1.
Sail
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A sail derives power from the wind to provide motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles. Sails mobilize lift and drag properties as air passes along the surface, in most cases sails are supported directly by a mast rigidly attached to the sailing craft or on a wire stay attached to the mast, however some craft employ a flexible mount for a mast. Sails also employ spars and battens to help determine their shape, as a result, sails come in a variety of shapes that include both triangular and quadrilateral configurations, usually with curved edges that promote three-dimensional curvature of the sail. Kites also power certain sailing craft, but do not employ a mast to support the airfoil and are beyond the scope of this article, sailing craft employ two types of rig, the square rig and the fore-and-aft rig. The square rig carries the primary driving sails are carried on horizontal spars and these spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship mainly so rigged is called a square-rigger, the square rig is aerodynamically most efficient when running. A fore-and-aft rig consists of sails that are set along the line of the rather than perpendicular to it. Vessels so rigged are described as fore-and-aft rigged, archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium onwards. Excavations of the Ubaid period in Mesopotamia provides direct evidence of sailing boats, Sails from ancient Egypt are depicted around 3200 BCE, where reed boats sailed upstream against the River Niles current. Ancient Sumerians used square rigged sailing boats at about the same time, the proto-Austronesian words for sail, lay, and other rigging parts date to about 3000 BCE when this group began their Pacific expansion. Greeks and Phoenicians began trading by ship by around 1,200 BCE, northern Europeans were resistant to adopting the fore-and-aft rig, despite having seen its use in the course of trade and during the Crusades. The lateen sail proved to have better performance for smaller vessels. Aerodynamic forces on sails depend on speed and direction and the speed. The direction that the craft is traveling with respect to the wind is called the point of sail. The speed of the craft at a point of sail contributes to the apparent wind —the wind speed. Depending on the alignment of the sail with the apparent wind, for apparent wind angles aligned with the entry point of the sail, the sail acts as an airfoil and lift is the predominant component of propulsion. For apparent wind angles behind the sail, lift diminishes and drag increases as the predominant component of propulsion, because of limitations on speed through the water, displacement sailboats generally derive power from sails generating lift on points of sail that include close-hauled through broad reach. Downwind sailing with a spinnaker Each rig is configured in a sail plan, a sail plan is a set of drawings, usually prepared by a naval architect which shows the various combinations of sail proposed for a sailing ship
2.
Sailing ship
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A modern sailing ship or sailship is any large wind-powered vessel. Traditionally a sailing ship is a vessel that carries three or more masts with square sails on each. Large sailing vessels that are not ship-rigged may be more referred to by their sail rig, such as schooner, barque, brig. There are many different types of sailing ships, but they all have certain basic things in common, every sailing ship has a hull, rigging and at least one mast to hold up the sails that use the wind to power the ship. The crew who sail a ship are called sailors or hands and they take turns to take the watch, the active managers of the ship and her performance for a period. Watches are traditionally four hours long, some sailing ships use traditional ships bells to tell the time and regulate the watch system, with the bell being rung once for every half hour into the watch and rung eight times at watch end. A severe storm could lead to shipwreck, and the loss of all hands, Sailing ships are limited in their maximum size compared to ships with heat engines, so economies of scale are also limited. The heaviest sailing ships never exceeded 14,000 tons displacement, there are many types of sailing ships, mostly distinguished by their rigging, hull, keel, or number and configuration of masts. There are also types of smaller sailboats not listed here. The steam power was used to drive the winches, hoists, a similar ship Kruzenshtern, a very large sailing vessel without mechanical assists, had a crew of 257 men, compared to the Preussen, which required only 48 men. In 2006, automated control had been taken to the point where sails could be operated by one using a central control unit. The DynaRig technology was first developed in the 1960s in Germany by W. Prolls as an alternative for commercial ships to prepare for a possible future energy crisis. The technology is a version of the same type of sail used by the Preussen. The main difference is that the yards do not swing around a fixed mast but are attached to a rotating mast. DynaRig along with extensive computerization was used in the proof-of-concept Maltese Falcon to enable it to be sailed with no crew aloft, as of 2013, with increasing restrictions on use of bunker fuel, attempts were underway to develop hybrid sailing ships using automated sail and alternative fuels. Tall ship Rigging Sail-plan List of large sailing vessels Cruising Shipbuilding, the History of a Ship from Her Cradle to Her Grave, With a Short Account of Modern Steamships and Torpedoes. The sailing-ship, six years of history. Media related to Sailing ships at Wikimedia Commons
3.
Sailboat
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A sailboat or sailing boat is a boat propelled partly or entirely by sails smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region, although sailboat terminology has varied across history, many terms have specific meanings in the context of modern yachting. A great number of sailboat-types may be distinguished by size, hull configuration, keel type, purpose, number and configuration of masts, and sail plan. Once a common racing configuration, today it gives versatility to cruising boats, a catboat has a single mast mounted far forward and does not carry a jib. Most modern designs have only one sail, the mainsail, however, a dinghy is a type of small open sailboat commonly used for recreation, sail training, and tending a larger vessel. They are popular in youth sailing programs for their short LOA, simple operation and they have three sails, the mainsail, jib, and spinnaker. Ketches are similar to a sloop, but there is a shorter mast astern of the mainmast. The second mast is called the mizzen mast and the sail is called the mizzen sail, a ketch can also be Cutter-rigged with two head sails. A schooner has a mainmast taller than its foremast, distinguishing it from a ketch or a yawl, a schooner can have more than two masts, with the foremast always lower than the foremost main. Traditional topsail schooners have topmasts allowing triangular topsails sails to be flown above their gaff sails, the most common modern sailboat is the sloop, which features one mast and two sails, typically a Bermuda rigged main, and a headsail. This simple configuration is very efficient for sailing into the wind, a smaller headsail is easier for a short-handed crew to manage. A yawl is similar to a ketch, with a mizzen mast carried astern the rudderpost more for balancing the helm than propulsion. Traditional sailboats are monohulls, but multi-hull catamarans and trimarans are gaining popularity, monohull boats generally rely on ballast for stability and usually are displacement hulls. This stabilizing ballast can, in boats designed for racing, be as much as 50% of the weight of the boat and it creates two problems, one, it gives the monohull tremendous inertia, making it less maneuverable and reducing its acceleration. Secondly, unless it has built with buoyant foam or air tanks, if a monohull fills with water. Multihulls rely on the geometry and the stance of the multiple hulls for their stability. Indeed, multihulls are designed to be as light-weight as possible and this absence of ballast also results in some very real performance gains in terms of acceleration, top speed, and maneuverability. The lack of ballast makes it easier to get a multihull on plane, reducing its wetted surface area and thus its drag. The absence of drag improves wind precision
4.
Windsurfing
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Windsurfing is a surface water sport that combines elements of surfing and sailing. It consists of a board usually 2.5 to 3 meters long, the rig is connected to the board by a free-rotating universal joint and consists of a mast, 2-sided boom and sail. The sail area generally ranges from 2.5 m2 to 12 m2 depending on the conditions, the skill of the sailor, the type of windsurfing being undertaken and the weight of the person windsurfing. Some credits S. Newman Darby with the origination of windsurfing by 1964 on the Susquehanna River, Pennsylvania, USA when he invented the sailboard, in 1964, Darby began selling his sailboards. A promotional article by Darby was published in the August 1965 edition of Popular Science magazine, while Darbys sailboard incorporated a pivoting rig, it was square rigged and suffered all the associated limitations. You operated the sailboard with your back to the lee side of the kite shaped square sail, Although it might be considered a minimalistic version of a sailboat, windsurfing offers experiences that are outside the scope of other sailing craft designs. Windsurfers can perform jumps, inverted loops, spinning maneuvers, extreme waves aside, many expert windsurfers will ride the same waves as surfers do. At one time referred to as surfings ginger haired cousin by the legendary champion, Robby Naish. As a result of attempts to claim the word windsurfer as a trademark, participants have been encouraged to use different names to describe the sport, the term windsurfing has persisted as the accepted name for the sport, and the word windsurfer persists for both participants and equipment. Windsurfing is predominately undertaken on a non-competitive basis, organised competition does take place at all levels across the world, including in the Olympics. Typical formats for competitive windsurfing include Formula Windsurfing, speed sailing, slalom, course racing, wave sailing, superX, the boom of the 1980s led windsurfing to be recognized as an Olympic sport in 1984. However, windsurfings popularity saw a decline in the mid-1990s, thanks to licensing battles. The sport experienced a modest revival, as new beginner-friendly designs became available, further pressure came as a proportion of avid windsurfers took up the similar sport of kitesurfing. Windsurfing, as a sport and recreational activity, did not emerge until the half of the 20th century. Darby did not file a patent for the sailboard, however, he is widely recognized as its inventor as well as the first to conceive, design, and build a sailboard with a universal joint. In 1964, Darby began selling his sailboards, twelve-year-old Peter Chilvers is often cited for inventing a sailboard in 1958. In the 1960s, Jim Drake was the first to many problems of getting the board to sail while Hoyle Schweitzer was the first to be successful in marketing the sailboard. That night they developed the idea of a kite-powered surfboard, on later reflection, Drake didnt like the integrity of the idea and dismissed it
5.
Ice boat
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An ice boat is a boat or purpose-built framework similar in functional design to a sail boat but fitted with skis or runners and designed to run over ice instead of through water. Ice yachting is the sport of sailing and racing iceboats, sail-able ice is known in the sport as hard water versus sailing on liquid or soft water. A related sport, land sailing, utilizes a configuration with a fuselage or frame equipped with wheels instead of runners. Iceboats commonly used for racing are usually only for one person, on some boats, a side car can be fitted to take others along for a ride. Traditional iceboats from before the late 19th century were used for transportation of goods and these boats reached lengths of 30 to 50 feet and were sometimes transported between sites on rail cars. Ice sailing was first developed in Europe, in America, it was done in several locations where the sport also continues today. Some of the older large stern steerer iceboats can seat several in their baskets, several of these boats are maintained and raced today. The Northwest Ice Yacht Association sponsors an annual regatta that includes classes for these boats and this annual regatta recently celebrated its 100th anniversary. The first iceboat in America is attributed to Oliver Booth in 1790 at Poughkeepsie and this craft was a small triangular box with two runners affixed to the front and a steering runner at the rear. One unique type of ice boat has its history in wide, stubby, scow-like vessels used in the 1800s, often for transportation across a mixed passage transitioning over sea-ice, wildly sailed by adjusting main and jib sail trim only, these boats had no rudder. Parallel rails were mounted on the bottom, like multiple sled runners, in 1869, one of the largest ice yachts ever was built for racing on the frozen Hudson River, called the Icicle. That boat occasionally raced the railroad which ran alongside the Hudson and these early ice sailing vessels led to the development of boats designed strictly for racing on ice. These stern-steerer iceboats were generally rigged as sloops, with a jib forward of the mast. This boat led to the Skeeter class, and the Skeeter Ice Boat Club formed on Geneva Lake, the Skeeter class adopted the logo of a mosquito on their sail, and has evolved into a very efficient aerodynamically clean machine. While the large stern-steerers could have up to 600 square feet of sail, in 1937, The Detroit News sponsored a new home-buildable ice boat design, which became the International DN. In 1968 Dick Slates of Pewaukee, Wisconsin designed and built the Nite with two wooden prototypes, the design was refined and fiberglass production began in 1970. Modern iceboats designs are generally supported by three skate blades called runners supporting a triangular or cross-shaped frame with the runner in front. Once the lateral force has been countered by the runner edge
6.
