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MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 03:31am 15 May 2009

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Has anyone ever done this besides me? I made one 35 years ago just for the
sport of it.

I used an aluminum sheet-metal, hollow, asymmetric-section blade about
ten feet long, 12 inches at the root and 3 inches at the tip. It was mounted
across from a solid-steel counter weight on a HAWT with a tail.

Turning slowly, quietly and very powerfully, it worked like a champ and drew
a lot of stares. Mounted atop a wooden telephone pole, the blade "beat"
each revolution as it passed the tower at moderate to high speed -- that
was the only "problem" I encountered aside from degrading remarks from
onlookers!

Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas

Gizmo

Admin Group

Joined: 05/06/2004
Location: Australia
Posts: 5119

Posted: 03:51am 15 May 2009

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Hi Macgyver, it sounds like you have a lot of expierence in windmills that others can learn from, I must say your posts have been very interresting.

Would love to see some pictures, but I understand getting the pictures online can be a little daunting at first. The Image Upload button above (

) will get you started. And you can always experiment by using the Preview Post button to see how your post is looking before you actually post it.

Anyway, keep the posts coming.

Glenn

The best time to plant a tree was twenty years ago, the second best time is right now.
JAQ

oztules

Guru

Joined: 26/07/2007
Location: Australia
Posts: 1686

Posted: 12:56pm 15 May 2009

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Yes Macgyver, I too have had a stab at this ... as a curiosity.

I carved a 60" blade, found the center of mass and whacked a hole in it right there. I had left the root very thick, so that there was over 2/3 of the blade out 1 side, and heavy root out the other.

It looked pretty harmless, so with simple stupidity, I poked a big screwdriver through the hole and walked outside into the breeze beside the shed.

It started turning slowly, and seemed pretty benign, so I walked further out of the wind shadow of the shed.

Suddenly it took off and became a blur. It was about this time I realised what a stupid thing I had done. I was attached to a whirring blade inches in front of me, and it was getting difficult to hold it... and it was getting faster by the second.

I couldn't turn it out of the wind without decapitation looking immanent, and so edged back into the wind shadow of the shed.

White and shaking.... I decided that yes single blades do work very well, and go incredibly fast.... and that I would not be repeating that any time soon.

It was apparent that the dynamic imbalance was going to be a problem for any bearing set up. The wind pushing the airfoil end of the blade puts an enormous amount of asymmetric bias on the shaft. The small turning out of the wind I did do, told me that it was going to have teeter trouble as with a 2 blade unit.

I didn't persue this any further, and decided that I would have to live with a heavier alternator and use three blades, rather then getting tangled up with the dynamic forces that would bedevil me with a 1 or 2 blade unit.

From and alternator perspective, 1 blade is the best, as rpm for a given wind and diameter is much superior to the 3 blade unit, so the magnets and coils can be smaller and lower resistance.... but from a survivability perspective it looks pretty poor.

The blade erosion of a single blade unit with a TSR of as much as 10 to 15:1 would be a problem for wooden blades also.

So it was back to three for me..... thats for electricity, for water I like my 18 blade southern cross.

..........oztules

Village idiot...or... just another hack out of his depth

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