Exercise 15. Do the two-way translation.

1. Чем создается сила для движения самолета в воздухе?   2. Из чего состоит двигательная система? 3. Что такое двигатель?   4. Каким требованиям должна отвечать двигательная система самолета? 5. Как распределяется полный вес самолета?   6. Как увеличить надежность двигательной системы? 7. Какие типы двигателей существуют?

1. The force is provided by the propulsion system to move an airplane through the air.   2. The propulsion system consists of the fuel and the engine. 3. The engine is the mechanical device by which the energy of the fuel is transformed into the propulsive force. 4. The propulsion system must meet certain requirements. It must have low weight, high reliability and low cost. 5. The total weight of an airplane can be divided among the airframe, the propulsion system and the payload.   6. Overall propulsion system reliability is increased by using more than one engine. 7. There are gasoline engines, diesel engines, gas turbines, steam engi­nes, steam turbines, jet engines and rocket engines.

Exercise 16. Ask questions.

1. …?

The power plant is a device that produces mechanical power or energy.

2. …?

Every propulsion system consists of the fuelwhich is the energy source and the engine which is the mechanical device.

3. …?

The total weight of the airplane can be divided among the airframe, the propulsion system and the payload.

4...?

The payload consists of the crew, equipment and cargo.

5…?

The designers work at the problem of getting lower specific fuel consumption.

6…?

Specific fuel consumption is obtained by dividing the weight of the fuel burned per hour by the horse power developed.

7…?

The engine must run smoothly and operate at all speeds and in all weather conditions.

8…?

Overall propulsion system reliability is increased by using more than one engine.

9…?

There are many types of engines used today for different purposes.

Texts For Reading And Writing Practice

Dialogue 1.

Instructor: Historically, there are three types of compressors, used in aviation jet engines. These are centrifugal compressors, axial flow compressors and hybrid compressors. Each of these types has its own advantages and disadvantages.

Nick: Up to now we have discussed only axial flow compressors. Does it mean that they are the most efficient type?

Instructor: Yes, it does. Axial flow compressors are the most efficient and the most complex type of compressors, and they are used in most jet engines. On the other hand, centrifugal compressors are very simple and robust, very easy to manufacture, but, unfortunately, their efficiency is low.

Nick: Are the axial compressors mounted on the turbine shaft?

Instructor: Yes. The axial compressors force the air straight backwards by means of a series of multi-blade fans mounted one behind the other.

 

Axial Compressor

Vocabulary:

1. duct 2. to upset 3. to stall 4. coughing 5. short-like sound 6. to surge 7. bangs 8. shrouding

- канал - нарушать - работать в режиме срыва потока - звуки, похожие на кашель - звуки, похожие на выстрел - работать в режиме помпажа - взрывоподобные звуки - бандажирование законцовок лопаток

An axial compressor is a mechanical device for causing a pressure rise in the air delivered to the combustion chamber. There is a constant relationship between the volume, the temperature and the pressure of the air as it passes through the axial compressor. The temperature of the air at any point of the duct is the product of the pressure and the volume of that air.

When the volume of the air is being reduced in an axial compressor, there is a rise in both pressure and temperature. The more efficient is the design of the compressor, the higher will be the rise in pressure. The efficiency of an axial-flow compressor depends primarily upon the design of its rotor and stator blades.

Rotor blades have airfoil cross-sections and are made of aluminum alloy, steel or titanium. They can operate with maximum efficiency only within a limited range of operating conditions. Outside this range the smooth flow of air in the compressor is usually upset by unwanted turbulence. When one stage of the compressor is upset by turbulence, it is said that the compressor stalls. The stalling compressor usually develops severe vibrations or coughing. Sometimes it may even produce shot-like sounds. When all stages of the compressor are upset by turbulence, it is said that the compressor surges. The surging compressor produces powerful bangs, the temperature of the exhaust gases rapidly rises and the engine may be partially or wholly damaged. Stator blades may be attached directly to the casing of the compressor, with connecting shrouding at the tips to give them greater stability.

 

Dialogue 2.

Instructor: This time we are going to discuss the central part of the jet engine - its combustion chamber. This is the place where fuel is mixed with the air from the compressor and ignited.

Peter: It must be quite complex!

Instructor: On the contrary, you'll be surprised by its simplicity! Just imagine two tubes, one inside the other. The inside one, called the flame tube, is fitted at the front with a perforated flare, located behind an entry snout. In the center of the flare there are a number of swirl vanes.

Nick: Up to now, it's quite simple.

Instructor: The air comes from the compressor at high velocity of one or two hundred meters per second...

Peter. It can surely blow out the flame.

Instructor: Very definitely it can. Besides, there is more available air than is needed for combustion. And this is the reason why there are two tubes: only the quantity of air needed for combustion goes into the inner tube, the rest passes outside it.

Nick: The flare clearly helps to decrease the velocity of the air entering the flame tube.

Peter: And also to raise its temperature and pressure.

Instructor: You're both right!

Peter: I don't see why the compressor should be made to deliver so much air when only part of it is needed for combustion.

Instructor: The temperature of the gases leaving the combustion zone may be as high as 2000 degrees Centigrade. This is too hot to feed into the turbine. About half of the excess air is needed to dilute and cool these exhaust gases.

 

The Combustion Chamber

Vocabulary:

1. multiple combustion chamber layout 2. layout 3. flame tube 4. tubo-annular 5. casing

- трубчатая конструкция камеры сгорания   - схема, расположение - жаровая труба - трубчато – кольцевая - корпус, кожух

 

Combustion chambers are mechanical devices for burning air-fuel mixture. They may be installed in the engine in a number of different ways. The multiple combustion chamber layout is used with engines having centrifugal compressors. In this layout a number of flame tubes are disposed radially round the engine. Annular and tubo-annular designs of combustion chambers are more often used presently.

