Misplaced Pages

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122-536: The word "keel" comes from Old English cēol , Old Norse kjóll , = " ship " or "keel". It has the distinction of being regarded by some scholars as the first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work De Excidio et Conquestu Britanniae , under the spelling cyulae (he was referring to the three ships that the Saxons first arrived in). Carina

244-613: A definite article ("the"), a demonstrative adjective ("that"), and demonstrative pronoun . Other demonstratives are þēs ("this"), and ġeon ("that over there"). These words inflect for case, gender, and number. Adjectives have both strong and weak sets of endings, weak ones being used when a definite or possessive determiner is also present. Verbs conjugate for three persons : first, second, and third; two numbers: singular, plural; two tenses : present, and past; three moods : indicative , subjunctive , and imperative ; and are strong (exhibiting ablaut) or weak (exhibiting

366-681: A version of the Latin alphabet . Englisċ , from which the word English is derived, means 'pertaining to the Angles '. The Angles were one of the Germanic tribes who settled in many parts of Britain in the 5th century. By the 9th century, all speakers of Old English, including those who claimed Saxon or Jutish ancestry, could be referred to as Englisċ . This name probably either derives from Proto-Germanic *anguz , which referred to narrowness, constriction or anxiety, perhaps referring to shallow waters near

488-398: A back vowel ( /ɑ/ , /o/ , /u/ ) at the time of palatalization, as illustrated by the contrast between fisċ /fiʃ/ ('fish') and its plural fiscas /ˈfis.kɑs/ . But due to changes over time, a knowledge of the history of the word in question is needed to predict the pronunciation with certainty (for details, see palatalization ). In word-final position, the pronunciation of sċ

610-406: A dental suffix). Verbs have two infinitive forms: bare and bound; and two participles : present and past. The subjunctive has past and present forms. Finite verbs agree with subjects in person and number. The future tense , passive voice , and other aspects are formed with compounds. Adpositions are mostly before but are often after their object. If the object of an adposition is marked in

732-404: A downward force applied to the air by the airfoil. Then Newton's third law requires the air to exert an upward force on the airfoil; thus a reaction force, lift, is generated opposite to the directional change. In the case of an airplane wing, the wing exerts a downward force on the air and the air exerts an upward force on the wing. The downward turning of the flow is not produced solely by

854-400: A downward force on the air as it flows past. According to Newton's third law , the air must exert an equal and opposite (upward) force on the airfoil, which is lift. As the airflow approaches the airfoil it is curving upward, but as it passes the airfoil it changes direction and follows a path that is curved downward. According to Newton's second law, this change in flow direction requires

976-517: A following ⟨m⟩ or ⟨n⟩ . Modern editions of Old English manuscripts generally introduce some additional conventions. The modern forms of Latin letters are used, including ⟨g⟩ instead of insular G , ⟨s⟩ instead of insular S and long S , and others which may differ considerably from the insular script, notably ⟨e⟩ , ⟨f⟩ and ⟨r⟩ . Macrons are used to indicate long vowels, where usually no distinction

1098-467: A friction that led to the erosion of the complicated inflectional word endings. Simeon Potter notes: No less far-reaching was the influence of Scandinavian upon the inflexional endings of English in hastening that wearing away and leveling of grammatical forms which gradually spread from north to south. It was, after all, a salutary influence. The gain was greater than the loss. There was a gain in directness, in clarity, and in strength. The strength of

1220-420: A given airspeed depends on the shape of the airfoil, especially the amount of camber (curvature such that the upper surface is more convex than the lower surface, as illustrated at right). Increasing the camber generally increases the maximum lift at a given airspeed. Cambered airfoils generate lift at zero angle of attack. When the chord line is horizontal, the trailing edge has a downward direction and since

1342-405: A keel uses the forward motion of the boat to generate lift to counteract the leeward force of the wind. As a counterweight, a keel increasingly offsets the heeling moment with increasing angle of heel. Related foils include movable centreplates, which -being metal- have the secondary purpose of being a counterweight, and centreboards and daggerboards , which are of lighter weight, do not have

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1464-436: A lift force roughly proportional to the angle of attack. As the angle of attack increases, the lift reaches a maximum at some angle; increasing the angle of attack beyond this critical angle of attack causes the upper-surface flow to separate from the wing; there is less deflection downward so the airfoil generates less lift. The airfoil is said to be stalled . The maximum lift force that can be generated by an airfoil at

1586-520: A period of 700 years, from the Anglo-Saxon settlement of Britain in the 5th century to the late 11th century, some time after the Norman invasion . While indicating that the establishment of dates is an arbitrary process, Albert Baugh dates Old English from 450 to 1150, a period of full inflections, a synthetic language . Perhaps around 85% of Old English words are no longer in use, but those that survived are

1708-463: A point is reached where the boundary layer can no longer remain attached to the upper surface. When the boundary layer separates, it leaves a region of recirculating flow above the upper surface, as illustrated in the flow-visualization photo at right. This is known as the stall , or stalling . At angles of attack above the stall, lift is significantly reduced, though it does not drop to zero. The maximum lift that can be achieved before stall, in terms of

1830-485: A pressure difference, and that the speed difference then leads to a pressure difference, by Bernoulli's principle. This implied one-way causation is a misconception. The real relationship between pressure and flow speed is a mutual interaction . As explained below under a more comprehensive physical explanation , producing a lift force requires maintaining pressure differences in both the vertical and horizontal directions. The Bernoulli-only explanations do not explain how

