Vertical Axis Wind Turbine - What is the best airfoil?

I've always been interested in windmills. The vertical axis wind turbine (VAWT) seem really cool. I discovered there is a company that (under contract) assembles them right here in my state of Michigan. So, on our summer vacation last year I diverted the family unit over to the assembly plant to see what's new, and exciting. Well, guess what, the plant is closed on weekend. Who knew. Well, for one, Momma thought I should have. Oh well, we got to see their demo unit Windspire up close anyway. It was just whipping.

Anyway, to my question, if I wanted to build a really efficient VAWT, what would be the best shape for the airfoil?

I've attached an old patent I found that has a drawing (Patent 4247252). I copied the drawing into Inkscape and redrew the airfoil using bezel curves.

But, is this the best shape to start with?

I'm hoping some aeronautical engineer out there can comment.


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Mikel994 years ago
I am starting with a naca0012 on my first prototype. But will investigate others.....
u don't have to start from a 'scratch'. As far as blade design is concerned i prefer u guys to view NACA airfoil Catalogs, they have complete details regarding chord length and corresponding lift to drag ratio!
jbc457 years ago
Take a look at It plots out a symmetrical NACA airfoil and curves the chord line to match the radius of your vertical axis wind turbine.
jimk3038 (author)  jbc457 years ago
Thanks for the info - looks like good stuff.

Also, I attached a couple of pictures of a vertical axis windmill I visited recently. They call this brand of windmill a "Windspire".

I zoomed in an the airfoil in the last picture so you can see the shape they used.

Just FYI info,
What you have there is a airfoil.  Yes that is probably the best shape to start and finish with.  It's been working for airplanes for over a hundred years, I'd say thats a good amount of testing on it.
jimk3038 (author)  RedneckEngineer7 years ago
Maybe I should have been more specific. I'm wondering about the actual shape of the airfoil. I'm asking if this specific shape is the best. Specifics like upper to lower camber, cord length, and maximum thickness.

Here is a link to a bunch of info on Wikipedia concerning airfoils.

One big question is, what is the best cord length for a given VAWT diameter.
Screenshot-Mozilla Firefox.jpg
I  seem to recall some members on a forum (which one I forget) suggesting the NACA 4 digit series airfoils as being most suitable.
Apparently the NACA 0015 is too thin with possible strength issues and the NACA 0030 was too thick, most seemed to agree on something in the middle like the 0025 region.
I'd suggest the TLAR  method for the chord length, personally Id be looking at a chord length of 1/10th to 1/15th of the VAWT dia.

I googled a lot of NACA0015 use on the Otherpower forum at
jimk3038 (author)  petercd7 years ago


Thanks for the helpful reply.

I also did some internet digging and found some interesting stuff. The following two pdf documents are packed with info about Giromill blades. The good news is, looks like most folks are using blades that are symmetrical. That sure makes constructing the blades easier.

For picking the cord length, what is the TLAR method? I have not heard of this acronym before. In fact, I have not seen much written at all about choosing cord length.

Thanks again for the good comments,
That Looks About Right :)

as in the Helical Vawt in the link

in this shot you can see the airfoil shape
jimk3038 (author)  petercd7 years ago
 Those are great pictures. Thanks for the links. Those are keeper pictures.

In fact, I was so impressed with the pictures I had to create a Flicker account just so I could leave some good feedback for the picture's author. 

His VAWT looks like a dandy! I wonder how much power he gets from it.

Thanks again,

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