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109-441: A sail provides propulsive force via a combination of lift and drag, depending on its angle of attack , its angle with respect to the apparent wind . Apparent wind is the air velocity experienced on the moving craft and is the combined effect of the true wind velocity with the velocity of the sailing craft. Angle of attack is often constrained by the sailing craft's orientation to the wind or point of sail . On points of sail where it

218-422: A fixed-wing aircraft and the vector representing the relative motion between the aircraft and the atmosphere. 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 chord line of the root of the wing is chosen as the reference line. Another choice is to use a horizontal line on the fuselage as the reference line (and also as

327-413: A sheet . In use, they may be designed to be curved in both directions along their surface, often as a result of their curved edges. Battens may be used to extend the trailing edge of a sail beyond the line of its attachment points. Other non-rotating airfoils that power sailing craft include wingsails , which are rigid wing-like structures, and kites that power kite-rigged vessels , but do not employ

436-433: A Turkish officer, Selim Bimbashi, were made between 1839 and 1842, and two got to the point about 30 kilometres (20 miles) beyond the present port of Juba , where the country rises and rapids make navigation very difficult. Lake Victoria was first sighted by Europeans in 1858 when British explorer John Hanning Speke reached its southern shore while traveling with Richard Francis Burton to explore central Africa and locate

545-767: A distance of 20 days' journey till it reaches the nearest Ethiopians." Modern exploration of the Nile basin began with the conquest of the northern and central Sudan by the Ottoman viceroy of Egypt, Muhammad Ali , and his sons from 1821 onward. As a result of this, the Blue Nile was known as far as its exit from the Ethiopian foothills and the White Nile as far as the mouth of the Sobat River. Three expeditions under

654-468: A factor of 15 at Aswan. Peak flows of over 8,212 m /s (290,000 cu ft/s) occurred during late August and early September, and minimum flows of about 552 m /s (19,500 cu ft/s) occurred during late April and early May. The Bahr al Ghazal and the Sobat River are the two most important tributaries of the White Nile in terms of discharge. The Bahr al Ghazal's drainage basin

763-404: A lateral force, resisted by the underwater foils, ice runners, or wheels of the sailing craft. 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. For a given true wind velocity over

872-705: A limited sense to describe the section between Lake No and Khartoum. At Khartoum, the river is joined by the Blue Nile . The White Nile starts in equatorial East Africa, and the Blue Nile begins in Ethiopia. Both branches are on the western flanks of the East African Rift . The source of the Blue Nile is Lake Tana in the Gish Abay region in the Ethiopian Highlands . The source of

981-412: A line or a hook may pass, as on Bermuda mainsails. Fore-and-aft sails may have tell-tales —pieces of yarn, thread or tape that are affixed to sails—to help visualize airflow over their surfaces. The lines that attach to and control sails are part of the running rigging and differ between square and fore-and-aft rigs. Some rigs shift from one side of the mast to the other, e.g. the dipping lug sail and

1090-430: A lower, flatter curve with a higher critical angle. The critical angle of attack is the angle of attack which produces the maximum lift coefficient. This is also called the " stall angle of attack". Below the critical angle of attack, as the angle of attack decreases, the lift coefficient decreases. Conversely, above the critical angle of attack, as the angle of attack increases, the air begins to flow less smoothly over

1199-438: 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 on horizontal spars , which are perpendicular or square , to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the lifts , are called the yardarms . A ship mainly so rigged

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1308-470: A maximum angle of attack is reached, regardless of pilot input. This is called the 'angle of attack limiter' or 'alpha limiter'. Modern airliners that have fly-by-wire technology avoid the critical angle of attack by means of software in the computer systems that govern the flight control surfaces. In takeoff and landing operations from short runways ( STOL ), such as Naval Aircraft Carrier operations and STOL backcountry flying, aircraft may be equipped with

1417-596: A peak flow of over 680 m /s (24,000 cu ft/s) in October. During the dry season (January to June) the White Nile contributes between 70% and 90% of the total discharge from the Nile. Below Renk , the White Nile enters Sudan, it flows north to Khartoum and meets the Blue Nile. The course of the Nile in Sudan is distinctive. It flows over six groups of cataracts , from the sixth at Sabaloka just north of Khartoum northward to Abu Hamad . The tectonic uplift of

1526-525: A place described as the source of the Rukarara tributary, and by hacking a path up steep jungle-choked mountain slopes in the Nyungwe Forest found (in the dry season ) an appreciable incoming surface flow for many kilometres upstream, and found a new source, giving the Nile a length of 6,758 km (4,199 mi). The White Nile leaves Lake Victoria at Ripon Falls near Jinja, Uganda , as

1635-414: A reduction in the rate of increase of the lift coefficient. The figure shows a typical curve for a cambered straight wing. Cambered airfoils are curved such that they generate some lift at small negative angles of attack. 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