Land sailing
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Land sailing, also known as sand yachting or land yachting, is the act of moving across land in a wheeled vehicle powered by wind through the use of a sail. The term comes from analogy with sailing, historically, land sailing was used as a mode of transportation or recreation. Since the 1950s, it has evolved primarily into a racing sport, vehicles used in sailing are known as sail wagons, sand yachts, or land yachts. They typically have three wheels and function much like a sailboat, except that they are operated from a sitting or lying position, Land sailing works best in windy flat areas, and races often happen on beaches, airfields, and dry lake beds in desert regions. Modern land sailors, generally known as pilots, can go three to four times faster than the wind speed, a gust of wind is considered more beneficial in a land sailing race than a favorable windshift. A similar sport, known as ice yachting, is practiced on frozen lakes, another variation is the Whike, which combines land sailing with bicycling and can therefore also be used in everyday traffic because it does not fully depend on wind. He wrote that Gaocang Wushu invented a wind-driven carriage which was able to carry thirty people at once, there was another built in about 610 for the Emperor Yang of Sui, as described in the Continuation of the New Discourses on the Talk of the Times. European travelers from the 16th century onwards mentioned sailing carriages with surprise, in 1585, Gonzales de Mendoza wrote that the Chinese had many coaches and wagons mounted with sails, and even depicted them in artwork of silk hanfu robes and on earthenware vessels. In the 1584 atlas Theatrum Orbis Terrarum written by the cartographer Abraham Ortelius, there are large Chinese carriages depicted with sails and masts. Likewise, there are the same Chinese vehicles with sails depicted in the Atlas of Gerardus Mercator, the English poet John Milton popularized the Chinese sailing carriage in Europe with a poem written in 1665. In the 1860s, windwagons were used to transport across the American great plains, the precursor to the modern land yacht was invented in the summer of the year 1600 by the Flemish scientist Simon Stevin in Flanders as a commission for Prince Maurice of Orange. It was used by Prince Maurice for entertaining his guests, in 1898, the Dumont brothers of De Panne, Belgium, developed a land yacht whose sails were based on contemporary Egyptian sailboats used on the Nile River. Louis Blériot, the French aviation pioneer was instrumental in developing landsailing as a sport and it was viewed as an alternative sport when strong winds would have made flying in early aircraft too dangerous. Bleriots landsailers were first tried on the Buc airstrip, bleriot machines gave their best on Channel and North Sea wide and windy beaches at low tide. The Blériot firm coined the name aéroplage and even registered it as a trademark, the first races were held on the beaches of Belgium and France in 1909. Land yachts were used in the late 19th century and early 20th century to transport goods on dry lakes in America. The modern land yacht, a four-wheeled polyester/fibreglass and metal cart, often with a wing-mast, in 1967 a French Foreign Legion officer organized a land yacht race across the Sahara Desert. The story made the cover of National Geographic in November 1967, a reenactment of this event took place three years later and was filmed by National Geographic
7.
Windmill sail
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Windmills are powered by their sails. Sails are found in different designs, from primitive common sails to the patent sails. The jib sail is found in Mediterranean countries and consists of a triangle of cloth wound round a spar. The mill must be stopped in order to adjust the reefing of the sail, though rare in the UK, at least two windmills are known to have had jib sails. The common sail is 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, the mill must be stopped in order to adjust the reefing of the sail. Spring sails were invented by Scottish millwright Andrew Meikle 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 bar. Although automatic in operation, the mill must be stopped in order to adjust the reefing of the sail, roller reefing sails were invented by Stephen Hooper in 1789. As with spring sails, the sail is divided into a number of bays, 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 and this type of sail was popular in Yorkshire, although the only remaining mill with roller reefing sails intact is Ballycopeland Windmill in Northern Ireland. Patent sails were invented by William Cubitt in 1807 and 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 and 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 have a spring to enable each sail to be adjusted individually, the system was not a common one. In the Netherlands, the common sail predominates, 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
8.
Wind turbine
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A wind turbine is a device that converts the winds kinetic energy into electrical power. Wind turbines are manufactured in a range of vertical and horizontal axis types. The smallest turbines are used for such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly larger turbines can be used for making contributions to a power supply while selling unused power back to the utility supplier via the electrical grid. Wind turbines were used in Persia about 500–900 A. D, the windwheel of Hero of Alexandria marks one of the first known instances of wind powering a machine in history. However, the first known practical wind turbines were built in Sistan and these Panemone were vertical axle wind turbines, which had long vertical drive shafts with rectangular blades. Made of six to twelve sails covered in reed matting or cloth material, these turbines were used to grind grain or draw up water. Wind turbines first appeared in Europe during the Middle Ages, the first historical records of their use in England date to the 11th or 12th centuries and there are reports of German crusaders taking their windmill-making skills to Syria around 1190. By the 14th century, Dutch wind turbines were in use to areas of the Rhine delta. Advanced wind mills were described by Croatian inventor Fausto Veranzio, in his book Machinae Novae he described vertical axis wind turbines with curved or V-shaped blades. The first electricity-generating wind turbine was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his home in Marykirk. Some months later American inventor Charles F, although Blyths turbine was considered uneconomical in the United Kingdom electricity generation by wind turbines was more cost effective in countries with widely scattered populations. In Denmark by 1900, there were about 2500 windmills for mechanical loads such as pumps and mills, the largest machines were on 24-meter towers with four-bladed 23-meter diameter rotors. By 1908 there were 72 wind-driven electric generators operating in the United States from 5 kW to 25 kW, around the time of World War I, American windmill makers were producing 100,000 farm windmills each year, mostly for water-pumping. By the 1930s, wind generators for electricity were common on farms, in this period, high-tensile steel was cheap, and the generators were placed atop prefabricated open steel lattice towers. A forerunner of modern wind generators was in service at Yalta. This was a 100 kW generator on a 30-meter tower, connected to the local 6.3 kV distribution system and it was reported to have an annual capacity factor of 32 percent, not much different from current wind machines. In the autumn of 1941, the first megawatt-class wind turbine was synchronized to a utility grid in Vermont, the Smith-Putnam wind turbine only ran for 1,100 hours before suffering a critical failure
9.
Force
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In physics, a force is any interaction that, when unopposed, will change the motion of an object. In other words, a force can cause an object with mass to change its velocity, force can also be described intuitively as a push or a pull. A force has both magnitude and direction, making it a vector quantity and it is measured in the SI unit of newtons and represented by the symbol F. The original form of Newtons second law states that the net force acting upon an object is equal to the rate at which its momentum changes with time. In an extended body, each part usually applies forces on the adjacent parts, such internal mechanical stresses cause no accelation of that body as the forces balance one another. Pressure, the distribution of small forces applied over an area of a body, is a simple type of stress that if unbalanced can cause the body to accelerate. Stress usually causes deformation of materials, or flow in fluids. In part this was due to an understanding of the sometimes non-obvious force of friction. A fundamental error was the belief that a force is required to maintain motion, most of the previous misunderstandings about motion and force were eventually corrected by Galileo Galilei and Sir Isaac Newton. With his mathematical insight, Sir Isaac Newton formulated laws of motion that were not improved-on for nearly three hundred years, the Standard Model predicts that exchanged particles called gauge bosons are the fundamental means by which forces are emitted and absorbed. Only four main interactions are known, in order of decreasing strength, they are, strong, electromagnetic, weak, high-energy particle physics observations made during the 1970s and 1980s confirmed that the weak and electromagnetic forces are expressions of a more fundamental electroweak interaction. Since antiquity the concept of force has been recognized as integral to the functioning of each of the simple machines. The mechanical advantage given by a machine allowed for less force to be used in exchange for that force acting over a greater distance for the same amount of work. Analysis of the characteristics of forces ultimately culminated in the work of Archimedes who was famous for formulating a treatment of buoyant forces inherent in fluids. Aristotle provided a discussion of the concept of a force as an integral part of Aristotelian cosmology. In Aristotles view, the sphere contained four elements that come to rest at different natural places therein. Aristotle believed that objects on Earth, those composed mostly of the elements earth and water, to be in their natural place on the ground. He distinguished between the tendency of objects to find their natural place, which led to natural motion, and unnatural or forced motion
10.
Wing
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A wing is a type of fin that produces lift, while moving through air or some other fluid. As such, wings have a shape, a streamlined cross-sectional shape. A wings aerodynamic efficiency is expressed as its lift-to-drag ratio, the lift a wing generates at a given speed and angle of attack can be one to two orders of magnitude greater than the total drag on the wing. A high lift-to-drag ratio requires a significantly smaller thrust to propel the wings through the air at sufficient lift, lifting structures used in water, include various foils, including hydrofoils. Hydrodynamics is the science, rather than aerodynamics. Applications of underwater foils occur in hydroplanes, sailboats and submarines, the word wing from the Old Norse vængr for many centuries referred mainly to the foremost limbs of birds. In nature wings have evolved in dinosaurs, birds, mammals, fish, reptiles, Wing forms in nature The design and analysis of the wings of aircraft is one of the principal applications of the science of aerodynamics, which is a branch of fluid mechanics. The properties of the airflow around any moving object can - in principle - be found by solving the Navier-Stokes equations of fluid dynamics, however, except for simple geometries these equations are notoriously difficult to solve. Fortunately, simpler explanations can be described, for a wing to produce lift, it must be oriented at a suitable angle of attack relative to the flow of air past the wing. When this occurs the wing deflects the airflow downwards, turning the air as it passes the wing, since the wing exerts a force on the air to change its direction, the air must exert a force on the wing, equal in size but opposite in direction. This force manifests itself as differing air pressures at different points on the surface of the wing, a region of lower-than-normal air pressure is generated over the top surface of the wing, with a higher pressure on the bottom of the wing. The lower air pressure on the top of the wing generates a smaller force on the top of the wing than the upward force generated by the higher air pressure on the bottom of the wing. Hence, a net force acts on the wing. This force is called the lift generated by the wing, the different velocities of the air passing by the wing, the air pressure differences, the change in direction of the airflow, and the lift on the wing are intrinsically one phenomenon. It is, therefore, possible to lift from any of the other three. For example, the lift can be calculated from the differences, or from different velocities of the air above and below the wing. Fluid dynamics offers other approaches to solving these problems—and all produce the same answers if done correctly, air velocity on the bottom of a wing is higher than that on the top, while the wing is generating lift. Wings with a cross section are the norm in subsonic flight
11.
