An Exploration of Discontinuous Time Synchronous Averaging Using Helicopter Vibration Data

This paper explores discontinuous time synchronous averaging (DTSA) as a means for minimizing torque and related nonstationary effects on the frequency content of transmission vibration signals. Unlike conventional time synchronous averaging (TSA), DTSA averages only data for revolutions that occur in regions of a predefined state space. Using this approach, flight vibration data from the Ames AH-1S Cobra and OH58C Kiowa helicopters were averaged for each state variable category combination of torque, residual shaft speed, and torque derivative. Category ranges were established empirically using quantile methods to assure an equal number of revolutions in each marginal distribution. The relative power associated with fundamental subsets of mesh frequencies in the power spectrum were found to change in a non-proportional but highly systematic manner within the state space. These results lend support to the use of DTSA methods in health monitoring systems, and point to the need for modeling the complex mesh frequency response relationships on a dynamic basis.