民航机务英语教程完整版.docx

1、民航机务英语教程完整版民航机务英语教程【完整版】(文档可以直接使用，也可根据实际需要修订后使用,可编辑放心下载）Lesson OneBernouIlis Principle Why Planes FlyAviation is dependent upon the principle discovered by an eighteenth century scientist，Daniel Bernoulli. Bernoullis principle helps to explain why an airplane flies，how a wing produces lift，and how f

2、uel flows in an aircraft carburetorIt explains the relationship between the pressure，the vo1ume and the velocity of a fluid in motionSimply stated，the velocity of a given volume of a fluid in motion is inversely proportional to its pressure. As velocity increases，pressure decreasesSince both gases a

3、nd liquids are classified as fluidsWell use air to demonstrate the properties of a fluid in motionThere are several simple experiments that demonstrate Bernoullis principleThe simplest may be conducted with only a sheet of paperHold the paper up to your lips find blow across the top surfaceNotice th

4、at the paper risesThe velocity of the air over the top of the paper is greater than that under the paperA low pressure area is created above the paper and the difference in pressure causes the paper to risePerhaps you walk past the vacuum cleaner department of department store and youll see a pingpo

5、ng ball suspended in the air above vacuum cleaner seemingly without sportThe air passing around the curved surface of the ball is traveling faster than the air just be on the surfaceAgain, the higher pressure outside the airflow causes the ball to remain in the center of the airflowAnother simple ex

6、periment uses a piece of paper, a straight pin and a simple sewing spoo1First，push the pin through the paper and insert it in the hole in the spool，the pin simply keep the paper from dropping to the floor . Now, blow through the other end of the spool, a low pressure area is created as the velocity

7、of the air increases between the spool and paperThe higher atmospheric pressure on the back of the paper holds the paper close to the end of the spoolThese experiments illustrate the fact that when the velocity of the fluid increases, the pressure decreasesConversely, when the velocity decreases, th

8、e pressure IncreasesHow does this apply to aviation? Lets place a restriction in the path of moving air in this wind tunnelSmoke injected into the air stream indicates the path the air takes around and through the restrictionThe restriction is called a venturi，a given volume of air travels through a

9、nd around the venturi in a given period of timeThe entire volume must pass al1 points in the system. Lets consider 3 molecules of air to be our given volume，all 3 molecules must pass around and through the venturi and meet at the other end at the same time. Notice that the molecule passing through t

10、he venturi must follow a longer curved path, traveling at greater distance in the same period of time as the molecule that follows a straight pathThat means the molecules traveling through the venturi must travel faster. According to Bernoullis principle，as the velocity increases, pressure decreases

11、，this causes a reduced pressure in the center of the venturi，while pressure remains the same at either endNow lets look at a half section of the venturi, does the shape remind you anything? You are looking at the cross section of an airfoil，such as a wing the primary lift producing surface of an air

12、craftThe same principle applies here as in the venturi，the 2 molecules of air represent a certain volume，both molecules must reach the trailing edge of the wing section in the same period of time，but the molecule traveling over the upper surface must travel further than the one traveling under the w

13、ing because a curved path it must follow. Again，the molecule traveling the curved path must travel taster than the one traveling the straight line. The pressure differential between the upper and lower surfaces of a wing produces lift that keeps the aircraft aloftWe may illustrate simply the tremend

14、ous amount of force that generated by liftSuppose the lower surface of the wing has an area of about 15，000 square inches, remembering that pressure is a force per unit area, a pressure of 15 lbsinch would produce a total force on the bottom of the wing of 225，000 poundsThe curved upper surface of t

15、he wing has a greater surface area than the lower surface，perhaps 20，000 square inchesHowever the pressure on the upper surface is less per square inchIf the pressure weve reduced to 10 lbsinch on the upper wing surface，the total force would be reduced to 200，000 poundsThe difference in pressure bet

16、ween the lower and upper wing surfaces is 25，000 poundsThe greater force acting on the bottom wing surface，this is an extremely over simplified explanation of the production of lift on the wingHowever，the basic idea is soundThere are other factors to consider，such as the shape of the airfoil，the ang

17、le of attack，and lift and drag coefficients as well as the speed of the airfoil through the airWeve seen how Bernoullis principle creates lift on an aircraft wing whether in powered or unpowered flightBut，the principle also applies to any important function in aircraft engines，specifically the fuel

18、flow through an aircraft carburetorLets return for a moment to the venturi in the wind tunnel，you recall that the pressure in the restriction of the venturi was lower than the pressure outside the venturiA venturi is found in the primary air passage of floattype aircraft carburetor. As air is drawn

