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2) Put the six index points A-F you identified before (the balance weights at their calculated angles) on the polar graph.
3) Put the balance weight (W1) at its calculated angle (A1) on the same polar graph you used to record the length and the phase angle (A1) of W1.
4) Find the residual vibration as follows: a) Measure the length (g-cm) between each of the indexed points (A-F) and the balance weight (W1). b) Divide this length by the sensitivity at the indexed point with this equation:
Residual vibration at A = Length between A and W1 -----------------------Sensitivity at A
5) Optimize the residual vibration level as follows:
NOTE: After the calculation, some of the residual
____ vibration can be too high. If this occurs, you must make the balancing weight better to make all the residual vibration amplitudes satisfactory.
a) Around each of the changed points, draw a circle whose
radius (g-cm) is equivalent to the sensitivity at each
point multiplied by the vibration amplitude.
R (g-cm) = Sensitivity (g-cm) x Vibration amplitude (mils)
------------------mils
b) Use the same formula given above to draw a circle
around each of the other points until the area that is
common to the intersecting circles is found.
NOTE: Because it is near to the common area, the
____ location of W1 can help you find the common area.
This common area can be made into a common intersecting point that will be the improved balancing weight W1.
c) Read the value of the improved W1 and its phase angle A1. 6) Find the balancing weight which agrees with the original balancing screws (W0) (Figs. 508 and 509). 7) Find the phase angle for the original balancing screws (A0) (Fig. 507). 8) Plot the vector W0 at the angle A0 on a graduated polar graph (Fig. 510).
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9) From the end of the vector W0, plot the vector W1 at the angle A1.
10) To find the resultant vector, draw a line from the origin of the polar graph (start of vector W0) to the end of the vector W1.
11) Find the value of the resultant weight (WS) and its phase angle (AS).
(d) Make a selection of the balance screws as follows: 1) Use the phase angle A1 to see if the center of the balance weight is on or between the screw holes (Fig. 507). 2) Get the part number(s) of the balance screw(s) from the applicable figures, Fig. 508 for centers on the screw holes or Fig. 509 for centers between the screw holes.
3) Write the selection of balance screw(s) and locations(s) on a balance screw location chart (Fig. 502).
(e) Install the new balance screws as follows:
CAUTION: MAKE SURE THAT YOU PUT COVERS ON ALL OF THE LOWER
_______ HALF OF THE INLET COWL SURFACE. ALSO MAKE SURE THAT THE EDGES OF THE MATS TOUCH OR ARE ATTACHED WITH SOME TAPE. IF THE EDGES ARE NOT, THEN THE TOOLS OR PARTS CAN FALL AND CAUSE DAMAGE TO THE INLET COWL SURFACE.
1) Use tape to put the protective mats on the inner lower half of the inlet cowl.
2) Remove the initial balance screws, WO, and install new (lubricated) balance screws W1 (or WS) that you claculated.
NOTE: If the balance weight WS was calculated, you must
____ remove all of the balance screws WO that were used to calculate WS. Then you can install the WS screws or P07 screws as necessary.
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