1. 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

2. 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.

3. 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.

4. 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

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

6. RAPTOR vs. Theory
The discrepancy is RAPTOR run driven

7. Monte Carlo vs. Theory
The discrepancy is < 3%

8. Monte Carlo – Weibull vs. Theory

9. 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.