why are blades different from a windmill

Re: why are blades different from a windmill

Do you mean the comparison between the multi blade, slow turning water pumper type. compared to the 3 blade high speed generator types?
Wayne

Re: why are blades different from a windmill

Well the sail types were excellent for their purpose, which was slow turning, with high torque. Their overall efficiency wasn't high at all, but they were very well suited for turning the heavy, rumpling mill stones etc.
However when we moved into generating electricity, that slow speed, required extensive gearing, or belting, with the losses involved, to bring the revs up to something useful for the generators of the day and indeed, most of the smaller wind turbines used for private dwellings today. These modern blades have far greater efficiency due to their proper airfoil designs. They also have greater efficiency because of the greatly reduced drag, compared to the many bladed water pumpers that used to dot the US landscape. Three blades to drag through the air instead of perhaps twenty. One might at first think that the more blades the better, but looking closer reveals that's not the case at all for high speed props. The best efficiency of all is 2 blade, but unfortunately, when changing direction to new headings, following the wind, the 2 blade units are very choppy and prone to extreme vibration. Thus the 3 blade designs, a good compromise.
Re the space between blades on the 3 blade units, keep in mind, that when the prop speed comes up, it begins to present itself to the rushing wind, as almost a solid disc, and actually at times forces the wind to fan out and go around the outside of the prop, rather than through the blades as one might at first think.
It's a very interesting study and I hope this has given you some understanding of the differences.
Cheers
Wayne