Propeller
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A propeller is a type of fan that transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the blade, and a fluid is accelerated behind the blade. Their disadvantages are higher mechanical complexity and higher cost, the principle employed in using a screw propeller is used in sculling. It is part of the skill of propelling a Venetian gondola but was used in a less refined way in parts of Europe. For example, propelling a canoe with a paddle using a pitch stroke or side slipping a canoe with a scull involves a similar technique. In China, sculling, called lu, was used by the 3rd century AD. In sculling, a blade is moved through an arc. The innovation introduced with the propeller was the extension of that arc through more than 360° by attaching the blade to a rotating shaft. Propellers can have a blade, but in practice there are nearly always more than one so as to balance the forces involved. The origin of the screw propeller starts with Archimedes, who used a screw to lift water for irrigation and bailing boats and it was probably an application of spiral movement in space to a hollow segmented water-wheel used for irrigation by Egyptians for centuries. Leonardo da Vinci adopted the principle to drive his theoretical helicopter, in 1784, J. P. Paucton proposed a gyrocopter-like aircraft using similar screws for both lift and propulsion. At about the time, James Watt proposed using screws to propel boats. This was not his own invention, though, Toogood and Hays had patented it a century earlier, by 1827, Czech-Austrian inventor Josef Ressel had invented a screw propeller which had multiple blades fastened around a conical base. He had tested his propeller in February 1826 on a ship that was manually driven. He was successful in using his bronze screw propeller on an adapted steamboat and his ship Civetta with 48 gross register tons, reached a speed of about six knots. This was the first ship successfully driven by an Archimedes screw-type propeller, after a new steam engine had an accident his experiments were banned by the Austro-Hungarian police as dangerous. Josef Ressel was at the time a forestry inspector for the Austrian Empire, but before this he received an Austro-Hungarian patent for his propeller. This new method of propulsion was an improvement over the paddlewheel as it was not so affected by either ship motions or changes in draft as the burned coal
12.
Kite
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A kite is traditionally a tethered heavier-than-air craft with wing surfaces that react against the air to create lift and drag. A kite consists of wings, tethers, pulleys, and anchors, Kites often have a bridle to guide the face of the kite at the correct angle so the wind can lift it. A kites wing also may be so designed so a bridle is not needed, when kiting a sailplane for launch, a kite may have fixed or moving anchors. Untraditionally in technical kiting, a kite consists of tether-set-coupled wing sets, even in technical kiting, though, the lift that sustains the kite in flight is generated when air moves around the kites surface, producing low pressure above and high pressure below the wings. The interaction with the wind also generates horizontal drag along the direction of the wind, the resultant force vector from the lift and drag force components is opposed by the tension of one or more of the lines or tethers to which the kite is attached. The anchor point of the line may be static or moving. The same principles of fluid flow apply in liquids and kites are used under water. A hybrid tethered craft comprising both a lighter-than-air balloon as well as a lifting surface is called a kytoon. Kites have a long and varied history and many different types are flown individually, Kites may be flown for recreation, art or other practical uses. Sport kites can be flown in aerial ballet, sometimes as part of a competition, even Man-lifting kites have been made. The kite has been claimed as the invention of the 5th-century BC Chinese philosophers Mozi, by 549 AD paper kites were certainly being flown, as it was recorded that in that year a paper kite was used as a message for a rescue mission. Ancient and medieval Chinese sources describe kites being used for measuring distances, testing the wind, lifting men, signaling, the earliest known Chinese kites were flat and often rectangular. Later, tailless kites incorporated a stabilizing bowline, Kites were decorated with mythological motifs and legendary figures, some were fitted with strings and whistles to make musical sounds while flying. From China, kites were introduced to Cambodia, Thailand, India, Japan, Korea, after its introduction into India, the kite further evolved into the fighter kite, known as the patang in India, where thousands are flown every year on festivals such as Makar Sankranti. Kites were known throughout Polynesia, as far as New Zealand, anthropomorphic kites made from cloth and wood were used in religious ceremonies to send prayers to the gods. Polynesian kite traditions are used by anthropologists get an idea of early primitive Asian traditions that are believed to have at one time existed in Asia, Kites were late to arrive in Europe, although windsock-like banners were known and used by the Romans. Stories of kites were first brought to Europe by Marco Polo towards the end of the 13th century, although they were initially regarded as mere curiosities, by the 18th and 19th centuries kites were being used as vehicles for scientific research. In 1750 Benjamin Franklin published a proposal for an experiment to prove that lightning was caused by electricity by flying a kite in a storm that appeared capable of becoming a lightning storm
13.
Point of sail
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Point of sail is a sailing boats orientation in relation to the current wind direction. Sailboats cannot sail directly into the wind, nor on a course that is too close to the direction from which the wind is blowing, the range of directions into which a boat cannot sail is called the no-go zone. When attempting to sail into the zone, the boats sails do not produce enough drive to maintain way or forward momentum through the water. Therefore, the boat will eventually coast to a stop, with the rudder becoming less and less effective at controlling the direction of travel, the size of the no-go zone varies, but all sailboats have one. Its width depends on the design of the boat, its rig, and its sails, as well as on the wind strength and the sea state. Depending on the boat and the conditions, the zone may be from 30 to 50 degrees either side of the wind. A sailboat is said to be in if it is stopped. This is also known as being taken aback, especially on a vessel whose sails can be blown back against the masts. A boat is said to be sailing close-hauled when its sails are trimmed in tightly and this point of sail lets the boat travel diagonally to the wind direction, or upwind. When the wind is coming from the side of the boat, a beam reach is when the wind is at a right angle to the boat. A close reach is a closer to the wind than a beam reach. I. e. any angle between a reach and close-hauled. The sails are trimmed in, but not as tight as for a close-hauled course, a broad reach is a course further away from the wind than a beam reach but above a run. In a broad reach, the wind is coming from behind the boat at an angle and this represents a range of wind angles between beam reach and running downwind. The sails are eased out away from the boat, but not as much as on a run or dead run, on this point of sail, the wind is coming from directly behind the boat. Running can be dangerous to those on board in the event of an accidental jibe, when running, the mainsail is eased out as far as it will go. The jib will collapse because the mainsail blocks its wind, and must either be lowered and replaced by a spinnaker, running with the jib to windward is known as gull wing, goose wing, butterflying or wing and wing. A genoa gull-wings well, especially if stabilized by a whisker pole, which is similar to but lighter than a spinnaker pole
14.
Apparent wind
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Apparent wind is the wind experienced by a moving object. The Apparent wind is the experienced by an observer in motion and is the relative velocity of the wind in relation to the observer. Apparent wind velocity is the sum of the true wind. In sailing, the apparent wind is the flow of air acting upon a sail. It is the wind as it appears to the sailor on a moving vessel and it differs in speed and direction from the true wind that is experienced by a stationary observer. In nautical terminology, these properties of the apparent wind are normally expressed in knots, on boats, apparent wind is measured or felt on face / skin if on a dinghy or looking at any telltales or wind indicators on board. True wind needs to be calculated or stop the boat and this must be corrected for when converting apparent wind angle to true wind direction. The same effect is found when the boat is altering course, modern instrumentation can calculate the true wind velocity when the apparent wind and boat velocity and direction are input. In sailboat racing, and especially in speed sailing, apparent wind is a vital factor, a vessel traveling at increasing speed relative to the prevailing wind will encounter the wind driving the sail at a decreasing angle and increasing velocity. Eventually, the drag and diminished degree of efficiency of a sail at extremely low angles will cause a loss of accelerating force. This constitutes the main limitation to the speed of wind-driven vessels, windsurfers and certain types of boats are able to sail faster than the true wind. These include fast multihulls and some planing monohulls, ice-sailors and land-sailors also usually fall into this category, because of their relatively low amount of drag or friction. In the foiling AC72 Americas cup catamarans, the boats sail through the water at up to double the wind strength. The effect of this is to change the apparent wind direction when sailing downwind. In these boats the forward speed is so great that the apparent wind is always forward—at an angle that varies between 2 and 4 degrees to the wing sail. This means that AC72s are effectively tacking downwind, although at a greater angle than the normal 45-degree upwind angle, in fixed-wing aircraft, apparent wind is what is experienced on board, and it determines the necessary speeds for take-off and landing. Aircraft carriers generally steam directly upwind at maximum speed, in order to increase apparent wind, land-based airport traffic, as well as most mid-sized and large birds generally take off and land facing upwind for the same reason. For port apparent winds, the true pointing angle has the sign, α = − arccos = − arccos Navigational Algorithms Apparent wind soft, math, vector solution
15.
Drag (physics)
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In fluid dynamics, drag is a force acting opposite to the relative motion of any object moving with respect to a surrounding fluid. This can exist between two layers or a fluid and a solid surface. Unlike other resistive forces, such as dry friction, which are independent of velocity. Drag force is proportional to the velocity for a laminar flow, even though the ultimate cause of a drag is viscous friction, the turbulent drag is independent of viscosity. Drag forces always decrease fluid velocity relative to the object in the fluids path. In the case of viscous drag of fluid in a pipe, in physics of sports, the drag force is necessary to explain the performance of runners, particularly of sprinters. Types of drag are generally divided into the categories, parasitic drag, consisting of form drag, skin friction, interference drag, lift-induced drag. The phrase parasitic drag is used in aerodynamics, since for lifting wings drag it is in general small compared to lift. For flow around bluff bodies, form and interference drags often dominate, further, lift-induced drag is only relevant when wings or a lifting body are present, and is therefore usually discussed either in aviation or in the design of semi-planing or planing hulls. Wave drag occurs either when an object is moving through a fluid at or near the speed of sound or when a solid object is moving along a fluid boundary. Drag depends on the properties of the fluid and on the size, shape, at low R e, C D is asymptotically proportional to R e −1, which means that the drag is linearly proportional to the speed. At high R e, C D is more or less constant, the graph to the right shows how C D varies with R e for the case of a sphere. As mentioned, the equation with a constant drag coefficient gives the force experienced by an object moving through a fluid at relatively large velocity. This is also called quadratic drag, the equation is attributed to Lord Rayleigh, who originally used L2 in place of A. Sometimes a body is a composite of different parts, each with a different reference areas, in the case of a wing the reference areas are the same and the drag force is in the same ratio to the lift force as the ratio of drag coefficient to lift coefficient. Therefore, the reference for a wing is often the area rather than the frontal area. For an object with a surface, and non-fixed separation points—like a sphere or circular cylinder—the drag coefficient may vary with Reynolds number Re. For an object with well-defined fixed separation points, like a disk with its plane normal to the flow direction
16.
