Fan Trim Balance

CFM56-7B

TRAINING MANUAL

ENGINE FAN TRIM BALANCE (3 SHOT PLOT)

Objectives: Given an Objective Exercise, the student will: - identify the conditions where fan trim balance must be performed on the CFM56-7engine. (1.A.a.) - state the purpose of the engine fan trim balance. (2.B.a.) - identify the methods used for balancing the engine. (1.B.a.) - Perform the maintenance practice calculations for the 3 shot plot procedure. (3.E.a.)

EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 1 Aug 99

CFM56-7B

TRAINING MANUAL

FAN TRIM BALANCE Introduction Why is fan trim balance necessary for the CFM56-7B engine? Purpose (2.B.a.) The purpose of the engine fan trim balance is to bring back the engine vibration level to a satisfactory level. This ensures that: - The engine reliability will not be affected by abnormal vibration, - Engine performance level is maintained for all operational phases, - Cabin noise is maintained to a satisfactory level.

The trim balance procedure should limit vibration levels measured on fan and Low Pressure Turbine to 1.5 AVM units during all engine ground runs.


71-00-00

Page 2 Aug 99

CFM56-7B

TRAINING MANUAL

FAN TRIM BALANCE EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 3 Aug 99

CFM56-7B

TRAINING MANUAL

FAN TRIM BALANCE Identification (1.A.a) These are the conditions where Fan Trim balance procedure is performed on the CFM56-7B to reduce engine vibration levels: - Fan or/and LPT vibrations are equal or more than 3 AVM units or 6 mils Double Amplitude. - After the replacement of 1or more fan blades and the correction weight installed on the spinner cone is more than 3.36 pound inches or 600 cm.g. - After the repair of 1or more fan blades and the correction weight installed on the spinner cone is more than 3.36 pound inches or 600 cm.g.


71-00-00

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CFM56-7B

TRAINING MANUAL

REASONS TO PERFORM A FAN TRIM BALANCE EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 5 Aug 99

CFM56-7B

TRAINING MANUAL

FAN TRIM BALANCE Maintenance Practice (3.E.a) These are the two different maintenance practice procedures available to perform fan trim balance: - Airborne Vibration Monitoring Unit (AVM) Method -The 3 Shot Plot Method Airborne Vibration Monitoring Unit (AVM) The procedure using the Boeing on board optional equipment installed in the airplane electronic bay on the E3-2 shelf. This procedure is uses the vibration data for phase angle and vibration levels collected during the last 32 flight legs and when necessary during engine ground runs. The AVM uses these signal inputs to calculate vibration levels: -Vibration sensor from N1 bearing -Vibration sensor from the FFCCV -N1 Speed Sensor -N2 Speed Sensor The AVM signal conditioner continuously calculates vibration data for several areas of each engine. -Fan and LP compressor -HPC Compressor -HPT Turbine -LPT turbine The highest vibration level is displayed on the CDS, on the vibration indicator. EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

The four possible vibration monitoring units are the (Endevco -203, -213 and Vibrometer -103, -113). These units calculate the amount and location of weight necessary to balance the engine back to a normal level. The PO weight is selected and then needs to be installed in the engine rear cone by the technician. (Refer to the AMM 71-00-00 for more information.) The 3 Shot Plot Method In case your aircraft is not equipped with such optional vibration monitoring units, you still have one way to get your engine balanced using the alternate manual procedure called "the 3 shot plot."

71-00-00

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CFM56-7B

TRAINING MANUAL


71-00-00

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CFM56-7B FAN TRIM BALANCE General (3.E.a) The 3 shot plot procedure philosophy This method is used when no equipment is available to find out the phase angle of the engine unbalance. To find out the location and amount of weight to install on the engine rear spinner cone, engine runs must be performed. A minimum of 5 runs are necessary. Initial run The actual engine unbalanced condition is recorded through different engine speeds. First run Balance weights are installed on the spinner cone, and engine is operating at the same speeds that during the initial run and vibration levels are recorded. Obviously, the vibration amplitudes change and are more or less important that the one recorded during the initial run. Second run Balance weights installed for the engine first run are removed and installed in different position 120° ap art) ,


