Chadwick-Helmuth 8500C - Blade Sweep; Tail Rotor Tracking

Performing a Visual Track
Mode l8500C/8500C+ Operators Manual
6-7
necessary, but a variable or changing profile suggests trim tab adjustments. Having determined the typ
of adjustment that is necessary, pitch link or trim tab, a vertical balance can be performed using the
appropriate balance chart.
6.4.4 Blade Sweep
Blade sweep
or
lead-lag
refers to the angle of separation between individual blades. Blades that are not
equiangular can cause subtle perturbations to the system's lateral balance. Visual tracking allows you
to view the blade spacing and gauge the relative separation between them. Balance solutions for some
aircraft require modifications to the rotors' blade sweep, which in turn alters spacing in an attempt to
redress lateral imbalance.
By stacking the blade images during a visual track it is possible to determine the amount of separation
between adjacent pairs of blades. The extent to which these distances vary from blade to blade is an
indication of the relative angular separation between them. Follow the aircraft manufacturer's
directions to align rotor blades that are not equiangular.
6.4.5 Tail Rotor Tracking
Tail rotor track can be performed with the Strobex and the Measurements Only chart. First, following
the instructions for a tail rotor balance, mount an velocimeter and apply reflective blade tip targets to
the ends of the blades. Put the 8500C/C+ into the Balance mode and select the Measurements Only
chart. Set the balance type to Strobex and set the balance frequency to the tail rotor's balance frequency
multiplied by the number of blades. For example, a two-bladed tail rotor with a frequency of
33 00revolutions per minute (RPM) requires a balance freque ncy of 2times 33 0 0, or 6600RPM.
Operate the aircraft at the setting used for tail rotor balance and press
START
to acquire balance data
(see Section 5.4.1 “Initiating Strobex Measurement” on pa ge5-9). When the Strobex is activated (see
Figur e5-7 on pag e5-10) flash it at the tail rotor blade tips. Position the targets for better viewing by
pressing the Lef tand Righ tArrow keys. Press
STOP
to terminate the track operation.
See Sectio n5.2.1 “Measurements Only Chart” on pa ge5-2 for more information on this chart.