HeavyMetallist
@RetiredF4: As I mentioned previously, an aerofoil doesn't cease to be an aerofoil and stop producing lift just because it's at high AoA and stalled. Yes, it produces a lot of drag (component of force parallel to the airflow) as your barndoor would, but there is still significant lift (component of force normal to the airflow). Since you don't want to just take my word for it (fair enough), here's a link to a study specifically of post-stall aerofoil behaviour; it has a good set of Cl/Cd/Cm-alpha graphs going up to extremely high AoA. You'll notice that the motivation for this study wasn't aircraft behaviour, but wind turbines; there's been a lot of interest in post-stall aerofoil chracteristics because they spend quite a bit of their time operating in a stalled condition!
Good reference, with witch i was familiar already. But i´m unable to see how you would prove your point of enough THS authority being available at 60° AOA.
Lets start on page 153 of
your reference with the lower graph, which shows how drag is a function of AOA. The more AOA, the higher the drag. To reduce drag, you have to reduce the AOA.
Now lets look at the upper table, Coefficient of lift versus AOA. Lift increases with AOA, until stall AOA is reached. In that graph that is at about 20°AOA. This drop in Lift continues till 30° AOA. From a max CL of 1.4 at 20°AOA CL has dropped to CL 0.9 at 30° AOA. If we continue to increase the AOA to 45°AOA, CL would increase to 1.2 again. But remember and check the lower graph, we just have increased the CD by the factor of six from stallspeed until 45° AOA. ! If we increase the AOA above 45° to 60° AOA, CL decreases again and CD continues to increase.
What does it tell for the A330?
First of all i dont know what kind of profile the THS represents, but your reference shows, that most mentioned airfoils have a similar behavior, just the numbers change. So lets use what we got until someone comes up with the correct profile.
Lets start with the 46.5°AOA of the THS (60° Aircraft AOA minus 13.5° NU trim) , which gives us a CL of 1.2 and a CD of 1.2. Lets do some ND input by trimming the THS to 0° and let´s see what it does to our numbers. We end up at 60° AOA at the THS, a CL of 1.0 and a CD of 1.6! Our upforce on the THS needed for lowering the nose has decreased and the drag has increased, our ND trim has caused the opposite of our desired outcome.
But that´s not all, lets start again at 47.5° AOA with CL1.2 and CD 1.2 and let us pull full aft stick. That decreases the AOA of the THS for example to 30°AOA, but at the same time we are loosing CL to 0.9, (loosing upforce on the THS again) but we improve CD to 0.5.
Conclusion in this simulated case with this airfoil: Somehow you are stuck between max CL pre-stall and max CL post stall and the airfoil itself has no authority to change that.
To make matters worse, the same applies to the other airfoil, the wings. There´s probably a similar change in CL and CD and any positive change on the THS (somehow generating ND force for the aircraft) might bring the AOA of the wing into the region, where the decrease of AOA initially causes an increase of CL thus rendering your success on the tail usesless for the complete fuselage.
As mentioned before, i´m no aerodynamics guy and might be completely wrong, but i like to make the point that the crew most probably had no conventional way to get AF447 out of a 60°AOA stall and that their behavior described by the BEA in the last 3 minutes of the fall might reflect the helpless situation they found themselves in due to normal aerodynamic layout and behavior of the aircraft, which has never been tested in that flight region.
Another point to remember: That THS has never been designed and tested to generate negative g or great nose down pitching momentum (like in a fighter aircraft), but to keep the nose up in cruise and especially during approach to land.
Another point: CG might have travelled aft (some fuel in the tanks not equally distributed, but now in the aft parts of the tanks, Some cargo in the belly falling to the rear part of the hold, and shift of the center of lift due to high AOA, a mixture which ruins your day.