TM 1-1520-238-T-4
Change 9
5–43
5–20.
INITIAL CHECK AND ADJUSTMENT USING AVA EQUIPMENT (cont)
5–20
(3) AVA’s goal is to give corrections that will drive vibration levels towards center of polar chart. The
question you ask when you’re viewing the polar chart is, did vibration levels move towards center of chart or go
through center of chart. In some cases you will see vibration trend go through center of chart and overshoot to
other side. This is a clear indication that the aircraft is responding to the moves in a normal manner, but the
amount of move was too much. Phase information is very important and these polar charts should be used to
verify reaction of aircraft. For example lets say there was an adjustment for initial, and Hover lateral went from a
.40 ips to .38 ips. If the phase information was ignored one might think the vibration did not change at all, in fact
this may have gone to other side of polar chart which is in fact a large move but it just went to far. See paragraph
5–21, for an example of this.
(4) If the vibration shoots to other side of polar plot through center, there are many variables that may have
caused this (this particular aircraft had a stronger reaction than AVA is programmed for, or an incorrect move was
made, etc.). If there was only one move made to the rotor and it made vibration levels shoot through center, then
the fix would to be to take some of that particular move back out (the AVA will normally recommend this in
diagnostics). If there were multiple moves performed on the rotor that made vibration levels shoot through center
of polar plot, then is not as easy to determine which move caused overreaction. Recommended procedure in this
case is to let AVA tell you what moves are required to bring vibration back, by utilizing custom solution options that
were described earlier.
e. WEIGHT ADJUSTMENT
WARNING
FLIGHT SAFETY PART
The main rotor blade is a flight safety part. Failure to follow maintenance
instructions may result in serious injury or death of crewmembers and/or
serious damage to the helicopter.
NOTE
This task is typical for all four main rotor blades.
a. Removal
NOTE
Weights are added or subtracted to
balance main rotor. A maximum of
nine weights may be installed.
(1). Remove two nuts (1) and washers (2) from
studs (3).
(2). Remove weights (4) from bracket (5).
b. Cleaning
a. Wipe bracket. Use cloth item 52, App F).
M58-0295-10
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