6. Турбовентиляторний двигун являє собою варіант турбогвинтового двигуна. 7. Турбовальні двигуни використовуються в гелікоптерах. 8.Турбовальний двигун приводить до руху привідний вал ротора гелікоптера 9. Силова установка рухає літак вперед та забезпечує необхідну піднімальну силу. 10. Поршневі двигуни повністю замінені реактивними.
Exercise 47. Translate and entitle text 6.
The ПС-90 A is a two-spool, high bypass ratio turbofan engine with flow mixing, fitted with a common exhaust nozzle and thrust reverser. Structurally the engine is made of 11 modules which except for the main one can be replaced. Provision has also been made for replacement of separate parts of the modules and of the parts most likely to get damaged, such as fan blades and compressor pressure stages, flame tubes, combustion chamber jets, thrust reverser cascade , vanes. I
The engine is equipped with the compressor and turbine radial clearances control system. The engine gas flow duct is fitted with / sound-absorbing components.
Exercise 48. Read and translate text 7 in a written form. , ,»
Text 7. Turbojets
Gas-turbine engines for aircraft come in many types and sizes, each of which has its advantages and also its limitations. The moat common type is die uncomplicated turbojet. Because they have щ added features such as a fan, propeller, or free turbine, turbojets ащ sometimes referred to as straight jets.
Most turbojets operate best at relatively high altitude, in th$ / 25,000 to 40,000-foot range, although they are able to go very mucjf, higher, if need be. There is no simple explanation for the fact that і turbojets are so well suited to high-altitude operation. The high-altitud«i capability of a turbojet is due to a number of reasons, some of which arq rather complex. For one thing, this capability is designed into an engine at the time the plans are first laid down on a drawing board. Far another, the cold temperature of the air at high altitude gives an engine extra thrust. More importantly, the rarified atmosphere at high altitude reduces airplane drag (which may be thought of as the air resistance of flight). Low drag means that the Mach number selected for cruising can be attained at a low engine thrust setting. This, in turn, results in a
relatively low fuel consumption for the airspeed attained — a feature that makes for economical operation.
But, good as they are at their optimum altitude, high thrust at low airspeed is not a turbo-jet characteristic. To be at their best, turbojets need the ram-air pressure at their inlet which comes only with speed. Therefore, they require very long runways for take-off.
Turbojets are classified according to the kind of compressor they use. For years, they had only centrifugal compressors because this was the type that designers knew best how to build. Centrifugal compressors operate by taking in air near a hub at the centre and rotating it with an impeller.
As the impeller whirls the air at high speed, centrifugal force carries the air to the perimeter of the impeller at a considerable velocity. Here the air is collected in a diffuser to increase the pressure, then led to a manifold which, in turn, feeds it to the engine's burners.
The early centrifugal compressor turbojets were (and still are) both reliable and simple. But the amount of thrust they can produce is relatively low because their compression ratio is not very high. Nevertheless, there are several turbo-prop and turbo-shaft engines now in current production that employ a compressor arrangement using one or more centrifugal-type compressors. The improved design of these engines makes them far superior to the centrifugal-compressor power- plants of several years ago.
The majority of today's turbojets use an axial compressor. Axial compressors are used, especially in the larger engines, because they are capable of producing high compression ratios, sometimes as high as 13 : 1, or more An axial compressor, as the name implies, compresses air as it flows in an axial direction through an engine. A series of rotating blades and stationary vanes work on the air as it passes through a series of stages inside the compressor. Each stage adds to the compression process.
There are two types of axial-compressor engines, those with so- called single compressors and those with dual compressors In dualcompressor engines (sometimes called twin-spool engines), there are two compressors that are mechanically independent of one another, although they are related as to airflow. Each compressor has its own turbine. The turbine for .the forward, or low-pressure compressor, is the rear turbine. It is connected to the low-pressure compressor by a dri1 shaft that passes through the hollow dnve shaft for the high-presj compressor and turbine unit.