1744-400: A sail going downwind is predominated by drag forces. Sails are unable to generate propulsive force if they are aligned too closely to the wind. Sails may be attached to a mast , boom or other spar or may be attached to a wire that is suspended by a mast. They are typically raised by a line, called a halyard , and their angle with respect to the wind is usually controlled by a line, called

1853-420: A sail is defined by its edges and corners in the plane of the sail, laid out on a flat surface. The edges may be curved, either to extend the sail's shape as an airfoil or to define its shape in use. In use, the sail becomes a curved shape, adding the dimension of depth or draft . Sail characteristics derive, in part, from the design, construction and the attributes of the fibers, which are woven together to make

1962-467: A sail to reinforce it, or to fix the sail into a groove in the boom, in the mast, or in the luff foil of a roller-furling jib. They may have stiffening features, called battens , that help shape the sail, when full length, or just the roach, when present. They may have a variety of means of reefing them (reducing sail area), including rows of short lines affixed to the sail to wrap up unused sail, as on square and gaff rigs, or simply grommets through which

2071-579: A shape that does not lie flat. Conventional sail panels are sewn together. Sails are tensile structures, so the role of a seam is to transmit a tensile load from panel to panel. For a sewn textile sail this is done through thread and is limited by the strength of the thread and the strength of the hole in the textile through which it passes. Sail seams are often overlapped between panels and sewn with zig-zag stitches that create many connections per unit of seam length. Whereas textiles are typically sewn together, other sail materials may be ultrasonically welded ,

2180-399: A technique whereby high frequency ultrasonic acoustic vibrations are locally applied to workpieces being held together under pressure to create a solid state weld . It is commonly used for plastics , and especially for joining dissimilar materials . Sails feature reinforcements of fabric layers where lines attach at grommets or cringles . A bolt rope may be sewn onto the edges of

2289-465: Is an archaeological site located in alluvial deposits formed by an ancient channel of the Nile in the Affad region of southern Dongola Reach , Sudan. There are two theories about the age of the integrated Nile. One is that the integrated drainage of the Nile is of young age and that the Nile basin was formerly broken into series of separate basins, only the most northerly of which fed a river following

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2398-656: Is called an-Nīl . In Biblical Hebrew , it is הַיְאוֹר ‎, Ha-Ye'or or הַשִׁיחוֹר ‎, Ha-Shiḥor . The English name Nile and the Arabic names en-Nîl and an-Nîl both derive from the Latin Nilus and the Ancient Greek Νεῖλος . Beyond that, however, the etymology is disputed. Homer called the river Αἴγυπτος , Aiguptos , but in subsequent periods, Greek authors referred to its lower course as Neilos ; this term became generalized for

2507-409: Is called a square-rigger . A fore-and-aft rig consists of sails that are set along the line of the keel rather than perpendicular to it. Vessels so rigged are described as fore-and-aft rigged . The invention of the sail was a technological advance of equal or even greater importance than the invention of the wheel. It has been suggested by some that it has the significance of the development of

2616-696: Is known as the Bahr al Jabal ("Mountain River" ). Just south of the town is the confluence with the Achwa River . The Bahr al Ghazal , 716 kilometers (445 mi) long, joins the Bahr al Jabal at a small lagoon called Lake No , after which the Nile becomes known as the Bahr al Abyad , or the White Nile, from the whitish clay suspended in its waters. When the Nile floods it leaves a rich silty deposit which fertilizes

2725-456: Is only indirectly related to stall behavior. Some military aircraft are able to achieve controlled flight at very high angles of attack, but at the cost of massive induced drag . This provides the aircraft with great agility. A famous example is Pugachev's Cobra . Although the aircraft experiences high angles of attack throughout the maneuver, the aircraft is not capable of either aerodynamic directional control or maintaining level flight until

2834-453: Is possible to align the leading edge of the sail with the apparent wind, the sail may act as an airfoil , generating propulsive force as air passes along its surface, just as an airplane wing generates lift , which predominates over aerodynamic drag retarding forward motion. The more that the angle of attack diverges from the apparent wind as a sailing craft turns downwind, the more drag increases and lift decreases as propulsive forces, until

2943-572: Is the largest of any of the Nile's sub-basins, measuring 520,000 square kilometers (200,000 sq mi) in size, but it contributes a relatively small amount of water, about 2 m /s (71 cu ft/s) annually, because tremendous volumes of water are lost in the Sudd wetlands. The Sobat River, which joins the Nile a short distance below Lake No, drains about half as much land, 225,000 km (86,900 sq mi), but contributes 412 cubic meters per second (14,500 cu ft/s) annually to

3052-417: Is usually a "flow through" structure) and a number of intervisible islands create both an invitation to travel and an environment where advanced navigation techniques are not needed. Alongside this, the Nile has a northward flowing current with a prevailing wind in the opposite direction, so giving the potential to drift in one direction and sail in the other. Many do not consider sails to have been used before

