five short tiebolts. Five longer tiebolts clamp this rotor assembly to the forward shaft through the
forward coupling. Loosening these five longer tiebolts does not disturb the rotor assembly itself,
permitting simple maintenance without special tools. Thirteen second-stage nozzle segments of two
vanes each are held by the outer support, which is also assembled with the first stage shroud segments
and second stage shroud support.
All airfoils (vanes) are internally cooled. The first stage nozzle leading edge is air-cooled,
with the air exiting through holes in the vane airfoils. The midchord region is convection-cooled, with
cooling air exiting both through pressure holes and trailing edge slots. Cooling air for the second stage
nozzle is bled from the centrifugal compressor exit and piped back through the turbine casting. The air
enters the second stage nozzle through bushings and cools the nozzles by internal airflow exiting
through trailing edge and inner band holes. The turbine blades are air-cooled through radial holes. Air
enters through the dovetail and exits at the tip. The first stage blades also employ trailing edge holes for
cooling.
10.7.
POWER TURBINE
This component is a two-stage uncooled tip-shrouded design with replaceable turbine blades
and nozzle segments. The output shaft governing speed range is from 17,000 to 23,000 rpm with a
maximum rated speed of 24,000 rpm.
The power turbine is a self-contained module which can be disassembled and reassembled to
the gas generator without special tools.
The rotor assembly consists of the third and fourth stage disks mounted on a drive shaft
supported by four bearings. The third stage disk is secured to the drive shaft by a flange, allowing quick
removal from the drive shaft without removal of the aft sump or rear frame. The third stage disk has
46 tip-shrouded blades attached to the disk through conventional dovetails and retained axially by bent
locking strips. A similar arrangement is used on stage four where 50 blades are employed.
The drive shaft is a hollow one-piece unit splined to the short output shaft at the forward
end. An integral feature of the drive shaft is the torque sensor that mechanically displays the total twist
of the drive shaft, which is electrically sensed and processed. This mechanical display of total twist is
accomplished by a reference shaft that is pinned to the front end and extends back to the aft end, where
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