Originally Posted by
RetiredF4
@ Dozy
you misunderstood my post, which is probably my fault. I'm with you in most of your posts in this thread here.
Much appreciated - I know we've crossed swords in the past, so maybe I was also a little quick to rush to judgement.
Therefore it is normal, that the pitch rate change of the increasing thrust enters the equation as just that, a pitch change. If the commanded pitch change corrected by the protections is less than the actual pitch change by thrust, then the elevators will command a pitch reduction despite the stick position.
Understood. However in the High AoA protection scenario, back-stick commands maximum or best possible alpha, based on the aircraft's previous, current and projected (via deltas/trends) state. If the current pitch attitude already corresponds with maximum/optimum AoA based on the current/projected state, then the command is to *maintain*, rather than change, that optimum attitude. So, as you say, if the EFCS detects even the slightest pitch-up tendency - e.g. from the gradual thrust increase - then it must counteract that, and because Alpha Floor was unavailable, the only aspect it could control to counter it was pitch.
By the way, a pilot in the loop in such a pitch up situation due to increasing engine thrust would react how (without available protections)? By controlling the pitchup by use of proper stick input, which might be stick forward!
I get your point, though I would say that there's no guarantee that a pilot *would* do that, no matter how "in the loop" or otherwise. It's worth remembering that the A320, while considered a very nimble airliner, is still nevertheless an airliner. The whole point of using digital technology in civil flight control systems is that they can, and do, detect and correct minute changes (as in fractions of a degree/knot etc.) in aircraft orientation more quickly and accurately than a human can. This is not because they're capable of outperforming humans in general, but because unlike a human pilot
that is all they are designed to do.
In a pre-FBW fighter or a specialist aerobatic aircraft, a pilot will be trained and given experience in recognising responses and making those split-second
decisions/inputs - and because those aircraft are designed to be lightweight and nimble above all else, momentum is less of a problem. Even smaller short/medium-haul airliners like the A320 are still big and unwieldy aircraft by comparison - and this is the reason high AoA protections were a very important thing to demonstrate in the early days, being a scenario no previous type could pull off safely. I'd be prepared to bet that if you asked any one of Yeager, Armstrong, Cunningham or Beamont et al. to get in a conventional jetliner and hold 15 degrees of AoA precisely while flying slowly (as in near stall speed) at 1000ft, let alone 100ft, their refusals would have been both emphatic and unprintable.
The flight envelope protections afforded by modern FBW systems have been consistently characterised by the doubters as being primarily a technological vote-of-no-confidence in piloting skills, and this has been a very difficult idea to dispel amongst pilots. Again at the risk of repeating myself, the overarching premise is nothing of the sort - the main impetus is in allowing pilots to have confidence in making positive maneouvres without having to worry about the aircraft's ability to stay in the air.