Anonymous asked in Cars & TransportationMaintenance & Repairs · 1 month ago

why is there a gap in the filler in every repair in sheet metal aircraft repair?

1 Answer

  • 1 month ago

    There is a break/gap between the repair part/section and the original structure so there aren't any pressure points (same reason you round off corners) to produce cracks and it allows for expansion and limited movement. Also, remember that when you make an airframe repair you use the next thickness up for the doubler(s) or extrusion section to provide the carrying strength that a stressed member (an intact skin for example) normally would provide. For example, on a KC-135 the skin is mostly 0.040" and if you need to make a patch the doubler is 0.50" while the filler is the 0.040". 

    Major issues on airframes are crack propagation and fatigue, and in flex areas, you can get not just fatigue but intergranular corrosion because the energy changes can affect the crystal structure/grain bonding by changing the electrical properties. 

    I did 20 years on KC-135s for my Air Guard unit, for the most part, we dealt with more mechanical repairs than fatigue (thankfully), but yes, there are those reasons for gapping repairs and why each repair has specific protocols. 

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