1952-499: A sailing ship. The lift discussed in this article is mainly in relation to airfoils, although marine hydrofoils and propellers share the same physical principles and work in the same way, despite differences between air and water such as density, compressibility, and viscosity. The flow around a lifting airfoil is a fluid mechanics phenomenon that can be understood on essentially two levels: There are mathematical theories , which are based on established laws of physics and represent

2074-433: A series of pre-fabricated, complete hull sections rather than being built around a single keel, so the shipbuilding process commences with the cutting of the first sheet of steel. The most common type of keel is the "flat plate keel", which is fitted in most ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers, tugs, and smaller ferries. Where grounding

2196-417: A steady flow without viscosity, lower pressure means higher speed, and higher pressure means lower speed. Thus changes in flow direction and speed are directly caused by the non-uniform pressure. But this cause-and-effect relationship is not just one-way; it works in both directions simultaneously. The air's motion is affected by the pressure differences, but the existence of the pressure differences depends on

2318-439: A wide area, producing a pattern called a velocity field . When an airfoil produces lift, the flow ahead of the airfoil is deflected upward, the flow above and below the airfoil is deflected downward leaving the air far behind the airfoil in the same state as the oncoming flow far ahead. The flow above the upper surface is sped up, while the flow below the airfoil is slowed down. Together with the upward deflection of air in front and

2440-406: Is cruising in straight and level flight, 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 act as downforce on the wing of a fixed-wing aircraft at the top of an aerobatic loop , and on the horizontal stabiliser of an aircraft. Lift may also be largely horizontal, for instance on

2562-407: Is a result of pressure differences and depends on angle of attack, airfoil shape, air density, and airspeed. Pressure is the normal force per unit area exerted by the air on itself and on surfaces that it touches. The lift force is transmitted through the pressure, which acts perpendicular to the surface of the airfoil. Thus, the net force manifests itself as pressure differences. The direction of

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2684-510: Is accepted as a phenomenon in inviscid flow. There are two common versions of this explanation, one based on "equal transit time", and one based on "obstruction" of the airflow. The "equal transit time" explanation starts by arguing that the flow over the upper surface is faster than the flow over the lower surface because the path length over the upper surface is longer and must be traversed in equal transit time. Bernoulli's principle states that under certain conditions increased flow speed

2806-548: Is also sparse early Northumbrian evidence of a sixth case: the locative . The evidence comes from Northumbrian Runic texts (e.g., ᚩᚾ ᚱᚩᛞᛁ on rodi "on the Cross"). Adjectives agree with nouns in case, gender, and number, and can be either strong or weak. Pronouns and sometimes participles agree in case, gender, and number. First-person and second- person personal pronouns occasionally distinguish dual-number forms. The definite article sē and its inflections serve as

2928-401: Is also used by flying and gliding animals , especially by birds , bats , and insects , and even in the plant world by the seeds of certain trees. While the common meaning of the word " lift " assumes that lift opposes weight, lift can be in any direction with respect to gravity, since it is defined with respect to the direction of flow rather than to the direction of gravity. When an aircraft

3050-422: Is as follows. The sounds enclosed in parentheses in the chart above are not considered to be phonemes : The above system is largely similar to that of Modern English , except that [ç, x, ɣ, l̥, n̥, r̥] (and [ʍ] for most speakers ) have generally been lost, while the voiced affricate and fricatives (now also including /ʒ/ ) have become independent phonemes, as has /ŋ/ . The open back rounded vowel [ɒ]

3172-410: Is associated with reduced pressure. It is concluded that the reduced pressure over the upper surface results in upward lift. While it is true that the flow speeds up, a serious flaw in this explanation is that it does not correctly explain what causes the flow to speed up. The longer-path-length explanation is incorrect. No difference in path length is needed, and even when there is a difference, it

3294-437: Is distinguished from other kinds of lift in fluids. Aerostatic lift or buoyancy , in which an internal fluid is lighter than the surrounding fluid, does not require movement and is used by balloons, blimps, dirigibles, boats, and submarines. Planing lift , in which only the lower portion of the body is immersed in a liquid flow, is used by motorboats, surfboards, windsurfers, sailboats, and water-skis. A fluid flowing around

3416-606: Is evidenced by the continued variation between their successors in Middle and Modern English. In fact, what would become the standard forms of Middle English and of Modern English are descended from Mercian rather than West Saxon, while Scots developed from the Northumbrian dialect. It was once claimed that, owing to its position at the heart of the Kingdom of Wessex, the relics of Anglo-Saxon accent, idiom and vocabulary were best preserved in

3538-646: Is followed by Middle English (1150 to 1500), Early Modern English (1500 to 1650) and finally Modern English (after 1650), and in Scotland Early Scots (before 1450), Middle Scots ( c.  1450 to 1700) and Modern Scots (after 1700). Just as Modern English is not monolithic, Old English varied according to place. Despite the diversity of language of the Germanic-speaking migrants who established Old English in England and southeastern Scotland, it

3660-614: Is negligible. The lift force frequency is characterised by the dimensionless Strouhal number , which depends on the Reynolds number of the flow. For a flexible structure, this oscillatory lift force may induce vortex-induced vibrations. Under certain conditions – for instance resonance or strong spanwise correlation of the lift force – the resulting motion of the structure due to the lift fluctuations may be strongly enhanced. Such vibrations may pose problems and threaten collapse in tall man-made structures like industrial chimneys . In

3782-521: Is not an example of the Coandă effect. Regardless of whether this broader definition of the "Coandă effect" is applicable, calling it the "Coandă effect" does not provide an explanation, it just gives the phenomenon a name. The ability of a fluid flow to follow a curved path is not dependent on shear forces, viscosity of the fluid, or the presence of a boundary layer. Air flowing around an airfoil, adhering to both upper and lower surfaces, and generating lift,

