Originally Posted by
TTex600
If the airplane consistently does what it is commanded to do, how do you explain "auto trim"? When does the pilot command trim?
To offload pressure on the primary flight surfaces, exactly the same as autotrim does. Autotrim is a way of solving the problem of not having the surfaces transmit the pressure through the primary flight controls - nothing more, nothing less.
Why does it wander around the selected speed? (for you Boeing , Embraer, Canadair, Douglas drivers - the bus will vary by ten or more knots below 10Kft when fully automated. It trims for flight path, not for speed)
I'm sure that other airframes also "wander" to some degree, and always have, because even calm air is never 100% calm - it may not have been as apparent in the steam-gauge days due to the analogue nature of the instruments.
Contrary to the spin (partisan positioning) you read here, the Airbus takes what you input, processes your input through its brain and outputs whatever it decides appropriate.
That's one way of describing it - another equally valid way is "gives you exactly what you ask for in a manner that is appropriate to the conditions". In terms of flight path stability (which is after all, what the manual combination of thrust, PFC input and trim were trying to achieve in conventional jets) it is relatively unmatched.
Imagine, if you will, the steering wheel on your automobile randomly varying tire steering angle for a given steering wheel angle. Fun, huh?
Except that is not a fair description in that it isn't "random". The whole point of the "graceful degradation" aspect of the design was that it gives you as close to Normal Law handling as possible despite the fact that some of the systems required to give you that handling are not functioning correctly. A fairer analogy would be a power steering setup that has a partial failure mode making the wheel half as heavy as it would be with power sterring out completely.