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Wing Flap and Spoiler Recesses (Piano hinge)

Wing Flap and Spoiler Recesses (Piano hinge)

  • Sometimes Dirt and water may collect in a flap and spoiler recesses unnoticed because they are normally retracted. For this reason, these recesses are potential corrosion problem areas. Inspect these areas with the spoilers and flaps in the fully deployed position.
External Skin Areas :
  • External aircraft surfaces are readily visible and accessible for inspection and maintenance. Even here, certain types of configurations or combinations of materials become troublesome under certain operating conditions and require special attention.
  • Relatively little corrosion trouble is experienced with magnesium skins if the original surface finish and insulation are adequately maintained. Trimming, drilling, and riveting destroy some of the original surface treatment and can never be completely restored by touchup procedures.  
  • Any inspection for corrosion must include all magnesium skin surfaces with special attention to edges, areas around fasteners, and cracked, chipped, or missing paint.
  • Piano-type hinges are prime spots for corrosion due to the dissimilar metal contact between the steel pin and aluminum hinge. They are also natural traps for dirt, salt, and moisture. 
  • Inspection of hinges must include lubrication and actuation through several cycles to ensure complete lubricant penetration. Use water-displacing lubricants when servicing piano hinges.
  • Corrosion of metal skins joined by spot welding is the result of the entrance and entrapment of corrosive agents between the layers of metal.
  •  This type of corrosion is evidenced by corrosion products appearing at the crevices where the corrosive agents enter. The more advanced corrosive attack causes skin buckling and eventual spot weld fracture.
  • Skin buckling in its early stages may be detected by sighting along spot-welded seams or by using a straightedge. The only technique for preventing this condition is to keep potential moisture entry points, including seams and holes created by broken spot welds, filled with a sealant or a suitable preservative compound.
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