0071 00TM 1-6625-724-13&P0071 00-28TASK 3 - TRACK AND BALANCE MAIN ROTOR IN FLIGHTTROUBLESHOOTINGIt is always recommended to compare the vibration from one measurement to the next (mainly to ensure that theaircraft is responding in a normal manner). For the FLIGHT flight plan the VERTICAL readings should be trended. Totrend more than one data set perform the following:With the latest flight ID picked enter the Display mode by pressing F2.Select Trend Flights and press DO.Select the desired channel to trend (Usually interested in vertical readings in flight, 60K, 80K, 100K, 120K, and140K) and press DO.Enter the number of Test States to trend (The easiest to understand is just trend the last two flights by entering2, this will trend the most current flight with the previous flight), then arrow down to Draw Axis and change toNO by pressing the RIGHT arrow key (this will make the polar chart easier to read), and then press DO.This will display the vibration trend from the latest flight with previous flights on a polar chart. This process isdisplayed in figure 12.The AVA’s goal is to give corrections that will drive the vibration levels towards the center of the polar chart. Thequestion when viewing the polar chart is, did the vibration levels move towards the center of the chart or go throughthe center of the chart. In some cases the vibration trend will go through the center of the chart and overshoot to theother side as figure 12 shows. This is a clear indication that the aircraft is responding to the moves in a normalmanner, but the amount of the move was too much. The phase information is very important and these polar chartsshould be used to verify the reaction of the aircraft.Figure 12. AVA Vibration TrendIf the vertical vibration is increasing and moving away from center, check the orientation of the vertical accelerometer.If the vertical accelerometer is mounted upside down (connector coming off to the top), all tab and pitch linkadjustments will drive vertical vibration in the wrong direction (i.e., increasing).If the AVA solutions are not effectively reducing the vibration levels flight-to-flight, ensure that the vertical and lateralaccelerometers are wired into correct DAU channels. If the vertical accelerometer is wired to the lateral channel(ACC1) and the lateral accelerometer is wired to the vertical channel (ACC2), the AVA solutions will be completelyerroneous.Fortachometer errors, check: a. The blade tracking test port switch is in the track position for the AH-64D. b. The tachometer connector on the AH-64 to DAU cable is connected to the TACHO 1 DAU port. c. The tabs on the double and single interrupters are properly bent and that the gap between them and the magpick-up is adjusted to a gap of 0.030 to 0.070 inch.d. The wiring between the mag pick-up and the SPU. The weak link in that wiring is the splice that is approximately6 inches below the mag pick-up connection.
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