Stan,
As I said before, you've already got airflow separation long before you start moving toward CLmax. In normal flight, airflow separation is occuring closer to 30% chord. You never have laminar flow, and always have some degree of separation, aft of about 25-30% chord, or as far back as 50% chord on laminar flow wings. never mind the last 20%...that's always in some state of separation in varying degrees. As you approah to higher and higher angles of attack, the evidence of this separation increases, but it's always there.
Would it be correct to say that GENERALLY for the simple situation I posted originally, if this wing is at an aoa that it is just stalled, can we expect some flow separation on the aft 20% OR SO of the chord, and hence cause an up force on the aft section of the chord due to pressure differential between surfaces?
I'm not really sure what you're asking. What up force...are you talking about airflow causing suction causing an upforce? Are you talking about the disparity between the center of pressure on the upper surface of the wing vs. the lower surface? Airflow separation, which isn't exactly the best description, isn't sucking up the aileron or applying an upward force (Lift) on the aft portion of the wing. It isn't picking up the aileron. It's turbulent airflow. A better way to think of it is loss of lift, rather than lifting anything up.
When the airflow separates, it stagnates, and the local flow velocity drops. When it drops, pressure rises, and what you have is an increase in pressure, as well as burbling air, aft of the flow separation. It's not a vacum back there, it's just not benifiting you.
If you've seen vortex generators, these serve the function of not separating airflow, but injecting high energy air into areas where separation and loss of lift is occuring. This can increase lift by keeping energized air (and lower pressures due to increased velocities) closer to the wing/boundary layer, as well as put unstagnated airflow around the controls surfaces.
Not trying to be difficult with your question...I just don't understand exactly where you're going.