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3904-852: Is possible to reconstruct proto-Old English as a fairly unitary language. For the most part, the differences between the attested regional dialects of Old English developed within England and southeastern Scotland, rather than on the Mainland of Europe. Although from the tenth century Old English writing from all regions tended to conform to a written standard based on Late West Saxon, in speech Old English continued to exhibit much local and regional variation, which remained in Middle English and to some extent Modern English dialects . The four main dialectal forms of Old English were Mercian , Northumbrian , Kentish , and West Saxon . Mercian and Northumbrian are together referred to as Anglian . In terms of geography

4026-406: Is possible, this type of keel is suitable with its massive scantlings , but there is always a problem of the increased draft with no additional cargo capacity. 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. Hydrodynamic keels have the primary purpose of interacting with

4148-404: Is proportional to the density of the air and approximately proportional to the square of the flow speed. Lift also depends on the size of the wing, being generally proportional to the wing's area projected in the lift direction. In calculations it is convenient to quantify lift in terms of a lift coefficient based on these factors. No matter how smooth the surface of an airfoil seems, any surface

4270-434: Is replaced by ⟨þ⟩ ). In contrast with Modern English orthography , Old English spelling was reasonably regular , with a mostly predictable correspondence between letters and phonemes . There were not usually any silent letters —in the word cniht , for example, both the ⟨c⟩ and ⟨h⟩ were pronounced ( /knixt ~ kniçt/ ) unlike the ⟨k⟩ and ⟨gh⟩ in

4392-409: Is rough on the scale of air molecules. Air molecules flying into the surface bounce off the rough surface in random directions relative to their original velocities. The result is that when the air is viewed as a continuous material, it is seen to be unable to slide along the surface, and the air's velocity relative to the airfoil decreases to nearly zero at the surface (i.e., the air molecules "stick" to

4514-454: Is the Latin word for "keel" and is the origin of the term careen (to clean a keel and the hull in general, often by rolling the ship on its side). An example of this use is Careening Cove , a suburb of Sydney, Australia , where careening was carried out in the early colonial days. The use of a keel in sailing vessels dates back to antiquity . The wreck of an ancient Greek merchant ship known as

4636-405: 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 ship's hull to be constructed, and laying the keel , or placing the keel in the cradle where the ship will be built, may mark the start time of its construction. Large, modern ships are now often built in

4758-516: Is typically much too small to explain the observed speed difference. This is because the assumption of equal transit time is wrong when applied to a body generating lift. There is no physical principle that requires equal transit time in all situations and experimental results confirm that for a body generating lift the transit times are not equal. In fact, the air moving past the top of an airfoil generating lift moves much faster than equal transit time predicts. The much higher flow speed over

4880-466: Is very different from Modern English and Modern Scots, and largely incomprehensible for Modern English or Modern Scots speakers without study. Within Old English grammar nouns, adjectives, pronouns and verbs have many inflectional endings and forms, and word order is much freer. The oldest Old English inscriptions were written using a runic system , but from about the 8th century this was replaced by

5002-517: The Angles , Saxons and Jutes . As the Germanic settlers became dominant in England, their language replaced the languages of Roman Britain : Common Brittonic , a Celtic language ; and Latin , brought to Britain by the Roman conquest . Old English had four main dialects, associated with particular Anglo-Saxon kingdoms : Kentish , Mercian , Northumbrian , and West Saxon . It was West Saxon that formed

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5124-449: The Kyrenia ship establishes the origin of the keel at least as far back as 315 BC. The Uluburun shipwreck ( c. 1325 BC) had a rudimentary keel, but it may have been more of a center plank than a keel. In carvel-built hulls, construction began with the laying of the keel, followed by the stern and stem . Frames were set up afterward, set at key points along the keel. Later,

5246-581: The Latin alphabet was introduced and adapted for the writing of Old English , replacing the earlier runic system. Nonetheless, the largest transfer of Latin-based (mainly Old French ) words into English occurred after the Norman Conquest of 1066, and thus in the Middle English rather than the Old English period. Another source of loanwords was Old Norse , which came into contact with Old English via

5368-625: The Magnus effect , a lift force is generated by a spinning cylinder in a freestream. Here the mechanical rotation acts on the boundary layer, causing it to separate at different locations on the two sides of the cylinder. The asymmetric separation changes the effective shape of the cylinder as far as the flow is concerned such that the cylinder acts like a lifting airfoil with circulation in the outer flow. As described above under " Simplified physical explanations of lift on an airfoil ", there are two main popular explanations: one based on downward deflection of

5490-597: The dialect of Somerset . For details of the sound differences between the dialects, see Phonological history of Old English § Dialects . The language of the Anglo-Saxon settlers appears not to have been significantly affected by the native British Celtic languages which it largely displaced . The number of Celtic loanwords introduced into the language is very small, although dialect and toponymic terms are more often retained in western language contact zones (Cumbria, Devon, Welsh Marches and Borders and so on) than in

5612-429: The drag force, which is the component of the force parallel to the flow direction. Lift conventionally acts in an upward direction in order to counter the force of gravity , but it is defined to act perpendicular to the flow and therefore can act in any direction. If the surrounding fluid is air, the force is called an aerodynamic force . In water or any other liquid, it is called a hydrodynamic force . Dynamic lift

