TM   55-4920-402-13&P a. First, using the information derived from the Balan- cer/Phazor. a point is plotted on the chart at the intersec- tion of the clock angle line and the IPS circle. The point is labeled no. 1. b. If the IPS reading is off scale (vibration level too high) The PUSH FOR SCALE 2 button is pushed to take the reading. Then when the point is plotted on the chart, the IPS reading should be divided by 2, or 10, or some number that will yield a result of less than 1.0; i.e., 1.8 IPS might be plotted at 0.9 etc. Then, the indicated weight changes must be multiplied by the same factor pre viously used (2 or 10, etc.) c. From this point, lines are drawn to each of the two axes of the chart to determine the weight change required for balance, or pitch link change required for track. Change only one axis fro the first move (select the one far- thest from the zero axis line). Additional readings are then taken, after corrective action, and replotted on the chart. The  replotted  line  should  now  move  to  the  zero  axis  line indicating  no  further  changes  is  required  to  the  axis  to which the change was made. Now the indicated weight should  be  added  to  the  other  axis,  which  should  move  its plotline to the center of the chart, thus achieving final balance.  This  is  illustrated  in  the  following  problem d. Refer to figure 2-7. A reading of 5:00 o’clock at 0.8 IPS is plotted on the chart as point 1. As can be seen, this calls for a weight addition of about 14 grams at A and 15 grams at B. Since the B reading is farther from the zero axis, we add 15 grams to B only and nothing to A. The next plot point is shown as 2 and should be at 7:15 o’clock, and about 0.35 IPS, The move line is now paral- lel to the arrow, corresponding to the span weight change. Now,  addition  of  the  14  grams  to  A  (chordwise)  should move the plot point to the center of the chart, point 3, for perfect balance. In practice, a reading of 0.2 or better is  acceptable. 2-10. Correction of Charts. Because IPS and clock angle, in  response  to  a  given  out-of-balance  condition,  are  a function of the mechanical response of the airframe, and since all airframes of a given helicopter type are not iden- tical,  there  is  some  spread  in  measurements.  ‘Thus,  it  may be necessary to correct the chart for the particular rotor being worked. Normally, the chart correction used for hover balance will apply to in-flight balance. This will have to be determined on a case by case basis as Air- frames exhibit different flight characteristics due to a variety of factors. a. Weights. Differences in airframe sensitivity can cause the move line to be the wrong length. Correction of this error is relatively simple since the length of the move line is in direct proportion to the amount of the weight change, e.g., if the move line is too long, too much weight was added; if the move line is too short, too little weight was used. c. Clock Corrector. To use the Balance Chart Clock Angle Corrector, refer to the instructions contained on the envelope, figure 2-8, and the Balance Chart Clock Angle  Corrector,  figure  2-9.  Detailed  instructions  are covered  in  the  following  balancing  problem. d. Balancing Problem Using Clock Angle Corrector. (1) Refer to figure .2-10. lf the chart and heli- copter are not perfectly matched, the read- ings might be as follows: (2) Assume the same first reading of 5:00 o’clock and 0.8 IPS. Add the same 15 grams at B and nothing at A. This time our sec- ond reading is 6:30 o’clock and 0.7 IPS as indicated by point 2 and the move line is not parallel to the span arrow. If we track back to the chord axis (A and C) it indicates that a change was made there however, the change was not actually made. Therefore, there  is  a  mismatch. (3) Use Clock Angle Corrector No. 3597 and place eyelet A on the first reading and align index A-C) in the direction the move line should have gone, and swing index A-B in the direction that the move line did go. We now see that we must subtract 1 hour from the  clock  numbers. (4) Then, when the two readings are plotted (1 and 2,) on the corrected chart, we see that the move line is now in the correct direction. (5) We can also see that too much weight was added to B because plot point 2 is beyond the zero line. This indicates we need to add about 25 grams to A, rather than the 14 ori- ginally shown, Thus, by subtracting about 4 from B, to which the 15 had been added, and adding 25 to A, the balance should be corrected. 2-11. Use of Gram Scale. The Gram Scale is set up as shown in figure 2-11. If small weights are to be weighed (less than 5 grams), it is important that it be set up out of the wind and very carefully balanced by the screw foot at the left end. The balancing is done with the pan attached and both the slide balance and the vernier balance at O. Small weights are measured using both the slide balance and  vernier  balance.  Larger  weights  (5  grams  or  over)  do not require the use of the vernier balance as the total range is a small percent of the weight being measured. 2-12. Use of VIBREX for Troubleshooting.  The  fol- lowing  procedures  will  assist  maintenance  personnel  in locating  vibration  problems  in  the  aircraft  that  are  caused by  faulty  linkages,  rod  end  bearings,  dampers,  transmission mounts, etc. b. Clock Angle. Clock angle error causes the chart to call for the weights in the wrong place (or in an incorrect ratio on a pair of points). A simple way to correct clock angle is to use the Balance Chart Clock Angie Corrector. 2-10 Change 4