Exercise 49. Make a summary of text 7.
Exercise 50. Write out all the terms referring to the “Turbojets”.
Exercise 51. Make up the plan of the topic “Turbojets ”.
Exercise 52. Translate text 8 in writing
Text 8. Rocket Engines 5'
There are two general types of rockets : the solid-propellant госЫ; and the liquid ся- bipropellant rocket Rocket fuels and oxidizers are called propellants.
Solid-propellant rockets are simplest in arrangement and leaif susceptible to control. Liquid-propellant rockets are somewhat complex than the solid type, but they are susceptible to a much ] range of control during operation. This control is accomplished by varying the rate of flow of the fuel and oxidizer to the combustion chamber. .
' ГГ?' • ■'''"■і:
The rocket engine consists of a propellant injector, combustirift ■ chamber surrounded by a cooling jacket, and a nozzle to allow the , natural expansion of the combustion gases.
The rocket engines all operate on the same principle whether the^; are solid-fuel or liquid-fuel types.
Exercise 53. Give your opinion on texts 5, 6, 7, 8 using theaM sentences. і
describes ... в тексті описується ... considers ... в тексті розглядається... Exercise 54. Speak on:
Jet engine operation.
Advantages of jet engines.
If a gas generator (turbojet) turns an aircraft propeller through a system of gears, it becomes a turboprop. The propeller-drive reduction gearing may be driven by the shaft from the same turbine that rotates the compressor, or the gearing may be driven by a shaft from a so-called free turbine that rotates independently in the exhaust gas stream of the basic gas generator. In either case, the gas generator for a turboprop might be either a single- or dual-compressor type, although, as this is written, there are no dual-axial compressor turboprops in production.
Although a turboprop is more complicated and heavier than a turbo-jet engine of equivalent size and power, it will deliver more thrust up to medium-high subsonic airspeeds. However, the advantage decreases as flight speed increases. In normal cruising-speed ranges, the propulsive efficiency (output divided by input) of a turboprop remains more or less constant, whereas the propulsive efficiency of a turbojet increases rapidly as airspeed increases The spectacular performance of a turboprop during take-off and climb is the result of the ability of the propeller to accelerate a large mass of air while the aircraft is moving at relatively low ground and flight speed.
Farrjets and turbofans are one and the same thing. In principle, the turbofan (or fanjet) is the same as the turboprop except that the ratio of the secondary airflow (i.e., the airflow through the fan or propeller) to the primary airflow through the basic engine is less. Also, in the
turbofan, the gear-driven propeller is replaced by a duct-enclosed, axial- ” flow fan whose rotating blades and stationary vanes are considerably ! larger but otherwise similar to the blades and vanes of an axial compressor.
There are two principal configurations for a turbofan, each off which has several variations, hi one configuration, the fan is placed at the front of the engine where it is an integral part of the compressor. When the engine is a dual-compressor type, it is a part of the forward, low-pressure compressor, hi the other configuration, the fan is mounted at the rear of the engine where it forms the rim, or outer perimeter, of a free turbine that rotates by itself in the exhaust gases discharged from the engine. These two turbo-fan designs are called forward-fen and aft- fan engines, respectively.
In both turbo-fan configurations, Де fen makes a substantial contribution to Де total thrust Over and above Де thrust produced by the basic engine, Де fen accelerates Де air passing through it to generate thrust of its own in Де manner of Де propeller of a turboprop. The fen air is exhausted without passing through the engine; it is not burned wiД fuel or used for internal engine cooling.
Two different duct designs are used wiA forward-fan engines. ЕіДег the air exhausted by Де fen may be ducted overboard directly after it leaves Де fen, or it may be ducted along Де outer case of Де basic engine to mix, or not mix (depending upon Де design), wiA the turbine exhaust gases before Де gases pass through Де jet nozzle.
