TM 1-1520-238-T-4
Change 9
5–55
5–21.
FLIGHT CHECK AND ADJUSTMENT USING AVA EQUIPMENT (cont)
5–21
Example: This data is from an actual move made on and aircraft for the flight readings, done according to the
AVA. The before and after vibration levels are per NOTE and illustration shown in Figure 5–25.
M58-0295-2
0.50
AH64
365
CURRENT 14:47:00 21 MAR 96
ID FLT
AMP
[ips]
PHASE
[deg]
60K
1R VER
A
B
0.80
AH64
365
CURRENT 14:47:00 21 MAR 96
ID FLT
AMP
[ips]
PHASE
[deg]
80K
1R VER
A
B
0.50
AH64
365
CURRENT 14:47:00 21 MAR 96
ID FLT
AMP
[ips]
PHASE
[deg]
140K
1R VER
A
B
0.80
AH64
365
CURRENT 14:47:00 21 MAR 96
ID FLT
AMP
[ips]
PHASE
[deg]
100K
1R VER
A
B
0.50
AH64
365
CURRENT 14:47:00 21 MAR 96
ID FLT
AMP
[ips]
PHASE
[deg]
120K
1R VER
A
B
NOTE:
60K
.31, 164
.21, 308
80K
.52, 148
.31, 336
100K
.51, 147
.37, 337
120K
.49, 145
.38, 360
140K
.44, 115
.44, 323
After
Before
A
B
CURRENT
12:23
0.21
0.31
307.83
163.65
A
B
CURRENT
12:23
0.31
0.52
335.61
147.75
A
B
CURRENT
12:23
0.37
0.51
336.64
146.90
A
B
CURRENT
12:23
0.38
0.49
0.41
145.04
A
B
CURRENT
12:23
0.44
0.44
323.22
114.65
Figure 5–25.
Before and After Vibration Levels on AVA
This is a perfect example of the vibration shooting across the center of the polar chart. If the phase information
was ignored one might think the vibration didn’t change much at all. At first glance of the vibration levels you
would think that the aircraft only got marginally better or at 140 the level did not change. This is not the case; in
fact, this was a substantial move that went to the other side of the polar chart (see polar charts above). This
should not be considered to be a wrong adjustment. The adjustment went in the correct direction (which is the
most important factor), but it just went to far. Remember the main thing that you view the trends for is to ensure
that the move went in the correct direction (towards the center of the polar chart).
If the vibration shoots to the other side of the polar plot through the center, there are many variables that may
have caused this (the trim tab or pitch link had a larger reaction on this particular blade, the trim tabs were bent
more than was required, this particular aircraft had a stronger reaction than the AVA is programmed for, or an
incorrect move was made, etc.). If there was only one move made to the rotor and it made the vibration levels
shoot through center, then the suffix would to be to take some of that particular move back out (the AVA will
normally recommend this in the diagnostics). If there were multiple moves performed on the rotor that made the
vibration levels shoot through the center of the polar plot, then it is not
