Knife edge 2

[hanosh]

hi,

could any one tell me what is meant by Knife edge condition and feather edge condition in relation to Aircraft structures.How to avoid these?

Thanks,

Hanosh

 

[prost]

Knife edge, in one meaning of the phrase, means there is little to no straight bore. Drill a countersunk hole in a sheet or plate, you get a countersink, and a straight bore hole. If the countersink is too big, so there is no straight bore in the hole, then you get a knife edge. Side
view of a hole countersunk in a thin sheet--see how sharp
the edge between the countersink and the bottom horizontal
surface? that's the knife edge:

_________ ________________
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\ /
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___________\ /______________

no idea about feather edge.

 

[rb1957]

Knife-edging is when the rivet/fastener countersink is more than 2/3rds the thickness of the sheet ... this is general practise. i'd guess feather edge means that the CSK is >=100% of the thickness

 

[InteroperabilityFix]

to avoid a knife edge, you need to dimple the skins under the head of the countersunk fastener.

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[prost]

Sorry about my little stick drawing; it looked ok in the Preview.