Chaps, in true PPrune fashion, there seems to be an unpleasant edge to these responses. Especially from Clandestino who seems to think its important to have a poke at my qualifications which wasn't a point I raised. But I find that edge really annoying.
I believe what the original poster was asking was to do with an aircraft in a steady state, coordinated, balanced turn. He wanted to know why the inner wing (that is the lower wing, the one on the inside of the turn) has a greater angle of attack than the outer wing and was asking why dihedral caused this. My suggestion is that dihedral doesn't cause this and unless your airspeed is very low indeed there is no discernable difference in the angle of attack of the two wings. It is the result of the very slightly different airspeed as the outer wing describes a larger turn radius but its only of theoretical interest until you are operating at very low airspeeds very close to the stall. At normal operating speeds it is of no concern at all.
The effect whereby dihedral will give a restoring couple is as follows. When an aircraft tips from wings-level into a bank, this causes the flight path to start to curve. To keep the aircraft's nose aligned with the actual direction of the flight path and relative wind at any given moment, the aircraft's yaw rate must increase. Until this happens, the aircraft's nose will point toward the outside of the turn in relation to the actual direction of the flight path and relative wind at any given moment. The aircraft's yaw polar inertia in yaw will tend to cause the aircraft's heading to remain constant as the flight path starts to curve. This is a sideslip. The resulting sideways component in the relative wind will interact with the aircraft's dihedral geometry to create a difference in angle-of-attack between the two wings, which will create a roll torque in the direction of a restoring couple.
But this effect has nothing to do with a steady state, coordinated, balanced turn. And if it does, I'm happy to hear about it because I haven't before.
Except that I'm tired of the underlying abusive tone on PPrune from contributors like Clandestino. I just don't care enough to carry on being interested in trying to contribute to intelligent debate to have someone have a pop at my ATPL - what does it even mean, perform it twice?