民航机务英语教程.doc

Lesson One
BernouIli’s Principle Why Planes Fly
Aviation is dependent upon the principle discovered by an eighteenth century scientist，Daniel Bernoulli. ①Bernoulli’s principle helps to explain why an airplane flies，how a wing produces lift，and how fuel flows in an aircraft carburetor．It explains the relationship between the pressure，the vo1ume and the velocity of a fluid in motion．Simply stated，the velocity of a given volume of a fluid in motion is inversely proportional to its pressure. As velocity increases，pressure decreases．Since both gases and liquids are classified as fluids．We’ll use air to demonstrate the properties of a fluid in motion．
There are several simple experiments that demonstrate Bernoulli’s principle．The simplest may be conducted with only a sheet of paper．②Hold the paper up to your lips find blow across the top surface．Notice that the paper rises．The velocity of the air over the top of the paper is greater than that under the paper．A low pressure area is created above the paper and the difference in pressure causes the paper to rise．Perhaps you walk past the vacuum cleaner department of department store and you’ll see a ping—pong ball suspended in the air above vacuum cleaner seemingly without sport．The air passing around the curved surface of the ball is traveling faster than the air just be on the surface．③Again, the higher pressure outside the airflow causes the ball to remain in the center of the airflow．
Another simple experiment uses a piece of paper, a straight pin and a simple sewing spoo1．First，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 of the air increases between the spool and paper．The higher atmospheric pressure on the back of the paper holds the paper close to the end of the spool．These experiments illustrate the fact that when the velocity of the fluid increases, the pressure decreases．Conversely, when the velocity decreases, the pressure Increases
How does this apply to aviation? Let's place a restriction in the path of moving air in this wind tunnel．Smoke injected into the air stream indicates the path the air takes around and through the restriction．The restriction is called a venturi，a given volume of air travels through and around the venturi in a given period of time．The entire volume must pass al1 points in the system. Let’s 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 the venturi must follow a longer curved path, traveling at greater distance in the same period of time as the molecule that follows a straight path．That means the molecules traveling through the venturi must travel faster. According to Bernoulli’s principle，as the velocity increases, pressure decreases，this causes a reduced pressure in the center of the venturi，while pressure remains the same at either end．
Now let’s 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 aircraft．The 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 wing 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 aloft④
We may illustrate simply the tremendous amount of force that generated by lift．Suppose 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 lbs／inch² would produce a total force on the bottom of the wing of 225，000 pounds．The curved upper surface of the wing has a greater surface area than the lower surface，perhaps 20，000 square inches．However the pressure on the upper surface is less per square inch．If the pressure we’ve reduced to 10 lbs／inch² on the upper wing surface，the total force would be reduced to 200，000 pounds．The difference in pressure between the lower and upper wing surfaces is 25，000 pounds．The greater force acting on the bottom wing surface，this is an extremely over simplified explanation of the production of lift on the wing．However，the basic idea is sound．⑤There are other factors to consider，such as the shape of the airfoil，the angle of attack，and lift and drag coefficients as well as the speed of the airfoil through the air．We’ve seen how Bernoulli’s principle creates lift on an aircraft wing whether in powered or unpowered flight．⑥But，the principle also applies to any important function in aircraft engines，specifically the fuel flow through an aircraft carburetor．Let’s 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 venturi．A venturi is found in the primary air passage of float—type aircraft carburetor. As air is drawn into the engine by the pistons，pressure is reduced in throat of the carburetor．Let’s insert a tube in the narrowest part of the venturi．and attach the tube to a fuel supply which is open to atmospheric pressure．The difference in pressure between atmospheric pressure on the fuel supply and pressure in the venturi causes fuel to flow into the venturi where fuel is mixed with air before entering the engine combustion chambers．Venturi 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 sides of the line，causing fluid to flow at a pre—determined rate．
Let’s review we’ve learnt about the relationship of pressure and velocity of a fluid in motion．Bernoulli’s principle says that as the velocity of fluid increases，its pressure decreases．As the velocity of air passing through a venturi increases，the pressure in the narrowest part of the venturi decreases．As 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 rise．Bernoulli’s principle is also partly responsible for fuel flow in an aircraft carburetor which uses a venturi in the primary air passage．Venturi may also be used to create a measured rate of fluid flow．Venturi-like orifices are found in aircraft hydraulic systems and in fuel controls．

Words and Phrases
Bernoulli’ s principle 贝努利原理
carburetor 汽化器n．
inversely proportional 反比于
lip 唇n．
throat 咽喉，狭口n．
property 性质n．
vacuum cleaner 真空吸尘器
suspend 悬挂v．
curved surface 弯曲表面
sewing spool 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．
cross section of an airfoil 翼型剖面
sound 完好的，合理的a．
angle of attack 攻角，迎角
piston 活塞n．
orifice 小孔n．
lift and drag coefficients 升力和阻力系数
hydraulic 液压的a．
reinforce 加强v.
concept 概念，基本原理n．

