Twisting Blades

[zymurgy]

Hi, I am building a small model of a windmill and i am having some troubles with the blade twists. Do you twist the blade 12 degrees at the base and end up with 5 or 6 degrees at the tip, or do you go all the way down to zero? I am using the ZACA 4412 and the stall point is a little over 12 degrees. please help. i would like any information you've got. thanks. bye

[Ungrounded Lightning Rod]

If I have it right, the tangent of the angle (i.e. the slope, the ratio of along-axis distance over along-circumference distance measured at the ends of the chord) goes with inverse of radius.  You never reach flat.

[wdyasq]

Well - at the root the angle should be 90 degrees less stall angle and transition to a good lift angle at the tip.  The angle can go negative on some designs.  All non-feathering blades are a comprimise dealing with available material, design speed and knowledge.

Ron

[richhagen]

I made some small blades based on that profile - NACA 4412.  Well they started out that way, I thickened them up a bit for strength.  They work ok once started up, but the way I made mine takes a little gust to get them going.  I put a post about it a while back, and received a bunch of good information which I hope to incorporate into an improved design.  Here is a link to that story:

http://www.fieldlines.com/story/2005/2/22/111119/599

Rich Hagen

[zymurgy]

Thanks to all of you. you all have helped me. Rich, i've been to your site and it helped me a lot as well. thanks to all of you again