When aircraft is rolling?

Question

Why is it that whenever an aircraft rolls, the lower wing will have a higher AOA compared to the upper wing (lower wing will generate more lift than the upper)? Every article that I've found only tells of the difference in AOA but never the reason why it happens.

Answer 1

Think relative wind. As the wing moves downward the relative wind changes from mostly forward of the wing to slightly under the wing, thus increasing the AOA.

Answer 2

The outer (high) wing will have a larger turn radius, so he has to turn faster. Both wings will have the same true angle compared to the earth. But angle of attack is compared to the airflow, and not to the earth. So it's actually the angle at which the air hits the wind. By going faster, the relative wind hitting the wing increases, thus decreasing the angle of attack. The lower wing will need that higher angle of attack to stay in the air, if the lower wing that's traveling slower had the same angle of attack that wing would be descending. I find it difficult to explain this, so maybe the drawing underneath will clarify more.

Answer 3

One explanation is that in a bank (not talking a roll, per se), in a low-wing aircraft, the lower (inside) wing  is closer to the horizontal than the raised (outside) wing. As a result, its lift is less deflected from the vertical. Here is a link to a discussion, with illustrations, in the context of dihedral and roll stability.

http://www.eaa838.org/dihedral.asp

By the way, the "gust of wind' reference is one thing, but the real roll experience to remember is a bona fide wake turbulence encounter, but I digress.

Answer 4

The reason for the higher aoa of the OUTER wing is because of a difference in relative airflow. Imagine an aircraft doing one complete rotation of a continuing climbing turn. Obviously all points on the airframe are going to take the same time to achieve the higher altitude, however the spiral followed by the outer wingtip must have a larger radius than that followed by the inner and therefore the path followed by the outer wingtip is not as steep as that followed by the inner. The less steep path of the outer wing (i.e. the relative airflow) means that the aoa of the outer wing will be greater than that of the inner. You might have to think about it a bit!

Answer 5

The lower wing should actually have a decreased total AOA due the fact that the the aileron is deflected up a couple of degrees and therefore decreasing the AOA on the outboard section of the wing.