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(b) Do the steps that follow with the six data points (A-F) that you used before.
NOTE: An example is in Fig. 512.
____
1) Write the initial run vector, UO, at angle AO as written in Fig. 504.
NOTE: On engines without CFMI SB 72-437, refer to Figure
____ 504 (Configuration 1). On engines with CFMI SB 72-437, refer to Figure 504 (Configuration 2).
2) Write the first run vector U1 (related to the same speed and sensor as vector UO) at angle A1, as written in Fig. 504.
NOTE: Vectors UO and U1 are in mils DA.
____
3) Make a record of the original run balancing weight W1 at the angle A1.
NOTE: W1 is in g-cm.
____
4) Write vector R from the end of vector UO to the end of vector U1. 5) Start at the center of the graph and make vector R', equal in length and direction to vector R.
(c)
Calculate the phase lag of each data point as follows and write each of them on a new worksheet (Fig. 511):
Phase lag = (Angle of vector W1) - (Angle of vector R') + 180°
(d)
Calculate the sensitivity of each data point as follows and write it on Fig. 511:
Sensitivity = W1 g-cm
----------------Vector R mils
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(2)
Write the UO and AO values (A-F) from Fig. 504 (the initial operation of the engine, before the balance screws were added) on Fig. 511.
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(3)
On a polar graph, use the applicable scale in g-cm that will include all the balance weights.
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(4) S 975-080-C00Put the six indexed points (A-F) and the balance weights (W) at their calculated angles (A) on the polar graph.
(5) S 975-081-C00Measure and make a record of the vector length (the distance between each pair of points) on the worksheet in Figure 511.
(6) S 975-082-C00Make a record of the sensitivity for all points on the worksheet in Figure 506. (a) Use the data from the worksheet of Figure 511.
(7) S 975-083-C00Add up the sensitivities of all points in groups of two.
(8) S 975-084-C00Calculate the minimum residual vibration amplitude as follows:
Residual Vibration Amplitude = Length between 2 points ---------------------------------
Total Sensitivity of the 2 points
As an example:
Minimum residual vibration amplitude of AB = Length of vector AB -----------------------------------
Sensitivity of A + Sensitivity of B
(9) S 975-085-C00Get the highest residual vibration amplitude and make a note of the vector which agrees with this highest amplitude (Fig. 506).
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CFM56 ENGINES
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S 975-086-C00
(10) Calculate the distance between the imbalance correction point and the first indexed point of the selcted line as follows:
Distance from first selected point =
(Corresponding residual vibration) x (Sensitivity of first selected point).
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