Lift (force)
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A fluid flowing past the surface of a body exerts a force on it. Lift is the component of force that is perpendicular to the oncoming flow direction. It contrasts with the force, which is the component of the surface force parallel to the flow direction. If the fluid is air, the force is called an aerodynamic force, in water, it is called a hydrodynamic force. Lift is also exploited in the world, and even in the plant world by the seeds of certain trees. When an aircraft is flying straight and level most of the lift opposes gravity, however, when an aircraft is climbing, descending, or banking in a turn the lift is tilted with respect to the vertical. Lift may also be entirely downwards in some aerobatic manoeuvres, or on the wing on a racing car, in this last case, the term downforce is often used. Lift may also be horizontal, for instance on a sail on a sailboat. Aerodynamic lift is distinguished from other kinds of lift in fluids, Aerodynamic lift requires relative motion of the fluid which distinguishes it from aerostatic lift or buoyancy lift as used by balloons, blimps, and dirigibles. An airfoil is a shape that is capable of generating significantly more lift than drag. A flat plate can generate lift, but not as much as a streamlined airfoil, there are several ways to explain how an airfoil generates lift. Some are more complicated or more rigorous than others, some have been shown to be incorrect. For example, there are based directly on Newton’s laws of motion. Either can be used to explain lift, an airfoil generates lift by exerting a downward force on the air as it flows past. According to Newtons third law, the air must exert an equal and opposite force on the airfoil, the air flow changes direction as it passes the airfoil and follows a path that is curved downward. According to Newtons second law, this change in flow direction requires a force applied to the air by the airfoil. Then, according to Newtons third law, the air must exert a force on the airfoil. The overall result is that a force, the lift, is generated opposite to the directional change
17.
Normal (geometry)
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In geometry, a normal is an object such as a line or vector that is perpendicular to a given object. For example, in the case, the normal line to a curve at a given point is the line perpendicular to the tangent line to the curve at the point. In the three-dimensional case a normal, or simply normal. The word normal is used as an adjective, a line normal to a plane, the normal component of a force. The concept of normality generalizes to orthogonality, the concept has been generalized to differentiable manifolds of arbitrary dimension embedded in a Euclidean space. The normal vector space or normal space of a manifold at a point P is the set of the vectors which are orthogonal to the tangent space at P, in the case of differential curves, the curvature vector is a normal vector of special interest. For a convex polygon, a surface normal can be calculated as the cross product of two edges of the polygon. For a plane given by the equation a x + b y + c z + d =0, the vector is a normal. For a hyperplane in n+1 dimensions, given by the equation r = a 0 + α1 a 1 + ⋯ + α n a n, where a0 is a point on the hyperplane and ai for i =1. N are non-parallel vectors lying on the hyperplane, a normal to the hyperplane is any vector in the space of A where A is given by A =. That is, any vector orthogonal to all in-plane vectors is by definition a surface normal. If a surface S is parameterized by a system of coordinates x, with s and t real variables. For a surface S given explicitly as a function f of the independent variables x, y, the first one is obtaining its implicit form F = z − f =0, from which the normal follows readily as the gradient ∇ F. The second way of obtaining the normal follows directly from the gradient of the form, ∇ f, by inspection, ∇ F = k ^ − ∇ f. Note that this is equal to ∇ F = k ^ − ∂ f ∂ x i ^ − ∂ f ∂ y j ^, if a surface does not have a tangent plane at a point, it does not have a normal at that point either. For example, a cone does not have a normal at its tip nor does it have a normal along the edge of its base, however, the normal to the cone is defined almost everywhere. In general, it is possible to define a normal almost everywhere for a surface that is Lipschitz continuous, a normal to a surface does not have a unique direction, the vector pointing in the opposite direction of a surface normal is also a surface normal. For an oriented surface, the normal is usually determined by the right-hand rule
18.
Airfoil
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An airfoil or aerofoil is the shape of a wing, blade, or sail. An airfoil-shaped body moved through a fluid produces an aerodynamic force, the component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag, subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the fluid are called hydrofoils. The lift on an airfoil is primarily the result of its angle of attack, when oriented at a suitable angle, the airfoil deflects the oncoming air, resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as force and can be resolved into two components, lift and drag. Most foil shapes require an angle of attack to generate lift. This turning of the air in the vicinity of the airfoil creates curved streamlines, resulting in pressure on one side. The lift force can be related directly to the average top/bottom velocity difference without computing the pressure by using the concept of circulation, a fixed-wing aircrafts wings, horizontal, and vertical stabilizers are built with airfoil-shaped cross sections, as are helicopter rotor blades. Airfoils are also found in propellers, fans, compressors and turbines, sails are also airfoils, and the underwater surfaces of sailboats, such as the centerboard and keel, are similar in cross-section and operate on the same principles as airfoils. Swimming and flying creatures and even many plants and sessile organisms employ airfoils/hydrofoils, common examples being bird wings, the bodies of fish, an airfoil-shaped wing can create downforce on an automobile or other motor vehicle, improving traction. Any object with an angle of attack in a fluid, such as a flat plate. Airfoils are more efficient lifting shapes, able to more lift. A lift and drag curve obtained in wind tunnel testing is shown on the right, the curve represents an airfoil with a positive camber so some lift is produced at zero angle of attack. With increased angle of attack, lift increases in a linear relation. At about 18 degrees this airfoil stalls, and lift falls off quickly beyond that, the drop in lift can be explained by the action of the upper-surface boundary layer, which separates and greatly thickens over the upper surface at and past the stall angle. The thicker boundary layer also causes an increase in pressure drag, so that the overall drag increases sharply near. Airfoil design is a facet of aerodynamics
19.
Euclidean vector
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In mathematics, physics, and engineering, a Euclidean vector is a geometric object that has magnitude and direction. Vectors can be added to other vectors according to vector algebra, a Euclidean vector is frequently represented by a line segment with a definite direction, or graphically as an arrow, connecting an initial point A with a terminal point B, and denoted by A B →. A vector is what is needed to carry the point A to the point B and it was first used by 18th century astronomers investigating planet rotation around the Sun. The magnitude of the vector is the distance between the two points and the direction refers to the direction of displacement from A to B. These operations and associated laws qualify Euclidean vectors as an example of the more generalized concept of vectors defined simply as elements of a vector space. Vectors play an important role in physics, the velocity and acceleration of a moving object, many other physical quantities can be usefully thought of as vectors. Although most of them do not represent distances, their magnitude and direction can still be represented by the length, the mathematical representation of a physical vector depends on the coordinate system used to describe it. Other vector-like objects that describe physical quantities and transform in a similar way under changes of the system include pseudovectors and tensors. The concept of vector, as we know it today, evolved gradually over a period of more than 200 years, about a dozen people made significant contributions. Giusto Bellavitis abstracted the basic idea in 1835 when he established the concept of equipollence, working in a Euclidean plane, he made equipollent any pair of line segments of the same length and orientation. Essentially he realized an equivalence relation on the pairs of points in the plane, the term vector was introduced by William Rowan Hamilton as part of a quaternion, which is a sum q = s + v of a Real number s and a 3-dimensional vector. Like Bellavitis, Hamilton viewed vectors as representative of classes of equipollent directed segments, grassmanns work was largely neglected until the 1870s. Peter Guthrie Tait carried the standard after Hamilton. His 1867 Elementary Treatise of Quaternions included extensive treatment of the nabla or del operator ∇, in 1878 Elements of Dynamic was published by William Kingdon Clifford. Clifford simplified the quaternion study by isolating the dot product and cross product of two vectors from the complete quaternion product and this approach made vector calculations available to engineers and others working in three dimensions and skeptical of the fourth. Josiah Willard Gibbs, who was exposed to quaternions through James Clerk Maxwells Treatise on Electricity and Magnetism, the first half of Gibbss Elements of Vector Analysis, published in 1881, presents what is essentially the modern system of vector analysis. In 1901 Edwin Bidwell Wilson published Vector Analysis, adapted from Gibbs lectures, in physics and engineering, a vector is typically regarded as a geometric entity characterized by a magnitude and a direction. It is formally defined as a line segment, or arrow
20.
Boldface
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In typography, emphasis is the exaggeration of words in a text with a font in a different style from the rest of the text—to emphasize them. It is the equivalent of prosodic stress in speech, the most common methods in Bold fall under the general technique of emphasis through a change or modification of font, italics, boldface and small caps. Other methods include the alteration of letter case and spacing as well as color, the human eye is very receptive to differences in brightness within a text body. Therefore, one can differentiate types of emphasis according to whether the emphasis changes the “blackness” of text. With one or the other of these techniques, words can be highlighted without making them out much from the rest of the text. This was used for marking passages that have a different context, such as words from languages, book titles. By contrast, a bold font weight makes text darker than the surrounding text, for example, printed dictionaries often use boldface for their keywords, and the names of entries can conventionally be marked in bold. Small capitals are used for emphasis, especially for the first line of a section, sometimes accompanied by or instead of a drop cap. If the text body is typeset in a typeface, it is also possible to highlight words by setting them in a sans serif face. It is still using some font superfamilies, which come with matching serif and sans-serif variants. In Japanese typography, due to the legibility of heavier Minchō type. Of these methods, italics, small capitals and capitalisation are oldest, with bold type, the house styles of many publishers in the United States use all caps text for, chapter and section headings, newspaper headlines, publication titles, warning messages, word of important meaning. Capitalization is used less commonly today by British publishers. All-uppercase letters are a form of emphasis where the medium lacks support for boldface, such as old typewriters, plain-text email, SMS. Culturally all-caps text has become an indication of shouting, for example when quoting speech and it was also once often used by American lawyers to indicate important points in a legal text. Another means of emphasis is to increase the spacing between the letters, rather than making them darker, but still achieving a distinction in blackness and this results in an effect reverse to boldface, the emphasized text becomes lighter than its environment. This is often used in typesetting and typewriter manuscripts. On typewriters a full space was used between the letters of a word and also one before and one after the word
21.
Italic type
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In typography, italic type is a cursive font based on a stylized form of calligraphic handwriting. Owing to the influence from calligraphy, italics normally slant slightly to the right, italics are a way to emphasise key points in a printed text, or when quoting a speaker a way to show which words they stressed. One manual of English usage described italics as the print equivalent of underlining, the name comes from the fact that calligraphy-inspired typefaces were first designed in Italy, to replace documents traditionally written in a handwriting style called chancery hand. Aldus Manutius and Ludovico Arrighi were the type designers involved in this process at the time. Different glyph shapes from roman type are usually used – another influence from calligraphy –, an alternative is oblique type, in which the type is slanted but the letterforms do not change shape, this less elaborate approach is used by many sans-serif typefaces. Italic type was first used by Aldus Manutius and his press in Venice in 1500, Manutius used italic not for emphasis but for the text of small, easily carried editions of popular books, replicating the style of handwritten manuscripts of the period. The choice of using italic type, rather than the type in general use at the time, was apparently made to suggest informality in editions designed for leisure reading. Manutius italic type, cut and conceived by his employee, punchcutter Francesco Griffo, replicated handwriting of the following from the style of Niccolò de Niccoli. The first use in a volume was a 1501 edition of Virgil dedicated to Italy. Manutius italic was different in some ways from modern italics, unlike the italic type of today, the capital letters were upright capitals on the model of Roman square capitals, shorter than the ascending lower-case italic letters. While modern italics are more condensed than roman types, historian Harry Carter describes Manutius italic as about the same width as roman type. To replicate handwriting, Griffo cut at least sixty-five tied letters in the Aldine Dante, Italic typefaces of the following century used varying but reduced numbers of ligatures. Manutius type rapidly became popular in its own day and was widely imitated. The Venetian Senate gave Aldus exclusive right to its use, a patent confirmed by three successive Popes, but it was widely counterfeited as early as 1502. Griffo, who had left Venice in a dispute, cut a version for printer Girolamo Soncino. The Italians called the character Aldino, while called it Italic. Italics spread rapidly, historian Hendrik Vervliet dates the first production of italics in Paris to 1512, chancery italics faded as a style over the course of the sixteenth century, although revivals were made beginning in the twentieth century. Chancery italics may have backward-pointing serifs or round terminals pointing forwards on the ascenders, Vervliet comments that among punchcutters the main name associated with the change is Granjons
22.
