAWT, but my question is, how can one create such curved surfaces? They aren't possible to be recreated using the primitive objects already available, so the question is how to add this quirky curve?I am a beginner and have learned a lot from the Blender Stack Exchange Community, so I'm requesting further assistance.

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You could cut a cylinder in two halfes and delete one half. Scale it, duplicate the remaining mesh 2 times and rotate it by 120° (preferably using the spin tool) –  stacker Apr 22 at 16:45
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Based on the quality of the questions you have been asking. I would highly recommend you watch a beginner series or read a simple introductory tutorial or two. These are rather trivial, overly simple (as in adding primitives or deleting faces) and redundant questions at most that could be accomplished using basic modeling techniques. Reference material is easily accessed from inside Blender itself by going to the manual for the desired tool/feature. See this meta post for some links to other resources. –  iKlsR Apr 22 at 17:21

2 Answers 2

up vote 4 down vote accepted

To me they just look like three half cylinders, rotated by 120°. Add a cylinder, select the top and bottom face and half of its shell and delete them.
enter image description here enter image description here enter image description here

Then select the remaining faces and move them so that the last straight edge is located on the center of the scene. Make sure the 3D cursos is located at the center as well. If it is not, hit [Shift+S] and select "Cursor to Center". Make the cursor your current transformation center by pressing [.]
enter image description here

Duplicate the vertices by pressing [Shift+D] and immediatly press [Esc] to cancel translation. Rotate the selected vertices by pressing [R] and moving your mouse or by typing the desired angle of 120 degrees on your keyboard. If you chose to use the mouse, you can hold [Ctrl] to make Blender increment the angle in five degree steps. This makes aiming for 120° easier. Hit enter to apply the rotation. Duplicate the selected vertices again and rotate them in the same manner.
The result should look something like this: enter image description here

If you want to give it some thickness, go to the modifiers tab and select the solidify modifier:enter image description hereenter image description here

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I tried doing this but the 3 part-cylinders don't stick together, do you mind sending me your .blend or assisting me further, @maddin45 –  Nib Apr 23 at 11:37
    
I am not sure what you mean by they "don't stick together". The mesh parts are still separate, if you mean that. you can select all vertices press [W] and select "Remove Doubles". The vertices that have the same location will be merged. But in this case this will probably not work well with the solidify modifier, since the face-normals switch direction at that point. You might have to apply the modifier and remodel some areas by hand. You can get my blend file from here. –  maddin45 Apr 23 at 12:14

One way is to use curves.

  1. Add bezier curve.

  2. Adjust it into a half circle. This can be easier from top view - press numpad7 You also want to move the curve to the side so that one curve point is at the object centre which is still located at the 3d cursor.

  3. Set the pivot point to 3d cursor - shortcut is .

    enter image description here

  4. Select both points on the curve and duplicate ShiftD then rotate 120 degrees - If you don't know the angle you want then let blender calculate it for you. R360/3 360 is a full rotation so we divide that by 3, then duplicate and rotate again for the third blade.

    enter image description here

  5. Set the extrude length to suit

    enter image description here

  6. Add a solidify modifier

    enter image description here

  7. Add a centre pole. You may also want to duplicate the original curve, remove the extrude and add a bevel depth to easily make the capping for the top and bottom.

    enter image description here

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