Windmill
A windmill is a machine operated by the force of wind acting on vanes or sails to mill grain, pump water, generate electricity, or drive other machinery.
Windmills were used throughout the high medieval and early modern periods; the horizontal or panemone windmill first appeared in Persia during the 9th century, and the vertical windmill first appeared in northwestern Europe in the 12th century. Regarded as an icon of Dutch culture, there are approximately 1,000 windmills in the Netherlands today.
Forerunners
machines have been used earlier. The Babylonian emperor Hammurabi had used wind mill power for his irrigation project in Mesopotamia in the 17th century BC.Later, Hero of Alexandria in first-century Roman Egypt described what appears to be a wind-driven wheel to power a machine. His description of a wind-powered organ is not a practical windmill but was either an early wind-powered toy or a design concept for a wind-powered machine that may or may not have been a working device, as there is ambiguity in the text and issues with the design. Another early example of a wind-driven wheel was the prayer wheel, which is believed to have been first used in Tibet and China, though there is uncertainty over the date of its first appearance, which could have been either, the 7th century, or after the 9th century.
One of the earliest recorded working windmill designs found was invented sometime around 700-900 AD in Persia. This design was the panemone, with vertical lightweight wooden sails attached by horizontal struts to a central vertical shaft. It was first built to pump water and subsequently modified to grind grain as well.
Horizontal windmills
The first practical windmills were panemone windmills, using sails that rotated in a horizontal plane, around a vertical axis. Made of six to 12 sails covered in reed matting or cloth material, these windmills were used to grind grain or draw up water. A medieval account reports that windmill technology was used in Persia and the Middle East during the reign of Rashidun caliph Umar ibn al-Khattab, based on the caliph's conversation with a Persian builder slave. The authenticity of part of the anecdote involving the caliph Umar is questioned because it was recorded only in the 10th century. The Persian geographer Estakhri reported windmills being operated in Khorasan already in the 9th century.Such windmills were in widespread use across the Middle East and Central Asia and later spread to Europe, China, and India from there. By the 11th century, the vertical-axle windmill had reached parts of Southern Europe, including the Iberian Peninsula and the Aegean Sea. A similar type of horizontal windmill with rectangular blades, used for irrigation, can also be found in thirteenth-century China, introduced by the travels of Yelü Chucai to Turkestan in 1219.
Vertical-axle windmills were built, in small numbers, in Europe during the 18th and nineteenth centuries, for example Fowler's Mill at Battersea in London, and Hooper's Mill at Margate in Kent. These early modern examples seem not to have been directly influenced by the vertical-axle windmills of the medieval period, but to have been independent inventions by 18th-century engineers.
Vertical windmills
The horizontal-axis or vertical windmill is a development of the 12th century, first used in northwestern Europe, in the triangle of northern France, eastern England and Flanders.It is unclear whether the vertical windmill was influenced by the introduction of the horizontal windmill from Persia-Middle East to Southern Europe in the preceding century.
The earliest certain reference to a windmill in Northern Europe dates from 1185, in the former village of Weedley in Yorkshire which was located at the southern tip of the Wold overlooking the Humber Estuary. Several earlier, but less certainly dated, 12th-century European sources referring to windmills have also been found.
These earliest mills were used to grind cereals.
Post mill
The evidence at present is that the earliest type of European windmill was the post mill, so named because of the large upright post on which the mill's main structure is balanced. By mounting the body this way, the mill can rotate to face the wind direction; an essential requirement for windmills to operate economically in north-western Europe, where wind directions are variable. The body contains all the milling machinery. The first post mills were of the sunken type, where the post was buried in an earth mound to support it. Later, a wooden support was developed called the trestle. This was often covered over or surrounded by a roundhouse to protect the trestle from the weather and to provide storage space. This type of windmill was the most common in Europe until the 19th century when more powerful tower and smock mills replaced them.Hollow-post mill
In a hollow-post mill, the post on which the body is mounted is hollowed out, to accommodate the drive shaft.This makes it possible to drive machinery below or outside the body while still being able to rotate the body into the wind. Hollow-post mills driving scoop wheels were used in the Netherlands to drain wetlands since the early 15th century onwards.
