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Forum Index : Windmills : how do you determine the right blade size

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jeff

Newbie

Joined: 29/05/2007
Location: United States
Posts: 4

Posted: 05:18am 29 May 2007

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Hi all , im new to the forum but have been reading it a few weeks.
I have alot of questions i would like to ask of you all but the one on my mind at the moment is, how do you know what size blades you need for different motors.
Is there a formula to calculate blade size to motor torque?

Thanks in advance

Storm

Regular Member

Joined: 12/09/2005
Location: Australia
Posts: 43

Posted: 12:38pm 29 May 2007

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Put simply NO, the enviroment is first!! speed of wind and density of wind, then different motors require different forces i.e. speed of motor, size of motor, torque of motor, wiring and resistance inside the motor then the amount of blades, blade angles blade width and then length of blades and their efficincy then there's expected output in volts, amps, watt hours, if you are just starting out you have a lot to learn, good luck and welcome.

Usually more torque requires longer blades or heavier angles but these also reduces RPM, mainly it depends on width, angle, length and wind speed.

Hope this helps!!

jeff

Newbie

Joined: 29/05/2007
Location: United States
Posts: 4

Posted: 04:12pm 29 May 2007

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Thanks for the prompt reply Storm , it all seems very complicated.
I was going under the assumption of the longer the blade , the more weight it would move , I have made a few sets of pvc blades and most were able to spin the small stepper motors i attached them to.
What im curious to know is , how do you know if your blades could have been smaller and still turned your motor faster , is it just trial and error of is there a formula or eqaution to determine torque to length , or blade angle to torque.
To me it would seem you would want the smallest size blades you could get by with ,that would still turn the motor you are using, anything more and you start losing RPMs.
This is all new to me so please correct me if I am missunderstanding something.

Highlander

Senior Member

Joined: 03/10/2006
Location: Australia
Posts: 266

Posted: 08:34am 30 May 2007

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Hi Jeff,
This might help.
http://warlock.com.au/bladecalc-abstract.htm

When I made mine the chord at the root was impractically high on the calculator so I reduced it and the tip was a little small so I increased it.
Just have a crack at it.
Mine aren't perfect but I don't care really.

Central Victorian highlands

thefinis
Regular Member

Joined: 23/08/2006
Location: United States
Posts: 53

Posted: 12:10pm 01 Jun 2007

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There are many sites for blade calculators which should give you some idea of output.

http://www.alton-moore.net/index.html

http://www.windpower.org/en/tour/wres/pow/index.htm

There are lots more but this may give you a start

Finis

Texas born and bred

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