Newton (unit)
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The newton is the International System of Units derived unit of force. It is named after Isaac Newton in recognition of his work on classical mechanics, see below for the conversion factors. One newton is the force needed to one kilogram of mass at the rate of one metre per second squared in direction of the applied force. In 1948, the 9th CGPM resolution 7 adopted the name newton for this force, the MKS system then became the blueprint for todays SI system of units. The newton thus became the unit of force in le Système International dUnités. This SI unit is named after Isaac Newton, as with every International System of Units unit named for a person, the first letter of its symbol is upper case. Note that degree Celsius conforms to this rule because the d is lowercase. — Based on The International System of Units, section 5.2. Newtons second law of motion states that F = ma, where F is the applied, m is the mass of the object receiving the force. The newton is therefore, where the symbols are used for the units, N for newton, kg for kilogram, m for metre. In dimensional analysis, F = M L T2 where F is force, M is mass, L is length, at average gravity on earth, a kilogram mass exerts a force of about 9.8 newtons. An average-sized apple exerts about one newton of force, which we measure as the apples weight, for example, the tractive effort of a Class Y steam train and the thrust of an F100 fighter jet engine are both around 130 kN. One kilonewton,1 kN, is 102.0 kgf,1 kN =102 kg ×9.81 m/s2 So for example, a platform rated at 321 kilonewtons will safely support a 32,100 kilograms load. Specifications in kilonewtons are common in safety specifications for, the values of fasteners, Earth anchors. Working loads in tension and in shear, thrust of rocket engines and launch vehicles clamping forces of the various moulds in injection moulding machines used to manufacture plastic parts
23.
Lift-induced drag
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In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is an aerodynamic drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift, with other parameters remaining the same, induced drag increases as the angle of attack increases. The total aerodynamic force acting on a body is thought of as having two components, lift and drag. By definition, the component of force parallel to the flow is called drag. At practical angles of attack the lift greatly exceeds the drag, lift is produced by the changing direction of the flow around a wing. The change of direction results in a change of velocity, which is an acceleration, to change the direction of the flow therefore requires that a force be applied to the fluid, lift is simply the reaction force of the fluid acting on the wing. To produce lift, air below the wing is at a higher pressure than the air pressure above the wing. On a wing of finite span, this pressure difference causes air to flow from the lower wing root, around the wingtip. This spanwise flow of air combines with chordwise flowing air, causing a change in speed and direction, the vortices created are unstable, and they quickly combine to produce wingtip vortices. The resulting vortices change the speed and direction of the airflow behind the edge, deflecting it downwards. The angular deflection is small and has little effect on the lift, however, there is an increase in the drag equal to the product of the lift force and the angle through which it is deflected. Since the deflection is itself a function of the lift, the drag is proportional to the square of the lift. According to the equations below, a wing of infinite aspect ratio, the characteristics of such a wing can be measured on a section of wing spanning the width of a wind tunnel, since the walls block spanwise flow and create what is effectively two-dimensional flow. A rectangular planform wing produces stronger wingtip vortices than does a tapered or elliptical wing, however, an elliptical planform is more efficient as the induced downwash is constant across the whole of the wingspan. Few aircraft have this planform because of manufacturing complications — the most famous examples being the World War II Spitfire, tapered wings with straight leading and trailing edges can approximate to elliptical lift distribution. Typically, straight edged non-tapered wings produce 5%, and tapered wings produce 1-2% more induced drag than an elliptical wing. Similarly, for a wing area, a high aspect ratio wing will produce less induced drag than a wing of low aspect ratio because there is less air disturbance at the tip of a longer, thinner wing. Induced drag can therefore be said to be proportional to aspect ratio
24.
Pressure
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Pressure is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure is the relative to the ambient pressure. Various units are used to express pressure, Pressure may also be expressed in terms of standard atmospheric pressure, the atmosphere is equal to this pressure and the torr is defined as 1⁄760 of this. Manometric units such as the centimetre of water, millimetre of mercury, Pressure is the amount of force acting per unit area. The symbol for it is p or P, the IUPAC recommendation for pressure is a lower-case p. However, upper-case P is widely used. The usage of P vs p depends upon the field in one is working, on the nearby presence of other symbols for quantities such as power and momentum. Mathematically, p = F A where, p is the pressure, F is the normal force and it relates the vector surface element with the normal force acting on it. It is incorrect to say the pressure is directed in such or such direction, the pressure, as a scalar, has no direction. The force given by the relationship to the quantity has a direction. If we change the orientation of the element, the direction of the normal force changes accordingly. Pressure is distributed to solid boundaries or across arbitrary sections of normal to these boundaries or sections at every point. It is a parameter in thermodynamics, and it is conjugate to volume. The SI unit for pressure is the pascal, equal to one newton per square metre and this name for the unit was added in 1971, before that, pressure in SI was expressed simply in newtons per square metre. Other units of pressure, such as pounds per square inch, the CGS unit of pressure is the barye, equal to 1 dyn·cm−2 or 0.1 Pa. Pressure is sometimes expressed in grams-force or kilograms-force per square centimetre, but using the names kilogram, gram, kilogram-force, or gram-force as units of force is expressly forbidden in SI. The technical atmosphere is 1 kgf/cm2, since a system under pressure has potential to perform work on its surroundings, pressure is a measure of potential energy stored per unit volume. It is therefore related to density and may be expressed in units such as joules per cubic metre. Similar pressures are given in kilopascals in most other fields, where the prefix is rarely used
25.
Stress (mechanics)
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For example, when a solid vertical bar is supporting a weight, each particle in the bar pushes on the particles immediately below it. When a liquid is in a container under pressure, each particle gets pushed against by all the surrounding particles. The container walls and the pressure-inducing surface push against them in reaction and these macroscopic forces are actually the net result of a very large number of intermolecular forces and collisions between the particles in those molecules. Strain inside a material may arise by various mechanisms, such as stress as applied by external forces to the material or to its surface. Any strain of a material generates an internal elastic stress, analogous to the reaction force of a spring. In liquids and gases, only deformations that change the volume generate persistent elastic stress, however, if the deformation is gradually changing with time, even in fluids there will usually be some viscous stress, opposing that change. Elastic and viscous stresses are usually combined under the mechanical stress. Significant stress may exist even when deformation is negligible or non-existent, stress may exist in the absence of external forces, such built-in stress is important, for example, in prestressed concrete and tempered glass. Stress may also be imposed on a material without the application of net forces, for example by changes in temperature or chemical composition, stress that exceeds certain strength limits of the material will result in permanent deformation or even change its crystal structure and chemical composition. In some branches of engineering, the stress is occasionally used in a looser sense as a synonym of internal force. For example, in the analysis of trusses, it may refer to the total traction or compression force acting on a beam, since ancient times humans have been consciously aware of stress inside materials. Until the 17th century the understanding of stress was largely intuitive and empirical, with those tools, Augustin-Louis Cauchy was able to give the first rigorous and general mathematical model for stress in a homogeneous medium. Cauchy observed that the force across a surface was a linear function of its normal vector, and, moreover. The understanding of stress in liquids started with Newton, who provided a formula for friction forces in parallel laminar flow. Stress is defined as the force across a small boundary per unit area of that boundary, following the basic premises of continuum mechanics, stress is a macroscopic concept. In a fluid at rest the force is perpendicular to the surface, in a solid, or in a flow of viscous liquid, the force F may not be perpendicular to S, hence the stress across a surface must be regarded a vector quantity, not a scalar. Moreover, the direction and magnitude depend on the orientation of S. Thus the stress state of the material must be described by a tensor, called the stress tensor, with respect to any chosen coordinate system, the Cauchy stress tensor can be represented as a symmetric matrix of 3×3 real numbers
26.
Gradient
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In mathematics, the gradient is a multi-variable generalization of the derivative. While a derivative can be defined on functions of a variable, for functions of several variables. The gradient is a function, as opposed to a derivative. If f is a differentiable, real-valued function of several variables, like the derivative, the gradient represents the slope of the tangent of the graph of the function. More precisely, the gradient points in the direction of the greatest rate of increase of the function, the components of the gradient in coordinates are the coefficients of the variables in the equation of the tangent space to the graph. The Jacobian is the generalization of the gradient for vector-valued functions of several variables, a further generalization for a function between Banach spaces is the Fréchet derivative. Consider a room in which the temperature is given by a field, T. At each point in the room, the gradient of T at that point will show the direction in which the temperature rises most quickly, the magnitude of the gradient will determine how fast the temperature rises in that direction. Consider a surface whose height above sea level at point is H, the gradient of H at a point is a vector pointing in the direction of the steepest slope or grade at that point. The steepness of the slope at point is given by the magnitude of the gradient vector. The gradient can also be used to measure how a scalar field changes in other directions, rather than just the direction of greatest change, suppose that the steepest slope on a hill is 40%. If a road goes directly up the hill, then the steepest slope on the road will also be 40%, if, instead, the road goes around the hill at an angle, then it will have a shallower slope. This observation can be stated as follows. If the hill height function H is differentiable, then the gradient of H dotted with a unit vector gives the slope of the hill in the direction of the vector. More precisely, when H is differentiable, the dot product of the gradient of H with a unit vector is equal to the directional derivative of H in the direction of that unit vector. The gradient of a function f is denoted ∇f or ∇→f where ∇ denotes the vector differential operator. The notation grad f is commonly used for the gradient. The gradient of f is defined as the vector field whose dot product with any vector v at each point x is the directional derivative of f along v. That is
27.
Angle of attack
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In fluid dynamics, angle of attack is the angle between a reference line on a body and the vector representing the relative motion between the body and the fluid through which it is moving. Angle of attack is the angle between the reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air, since a wing can have twist, a chord line of the whole wing may not be definable, so an alternate reference line is simply defined. Often, the line of the root of the wing is chosen as the reference line. Another choice is to use a line on the fuselage as the reference line. Some authors do not use a chord line, but use the zero lift axis. Some British authors have used the angle of incidence instead of angle of attack. However, this can lead to confusion with the term angle of incidence meaning the angle between the chord of an airfoil and some fixed datum in the airplane. The lift coefficient of a fixed-wing aircraft varies with angle of attack, increasing angle of attack is associated with increasing lift coefficient up to the maximum lift coefficient, after which lift coefficient decreases. The figure shows a curve for a cambered straight wing. A symmetrical wing has zero lift at 0 degrees angle of attack, the lift curve is also influenced by the wing shape, including its airfoil section and wing planform. A swept wing has a lower, flatter curve with a critical angle. The critical angle of attack is the angle of attack which produces maximum lift coefficient and this is also called the stall angle of attack. Below the critical angle of attack, as the angle of attack increases, conversely, above the critical angle of attack, as angle of attack increases, the air begins to flow less smoothly over the upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, at the critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum coefficient of lift. As angle of attack increases further, the surface flow becomes more and more fully separated. Above this critical angle of attack, the aircraft is said to be in a stall, a fixed-wing aircraft by definition is stalled at or above the critical angle of attack rather than at or below a particular airspeed. The airspeed at which the aircraft stalls varies with the weight of the aircraft, the load factor, however the aircraft always stalls at the same critical angle of attack
28.
