d.
Turbine exhaust thermal switch. A thermocouple projects into the exhaust gas stream
at the aft end of the combustor. If an over temperature occurs, the contacts normally closed in the
turbine exhaust thermal switch will open, close the main fuel solenoid valve, and shut the engine down.
e.
Tachometer generator. The APU tachometer generator is mounted in tandem with the
speed switch on the accessory drive assembly. A synchronous rotor in the tachometer generator
produces three-phase ac voltage proportional to the speed at which the rotor is turning. This voltage is
transmitted to a tachometer indicator in the cockpit which indicates the engine speed in percent of rated
rpm.
f.
Hour meter. Engine operating time is recorded by the hour meter attached to the
engine. The meter operates on 24v dc supplied by the aircraft bus.
6.12.
SUMMARY
The T62 is used on the CH-47 and CH-54 helicopters as an auxiliary power unit. The engine
consists of a combustor, turbine, and reduction and accessory drive assemblies. Both the compressor
and turbine rotor are mounted on the same shaft. A fuel control, hydraulic starter motor, and ignition
unit are mounted on the engine. Operating time for the APU is maintained separately from the aircraft
engine time by an hour meter mounted on the APU.
The T62 is equipped with protective devices that shut the APU down if any of the operating
limitations are exceeded. If the oil pressure, rpm, or exhaust temperature limits are exceeded, a light on
the instrument panel will be illuminated and the APU shut down.
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