Figure 8-5.-Reduction gear and torquemeter assemblies.
torque conditions. When a predetermined
automatically whenever a system-related hazard
negative torque is applied to the reduction gear-
occurs. The following text discusses some of the
box, a stationary (nonrotating) ring gear moves
hazards and their related safety features.
forward against spring force. This action results
Thrust Sensitive Signal (TSS)
in a rod moving forward through the reduction
The thrust sensitive signal system is a safety
gear nose case. The rod positions the feather valve
in the valve housing to an increased blade angle.
device used during takeoffs. The TSS auto-
When the propeller blade angle has increased
magically initiates propeller feathering and shuts
enough to relieve negative torque conditions, the
down the turboprop engine in case of power loss.
plunger retracts and the propeller returns to
This allows the pilot to concentrate on flying the
aircraft during the critical takeoff period. Feather-
normal operation.
The NTS system functions in flight during
ing the propeller reduces the yawing action (caused
temporary fuel interruptions, air gust loads on
by drag) and asymmetric flight characteristics on
the propeller, normal descents with lean fuel
multiengined aircraft. The TSS system is on the
scheduling, or high compressor bleed-air condi-
reduction gearbox (RGB), and it is armed through
tions at low-power settings.
a switch in the flight station.
Safety Coupling
Negative Torque Signal (NTS)
The safety coupling is an automatic mechan-
The negative torque signal system momen-
ical device that decouples (disconnects) the power
tarily prevents the propeller from driving the
section from the reduction gearbox assembly when
engine during in-flight conditions. The NTS
negative torque exceeds the setting of the safety
system is mechanically locked out during engine
coupling. The safety coupling is between the main
operation in the ground range. The system's
input pinion gear shaft on the reduction gearbox
mechanical linkage and plunger are inside the
and the outer member of the torquemeter drive
front case of the reduction gearbox. They work
shaft. Any transfer of torque, positive or negative,
with the propeller valve housing assembly to
between the power section and the reduction gear
increase propeller blade angle during negative
8-5