3161-659: The Murchison Falls until it reaches the northern shores of Lake Albert where it forms a significant river delta. Lake Albert is on the border of the Democratic Republic of the Congo, but the Nile is not a border river at this point. After leaving Lake Albert, the river continues north through Uganda and is known as the Albert Nile . The White Nile flows into South Sudan just south of Nimule , where it

3270-680: The Nubian Swell diverts the river south-west for over 300 km, following the structure of the Central African Shear Zone embracing the Bayuda Desert . At Al Dabbah it resumes its northward course towards the first cataract at Aswan forming the S-shaped Great Bend of the Nile mentioned by Eratosthenes . In the north of Sudan, the river enters Lake Nasser (known in Sudan as Lake Nubia),

3379-651: The Paleogene and Neogene Periods (66 million to 2.588 million years ago) a series of separate closed continental basins each occupied one of the major parts of the Sudanese Rift System: Mellut rift , White Nile rift , Blue Nile rift , Atbara rift and Sag El Naam rift . The Mellut Basin is nearly 12 kilometers (7.5 mi) deep at its central part. This rift is possibly still active, with reported tectonic activity in its northern and southern boundaries. The Sudd swamp which forms

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3488-512: The Rhône and Po , one of the three Mediterranean rivers with the largest water discharge . The standard English names "White Nile" and "Blue Nile" refer to the river's source, derived from Arabic names formerly applied to only the Sudanese stretches that meet at Khartoum . In the ancient Egyptian language , the Nile is called Ḥꜥpy (Hapy) or Jtrw (Iteru), meaning "river". In Coptic ,

3597-471: The Sudd region. More than half of the Nile's water is lost in this swamp to evaporation and transpiration . The average flow rate of the White Nile at the tails of the swamps is about 510 m /s (18,000 cu ft/s). From here it meets with the Sobat River at Malakal . On an annual basis, the White Nile upstream of Malakal contributes about 15% of the total outflow of the Nile. The average flow of

3706-572: The caravel in Northern European waters from about 1440 made lateen sails familiar in this part of the world. Additionally, lateen sails were used for the mizzen on early three-masted ships, playing a significant role in the development of the full-rigged ship . It did not, however, provide much of the propulsive force of these vessels – rather serving as a balancing sail that was needed for some manoeuvres in some sea and wind conditions. The extensive amount of contemporary maritime art showing

3815-423: The linear mass density of fibers). Cross-cut sails have the panels sewn parallel to one another, often parallel to the foot of the sail, and are the least expensive of the two sail constructions. Triangular cross-cut sail panels are designed to meet the mast and stay at an angle from either the warp or the weft (on the bias ) to allow stretching along the luff, but minimize stretching on the luff and foot, where

3924-638: The longest river in the world , though this has been contested by research suggesting that the Amazon River is slightly longer. Of the world's major rivers, the Nile is one of the smallest, as measured by annual flow in cubic metres of water. About 6,650 km (4,130 mi) long, its drainage basin covers eleven countries: the Democratic Republic of the Congo , Tanzania , Burundi , Rwanda , Uganda , Kenya , Ethiopia , Eritrea , South Sudan , Sudan , and Egypt . In particular,

4033-400: 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 body's 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. In aerodynamics , angle of attack specifies the angle between the chord line of the wing of

4142-428: The "Victoria Nile." It flows north for some 130 kilometers (81 mi) to Lake Kyoga . The last part of the approximately 200 kilometers (120 mi) river section starts from the western shores of the lake and flows at first to the west until just south of Masindi Port , where the river turns north, then makes a great half circle to the east and north to Karuma Falls . For the remaining part, it flows westerly through

4251-501: The 11th into the 19th centuries. Materials used in sails, as of the 21st century, include nylon for spinnakers, where light weight and elastic resistance to shock load are valued and a range of fibers, used for triangular sails, that includes Dacron , aramid fibers including Kevlar , and other liquid crystal polymer fibers including Vectran . Woven materials, like Dacron, may specified as either high or low tenacity , as indicated, in part by their denier count (a unit of measure for

4360-612: The 5th millennium BCE. Others consider sails to have been invented much earlier. Archaeological studies of the Cucuteni-Trypillian culture ceramics show use of sailing boats from the sixth millennium BCE onwards. Excavations of the Ubaid period (c. 6000–4300 BCE) in Mesopotamia provide direct evidence of sailing boats. Sails from ancient Egypt are depicted around 3200 BCE, where reed boats sailed upstream against

4469-414: The Ethiopian rainy season when rainfall is especially high in the Ethiopian Highlands ; the rest of the year, the great rivers draining Ethiopia into the Nile have a weaker flow. In harsh and arid seasons and droughts, the Blue Nile dries out completely. The flow of the Blue Nile varies considerably over its yearly cycle and is the main contribution to the large natural variation of the Nile flow. During

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4578-630: The Ethiopian Highlands, satellite imagery was used to identify dry watercourses in the desert to the west of the Nile. A canyon, now filled by surface drift, represents the Eonile that flowed during 23–5.3 million years before present. The Eonile transported clastic sediments to the Mediterranean; several natural gas fields have been discovered within these sediments. During the late- Miocene Messinian salinity crisis , when

