(15) In the table of figure, record the initial vibrations registered during the first flight. (Ref. Fig. 528/TASK 71-00-00-991-358) See example: (Ref. Fig. 529/TASK 71-00-00-991-359)
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Calculation of Added Balancing Weight Figure 527/TASK 71-00-00-991-357
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Calculation of the Vectorial Analysis Balancing Weight
Figure 528/TASK 71-00-00-991-358
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Calculation Chart of the Vectorial Analysis Balancing Weight - Calculation
Example
Figure 529/TASK 71-00-00-991-359
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(16) The improved balancing weights are obtained by multiplying the
figures of column 1 by the figures of column 2.
Example for 96 percent N1: 2.6 x 107 = 283 g.cm.
(17) The angles of the improved balancing weights are obtained by subtracting the figures of column 5 from the figures of column 4. Example for 96 percent N1: 131 - 236 = -105, i.e. 255 degrees.
(18) Three balancing weights A, B and C are obtained.
They correspond to the weights which cancel the No. 1 bearing
vibration at the three speeds.
Example: A = 283 g.cm at 255 degrees B = 304 g.cm at 257 degrees C = 351 g.cm at 235 degrees
(19) On a polar graph using a g.cm scale, plot these three points.
(Ref. Fig. 530/TASK 71-00-00-991-360)
(20) To determine the balancing weight corresponding to the best compromise, search for the intersection of three circles by setting vibration level targets for each speed.
(21) The balancing is within triangle ABC.
(22) These vibration targets are: 1 mil As the 1 mil circles are larger than the triangle defined by ABC, then the targets are decreased by 0.5 mils.
(23) About points A, B, C, respectively, draw circles with radiuses defined by multiplying the sensitivities calculated in figure and the targets stated above. (Ref. Fig. 530/TASK 71-00-00-991-360)
Example: 96 percent N1 = 0.5 x 107 = 53 g.cm 84 percent N1 = 0.5 x 152 = 76 g.cm 64 percent N1 = 0.5 x 432 = 216 g.cm
The balancing weight 288 g.cm at 250 degrees is located within the
0.5 mils circles of the 96, 84 percent N1 and 64 percent N1. It is adequate for balancing the engine.
(24) The initial weight (for example: 236 g.cm at 229 degrees) must be added to the determined balancing weight (example: 288 g.cm at 250 degrees). To do so, a vectorial addition of these two vectors must be made, using the polar graph, (Ref. Fig. 531/TASK 71-00-00-991-373)
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Balancing Weight Calculation (Vectorial Analysis) Figure 530/TASK 71-00-00-991-360
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Example of Addition Weight and Correction Weight Figure 531/TASK 71-00-00-991-373
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(25) Determine the screws to be used and their position: (Ref. Fig. 516/TASK 71-00-00-991-335, 517/TASK 71-00-00-991-337, 518/TASK 71-00-00-991-343) and Example: 240 degrees corresponds to position No. 13. The weights are therefore centered on one screw. The screws to be installed on the spinner are the following:
- P03 screw in position No. 9
- P02 screw in position No. 13
- P03 screw in position No. 17. All the other positions are equipped with P07 screws. Explanation: 2 screws P03 in position No. 9 and No. 17 is equal to 328 g.cm centered on position No. 13 and one screw PO2 is equal to 158 g.cm giving a total of 358 + 158 = 516 g.cm.
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