Hydraulic System Internal and External Leakage Diagnostics

The Sikorsky Aircraft Corporation and the U.S. Army Aviation Development Directorate - Aviation Applied Technology Directorate (ADD-AATD) are jointly sponsoring the Capability-Based Operations and Sustainment Technology-Aviation (COST-A) program. The objective of COST-A is to demonstrate an integrated set of high-value diagnostics, prognostics, and system health management technologies that reduce the maintenance burden, without sacrificing safety, of six different rotorcraft systems. The major goals of the COST-A vehicle management system (VMS) effort include developing diagnostics for assessing external leakage throughout a rotary wing aircraft hydraulic flight control system as well as diagnostic assessment of internal leakage in key flight control servos. Leakage is a major driver of removals and overall maintenance burden for hydraulic flight controls systems. A technique was developed to accurately assess external leakage from a hydraulic flight control system. The goal of this effort was to optimize maintenance practice by eliminating early or unnecessary removals of hydraulic components while ensuring that conditions that actually impact aircraft safety or availability are resolved with reduced system inspections and troubleshooting effort. An approach was also developed for diagnosing internal leakage in flight control servos, providing early detection of a critical fault mode, which results in degraded performance and eventual replacement. The work included the creation of a new hydraulic test resource that enables the characterization of VMS response for baseline and faulted system states. The results of experimental fault mode studies were used to develop diagnostic approaches, and flight data playback capability enabled demonstration and validation of the resulting technologies in a representative environment as required for achieving technology readiness level 6.