engine power trim (PT indicator) and N 1
spinning around the disk of conducting material
overspeed caution (L or R N1OVSP caution
produces torque on the disk.
indicator light),
The drag disk connects to the lower end of the
indicator assembly shaft. When the disk rotates,
TACHOMETER INDICATOR. --The elec-
the indicator pointer moves to show the speed of
trical tachometer (RPM) indicator displays
the aircraft engine. The indicating element is
percentage of engine N2 rotor speed on two
supported by three posts. These post have
vertical scales. One each for the left and right
adjustable nuts (callout 8) for leveling the
engines. The indicator scales are linear from 0 to
assembly as necessary. You can obtain further
6, and from 6 to 11 multiplied by 10 to get percent
positioning by the adjusting arm (callout 7).
of RPM. Upper left and right limit range markers
The scale plate (callout 5) is calibrated either
and OFF failure flags appear between the 10.4 and
in RPM or percentage and shows engine speed.
11 points of the scales. The absence of the OFF
The cover assembly (callout 6) serves as a
failure flags confirms the indicator channels are
protective container for the mechanism. Electrical
receiving power. The indicator receives variable-
connection to the tachometer generator is by the
receptacle (callout 10) at the rear of the indicator.
speed from each engine tachometer generator. The
Dual Indicators
signals go to solid-state circuitry to produce a
proportional drive signal for a servomotor. The
With the increasing requirement for more
servomotor drives gears and sprockets to position
a tape on the indicator face, showing percentage
instruments for efficient flight, the combination
of engine N2 rotational speed.
of several instruments in one has become very
The test selector switch on the MASTER
common. The dual tachometer is an example of
TEST panel is used to test the indicators. It
a combination of instruments. Some multi-engine
disconnects a self-test circuit in the indicators from
aircraft use dual tachometers.
the tachometer-generator input circuits. The
T h e dual tachometer consists of two
self-test circuit then connects with the appropriate
synchronous-motor magnetic-drag tachometer
test signal within the two indicator channels. The
indicators housed in a single case. The indicators
channel circuitry processes the test signal and
show the speed of rotation of the engines
drives the indicator tapes to show 80 percent of
simultaneously on a single dial. There is one
RPM.
tachometer indicator for each pair of engines on
the aircraft.
Vertical Scale Indicators
two-phase alternator types. They supply electrical
Vertical scale indicators are used on some
signals directly proportional to engine-compressor
rotational speed. The N1 tachometer generator for
models of naval aircraft. A vertical scale shows
the left and right engines is driven by the N2
engine performance data such as fuel flow, engine
low-pressure compressor rotor. An output from
speed, exhaust gas temperature, and accelerometer
readings. Vertical scale indicators are compact,
this generator goes to the engine rotor overspeed
light in weight, and easily read.
r e v o l u t i o n s p e r m i n u t e ( R P M ) . T h e N2
Basically, all vertical scale indicators consist
tachometer generator is driven by the N2 high-
of a vertical tape that operates by an amplifier,
pressure compressor through the engine accessory
motor, gears, and sprockets. These systems (fig.
gearbox. Signals from this generator go directly
6-46) are basically the same as systems used on
to the electrical tachometer indicator (RPM
other aircraft. There may be possible changes in
nomenclature due to the various aircraft and
indicator) at the pilot station. The indicator
displays percentage of N2 rotor speed.
engine manufacturers.
The engine indicating groups consist of cockpit
indicators and associated sensing devices required
ENGINE ROTOR OVERSPEED DETEC-
TOR. --The engine rotor overspeed detector
to monitor left and right engine performance.
Dual indicators display percentage of engine N2
receives electrical signals from the left and right
rotor speed (RPM indicator), turbine inlet
N1 tachometer generator. The detector consists
temperature (TIT indicator), and engine fuel flow
of three solid-state circuit boards--a crystal
(FF indicator). Individual indicators display
oscillator (clock) board and two identical gated
