RRT
Please could you explain the forces acting on the tail during the stall for me?
Normally, the elevator and stab produce a down force at the tail. (to balance the nose down couple with the c of G being forward of the Centre of Lift).
During the stall, with an angle of attack of about 45 degs on the elevator and Stab, the forces on the tail must have been upwards. If not - then I don't understand why.
Please explain how holding full back side stick kept the attitude at around 15 degs until impact.
Since you ask ....
First thing is that MM43's excellent graphic of THS flow (Thread 4 #1042) is missing one important parameter. A lifting wing, even a stalled wing, produces downwash at the tail. A ballpark range for this would be between 0.4 and 0.5 times body AoA. So at 60 deg AoA as in the graphic, the THS AoA would have been around 17 or 18 deg. With zero elevator this would have been
on the point of stalling - but it would have been stalling with UPWARDS lift.
That means that without any elevator the THS would have been giving a substantial ND moment. The centre of lift of a fully stalled wing is probably fairly close to the centre of area, which on the A330 is slightly aft of the CG given for AF447. So both of these are ND. What could hold the nose up then?
The forward fuselage has roughly the same moment arm about the CG as the THS, but nobody would pretend that it has the same aerodynamic lift efficiency, so that cannot balance the THS ND moment. Thrust? sure, but do the sums and you will find that the NU moment even with both at TOP won't come anywhere near what is needed.
What's left? Up elevator! Enough of it to make the THS plus elevator force downwards and give enough NU moment to balance the AoA at (in this case) 60 deg. Up elevator would also take the THS away from upwards stall.
For lower AoAs the THS would be even further from upwards stall.
Full back sidestick put the aircraft at 60 deg AoA - the FPA was 45 deg downwards, so the pitch was 15 deg. OK?