TRAINING MANUAL

Engine is run again at the same speeds that the earlier runs, and vibration levels are recorded. Once again, Vibration amplitudes change, and are more or less important that previous engine runs. Third run Balance weights installed for the engine second run are removed and installed in a different position (120° apart) from the second run. Engine is run again at the same speeds, and vibration levels are recorded. Once again, Vibration amplitudes change, and are more or less important that amplitudes recorded during previous engine runs depending on the position of unbalance. Engine runs analysis From the engine runs recorded data, a manual vectorial construction is performed to determine the amount of balance weight to install, and the position to install the weight. This is calculated using the different forms available within the Boeing Maintenance Manual. Weight is then installed on the engine rear spinner cone according to the analysis calculation. Final run The engine is operated to record the engine vibration amplitude, and to verify that the level is within limits. NOTE: If during engine run with test weights installed the vibration level is measured within limits, the fan trim balance procedure is finished.

71-00-00

Page 8 Aug 99

CFM56-7B

TRAINING MANUAL

3 SHOT PLOT PHILOSOPHY EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 9 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Aircraft and engine preparation is to be performed prior to operation of the engine. To read vibration in mils, vibration equipment is to be installed. The vibration indicator in the flight compartment reads in units and is not possible to read vibration in mils. If the aircraft is not equipped with unbalance phase angle recording features, it is not possible to know if vibration is generated by the N°1 bearing vibration sensor or th e FFCCV sensor. It isn't possible to read vibration in mils either. To obtain more information, install a selector switch which isolates the signals coming from the vibration sensors, and install the breakout cable. Disconnect the AVM signal conditioner from its support (Refer to the AMM 77-31-00), and connect the breakout cable to the electronic shelf connector. Route the breakout cable up to the flight compartment area and connect it with the selector switch.


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CFM56-7B

TRAINING MANUAL

PREPARATION EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 11 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Initial run Prior to start the engine, a careful record of the actual balanced screws installed on the rear spinner cone must be performed. Record the configuration on the Balance screw location chart. Then start the engine, and bring it to stabilized thermal condition if the engine was shut down for more than 6 hours. The stabilized engine thermal condition is obtained running the engine at 80% N1 for at least 5 minutes. If the engine was not shut down the last 6 hours, stabilize the engine in idle for 3 minutes, and then slowly accelerate the engine until the takeoff N1 target of the day is reached.

Decrease the engine speed to the next lower N1 speed target defined in the AMM, (now 93,7%) and record the vibration levels red from the N°1 bearing sensor an d FFCCV sensor. Important: Wait engine EGT and N1 parameters to stabilize prior to record those data. Follow the same exact procedure to record vibration levels for the next lower speeds. (85%, 81%, 66%, and 54%). Shut down the engine, and prepare balance weights for the next run called engine first run.

Important: Stop engine acceleration if the vibration level equals 4 units on the vibration gage or 8 mils scale on the indicator overlay. Stabilize the engine at the T/O N1 target (if you can reach this RPM) and record the vibration amplitude for both N°1 bearing sensor and FFCCV sensor. Selection of sensors output is selected through the selector switch. EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

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CFM56-7B

TRAINING MANUAL

ENGINE INITIAL RUN EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 13 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) First run Install three balance screws P05 instead of P07 balance screws installed on the rear spinner cone. You can now start the engine, stabilize it in idle. The engine warm up procedure (stabilization at 80% N1) is not needed. Repeat exactly the same running procedure that the initial run to record vibration amplitudes for both N°1 bearing sensor and FFCCV sensor. Record the vibration amplitudes into the second column of the three shot plot worksheet form.


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CFM56-7B

TRAINING MANUAL

ENGINE FIRST RUN EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 15 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Second run Remove the three P05 screws which have been installed during the last run, and replace them with P07 screws. 120° apart from their latest position, install the three balance screws P05 instead of P07 balance screws . You can now start the engine, stabilize it in idle. The engine warm up procedure (stabilization at 80% N1) is not needed. Repeat exactly the same running procedure that the last run to record vibration amplitudes for both N°1 bea ring sensor and FFCCV sensor. Record the vibration amplitudes into the third column of the three shot plot worksheet form.


