Investigation of F/A-18 AMAD Gearbox Driveshaft Vibration

摘要

The RAAF has experienced several failures of the input bearing of the F/A-18 AMAD (Aircraft Mounted Accessory Drive) gearbox. Two of these failures have resulted in in-flight fires. Measurements of input housing vibration showed very high vibration levels on some aircraft, apparently due to unbalance in the driveshaft assembly. Subsequent measurement of drive-shaft motion confirmed synchronous forward whirl of the driveshaft. The driveshaft system appears to operate below its first critical speed, but there are indications that the first critical speed may not be far above running speed. There is no evidence of significant driveshaft system resonances during the operating speed range of idle to full military power. The unbalance appears to result primarily from clearances in the AMAD gearbox input shaft assembly. These clearances will bring about an initial unbalance of the assembly much greater than specified component tolerances. Partial alleviation of the high vibration has been brought about by rotation of the 19E215-1 driveshaft relative to the input power take-off shaft assembly.