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I've found that as the angle of attack increases, the moment becomes more negative. I wanted to know what does that negative value say about the characteristics of the airfoil, and what is its importance.
A negative pitching moment is stabilising: it is a nose down pitching moment, which is what is required for static stability.
If the stabilising moment of the wing profile increases with AoA, the horizontal tail volume can be smaller - less resistance.
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