A Helicopter Planetary Gear Plate Crack Analysis and Feature Extraction Based on Ground and Aircraft Data

Fatigue cracks of considerable length were discovered in two separate main transmissions planetary gear carrier plates of U.S. Army helicopters. These cracks originated at the blend between the gear post and the plate and later diagnosed as low cycle fatigue. Cracks on the planet carrier plate are a very serious but rare type of fault that may require the redesign of this critical part. In this paper, an investigation of the problem is attempted using experimental data from ground and aircraft tests. Two features based on the signal energy are used to distinguish the faulty from the healthy plate using the signals from four one-dimensional accelerometers. A data analysis based on the time synchronous averaging signal transformation, tends to indicate that besides any machining error or material fault that may have initiated the crack, there is evidence of a non-rotating fault. A possible explanation of this fault is a deformation of the ring gear, or a considerable non-uniform distribution of forces among the planet gears that may have been generated by the presence of the crack and or may have promoted its rapid development