Originally Posted by
Chris Scott
Dozy,
That's an interesting hypothesis, i.e., the EFCS might deliberately keep a margin to alpha-max in idle thrust. I wonder.
Not so much that it keeps a margin for idle thrust (though it may do so) as it takes into account whether the aircraft is accelerating/decelerating and by how much, then uses the trends to stay ahead of the aircraft.
I tried to illustrate this earlier:
Originally Posted by me
For example, it would do no good to set pitch attitude to match an AoA of 17.5 degrees based on the current airspeed if, by the time that pitch attitude was reached, the aircraft was flying a few knots slower.
Capt. Corps alludes to the idea that the overriding ethos behind the EFCS in this particular mode is retaining stability and keeping the aircraft flying.
[EDIT : In fact, if we go back to Chris Scott's earlier post:
Originally Posted by
Chris Scott
In case it helps anyone, this is my translation into received English:
This flight law provides a special automatic protection preventing the aeroplane from reaching an incidence [angle of attack] greater than 17.5 degrees, to conserve a sufficient margin with respect to the stall, even if the pilot maintains a full climb [pitch-up] demand.
Note that this BEA description does not specify that an alpha of 17.5 deg will be achieved if the pilot maintains full back-stick.
What if the hypothesis that 17.5 degrees should be consistently held with full back-stick in High AoA mode is incorrect?
Is it not possible that 17.5 degrees AoA represents the absolute "do-not-exceed" maximum alpha from a normal limit of around 15 degrees AoA? If Chris's translation is correct, the wording of the BEA report is certainly consistent with that scenario. This interpretation would also be consistent with Capt. Corps' narration on the video.
]