Main Gear Box & Oil System

Question 1

Purpose of the MGB (transmission)

Answer 1

Modular design allows
- change in angle of drive
- reduction of the rotation speed

Question 2

Where is the freewheeling unit located?

Answer 2

Between the engine transmission shaft driven by the free turbine wheel and power shaft

Question 3

How is the MGB mounted?

Answer 3

Four rigid suspension bars and a
Flexible suspension system

Question 4

Purpose of the four rigid suspension bars

Answer 4

Carry lift power from the rotor head to the frame

Question 5

What are the 3 modules of the MGB

Answer 5

1. Epicyclic gear set: 2nd stage reduction with a chip detector
2. 90deg spiral bevel gear set: 1st stage reduction
3. Oil sump and flexible suspension with a chip detector and temp sensor

Question 6

Components of the flexible suspension system

Answer 6

• 4 elastomeric laminated rubber blocks stabilize the MGB oscillations
• cross member under MGB makes a link between the deck and the casing

Question 7

How do the Elastomeric laminated rubber blocks function?

Answer 7

4 elastomeric laminated rubber blocks stabilize the MGB oscillations
- flexible in shear
- rigid in compression

Question 8

In what planes is the suspension flexible vs rigid

Answer 8

Flexible in shear
Rigid in compression

Question 9

Purpose of the Articulated coupling

Answer 9

• Maintains MGB/Engine spacing and alignment
• relieves stress from the drive shaft

Question 10

Components of the Articulated Coupling

Answer 10

1. Connector casing (forward)
2. Gimbal ring (step down)
3. Coupling tube (aft)
4. Drive shaft (inner)

Question 11

What is the purpose of the Gimbal ring?

Answer 11

Compensates for slight misalignments between the engine drive shaft and the MGB power input

Question 12

What are the Flex (Thomas) Couplings

Answer 12

A stack of stainless steel disks mounted between two triangular coupling flanges (integrated to the shaft)
Flexible coupling deforms to absorb small shaft misalignments

Question 13

How does the rotor brake work?

Answer 13

Mechanical rotor brake
- actuated by a flexball cable
- feredo pads clamp against a disk

Located on the left side of the connector casing

Question 14

What is the rotor brake inhibition switch?

Answer 14

Prohibits start with the rotor brake engaged
(out of the forward locked position)

Question 15

What are the rotor brake limits?

Answer 15

170 RPM - max, for high winds
140 RPM - normal operation
100 RPM - AMC policy
Five minutes between braking applications

Question 16

When does the (MGB P) red light come on?

Answer 16

When the pressure drops below 1 bar

Question 17

When does the (MGB Temp) yellow light come on?

Answer 17

When the oil temp exceeds 115C

Question 18

What is the purpose of the oil system’s pressure relief valve?

Answer 18

Maintains constant pressure in the circuit
Opens during cold weather starts when the oil pressure reaches 6.5 bar.
- this reduces the oil flow through the cooler to increase temp quickly

Question 19

Does the MGB oil filter have bypass capability?

Answer 19

Yes

Question 20

Is there any cockpit indication if the oil filter has bypassed?

Answer 20

No
- only by visual inspection via the LRB on post/pre flight

Question 21

How many chip detectors are there in the MGB oil system and location?

Answer 21

2 total
- upper right
- lower left, in conjunction with the drain plug

Question 22

Describe the oil flowing through the system

Answer 22

1. Oil from the basin of the casing is drawn through an intake strainer (inside the MGB)
2. Drawn through the pump (inside the MGB)
3. Passes the pressure relief valve (inside the MGB)
4. Goes through the oil cooler
5. Through either the oil filter or its integrated bypass
6. Passes the Low Press Switch (< 1 bar) - turquoise color switch on right hand side
7. Lubricates the MGB
8. Passes the Upper Right and Lower Left chip detectors and the High Temp Switch (>115C) - located next to the lower chip detector

Question 23

Components of the Rotor brake system

Answer 23

• Rotor brake
• flexible ball type control
• rotor brake handle
• the fork