Owain Glyndwr;
I don't think PJ2 will be upset if I say that in my conversations with him he confirmed that on at least one occasion he executed a recovery from 30 deg AoA using 10 deg ND pitch - it took about 15000 ft.
Not at all, as such was the case in most scenarios we did. The 20,000ft + scenario had a number of factors which delayed recovery including a NU SS held, and thrust in the CLB detent.
What I have learned in these discussions with
Owain Glyndwr and
HN39 are the aerodynamics behind recovery and that one need not necessarily be extraordinarily aggressive with the airplane to effect a recovery. Now, maintaining a 10deg ND pitch initially required full-forward SS. The FPA indicator moved upwards from about 30deg ND to < 10degND at a rate of about 1 to 2deg/sec, more rapidly as the 10deg's was approached.
These understandings are not normally conveyed or taught in initial or recurrent groundschool or simulator sessions.
Even for those who have a deeper-than-expected understanding of high-altitude, high-Mach Number, swept-wing aerodynamics, I think there is great value for airline pilots in the following, which is I believe a rare glimpse into aerodynamic thinking which is quite apart from our traditional understanding autoflight systems and SOPs...
From Owain Glyndwr's
Post #175
Suppose we start with pitch +15, Gamma -25, AoA +40 and instantaneously pitch
down through 25 deg to -10. (this is a thought experiment so we can do
that):
AoA remains at +40 for the moment as you suggest, but that means gamma goes
to -50. EAS hasn't changed, neither have CL and Cd at constant AoA so drag and
lift are unchanged. However we now have a large additional gravity component so
the aircraft will accelerate in absolute terms, i.e.TAS will increase, again as
suggested in a later post.
But in addition the aircraft is now descending more rapidly into denser air
so there is a double effect on EAS, and the thrust is also increasing due to
altitude effects which also helps a bit although this is not anything like as
important as the gravity effect since the maximum thrust one might get at say
FL350 is only about 7%W whereas a 25 deg FPA shift is worth 42%W.
If EAS increases at constant AoA the aircraft will develop an upwards
acceleration normal to the flight path and thence an upward velocity component
which, with the increased airspeed will result in a reduction in FPA. You can
see this in HN39's traces. [It will also of course experience an increase in
drag which partially offsets the benefits, but I think this only partially
offsets them]
A reduction in FPA, WITH PITCH HELD CONSTANT, will
give a reduction in AoA.
Cd is very sensitive to AoA above the stall, so the drag reduces more than
the effect of increased EAS and the whole response is "speed unstable" as it
were, with an increasing acceleration and reduction in AoA as time goes on until
the AoA is reduced to below S/W limits.