The Nz command I am talking about would be that from a "strapdown" style sensor referenced to the aircraft, not a space-stabilized inertial sensor such as used for navigation and weapon delivery.
OK, A330 has a strapdown sensor so we are talking same language
The difference between my FBW system of old and that in the 'bus is we did not correct for attitude WRT the Earth coordinate system. Ours was and is still body-oriented for the Nz command. Because the 'bus corrects for attitude, it appears to command an attitude.
That is an important difference, but I don't see how that implies that the 'bus commands an attitude. I see the pitch correction as a technical requirement brought about by the laws of physics, not a deliberate attempt to manipulate flight path. [Which is why I think that the phrase "tries to achieve one gee corrected for pitch attitude" might give the wrong impression].
The point I keep trying to make is that the 'bus appears to command an attitude, but it's a gee/rate command with bias for pitch attitude.
This is the point I don't get. The AI system, as I understand it, seeks to maintain a commanded gee in earth axes not body axes as in your Viper. With that assumption the pitch attitude term is a necessary correction feature but not a command. The basic system is a simple gee demand with gee/pitch rate feedback arranged to optimise transient response throughout the envelope. [For completeness, the THS becomes the integral part of a standard P/I control system]
My second point is "hands off" and even at small pitch attitudes like 10 or 15 degrees, that trying to maintain a constant Nz will cause the elevator to trim nose up, and then the THS. Because the 'bus has more drag than our Viper, speed/energy decays quickly, and it is possible to reach a stall AoA even with "hands off" ( as BEA report asserts). With no AoA protections, you're on your own. Holding the stick back for minutes doesn't help at all.
Agreed, except to remark that in A330 terms 15 degrees is not a "small" attitude. One needs to add a proviso though - the speed divergence only kicks in when the (thrust - drag) vs speed curve slope goes negative and even then the initial rate of divergence would be very low, although it gets more exciting as one nears stall conditions. The argument that the A330 system could take the aircraft into stall even "hands off" is a valid one, but really only becomes significant (in AF447 terms) because the aircraft was put in the vicinity of stall in the first place.
Lastly, the "feel" of non-FBW planes with positive static stability is helpful, as trying to fly slower than the trimmed speed/AoA requires more back stick. Trying to fly faster requires forward stick pressure/movement. OTOH, most FBW systems provide "neutral speed stability" regardless of the AoA, cee gee and/or static stability margins. So we don't get that feedback like in the old days, even with fully hydraulic control valves and no artificial "feel" such as the B777 has.
Agreed
Pretty good discussion on this aspect of the control laws, way I see it.
Yup!