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In principle, this engine is very similar to the turbojet engine, differing only in that it uses a propeller to provide most of the propulsive thrust.
The engine consists of a diffuser, a mechanical compressor, a combustion chamber, a turbine, an exhaust nozzle, a reduction gear and a propeller. The diffuser, mechanical compressor and combustion chamber function in the same manner as in the turbojet engine. However, in the turboprop engine, the turbine extracts much more power than it does in the turbojet engine, because the turbine provides power for both the compressor and the propeller. When all of this energy is extracted from the high temperature gases, there is little energy left for producing jet thrust. Thus, the turboprop engine derives most of its propulsive thrust from the propeller and derives only a small portion (10 to 25 % depending on the flight velocity) from the exhaust nozzle.
Since the shaft rotation speed of gas turbine engines is very high (approximately 12,000 rpm), a reduction gear must be placed between the turbine shaft and the propeller to operate efficiently. The turboprop engine is essentially a gas turbine power plant because, as pointed out before, little power is derived from the exhaust nozzle; still as flight speeds are increased, the ratio of nozzle power to propeller power for maximum thrust tends to become higher. The propulsive thrust is provided by a dual momentum change of the air. First, the propeller increases the air momentum, and second, the over-all engine from diffuser to nozzle, provides an internal momentum increase. The sum of these thrusts is the total thrust developed by the engine.
The turboprop engine is often used in transport aircraft, but can be adapted for use in single-engine aircraft. A variation of the turboprop engine known as the turboshaft engine, is a gas turbine power plant in which all delivered power is in the form of shaft power. Turboshaft engines are currently used both to power helicopters and for various land and marine applications.
Задание 8. Дайте английские эквиваленты:
в зависимости от скорости полета, как указывалось выше, мощность на валу, раскаленный газ, во-первых, известный как, в настоящее время, как... так и.
Задание 9. Согласитесь или опровергните утверждение. Начинайте предложения с фраз: I’m afraid that’s wrong. You are quite right/ you are not quite right (you are wrong). That’s not quite so. I think you are mistaken. As far as I know. I think so. According to the text.
1. In principle, the turbojet engine is similar to turboprop engine.
2. In the turboprop engine the turbine extracts less power than it does in the turbojet engine.
3. The turboprop engine derives most of its propulsive thrust from the exhaust nozzle.
4. The shaft rotation speed of gas turbine engines is not very high.
5. The turboprop engine is seldom used in transport aircraft.
6. The turboprop engine is often used in single-engine aircraft.
Задание 10. Не глядя в текст, дополните предложения.
The turboprop engine consists of.…..
The diffuser, mechanical compressor and combustion chamber of the turbojet engine function …...
The turboprop engine derives most of its propulsive thrust from …...
A reduction gear is placed.…..
The propulsive thrust is provided by.…..
The turboprop engine is used …...
The turboshaft engine is …...
Задание 11. Переведите на английский язык:
1. Турбовинтовой двигатель находит в авиации широкое применение.
2. Что общего имеют турбовинтовые и турбореактивные двигатели?
3. Основное отличие состоит в том, что турбина приводит во вращение воздушный винт. Только незначительная часть тяги создается за счет реактивной струи.
4. Турбовинтовой двигатель используется для полета на скоростях до 900 км в час.
Задание 12. Расскажите по-английски тему “Turboprop Engines”.
Задание 13. Письменно переведите текст:
Turboprop engines having two independently rotating turbines have proved quite successful. One of the turbines drives the compressor, while the other drives the propeller. The independent turbine has some advantages over the direct connected type. Both the propeller and the compressor may be operated at rotational speeds that produce the best respective efficiencies. This allows the propeller to operate at high speed during take-off and climb, thus reducing the tendency of the propeller to stall. Propeller speed can be lowered at altitude, with a subsequent reduction in tip compressibility losses.
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