FMECA & Reliability Analysis of an Elastomeric Rotating Scissor Bearing of Helicopter Jacques Virasak RPI DSES-6070 HV5 Statistical Methods for Reliability Engineering Spring 2008 3/31/2008

Objectives To perform both FMECA and reliability analyses on a typical helicopter main rotor scissor bearing assembly. To evaluate the response of the scissor bearing to failures occurring in any of its components with respect to aircraft and personnel safety as well as scissor bearing operational efficiency. To perform Failure Mode, Effects and Criticality Analysis (FMECA) in accordance with MIL-STD-1629A to address the qualitative safety requirements identified in the requirement specification. To analyze the reliability of the elastomeric shim package of the scissor bearing based on both Sikorsky and US government experiences with laminated elastomeric and metallic shim packaged production parts. To demonstrate the application of diverse techniques learned throughout the current reliability analysis classes.

If An Rotating Scissor Bearing (RSB) Fails… The loss of relative motion between the rotating scissors and the rotating swashplate will result in loss of the controllability of the main rotor, increase rotor vibration, and decrease response to control input. The loss of load transmission from the rotating scissor to the rotating swashplate will create an unbalanced rotor and increase rotor vibration.

What Is An Elastomeric RSB? Outer Member Inner Member Metallic Shims and Elastomeric Shims Z Bushings Sleeve K1 K2 K5 K6 K10 K11 Force Force

Failure Mode, Effects and Criticality Analysis (FMECA) Outer Member Inner Member Metallic Shims Elastomeric Shims

RAPTOR vs. Theory The discrepancy is RAPTOR run driven

Monte Carlo vs. Theory The discrepancy is < 3%

Monte Carlo – Weibull vs. Theory

Conclusions Elastomeric RSB is an on-condition replacement and non-repairable part. FMECA was used to ensure the save usage of the elastomeric RSB. Diverse reliability analytical tool and techniques were successfully used to analyze the elastomeric RSB.