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By Salvatore Piu

By Salvatore Piu. Navy Landing Gear Perspective Tribaloy-Treated F/A-18C/D Main Gear Shock Absorber. August 2001 HCAT mtg. F/A-18A-D Main Landing Gear Tribaloy T-400 - Treated Shock Absorber. Issue Proposed modifications Tests and flight evaluation Status. Issue.

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By Salvatore Piu

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  1. BySalvatore Piu Navy Landing Gear Perspective Tribaloy-Treated F/A-18C/D Main Gear Shock Absorber August 2001 HCAT mtg

  2. F/A-18A-D Main Landing GearTribaloy T-400 - Treated Shock Absorber • Issue • Proposed modifications • Tests and flight evaluation • Status

  3. Issue • Severe wear/scoring found on cylinder and piston at overhauls: • Currently replace 100% Piston Rings (P/N 74A410855-2001/-7001) and Snubber Rings (P/N 74A410611-2001/-7001 • Currently replace @ 90 % Piston Heads (P/N 74A410853-2003/-7001)

  4. Shock Absorber ConfigurationP/N 74A410850-1009 • Two stages • Low pressure chamber, 150 psig, 8.87 inch stroke (shown in blue) • High pressure chamber, 1265 psig, 4.25 inch stroke (shown in green) • Total Stroke: 13.12 inches

  5. Proposed Modifications • Purpose: • Reduce wear and internal damage of parts that typically get scrapped when worn -> increase time between overhauls • Changes: • Piston ring & snubber ring material change: from hard anodized aluminum to beryllium copper • Piston head treated with Tribaloy SWA UHP-180 T-400 HVOF-deposited coating • Tribaloy 400 Treated Area: • Not the main piston area typically treated with Hard Chrome • On an area where no previous coating applied

  6. Piston head

  7. Potential Benefits • Increased MTBF • Improved fleet readiness • Longer component life • Reduced overhaul costs • Increased safety

  8. Tests and Fight Evaluation • Two shocks modified, S/N EMC 0632 & EMC 0635 • Lab Tests • Shock absorber ATP (service pressure) • Load-stroke tests (verify consistency of static, load-stroke performance)

  9. Tests and Flight Evaluation • Flights • Both shocks installed on product support plane (at Boeing, St. Louis, October, 1997): 23 flights (31 touchdowns) • Performed post-flight load/stroke test (replaced leaking schroeder valve) • Both shocks installed on one in-service aircraft (May 5, 1998) • Request @ 30 CV arrested landings to provide meaningful data • Flight clearance limited to 40 CV arrested landings • Extended flight clearance to avoid interfering with fleet operations • Right main landing gear experienced planing mechanism failure with EMC 0635 ( 60 field landings, 13 FCLP, & 80 CV arrested landings • Removed both shocks immediately after planing mechanism failure

  10. Tests and Flight Evaluation • F/A-18A-D Planing Mechanism • Function: plane the main wheel axle and compress the gear (shock absorber) to fit in the wheel well • System has historical failures • 8 primary components in system • Improperly functioning shock is a suspect contributor to failures

  11. Tests and Flight Evaluation • Teardown inspection: shocks in excellent condition • Goal reset by Navy: 200 CV landings • Inspected, serviced, and placed shocks back on a fleet aircraft • Shocks on various aircraft from May 99 to June 00 • Modified shocks both participated in planing mechanism failures • For each planing mechanism occurrence, shock removed from the failed gear, inspected, re-serviced, and placed on a fleet aircraft • 5 on MLG’s with EMC 0635 (3 different MLG’s) • 1 on a MLG with EMC 0632 (one of the MLG’s previously failed with EMC 0635)

  12. Status • Flight Evaluation • Achieved 200 CV arrestments with one shock • Personnel associate modified shocks with planing mechanism failures due to repeated participation • In-service fleet evaluation halted by US Navy • Teardown inspection: • Wear observed was considerably less than would be expected (based on usage & compare to previous overhauled shocks)

  13. Status • Notes: • EMC 0635 participated in 2 planing system failures, not included in qty (5), prior to Triballoy-associated modifications. • Aircraft with modified shocks squawked for a pause in the stroking of the landing gear during landing (EMC 0635 lab tested for cause: nothing found) • EMC 0632 exhibited slow to extend characteristics prior to modifications

  14. S/N EMD 0635: Piston Head & Ring

  15. S/N EMD 0635: Cylinder

  16. Current Plan • One Additional Flight Evaluation • One aircraft with one new shock and and new-modified shock • 200+ CV & FCLP landing • Tear-down and compare both shocks • If no issues found, implement change to spares and normal overhaul of existing shocks

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