19、into the engine by the pistons，pressure is reduced in throat of the carburetorLets insert a tube in the narrowest part of the venturiand attach the tube to a fuel supply which is open to atmospheric pressureThe difference in pressure between atmospheric pressure on the fuel supply and pressure in th

20、e venturi causes fuel to flow into the venturi where fuel is mixed with air before entering the engine combustion chambersVenturi or orifices may be found in other parts of the aircraft，in a hydraulic line or a fuel control，a measured orifice produces a measured pressure differential between two sid

21、es of the line，causing fluid to flow at a predetermined rateLets review weve learnt about the relationship of pressure and velocity of a fluid in motionBernoullis principle says that as the velocity of fluid increases，its pressure decreasesAs the velocity of air passing through a venturi increases，t

22、he pressure in the narrowest part of the venturi decreasesAs the velocity of air increases over the upper surface of a wing，the pressure decreases，the imbalance of forces between the upper and lowar surfaces causes the wing to riseBernoullis principle is also partly responsible for fuel flow in an a

23、ircraft carburetor which uses a venturi in the primary air passageVenturi may also be used to create a measured rate of fluid flowVenturi-like orifices are found in aircraft hydraulic systems and in fuel controls Words and PhrasesBernoulli s principle 贝努利原理carburetor 汽化器ninversely proportional 反比于li

24、p 唇nthroat 咽喉，狭口nproperty 性质nvacuum cleaner 真空吸尘器suspend 悬挂vcurved surface 弯曲外表sewing spool 缝纫机线轴conversely 相反地adrestriction 限定，节流nventuri 文氏管，细腰管nmolecule 分子ncross section of an airfoil 翼型剖面sound 完好的，合理的aangle of attack 攻角，迎角piston 活塞norifice 小孔nlift and drag coefficients 升力和阻力系数hydraulic 液压的areinf

25、orce 加强v.concept 概念，根本原理nNotesAviation is dependent upon the principle discovered by an eighteenth century scientist，Daniel Bernoulli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。to be dependent upon意为“依靠于“取决于。discovered by是过去分词引导的定语修饰the principle。The simplest may be conducted with only a sheet of paper 可用一张纸来进行最简单的

26、试验。to be conducted with意为“由处理“由进行。a sheet of paper意为“一张纸，paper是不可数名词，所以一张纸必须用a sheet of来表示，同样的用法还有许多。The air passing around the curved surface of the ball is traveling faster than the air just be on the surface绕球曲面流过的气流比即将到达球外表的气流速度要快。passing around the curved surface是现代分词引起的定语，修饰the air；faster than

27、意为“比快，比拟的内容前后要一致。 The pressure differential between the upper and lower surfaces of a wing produces lift that keeps the aircraft aloft机翼上下外表的压差产生了升力，使飞机保持在空中。However the basic idea is sound但根本思想是正确的。sound在这里是形容词。Weve seen how Bernoullis principle creates lift on an aircraft wing whether in powered o

28、r unpowered flight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。whetheror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：It is often inconvenient to combine vectors by the geometric method用几何方法来合成矢量通常是不便当的。It is worthwhile to use an ultrahigh vacuum system for such purpose把超高真空装置用于这种场合是有价值的。If a body moves fr

29、om one position to another，it is said to have had displacement如果物体从一处移到另一处，就认为它有了位移。It is common practice to build rockets in pieces通常的做法是把火箭分级制造。It takes sunlight over eight minutes to travel to the earth太阳光传播到地球要8分多钟。It requires a longterm practice to be a good pilot要成为优秀的飞行员需要长时间的实践。It makes stee

30、l weak in strength to rust生锈使钢的强度下降。 Exercises1. Answer the following questions：1) What relationship is described mainly by Bernoullis principle?2) How the paper be moved when you hold the paper up to your lips and blow across the top surface? and why?3) In which section of the venturi the pressure

31、is lowest when the air stream passes the tube?4) Why the air traveling over the upper surface must travel further than the air traveling under the wing?5) List some factors that must be consider to calculate the lift except the pressure difference6) What is the function of the measured orifice in a

32、hydraulic line or a fuel contr01 77) Why the powered flight come into being? (The lift can be created by just the wings according to Bernoullis principle)2. Choose the correct answer：1) Which one is not correct?ABernoullis principle have not applied in the aviationBWhen the velocity increases，pressure decreaseCBernoullis principle is the only scientific principle related to flight