5734-517: The keelson was attached to the keel, either bolted or with treenails . A plank first building system that is still in use today is clinker construction , using overlapping planks which are shaped to produce the hull form. Older systems include the bottom-based method used for the planking on either side of the keel of a cog (and also in Dutch shipbuilding up to and including the 17th century). This involves flush-fitted planks that have been cut to provide

5856-544: The kingdom of Northumbria . Other parts of the island continued to use Celtic languages ( Gaelic – and perhaps some Pictish – in most of Scotland, Medieval Cornish all over Cornwall and in adjacent parts of Devon , Cumbric perhaps to the 12th century in parts of Cumbria , and Welsh in Wales and possibly also on the English side of the Anglo-Welsh border ); except in the areas of Scandinavian settlements, where Old Norse

5978-446: The streamline curvature theorem , was derived from Newton's second law by Leonhard Euler in 1754: The left side of this equation represents the pressure difference perpendicular to the fluid flow. On the right side of the equation, ρ is the density, v is the velocity, and R is the radius of curvature. This formula shows that higher velocities and tighter curvatures create larger pressure differentials and that for straight flow (R → ∞),

6100-422: The 8th century, the runic system came to be supplanted by a (minuscule) half-uncial script of the Latin alphabet introduced by Irish Christian missionaries. This was replaced by Insular script , a cursive and pointed version of the half-uncial script. This was used until the end of the 12th century when continental Carolingian minuscule (also known as Caroline ) replaced the insular. The Latin alphabet of

6222-406: The English language; some of them, such as Pope Gregory I 's treatise Pastoral Care , appear to have been translated by Alfred himself. In Old English, typical of the development of literature, poetry arose before prose, but Alfred chiefly inspired the growth of prose. A later literary standard, dating from the late 10th century, arose under the influence of Bishop Æthelwold of Winchester , and

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6344-598: The Great . From that time on, the West Saxon dialect (then in the form now known as Early West Saxon) became standardised as the language of government, and as the basis for the many works of literature and religious materials produced or translated from Latin in that period. The later literary standard known as Late West Saxon (see History , above), although centred in the same region of the country, appears not to have been directly descended from Alfred's Early West Saxon. For example,

6466-410: The Northumbrian dialect retained /i(ː)o̯/ , which had merged with /e(ː)o̯/ in West Saxon. For more on dialectal differences, see Phonological history of Old English (dialects) . Some of the principal sound changes occurring in the pre-history and history of Old English were the following: For more details of these processes, see the main article, linked above. For sound changes before and after

6588-857: The Northumbrian region lay north of the Humber River; the Mercian lay north of the Thames and south of the Humber River; West Saxon lay south and southwest of the Thames; and the smallest, Kentish region lay southeast of the Thames, a small corner of England. The Kentish region, settled by the Jutes from Jutland, has the scantest literary remains. The term West Saxon actually is represented by two different dialects: Early West Saxon and Late West Saxon. Hogg has suggested that these two dialects would be more appropriately named Alfredian Saxon and Æthelwoldian Saxon, respectively, so that

6710-462: The Old English period is also often attributed to Norse influence. The influence of Old Norse certainly helped move English from a synthetic language along the continuum to a more analytic word order , and Old Norse most likely made a greater impact on the English language than any other language. The eagerness of Vikings in the Danelaw to communicate with their Anglo-Saxon neighbours produced

6832-478: The Old English period, see Phonological history of English . Nouns decline for five cases : nominative , accusative , genitive , dative , instrumental ; three genders : masculine, feminine, neuter; and two numbers : singular, and plural; and are strong or weak. The instrumental is vestigial and only used with the masculine and neuter singular and often replaced by the dative . Only pronouns and strong adjectives retain separate instrumental forms. There

6954-515: The Scandinavian rulers and settlers in the Danelaw from the late 9th   century, and during the rule of Cnut and other Danish kings in the early 11th   century. Many place names in eastern and northern England are of Scandinavian origin. Norse borrowings are relatively rare in Old English literature, being mostly terms relating to government and administration. The literary standard, however,

7076-602: The Viking influence on Old English appears from the fact that the indispensable elements of the language – pronouns , modals , comparatives , pronominal adverbs (like hence and together ), conjunctions and prepositions – show the most marked Danish influence; the best evidence of Scandinavian influence appears in the extensive word borrowings because, as Jespersen indicates, no texts exist in either Scandinavia or Northern England from this time to give certain evidence of an influence on syntax. The effect of Old Norse on Old English

7198-439: The air follows the trailing edge it is deflected downward. When a cambered airfoil is upside down, the angle of attack can be adjusted so that the lift force is upward. This explains how a plane can fly upside down. The ambient flow conditions which affect lift include the fluid density, viscosity and speed of flow. Density is affected by temperature, and by the medium's acoustic velocity – i.e. by compressibility effects. Lift

7320-418: The air's motion. The relationship is thus a mutual, or reciprocal, interaction: Air flow changes speed or direction in response to pressure differences, and the pressure differences are sustained by the air's resistance to changing speed or direction. A pressure difference can exist only if something is there for it to push against. In aerodynamic flow, the pressure difference pushes against the air's inertia, as

7442-490: The airfoil and behind also indicate that air passing through the low-pressure region above the airfoil is sped up as it enters, and slowed back down as it leaves. Air passing through the high-pressure region below the airfoil is slowed down as it enters and then sped back up as it leaves. Thus the non-uniform pressure is also the cause of the changes in flow speed visible in the flow animation. The changes in flow speed are consistent with Bernoulli's principle , which states that in