Tower mill
By the end of the 13th century, the masonry tower mill, on which only the cap is rotated rather than the whole body of the mill, had been introduced. The spread of tower mills came with a growing economy that called for larger and more stable sources of power, though they were more expensive to build. In contrast to the post mill, only the cap of the tower mill needs to be turned into the wind, so the main structure can be made much taller, allowing the sails to be made longer, which enables them to provide useful work even in low winds. The cap can be turned into the wind either by winches or gearing inside the cap or from a winch on the tail pole outside the mill. A method of keeping the cap and sails into the wind automatically is by using a fantail, a small windmill mounted at right angles to the sails, at the rear of the windmill. These are also fitted to tail poles of post mills and are common in Great Britain and English-speaking countries of the former British Empire, Denmark, and Germany but rare in other places. Around some parts of the Mediterranean Sea, tower mills with fixed caps were built because the wind's direction varied little most of the time.Smock mill
The smock mill is a later development of the tower mill, where the masonry tower is replaced by a wooden framework, called the "smock", which is thatched, boarded, or covered by other materials, such as slate, sheet metal, or tar paper. The smock is commonly of octagonal plan, though there are examples with different numbers of sides.Smock windmills were introduced by the Dutch in the 17th century to overcome the limitations of tower windmills, which were expensive to build and could not be erected on wet surfaces. The lower half of the smock windmill was made of brick, while the upper half was made of wood, with a sloping tower shape that added structural strength to the design. This made them lightweight and able to be erected on unstable ground.
The smock windmill design included a small turbine in the back that helped the main mill to face the direction of the wind.
Mechanics
Sails
Common sails consist of a lattice framework on which the sailcloth is spread. The miller can adjust the amount of cloth spread according to the wind and the power needed. In medieval mills, the sailcloth was wound in and out of a ladder-type arrangement of sails. Later mill sails had a lattice framework over which the sailcloth was spread, while in colder climates, the cloth was replaced by wooden slats, which were easier to handle in freezing conditions. The jib sail is commonly found in Mediterranean countries and consists of a simple triangle of cloth wound round a spar.In all cases, the mill needs to be stopped to adjust the sails. Inventions in Great Britain in the late eighteenth and nineteenth centuries led to sails that automatically adjust to the wind speed without the need for the miller to intervene, culminating in patent sails invented by William Cubitt in 1807. In these sails, the cloth is replaced by a mechanism of connected shutters.
In France, Pierre-Théophile Berton invented a system consisting of longitudinal wooden slats connected by a mechanism that lets the miller open them while the mill is turning. In the twentieth century, increased knowledge of aerodynamics from the development of the airplane led to further improvements in efficiency by German engineer Bilau and several Dutch millwrights.
The majority of windmills have four sails. Multiple-sailed mills, with five, six, or eight sails, were built in Great Britain, Germany, and less commonly elsewhere. Earlier multiple-sailed mills are found in Spain, Portugal, Greece, parts of Romania, Bulgaria, and Russia. A mill with an even number of sails has the advantage of being able to run with a damaged sail by removing both the damaged sail and the one opposite, which does not unbalance the mill.
File:Korenmolen "De Valk" in rouwstand naar aanleiding van bijzetting te Delft van Koningin Wilhelmina - Leiden - 20137630 - RCE.jpg|thumb|De Valk windmill in mourning position following the death of Queen Wilhelmina of the Netherlands in 1962
In the Netherlands, the stationary position of the sails, i.e. when the mill is not working, has long been used to give signals. If the blades are stopped in a "+" sign, the windmill is open for business. When the blades are stopped in an "X" configuration, the windmill is closed or not functional. A slight tilt of the sails signals joy, such as the birth of a healthy baby. A tilt of the blades to 11-2-5-8 o'clock signals mourning, or warning. It was used to signal the local region during Nazi operations in World War II, such as searches for Jews. Across the Netherlands, windmills were placed in mourning positions in honor of the Dutch victims of the 2014 Malaysian Airlines Flight 17 shootdown.