Anemometer Modified II

A commercial anemometer was modified by replacing the four cups with four identical two-dimensional blades, each with a circular arc side and a flat side. The flat sides are fixed to four arms radiating from a pivot so that they are parallel to the wind direction. The rounded sides all point in the same direction around a circle. When the wind blows, there is a lift force on the rounded side of each blade and they unite in causing rotation about the pivot with the curved sides leading. The more blades the faster the rotation is a prediction.