> > But the most efficient turbine is the two-blade 'propeller' 
> type, by 
> > far.
> > 
> 
> Are you sure ? Why is that 'ALL' wind turbines is the 3 blade type ! 

IIRC the number of blades (for N>0) does not affect the maximum
efficiency, but it determines the optimum rotation frequency for a given
windspeed. Somthing like: optimal is [tip linear speed] * [number of
blades] = [some constant] * windspeed. So less blades means higher
frequency. Most commercial windmills generate electricity, which
requires a high frequency to drive the generator. So less blades == less
gearboxing = less losses etc. 1 blade is impractical, 2 can be done, 3
is much more stable than two, 4 does not add much beyond 3. So most
designs are 2 or 3. Except for the american 'slow runners' with lots of
blades, which are not used to generate electricity (used for water
pumping?).

Wouter van Ooijen

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Van Ooijen Technische Informatica: www.voti.nl
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docent Hogeschool van Utrecht: www.voti.nl/hvu
 

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