The fundamental difference between a turbofan and a turboprop is that Де airflow through Де fan is controlled by Де design of the engine in such a manner that the air velocity through Де fen blades is not affected very much by Де speed of Де aircraft (How this is accomplished will be explained later.) This means that Де loss of operational efficiency at high air speeds that limits the airspeed capability of turbo-prop aircraft is eliminated in turbo-fen aircraft Indeed, supersonic aircraft not only can, but are being powered by turbofans.
Turbofans are rapidly becoming Де most widely used of all the types of jet engines, particularly in large multi-engine aircraft. The turbofan is, in effect, a compromise between Ae good operating efficiency and high-thrust capability of a turboprop and Де high-speed,
high-altitude capability of a turbojet. At cruising altitude, Hie engine- propeller combination of a turboprop loses efficiency rapidly at airspeeds above 400 knots. Not only does the turbofan have no such limitation but it is much simpler than a turboprop.
The complexity and weight of the propeller reduction gearing and the intricate propeller-governing feature of a turboprop are completely eliminated in a turbofan. The turbofan is therefore not only lighter than a turboprop but cat never be plagued by any of the malfunctions to which a propeller and its associated systems are susceptible.
The fact that the fan air does not pass through die basic engine enables a turbofan to achieve a relatively low specific fuel consumption. In addition, because it accelerates a large mass of air to relatively low velocity, even at very low aircraft speeds, a turbofan, like a turboprop,
produces much more thrust than a turbojet during take-off and die initial climb.
Another advantage of the turbofan is a lower noise level, which is an important feature at all commercial airports. The lower level of noise occurs because a turbo-fan engine has at least one additional turbine stage to drive the fan. Extraction of more power from the engine exhaust gases as they pass through the additional turbine (or turbines) serves to reduce the velocity of the engine exhaust. Less velocity through the jet nozzle results in less noise.
Ramjets and Pulsejets
The simplest jet engine of all is the ramjet, which has no moving parts. Such an engine is but little more than a pipe equipped with a fuel metering and injection Systran. Because a ramjet must be accelerated by some means other than the engine's own power to a very high speed before it will operate, the engines have limited use. They have principally been employed in guided missiles that must be carried aloft and launched by a conventional aircraft.
A pulsejet is a ramjet with a set of shutters, spring-loaded to remain in the closed position normally, placed across the engine's air inlet. When the engine is launched at a speed sufficient to maintain operation, ram air pressure forces the shutters open. Fuel is injected and burned continuously in the combustion chamber. As soon as the
combustion chamber pressure equals the ram air pressure, the shutters close. The combustion gases are ejected through the jet nozzle at the; rear, generating thrust. When the pressure in the combustion chamber/ drops off, the shutters open again, admitting more air. The cycle repeats itself with great rapidity.
Auxiliary Power Unit (APU)
The APU is located in the aft end of the fuselage, behind the pressure bulkhead and below the horizontal stabilizer The APU generator is mounted on the accessory drive pad and is used to furnish 60 KVA of electrical power on the ground or it can be used as ark alternate power source of 50 KVA in flight. Bleed air from the APU can be used to operate of the two air-conditioning packs or for main engine starting. Using APU bleed air for air-conditioning during takeoff improves takeoff performance. Airplane ground servicing, including/ ldrieling, may be accomplished with the APU operating. Exhaust noise heard by passengers and the ground crew is minimized through two factors;
Use of an acoustically treated air inlet and exhaust duct.
Its distance from the cabin and ground service points.
The APU is readily accessible for inspection, maintenance or removal through a large door in the fuselage directly below it. Removal is accomplished by lowering the assembly with a simple hoist and cable system.
The APU is a single shaft gas turbine engine with a two-stage centrifugal compressor, a single combustion chamber and one radial inflow turbine. The accessories group, driven by the gear box, is at the front of the unit.
The APU is a single shaft gas turbine engine with two centrifugal impellers and a single centrifugal turbine with a containment ring The power section drives the load compressor and accessary gearbox. The unit is monitored and controlled tty a Full Authority Digital Electronic Control (FADEC). The FADEC provides both built-in tests (BITE) and historical information.
