Why do windmills typically have 4 blades, yet all modern wind turbines have 3?
In: 9124
There are already a few good answers, but there’s one overarching truth to why modern windmills usually have 3 blades: optimization.
There are many tradeoffs, and 3 blades just happens to be how the math works out for balancing the design against size, materials, structure, generator power limits, design complexity, geometry, expected wind speed, etc and your optimization spits out 3 blades as the best for the typical sizes of power generating windmills.
They’re far, far higher-performance than the old 4-bladed cloth and frame windmills, which are just much easier to build and balance than 3-bladed fans.
If the fans were a different size, or made of different materials, or exposed to different wind speeds, or any number of other major factors, the optimal design might have been 5 blades, or 7, or 9.
For examples of when 3 blades are not optimal, look at many helicopters, which range from 2 to 9 blades depending on size, power, noise and other requirements. Computer cooling fans are also often highly optimized and have varying numbers of blades for various applications.
It’s a big, giant “it depends,” so 3 may not be the magic number forever, and there’s no canonical, set answer.
As for why 4 blades on old windmills, though: it’s just easier, and the technology wasn’t there for engineering and building windmills like we do now.
Why do windmills typically have 4 blades, yet all modern wind turbines have 3?
In: 9124
There are already a few good answers, but there’s one overarching truth to why modern windmills usually have 3 blades: optimization.
There are many tradeoffs, and 3 blades just happens to be how the math works out for balancing the design against size, materials, structure, generator power limits, design complexity, geometry, expected wind speed, etc and your optimization spits out 3 blades as the best for the typical sizes of power generating windmills.
They’re far, far higher-performance than the old 4-bladed cloth and frame windmills, which are just much easier to build and balance than 3-bladed fans.
If the fans were a different size, or made of different materials, or exposed to different wind speeds, or any number of other major factors, the optimal design might have been 5 blades, or 7, or 9.
For examples of when 3 blades are not optimal, look at many helicopters, which range from 2 to 9 blades depending on size, power, noise and other requirements. Computer cooling fans are also often highly optimized and have varying numbers of blades for various applications.
It’s a big, giant “it depends,” so 3 may not be the magic number forever, and there’s no canonical, set answer.
As for why 4 blades on old windmills, though: it’s just easier, and the technology wasn’t there for engineering and building windmills like we do now.
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