Main Gear Box & Oil System Flashcards
Purpose of the MGB (transmission)
Modular design allows
- change in angle of drive
- reduction of the rotation speed
Where is the freewheeling unit located?
Between the engine transmission shaft driven by the free turbine wheel and power shaft
How is the MGB mounted?
Four rigid suspension bars and a
Flexible suspension system
Purpose of the four rigid suspension bars
Carry lift power from the rotor head to the frame
What are the 3 modules of the MGB
- Epicyclic gear set: 2nd stage reduction with a chip detector
- 90deg spiral bevel gear set: 1st stage reduction
- Oil sump and flexible suspension with a chip detector and temp sensor
Components of the flexible suspension system
- 4 elastomeric laminated rubber blocks stabilize the MGB oscillations
- cross member under MGB makes a link between the deck and the casing
How do the Elastomeric laminated rubber blocks function?
4 elastomeric laminated rubber blocks stabilize the MGB oscillations
- flexible in shear
- rigid in compression
In what planes is the suspension flexible vs rigid
Flexible in shear
Rigid in compression
Purpose of the Articulated coupling
- Maintains MGB/Engine spacing and alignment
- relieves stress from the drive shaft
Components of the Articulated Coupling
- Connector casing (forward)
- Gimbal ring (step down)
- Coupling tube (aft)
- Drive shaft (inner)
What is the purpose of the Gimbal ring?
Compensates for slight misalignments between the engine drive shaft and the MGB power input
What are the Flex (Thomas) Couplings
A stack of stainless steel disks mounted between two triangular coupling flanges (integrated to the shaft)
Flexible coupling deforms to absorb small shaft misalignments
How does the rotor brake work?
Mechanical rotor brake
- actuated by a flexball cable
- feredo pads clamp against a disk
Located on the left side of the connector casing
What is the rotor brake inhibition switch?
Prohibits start with the rotor brake engaged
(out of the forward locked position)
What are the rotor brake limits?
170 RPM - max, for high winds
140 RPM - normal operation
100 RPM - AMC policy
Five minutes between braking applications
When does the (MGB P) red light come on?
When the pressure drops below 1 bar
When does the (MGB Temp) yellow light come on?
When the oil temp exceeds 115C
What is the purpose of the oil system’s pressure relief valve?
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
Does the MGB oil filter have bypass capability?
Yes
Is there any cockpit indication if the oil filter has bypassed?
No
- only by visual inspection via the LRB on post/pre flight
How many chip detectors are there in the MGB oil system and location?
2 total
- upper right
- lower left, in conjunction with the drain plug
Describe the oil flowing through the system
- Oil from the basin of the casing is drawn through an intake strainer (inside the MGB)
- Drawn through the pump (inside the MGB)
- Passes the pressure relief valve (inside the MGB)
- Goes through the oil cooler
- Through either the oil filter or its integrated bypass
- Passes the Low Press Switch (< 1 bar) - turquoise color switch on right hand side
- Lubricates the MGB
- Passes the Upper Right and Lower Left chip detectors and the High Temp Switch (>115C) - located next to the lower chip detector
Components of the Rotor brake system
- Rotor brake
- flexible ball type control
- rotor brake handle
- the fork
