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Structures and Materials Division Research and Technology Directorate NASA Glenn Research Center

Tribology and mechanical Components Branch
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Aero Drive Systems - Drive Systems Health Management
Research Objectives
Helicopter safety depends on the reliability and integrity of the mechanical components in the transmission. Damage to transmission components produce specific fault patterns in vibration signatures. Vibration-based Condition Indicators (CI) are used to assess transmission health and diagnose component damage. Components monitored in the Health Usage Monitoring System (HUMS) include the main and tail rotors, their gear boxes and drive trains. Research objectives for drive system health management include:
  • Develop performance metrics (detection rates/false alarms) for drive system diagnostic tools used to identify the transmission health.
  • Develop diagnostic technology and physics based tools to correlate drive system health with damage magnitude and predict when the component requires maintenance action or removal.
  • Validate transmission component damage life prediction models using component failure characteristics to measure remaining useful life.
  • Partner with the U.S. Army to incorporate health usage monitoring and condition based maintenance technologies into the Army's Helicopter fleet.
  • Partner with the FAA to validate transmission mechanical system condition indicators to be used to obtain maintenance credits for specific mechanical components.
Technical Challenges
Although commercially available Health Usage Monitoring Systems (HUMS) for monitoring drive system components are providing significant safety benefits when installed on rotorcraft, the fault detection success rate of today’s helicopter health monitoring systems through vibration analysis is still in need of improvements. HUMS experience documented by the CAA (UK Civil Aviation Authority) in 1997, and informally updated in 2002, shows a success rate of 70 percent in detecting faults. The following obstacles still need to be overcome to achieve full safety and economic potential of an integrated health monitoring system:
  • Limited helicopter vibration fault data.
  • Systems complex - Experts required for data analysis.
  • Standard thresholds for types/levels of damage are not clearly defined.
  • Performance assessment methods have not been developed.
  • Tools required to assess damage magnitude/severity
  • Correlating seeded fault tests with field data
  • Development of life prediction technologies
  • Health monitoring outputs providing maintenance actions
Current Research
NASA TM 215262, “Signal Detection Theory Applied to Helicopter Transmission Diagnostic Thresholds,” has been published. In the paper, signal detection theory analysis techniques were applied to the gear and bearing condition indicators (CI) from the bearing and gear anomalies confirmed to date on the Blackhawk and Apache helicopters. Identifying a CI that reliably detects damage to specific components is required for the credit validation phase of HUMS airworthiness approval. The analysis was applied to helicopter faulted and healthy datasets to create a set of Receiver Operating Characteristic Curves (ROC) curves. Receiver Operating Characteristics (ROC) curves are used in signal detection theory to identify tradeoffs between hit rates and false alarm rates. They are used in medical fields for health decision making and to assess the predictive accuracy of the tools used to make these decisions.

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Dr. Paula Dempsey
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Last Updated: April 21, 2009