INNOVATIVE METHODOLOGY TO ELIMINATE THE FLICKERING OF NEEDLES IN THE ENGINE RPM (TACHO) INDICATOR BY INTRODUCING ONLINE THREE AXIS VIBRATION FASCILITY DURINF FUNCTIONAL TESTING

摘要

Tacho indicator unit is used to measure the Engine RPM. Since the number of premature withdrawal of aggregates from aircraft as well as the increased number of snags observed during control test station checks before test flight the above tacho indicator unit was categorized as High failure unit. . The tacho indicator has two needles engaged to the gears for indicating the N-l & N-2 RPM of engine shaft . There is a very fine adjustment and setting required for the meshing gears of the mechanism . In the test lab this adjustment of the matching / meshing gears was done as per the standards however during the actual testing on aircraft the fine or optimal meshing was disturbed due to gap or tight mesh during assembly . It was necessary to simulate the conditions on the aircraft during the functional test of the tacho meter so as to achieve optimum meshing to have uniform rotation of the gears and eliminate the flickering of the needles . An elliptical holes are made in the body of the housing where the shaft is fitted , this enables the axis of the shaft to be aligned so as to achieve optimal mesh without gap or over interference. A Three-axis Vibration facility has been set-up so that the functional test and the optimal setting of the needles can be done on line . The vibrations in all the three axis provides a perfect setup which is similar to the conditions when the aircraft is in running condition. This helps in measuring the amount of flickering of the needles of the tacho indicator and take necessary measures to achieve the correct setting of the gears to eliminate the flickering of needles. Thus the setting as well as the functional tests of the tacho indicator is carried out simultaneously during the same setup .