Two Pratt & Whitney of Canada JT15D engines power the Cessna Citation aircraft. The JT15D is a lightweight, two-spool, medium bypass turbofan that produces between 2,200 and 2,550 lbs of static takeoff thrust.
After air enters the engine inlet, a front fan driven by the low pressure (LP) turbine accelerates air rearward toward the axial and centrifugal compressors and the full-length, annular bypass duct. Approximately 75 % to 66 % of the total air flows around the engine core through the bypass duct.
After air passes through the fan, an axial compressor, driven by the low pressure turbine, accelerates the air before passing it to the centrifugal compressor. The compressor, driven by the high-pressure (LP) turbine, slings air outward to accelerate it to a high-velocity, low- pressure flow. The diffuser converts the high-velocity flow into a low- velocity flow into a low-velocity, high-pressure flow before it reaches the combustion section.
The Rolls-Royce RB.211-22B is a three-shaft, high-bypass ratio, turbofan engine. Advantages of this compact design include great structural rigidity, fewer parts, low specific fuel consumption, reduced noise and smoke, and outstanding thrust growth potential.
Two engines are pylon-mounted on the wing; the third is located in the aft fuselage. This arrangement satisfied the design requirements for the optimum airplane balance, low structural weight, ease of access and maintainability, minimum drag.
Engines are interchangeable between wing and tail locations with some minor components changes. On-the-wing maintenance is facilitated by new design internal couplings that allow major assemblies to be separated from each other if replacement is required.
The 737 aiiplanes are powered by two wing-mounted, CFM564 3 high bypass-ratio turbofan engines at several thrust ratings, engine is an axial flow turbofan with two spools and variable st vanes. The single-stage fan and three-stage low pressure compressor і driven, via the low-speed (№1) shaft, by a four-stage low pressur e turbine. The nine-stage high pressure compressor is driven, via the high? speed (№2) shaft, by a single stage high pressure turbine. The fan ■ core airflows have separate exhaust nozzles and the fan exhaust syst includes a cascade type thrust reverser. Power for aircraft and engine accessories is provided by the main gearbox side mounted on the fm case. The gearbox is driven by the high-speed (№2) engine rotor.
During engine buildup, the following components are installed on! the basic engine: starter, constant speed drive (CSD) generator or optional variable speed constant frequency (VSCF) generator, hydraulic pump, cowling, thrust reverser, thrust reverser extension ring,' fire/overheat detectors, engine instrumentation, pneumatic ducting, potable water pressurization tubing, and electrical harness. Except for the vortex control device on the fan cowl and the thrust reverser, engine buildup is identical for left or right engines.
The engine nacelle is composed of the nose cowl and fixed and hinged cowl panels to provide smooth airflow over the engines and to protect exterior engine components from damage.
Cowl panels, hinged at the top, may be opened or completely removed to provide ground level access to the engine without using ground stands. Three cone bolts secure the engine to the wing. Two front cone bolts take thrust, vertical, and side loads. The one rear cone bolt takes vertical and side loads.
Special options allow the installation of nearly any of the above engines on the -300, -400. -500 airframes because of a unique thrust- limiting system at the interface.
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[ ~~ M I M I № 152
АКМАЛДІНОВА Олександра Миколаївна БУДКО Людмила Василівна КАРПЕНКО Маргарита Веніамінівна КРАВЧУК Оксана Юріївна ТКАЧЕНКО Світлана Іванівна
AIRCRAFT AND ENGINE DESIGN
Редактор Н.М. Угляренко Технічний редактор А.І. Лаврінович
Підписано до друку 05.11. 02. Формат 60x84/16. Папір офсетв Офсетний друк. Ум.фарбовідб. 52. Ум.друк.арк. 11,86. Обл.вид.арк. 12. Тираж 200 прим. Замовлення №208 -1. Ввд. №11/1