(c)
Start the engine and let it idle for 3 minutes
(AMM 71-00-00/201).
(d)
Accelerate the engine to 80 percent N1 and let it stabilize for 5 minutes.
(e)
Slowly accelerate the engine up to maximum takeoff N1.
(f)
Decelerate the engine until it is stable at the %N1 targets that are on the applicable trim balance worksheet (Fig. 516).
(g)
If the vibration level shown by the TRF sensor is more than 8.0 mils, use the residual vibration level optimization method to find a different weight for the spinner.
NOTE: Use the vectorial analysis procedure.
____
(h) If the fan vibration is approximately 1.0 mils DA and the TRF vibration is 8.0 mils or less, make a record of the vibration amplitudes (U5), and phase angles (A5)of the No. 1 bearing (or FFCCV) and the TRF.
NOTE: ENGINES WITHOUT CFMI SB 72-437;
____ Refer to Figure 517 (Sheet 1) (Configuration 1).
NOTE: ENGINES WITH CFMI SB 72-437;
____ Refer to Figure 517 (Sheet 2) (Configuration 2).
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(6) If the vibrations do not stabilize at one of the speeds given in Figure 517 after 2 minutes, do these steps:
(a)
Do not make a record the amplitude and phase angles.
(b)
Decelerate to the next lower N1 speed.
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(c) When the vibrations have stabilized, do as follows:
1) Make a record of the data.
2) Decrease the power to the idle position.
3) Let the engine stabilize for 5 minutes.
4) Shutdown the engine (AMM 71-00-00/201).
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(7) If the balancing clips (Ref: AIPC 72-56-00-15, item 045) are already installed, find the total installed weight as follows:
(a)
Divide the installed clips into sectors that are separated by turbine blades that do not have clips installed.
(b)
Find the weight W0 of the first sector (Fig. 518).
(c)
Turn the fan and move the middle of the first sector to the 6 o'clock position. Keep the first sector in this position.
NOTE: The right weld bead on the shroud inner face is the
____
LPT 6 o'clock reference line.
(d) Identify the balancing hole(s) at the 6 o'clock position on the fan spinner.
NOTE: The 6 o'clock reference line for the fan is the RTV
____ bead found between the two 6 o'clock acoustic panels.
(e)
Find the angular position A0 of the clip vector (Fig. 507).
(f)
On a polar graph, draw the balancing weight vector W0
(Fig. 505).
(g)
Find the weight W0 and angular position A0 of the other clip sectors. 1) Use the steps given above.
(h)
On a polar graph, vectorially add the weight vector to find the total installed weight WT and angle AT (Fig. 519).
(i)
Calculate the new LPT balancing weight as follows:
1) Use the fan one-shot plot procedure and the data written in the LPT trim balancing worksheet (Fig. 517) to find the balancing weight WC and angle AC.
2) On a polar graph scaled in g-cm, add the weight vector WC at the angle AC to the weight vector WT and the angle AT to get the total weight WI and the angle AI.
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3) Use the balance weight WI to find the correct balance clip locations around the center blade of the 4th-stage LPT blades.
As an example:
If 500 g-cm is necessary at a 90-degree angular position, move the fan blades Nos. 29 and 30 to the 6 o'clock position. Keep the fan in this position and install 10 adjacent clips at the 6 o'clock position on the LPT blade tip shrouds.
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