An Analysis of Maneuvering Effects on Transmission Vibrations in an AH-1 Cobra Helicopter

During the past several years, an AH-1 Cobra aircraft at the NASA Ames Research Center has been instrumented with tri-axial accelerometers and a data acquisition system to support the experimental study of in-flight transmission vibration patterns. This paper describes the on-board HealthWatch system and presents important statistical analyses of the collected data sets. These analyses provide insight into how transmission vibration responds to several factors typically related to health and usage monitoring systems (HUMS), such as maneuver condition, order of execution, and pilot differences. Although a large database of flight recordings has been collected, these results focus on an overall analysis of planetary ring gear data that were recorded in two sets of flights. It is shown that variability due to torque is a major factor to be considered in real-time HUMS design and that certain steady state maneuvers yield a dramatically higher percentage of stationary recordings. Finally, it is conjectured that multi-axis recording may have previously unrecognized advantages for signal conditioning or analysis.