民航机务英语教程完整版.docx

民航机务英语教程完整版.docx

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民航机务英语教程完整版

民航机务英语教程【完整版】

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LessonOne

BernouIli’sPrincipleWhyPlanesFly

Aviationisdependentupontheprinciplediscoveredbyaneighteenthcenturyscientist，DanielBernoulli.①Bernoulli’sprinciplehelpstoexplainwhyanairplaneflies，howawingproduceslift，andhowfuelflowsinanaircraftcarburetor．Itexplainstherelationshipbetweenthepressure，thevo1umeandthevelocityofafluidinmotion．Simplystated，thevelocityofagivenvolumeofafluidinmotionisinverselyproportionaltoitspressure.Asvelocityincreases，pressuredecreases．Sincebothgasesandliquidsareclassifiedasfluids．We’lluseairtodemonstratethepropertiesofafluidinmotion．

ThereareseveralsimpleexperimentsthatdemonstrateBernoulli’sprinciple．Thesimplestmaybeconductedwithonlyasheetofpaper．②Holdthepaperuptoyourlipsfindblowacrossthetopsurface．Noticethatthepaperrises．Thevelocityoftheairoverthetopofthepaperisgreaterthanthatunderthepaper．Alowpressureareaiscreatedabovethepaperandthedifferenceinpressurecausesthepapertorise．Perhapsyouwalkpastthevacuumcleanerdepartmentofdepartmentstoreandyou’llseeaping—pongballsuspendedintheairabovevacuumcleanerseeminglywithoutsport．Theairpassingaroundthecurvedsurfaceoftheballistravelingfasterthantheairjustbeonthesurface．③Again,thehigherpressureoutsidetheairflowcausestheballtoremaininthecenteroftheairflow．

Anothersimpleexperimentusesapieceofpaper,astraightpinandasimplesewingspoo1．First，pushthepinthroughthepaperandinsertitintheholeinthespool，thepinsimplykeepthepaperfromdroppingtothefloor.Now,blowthroughtheotherendofthespool,alowpressureareaiscreatedasthevelocityoftheairincreasesbetweenthespoolandpaper．Thehigheratmosphericpressureonthebackofthepaperholdsthepaperclosetotheendofthespool．Theseexperimentsillustratethefactthatwhenthevelocityofthefluidincreases,thepressuredecreases．Conversely,whenthevelocitydecreases,thepressureIncreases

Howdoesthisapplytoaviation?

Let'splacearestrictioninthepathofmovingairinthiswindtunnel．Smokeinjectedintotheairstreamindicatesthepaththeairtakesaroundandthroughtherestriction．Therestrictioniscalledaventuri，agivenvolumeofairtravelsthroughandaroundtheventuriinagivenperiodoftime．Theentirevolumemustpassal1pointsinthesystem.Let’sconsider3moleculesofairtobeourgivenvolume，all3moleculesmustpassaroundandthroughtheventuriandmeetattheotherendatthesametime.Noticethatthemoleculepassingthroughtheventurimustfollowalongercurvedpath,travelingatgreaterdistanceinthesameperiodoftimeasthemoleculethatfollowsastraightpath．Thatmeansthemoleculestravelingthroughtheventurimusttravelfaster.AccordingtoBernoulli’sprinciple，asthevelocityincreases,pressuredecreases，thiscausesareducedpressureinthecenteroftheventuri，whilepressureremainsthesameateitherend．

Nowlet’slookatahalfsectionoftheventuri,doestheshaperemindyouanything?

Youarelookingatthecrosssectionofanairfoil，suchasawingtheprimaryliftproducingsurfaceofanaircraft．Thesameprincipleapplieshereasintheventuri，the2moleculesofairrepresentacertainvolume，bothmoleculesmustreachthetrailingedgeofthewingsectioninthesameperiodoftime，butthemoleculetravelingovertheuppersurfacemusttravelfurtherthantheonetravelingunderthewingbecauseacurvedpathitmustfollow.Again，themoleculetravelingthecurvedpathmusttraveltasterthantheonetravelingthestraightline.Thepressuredifferentialbetweentheupperandlowersurfacesofawingproducesliftthatkeepstheaircraftaloft④

Wemayillustratesimplythetremendousamountofforcethatgeneratedbylift．Supposethelowersurfaceofthewinghasanareaofabout15，000squareinches,rememberingthatpressureisaforceperunitarea,apressureof15lbs／inch²wouldproduceatotalforceonthebottomofthewingof225，000pounds．Thecurveduppersurfaceofthewinghasagreatersurfaceareathanthelowersurface，perhaps20，000squareinches．Howeverthepressureontheuppersurfaceislesspersquareinch．Ifthepressurewe’vereducedto10lbs／inch²ontheupperwingsurface，thetotalforcewouldbereducedto200，000pounds．Thedifferenceinpressurebetweenthelowerandupperwingsurfacesis25，000pounds．Thegreaterforceactingonthebottomwingsurface，thisisanextremelyoversimplifiedexplanationoftheproductionofliftonthewing．However，thebasicideaissound．⑤Thereareotherfactorstoconsider，suchastheshapeoftheairfoil，theangleofattack，andliftanddragcoefficientsaswellasthespeedoftheairfoilthroughtheair．We’veseenhowBernoulli’sprinciplecreatesliftonanaircraftwingwhetherinpoweredorunpoweredflight．⑥But，theprinciplealsoappliestoanyimportantfunctioninaircraftengines，specificallythefuelflowthroughanaircraftcarburetor．Let’sreturnforamomenttotheventuriinthewindtunnel，yourecallthatthepressureintherestrictionoftheventuriwaslowerthanthepressureoutsidetheventuri．Aventuriisfoundintheprimaryairpassageoffloat—typeaircraftcarburetor.Asairisdrawnintotheenginebythepistons，pressureisreducedinthroatofthecarburetor．Let’sinsertatubeinthenarrowestpartoftheventuri．andattachthetubetoafuelsupplywhichisopentoatmosphericpressure．Thedifferenceinpressurebetweenatmosphericpressureonthefuelsupplyandpressureintheventuricausesfueltoflowintotheventuriwherefuelismixedwithairbeforeenteringtheenginecombustionchambers．Venturiororificesmaybefoundinotherpartsoftheaircraft，inahydrauliclineorafuelcontrol，ameasuredorificeproducesameasuredpressuredifferentialbetweentwosidesoftheline，causingfluidtoflowatapre—determinedrate．

