Origin of "By the seat of your pants"

Quote:

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By the seat of your pants If you do something by the seat of your pants, you do it without help from anyone.

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Hi! I got the idiom from this BBS.
http://www.usingenglish.com/reference/idioms/by+the+seat+of+your+pants.html


Would you please tell me something about its origin? Thanks. :roll:

Go here:
Fly by the seat of one's pants

Thank you, oregeezer! I got it.:-)