Chord (aeronautics)
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In aeronautics, chord refers to the imaginary straight line joining the leading and trailing edges of an aerofoil. The chord length is the distance between the edge and the point on the leading edge where the chord intersects the leading edge. The point on the edge that is used to define the chord can be defined as either the surface point of minimum radius. The wing, horizontal stabilizer, vertical stabilizer and propeller of an aircraft are all based on sections. The chord of a wing, stabilizer and propeller is determined by measuring the distance between leading and trailing edges in the direction of the airflow, the term chord is also applied to the width of wing flaps, ailerons and rudder on an aircraft. The term is applied to aerofoils in gas turbine engines such as turbojet, turboprop. Most wings are not rectangular so they have a different chord at different positions along their span, to give a characteristic figure that can be compared among various wing shapes, the mean aerodynamic chord, or MAC, is used. The MAC is somewhat complex to calculate, because most wings vary in chord over the span. This means that lift is generated on the wider inner portions. Standard mean chord is defined as wing area divided by wing span, SMC = S b, thus, the SMC is the chord of a rectangular wing with the same area and span as those of the given wing. This is a geometric figure and is rarely used in aerodynamics. Mean aerodynamic chord is defined as, MAC =2 S ∫0 b 2 c 2 d y, other terms are as for SMC. The MAC is a representation of the whole wing. The pressure distribution over the wing can be reduced to a single lift force on. Therefore, not only the length but also the position of MAC is often important. In particular, the position of center of mass of an aircraft is measured relative to the MAC. Note that the figure to the right implies that the MAC occurs at a point where leading or trailing edge sweep changes, in general, this is not the case. Any shape other than a simple trapezoid requires evaluation of the above integral, the ratio of the length of a rectangular-planform wing to its chord is known as the aspect ratio, an important indicator of the lift-induced drag the wing will create
29.
Parasitic drag
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Parasitic drag is drag that results when an object is moved through a fluid medium. In the case of aerodynamic drag, the medium is the atmosphere. Parasitic drag is a combination of form drag, skin friction drag, the other components of total drag, induced drag, wave drag, and ram drag, are separate types of drag, and are not components of parasitic drag. Parasitic drag does not result from the induction of lift on the body, in flight, induced drag results from the lift force that must produced so that the craft can maintain level flight. Induced drag is greater at lower speeds where a high angle of attack is required, as speed increases, the induced drag decreases, but parasitic drag increases because the fluid is striking the object with greater force, and is moving across the objects surfaces at higher speed. As speed continues to increase into the transonic and supersonic regimes, each of these drag components changes in proportion to the others based on speed. The combined overall drag curve therefore shows a minimum at some airspeed, pilots will use this speed to maximize the gliding range in case of an engine failure. However, to maximize the gliding endurance, the speed would have to be at the point of minimum power. At the point of minimum drag, CD, o is equal to CD, at the point of minimum power, CD, o is equal to one third times CD, i. Form drag follows the equation, meaning that it increases with velocity. Form drag depends on the section of the body. A prudent choice of body profile is essential for a low drag coefficient, streamlines should be continuous, and separation of the boundary layer with its attendant vortices should be avoided. Profile drag is usually defined as the sum of form drag, however, the term is often used synonymously with form drag. Interference drag results when airflow around one part of an object must occupy the space as the airflow around another part. This velocity increase is present at all airspeeds, but becomes more important in the transonic range when the resulting velocity becomes sonic. Interference drag plays a role throughout the aircraft and its detrimental effect is always kept in mind by designers. Ideally, the distributions on the intersecting bodies should complement each other’s pressure distribution. If one body locally displays a negative coefficient, the intersecting body should have a positive pressure coefficient
30.
Lift coefficient
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The lift coefficient is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity and an associated reference area. A lifting body is a foil or a complete foil-bearing body such as a fixed-wing aircraft, CL is a function of the angle of the body to the flow, its Reynold number and its Mach number. The lift coefficient cl refers to the lift characteristics of a two-dimensional foil section. The choice of the surface should be specified since it is arbitrary. Lift coefficient may also be used as a characteristic of a shape of an airfoil. In this application it is called the lift coefficient c l. It is common to show, for an airfoil section. It is also useful to show the relationship between section lift coefficient and drag coefficient, note this is directly analogous to the drag coefficient since the chord can be interpreted as the area per unit span. Plots of cl versus angle of attack show the general shape for all airfoils. They show an almost linear increase in lift coefficient with increasing angle of attack with a gradient known as the lift slope, for a thin airfoil of any shape the lift slope is π2/90 ≃0.11 per degree. At higher angles a maximum point is reached, after which the lift coefficient reduces, the angle at which maximum lift coefficient occurs is the stall angle of the airfoil, which is approximately 10 to 15 degrees on a typical airfoil. That is, the angle at which cl =0 is negative, on such airfoils at zero angle of attack the pressures on the upper surface are lower than on the lower surface. Lift-to-drag ratio Drag coefficient Foil Pitching moment Circulation control wing Zero lift axis Clancy, pitman Publishing Limited, London, ISBN 0-273-01120-0 Abbott, Ira H. and Doenhoff, Albert E. von, Theory of Wing Sections. New York, Standard Book Number 486-60586-8
31.
Stall (fluid mechanics)
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In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the angle of attack of the foil is exceeded. The critical angle of attack is typically about 15 degrees, but it may vary depending on the fluid, foil. Stalls in fixed-wing flight are often experienced as a reduction in lift as the pilot increases the wings angle of attack. A stall does not mean that the engine have stopped working, vectored thrust in manned and unmanned aircraft is used to surpass the stall limit, thereby giving rise to post-stall technology. Because stalls are most commonly discussed in connection with aviation, this article discusses stalls as they relate mainly to aircraft, the principles of stall discussed here translate to foils in other fluids as well. A stall is a condition in aerodynamics and aviation wherein the angle of attack increases beyond a point such that lift begins to decrease. The angle at which this occurs is called the angle of attack. The critical angle of attack is the angle of attack on the lift coefficient versus angle-of-attack curve at which the lift coefficient occurs. Flow separation begins to occur at angles of attack while attached flow over the wing is still dominant. As angle of attack increases, the regions on the top of the wing increase in size. At the critical angle of attack, separated flow is so dominant that additional increases in angle of attack produce less lift, a fixed-wing aircraft during a stall may experience buffeting or a change in attitude. Most aircraft are designed to have a stall with characteristics that will warn the pilot. For example, an aircraft that does not buffet before the stall may have an alarm or a stick shaker installed to simulate the feel of a buffet by vibrating the stick fore. The buffet margin is, for a set of conditions, the amount of ‘g’. The critical angle of attack in steady straight and level flight can be attained only at low airspeed, attempts to increase the angle of attack at higher airspeeds can cause a high-speed stall or may merely cause the aircraft to climb. Any yaw of the aircraft as it enters the stall regime can result in autorotation, as air no longer flows smoothly over the wings during a stall, aileron control of roll becomes less effective, whilst simultaneously the tendency for the ailerons to generate adverse yaw increases. This characteristic increases the lift from the wing and increases the likelihood of the aircraft entering into a spin
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Drag coefficient
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In fluid dynamics, the drag coefficient is a dimensionless quantity that is used to quantify the drag or resistance of an object in a fluid environment, such as air or water. It is used in the equation in which a lower drag coefficient indicates the object will have less aerodynamic or hydrodynamic drag. The drag coefficient is associated with a particular surface area. The drag coefficient of any object comprises the effects of the two contributors to fluid dynamic drag, skin friction and form drag. The drag coefficient of an airfoil or hydrofoil also includes the effects of lift-induced drag. The drag coefficient of a structure such as an aircraft also includes the effects of interference drag. The reference area depends on type of drag coefficient is being measured. For automobiles and many objects, the reference area is the projected frontal area of the vehicle. This may not necessarily be the sectional area of the vehicle. For example, for a sphere A = π r 2, for airfoils, the reference area is the nominal wing area. Since this tends to be compared to the frontal area, the resulting drag coefficients tend to be low, much lower than for a car with the same drag, frontal area. Airships and some bodies of revolution use the drag coefficient. Submerged streamlined bodies use the surface area. Two objects having the same reference area moving at the speed through a fluid will experience a drag force proportional to their respective drag coefficients. Coefficients for unstreamlined objects can be 1 or more, for streamlined objects much less, cd is not a constant but varies as a function of flow speed, flow direction, object position, object size, fluid density and fluid viscosity. Speed, kinematic viscosity and a length scale of the object are incorporated into a dimensionless quantity called the Reynolds number R e. C d is thus a function of R e, in a compressible flow, the speed of sound is relevant, and C d is also a function of Mach number M a. For certain body shapes, the drag coefficient C d only depends on the Reynolds number R e, Mach number M a, for low Mach number M a, the drag coefficient is independent of Mach number
33.