Let’sreviewwe’velearntabouttherelationshipofpressureandvelocityofafluidinmotion．Bernoulli’sprinciplesaysthatasthevelocityoffluidincreases，itspressuredecreases．Asthevelocityofairpassingthroughaventuriincreases，thepressureinthenarrowestpartoftheventuridecreases．Asthevelocityofairincreasesovertheuppersurfaceofawing，thepressuredecreases，theimbalanceofforcesbetweentheupperandlowarsurfacescausesthewingtorise．Bernoulli’sprincipleisalsopartlyresponsibleforfuelflowinanaircraftcarburetorwhichusesaventuriintheprimaryairpassage．Venturimayalsobeusedtocreateameasuredrateoffluidflow．Venturi-likeorificesarefoundinaircrafthydraulicsystemsandinfuelcontrols．

WordsandPhrases

Bernoulli’sprinciple贝努利原理

carburetor汽化器n．

inverselyproportional反比于

lip唇n．

throat咽喉，狭口n．

property性质n．

vacuumcleaner真空吸尘器

suspend悬挂v．

curvedsurface弯曲外表

sewingspool缝纫机线轴

conversely相反地ad．

restriction限定，节流n．

venturi文氏管，细腰管n．

molecule分子n．

crosssectionofanairfoil翼型剖面

sound完好的，合理的a．

angleofattack攻角，迎角

piston活塞n．

orifice小孔n．

liftanddragcoefficients升力和阻力系数

hydraulic液压的a．

reinforce加强v.

concept概念，根本原理n．

Notes

①Aviationisdependentupontheprinciplediscoveredbyaneighteenthcenturyscientist，DanielBernoulli．航空学与十八世纪科学家丹诺尔·贝努利所发现的原理密切相关。

tobedependentupon意为“依靠于…〞“取决于…〞。

discoveredby…是过去分词引导的定语修饰theprinciple。

②Thesimplestmaybeconductedwithonlyasheetofpaper．可用一张纸来进行最简单的试验。

tobeconductedwith意为“由…处理〞“由…进行〞。

asheetofpaper意为“一张纸〞，paper是不可数名词，所以一张纸必须用asheetof来表示，同样的用法还有许多。

③Theairpassingaroundthecurvedsurfaceoftheballistravelingfasterthantheairjustbeonthesurface．绕球曲面流过的气流比即将到达球外表的气流速度要快。

passingaroundthecurvedsurface是现代分词引起的定语，修饰theair；fasterthan…意为“比…快〞，比拟的内容前后要一致。

④Thepressuredifferentialbetweentheupperandlowersurfacesofawingproducesliftthatkeepstheaircraftaloft．机翼上下外表的压差产生了升力，使飞机保持在空中。

⑤Howeverthebasicideaissound．但根本思想是正确的。

sound在这里是形容词。

⑥We’veseenhowBernoulli’sprinciplecreatesliftonanaircraftwingwhetherinpoweredorunpoweredflight．我们已经看到了，不管是有动力飞行还是无动力飞行，贝努利原理是如何在机翼上产生升力的。

whether…or…意为“不管…还是…〞。

Grammar

用it作形式主语的各种结构

常见形式有：

请看下面例句：

Itisofteninconvenienttocombinevectorsbythegeometricmethod．

用几何方法来合成矢量通常是不便当的。

Itisworthwhiletouseanultra—highvacuumsystemforsuchpurpose．

把超高真空装置用于这种场合是有价值的。

Ifabodymovesfromonepositiontoanother，itissaidtohavehaddisplacement．

如果物体从一处移到另一处，就认为它有了位移。

Itiscommonpracticetobuildrocketsinpieces．

通常的做法是把火箭分级制造。

Ittakessunlightovereightminutestotraveltotheearth．

太阳光传播到地球要8分多钟。

Itrequiresalong—termpracticetobeagoodpilot．

要成为优秀的飞行员需要长时间的实践。

Itmakessteelweakinstrengthtorust．

生锈使钢的强度下降。

Exercises

1.Answerthefollowingquestions：

1）WhatrelationshipisdescribedmainlybyBernoulli’sprinciple?

2）Howthepaperbemovedwhenyouholdthepaperuptoyourlipsandblowacrossthetopsurface?

andwhy?

3）Inwhichsectionoftheventurithepressureislowestwhentheairstreampassesthetube?

4）Whytheairtravelingovertheuppersurfacemusttravelfurtherthantheairtravelingunderthewing?

5）Listsomefactorsthatmustbeconsidertocalculatetheliftexceptthepressuredifference．

6）Whatisthefunctionofthemeasuredorificeinahydrauliclineorafuelcontr017

7）Whythepoweredflightcomeintobeing?

（TheliftcanbecreatedbyjustthewingsaccordingtoBernoulli’sprinciple．）

2.Choosethecorrectanswer：

1）Whichoneisnotcorrect?

A．Bernoulli’sprinciplehavenotappliedintheaviation．

B．Whenthevelocityincreases，pressuredecrease．

C．Bernoulli’sprincipleistheonlyscientificprinciplerelatedtoflight．