Helicopter Components & Systems

Question 1

Define a semirigid rotor system.

Answer 1

Usually composed of two blades that are rigidly mounted to the main rotor hub. The main rotor hub is free to tilt with respect to the main rotor shaft on what is known as a teetering or flapping hinge.

Question 2

What are the three types of potential movements of a rotor system?

Answer 2

• Feathering (changing pitch)
• Flapping
• Lead/Lag

Question 3

What are the basic parts of a turbine engine?

Answer 3

• Compressor
• Combustion Chamber
• Turbine

Question 4

What is the function of the compressor in a turbine engine?

Answer 4

A fan assembly consisting of multiple blades fixed on a rotating spindle. As the turbine rotor turns, air is drawn rearwards. Stator vanes are arranged in fixed rows between the rotor blades and act as a diffuser at each stage to decrease air velocity and increase air pressure (compression effect). Each row constitutes a pressure stage, and the number of stages depends on the amount of air and pressure rise required for a particular engine.

Question 5

What is the function of the combustion chamber in a turbine engine?

Answer 5

Unlike a piston engine, the combustion in a turbine engine is continuous. An igniter plug only ignites the fuel/air mixture when starting the engine. Once the fuel/air mixture is ignited, it will continue to burn as long as the fuel/air mixture is present. If there is an interruption of fuel, air, or both, combustion ceases (known as a flame-out) and the engine has to be restarted or relit. Some engines are equipped with auto-relight.

Question 6

What is the function of the turbine in a turbine engine?

Answer 6

The turbine section consists of a series of turbine wheels that are used to drive the compressor section and rotor system.

The first stage, which is usually referred to as the gas producer or N1 may consist of one or more turbine wheels. This stage drive the components necessary to complete the turbine cycle (make the engine self-sustaining). Common components driven by the N1 stage are the compressor, oil pump, and fuel pump.

The second stage, which may also consist of multiple wheels, is dedicated to driving the main rotor system and accessories from the engine gearbox. This is referred to as the power turbine (N2 or Nr).

If the first and second stage turbines are mechanically coupled, the system is said to be a direct-drive or fixed turbine. These types share a common shaft, which means the first and second stage turbines, and thus compressor and output shaft, are connected.

On most turbine assemblies used in helicopters, the first stage and second stage turbines are not mechanically connected to each other, but mounted on independent shafts and turn freely with respect to each other. This is referred to as a free turbine.