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7564-408: The airfoil is pushed outward from the center of the high-pressure region. According to Newton's second law , a force causes air to accelerate in the direction of the force. Thus the vertical arrows in the accompanying pressure field diagram indicate that air above and below the airfoil is accelerated, or turned downward, and that the non-uniform pressure is thus the cause of the downward deflection of

7686-429: The airfoil's surfaces. Pressure in a fluid is always positive in an absolute sense, so that pressure must always be thought of as pushing, and never as pulling. The pressure thus pushes inward on the airfoil everywhere on both the upper and lower surfaces. The flowing air reacts to the presence of the wing by reducing the pressure on the wing's upper surface and increasing the pressure on the lower surface. The pressure on

7808-494: The amount of constriction or obstruction do not predict experimental results. Another flaw is that conservation of mass is not a satisfying physical reason why the flow would speed up. Effectively explaining the acceleration of an object requires identifying the force that accelerates it. A serious flaw common to all the Bernoulli-based explanations is that they imply that a speed difference can arise from causes other than

7930-501: The basic elements of Modern English vocabulary. Old English is a West Germanic language , and developed out of Ingvaeonic (also known as North Sea Germanic) dialects from the 5th century. It came to be spoken over most of the territory of the Anglo-Saxon kingdoms which became the Kingdom of England . This included most of present-day England, as well as part of what is now southeastern Scotland , which for several centuries belonged to

8052-570: The basis for the literary standard of the later Old English period, although the dominant forms of Middle and Modern English would develop mainly from Mercian, and Scots from Northumbrian. The speech of eastern and northern parts of England was subject to strong Old Norse influence due to Scandinavian rule and settlement beginning in the 9th century. Old English is one of the West Germanic languages , and its closest relatives are Old Frisian and Old Saxon . Like other old Germanic languages, it

8174-552: The beginnings of the compound tenses of Modern English . Old English verbs include strong verbs , which form the past tense by altering the root vowel, and weak verbs , which use a suffix such as -de . As in Modern English, and peculiar to the Germanic languages, the verbs formed two great classes: weak (regular), and strong (irregular). Like today, Old English had fewer strong verbs, and many of these have over time decayed into weak forms. Then, as now, dental suffixes indicated

8296-488: The borrowing of individual Latin words based on which patterns of sound change they have undergone. Some Latin words had already been borrowed into the Germanic languages before the ancestral Angles and Saxons left continental Europe for Britain. More entered the language when the Anglo-Saxons were converted to Christianity and Latin-speaking priests became influential. It was also through Irish Christian missionaries that

8418-499: The cluster ending in the palatal affricate is sometimes written ⟨nċġ⟩ (or ⟨nġċ⟩ ) by modern editors. Between vowels in the middle of a word, the pronunciation can be either a palatalized geminate /ʃː/ , as in fisċere /ˈfiʃ.ʃe.re/ ('fisherman') and wȳsċan , /ˈwyːʃ.ʃɑn 'to wish'), or an unpalatalized consonant sequence /sk/ , as in āscian /ˈɑːs.ki.ɑn/ ('to ask'). The pronunciation /sk/ occurs when ⟨sc⟩ had been followed by

8540-457: The coast, or else it may derive from a related word *angô which could refer to curve or hook shapes including fishing hooks. Concerning the second option, it has been hypothesised that the Angles acquired their name either because they lived on a curved promontory of land shaped like a fishhook , or else because they were fishermen (anglers). Old English was not static, and its usage covered

8662-421: The dative case, an adposition may conceivably be located anywhere in the sentence. Remnants of the Old English case system in Modern English are in the forms of a few pronouns (such as I/me/mine , she/her , who/whom/whose ) and in the possessive ending -'s , which derives from the masculine and neuter genitive ending -es . The modern English plural ending -(e)s derives from the Old English -as , but

8784-421: The downward deflection of the air immediately behind, this establishes a net circulatory component of the flow. The downward deflection and the changes in flow speed are pronounced and extend over a wide area, as can be seen in the flow animation on the right. These differences in the direction and speed of the flow are greatest close to the airfoil and decrease gradually far above and below. All of these features of

8906-422: The downward turning, but this is false. (see above under " Controversy regarding the Coandă effect "). The arrows ahead of the airfoil indicate that the flow ahead of the airfoil is deflected upward, and the arrows behind the airfoil indicate that the flow behind is deflected upward again, after being deflected downward over the airfoil. These deflections are also visible in the flow animation. The arrows ahead of

9028-431: The east. However, various suggestions have been made concerning possible influence that Celtic may have had on developments in English syntax in the post–Old English period, such as the regular progressive construction and analytic word order , as well as the eventual development of the periphrastic auxiliary verb do . These ideas have generally not received widespread support from linguists, particularly as many of

9150-467: The effect to include the tendency of any fluid boundary layer to adhere to a curved surface, not just the boundary layer accompanying a fluid jet. It is in this broader sense that the Coandă effect is used by some popular references to explain why airflow remains attached to the top side of an airfoil. This is a controversial use of the term "Coandă effect"; the flow following the upper surface simply reflects an absence of boundary-layer separation, thus it

9272-414: The flow (Newton's laws), and one based on pressure differences accompanied by changes in flow speed (Bernoulli's principle). Either of these, by itself, correctly identifies some aspects of the lifting flow but leaves other important aspects of the phenomenon unexplained. A more comprehensive explanation involves both downward deflection and pressure differences (including changes in flow speed associated with

9394-444: The flow accurately, but which require solving equations. And there are physical explanations without math, which are less rigorous. Correctly explaining lift in these qualitative terms is difficult because the cause-and-effect relationships involved are subtle. A comprehensive explanation that captures all of the essential aspects is necessarily complex. There are also many simplified explanations , but all leave significant parts of

