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Smart maintenance of Aviation Hydraulic Fluid using an onboard monitoring and reconditioning System

Final Report Summary - SUPERSKYSENSE (Smart Maintenance of Aviation Hydraulic Fluid Using an Onboard Monitoring and reconditioning System)

This project SKYSENSE proposed the development of an optimised maintenance concept for aviation hydraulic fluids based on an autonomous onboard system capable of monitoring fluid condition and restoring it when required, thereby increasing its lifetime and preventing possible damages to the aircraft caused by fluid degradation.

Aviation hydraulic fluids are hygroscopic and, as a result, their lifetime is highly unpredictable. The performance of the entire aircraft hydraulic system is affected by the condition of the hydraulic fluid and if degradation goes undetected, it may cause damages with serious consequences. These may be economic at best or catastrophic at worst. At present, assessing the condition of the hydraulic fluid in an aircraft is laborious, time consuming and expensive. Therefore, the fluid is typically tested less than once a year, with the risk of unscheduled maintenance if the fluid has exceeded its limits of usage. Consequential interruption of the airline service bears a significant economic cost.

The project defined clear technical objectives, as follows:
- to develop an optimised hydraulic fluid maintenance program to reduce cost, downtime and environmental impact, and to increase safety and reliability of aeronautical hydraulics;
- to design, develop and validate an on-board intelligent multisensory system to monitor the critical parameters and evaluate the condition of the aviation hydraulic fluid used in most civil aircraft (phosphate ester-based fluids);
- to design, develop and validate an on-board hydraulic fluid reconditioning system to stop fluid degradation and as such enhance the fluid's lifetime almost indefinitely.

The project was structured into individual work packages (WPs), as follows:
- WP 1: Concept and system specifications
- WP 2: Selection and development of measurement techniques
- WP 3: Selection and development of water separation techniques
- WP 4: System architecture and sub-system design
- WP 5: Manufacture of test units.
- WP 6: Testing.

Three identical monitoring prototypes have been manufactured, each destined to a different set of test. The control system unit (CSU) gathers the data from the sensors and that provides the connections to the test bench. The power supply and protection boards are considered as part of the CSU. Unit 1 was put through vibration tests and unit 2 was tested against endurance and fatigue. Unit 3 was intended for the functional testing, performed by Airbus France.

The design was deemed sufficiently robust to withstand possible vibrations during functional tests and therefore does not present any relevant risk to the Esther test bench. Furthermore, it was noted that when pushing the tests to the extreme nearly all the sensors and their parts, in particular the luminescent sensors and the conductivity and capacitance sensor successfully withstand the tests. Only the infrared and particle counter sensor's electronics were damaged after prolonged vibration. Five thousand (5 000) pressure cycles and electronic cycles were performed on the unit. At regular intervals of one thousand (1 000) cycles, a check of the CSU was performed to validate that the system was behaving as expected. The unit has passed successfully the endurance test and its design is deemed fit to be integrated in Airbus Esther test bench for functional tests. Some issues related to leakage have manifested themselves due to the degradation of Orings which were incompatible with hydraulic fluid. After the fatigue test, a product acceptance test was performed, except for the part of the PAT corresponding to conductivity and capacitance sensor unit. The results of the test were within tolerance and no further leakage or problems were detected. The results were similar to the results of the initial PAT and therefore the design was deemed to have passed sufficiently the fatigue test in order to undergo tests in the Esther test bench. During the functional tests, tests were performed at two different temperatures: 41 degrees Celsius and 56 degrees Celsius (measured at SSK unit outlet). Fluid samples were taken periodically, prior to any new contamination or relevant changes applied to the hydraulic fluid under test, and for every change of temperature. This was done using the AC sampling valve on the HP manifold. These samples were sent to be tested by conventional laboratory methods in order to contrast the performance of the SSK monitoring unit against the present state-of-the-art. In general, tests were deemed a success, apart from the electrical capacitance and reconditioning tests which were inconclusive.

All relevant information can be found at the project's website, at: