Windmill sail
Encyclopedia
Windmill
s are powered by their sails. Sails are found in different designs, from primitive common sails to the advanced patent sails.
of the sail. Though rare in the UK, at least two windmills are known to have had jib sails (St Mary's, Isle of Scilly and Cann Mills, Melbury Abbas).
in 1772. The sail is divided into a number of bays, each having a number of shutters. All the shutters are joined together by a shutter bar, and the force required for the wind to open the shutters is adjusted by a separate spring
on each sail. Although automatic in operation, the mill must be stopped in order to adjust the reefing of the sail.
, although the only remaining mill with roller reefing sails intact is Ballycopeland Windmill
in Northern Ireland
.
in 1813. They combine the shutters of the spring sail with automatic adjustment of the roller reefing sail. Their construction is similar to that of the spring sail. Adjustment of patent sails can be made without stopping the mill.
Air brakes
In 1860, the English millwright Catchpole fitted an automatic air brake to the ends of patent sails. These were longitudinal shutters at the tip of each sail, which opened up if the wind got too strong, thus slowing the sail.
, the common sail predominates. During the nineteenth and twentieth centuries, Dutch millwright
s developed the windmill sail to make it more efficient aerodynamically and operation easier in an effort to keep the traditional windmill economically viable in competition with factories and electric pumping stations.
Dekker / Van Bussel system
The Dutch millwright A. J. Dekker improved on the efficiency of the common sail. The stock is given an airfoil
shape by completely covering it with galvanised steel plates. Dekkerised sails provide enough surface area to be able to work the mill with no sailcloth spread if the wind is strong enough. As with the common sail, they are not adjustable except by adding more sailcloth. Some disadvantages of the Dekker system led millwright Van Bussel of Weert
to invent a similar system, though with just a more rounded airfoil replacing the leading boards and not covering the stock itself.
Ten Have
Invented by Dutch millwright Ten Have of Vorden
, Ten Have sails have a small number of wide longitudinal shutters, operating by centrifugal weights and often also by the miller at the tail of the mill similar to patent sails. This way the sail can be adjusted without stopping the mill. The leading edge is commonly streamlined by the Van Bussel system. Ten Have shutters are normally only used on one stock as the wide Ten Have shutters standing open on a vertical stock would leave this stock vulnerable to side winds during a storm.
Fauël or Fok system
The Fok system, invented by engineer P.L. Fauël, was inspired by the jib
on a sailing boat ('fok' is the Dutch
word for jib). In this design the leading boards are replaced by a rounded profile of wooden slats in the form of a foresail leaving a small slot between this profile and the stock. It's working principle can be compared to a leading edge slot
on an aircraft wing. It enables the mill to work in a lower windspeed but in variable windspeeds tends to make it difficult to have the mill run at a steady pace. For this reason it is often equipped with air brakes operating by centrifugal force. The Fauël system is used in addition to common sails (see photo).
Bilau Ventisails/ Van Riet system
The Bilau system uses sails with an streamline covering of the stock, coupled with a full length air brake on the trailing edge, together forming an airfoil. The airbrake is opened by centrifugal weights in the sails but can also be operated by the miller similar to the patent system. When opening the airbrake disturbs the airfoil shape thereby slowing the mill. It was invented by German
airplane engineer Kurt Bilau early in the twentieth century and became quite popular in Germany where it was fitted to over 140 mills. A similar system was invented by a millwright by the name of Van Riet of Goes
where the leading edge and the airbrake together form a more complete airfoil.
some mills have a system of longitudinal shutters running the length of the sail. The system is called Ailes Berton, which translates as Berton sails. These sails can be adjusted without stopping the mill.
A few mills had annular sails, forming a circle. These sails utilised the patent system, enabling adjustment to be made without stopping the mill. One example of a mill with annular sails was at Feltwell
, Norfolk
. Others are known to have existed at Haverhill
, Suffolk
, Boxford
, Suffolk
and Roxwell
, Essex
. Annular sails were also employed on large wind engines, such as the Titt
engine at Crux Easton
, Hampshire
.
Windmill
A windmill is a machine which converts the energy of wind into rotational energy by means of vanes called sails or blades. Originally windmills were developed for milling grain for food production. In the course of history the windmill was adapted to many other industrial uses. An important...
s are powered by their sails. Sails are found in different designs, from primitive common sails to the advanced patent sails.