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CFM56-7B

TRAINING MANUAL

ENGINE SECOND RUN EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Third run Remove the three P05 screws which have been installed during the second run, and replace them with P07 screws. Next install 120° from P05 second run posit ion, install the next three balance PO5 screws after removing the P07 balance screws. Now start the engine, stabilize it in idle. The engine warm up procedure (stabilization at 80% N1) is not needed. Repeat exactly the same running procedure that the last run to record vibration amplitudes for both N°1 bea ring sensor and FFCCV sensor. Record the vibration amplitudes into the fourth column of the three shot plot worksheet form. Shut down the engine and proceed to the next step.


71-00-00

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CFM56-7B

TRAINING MANUAL

ENGINE THIRD RUN EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 19 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Once all data have been accurately recorded, determinate the location and amount of weight to install on the rear spinner cone to correct the engine unbalance. Note: To facilitate the calculation, select only the speeds where the three highest vibration amplitudes from each sensor have been recorded in the initial run. Give an identification letter to each one of the recorded vibration amplitude; - A = highest vibration level - B = second highest vibration level - C = third highest vibration level for N°1 bearing sensor. - D = highest vibration level - E = second highest vibration level - F = third highest vibration level for the FFCCV sensor.


71-00-00

Page 20 Aug 99

CFM56-7B

TRAINING MANUAL

3 SHOT PLOT EXERCISE EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

Page 21 Aug 99

CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Represent the initial unbalance on a polar graph. Choose a correct scale size that will fit on the polar graph. Represent each of the 6 points A-B-C and D-E-F on a different polar graph to get accurate representation. For each point, draw one circle from the center of the polar graph. The radius of the circle you draw is equal to the vibration amplitude that was recorded for the point selected. Note: For training purposes, only one point (A) construction will be demonstrated in detail, the other points will be shown later. For the point A, the vibration amplitude equals to 6.5 mils. First define a scale which suits the amplitudes for point A, and then draw a circle of radius 6.5 from the center of the polar graph.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Represent the First engine run vibration behavior with the set of PO5 balance weights installed. To represent it, draw a circle which has the radius of the vibration level for the selected point (A), using the identical scale used the step earlier. For this example, the vibration level recorded for the point A was 4 mils, so, draw a circle with the radius taken from the scale. Its center is located at the intersection of the initial unbalanced condition circle and the radius passing from the center of the graph to the central balance screw position (here position 35).


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CFM56-7B

TRAINING MANUAL


71-00-00

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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Represent the second engine run vibration behavior with the set of PO5 balance weights installed. To represent it, you must draw a circle which has the radius of the Vibration level for the selected point (A), using the identical scale you used the step earlier. For this example, the vibration level recorded for the point A was 8.6 mils. Its center is located at the intersection of the initial unbalanced condition circle and the radius passing from the center of the graph to the central balance screw position (here position 23).


71-00-00

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CFM56-7B

TRAINING MANUAL


71-00-00

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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Represent the third engine run vibration behavior with the set of PO5 balance weights installed. To represent it, you must draw a circle which has the radius of the balance level recorded at the third run for the selected point for the (A). For this example, the vibration level recorded for the point A was 7.8 mils, so, with the scale, it is represented with a 47 mm radius circle. Its center is located at the intersection of the initial unbalanced condition circle and the radius passing from the center of the graph to the central balance screw position (here position 11). The scale used is: 6 mm for 1 mils of vibration.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process The resultant R for the point (A) is the vector which is drawn from the center of the polar graph, and the intersection of the 3 circles drawn for each run. NOTE: If during your construction, the 3 circles do not cross in one point, draw the vector from the center of the polar graph to the center of the common area of those 3 circles. For this point (A), according to the scale we used, the amplitude in mils equals 2.7 mils. The angle of this vector has to be measured from the vertical axis, so for this point (A), the angle equals 5 degrees.

W6 = 831.8 x U0 (initial unbalance) R1 (calculated resultant for point A) For point (A), this is 831.8 x 6.5 = 2002 cm.g 2.7 The final calculation for the point (A) concerns the sensitivity. It represents how the additional weights PO5 added to the engine in 3 different positions (120 ° apart) affect the balance condition of the engine for this particular speed. Sensitivity = 831.8 = 831.8 = 308 R1 2.7 Calculate and fill in the information for all the remaining points onto the corresponding form .

