TOWARD HELICOPTER GEARBOX DIAGNOSTICS FROM A SMALL NUMBER OF EXAMPLES

The United States Navy funded Westland Helicopters LTD to carry out a series of tests on the CH-46E helicopter transmission for the purpose of generating a database that can be used to evaluate diagnostic tools in general, and neural networks in particular. The database is extensive in the number of accelerometers, load conditions and diversity of faults. However, only 1–4 instances (levels) of each fault were included. Thus, the number of examples that can be extracted to train any classification scheme is limited, and well below the minimum required. We argue that instead the database is best used to develop specific signal generation models for the CH-46E helicopter gearbox. Such models can then be used to suggest meaningful features and derive appropriate signal-processing tools. Specifically, we demonstrate that the meshing vibrations induced by the large collector gear located on the quill shaft are significant and may interact with the vibrations induced by other elements attached to the same shaft. An appropriate model is developed and the effect, termed cross-gear-pair interaction, is studied using different signal-processing tools.