Windmill sails work by harnessing the pressure of the wind, which causes them to rotate, with their speed controlled by adjustable sections called shutters.
The Basic Principle: Wind Pressure
The fundamental principle behind how windmill sails operate is their interaction with wind. As the wind blows, it exerts pressure against the large surface area of the sails. This force, acting on the angled surfaces, creates a turning moment around the central axle, causing the sails to rotate.
According to the provided reference, "The mill works in response to the pressure of the wind on its sails." This direct pressure is the engine that drives the entire mechanism.
Anatomy of a Windmill Sail
Unlike simple flat panels, traditional windmill sails, particularly those mentioned in the reference, are more complex.
- Each sail is made up of hinged flaps.
- These flaps are specifically called shutters.
These shutters cover the frame of the sail and can be opened or closed to adjust how the wind interacts with the sail.
Regulating Speed with Shutters
One of the key functional aspects of these sails is the ability to control the rotational speed of the mill. This is achieved by manipulating the angle of the shutters.
- The miller can change the angle of these shutters.
- Adjusting the angle allows the miller to regulate the speed of the mill.
When the shutters are more closed, the sail presents a larger, flatter surface to the wind, capturing more pressure and potentially increasing speed (or starting rotation). When the shutters are opened more, wind can pass through them, reducing the pressure on the sail and slowing the mill down. This is crucial for preventing damage in high winds and for controlling the grinding speed of the millstones inside.
Getting Started
To initiate movement, certain conditions must be met. As the reference states, "With the brake released, and the shutters closed, the sails will turn."
- Brake Released: The primary brake mechanism must be disengaged to allow free rotation.
- Shutters Closed: With the shutters closed, the sails offer maximum surface area to the wind, allowing the pressure to build up and start the rotation from a standstill.
Once turning, the miller can then adjust the shutter angles to achieve the desired operational speed based on wind conditions and the task at hand.
In summary, windmill sails are sophisticated structures that capture wind pressure using adjustable shutters, allowing for both power generation (rotation) and crucial speed control necessary for the mill's operation.
