c.g. and longitudinal stability
And yes, TK, I have been here recently.
Good points Harry, no problem with you jumping in.
As the c.g. moves back to the center of aero pressure, or so called neutral point, the jet has less tendency to revert to the 'trimmed" condition that existed when a disturbence upsets the flight path. In short, a very statically stable jet tries to get back to the trimmed state real quick. In non-FBW systems this is very apparent, as you have to "hold" control pressures to keep the beast from returning to its happy, trimmed state. This all goes out the window with most FBW implementations.
Flying with an aft c.g. is like balancing on the point of a needle. Lottsa work, and you better be good. So your inputs might, indeed. be very effective for a second or less. Then you overshoot your desired attitude or AoA or gee and you can get into the classic PIO or worse.
If you get the c.g. sufficiently rearward, the plane will flop end over end. Think about an arrow. See where the center of aero pressure is compared to the weight of the arrowhead and shaft. Ever see an arrow flip end over end? Didn't think so, heh heh.
One way to experience the real static stability of a FBW jet is to go to something like the "direct law", where all the electrons are doing is commanding a control surface movement. Then you make a small stick movement, relax pressure and see what the jet does.
I would take the forward c.g., and I have a feeling that the AF447 folks knew there was a possibility of some turbulence and didn't move a lotta gas rearward for the improved trim drag and such. If I got close to a stall I would have basic aero laws helping me as much as HAL's laws.
As a point ( short war story), our little jet had a negative static stability margin until about M 0.9 to 0.95. Like the 'bus, the "auto trim" tried to maintain our "hands off" gee command. Due to the negative static margin, our HS was actually providing "up" force. Hence, our first complete loss of the confusers at about M 0.6 or so resulted in the jet going nose down and between 10 and 20 negative gees on the pilot. He got to the bar that night with two super shiners and had bloodshot eyes for a week, heh heh. Next one was a fatality, and estimated 22 negative gees ( too low for a good ejection).