9516-409: The flow visible in the flow animation. To produce this downward turning, the airfoil must have a positive angle of attack or have sufficient positive camber. Note that the downward turning of the flow over the upper surface is the result of the air being pushed downward by higher pressure above it than below it. Some explanations that refer to the "Coandă effect" suggest that viscosity plays a key role in

9638-481: The flow-deflection explanation of lift cite the Coandă effect as the reason the flow is able to follow the convex upper surface of the airfoil. The conventional definition in the aerodynamics field is that the Coandă effect refers to the tendency of a fluid jet to stay attached to an adjacent surface that curves away from the flow, and the resultant entrainment of ambient air into the flow. More broadly, some consider

9760-639: The former diphthong /iy/ tended to become monophthongised to /i/ in EWS, but to /y/ in LWS. Due to the centralisation of power and the destruction wrought by Viking invasions, there is relatively little written record of the non-West Saxon dialects after Alfred's unification. Some Mercian texts continued to be written, however, and the influence of Mercian is apparent in some of the translations produced under Alfred's programme, many of which were produced by Mercian scholars. Other dialects certainly continued to be spoken, as

9882-526: The futhorc. A few letter pairs were used as digraphs , representing a single sound. Also used was the Tironian note ⟨⁊⟩ (a character similar to the digit 7) for the conjunction and . A common scribal abbreviation was a thorn with a stroke ⟨ꝥ⟩ , which was used for the pronoun þæt ( that ). Macrons over vowels were originally used not to mark long vowels (as in modern editions), but to indicate stress, or as abbreviations for

10004-590: The inscriptions on the Franks Casket ) date to the early 8th century. The Old English Latin alphabet was introduced around the 8th century. With the unification of several of the Anglo-Saxon kingdoms (outside the Danelaw ) by Alfred the Great in the later 9th century, the language of government and literature became standardised around the West Saxon dialect (Early West Saxon). Alfred advocated education in English alongside Latin, and had many works translated into

10126-478: The language of the upper classes. This is regarded as marking the end of the Old English era, since during the subsequent period the English language was heavily influenced by Anglo-Norman, developing into what is now known as Middle English in England and Early Scots in Scotland. Old English developed from a set of Anglo-Frisian or Ingvaeonic dialects originally spoken by Germanic tribes traditionally known as

10248-449: The latter applied only to "strong" masculine nouns in the nominative and accusative cases; different plural endings were used in other instances. Old English nouns had grammatical gender , while modern English has only natural gender. Pronoun usage could reflect either natural or grammatical gender when those conflicted, as in the case of ƿīf , a neuter noun referring to a female person. In Old English's verbal compound constructions are

10370-410: The lift by a modest amount and modifies the pressure distribution somewhat, which results in a viscosity-related pressure drag over and above the skin friction drag. The total of the skin friction drag and the viscosity-related pressure drag is usually called the profile drag . An airfoil's maximum lift at a given airspeed is limited by boundary-layer separation . As the angle of attack is increased,

10492-421: The lift coefficient, is generally less than 1.5 for single-element airfoils and can be more than 3.0 for airfoils with high-lift slotted flaps and leading-edge devices deployed. The flow around bluff bodies – i.e. without a streamlined shape, or stalling airfoils – may also generate lift, in addition to a strong drag force. This lift may be steady, or it may oscillate due to vortex shedding . Interaction of

10614-477: The lower surface of the airfoil, and the air flow above the airfoil accounts for much of the downward-turning action. This explanation is correct but it is incomplete. It does not explain how the airfoil can impart downward turning to a much deeper swath of the flow than it actually touches. Furthermore, it does not mention that the lift force is exerted by pressure differences , and does not explain how those pressure differences are sustained. Some versions of

10736-403: The lower surface pushes up harder than the reduced pressure on the upper surface pushes down, and the net result is upward lift. The pressure difference which results in lift acts directly on the airfoil surfaces; however, understanding how the pressure difference is produced requires understanding what the flow does over a wider area. An airfoil affects the speed and direction of the flow over

10858-451: The modern knight ( /naɪt/ ). The following table lists the Old English letters and digraphs together with the phonemes they represent, using the same notation as in the Phonology section above. After /n/ , /j/ was realized as [dʒ] and /ɣ/ was realized as [ɡ] . The spellings ⟨ncg⟩ , ⟨ngc⟩ and even ⟨ncgg⟩ were occasionally used instead of

10980-496: The naive reader would not assume that they are chronologically related. Each of these four dialects was associated with an independent kingdom on the islands. Of these, Northumbria south of the Tyne , and most of Mercia , were overrun by the Vikings during the 9th century. The portion of Mercia that was successfully defended, and all of Kent , were then integrated into Wessex under Alfred

11102-494: The net force implies that the average pressure on the upper surface of the airfoil is lower than the average pressure on the underside. These pressure differences arise in conjunction with the curved airflow. When a fluid follows a curved path, there is a pressure gradient perpendicular to the flow direction with higher pressure on the outside of the curve and lower pressure on the inside. This direct relationship between curved streamlines and pressure differences, sometimes called

11224-413: The object's flexibility with the vortex shedding may enhance the effects of fluctuating lift and cause vortex-induced vibrations . For instance, the flow around a circular cylinder generates a Kármán vortex street : vortices being shed in an alternating fashion from the cylinder's sides. The oscillatory nature of the flow produces a fluctuating lift force on the cylinder, even though the net (mean) force

