CH47D Engine Transmission Input Pinion Seeded Fault Test


Authors: Joseph P. Petrella, James S. Kachelries and Scott M. Holder, The Boeing Company
and Thomas E. Neupert, U.S. Army
This paper summarizes an Engine Transmission Input Pinion Seeded Fault Test that was accomplished as a
portion of the validation process for the Boeing Rotorcraft Transmission Vibration Diagnostic System (TVDS)
Analyzer. The test specimen was a high speed CH47D (Chinook) engine transmission input pinion with a
known defect (i.e., seeded fault) machined into a high stress area of a gear tooth root. The specimen was
operated at "overload" conditions in order to initiate and propagate a fatigue crack from the seeded fault.
During the testing, the TVDS analyzer monitored the test pinion real time and successfully provided a
sufficient warning time of the impending failure. (Note: No metallic chips were generated during the test).
Following testing, the TVDS data (acquired real time) was evaluated along with a post--test fractographic
evaluation of the fatigue crack. During the post--test fractographic evaluation, arrest lines and fatigue
striations were analyzed to develop crack propagation data as a function of thenumber of applied load cycles.
This data was then correlated with the collected TVDS data to better understand the potential warning signals
the TVDS system could provide about the impending failure of a helicopter's primary drive system
components. In this test, the TVDS analyzer provided a minimum of eleven minutes warning time (at higher
than normal operation loads) of the impending failure, which would allow the pilot enough time to unload the
suspect engine transmission and continue to fly on the remaining engine.
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