4687-491: The Ethiopian Highlands. The Blue Nile flows about 1,400 kilometres to Khartoum, where the Blue Nile and White Nile join to form the Nile. Ninety percent of the water and ninety-six percent of the transported sediment carried by the Nile come from the Atbarah and Blue Nile, both of which originate in Ethiopia, with fifty-nine percent of the water coming from the Blue Nile. The erosion and transportation of silt only occurs during

4796-482: The Mediterranean Sea was a closed basin and evaporated to the point of being empty or nearly so, the Nile cut its course down to the new base level until it was several hundred metres below world ocean level at Aswan and 2,400 m (7,900 ft) below Cairo. This created a very long and deep canyon which was filled with sediment after the Mediterranean was recreated. At some point the sediments raised

4905-581: The Middle East and Africa, and described being told of the source of the Nile in Abyssinia (Ethiopia). Later in the 15th and 16th centuries, travelers to Ethiopia visited Lake Tana and the source of the Blue Nile in the mountains south of the lake. Supposedly, Paolo Trevisani ( c.  1452 –1483), a Venetian traveller in Ethiopia, wrote a journal of his travels to the origin of the Nile that has since been lost. Although James Bruce claimed to be

5014-522: The Nile carries little water (5% of that of the Congo River , for example). The Nile basin is complex, and because of this, the discharge at any given point along the main stem depends on many factors including weather, diversions, evaporation and evapotranspiration , and groundwater flow. Upstream from Khartoum (to the south), the river is known as the White Nile , a term also used in

5123-399: The Nile is the primary water source of Egypt, Sudan and South Sudan. The Nile is an important economic driver supporting agriculture and fishing. The Nile has two major tributaries : the White Nile and the Blue Nile . The White Nile is traditionally considered to be the headwaters stream. However, the Blue Nile is the source of most of the water of the Nile downstream, containing 80% of

5232-676: The Nile near the southern point of the Great Bend. The Nile has been the lifeline of civilization in Egypt since the Stone Age , with most of the population and all of the cities of Egypt developing along those parts of the Nile valley lying north of Aswan. However, the Nile used to run much more westerly through what is now Wadi Hamim and Wadi al Maqar in Libya and flow into the Gulf of Sidra . As

5341-526: The Nile since ancient times. A tune, Hymn to the Nile , was created and sung by the ancient Egyptian peoples about the flooding of the Nile River and all of the miracles it brought to Ancient Egyptian civilization. Water buffalo were introduced from Asia, and the Assyrians introduced camels in the 7th century BCE. These animals were raised for meat and were domesticated and used for ploughing—or in

5450-647: The Nile. When in flood the Sobat carries a large amount of sediment, adding greatly to the White Nile's color. The Yellow Nile is a former tributary that connected the Ouaddaï highlands of eastern Chad to the Nile River Valley c.  8000 to c.  1000 BCE . Its remains are known as the Wadi Howar . The wadi passes through Gharb Darfur near the northern border with Chad and meets up with

5559-585: The River Nile 's current. Ancient Sumerians used square rigged sailing boats at about the same time, and it is believed they established sea trading routes as far away as the Indus valley . Greeks and Phoenicians began trading by ship by around 1200 BCE. V-shaped square rigs with two spars that come together at the hull were the ancestral sailing rig of the Austronesian peoples before they developed

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5668-554: The Sudd wetlands of South Sudan, the upper reaches of the White Nile remained largely unknown to the ancient Greeks and Romans. Vitruvius thought that source of the Nile was in Mauritania, on the "other" (south) side of the Atlas Mountains . Various expeditions failed to determine the river's source. Agatharchides records that in the time of Ptolemy II Philadelphus , a military expedition had penetrated far enough along

5777-545: The White Nile at Lake Kawaki Malakal, just below the Sobat River, is 924 m /s (32,600 cu ft/s); the peak flow is approximately 1,218 m /s (43,000 cu ft/s) in October and minimum flow is about 609 m /s (21,500 cu ft/s) in April. This fluctuation is caused by the substantial variation in the flow of the Sobat, which has a minimum flow of about 99 m /s (3,500 cu ft/s) in March and

5886-836: The White Nile, even after centuries of exploration, remains in dispute. The most remote source that is indisputably a source for the White Nile is the Kagera River ; however, the Kagera has tributaries that are in contention for the farthest source of the White Nile. Two start in Burundi: the Ruvyironza River (also known as the Luvironza) and the Rurubu River . In addition, in 2010, an exploration party in Rwanda went to

5995-606: The afterlife. The east was thought of as a place of birth and growth, and the west was considered the place of death, as the god Ra , the Sun, underwent birth, death, and resurrection each day as he crossed the sky. Thus, all tombs were west of the Nile, because the Egyptians believed that in order to enter the afterlife, they had to be buried on the side that symbolized death. As the Nile was such an important factor in Egyptian life,

