Why do windmills have 3 blades? Wouldn't more blades be better?

Question

Why do windmills have 3 blades? Wouldn't more blades be better?

Answer 1

No, the extra weight from the baldes causing friction on the gear counteracts any benefit from having more blades.

Answer 2

If you have just three blades but these three blade are wide then you can capture more air and be efficient at the same time. This makes for more power!!

Answer 3

I read this somewhere, it said something like: 2 or 3 blades are the most efficient, if there are more, the blades would prevent wind reaching the blades next to it, affecting all the blades.

Answer 4

In theory, more blades would generate more torque, so the benefit would be there, even factoring in friction.  You can think of it as though each blade offers a given amount of force that converts to torque.  Each blade you add offers a little more, until the blades become too crowded to get the benefits of the air passing by.

The main reason large windmills have less blades is that 1) they have less weight being supported, making them less likely to fail (i.e., fall down), and 2) less cost from less materials.  The benefits you get from more blades are not that much, compared to the increase in cost.

Answer 5

A windmill is an ancient device for grinding corn, sawing logs, or other low-speed application.  These often have many blades, vanes, or sails fitted in various ways.

If you are looking at a machine with only three narrow blades, it is called a Wind Turbine, and most of these are for generating electricity.  A wind electric turbine is emphatically NOT a "windmill."

In wind electric turbines, the optimum speed of operation calls for long, narrow blades, and the simplest way to construct one so as to be easy to balance and easy to assemble is to fit it with two or three blades.  At these speeds, it is the "disc area" rather than the surface area of the combined blades that determines the power output, like an airplane propeller.  So the fewer blades of a certain length, the better.