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I've discussed this with my instructor numerous times, and I have the concept memorized, but from an aerodynamic point of view, I can't see how the angle of relative wind to chord line is different per wing (assuming a Cessna 172, if that makes much of a difference).

The wings are essentially a straight line over the top of the plane, and relative wind is a single vector - to me, it looks like they should have identical AoAs.

If you know of a graphic or video, I think it would help explain best.

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Most, but not all, wings have some dihedral (the 172 does), and I don't think a wing with dihedral (or one with anhedral) can be treated as a straight wing. – Terry Aug 2 '14 at 17:50
@Terry wow you're right; I remember learning that in class a while ago - wonder how I forgot. – Josh Toth Aug 4 '14 at 13:45
up vote 9 down vote accepted

You are mostly correct, but the fuselage distorts the airflow in sideslip such that the windward wing sees a higher angle of attack near the root, and the leeward wing a lower angle of attack. Please see the drawing below for an explanation.

Comparison of two wing positions and their effects in crossflow

The blue lines show the sideward component of air flow and the red arrows the resulting rolling moment.

This is why low wing airplanes need more dihedral, and high wing planes like your 172 almost none. Wing sweep adds more directional stability, and then you even find aircraft with pronounced anhedral, like the Harrier jump jet or the F-104 Starfighter. See this answer for more detail on this.

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Thank you! It's still slowly sinking in, but I believe it makes sense :) – Josh Toth Aug 4 '14 at 13:42

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