mm43
The abnormal airflow and drag conditions during this high and increasing angle of attack appears to have had a stabilizing affect. ND on the elevator would have increased the surface area facing the airflow and provided the initial lever to pitch the nose down. Provided the THS followed along, the area and angle to the airflow would have been maintained and eventually all the airfoils would have slipped into an unstalled regime.
There are other issues to be observed, and which could have favoured the establishing into this high AOA and prevented recovery.
As we know, airfoils produce lift also after CLmax is left behind, which means in the stall condition. We have two airfoils (wing and THS) and the complete fuselage producing lift at those stalled AOA areas. Prior to AF447 nobody would have believed that it would be possible to get such a big transport aircraft into an AOA above 35°
and keep it there (disregard the protections, i mean just from the aerodynamic point of view). Everybody would have expected that there would be not enough THS / elevator authority to get it there and keep it there. This applies especially if the CG is that much forward like with AF447. So we have to ask ourself, are there factors in this post stall region which helped to stabilize AF447 in that high AOA besides the THS input?
As mentioned, both airfoils produce lift in stalled condition, and if the highly sophisticated main wing of AF447 produces more upward lift at a given stall AOA than the THS is able to counter with an upward lift (Full ND) as well, then we have a big problem to get the nose down. To get the nose moving down, the THS has to produce more upforce than the wings (we for sure have to take the leverage into the equation). Do we know, how the lift generating capabilities of those airfoils changed in this high AOA regions? No, we dont know. Do we know, how the lift will change, when we go f.e. from 50° AOA to 35° AOA by THS input (assuming it has enough authority at 50AOA)? No, we dont know.
Aditional lift producing parts would be the fuselage. Would the forward part produce more lift then the rear parts, or equal or less? We dont know. How would the lift change, when we change fuselage AOA from 50°AOA to 35° AOA? We dont know.
Travel of center of lift is another issue, we have not adressed yet. How far does center of lift move (aft or forward? In normal unstalled AOA conditions center of lift moves forward with increasing AOA?) with that high AOA? We dont know.
Maybe somebody has answers to those points, but its no use to disregard those issues when judging wether THS would be effective or not and only assume them to be a non issue.
Yes i know, We seem to have evidence that THS was effective. They did some nose down and AOA and speed changed....., but those changes might not be related to the ND input, or they might have not been effective enough (due to change of effectiveness in relation to different AOA), see my comment some posts before.
Edit: Center of lift = Center of pressure Cp