Hmmm. I fly model planes, and regularly there are discussions about 
propeller efficiency. It appears that 2 bladed props are more efficient 
than 3, and that 1 is better than two. The problem is that there are 
pragmatic issues with mounting 1-bladed props.... un-even thrust and a 
corkscrewing motion of the plane behind it (even when counterbalanced 
correctly). Also the landing gear needs to be really long.

http://www.hartzellprop.com/engineering/engineering_faqs.htm

http://www.pilotsofamerica.com/forum/archive/index.php/t-3247.html

I was about to shelve this mail as not adding much to the discussion 
until I cam across the following. Really fascinating article (and mostly 
on topic):

http://www.windmission.dk/workshop/Marcellus%20Jacobs.htm

Enjoy

Rolf

Lars Bloch Gravengaard wrote:
> ----- Original Message ----- 
> From: "Lars Bloch Gravengaard" <mail1@lg-web.dk>
>
>
>   
>> ----- Original Message ----- 
>> From: "Peter" <plp@actcom.co.il>
>>
>>     
>>> 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 !
>>
>> Lars
>>     
>
> http://www.windpower.org/en/tour/design/concepts.htm
>
> "Two-bladed wind turbine designs have the advantage of saving the cost of 
> one rotor blade and its weight, of course. However, they tend to have 
> difficulty in penetrating the market, partly because they require higher 
> rotational speed to yield the same energy output. This is a disadvantage 
> both in regard to noise and visual intrusion. Lately, several traditional 
> manufacturers of two-bladed machines have switched to three-bladed designs."
>
> "Yes, one-bladed wind turbines do exist, and indeed, they save the cost of 
> another rotor blade! If anything can be built, engineers will do it. 
> One-bladed wind turbines are not very widespread commercially, however, 
> because the same problems that are mentioned under the two-bladed design 
> apply to an even larger extent to one-bladed machines."
>
> The bedst :-)
>
> "The Danish Three-Bladed Concept
>  Most modern wind turbines are three-bladed designs with the rotor position 
> maintained upwind (on the windy side of the tower) using electrical motors 
> in their yaw mechanism. This design is usually called the classical Danish 
> concept , and tends to be a standard against which other concepts are 
> evaluated. The vast majority of the turbines sold in world markets have this 
> design."
>
> Lars 
>
>   

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