06 - System: Transmissions

Question 1

Power Transmission: What is the purpose of the main transmisison assembly?

Answer 1

Transmits engine power to the rotor, while reducing the output speed and changing the direction of drive ~90°

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.1)

Question 2

Power Transmission: How is the Main Gear Box mounted to the airframe?

Answer 2

Flexibly, and moves in relation to the airframe in flight.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.2.1)

Question 3

Power Transmission: How is the Main Gear Box mounted to the engine?

Answer 3

Rigidly, through the housing and barrel junction assembly.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.2.1)

Explanation: The engine has to be rigidly mounted to the MGB, since this is flexibly mounted to the airframe.

Question 4

Power Transmission: What is the purpose of the flexible cuplings in the power transmission from engine to Main Gear Box?

Answer 4

To compensate for small misalignments between the engine and MGB.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.2.1)

Question 5

Power Transmission: What is the purpose of the Main Gear Box?

Answer 5

Transmits engine torque to the main rotor

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3)

Question 6

Power Transmission: How many RPM does the transmission input receive from the engine?

Answer 6

6125 RPM

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.1)

Question 7

Power Transmission: What gears does the main gear box consist of?

Answer 7

• Epicyclic (planetary) reduction gear
• Bevel reduction gear

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.1)

Question 8

Power Transmission: Regarding the Main Gear Box, what is the purpose of the bevel gear?

Answer 8

• Recieves the engine power input and changes direction ~ 90°
• Reduces by a ratio of 61 / 17 = 3.59
• Drives the Epicyclic Sun gear

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.1)

(6125 RPM -> 1706 RPM)

Question 9

Power Transmission: Regarding the Main Gear Box, what is the purpose of the Epicyclic gear?

Answer 9

• Planet gears, driven by sun gear, spins along a fixed ring gear, and drives the planet gear cage -> Drives the rotor
• Further reduces by a ratio of 4.33

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.1)

1706 RPM -> 394 RPM

Question 10

Power Transmission: What is the purpose of the Main Gear Box Oil System?

Answer 10

• Lubrication
• Cooling

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.3)

Question 11

Power Transmission: What happens in case of low oil quantity (or wrong lubrican being used) ?

Answer 11

• Increase of stress on gears, resulting in fatigue and eventually failure
• Increased friction and temperature, leading to bearing seizure above a certain temp.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.1)

Question 12

Power Transmission: When does the MGB T light illuminate?

Answer 12

MGB temp above 115°C

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.2)

Question 13

Power Transmission: When does the MGB P light illuminate?

Answer 13

MGB oil pressure below 1 bar

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.2)

Question 14

Power Transmission: What is the purpose of the Rotor Brake?

Answer 14

• Stop rotor quickly
• Prevent from turning when parked

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.4)

Question 15

Power Transmission: What is the time interval between two rotor brakings?

Answer 15

5 minutes

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.4.2)

Question 16

Power Transmission: When does the MGB CHIP light illuminate?

Answer 16

When enough metallic particles have built up on the magnetic chip detector, thus closing the circuit.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.4.2)

Question 17

Power Transmission: How is the Main Gear box oil cooled?

Answer 17

• By the motor driven oil cooler, installed in the air duct.
• Oil pump driven by the gear box

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.2)

Question 18

Power Transmission: What determines whether the MGB oil is being cooled?

Answer 18

The engine oil temperature.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.2)

Question 19

Power Transmission: What does the relief valve do?

Answer 19

• Opens during cold weather starting when the MGB oil pressure reaches 6.5 bar.
• The quantity of oil to oil cooler is reduced and temperature increases quickly.

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.3.4.2)

Question 20

Power Transmission: Why is the MGB attached flexibly to the structure?

Answer 20

To absorb vibrations

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.5.1)

Question 21

Power Transmission: How is the mast attached to the helicopter?

Answer 21

By 4 rigid bars that transfer lift from the rotor to the structure

(Instruction Manual - Basic 1 - Main Systems, Chapter 3, Paragraph 3.5.1)

Question 22

Tail Transmission: What are the components comprising the tail transmission system?

Answer 22

1. Tail Rotor Gear Box
2. Tail Rotor drive shaft
3. Forward drive shaft

(Instruction Manual - Basic 1 - Main Systems, Chapter 5, Paragraph 5.1)

Question 23

Tail Transmission: What is the oil capacity of the tail gear box?

Answer 23

0.33 L (Soda can)

(“Dash-1”, FM CH7.0, Paragraph 6)

Question 24

Tail Transmission: How is the Tail Rotor Gear Box lubricated and cooled?

Answer 24

• Splash lubrication
• Heat developed in lubrication is fully dissipated by radiation from housing.

(Instruction Manual - Basic 1 - Main Systems, Chapter 5, Paragraph 5.3.2)