Jib sails
The jib sail is found in Mediterranean countries, and consists of a simple triangle of cloth wound round a spar. The mill must be stopped in order to adjust the reefingReefing
Reefing is a sailing manoeuvre intended to reduce the area of a sail on a sailboat or sailing ship, which can improve the ship's stability and reduce the risk of capsizing, broaching, or damaging sails or boat hardware in a strong wind...
of the sail. Though rare in the UK, at least two windmills are known to have had jib sails (St Mary's, Isle of Scilly and Cann Mills, Melbury Abbas).
Common sails
The simplest form of sail. In medieval mills the sailcloth was wound in and out of a ladder type arrangement of sails. Medieval sails could be constructed with or without outer sailbars. Post-medieval mill sails have a lattice framework over which the sailcloth is spread. There are various "reefs" for the different spread of sails; these are full sail, dagger point, sword point and first reef. The mill must be stopped in order to adjust the reefing of the sail.Spring sails
Spring sails were invented by Scottish millwright Andrew MeikleAndrew Meikle
Andrew Meikle was an early mechanical engineer credited with inventing the threshing machine, a device used to remove the outer husks from grains of wheat. This was regarded as one of the key developments of the British Agricultural Revolution in the late 18th century...
in 1772. The sail is divided into a number of bays, each having a number of shutters. All the shutters are joined together by a shutter bar, and the force required for the wind to open the shutters is adjusted by a separate spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
on each sail. Although automatic in operation, the mill must be stopped in order to adjust the reefing of the sail.
Roller reefing sails
Roller reefing sails were invented by Stephen Hooper in 1789. As with spring sails, the sail is divided into a number of bays, each with a number of spars with cloth wound around them. The cloth is extended or retracted by a rod and lever system, and connected with a shutter bar on each sail. Adjustment of the roller reefing sail can be made without stopping the mill. This type of sail was popular in YorkshireYorkshire
Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...
, although the only remaining mill with roller reefing sails intact is Ballycopeland Windmill
Ballycopeland Windmill
Ballycopeland Windmill is a functioning windmill located one mile west of Millisle, County Down, Northern Ireland. It is managed by the Northern Ireland Environment Agency and is open to the public.-Features:...
in Northern Ireland
Northern Ireland
Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...
.
Patent sails
Patent sails were invented by William CubittWilliam Cubitt
Sir William Cubitt was an eminent English civil engineer and millwright. Born in Norfolk, England, he was employed in many of the great engineering undertakings of his time. He invented a type of windmill sail and the prison treadwheel, and was employed as chief engineer, at Ransomes of Ipswich,...
in 1813. They combine the shutters of the spring sail with automatic adjustment of the roller reefing sail. Their construction is similar to that of the spring sail. Adjustment of patent sails can be made without stopping the mill.
Air brakes
In 1860, the English millwright Catchpole fitted an automatic air brake to the ends of patent sails. These were longitudinal shutters at the tip of each sail, which opened up if the wind got too strong, thus slowing the sail.
Spring patent sails
Spring patent sails have a spring to enable each sail to be adjusted individually, with the patent sail system allowing all sails to be adjusted without stopping the mill. The system was not a common one.Dutch sail types
In the NetherlandsNetherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, the common sail predominates. During the nineteenth and twentieth centuries, Dutch millwright
Millwright
A millwright is a craftsman or tradesman engaged with the construction and maintenance of machinery.Early millwrights were specialist carpenters who erected machines used in agriculture, food processing and processing lumber and paper...
s developed the windmill sail to make it more efficient aerodynamically and operation easier in an effort to keep the traditional windmill economically viable in competition with factories and electric pumping stations.
Dekker / Van Bussel system
The Dutch millwright A. J. Dekker improved on the efficiency of the common sail. The stock is given an airfoil
Airfoil
An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....
shape by completely covering it with galvanised steel plates. Dekkerised sails provide enough surface area to be able to work the mill with no sailcloth spread if the wind is strong enough. As with the common sail, they are not adjustable except by adding more sailcloth. Some disadvantages of the Dekker system led millwright Van Bussel of Weert
Weert
Weert is a municipality and city in the southeastern Netherlands. As of 2010, Weert had a population of 48,405. It lies on the Eindhoven–Maastricht railway line, and is also astride the Zuid-Willemsvaart canal.- Population centres :* Altweerterheide...
to invent a similar system, though with just a more rounded airfoil replacing the leading boards and not covering the stock itself.
Ten Have
Invented by Dutch millwright Ten Have of Vorden
Vorden
Vorden is a former municipality and a town in the eastern Netherlands, about 10 kilometres south-east of Zutphen. On 1 January 2005 the municipality merged with Hummelo en Keppel, Steenderen, Hengelo en Zelhem, to form the new municipality Bronckhorst....