6104-403: The aircraft of speed very quickly due to induced drag, and, in extreme cases, increased frontal area and parasitic drag. Not only do such maneuvers slow the aircraft down, but they cause significant structural stress at high speed. Modern flight control systems tend to limit a fighter's angle of attack to well below its maximum aerodynamic limit. In sailing , the physical principles involved are

6213-407: 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. As the angle of attack of a fixed-wing aircraft increases, separation of the airflow from the upper surface of the wing becomes more pronounced, leading to

6322-482: The ancient calendar was even based on the three cycles of the Nile. These seasons, each consisting of four months of thirty days each, were called Akhet , Peret , and Shemu . Akhet, which means inundation, was the time of the year when the Nile flooded, leaving several layers of fertile soil behind, aiding in agricultural growth. Peret was the growing season, and Shemu, the last season, was the harvest season when there were no rains. Owing to their failure to penetrate

6431-579: The angle of attack or Lift Reserve Indicators . These indicators measure the angle of attack (AOA) or the Potential of Wing Lift (POWL, or Lift Reserve) directly and help the pilot fly close to the stalling point with greater precision. STOL operations require the aircraft to be able to operate close to the critical angle of attack during landings and at the best angle of climb during takeoffs. Angle of attack indicators are used by pilots for maximum performance during these maneuvers, since airspeed information

6540-411: The camels' case, carriage. Water was vital to both people and livestock. The Nile was also a convenient and efficient means of transportation for people and goods. The Nile was also an important part of ancient Egyptian spiritual life. Hapi was the god of the annual floods, and both he and the pharaoh were thought to control the flooding. The Nile was considered to be a causeway from life to death and

6649-412: The center of gravity of the aircraft and other factors. However, the aircraft normally stalls at the same critical angle of attack, unless icing conditions prevail. The critical or stalling angle of attack is typically around 15° - 18° for many airfoils. Some aircraft are equipped with a built-in flight computer that automatically prevents the aircraft from increasing the angle of attack any further when

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6758-479: The central part of the basin may still be subsiding. The White Nile Rift system, although shallower than the Bahr el Arab rift , is about 9 kilometers (5.6 mi) deep. Geophysical exploration of the Blue Nile Rift System estimated the depth of the sediments to be 5–9 kilometers (3.1–5.6 mi). These basins were not interconnected until their subsidence ceased, and the rate of sediment deposition

6867-589: The confluence with the Blue Nile the only major tributary is the Atbarah River , also known as the Red Nile. Roughly halfway to the sea, it originates in Ethiopia north of Lake Tana , and is around 800 kilometers (500 mi) long. The Atbarah flows only while there is rain in Ethiopia and dries very rapidly. During the dry period of January to June, it typically dries up north of Khartoum . The Blue Nile ( Amharic : ዓባይ , ʿĀbay ) springs from Lake Tana in

6976-463: The course of the Blue Nile to determine that the summer floods were caused by heavy seasonal rainstorms in the Ethiopian Highlands, but no European of antiquity is known to have reached Lake Tana. The Tabula Rogeriana depicted the source as three lakes in 1154. Europeans began to learn about the origins of the Nile in the 14th century when the Pope sent monks as emissaries to Mongolia who passed India,

7085-492: The development of Egyptian civilization. Because the river overflowed its banks annually and deposited new layers of silt, the surrounding land was very fertile. The Ancient Egyptians cultivated and traded wheat, flax , papyrus and other crops around the Nile. Wheat was a crucial crop in the famine-plagued Middle East. This trading system secured Egypt's diplomatic relationships with other countries and contributed to economic stability. Far-reaching trade has been carried on along

7194-402: The dry season the natural discharge of the Blue Nile can be as low as 113 m /s (4,000 cu ft/s), although upstream dams regulate the flow of the river. During the wet season, the peak flow of the Blue Nile often exceeds 5,663 m /s (200,000 cu ft/s) in late August (a difference of a factor of 50). Before the placement of dams on the river the yearly discharge varied by

7303-605: The entire river system. Thus, the name may derive from Ancient Egyptian expression n ꜣ r ꜣ w-ḥ ꜣ w(t) (lit. 'the mouths of the front parts'), which referred specifically to the branches of the Nile transversing the Delta, and would have been pronounced ni-lo-he in the area around Memphis in the 8th century BCE. Hesiod at his Theogony refers to Nilus (Νεῖλος) as one of the Potamoi (river gods), son of Oceanus and Tethys . Another derivation of Nile might be related to

7412-421: The fibers are aligned with the edges of the sail. Radial sails have panels that "radiate" from corners in order to efficiently transmit stress and are typically of higher performance than cross-cut sails. A bi-radial sail has panels radiating from two of three corners; a tri-radial sail has panels radiating from all three corners. Mainsails are more likely to be bi-radial, since there is very little stress at

