TM 55-4920-402-13&P
CHAPTER 1
INTRODUCTION
Section l. GENERAL INFORMATION
1-1. Scope. The VIBREX Balancing Kit (fig.l-l) (here-
troubleshooting by measuring the revolutions-per-minute
after referred to as VIBREX) is used to measure and indi-
(RPM) or frequency of unknown disturbances.
cate the level of vibrations induced by the main rotor and
tail rotor of a helicopter. The VIBREX analyzes the vibra-
tion induced by out-of-track, or out-of-balance rotors, and
1-2. Forms
and Records. Maintenance forms,
then by plotting vibration amplitude and clock angle on a
records, and reports which are to be used by mainte-
chart, the amount and location of rotor track or weight
nance personnel at all maintenance levels are listed
changes is determined. In addition, the VIBREX is used in
and prescribed by DA PAM 738-751.
Section II. DESCRIPTION AND LEADING PARTICULARS
1-3. Description. The VIBREX is housed in a Carrying
Case and consists of the components listed in table 1-1.
The main units of the VIBREX are Balancer/Phazor
177M6A, Strobex Tracker 135M11, and VIBREX Tester
11. The primary airframe mounted components are three
Accelerometers 4177B and two Magnetic Pickups 3030AN.
CAUTlON
Extreme care should be exercised when
using the VIBREX test set. This unit
contains delicate electronic com-
ponents and assemblies which may be
easily damaged if subjected to physical
abuse due to improper handling.
a. Balancer/Phazor 177M6A. The key feature of the
Balancer/Phazor (fig. 1-2) (hereafter referred to as Balancer)
is a tune able, electronic bandpass filter which is tuned to
reject all but one frequency, or vibration under study. The
meter reads the level of vibration at the rate (RPM) of con-
cern, which is indicative of 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.
b. Strobex Tracker 135M11. The Strobex Tracker
(fig. 1-3) (hereafter referred to as Strobex) is a small hand
held lightweight combination power supply and strobe
flash tube. 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.
c. VIBREX Tester 11. The VIBREX Tester (fig. 1-4)
(hereafter referred to as Tester) provides accurate calibra-
tion and complete functional check of the VIBREX. The
Tester shakes (vibrates) the Accelerometer to measure vi-
bration 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
interrupt e r logic signals. The RPM dial of the St robex is
accurately checked against the known rotor speed of the
Tester motor.
d. Accessories. Following is a list of accessories (fig.
1-1 ) that are used with the Balancer, Strobex, and Tester:
(1) Magnetic Pickups and Interrupter Sets. Pickup
device to provide magnetic impulses from rotor to Balancer.
Magnetic Pickups are located on stationary platforms while
Interrupter Sets are located on rotating platforms.
(2) Accelerometers. Provides the Balancer with an
electrical representation of the physical motion of the
point to which it is attached.
(3) Reflective and Tip Target Sets. Reflects Strobex
flash pulses back to St robex operator.
(4) Balance and Tracking Charts. Used to calculate
weight, sweep, pitch link, tab, etc., to correct rotor pro-
blems.
Change 5
1-1