Notes
①Aviation 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。
②The simplest may be conducted with only a sheet of paper． 可用一张纸来进行最简单的试验。
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。
③The 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表面的气流速度要快。
passing around the curved surface是现代分词引起的定语，修饰the air；faster than…意为“比…快”，比较的内容前后要一致。
④The pressure differential between the upper and lower surfaces of a wing produces lift that keeps the aircraft aloft．机翼上下表面的压差产生了升力，使飞机保持在空中。
⑤However the basic idea is sound．但基本思想是正确的。sound在这里是形容词。
⑥We’ve seen how Bernoulli’s principle creates lift on an aircraft wing whether in powered or unpowered flight．我们已经看到了，不论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：
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 ultra—high 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 from 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 long—term 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 steel weak in strength to rust．
生锈使钢的强度下降。

Exercises
1. Answer the following questions：
1) What relationship is described mainly by Bernoulli’s 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 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 difference．
6) What is the function of the measured orifice in a hydraulic line or a fuel contr01 7
7) Why the powered flight come into being? (The lift can be created by just the wings according to Bernoulli’s principle．)
2. Choose the correct answer：
1) Which one is not correct?
A．Bernoulli’s principle have not applied in the aviation．
B．When the velocity increases，pressure decrease．
C．Bernoulli’s principle is the only scientific principle related to flight．
D．Airfoil can be considered as a part of venturi．
2) Bernoulli’s principle expresses the relationship between ·
A．time and velocity of a fluid in motion
B．velOCity and distance of a motion fluid
C．pressure and friction of a liquid
D．velocity and pressure of motion fluid
3) several simple experiments that demonstrate Bernoulli’s principle．
A．There is B．Here is
C．This are D．There are
4) The curved upper surface of the wing has a surface area than the lower surface．
A．great B．greatly
C．greatest D．greater
5) It is that keeps the aircraft aloft．
A．the pressure differential between’ the upper and lower surface of a wing
B．the high velocity of air below the lower wing surface
C．the small area of upper wing surface
D．the large area of lower wing surface
6) The basic idea is sound，means that
A．the basic idea is noise
B．the basic idea is well voice
C．the basic idea is correct
D．the basic idea is hearing
7) The same principle applies here in the venturi．
A．as B. than C．that D．to
8) Since both gases and liquids as fluids．We will use air to demonstrate the principle of a fluid in motion．
A．be classified
B．classify
C．is classified
D．are classified
9) Aviation is dependent the Bernoulli’s principle．
A．to B．for C．upon D．at
10) The fuel is mixed air．
A．with B．to C．in D．at

Lesson Two
Area and Volume
The study of mathematics is basic to the training of professional aviation maintenance technician．To watch your career，you’ll be required to make mathematic calculations that are vital to the successful completion 0f many tasks．We study in practice，①these calculations may be made safely and easily ensuring the accuracy of your work．Among the most important these calculations used frequently in aviation maintenance，are the measurement of area and volume．Sheet metal for airframe repairs is ordered and sold by the square foot，know exactly how much material to order for particular job，save the customer and your employer money by eliminating waste．Engine horsepower is based in part on the cubic inch displacement or volume of the engine cylinders．
First，let’s consider the calculation of area．Everyday objects such as this wooden block are measured in three dimensions：length，width and thickness or depth．In calculating the area of one surface of the block，we concern with②only two of these dimensions：length and width．These two measurements describe a plane surface．A rectangle is a four sided plane surface with opposite side equally length and with 90 degrees or right angles between adjacent sides③．It is one of simplest plane surfaces．
The formula for calculating the area of rectangle is length multiplied by width④．L being the length of one of the sides，and W being the width of one of adjacent sides．In our example，the length of one side is 144 inches，and width of the other side is 48 inches，multiply，we find the area of the rectangle is 6，912 square inches．Area measurements are described in square units．
Square is a unique form of rectangle in which all sides are equal lengths．The angle between adjacent sides is again 90 degrees．The calculation of the area of a square is done basically the same as that of rectangle．Since all sides are the same lengths，we can give them all the same symbol：S．Simply multiply the length of one side by the same number，this is called squaring the number．Our formula for the area of a square becomes simply as S②．
The next figure we’ll consider is the triangle．A triangle is a three sided plane figure，the sum of the three angles in a triangle always equals 180 degrees．As some interesting comparisons between the triangle and rectangle，that may help you better understand the method of calculating the area of the triangle．You notice that the rectangle has four angles that when added together equals 360 degrees．The sum of three angles of triangle add up to 1 80 degrees or half of the angular measurement of the rectangle．The area of the triangle is equal to half of the area of rectangle that would enclose it．Here is how that works，the three sides of triangle are the base，indicated by the letter B，the altitude，shown here in the letter A，and hypotenuse．For calculating the area，only the base and altitude measurements are necessary．If we will do a enclosure of our triangles into a rectangle，we would see that the base and altitude measurements are equivalent to the length and width measurements of rectangle．⑤However，the area of the triangle would only be half the area of the rectangle．Using the formula for calculating the area of rectangle and substituting the base and altitude notations for the length and width of rectangle．We see that the area of the triangle is the base multiplied by the altitude，that product divided by two，this formula will work for the calculations of all triangles．We’ve just used an isosceles triangle for our example，and isosceles triangle is on