Sailing
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Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the water, on ice or on land over a chosen course, which is often part of a larger plan of navigation. A course defined with respect to the wind direction is called a point of sail. Conventional sailing craft cannot derive power from sails on a point of sail that is too close into the wind, on a given point of sail, the sailor adjusts the alignment of each sail with respect to the apparent wind direction to mobilize the power of the wind. In the 21st century, most sailing represents a form of recreation or sport, recreational sailing or yachting can be divided into racing and cruising. Cruising can include extended offshore and ocean-crossing trips, coastal sailing within sight of land, until the end of the 19th century, sailing ships were the primary means for marine commerce. The earliest representation of a ship under sail appears on a painted disc found in Kuwait dating between 5000 and 5500 BCE, polynesian oceanfarers traveled vast distances of open ocean in outrigger canoes using navigation methods such as stick charts. Advances in sailing technology from the Middle Ages onward enabled Arab, Chinese, Indian and European explorers to make longer voyages into regions with extreme weather and climatic conditions. There were improvements in sails, masts and rigging, improvements in marine navigation including the tree and charts. Sailing has contributed to many great explorations in the world, the air interacting with the sails of a sailing vessel creates various forces, including reaction forces. If the sails are properly oriented with respect to the wind, however, boats propelled by sails cannot sail directly into the wind. They must tack back and forth in order to progress directly upwind, sails are airfoils that work by using an airflow set up by the wind and the motion of the boat. Sails work in two modes to use the wind to force, PUSH, when the boat is going in the same direction as the wind. The force on the sail is mostly aerodynamic drag, and sails acting in this way are aerodynamically stalled. This force manifests itself as pressure differences between the two sides of the sail - there is a region of low pressure on the front side of the sail and a region of high pressure on the back. Another way to say this is that sails generate lift using the air flows around them in the same way as an aircraft wing. The wind that a boat experiences is the combination of the true wind and this combination is the apparent wind, which is the relative velocity of the wind relative to the boat. When sailing upwind the apparent wind is greater than the true wind, iceboats can typically sail at 5 times the speed of the wind. Where there is a difference in motion, then there is energy to be extracted at the interface, the sailboat does this by placing the sail in the air and the hull in the water
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High-performance sailing
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High-performance watercraft that can exceed the velocity of the true wind include catamarans and foiling vessels. Ice boats and land-sailing craft are able to do so. There are also rotor-driven craft, such as the yacht, Blackbird. In 2013, a new class of catamaran was announced for the Americas Cup which can achieve well in excess of double the speed of the wind. The catamarans used for the 2013 Americas Cup were expected to sail upwind at 1.2 times the speed of the true wind and they proved to be faster, averaging about 1.8 times the speed of the wind with peaks slightly over 2.0. The Extreme 40 catamaran can sail at 35 knots in 20–25-knot winds, the high-performance International C-Class Catamaran can sail at twice the speed of the wind. In 2009, the speed sailing record on water was set by a hydrofoil trimaran sailing at 1.71 times the speed of the wind. In late 2012 the Vestas Sailrocket 2 skippered by Paul Larsen achieved a new world speed record of 65.45 knots on water. Iceboats can typically sail at five times the speed of the wind, by sailing downwind at 135° off the wind, a sand yacht can sail much faster than the wind. The velocity made good downwind is often twice as fast compared to the same land yacht sailing directly downwind. For example, assuming that surface resistance is negligible, if a boat sails at 90° to the true wind and that is, if the wind speed is V, then the boats speed is also V. The table below shows the values of this function, as a multiple of windspeed, the actual speed of a sailing vessel depends on the wind speed, how close to the wind it is sailing, the resistance of the surface, and leeway. The points of sail at which sailing craft can achieve highest speeds span between a reach and a broad reach. Normal cruising boats yachts can sail at about 45° off the apparent wind, High performance racing yachts at about 27°. High-performance multihulls can sail at 20° off the apparent wind, iceboats can sail even closer to the apparent wind. According to the data provided on p.406 of the cited book High Performance Sailing, a fast keelboat such as a Soling can sail at 30° off the apparent wind, an 18ft Skiff at 20°, and an iceboat at 7°. For example, a boat can sail a course that is perpendicular to the true wind, as it accelerates, the wind as seen from the boat increases and the wind appears to shift forward. This is the effect that causes rain to appear to fall at an angle when seen from a moving car
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Nautical terminology
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This is a partial glossary of nautical terms, some remain current, while many date from the 17th to 19th centuries. See also Wiktionarys nautical terms, Category, Nautical terms, See the Further reading section for additional words and references. A & AS Alterations and additions to the structure, rigging, abaft Toward the stern, relative to some object. Abaft the beam Further aft than the beam, a bearing of greater than 90 degrees from the bow. That would describe an object lying 22.5 degrees toward the rear of the ship, as measured clockwise from a line from the right side, center, of the ship. An imperative to leave the vessel immediately, usually in the face of some imminent overwhelming danger and it is an order issued by the Master or a delegated person in command. Abeam On the beam, a bearing at right angles to the ships keel. A merchant seaman qualified to perform all duties, or a junior rank in some navies. Aboard On or in a vessel, about To go about is to change the course of a ship by tacking. Ready about, or boutship, is the order to prepare for tacking, above board On or above the deck, in plain view, not hiding anything. Pirates would secret their crews below decks, thereby creating the impression that an encounter with another ship was a casual matter of chance. Above-water hull The hull section of a vessel above the waterline, absentee pennant Special pennant flown to indicate absence of commanding officer, admiral, his chief of staff, or officer whose flag is flying. Absolute bearing The bearing of an object in relation to north, either true bearing, using the geographical or true north, or magnetic bearing, using magnetic north. See also bearing and relative bearing, accommodation ladder A portable flight of steps down a ships side. Accommodation ship A ship or hulk used as housing, generally there is a lack of quarters available ashore. An operational ship can be used, but more commonly a hulk modified for accommodation is used, Act of Pardon or Act of Grace A letter from a state or power authorising action by a privateer. Admiral Senior naval officer of Flag rank, in ascending order of seniority, Rear Admiral, Vice Admiral, Admiral and Admiral of the Fleet. A high naval authority in charge of a states Navy or a territorial component
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Knot (unit)
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The knot is a unit of speed equal to one nautical mile per hour, approximately 1.151 mph. The ISO Standard symbol for the knot is kn, the same symbol is preferred by the IEEE, kt is also common. The knot is a unit that is accepted for use with the SI. Etymologically, the term derives from counting the number of knots in the line that unspooled from the reel of a log in a specific time. 1 international knot =1 nautical mile per hour,1.852 kilometres per hour,0.514 metres per second,1.151 miles per hour,20.254 inches per second,1852 m is the length of the internationally agreed nautical mile. The US adopted the definition in 1954, having previously used the US nautical mile. The UK adopted the international nautical mile definition in 1970, having used the UK Admiralty nautical mile. The speeds of vessels relative to the fluids in which they travel are measured in knots, for consistency, the speeds of navigational fluids are also measured in knots. Thus, speed over the ground and rate of progress towards a distant point are given in knots. Until the mid-19th century, vessel speed at sea was measured using a chip log, the chip log was cast over the stern of the moving vessel and the line allowed to pay out. Knots placed at a distance of 8 fathoms -47 feet 3 inches from each other, passed through a sailors fingers, the knot count would be reported and used in the sailing masters dead reckoning and navigation. This method gives a value for the knot of 20.25 in/s, the difference from the modern definition is less than 0. 02%. On a chart of the North Atlantic, the scale varies by a factor of two from Florida to Greenland, a single graphic scale, of the sort on many maps, would therefore be useless on such a chart. Recent British Admiralty charts have a latitude scale down the middle to make this even easier, speed is sometimes incorrectly expressed as knots per hour, which is in fact a measure of acceleration. Prior to 1969, airworthiness standards for aircraft in the United States Federal Aviation Regulations specified that distances were to be in statute miles. In 1969, these standards were amended to specify that distances were to be in nautical miles. At 11000 m, an airspeed of 300 kn may correspond to a true airspeed of 500 kn in standard conditions. Beaufort scale Hull speed, which deals with theoretical estimates of maximum speed of displacement hulls Knot count Knotted cord Metre per second Orders of magnitude Rope Kemp
37.
Degree (angle)
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A degree, usually denoted by °, is a measurement of a plane angle, defined so that a full rotation is 360 degrees. It is not an SI unit, as the SI unit of measure is the radian. Because a full rotation equals 2π radians, one degree is equivalent to π/180 radians, the original motivation for choosing the degree as a unit of rotations and angles is unknown. One theory states that it is related to the fact that 360 is approximately the number of days in a year. Ancient astronomers noticed that the sun, which follows through the path over the course of the year. Some ancient calendars, such as the Persian calendar, used 360 days for a year, the use of a calendar with 360 days may be related to the use of sexagesimal numbers. The earliest trigonometry, used by the Babylonian astronomers and their Greek successors, was based on chords of a circle, a chord of length equal to the radius made a natural base quantity. One sixtieth of this, using their standard sexagesimal divisions, was a degree, Aristarchus of Samos and Hipparchus seem to have been among the first Greek scientists to exploit Babylonian astronomical knowledge and techniques systematically. Timocharis, Aristarchus, Aristillus, Archimedes, and Hipparchus were the first Greeks known to divide the circle in 360 degrees of 60 arc minutes, eratosthenes used a simpler sexagesimal system dividing a circle into 60 parts. Furthermore, it is divisible by every number from 1 to 10 except 7 and this property has many useful applications, such as dividing the world into 24 time zones, each of which is nominally 15° of longitude, to correlate with the established 24-hour day convention. Finally, it may be the case more than one of these factors has come into play. For many practical purposes, a degree is a small enough angle that whole degrees provide sufficient precision. When this is not the case, as in astronomy or for geographic coordinates, degree measurements may be written using decimal degrees, with the symbol behind the decimals. Alternatively, the sexagesimal unit subdivisions can be used. One degree is divided into 60 minutes, and one minute into 60 seconds, use of degrees-minutes-seconds is also called DMS notation. These subdivisions, also called the arcminute and arcsecond, are represented by a single and double prime. For example,40. 1875° = 40° 11′ 15″, or, using quotation mark characters, additional precision can be provided using decimals for the arcseconds component. The older system of thirds, fourths, etc. which continues the sexagesimal unit subdivision, was used by al-Kashi and other ancient astronomers, but is rarely used today
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Torque
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Torque, moment, or moment of force is rotational force. Just as a force is a push or a pull. Loosely speaking, torque is a measure of the force on an object such as a bolt or a flywheel. For example, pushing or pulling the handle of a wrench connected to a nut or bolt produces a torque that loosens or tightens the nut or bolt, the symbol for torque is typically τ, the lowercase Greek letter tau. When it is called moment of force, it is denoted by M. The SI unit for torque is the newton metre, for more on the units of torque, see Units. This article follows US physics terminology in its use of the word torque, in the UK and in US mechanical engineering, this is called moment of force, usually shortened to moment. In US physics and UK physics terminology these terms are interchangeable, unlike in US mechanical engineering, Torque is defined mathematically as the rate of change of angular momentum of an object. The definition of states that one or both of the angular velocity or the moment of inertia of an object are changing. Moment is the term used for the tendency of one or more applied forces to rotate an object about an axis. For example, a force applied to a shaft causing acceleration, such as a drill bit accelerating from rest. By contrast, a force on a beam produces a moment, but since the angular momentum of the beam is not changing. Similarly with any force couple on an object that has no change to its angular momentum and this article follows the US physics terminology by calling all moments by the term torque, whether or not they cause the angular momentum of an object to change. The concept of torque, also called moment or couple, originated with the studies of Archimedes on levers, the term torque was apparently introduced into English scientific literature by James Thomson, the brother of Lord Kelvin, in 1884. A force applied at an angle to a lever multiplied by its distance from the levers fulcrum is its torque. A force of three newtons applied two metres from the fulcrum, for example, exerts the same torque as a force of one newton applied six metres from the fulcrum. More generally, the torque on a particle can be defined as the product, τ = r × F, where r is the particles position vector relative to the fulcrum. Alternatively, τ = r F ⊥, where F⊥ is the amount of force directed perpendicularly to the position of the particle, any force directed parallel to the particles position vector does not produce a torque
39.