, Ten Have sails have a small number of wide longitudinal shutters, operating by centrifugal weights and often also by the miller at the tail of the mill similar to patent sails. This way the sail can be adjusted without stopping the mill. The leading edge is commonly streamlined by the Van Bussel system. Ten Have shutters are normally only used on one stock as the wide Ten Have shutters standing open on a vertical stock would leave this stock vulnerable to side winds during a storm.
Fauël or Fok system
The Fok system, invented by engineer P.L. Fauël, was inspired by the jib
Jib
A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...
on a sailing boat ('fok' is the Dutch
Dutch language
Dutch is a West Germanic language and the native language of the majority of the population of the Netherlands, Belgium, and Suriname, the three member states of the Dutch Language Union. Most speakers live in the European Union, where it is a first language for about 23 million and a second...
word for jib). In this design the leading boards are replaced by a rounded profile of wooden slats in the form of a foresail leaving a small slot between this profile and the stock. It's working principle can be compared to a leading edge slot
Leading edge slot
A leading edge slot is an aerodynamic feature of the wing of some aircraft to reduce the stall speed and promote good low-speed handling qualities. A leading edge slot is a span-wise gap in each wing, allowing air to flow from below the wing to its upper surface...
on an aircraft wing. It enables the mill to work in a lower windspeed but in variable windspeeds tends to make it difficult to have the mill run at a steady pace. For this reason it is often equipped with air brakes operating by centrifugal force. The Fauël system is used in addition to common sails (see photo).
Bilau Ventisails/ Van Riet system
The Bilau system uses sails with an streamline covering of the stock, coupled with a full length air brake on the trailing edge, together forming an airfoil. The airbrake is opened by centrifugal weights in the sails but can also be operated by the miller similar to the patent system. When opening the airbrake disturbs the airfoil shape thereby slowing the mill. It was invented by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
airplane engineer Kurt Bilau early in the twentieth century and became quite popular in Germany where it was fitted to over 140 mills. A similar system was invented by a millwright by the name of Van Riet of Goes
Goes
Goes is a municipality and a city in the southwestern Netherlands in Zuid-Beveland, in the province Zeeland. The city of Goes has approximately 27,000 residents.-History of Goes:...
where the leading edge and the airbrake together form a more complete airfoil.
Berton sails
In FranceFrance
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
some mills have a system of longitudinal shutters running the length of the sail. The system is called Ailes Berton, which translates as Berton sails. These sails can be adjusted without stopping the mill.
Annular sails
Feltwell
Feltwell is a village 10 miles west of Thetford, Norfolk, England, and is in the borough of King's Lynn and West Norfolk.Feltwell is a small village with a thriving community. The village has a small primary school which was originally built as a hospital. The pubs, The Lodge and the West End, are...
, Norfolk
Norfolk
Norfolk is a low-lying county in the East of England. It has borders with Lincolnshire to the west, Cambridgeshire to the west and southwest and Suffolk to the south. Its northern and eastern boundaries are the North Sea coast and to the north-west the county is bordered by The Wash. The county...
. Others are known to have existed at Haverhill
Haverhill, Suffolk
Haverhill is an industrial market town and civil parish in the county of Suffolk, England, next to the borders of Essex and Cambridgeshire. It lies southeast of Cambridge and north of central London...
, Suffolk
Suffolk
Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...
, Boxford
Boxford
Boxford may refer to:* Boxford, Berkshire, England* Boxford, Suffolk, England* Boxford, Massachusetts, United States...
, Suffolk
Suffolk
Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...
and Roxwell
Roxwell
Roxwell is a village and a parish in the Chelmsford District, in the English county of Essex.The parish church is St Michael & All Angels. There is a primary school and a public house...
, Essex
Essex
Essex is a ceremonial and non-metropolitan county in the East region of England, and one of the home counties. It is located to the northeast of Greater London. It borders with Cambridgeshire and Suffolk to the north, Hertfordshire to the west, Kent to the South and London to the south west...
. Annular sails were also employed on large wind engines, such as the Titt
John Wallis Titt
John Wallis Titt was a late nineteenth-century mechanical engineer and builder of a particular design of large wind engine.-Early life:...
engine at Crux Easton
Crux Easton wind engine
Crux Easton wind engine is a Grade II listed Titt wind engine at Crux Easton, Hampshire, England which has been restored to working order.-History:...
, Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
.