An Experimental Comparison of Transmission Vibration Responses from OH-58 and AH-1 Helicopters

Statistical analyses of transmission vibration patterns from an AH-1 Cobra helicopter were previously reported. Fourteen steady-state maneuvers were analyzed using multi-factor analysis of covariance. Based on triaxial recordings, it was found that only two maneuvers displayed reliably stationary time-series: low and high power forward climb. Principal Components Analysis of the triaxial RMS data was shown to aggregate a large portion of variance associated with engine torque on the fist component. In the present study the experimental procedures were repeated on an OH-58c Kiowa helicopter. Statistical results are compared with those from the earlier study, and also with data from the Glenn Research Center OH-58c transmission test facility. Analyses are also included of the comparative frequency responses of these three transmission systems, and general conclusions are drawn with regard to HUMS design requirements. Finally, future research directions are summarized for in-flight HUMS research using NASA/Army aircraft and transmission test facilities.