Friction
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Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction, Dry friction resists relative lateral motion of two surfaces in contact. Dry friction is subdivided into static friction between non-moving surfaces, and kinetic friction between moving surfaces, fluid friction describes the friction between layers of a viscous fluid that are moving relative to each other. Lubricated friction is a case of fluid friction where a lubricant fluid separates two solid surfaces, skin friction is a component of drag, the force resisting the motion of a fluid across the surface of a body. Internal friction is the force resisting motion between the making up a solid material while it undergoes deformation. When surfaces in contact move relative to other, the friction between the two surfaces converts kinetic energy into thermal energy. This property can have consequences, as illustrated by the use of friction created by rubbing pieces of wood together to start a fire. Kinetic energy is converted to thermal energy whenever motion with friction occurs, another important consequence of many types of friction can be wear, which may lead to performance degradation and/or damage to components. Friction is a component of the science of tribology, Friction is not itself a fundamental force. Dry friction arises from a combination of adhesion, surface roughness, surface deformation. The complexity of interactions makes the calculation of friction from first principles impractical and necessitates the use of empirical methods for analysis. Friction is a non-conservative force - work done against friction is path dependent, in the presence of friction, some energy is always lost in the form of heat. Thus mechanical energy is not conserved, the Greeks, including Aristotle, Vitruvius, and Pliny the Elder, were interested in the cause and mitigation of friction. They were aware of differences between static and kinetic friction with Themistius stating in 350 A. D. that it is easier to further the motion of a moving body than to move a body at rest. The classic laws of sliding friction were discovered by Leonardo da Vinci in 1493, a pioneer in tribology and these laws were rediscovered by Guillaume Amontons in 1699. Amontons presented the nature of friction in terms of surface irregularities, the understanding of friction was further developed by Charles-Augustin de Coulomb. Coulomb further considered the influence of sliding velocity, temperature and humidity, the distinction between static and dynamic friction is made in Coulombs friction law, although this distinction was already drawn by Johann Andreas von Segner in 1758. Leslie was equally skeptical about the role of adhesion proposed by Desaguliers, in Leslies view, friction should be seen as a time-dependent process of flattening, pressing down asperities, which creates new obstacles in what were cavities before
40.
Sail plan
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A sail plan is a set of drawings, usually prepared by a naval architect which shows the various combinations of sail proposed for a sailing ship. Alternatively, as a term of art, it refers to the way such vessels are rigged as discussed below, the combinations shown in a sail plan almost always include three configurations, A light air sail plan. Over most of the Earth, most of the time, the force is Force 1 or less. Thus a sail plan should include a set of huge, lightweight sails that will keep the ship underway in light breezes and this is the set of sails that are changed rapidly in variable conditions. They are much stronger than the light air sails, but still lightweight, an economical sail in this set will include several sets of reefing ties, so the area of the sail can be reduced in a stronger wind. This is the set of small, very rugged sails flown in a gale, to keep the vessel under way. In all sail plans, the attempts to balance the force of the sails against the drag of the underwater keel in such a way that the vessel naturally points into the wind. In this way, if control is lost, the vessel will avoid broaching, broaching always causes uncomfortable motion, and in a storm, the breaking waves can destroy a lightly built boat. The architect also tries to balance the force on each sail plan against a range of loads. The calculation assures that the sail will not knock the vessel sideways with its mast in the water, capsizing, fore-and-aft rig features flat sails that run fore and aft. These types of sails are the easiest to manage, because they often do not need to be relaid when the ship changes course, Bermuda rig is a type of fore-and-aft rig with a triangular mainsail. Gaff rig features fore-and-aft sails shaped like a triangle minus its point, the top of the sail tends to twist away from the wind reducing its efficiency when close-hauled. However, due to the gaff on the top edge of the sail the centre of effort is typically lower, square rig features sails set square to the mast from a yard, a spar running transversely in relation to the hull. In ships built using designs of the square rig, sailors would have to climb the rigging. In a modern square rigged design the crew can furl and unfurl sails by remote control from the deck, lateen rig features a triangular sail set on a long yard, mounted at an angle on the mast and running in a fore-and-aft direction. This is one of the lowest drag sails, each form of rig requires its own type of sails. Among them are, A staysail is a piece of cloth that has one or two attached to a stay, that is, one of the ropes or wires that helps hold the mast in place. A staysail was classically attached to the stay with wooden or steel hoops, sailors would test the hoops by climbing on them
41.
Camber (aerodynamics)
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In aeronautics and aeronautical engineering, camber is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetrical aerofoil, the benefits of camber, in contrast to symmetrical aerofoils, were discovered and first utilized by Sir George Cayley in the early 19th century. Camber is usually designed into an aerofoil to increase the lift coefficient. This minimizes the speed of aircraft using the aerofoil. Aircraft with wings based on cambered aerofoils usually have lower stalling speeds than similar aircraft with wings based on symmetric aerofoils, an aircraft designer may also reduce the camber of the outboard section of the wings to increase the critical angle of attack at the wing tips. Some recent designs use negative camber, one such design is called the supercritical aerofoil. It is used for flight, and produces a higher lift to drag ratio at near supersonic flight than traditional aerofoils. Supercritical aerofoils employ a flattened surface, highly cambered aft section. These changes delay the onset of wave drag, the camber of an aerofoil can be defined by a camber line, which is the curve that is halfway between the upper and lower surfaces of the aerofoil. To fully define an aerofoil we also need a thickness function T, such an aerofoil is useful in certain situations, such as with tailless aircraft, because the moment about the aerodynamic center of the aerofoil can be 0. A camber line for such an aerofoil can be defined as follows, the thickness distribution for a NACA 4-series aerofoil was used, with a 12% thickness ratio. The equation for this distribution is, T ¯ = t 0.2 Where t is the thickness ratio. Chord NACA airfoil Aerodynamic drag Zero lift axis Sources Desktop Aerodynamics Digital Textbook, theory of Wing Sections, Ira H. Abbott and Albert E. Von Doenhoff ISBN 0-486-60586-8
42.
Translation (geometry)
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In Euclidean geometry, a translation is a geometric transformation that moves every point of a figure or a space by the same amount in a given direction. In Euclidean geometry a transformation is a correspondence between two sets of points or a mapping from one plane to another. )A translation can be described as a rigid motion. A translation can also be interpreted as the addition of a constant vector to every point, a translation operator is an operator T δ such that T δ f = f. If v is a vector, then the translation Tv will work as Tv. If T is a translation, then the image of a subset A under the function T is the translate of A by T, the translate of A by Tv is often written A + v. In a Euclidean space, any translation is an isometry, the set of all translations forms the translation group T, which is isomorphic to the space itself, and a normal subgroup of Euclidean group E. The quotient group of E by T is isomorphic to the orthogonal group O, E / T ≅ O, a translation is an affine transformation with no fixed points. Matrix multiplications always have the origin as a fixed point, similarly, the product of translation matrices is given by adding the vectors, T u T v = T u + v. Because addition of vectors is commutative, multiplication of matrices is therefore also commutative. In physics, translation is movement that changes the position of an object, for example, according to Whittaker, A translation is the operation changing the positions of all points of an object according to the formula → where is the same vector for each point of the object. When considering spacetime, a change of time coordinate is considered to be a translation, for example, the Galilean group and the Poincaré group include translations with respect to time
43.
Rolling resistance
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Rolling resistance, sometimes called rolling friction or rolling drag, is the force resisting the motion when a body rolls on a surface. It is mainly caused by non-elastic effects, that is, not all the energy needed for deformation of the wheel, roadbed, two forms of this are hysteresis losses, and permanent deformation of the object or the surface. Another cause of rolling resistance lies in the slippage between the wheel and the surface, which dissipates energy, note that only the last of these effects involves friction, therefore the name rolling friction is to an extent a misnomer. In analogy with sliding friction, rolling resistance is often expressed as a coefficient times the normal force and this coefficient of rolling resistance is generally much smaller than the coefficient of sliding friction. Factors that contribute to rolling resistance are the deformation of the wheels, the deformation of the roadbed surface, additional contributing factors include wheel diameter, speed, load on wheel, surface adhesion, sliding, and relative micro-sliding between the surfaces of contact. The losses due to also depend strongly on the material properties of the wheel or tire. For example, a tire will have higher rolling resistance on a paved road than a steel railroad wheel on a steel rail. Also, sand on the ground will give more rolling resistance than concrete, the primary cause of pneumatic tire rolling resistance is hysteresis, A characteristic of a deformable material such that the energy of deformation is greater than the energy of recovery. The rubber compound in a tire exhibits hysteresis, as the tire rotates under the weight of the vehicle, it experiences repeated cycles of deformation and recovery, and it dissipates the hysteresis energy loss as heat. Hysteresis is the cause of energy loss associated with rolling resistance and is attributed to the viscoelastic characteristics of the rubber. -- National Academy of Sciences This main principle is illustrated in the figure of the rolling cylinders, if two equal cylinders are pressed together then the contact surface is flat. In the absence of friction, contact stresses are normal to the contact surface. Consider a particle that enters the area at the right side, travels through the contact patch. Initially its vertical deformation is increasing, which is resisted by the hysteresis effect, therefore, an additional pressure is generated to avoid interpenetration of the two surfaces. Later its vertical deformation is decreasing and this is again resisted by the hysteresis effect. In this case this decreases the pressure that is needed to keep the two bodies separate, the resulting pressure distribution is asymmetrical and is shifted to the right. The line of action of the vertical force no longer passes through the centers of the cylinders and this means that a moment occurs that tends to retard the rolling motion. Low rolling resistance tires typically incorporate silica in place of black in their tread compounds to reduce low-frequency hysteresis without compromising traction
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Keel
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On boats and ships, keel can refer to either of two parts, a structural element that sometimes resembles a fin and protrudes below a boat along the central line, or a hydrodynamic element. As the laying down of the keel is the step in the construction of a ship, in British. Only the ships launching is considered significant in its creation. The word can also be used as a synecdoche to refer to a complete boat, a structural keel is the bottom-most structural member around which the hull of a ship is built. The keel runs along the centerline of the ship, from the bow to the stern. The keel is often the first part of a hull to be constructed. The most common type of keel is the plate keel. A form of keel found on smaller vessels is the bar keel, which may be fitted in trawlers, tugs, and smaller ferries. Where grounding is possible, this type of keel is suitable with its massive scantlings, if a double bottom is fitted, the keel is almost inevitably of the flat plate type, bar keels often being associated with open floors, where the plate keel may also be fitted. Duct keels are provided in the bottom of some vessels and these run from the forward engine room bulkhead to the collision bulkhead and are utilized to carry the double bottom piping. The piping is then accessible when cargo is loaded, the keel surface on the bottom of the hull gives the ship greater directional control and stability. In non-sailing hulls, the helps the hull to move forward. In traditional boat building, this is provided by the structural keel, in modern construction, the bar keel or flat-plate keel performs the same function. There are many types of fixed keels, including full keels, long keels, fin keels, winged keels, bulb keels, the rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion. A secondary purpose of the keel is to provide ballast, keels are different from centreboards and other types of foils in that keels are made of heavy materials to provide ballast to stabilize the boat. Keels may be fixed, or non-movable, or they may retract to allow sailing in shallower waters, retracting keels may pivot or slide upwards to retract, and are usually retracted with a winch due to the weight of the ballast. Since the keel provides far more stability when lowered than when retracted, types of non-fixed keels include swing keels and canting keels. Canting keels can be found on racing yachts, such as competing in the Volvo Ocean Race
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