Propeller Overspeed Governor
The propeller overspeed governor is installed at the 10 o’clock position on the
front case of the propeller reduction gearbox. The governor acts a backup
to the propeller governor, preventing an overspeed condition should the
main propeller governor fail to properly limit propeller RPM. The propeller
overspeed governor regulates the oil ow to the propeller pitch-change
mechanism by means of a yweight and speeder spring arrangement similar
to the primary propeller governor. Since it has no mechanical controls, the
overspeed governor is equipped with a test solenoid to reset the overspeed
governor below its normal overspeed setting for ground testing of the unit.
The overspeed governor test switch is located on the upper left portion of the
instrument panel.
ENGINE MOUNT
The engine mount is a 13-element welded frame fabricated from 4130 steel.
The frame attaches to the rewall at four points and contains an engine
mounting bracket providing 3 engine attach-points.
Propeller Reduction Gearbox
The reduction gears and propeller shaft are housed in two magnesium alloy
castings which are bolted together at the exhaust duct ange. The gearbox
contains a two-stage planetary gear train, three accessory drives and the
propeller shaft. The rst-stage reduction gear is contained in the rear case,
while the second-stage reduction gear, accessory drives and propeller shaft
are contained in the front case. Torque from the power turbine is transmitted
to the rst-stage reduction gear, from there to the second-stage reduction
gear and then to the propeller shaft. The reduction ratio of .0663:1 provides
a maximum propeller speed of 2200 RPM from a power turbine speed of
approximately 33,200 RPM.
The accessories, located on the front case of the reduction gearbox, are
driven by a bevel gear mounted at the rear of the propeller shaft thrust
bearing assembly. Drive shafts from the bevel drive gear transmit rotational
power to the three pads located at the 12, 3 and 9 o’clock positions.
Propeller thrust loads are absorbed by a anged ball bearing assembly
located in the center bore at the forward face of the reduction gearbox. The
bevel drive gear adjusting spacer, thrust bearing and seal runner are stacked
and secured to the propeller shaft by a key-washer and spanner nut. A thrust
bearing cover assembly is secured by bolts at the front ange of the reduction
gearbox front case.
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