Ancient Chinese windmills have obvious characteristics. Except for the horizontal axles, the sails are sails. The sail is not installed at the radial position of the wheel shaft, but on the eight poles around the shaft frame. The sail is also partly installed, that is, the canvas is narrow on one side of the pole and wider on the other side, and is tightened with a rope. As shown in the figure, when the wind acts on A, the sail is downwind, and the sail is perpendicular to the wind direction (the maximum force is applied) and is tightened by the rope; when turning to position C, the sail is blown outward, and the sail surface is parallel to the wind direction; to E Resume
Recover the windward position. Using the tightness of the rope and the partial installation of the sail, it can take advantage of the wind or headwind, just like in a sail. This device method allows the sail to swing freely with the wind without generating special resistance. The effective wind force range of the sail rotating on the outer circumference exceeds 180 degrees. If at position G, it starts to turn downwind, and the sail can also use part of the wind to operate in a small amount. The characteristics of this sail-style windmill are unique to China.