TM 55-4920-402-13&P
BALANCE CHART CLOCK ANGLE CORRECTOR #3597
Balance charts are made for each rotor of each heli-
copter type.
The angle between the axes (heavy lines at
edges) is determined by the geometry of the available
weight attachment points, as is the ratio of the amounts
of weight called for.
The rotation of the graph on the
clock, and the actual amounts of weight, are determined
experimentally.
The charts represent the best average of
many samples.
However, because of differences in manufacture or
repairs, etc. , not all airframes of the same type are
identical.
Differences in mechanical stiffness and reso-
nant frequencies may call for different weights---AND
DIFFERENT CLOCK ANGLE---(rotation of graph on clock) for
some helicopters of a given type.
Correction of weight is fairly straightfoward and
obvious (if the Move Line is too long, use less weight,
etc.) but correction of the clock is more difficult.
The
CORRECTOR makes it simple.
To use the CORRECTOR it is important to understand
the direction the move line should take on the chart.
1)
If a pair of moves is made EXACTLY as called
for, the move line SHOULD go toward or through the center
of the Chart. Keep in mind that if one weight is changed
exactly as called for, but the other is only approximate,
the Line would not be expected to go to the center.
2) If only one of the two weights is changed, the
Move Line should be PARALLEL to the fine lines extending
from the UNCHANGED axis.
In other words, the weight
on the second axis was not changed, so no change should
be indicated.
(On 3, 5, and 6 Blade Charts, consider
only the “pie section” in which the first point lies.)
If the Move Line is not as indicated, use the
CORRECTOR, and re-label the Clock.
If the rotor does not respond in an orderly manner
to balancing efforts, restore to the original condition
and see if the first reading repeats.
IF NOT, LOOK FOR
PROBLEMS IN THE ROTOR (Bearings, linkages, mounts, rod-
ends,
etc.).
Figure 2-8. Balance Chart Clock Angle Corrector Instructor Sheet
2-12
