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MAIN DRIVE SHAFT CONNECTION TO THE TRANSMISSION

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FREEWHEELING UNIT/MAIN DRIVE SHAFT CONNECTION TO THE TRANSMISSION
1. State the purpose of the power train system.
The power train system provides a means of transmitting engine power to the main and tail rotor systems.
2. State the purpose of the freewheeling unit/sprag clutch assembly.
The sprag clutch, in the freewheeling unit, provides a disconnect from the engine enabling autototational
forces to drive the transmission, tail rotor, and all transmission mounted accessories in the event of an
engine failure.
3. What is the lubrication source for the freewheeling unit?
The freewheeling unit is lubricated by transmission oil.
4. Does the freewheeling unit have a chip detection capability?
Yes, but the chip detector is not electrically wired for a “caution light” indication in the cockpit.
5. What does the main driveshaft connect?
It is a flexible coupling that connects the freewheeling unit to the transmission input drive.
6. Why is the main drive shaft a flexible coupling?
The movement between the transmission (a floating pylon mount) and the freewheeling unit mounted on the
engine (a rigid mount) requires coupling.
7. In the event of an engine failure, what drives the tail rotor in autorotation?
The main drive shaft transfers transmission RPM (inflow of air through the rotor system) to the
freewheeling unit to drive the tail rotor.
CHARACTERISTICS OF THE MAIN TRANSMISSION
1. What mounting technique is used to secure the transmission to the airframe?
An isolation mounting technique (it is not rigidly mounted)
2. What is the purpose of the pylon support links?
To mount the transmission to the airframe and bear the aircraft’s weight.
3. What effect does a focused pylon mount have on the transmission?
A focused pylon mount lowers the CG of the transmission. This reduces the transmission’s movement.
4. Why is the transmission mounted with a 5º forward tilt?
To provide a more comfortable attitude in forward flight.
5. Why is the transmission mounted with a 1.25º tilt to the left?
To help compensate for translating tendency.
6. What does a rubber isolation mount provide?
A rubber isolation mount provides for lateral centering and shock absorption.
7. What does the drag link’s round pin and the pylon stop’s square hole provide?
Positive travel limits for the pylon.

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CHARACTERISTICS OF THE LUBRICATION SYSTEM
1. Where does the TRANS OIL TEMP caution light get its information?
From the switch located on the transmission oil filter’s housing.
2. Where does the transmission oil temperature gauge get its information?
From the thermo bulb/transducer on the oil filter’s housing?
3. Does the transmission oil cooler have a bypass capability?
The transmission oil cooler has a thermal bypass at temperatures below 71 ºC. Above 81 ºC the bypass
valve closes and the oil must be cooled.
4. How is the transmission oil cooled?
A flexible duct/hose assembly transport cooling air from the engine oil cooler housing to the transmission
oil cooler where some air about to cool the transmission oil is scavenged to cool the hydraulic reservoir.
5. How many chip detectors are there on the transmission oil system?
There are four transmission chip detectors (sump, pump, chip pan, and freewheeling unit) on the oil system.
6. How many chip detectors are there on the transmission that can activate the TRANS CHIP caution light?
There are three chip detectors (sump, pump, chip pan) that can activate the TRANS CHIP light.
7. Where is the transmission oil level sight glass located?
The sight glass is located on the right side of the transmission.
CHARACTERISTICS OF THE MAST
1. What are the three splined areas on the mast?
The mast is splined to the planetary gear case, the collar set, and the trunnion.
2. Why is the mast hollow?
A hollow mast is stronger, flexible, and lighter weight.
CHARACTERISTICS OF THE TH-67 TAIL ROTOR POWER TRAIN SYSTEM
1. How many tail rotor drive shaft segments are there?
There are eight tail rotor drive shaft segments. Two are made of steel, and six are aluminum alloy.
2. How many tail rotor drive shaft segments are on top of the tail boom section of the aircraft?
Five of the eight tail rotor drive shaft segments are on top of the tail boom.
3. What are the hanger bearing assemblies used for?
Hanger-bearing assemblies are used to support the drive shaft and maintain drive train alignment in its
position over the tail boom .
4. What is used to connect a drive shaft segment to another component?
Thomas couplings are used at every drive shaft connection to provide a strong yet flexible connection
requiring no lubrication.
5. Why are the indexing flats in Thomas couplings alternated?
Alternating indexing flats increases the tensile strength in these flexible couplings.

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FREEWHEELING UNIT/MAIN DRIVE SHAFT CONNECTION TO THE TRANSMISSION 1. State the purpose of the power train system. The power train system provides a means of transmitting engine power to the main and tail rotor systems. 2. State the purpose of the freewheeling unit/sprag clutch assembly. The sprag clutch, in the freewheeling unit, provides a disconnect from the engine enabling autototational forces to drive the transmission, tail rotor, and all transmission mounted accessories in the event of an engine failure. 3. What is the lubrication source for the freewheeling unit? The freewheeling unit is lubricated by transmission oil. 4. Does the freewheeling unit have a chip detection capability? Yes, but the chip detector is not electrically wired for a “caution light” indication in the cockpit. 5. What does the main driveshaft connect? It is a flexible coupling that connects the freewheeling unit to the transmission input drive. 6. Why is the main drive shaft a flexible coupling? The movement between the transmission (a floating pylon mount) and the freewheeling unit mounted on the engine (a rigid mount) requires coupling. 7. In the event of an engine failure, what drives the tail rotor in autorotation? The main drive shaft transfers transmission RPM (inflow of air through the rotor system) to the freewheeling unit to drive the tail rotor. CHARACTERISTICS OF THE MAIN TRANSMISSION 1. What mounting technique is used to secure the transmission to the airframe? An iso ...
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Very useful material for studying!

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