106 Chadwick-Helmuth Company, Inc.
Chapter 5 - General Operation
3. Using the blue (counter-clockwise) side of the Rotor Protractor, align
the photocell on the protractor with the azimuth of the photocell on
the helicopter.
4. Plot the balance point from the Vibrex unit onto the chart, using the
clock numbering on the Rotor Protractor aligned, as in step 4 on the
chart. For an explanation of how to use the Rotor Protractor, see
Section 5.5.3 “Using the Rotor Protractor” on page 96.
5. From the balance point on the chart, plot parallel to the fine lines that
extend from the heavy borders to the edges of the chart.
6. Read the adjustment to the rotor from the scale and notation on the
heavy borders.
NOTE: It is possible on some rotors to use the Propeller Balance
screens and their propeller balance procedures (using the Propeller
Protractor) for determining correct balance weights, instead of a
polar chart. The Propeller Balance screens’ menus are especially
suited to tail rotors equipped with a balance wheel or balance points
equidistant from the center of rotation.
5.5.5 Tail Rotor Track
Even though many helicopters have fixed pitch change links (PCLs) for
the tail rotor, this feature does not mean track is never a problem. On such
aircraft, track differences can cause difficulty in balancing to low levels or
may result in high IPS levels during forward flight.
Track the tail rotor by using the Strobex. In general, do this operation, as
follows:
1. Install the photocell system so one of the blade tips points towards the
cabin. Make sure the retro-reflective target that triggers the photocell
probe is in line with the probe beam.
2. Apply a thin retro-reflective target along the chord line on one blade
tip and across the chord line on the other blade tip.
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