Example: A = 533 g.cm at 284 degrees B = 450 g.cm at 312 degrees C = 290 g.cm at 289 degrees
(11) On a polar graph, take a g.cm scale and plot the three points. (Ref. Fig. 512/TASK 71-00-00-991-331, 513/TASK 71-00-00-991-332)
(12) To determine the balancing weight corresponding to the best compromise, we must search for the intersection of 3 circles, by setting vibration level targets for each speed.
(13) The balancing weight is within triangle A, B, C.
The vibration targets are: 1 mil.
0.5 mils at 96 percent of N1
1.0 mils at 84 percent of N1
1.2 mils at 62 percent of N1
(14) About points A, B and C draw 3 circles with the following radiuses (sensitivity x vibration target):
(a) 205 x 1.0 = 205 g.cm
(b) 225 x 1.0 = 225 g.cm
(c) 365 x 1.0 = 365 g.cm
(15) The balancing weight which meets the target requirements is at the intersection of the 3 intersecting circles. (Ref. Fig. 513/TASK 71-00-00-991-332) In the example of the figure, weight M is within the common hatched area. Since this weight is within the triangle A, B, C, the vibration targets can be improved.
(16) If the circles do not intersect, the targets must be widened or made narrower by modifying the radius of the circles corresponding to 94, 84 and 64 percent N1.
(17) If all three points A, B and C are within the three circles, the targets must be reduced to determine the balancing weight. Example: If you take the same 0.5 mils target for the three points A, B and C, the respective radiuses will be as follows: (Ref. Fig. 514/TASK 71-00-00-991-333)
(a) 0.5 x 205 = 102 g.cm.
(b) 0.5 x 225 = 112 g.cm.
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(c) 0.5 x 365 = 182 g.cm. Weight M, common to the three circles, will be 479 g.cm at 296 degrees.
(18) On the Fan spinner rear cone, a spherical mark is machined to show the Fan blade No. 1 location. This first blade is to the left of the mark, forward looking aft. (The blades are counted counterclockwise). (Ref. Fig. 515/TASK 71-00-00-991-334)
(19) Determine the position of the balancing screws to be installed on the spinner rear cone according to the angle. (Ref. Fig. 516/TASK 71-00-00-991-335, 517/TASK 71-00-00-991-337) Example: 296 degrees correspond to blade positions No. 7 and No. 8.
(20) To determine the number of screws to be installed and their respective positions: (Ref. Fig. 517/TASK 71-00-00-991-337) and (Ref. Fig. 518/TASK 71-00-00-991-343) Example: 478 g.cm at 296 degrees corresponds to the installation of the following screws:
- P06 in position No. 2
- P06 in position No. 13.
(Ref. Fig. 518/TASK 71-00-00-991-343)
(21) If there are no balancing screws other than P07 in the rear spinner cone, install the above screws.
(22) If there are balancing screws already installed on the rear spinner cone, the weight equivalent to the initial weight installed must be calculated and added as well as the weight determined above.
NOTE : This addition is recommended in order to avoid an excessive
____ number of screws installed on the spinner rear cone after several balancing operations.
(23) Record the initial configuration of the engine. Refer to the table of following figures to determine the installed weight and its position. (Ref. Fig. 516/TASK 71-00-00-991-335, 517/TASK 71-00-00-991-337) and (Ref. Fig. 518/TASK 71-00-00-991-343)
(24) If the tables do not contain the initial configuration of the
spinner, a vectorial addition of each screw is necessary.
Example: Assume that the configuration was as follows:
- One screw P06 in position No. 23
- One screw P04 in position No. 3
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Balancing Weight Centered between Two Screws Figure 518/TASK 71-00-00-991-343- 13 (SHEET 1)
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Balancing Weight Centered between Two Screws Figure 518/TASK 71-00-00-991-343- 23 (SHEET 2)
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