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Landing Gear Strut Operational Readiness Monitoring


OBJECTIVE: Develop an innovative approach for monitoring and assessing the operational readiness of landing gear struts. Specific considerations for fluid level confirmation, pressure verification and temperature measurement. DESCRIPTION: Landing gear shock struts utilize an oleo-pneumatic (oil/gas) design which provides the primary load path from ground reactionary forces to the airframe structure. Ground maneuvers from stopping, turning and towing transmit loads through the shock strut to the airframe. A critical characteristic role of the shock strut is to cushion impact forces due to landing by converting some of the aircraft's kinetic energy into heat, which is dissipated through the conduction/convection heat transfer from the fluid through the outer cylinder and piston. This critical function ensures that the airframe structure does not experience high impact loads which could negatively impact the structural integrity of the airframe, increasing mishap risk and/or maintenance burden and costs. In order for the shock strut to operate and function properly it must have the correct gas to fluid ratio. Once a strut is serviced, it is a closed fluid and gas system with minimal external indications of proper and/or improper servicing. Physical inspections are the primary means of monitoring and assessing the operational readiness of shock strut systems. These inspections, many required on a daily basis, are time-consuming and often result in improper servicing in order to satisfy mission schedules and demands. Accurate assessment of landing gear operational readiness is not a trivial requirement and must be addressed appropriately if mishaps and airframe damage are to be avoided. Given recent technological improvements, including robust sensors, wireless communication devices, and miniaturized data acquisition systems; a multi-function system can be developed which has the ability to measure and transmit landing gear operational parameters to the maintainer in real-time and have the capability for data storage. Critical primary characteristics to be measured and transmitted are hydraulic fluid level and gas pressure with additional information such as temperature being secondary. The acquisition system and data transmittal need be unobtrusive with minimal impact to the strut configuration. Power for system operation shall be self contained. The system needs to be easily accessible for removal and replacement if necessary. The ability to check and verify the condition of landing gear shock struts without physical inspection will significantly reduce the maintenance burden and support readiness objectives. PHASE I: Determine the technical feasibility of developing a multi-function system that can be used to capture and assess the operational readiness (fluid level, pressure, and temperature) of shock strut systems. Conduct preliminary feasibility evaluations and down-select those approaches considered to be most appropriate for further consideration. PHASE II: Fully develop, demonstrate, and validate a multi-function landing gear shock strut monitoring system, using the equipment/approaches identified in Phase I, on a representative landing gear system. Ensure that the proposed system is highly reliable and that it satisfies the performance objectives defined in Phase I. Develop and provide an overall cost benefit analysis for the multi-function system developed as well as a conceptual implementation strategy plan for a fleet-wide retrofit program. PHASE III: Commercial aircraft landing gear are functionally equivalent to military aircraft landing gear. The desire for reduced maintenance on commercial aircraft will mirror the USAF requirement. Validated shock strut monitoring equipment will benefit both commercial and USAF market. REFERENCES: 1. Aircraft Landing Gear Design: Principles and Practices; Norman S. Currey; 1988. 2. Flying Safety Magazine, The Mysterious x-Dimension; Chad Hogan P.E. and Craig Pessetto P.E.; August 2002. 3. Metallic Materials Properties Development and Standardization (MMPDS); Battelle Memorial Institute.
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