11346-478: The oncoming flow direction. Lift is always accompanied by a drag force, which is the component of the surface force parallel to the flow direction. Lift is mostly associated with the wings of fixed-wing aircraft , although it is more widely generated by many other streamlined bodies such as propellers , kites , helicopter rotors , racing car wings , maritime sails , wind turbines , and by sailboat keels , ship's rudders , and hydrofoils in water. Lift

11468-512: The past tense of the weak verbs, as in work and worked . Old English syntax is similar to that of modern English . Some differences are consequences of the greater level of nominal and verbal inflection, allowing freer word order . Old English was first written in runes , using the futhorc —a rune set derived from the Germanic 24-character elder futhark , extended by five more runes used to represent Anglo-Saxon vowel sounds and sometimes by several more additional characters. From around

11590-481: The phenomenon unexplained, while some also have elements that are simply incorrect. An airfoil is a streamlined 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, and with somewhat higher drag. Most simplified explanations follow one of two basic approaches, based either on Newton's laws of motion or on Bernoulli's principle . An airfoil generates lift by exerting

11712-422: The pressure difference is zero. The angle of attack is the angle between the chord line of an airfoil and the oncoming airflow. A symmetrical airfoil generates zero lift at zero angle of attack. But as the angle of attack increases, the air is deflected through a larger angle and the vertical component of the airstream velocity increases, resulting in more lift. For small angles, a symmetrical airfoil generates

11834-435: The pressure differences in the vertical direction are sustained. That is, they leave out the flow-deflection part of the interaction. Although the two simple Bernoulli-based explanations above are incorrect, there is nothing incorrect about Bernoulli's principle or the fact that the air goes faster on the top of the wing, and Bernoulli's principle can be used correctly as part of a more complicated explanation of lift. Lift

11956-405: The pressure differences), and requires looking at the flow in more detail. The airfoil shape and angle of attack work together so that the airfoil exerts a downward force on the air as it flows past. According to Newton's third law, the air must then exert an equal and opposite (upward) force on the airfoil, which is the lift. The net force exerted by the air occurs as a pressure difference over

12078-439: The richest and most significant bodies of literature preserved among the early Germanic peoples. In his supplementary article to the 1935 posthumous edition of Bright's Anglo-Saxon Reader , Dr. James Hulbert writes: Lift (force) When a fluid flows around an object, the fluid exerts a force on the object. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with

12200-468: The secondary purpose of being a counterweight. Moveable sailboat keels may pivot (a centreboard, centreplate or swing keel), retract upwards (lifting/retracting keel or daggerboard), or swing sideways in the water ( canting keels ) to move the ballasting effect to one side and allow the boat to sail in a more upright position. Old English language Old English ( Englisċ or Ænglisc , pronounced [ˈeŋɡliʃ] ), or Anglo-Saxon ,

12322-455: The shape of the hull. Still older is the mortice and tenon edge-to-edge joining of hull planks in the Mediterranean during the classical period . In this system, much of the strength of the hull is derived from the planking, with the frames providing some extra strength. In all these systems, the joining of the keel, stem and sternpost are the starting point of construction. A structural keel

12444-406: The streamlines to pinch closer together, making the streamtubes narrower. When streamtubes become narrower, conservation of mass requires that flow speed must increase. Reduced upper-surface pressure and upward lift follow from the higher speed by Bernoulli's principle , just as in the equal transit time explanation. Sometimes an analogy is made to a venturi nozzle , claiming the upper surface of

12566-432: The surface instead of sliding along it), something known as the no-slip condition . Because the air at the surface has near-zero velocity but the air away from the surface is moving, there is a thin boundary layer in which air close to the surface is subjected to a shearing motion. The air's viscosity resists the shearing, giving rise to a shear stress at the airfoil's surface called skin friction drag . Over most of

12688-416: The surface is just part of this pressure field. The non-uniform pressure exerts forces on the air in the direction from higher pressure to lower pressure. The direction of the force is different at different locations around the airfoil, as indicated by the block arrows in the pressure field around an airfoil figure. Air above the airfoil is pushed toward the center of the low-pressure region, and air below

12810-405: The surface of a solid object applies a force on it. It does not matter whether the object is moving through a stationary fluid (e.g. an aircraft flying through the air) or whether the object is stationary and the fluid is moving (e.g. a wing in a wind tunnel) or whether both are moving (e.g. a sailboat using the wind to move forward). Lift is the component of this force that is perpendicular to

12932-428: The surface of most airfoils, the boundary layer is naturally turbulent, which increases skin friction drag. Under usual flight conditions, the boundary layer remains attached to both the upper and lower surfaces all the way to the trailing edge, and its effect on the rest of the flow is modest. Compared to the predictions of inviscid flow theory, in which there is no boundary layer, the attached boundary layer reduces

13054-409: The theorized Brittonicisms do not become widespread until the late Middle English and Early Modern English periods, in addition to the fact that similar forms exist in other modern Germanic languages. Old English contained a certain number of loanwords from Latin , which was the scholarly and diplomatic lingua franca of Western Europe. It is sometimes possible to give approximate dates for

13176-564: The time still lacked the letters ⟨j⟩ and ⟨w⟩ , and there was no ⟨v⟩ as distinct from ⟨u⟩ ; moreover native Old English spellings did not use ⟨k⟩ , ⟨q⟩ or ⟨z⟩ . The remaining 20 Latin letters were supplemented by four more: ⟨ æ ⟩ ( æsc , modern ash ) and ⟨ð⟩ ( ðæt , now called eth or edh), which were modified Latin letters, and thorn ⟨þ⟩ and wynn ⟨ƿ⟩ , which are borrowings from