The flame tube of annular combustion chambers is in the form of a double ring which in turn is fitted into an annular casing of two more rings. Tubo-annular combustion chambers have flame tubes grouped round the engine, as in the multiple layout, but instead of each having a separate outer casing, they are all disposed in a common annular cas­ing, shaped like two broad rings, one inside the other.

Tubo-annular chambers are easier to manufacture and overhaul, while annular chambers, besides possessing these advantages, are also more compact. Annular chambers are more fuel-efficient and reduce many of the problems of air pollution. All combustion chambers must be capable to withstand very high temperatures, rapid changes of temperature and corrosive effects produced by the products of combustion.

 

Dialogue 3.

Instructor: The basic principles of gas turbine design are easy to understand, but their practical application is very complicated, to say the least. First, what does the turbine do?

Peter: It drives the compressor, of course.

Instructor: Anything else?

Nick: I suppose it drives various accessories, too. Fuel pumps, electric generators, and things like that.

Peter: In turbo-prop aircraft it drives the propeller shaft, in helicopters it drives the rotor shaft, both through reduction gears.

Instructor: You're both well in the picture! I am very impressed!

Now let's see how a turbine operates. The hot exhaust gases from the combustion chamber first pass fixed nozzle guide vanes.

Peter: They look like stator vanes in a compressor, don't they?

Instructor: Yes, in a way. But actually they are quite different. Firstly, they have complex cooling ducts inside. Secondly, they are monocrystallic that is produced from a piece of metal, grown as a single crystal.

Nick: What substance is used as a cooling agent?

Instructor: As a cooling agent is used common air, bled from a compressor stage. Immediately behind the fixed nozzle guide vanes are the rotating blades of the turbine. These are the most critical items of the whole jet engine. In modern jet engines they have to withstand temperatures of up to 1400 degrees Centigrade and strains of up to three or four tons.

Peter: I think that design and manufacture of such blades must be quite a problem!

Instructor: This is the field of what is known as very high technologies and top secret know-how.

Nick: How many turbines may modern high bypass ratio engines have?

Instructor: Modern high bypass ratio jet engines may have three gas turbines, and three concentric shafts, running independently. Such engines are very fuel efficient and also extremely quiet.

The Gas Turbine

Vocabulary:

1. driving torque 2. triple-spool system 3. power-to-weight ratio 4. bearing

- вращающийся момент - трехвальная система - удельная мощность - подшипник

The gas turbine provides the power to drive the compressor and accessories. It does this by extracting energy from the hot gases released from the combustion chamber and expanding them to lower pressure and temperature. High stresses are involved in this process, and for efficient operation, the turbine blade tips may rotate at speeds up to 500 meters per second. The continuous flow of gas, to which the turbine is exposed may have an entry temperature of up to 1400°C and may reach a velocity up to 700 meters per second in some parts of the turbine.

To produce the driving torque, the turbine may consist of several stages, each employing one row of stationary nozzle guide vanes and one row of moving blades. The number of stages depends on whether the engine has one shaft or two and also on the relation between the power required from the gas flow, the rotational speed at which it must be produced and the diameter of turbine permitted.

The number of shafts varies with the type of engine. High compression ratio engines usually have two shafts driving high and low pressure compressors. On high bypass ratio fan engines another turbine is interposed between the high and low pressure turbines, thus forming a triple-spool system.

The bypass engine enables a smaller turbine to be used than in a pure jet engine for a given thrust output and it operates at a higher gas inlet temperature, thereby obtaining improved thermal efficiency and power-to-weight ratio.

The balancing of a turbine is an extremely important operation in its manufacture and maintenance. In view of the high rotational speeds and the mass of materials, any unbalance could seriously affect the rotating assembly bearings and engine operation. Balancing is effected on a special balancing machine and is conducted after each maintenance operation connected with replacements of blades, discs and bearings.

 

The Exhaust System

Vocabulary:

1. to impede 2. afterburning 3. eyelids 4. nozzle aperture 5. pneumatic rams 6. divergent passage

- препятствовать - дожиг топлива - створки, заслонки - отверстие сопла - пневматические толкатели - расширяющийся канал

 

The exhaust system of a jet engine passes the turbine discharge gases to atmosphere at a velocity, and in the required direction to provide the resultant thrust. Great care must be taken in the design of the exhaust system at the rear of the engine. If the flow of exhaust gases is impeded by too small an exit, temperatures and pressures will be built up inside the engine, while too large an exit will make them fall, and create a loss of thrust.

When afterburning is in operation, the area of the exhaust nozzle can be increased by opening two eyelids that partially obstruct the nozzle aperture when closed. The pilot actuates these eyelids by pneumatic rams which in turn are linked to the fuel supply system. As they open the supply of fuel is increased.

Bypass engines can benefit spectacularly from the use of afterburning. Thrust can be increased by 70% or more for short periods of time. This enables the airplanes to reach an economical cruising height far more quickly than planes not fitted with afterburners.

As a rule it can be said that forward thrust is created wherever there are divergent passages which convert velocity into pressure energy. Following the air as it passes through the engine, we see that considerable thrust is developed in the compressor because of the rise in pressure there.

 

Exercise 1. Group the words according to the theme:

a) engine components

b) engine operation

c) classification of the jet engines

 

To have some limitations, combustion chamber, to eject with high velocity, in comparison with, axial compressor, to belong to the family of gas - turbine engines, discharge nozzle, in contrast to, to deliver the air, the simplest type of air-breathing engines, fuel-air mixture, inlet assembly, to expand in the exhaust nozzle, to differ from other engines, liquid propellant rocket engines, to utilize air from the atmosphere, to combine features of some engines, to produce high temperature gases, to find wide application in aviation.