Lyman
No natural tendency to lower its nose in Stall? Are you sure? I thought that was one of the cues for a Stall suss. Is there something I am missing re: CG?
Yes, you are missing something. I gave a description of stall on modern airliners is Post #294 of Thread 5.
Franzl
Imho it is even more difficult, when we consider that the aircraft was not that stable at all. Well, it did not depart into some kind of spin, but looking at the traces we had rolling, banking and pitching movements of the aircraft, and those might have been present due to pilot action or despite pilot reaction on aircraft behaviour. Those aircraft movements and associated flight control deflections cause aditional drag and prolong any kind of recovery.
Yeah I agree the lateral behaviour complicates matters. A lot of that motion might be the natural response of the airframe when taken to those levels of AoA, not helped by the fact that the wing mounted roll controls would have been virtually ineffective and that the fin/rudder effectiveness was also compromised by their high effective sweep at high AoA. Not sure about drag, although there was a lot of scatter in the results which could have been disguised roll/sideslip effects, but also there might have been induced AoA effects.
The assumption of instantaneous pitch down by 25° assumes, that enough authority is available even with thrust at TOGA, or when thrust would be in idle we would have to consider the later application of thrust, its effect on pitching moment and the spool up time, which again would influence the acceleration. We assume, a pilot in this situation can decrease the pitch in a most expedite way by 25° and maintain exactly -10° pitch over a time period of more then 30 seconds, while still stalled despite the fact, that his aircraft is in a degraded mode of operation (not to talk about the stress of the crew itself). Those 30 seconds with an unwinding altimeter would be like ages.
Hey, I wasn’t assuming the aircraft could be pitched down instantaneously! That was a gross simplification to get the explanation across more easily. Neither would I assume that a pilot would in practice be able to maintain an exact nose down pitch. The sums, such as they were, were intended to give some idea of what MIGHT have been possible if mental blocks hadn’t got in the way not as actual recoveries.
I buy that value, it is a fifty percent increase against the posted values in the graph. If we further consider, that the average descent rate at that time was around 15.000´/min (at 02:11:45 at 35372 feet, 22 seconds later at 02:12:07 at 29736 feet, and that those values where present without stuffing the nose down (which would increase initally the descentrate), we can assume an aditional altitude loss of at least 5.000 feet for time delays due to this unplanned stall situation any crew would be confronted with even after this discussion here.
The starting conditions included the rate of descent, so that bit shouldn’t apply. My typical calculation for recovery from FL350 took about 12000 ft, and I was fairly happy to say that looked reasonable against 15000 ft especially when one considers that the simulator modelling was probably even less representative than mine.
Let me put it clearly – my sums are intended to illustrate the sort of recovery that MIGHT have been possible. I am only too aware of their shortcomings. But even so I think they are a good indication that, as Gums says, the aircraft could have been flown out of it – if only!
My harsh assesment (no offence intended) would be, it might look good on a piece of paper in a warm office, but i doubt the practical use of it.
Well I leave that to others more skilled than I in practical piloting.
Reduce the AOA until stall warning stops, and the sooner it stops, the better it will be.