7521-508: The first European to have visited the headwaters, modern writers give the credit to the Jesuit Pedro Páez . Páez's account of the source of the Nile is a long and vivid account of Ethiopia. It was published in full only in the early 20th century, although it was featured in works of Páez's contemporaries, including Baltazar Téllez, Athanasius Kircher and Johann Michael Vansleb . Europeans had been resident in Ethiopia since

7630-427: The following. Sails on high-performance sailing craft. Sails on craft subject to low forward resistance and high lateral resistance typically have full-length battens. Angle of attack In fluid dynamics , angle of attack ( AOA , α , or α {\displaystyle \alpha } ) is the angle between a reference line on a body (often the chord line of an airfoil ) and

7739-444: The force component in the direction of the apparent wind and lift , the force component normal (90°) to the apparent wind. Depending on the alignment of the sail with the apparent wind, lift or drag may be the predominant propulsive component. Total aerodynamic force also resolves into a forward, propulsive, driving force, resisted by the medium through or over which the craft is passing (e.g., through water, air, or over ice, sand) and

7848-437: The fore-and-aft crab claw , tanja and junk rigs . The date of introduction of these later Austronesian sails is disputed. Lateen sails emerged by around the 2nd century CE in the Mediterranean. They did not become common until the 5th century, when there is evidence that the Mediterranean square sail (which had been in wide use throughout the classical period ) was undergoing a simplification of its rigging components. Both

7957-459: The great lakes. Believing he had found the source of the Nile on seeing this "vast expanse of open water" for the first time, Speke named the lake after Queen Victoria . Burton, recovering from illness and resting further south on the shores of Lake Tanganyika , was outraged that Speke claimed to have proven his discovery to be the true source of the Nile when Burton regarded this as still unsettled. A quarrel ensued which sparked intense debate within

8066-479: The increasing popularity of the lateen and the changes to the contemporary square rig are suggested to be cost saving measures, reducing the number of expensive components needed to fit out a ship. It has been a common and erroneous presumption among maritime historians that lateen had significantly better sailing performance than the square rig of the same period. Analysis of voyages described in contemporary accounts and also in various replica vessels demonstrates that

8175-429: The islands of Maritime Southeast Asia , then later sailed further onwards to Micronesia , Island Melanesia , Polynesia , and Madagascar , eventually settling a territory spanning half the globe. The proto- Austronesian words for sail, lay(r) , and some other rigging parts date to about 3000 BCE when this group began their Pacific expansion. Austronesian rigs are distinctive in that they have spars supporting both

8284-708: The larger part of which is in Egypt. Below the Aswan Dam , at the northern limit of Lake Nasser, the Nile resumes its historic course. North of Cairo , the Nile splits into two branches (or distributaries) that feed the Mediterranean: the Rosetta Branch to the west and the Damietta to the east, forming the Nile Delta . The annual sediment transport by the Nile in Egypt has been quantified. Below

8393-609: The late 15th century, and one of them may have visited the headwaters even earlier without leaving a written trace. The Portuguese João Bermudes published the first description of the Tis Issat Falls in his 1565 memoirs, compared them to the Nile Falls alluded to in Cicero 's De Republica . Jerónimo Lobo describes the source of the Blue Nile, visiting shortly after Pedro Páez. Telles also uses his account. The White Nile

8502-531: The lateen mizzen on 16th and 17th century ships often has the sail furled. Practical experience on the Duyfken replica confirmed the role of the lateen mizzen. Austronesian invention of catamarans , outriggers , and the bi-sparred triangular crab claw sails enabled their ships to sail for vast distances in open ocean. It led to the Austronesian Expansion . From Taiwan, they rapidly settled

8611-401: The lateen. The lines can be categorized as those that support the sail, those that shape it, and those that control its angle to the wind. Fore-and-aft rigged vessels have rigging that supports, shapes, and adjusts the sails to optimize their performance in the wind, which include the following lines: Square-rigged vessels require more controlling lines than fore-and-aft rigged ones, including

8720-436: The longitudinal axis). Some authors do not use an arbitrary chord line but use the zero lift axis where, by definition, zero angle of attack corresponds to zero coefficient of lift . Some British authors have used the term angle of incidence instead of angle of attack. However, this can lead to confusion with the term riggers' angle of incidence meaning the angle between the chord of an airfoil and some fixed datum in

8829-407: The low density of air in the upper atmosphere as well as at low speed at low altitude where the margin between level flight AoA and stall AoA is reduced. The high AoA capability of the aircraft provides a buffer for the pilot that makes stalling the airplane (which occurs when critical AoA is exceeded) more difficult. However, military aircraft usually do not obtain such high alpha in combat, as it robs

8938-580: The main Nile during the 70,000–80,000 years B.P. wet period. The White Nile system in Bahr El Arab and White Nile Rifts remained a closed lake until the connection of the Victoria Nile to the main system some 12,500 years ago during the African humid period . The Greek historian Herodotus wrote that "Egypt was the gift of the Nile". An unending source of sustenance, it played a crucial role in

