Reduction Gearbox

CHAPTER SIX

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION

CHANGE 1

WORKBOOK

602.

REDUCTION GEARBOX

Because the power turbine (Nf) operates at high speeds, it is necessary to reduce that rotational

speed to one that is usable by the propeller. This is done through the reduction gearbox, which is

bolted to the front flange of the exhaust duct and driven by a shaft extending from the power

turbine. The gearbox also provides a mounting and drive for the propeller and certain propeller-

related accessories. All prop-driven accessories are driven at the same speed by the propeller

shaft. The rear half of the gearbox contains a two-stage reduction gear system that reduces the

power turbine RPMs at a 15:1 ratio. The propeller shaft extends from the front half of the

reduction gearbox. This shaft is hollow to allow passage of high pressure oil for propeller pitch

control.

Magnetic Chip Detector

A magnetic chip detector is located at the bottom of the reduction gearbox to provide the pilot

with a warning signal for metal particles in the oil and possible engine failure. The chip detector

is a dual-element probe with one probe magnetized and connected to a DC potential and a second

element comprised of an insulated wire to the fault circuit. The detector is exposed to the oil

flow, and functions as a normally open switch. If a large metal chip or mass of small metal

particles bridges the detector gap, a circuit is completed, illuminating the flashing MASTER

CAUTION light and a yellow CHIP light on the annunciator panel.

Torque Indicating System

One of the propeller-related accessories is the torque indicating system. The torquemeter,

located inside the first stage of the reduction gear housing, provides an indication of engine

power output to the propeller shaft. It is a hydromechanical device which meters a given

quantity of oil based on the amount of torque applied to the reduction gearbox. The torquemeter

oil pressure is routed to three power plant accessories: the torque limiter, autoignition sense

switch, and torque transmitter. The torque transmitter, located on the reduction gearbox flange,

converts the torquemeter oil pressure to a 26 VAC electrical signal to operate the torque

indicators in the cockpits. There is a torque indicator on each instrument panel which is

graduated in 50 ft-lbs. increments. The maximum torque is 1315 ft-lbs. (550 SHP); however,

NATOPS restricts the maximum allowable torque to 1015 ft-lbs. (425 SHP), which is indicated

by a red line on the torque indicator.

6-2 REDUCTION GEARBOX