13298-414: The upper surface can be clearly seen in this animated flow visualization . Like the equal transit time explanation, the "obstruction" or "streamtube pinching" explanation argues that the flow over the upper surface is faster than the flow over the lower surface, but gives a different reason for the difference in speed. It argues that the curved upper surface acts as more of an obstacle to the flow, forcing

13420-404: The usual ⟨ng⟩ . The addition of ⟨c⟩ to ⟨g⟩ in spellings such as ⟨cynincg⟩ and ⟨cyningc⟩ for ⟨cyning⟩ may have been a means of showing that the word was pronounced with a stop rather than a fricative; spellings with just ⟨nc⟩ such as ⟨cyninc⟩ are also found. To disambiguate,

13542-445: The velocity field also appear in theoretical models for lifting flows. The pressure is also affected over a wide area, in a pattern of non-uniform pressure called a pressure field . When an airfoil produces lift, there is a diffuse region of low pressure above the airfoil, and usually a diffuse region of high pressure below, as illustrated by the isobars (curves of constant pressure) in the drawing. The pressure difference that acts on

13664-410: The water and are typical of certain sailboats. Fixed hydrodynamic keels have the structural strength to support the boat's weight. In sailboats , keels serve two purposes: 1) as an underwater foil to minimize the lateral motion of the vessel under sail ( leeway ) and 2) as a counterweight to the lateral force of the wind on the sail(s) that causes rolling to the side ( heeling ). As an underwater foil,

13786-525: The wing acts like a venturi nozzle to constrict the flow. One serious flaw in the obstruction explanation is that it does not explain how streamtube pinching comes about, or why it is greater over the upper surface than the lower surface. For conventional wings that are flat on the bottom and curved on top this makes some intuitive sense, but it does not explain how flat plates, symmetric airfoils, sailboat sails, or conventional airfoils flying upside down can generate lift, and attempts to calculate lift based on

13908-423: The word was so nearly the same in the two languages that only the endings would put obstacles in the way of mutual understanding. In the mixed population which existed in the Danelaw, these endings must have led to much confusion, tending gradually to become obscured and finally lost. This blending of peoples and languages resulted in "simplifying English grammar". The inventory of Early West Saxon surface phones

14030-443: Was an allophone of short /ɑ/ which occurred in stressed syllables before nasal consonants (/m/ and /n/). It was variously spelled either ⟨a⟩ or ⟨o⟩. The Anglian dialects also had the mid front rounded vowel /ø(ː)/ , spelled ⟨œ⟩, which had emerged from i-umlaut of /o(ː)/ . In West Saxon and Kentish, it had already merged with /e(ː)/ before the first written prose. Other dialects had different systems of diphthongs. For example,

14152-439: Was based on the West Saxon dialect , away from the main area of Scandinavian influence; the impact of Norse may have been greater in the eastern and northern dialects. Certainly in Middle English texts, which are more often based on eastern dialects, a strong Norse influence becomes apparent. Modern English contains many, often everyday, words that were borrowed from Old Norse, and the grammatical simplification that occurred after

14274-481: Was either /ʃ/ or possibly /ʃː/ when the preceding vowel was short. Doubled consonants are geminated ; the geminate fricatives ⟨ff⟩ , ⟨ss⟩ and ⟨ðð⟩ / ⟨þþ⟩ / ⟨ðþ⟩ / ⟨þð⟩ are always voiceless [ff] , [ss] , [θθ] . The corpus of Old English literature is small but still significant, with some 400 surviving manuscripts. The pagan and Christian streams mingle in Old English, one of

14396-603: Was followed by such writers as the prolific Ælfric of Eynsham ("the Grammarian"). This form of the language is known as the " Winchester standard", or more commonly as Late West Saxon. It is considered to represent the "classical" form of Old English. It retained its position of prestige until the time of the Norman Conquest, after which English ceased for a time to be of importance as a literary language. The history of Old English can be subdivided into: The Old English period

14518-562: Was made between long and short vowels in the originals. (In some older editions an acute accent mark was used for consistency with Old Norse conventions.) Additionally, modern editions often distinguish between velar and palatal ⟨c⟩ and ⟨g⟩ by placing dots above the palatals: ⟨ċ⟩ , ⟨ġ⟩ . The letter wynn ⟨ƿ⟩ is usually replaced with ⟨w⟩ , but ⟨æ⟩ , ⟨ð⟩ and ⟨þ⟩ are normally retained (except when ⟨ð⟩

14640-411: Was spoken and Danish law applied. Old English literacy developed after Christianisation in the late 7th century. The oldest surviving work of Old English literature is Cædmon's Hymn , which was composed between 658 and 680 but not written down until the early 8th century. There is a limited corpus of runic inscriptions from the 5th to 7th centuries, but the oldest coherent runic texts (notably

14762-425: Was substantive, pervasive, and of a democratic character. Old Norse and Old English resembled each other closely like cousins, and with some words in common, speakers roughly understood each other; in time the inflections melted away and the analytic pattern emerged. It is most important to recognize that in many words the English and Scandinavian language differed chiefly in their inflectional elements. The body of

14884-546: Was the earliest recorded form of the English language , spoken in England and southern and eastern Scotland in the early Middle Ages . It developed from the languages brought to Great Britain by Anglo-Saxon settlers in the mid-5th century, and the first Old English literary works date from the mid-7th century. After the Norman Conquest of 1066, English was replaced for several centuries by Anglo-Norman (a type of French ) as

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