9047-513: The maneuver ends. The Cobra is an example of supermaneuvering as the aircraft's wings are well beyond the critical angle of attack for most of the maneuver. Additional aerodynamic surfaces known as "high-lift devices" including leading edge wing root extensions allow fighter aircraft much greater flyable 'true' alpha, up to over 45°, compared to about 20° for aircraft without these devices. This can be helpful at high altitudes where even slight maneuvering may require high angles of attack due to

9156-480: The neolithic lifestyle or the first establishment of cities. Yet it is not known when or where this invention took place. Much of the early development of water transport is believed to have occurred in two main "nursery" areas of the world: Island Southeast Asia and the Mediterranean region. In both of these you have warmer waters, so that use of rafts is possible without the risk of hypothermia (a raft

9265-582: The performance of square rig and lateen were very similar. Lateen provided a cheaper rig to build and maintain, with no degradation of performance. The lateen was adopted by Arab seafarers (usually in the sub-type: the settee sail ), but the date is uncertain, with no firm evidence for their use in the Western Indian Ocean before 1500 CE. There is, however, good iconographic evidence of square sails being used by Arab, Persian and Indian ships in this region in, for instance, 1519. The popularity of

9374-575: The present course of the Nile in Egypt and Sudan. Rushdi Said postulates that Egypt supplied most of the waters of the Nile during the early part of its history. The other theory is that the drainage from Ethiopia via rivers equivalent to the Blue Nile, the Atbara and the Takazze flowed to the Mediterranean via the Egyptian Nile since well back into Tertiary times. Salama suggests that during

9483-530: The rest of Austronesia , crab claw sails were mainly for double-outrigger ( trimarans ) and double-hulled ( catamarans ) boats, which remained stable even leeward. In western Island Southeast Asia , later square sails also evolved from the crab claw sail, the tanja and the junk rig , both of which retained the Austronesian characteristic of having more than one spar supporting the sail. Aerodynamic forces on sails depend on wind speed and direction and

9592-414: The river flows into the Mediterranean Sea at Alexandria . Egyptian civilization and Sudanese kingdoms have depended on the river and its annual flooding since ancient times. Most of the population and cities of Egypt lie along those parts of the Nile valley north of the Aswan Dam . Nearly all the cultural and historical sites of Ancient Egypt developed and are found along river banks. The Nile is, with

9701-532: The riverbed sufficiently for the river to overflow westward into a depression to create Lake Moeris . Lake Tanganyika drained northwards into the Nile until the Virunga Volcanoes blocked its course in Rwanda. The Nile was much longer at that time, with its furthest headwaters in northern Zambia. The currently existing Nile first flowed during the former parts of the Würm glaciation period. Affad 23

9810-440: The sail cloth. There are several key factors in evaluating a fiber for suitability in weaving a sail-cloth: initial modulus , breaking strength (tenacity) , creep , and flex strength . Both the initial cost and its durability of the material define its cost-effectiveness over time. Traditionally, sails were made from flax or cotton canvas , although Scandinavian, Scottish and Icelandic cultures used woolen sails from

9919-590: The same as for aircraft—a sail is an airfoil. A sail's angle of attack is the angle between the sail's chord line and the direction of the relative wind. Nile The Nile (also known as the River Nile or Nile River ) is a major north-flowing river in northeastern Africa . It flows into the Mediterranean Sea . The Nile is the longest river in Africa. It has historically been considered

10028-407: The scientific community and interest by other explorers keen to either confirm or refute Speke's discovery. British explorer and missionary David Livingstone pushed too far west and entered the Congo River system instead. It was ultimately Welsh-American explorer Henry Morton Stanley who confirmed Speke's discovery, circumnavigating Lake Victoria and reporting the great outflow at Ripon Falls on

10137-588: The sea level rose at the end of the most recent ice age , the stream which is now the northern Nile captured the ancestral Nile near Asyut . This change in climate also led to the current extents of the Sahara desert, around 3400 BCE. The Giza pyramid complex originally overlooked a branch of the Nile that no longer exists. This branch was highest during the African Humid Period . The existing Nile has five earlier phases: Flowing north from

10246-484: The soil. The Nile no longer floods in Egypt since the completion of the Aswan Dam in 1970. An anabranch river, the Bahr el Zeraf , flows out of the Nile's Bahr al Jabal section and rejoins the White Nile. The flow rate of the Bahr al Jabal at Mongalla is almost constant throughout the year and averages 1,048 m /s (37,000 cu ft/s). After Mongalla, the Bahr Al Jabal enters the enormous swamps of

10355-445: The speed and direction of the craft. The direction that the craft is traveling with respect to the true wind (the wind direction and speed over the surface) is called the "point of sail". The speed of the craft at a given point of sail contributes to the apparent wind ( V A ), the wind speed and direction as measured on the moving craft. The apparent wind on the sail creates a total aerodynamic force, which may be resolved into drag ,

