Hi Geoff,<p>
From what we've seen so far, and from experiences of others, 3 blades seems to be more favorable over 2 (or 1), and possibly 5 over 4. It has more to do with ballance and vibrations than anything else. 2 or 4 blade models will tend to vibrate more because of the cyclic loading, the power peaks and vibrations peaks are synchronized, kind of like an unballanced washing machine that starts walking across the floor on the spin cycle. The blades on a 3 or 5 blade turbine will contribute vibrations peaks & power peaks out of phase, making for smoother operation.<p>
You probably don't see too many 5 bladers because more blades makes the turbine solidity higher (ratio of solid space to empty space in the swept area, for anyone who may not know what solidity is). That being said, check out this link for a 5-blade water-based Darrieus:<p>
http://www.althydrosolutions.com/<p>
You can get a lower soliditiy turbine with 2 blades, but more vibration.
Less vibration with 3 blades, but higher solidity, but the blades could also be made smaller.<p>
Or turbine has a solidity of 0.3, which is pretty high. We`ve actually made a 2-blade adapter, but haven`t used it for any testing yet. See some of the competing models, quietRevolution and Turby:<p>
http://www.quietrevolution.co.uk/
http://www.turby.nl/ (hit the English link)<p>
Cheers,
Shawn
I have a solidity close to 0,5 on a 2 blader VAWT. Older was 0,36....and 2-blader too.
I have an articulating system...and I seek self starting ability and no stall at high speed situation.
At least I can tell after this being tested which was the better way.