Calculate the balance weight W6 corresponding to the point (A) using the formula.


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CFM56-7B

TRAINING MANUAL


71-00-00

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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process The angle of this vector has to be measured from the vertical axis, so for this point (A), the angle equals 5 degrees. You must also calculate the balance weight W6 corresponding to the point (A) using the formula The angle of this vector has to be measured from the vertical axis, so for this point (A), the angle equals 5 degrees. Calculate the balance weight W6 corresponding to the point (A) using the formula The next step is to represent graphically each calculated balance weight W6 for all the different points A, B, C, D, E, F onto one polar graph. Note: You must select a scale which permits you to draw each point onto the polar graph. For this example a scale of 1 cm for 500 cm.g is selected. Report each balance weight point at the correct angle onto the polargraph.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Using the last polar graph fill out the form to calculate the maximum amplitude for each vector. To calculate it, you must graphically joint each point which is mentioned in the form, starting by AB, then AC, then AD, up to EF. Note: Once you measure the distance in between a and B, A and C, don't forget to transform this distance into moment weight using the same scale as used earlier 1 cm corresponding to 500 cm.g.

Do the same for all the remaining vectors AC, AD, etc. Once all amplitudes (U) have been calculated, select the highest one to calculate the distance from P1. In this example, the selected one is corresponding to the vector AD, where the amplitude equals 2.623. Using the formula which is the amplitude multiplied by the sensitivity of the point A, we will find the distance from point A.

For vector AB: To fill out the first Sensitivity P1 column, get the information (point A) from the chart . To fill out the second Sensitivity P1, get the information (point B) from the chart. You just need to make the addition of those two columns to fill out the SP1+SP2 column. To calculate the amplitude (U), use the formula provided into the form which corresponds to the distance of the considered vector (AB) divided by the sum of the sensitivity you calculated in column SP1+SP2. EFFECTIVITY 737-600/700/800/900/BBJ/COMBI/C40A CFMI PROPRIETARY INFORMATION

71-00-00

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CFM56-7B

TRAINING MANUAL


71-00-00

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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process On the polar graph you used earlier and using the same scale, report the distance you calculated onto the form, starting at the point A. Draw the vector from the center of the graph to this point, and measure it. Transform this distance into balance weight using the scale, and measure the angle from the vertical axis. Record this value on the form, this is what you need to balance the engine. In this example, the result is 1550 cm.g at 26°.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process In this example, the result is 1550 cm.g at 26°. Going to the balancing weight location form, find out the physical location of balancing weight position. In this example, the measured angle is 26°, so the calculated angle selection is the one in between 23 and 27 degrees. The balancing weight must be centered into 2 screws positioned in 34 and 35.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Balancing weights calculation process Using the PO weight chart, find the balancing weight required centered into two screws in figure 514. Find on the right hand side column, the closest balance weight corresponding to the calculated balance weight needed. For this example, 1527cm.g is the closest to the 1550 cm.g needed. Balance screws selection is mentioned on the horizontal line corresponding to the 1527 cm.g. For this example, 6 screws are needed, and they are: - 2 P06 screws - 4 P04 screws. To install them, number the screws from the horizontal centerline in counterclockwise direction, corresponding to the balance screws position Aft Looking Forward. In this example, install P06 screws in position 34 and 35, and P04 screws in position 32, 33, and 36 and 1.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

THE 3 SHOT PLOT EXERCISE Maintenance Practice (3.E.a) Last Engine Run Remove the old balance screws and install the new balance screws at the correct position in the rear spinner cone. Start the engine and operate it at the same speeds as before on the run sheets. Record the vibration levels at the determined speeds and record them onto the vibration recording form. Check that all vibration levels are below the limits found in the AMM 71-00-00. This concludes the fan trim balance "3 shot plot" procedure.


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CFM56-7B

TRAINING MANUAL


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CFM56-7B

TRAINING MANUAL

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Fan Trim Balance

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