10464-551: The surface, a sail can propel a craft to a higher speed, on points of sail when the entry point of the sail is aligned with the apparent wind, than it can with the entry point not aligned, because of a combination of the diminished force from airflow around the sail and the diminished apparent wind from the velocity of the craft. 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 (approximately 40° to 135° off

10573-407: The tack, whereas head sails (spinnakers and jibs) are more likely to be tri-radial, because they are tensioned at their corners. Higher performance sails may be laminated, constructed directly from multiple plies of filaments , fibers , taffetas , and films , instead of woven textiles that are adhered together. Molded sails are laminated sails formed over a curved mold and adhered together into

10682-515: The term Nil ( Sanskrit : नील , romanized :  nila ; Egyptian Arabic : نيلة ), which refers to Indigofera tinctoria , one of the original sources of indigo dye . Another may be Nymphaea caerulea , known as "The Sacred Blue Lily of the Nile", which was found scattered over Tutankhamun 's corpse when it was excavated in 1922. Another possible etymology derives from the Semitic term Nahal , meaning "river". Old Libyan has

10791-422: The term lilu , meaning water (in modern Berber ilel ⵉⵍⴻⵍ means sea ). With a total length of about 6,650 km (4,130 mi) between the region of Lake Victoria and the Mediterranean Sea , the Nile is among the longest rivers on Earth. The drainage basin of the Nile covers 3,254,555 square kilometers (1,256,591 sq mi), about 10% of the area of Africa. Compared to other major rivers, though,

10900-542: The upper and lower edges of the sails (and sometimes in between). The sails were also made from salt-resistant woven leaves, usually from pandan plants. Crab claw sails used with single-outrigger ships in Micronesia , Island Melanesia , Polynesia , and Madagascar were intrinsically unstable when tacking leeward. To deal with this, Austronesians in these regions developed the shunting technique in sailing, in conjunction with uniquely reversible single-outriggers. In

11009-411: The upper surface flow becomes more fully separated and the lift coefficient reduces further. 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 ,

11118-422: The upper surface of the airfoil and begins to separate from the upper surface. On most airfoil shapes, as the angle of attack increases, the upper surface separation point of the flow moves from the trailing edge towards the leading edge. At the critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum lift coefficient. As the angle of attack increases further,

11227-650: The various combinations of sail proposed for a sailing ship . Sail plans may vary for different wind conditions—light to heavy. Both square-rigged and fore-and-aft rigged vessels have been built with a wide range of configurations for single and multiple masts with sails and with a variety of means of primary attachment to the craft, including: High-performance yachts, including the International C-Class Catamaran , have used or use rigid wing sails , which perform better than traditional soft sails but are more difficult to manage. A rigid wing sail

11336-559: The water and silt . The White Nile is longer and rises in the Great Lakes region. It begins at Lake Victoria and flows through Uganda and South Sudan. The Blue Nile begins at Lake Tana in Ethiopia and flows into Sudan from the southeast. The two rivers meet at the Sudanese capital of Khartoum . The northern section of the river flows north almost entirely through the Nubian Desert to Cairo and its large delta , and

11445-403: The wind). Because of low friction over the surface and high speeds over the ice that create high apparent wind speeds for most points of sail, iceboats can derive power from lift further off the wind than displacement boats. Each rig is configured in a sail plan , appropriate to the size of the sailing craft. A sail plan is a set of drawings, usually prepared by a naval architect which shows

11554-480: The word ⲫⲓⲁⲣⲟ , pronounced piaro ( Sahidic ) or phiaro ( Bohairic ), means "the river" (lit. p(h).iar-o "the.canal-great"), and comes from the same ancient name. In Nobiin , the river is called Áman Dawū , meaning "the great water". In Luganda , the river is called Kiira or Kiyira . In Runyoro , it is called Kihiira . In Egyptian Arabic , the Nile is called en-Nīl , while in Standard Arabic it

11663-574: Was enough to fill and connect them. The Egyptian Nile connected to the Sudanese Nile, which captures the Ethiopian and Equatorial headwaters during the current stages of tectonic activity in the Eastern, Central and Sudanese Rift systems. The connection of the different Niles occurred during cyclic wet periods. The Atbarah overflowed its closed basin during the wet periods that occurred about 100,000 to 120,000 years ago. The Blue Nile connected to

11772-597: Was even less understood. The ancients mistakenly believed that the Niger River represented the upper reaches of the White Nile. For example, Pliny the Elder writes that the Nile had its origins "in a mountain of lower Mauretania ", flowed above ground for "many days" distance, then went underground, reappeared as a large lake in the territories of the Masaesyli , then sank again below the desert to flow underground "for

11881-422: Was used by Stars and Stripes , the defender which won the 1988 America's Cup , and by USA-17 , the challenger which won the 2010 America's Cup . USA 17' s performance during the 2010 America's Cup races demonstrated a velocity made good upwind of over twice the wind speed and downwind of over 2.5 times the wind speed and the ability to sail as close as 20 degrees off the apparent wind. The shape of

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