Principle of Operation and Control

 

The helicopter derives lift from rotating an airfoil called the rotor. Usually it is equipped with one or more power-driven rotors. When the angle of attack of rotating rotor blades attains a certain value, the lift overcomes the weight of the aircraft and then it takes off vertically.

To achieve horizontal flight, the pilot tilts the rotor forward at a certain angle. This is done by what is known as cyclic pitch change, i.e. changing the pitch of each blade once per revolution. More particularly, the angle of attack of each blade is increased every time it sweeps over the tail of the machine, thereby temporarily developing a greater amount of thrust than the other blades. 

Additionally each blade can swivel about its longitudinal axis and its pitch is changed cyclically, through a linkage system, by a so called swash-plate, which performs a sort of wobbling rotary motion around the shaft and swivels the blades to and fro as they rotate. The tilt of the swash-plate can be varied by the pilot, and the tilt of the rotor follows the tilt of the plate.

So, by changing the pitch angle of the main rotor blades, by manipulating the engine speed and by tilting the main rotor, the pilot controls the helicopter's flight in any direction.

Hovering over one point is done by selecting the correct speed and setting the rotor blades so that their vertical lift is exactly equal to the weight of the helicopter.

 

Т EXT

Classification of Military Helicopters

 

Hels are a separate group of acft and have now begun to displace mil fixed-wing acft in many roles. They are classified as atk, obsn, utility, cbt assault transport, electronic warfare and target acquisition, antiarmor, etc.

 

 

EXERCISES

 

1. Ответьте на вопросы.

 

1. What is a helicopter?

2. What is the origin of the word helicopter?

3. What are the general characteristics of modern helicopters?

4. What are the principal structural elements of the helicopter?

5. What does the airframe consist of?

6. What does the fuselage house?

7. What does the undercarriage consists of?

8. What are the general components of the propulsion system?

9. Which type of engines is currently used in helicopters?

10. What is the purpose of the tail rotor in single-rotor helicopters?

11. Where does the helicopter derive lift from?

12. In which way does the pilot achieve horizontal flight?

13. What is the purpose of the swash-plate?

14. By means of what can the pilot control the helicopter's flight?

15. How can hovering over one point be achieved?

16. How are military helicopters classified?

 

Переведите предложения.

 

1. Вертолет - ЛА тяжелее воздуха, у которого подъемная сила и поступательное движение обеспечивается одним или несколькими несущими винтами.

2. The airframe includes a fuselage with a cabin, cargo compartment and tail boom, and undercarriage with main and nose landing gears and tail support.

3. Вертолет способен совершать вертикальный взлет и посадку, полет в различных направлениях, а также висеть над заданной точкой и на заданной высоте.

4. According to their mission helicopters are classified as atk, obsn, utility, cbt assault transport, electronic warfare and target acquisition, antiarmor, etc.

5. Одновинтовой вертолет состоит из следующих основных частей: фюзеляжа с хвостовой балкой, силовой установки, трансмиссии, несущего винта, рулевого винта, органов управления и шасси.

6. An axial-flow turboshaft engine having a high power-to-weight ratio is comprised of a compressor, combustion chamber, turbines, and main gear box.

7. Трансмиссия вертолета служит для передачи мощности от двигателя к несущему и рулевому винтам.

8. By the swash-plate the pitch angle of the main rotor can be varied simultaneously on all blades to change the lift and vertical movement of the helicopter.

9. Или же он может варьироваться циклически - для изменения наклона несущего винта и осуществления поступательного движения и управления вертолетом.