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Optimum pitch of Blades?  RSS feed

 
Barry Fitzgerald
Posts: 43
Location: Welland, Ontario, Canada
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I am building my own turbine with 5 blades 30" long attached to an 11" hub. I am ready to to twist the blades but I am not sure of how much pitch would be best. Anyone have any ideas as to the best angle?
 
Chris Olson
Posts: 84
Location: Northern Wisconsin
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I don't know what material you are using, but a lot depends on the airfoil. For a 5 foot diameter rotor with a NACA 4412 or 4415, or a Clark-Y, I would go with 1 degree pitch at the tip of the blade and 10 degrees at the root. For GOE 222 airfoils you will have no twist with a constant 7-10 degree pitch along the entire length of the blade. If I knew more about the airfoil I could advise better.
 
Barry Fitzgerald
Posts: 43
Location: Welland, Ontario, Canada
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Thanks Chris for your reply. I have already started to build it. It should turn but probably not that efficiently.
I am using aluminum for the blades and have twisted them 15'.
This will be mounted on a 8 KW AC servo motor for the generator.
Let me know if there is anything that I should change before I go any farther.
I am trying to attach a photo, hope it shows up in the post.
IMGP3069.JPG
[Thumbnail for IMGP3069.JPG]
Rotor and Blades
 
Chris Olson
Posts: 84
Location: Northern Wisconsin
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Hi Barry,

It looks like aluminum flat stock and no real airfoil at all. For a wind turbine blade to work properly it must create lift like an airplane wing. That requires an airfoil. If the blades are just flat paddles basically, it will go around but won't make much power. When you design a turbine blade with an airfoil, the tip of the blade travels much faster than the root section. So the blade is pitched higher at the root than at the tip so as to achieve a fairly constant angle of attack for the airfoil over the full length of the blade.

For flat blades like that with no airfoil I really can't say what the proper pitch angle should be. They WILL run but I suspect will have a quite low TSR (Tip Speed Ratio). It looks like your hub can accept different type of blades. So as long as you have those made I'd go ahead and run them and starting working on a more efficient set of blades. A good place to start is to buy Hugh Piggot's book on building homebrew wind turbines, as Hugh covers blade building in there:
http://scoraigwind.com/axialplans/index.htm
 
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