For propellors: At low airspeeds angle-of-attack is almost the same as the angle between the chord line and the plane of rotation. At high airspeeds, relative wind changes this so that the wind that hits the prop comes more from the direction of movement, and thereby reducing aoa.
This also applies for differencial thrust between upgoing/downgoing prop blades. At low airspeeds: The upgoing has a larger angle between relative wind and plane of rotation than the downgoing, this causes a larger proportion of rel. wind to decrease the aoa. The downgoing has a smaller angle between relative wind and plane of rotation, so the wind hitting the blade is closer to the plane of rotation than on the other side.
Make a drawing, it's quit easy to see!
Cheers!
How about this:
The upgoing blade is moving a bit backwards, the downgoing a bit forward.
To get a descent lift from any profile, you need a positive aoa.
Sitting in a moving car with your hand out in the air, it's quit easy to feel the lift because of forward motion and positive aoa. Consider moving your hand backwards to create lift...it can't be done because you can't get a positive aoa due to the movement of the car.