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GWatPE

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Joined: 01/09/2006
Location: Australia
Posts: 2127

Posted: 01:47pm 09 Jun 2010

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My first windmill was a single blade unit, with a couterbalance weight.

Looked really wierd. There are too many problems associated with a single blade, that outweigh the aerodynamic and speed benefits. The dynamic wind pressure on the single blade exerts terrible loadings on the bearings during rotation. I did see a unit with 2 stumpy counterbalance weights, that was better, but I just progressed to 2 blades, and then now have 3 blades. I won't be going to any more blades, as there don't sweem to be any yaw, or balance problems with a 3 blade system. Electricity is not as demanding as water either.

Ironless cores, and good magnets have all but eliminated the need to have variable pitch.

Gordon.

become more energy aware

MacGyver

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

Posted: 06:00pm 09 Jun 2010

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Jarbar

Thanks for that Link. It's too bad they didn't show their "new design" running. I imagine it does two things, namely makes LOTS of noise and also "hunt". Hunting is when it goes from over-speeding to it's default fail-safe position and then back and forth, not happy with either extreme.

A single-bladed windmill even WITH a pitch-control set-up has two other problems: yaw and tower shadow.

The yaw part is it doesn't like to yaw when the blade is horizontal to the tower. It's merely physics; the angular momentum of the whirling blade fights spinning about it's perpendicular, vertical axis.

Secondly, when the blade passes in front of the tower, there is a "shadow" associated with the wind flow as the tower blocks the smooth flow. This creates a "beat" and it makes the thing shake at low wind speeds and actually vibrate at high rpms.

A single-blade design only really makes sense when it doesn't have to yaw. That means it runs in a fixed position and only works well where the wind direction is constant, like through a mountain pass.

Still, they are fun to build and watch. Like I said somewhere here, I'll build one with a variable-pitching mechanism and post it. That takes care of one of the three major problems at least!

Also, if you'd like to make it easier for folks to read your posts, there is a little blue, underlined "Forum Codes" thing at the bottom of the "Post Reply" box. If you click on it and go to "Images and Links" then copy and paste the second code into your post, you can replace the URL with that of where you want to redirect your reader's interest and replace "My Link" with a keyword, such as "Link" as I have done in this post.

Thanks again for the video.

. . . . . Mac

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

MacGyver

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

Posted: 06:09pm 09 Jun 2010

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DTMC

The blade-pitching system you mentioned here is for a drive component of an airplane, I think.

CAMEWA was the system used by the US Coast Guard to adjust their underwater propellers (screws) on icebreakers some years back and they worked basically the same way only used hydraulics instead of electric input as does the one in your example.

Also, just so you know; I build stuff because I enjoy building. I'm not actually after a windmill that will necessarily set the world afire with efficiency; it's just a hobby to me.

Thanks for the post.

. . . . . Mac

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

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