Re @ Henra
Re Henra
Lets face the fact, that finally it´is the sum of all moments, which lead to the desired outcome. Wether the CD produces some ND input and CL produces some NU input or vice versa, the effectiveness of it depends on the sum of the individual forces. And as stated before, the CD and CL change of the wing has its share in the equation as well.
If we agree, that it never was the designed specification of this THS to get the AC out of a 60° AOA but to keep the aircraft in balance under the normal flight conditions by creating less or more ANU forces (curvature to produce downward lift on the THS), then the regime we are talking about here is as distant as the moon from the sun.
To get the desired AND vector, the THS airfoil has to produce lift opposite to its original design ( like if the main wing would have to produce not upward lift, but downward lift like during extreme pushover). I´m not saying that that is not possible, there are airfoils with symetrical curvature working as well by just changing the AOA of the airfoil (like the F-104 Starfighter main wing), but those designs are specifically crafted for that aircraft and its desired performance, and despite that, it had been highly succeptable to stalls and creating high amount of drag once outside desired flight envelope. I´ve lost lots of friends in accidents with this otherwise wonderful aircraft.
Another point i´m still curious, but have no expierience in it, so just correct me. I get the impression, that some posters simplify the function between lift and drag to the region of the pre stall flight envelope, and thus setting a constant between drag and lift, meaning where there is drag on an airfoil, there also has to be equivalent lift. 35 years ago i learnt in my academics classes, that if the airfoil produces lift, it also causes drag called induced drag (but not vice versa) up to max CL is reached (nearly linear function of drag and lift), but after that point drag continuous to increase while lift decreases. In our post stall discussion there are no formulas available to compute lift from drag, because there is no constant behaviour anymore outside the wind tunnel.
It is also way off reality to disregard the huge amount of drag produced by that stalled airfoil in the context of recovery efforts. To get any usefull output of the ND movement, we have to get the wind flowing over the lifting devices by increasing speed (which is the ultimate reason to decrease the AOA). When we increase the drag and thus reduce the forward velocity vector even more, we increase the descent rate by a comparable amount, thus increasing the total AOA again.
So it is no sense in discussing single points of some more or some less lift if it is not changing the overall problem to get the aircraft out of the extreme AOA condition within the available altitude.
One thing i´m sure : The simple stick forward and wait, like some are saying here, would only have worked up to a defined value of AOA and speed, and i see that value of AOA well below 45°. The discussion what the crew did do wrong in recovering the aircraft once established in the descent (estimnated FL 300 downward ) is IMHO useless, because there was no "conventional method" available which would have brought AF447 out of this position.
The problem lies in the beginning with the extreme climb rate, the chance to recover the following upset ended somewhere between FL 370 and FL 300.
Last edited by RetiredF4; 18th Jun 2011 at 11:13.