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larger than the other. All tracking should be done at
engine-rated RPM to obtain the best track (or as
specified in the applicable repair manual). Refer to
Figure 4-5 for an example.
Strobe Light
The strobe light blade-tracking system includes—
A portable power supply.
A hand-held strobe lamp.
4-4
FM 1-514
•
•
•
Blade tip targets.
Magnetic phase pickup.
Pickup plates.
A concentrated parallel light beam from the strobe
light is manually directed toward a predetermined
spot on the rotor blade disc to strike the blade tip
targets. The strobe light trigger switch is then
depressed to allow strobing of the blade tip targets.
The pulse signal for strobe effect is provided by the
magnetic pickup unit mounted on the stationary
swash plate ring. This strobe effect sends a pulse
each time one of the pickup plates passes over the
magnetic pickup unit. The pickup is mounted on
each rotor blade pitch-change link lower attaching
bolt. The strobe light targets are attached to the
blade tips with patterns facing inboard. The targets
vertically relative to the others, the colored lines of
the affected blade target will become visible to the
operator. Refer to Figure 4-6 for an example.
VIBREX BALANCING KIT
The Vibrex balancing kit (hereinafter referred to
as Vibrex) is used to measure and indicate the level
of vibrations induced by the main and tail rotors of a
helicopter. The Vibrex analyzes the vibration induced
by out-of-track or out-of-balance rotors.
Then by plotting vibration amplitude and clock angle
on a chart, it determines the amount and location of
rotor track or weight changes. The Vibrex is also
used in troubleshooting to measure the RPM or frequency
of unknown disturbances. DA Pam 738-751
prescribes forms, records, and reports to be used by
maintenance personnel at all levels.
hfoavr ee asiclvhe br lraedflee c(taiv set rtaapigeh wt iltihn ea np iadtetenrtinfy oinng thpaet treerdn The Vibrex is housed in a carrying case; it consists of
blade, a right-slanting pattern on the yellow blade, a the components detailed in Figure 4-7. The main
left-slanting pattern on the green blade). When the units of the Vibrex are the Balancer/Phazor,
177M6A; the Strobex tracker, 135M11; and the
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4-5
FM 1-514
Balancer/Phazor, 177M6A
The key feature of the Balancer/Phazor (hereinafter
referred to as a balancer) is a tunable, electronic
hand-pass filter which is tuned to reject all but the
one frequency or vibration under study (Figure 4-8).
The meter reads the level of vibration at the rate
(RPM) of concern, which indicates the amount of the
required change (track or balance). The Phazor
section contains a phase meter that reads clock angle,
or phase angle, between a one-per-revolution magnetic
pickup azimuth signal from the rotor and a
vibration signal from the accelerometer.
Strobex Tracker, 135M11
The Strobex tracker (hereinafter referred to as a
Strobex) is a small hand-held, lightweight, combination
power supply and strobe flash tube (Figure 4-9).
It illuminates reflective targets on the tail rotor to
measure tail rotor clock angle and on the main rotor
to indicate rotor track and lead-lag.
Vibrex Tester 11
The Vibrex tester (hereinafter referred to as a tester)
provides accurate calibration and a complete functional
check of the Vibrex (Figure 4-10). The tester
4-6
FM 1-514
4-7
FM 1-514
4-8
FM 1-514
shakes (vibrates) the accelerometer to measure •
vibration amplitude in inches per second (IPS) and
rate (RPM) functions of the balancer. Phase or clock
angle functions of the Phazor section are verified by
a rotating interrupter plate and the magnetic pickup
to provide double and single interrupter logic signals.
The RPM dial of the Strobex is accurately checked
against the known rotor speed of the tester motor.
Accessories
Following is a list of accessories that are used with the
balancer, Strobex, and tester:
•
Magnetic pickups and interrupter sets.
These devices provide magnetic impulses
from rotor to balancer. Magnetic pickups are
located on stationary platforms; interrupter
sets are located on rotating platforms.
Accelerometers. Accelerometers provide
the balancer with an electrical representation
　
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