The pickup assembly consists of electro-
housing. The power section assembly contains oil,
magnetic pickups mounted radially over the teeth
fuel, ignition, control, and cooling air systems.
It also has a compressor extension shaft to which
of the torque and reference shaft flanges. These
pickups produce electrical impulses at the passage
the torquemeter attaches.
of each exciter tooth. The pickups are displaced
Torquemeter Assembly
so that the reference flange impulse from its
The torquemeter assembly is located between
pickup and the torque flange impulse from its
pickup are slightly out of phase at zero load.
the power section and reduction gear box
Because zero torque indications are not at the
assemblies. Its purpose is to transmit and measure
electrical zero of the indicator, both positive and
the shaft output from the power section to the
reduction gearbox assembly.
negative torque conditions are measured.
The torquemeter operates on the principle of
Reduction Gear Assembly
accurate measurement of torsional deflection
The reduction gear assembly changes the high
(twist) that occurs in any power transmitting shaft.
This torsional deflection is detected by magnetic
rpm, low torque of the turbine section to low rpm,
high torque necessary for efficient propeller
pickups. The deflection is measured electronically,
and displayed on the cockpit instrument panel in
operation. This change is made through a two-
stage reduction system of sun and planetary gears.
t e r m s of inch-pounds of torque, or shaft
See figure 8-5. The two stages of reduction
horsepower (SHP). The principle parts of the
provide an overall speed reduction of 13.54 to 1;
torquemeter assembly are shown in figure 8-4.
for example, when power section rpm is 13,820,
Two concentric shafts make up the torque-
the propeller shaft rpm is 1,020. The reduction
meter assembly. The inner shaft (torque shaft)
gear case also provides the drive and location to
carries the load and produces the measured twist.
mount the propeller and accessories. Accessories
The outer shaft (reference shaft for measuring
mounted on the case include a starter, generator,
purposes) is rigidly connected to the torque shaft
engine-driven compressor (EDC), oil pump, and
at the drive input end only. There are separate
flanges on both the torque and reference shafts
tachometer generator. The reduction gearbox
assembly also uses safety systems that we will
at the reduction gear assembly end. Rectangular
discuss next.
exciter "teeth" are machined in line on each
flange, which enable the pickups to detect the
TURBOPROP SAFETY SYSTEMS
relative displacement of the two flanges.
The complexity of the turboprop configura-
The torquemeter housing serves as a rigid
tion brought about the possibility of certain
lower support between the power unit and the
hazardous in-flight situations. Safety features
reduction gear assembly. It provides a mounting
have been designed into the system to activate
for the pickup assembly at the reduction gear end.
Figure 8-4.-Torquemeter assembly.
8-4
