96 Chadwick-Helmuth Company, Inc.
Chapter 5 - General Operation
5.5.3 Using the Rotor Protractor
By way of a typical example, this section explains how to use the
Chadwick-Helmuth Rotor Protractor for balancing helicopter rotors.
In the current example, the operator is balancing a tail rotor with the
Vibrex unit. The installation uses a Velocimeter in the standard location,
as called for in the paper polar chart, and a convenient location for the
photocell at the 11:00 position. The resulting reading from the Vibrex unit
was 0.7 IPS in the 10:20 direction.
To derive a solution from the chart, place the protractor on the chart so the
photocell on the protractor aligns with the angle of the target when the
beam leaves the reflective tape. In other words, the photocell may be
mounted at 11:00 o’clock azimuth, but the beam actually hits the retro
target when it leaves at 12:00. Then the clock corrector will be placed at
12:00 o’clock on the chart. In the example, the photocell is located at
11:00 and the target is also triggered at 11:00 o’clock. In that case the
protractor would be placed on the chart so the photocell is at 11:00. See
illustrations on page 97 and page 98.
For more information on tail rotor balancing with the Vibrex 2000 or
Vibrex 2000 Plus, see Section 5.5.4 “Tail Rotor Balance” on page 104.
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