back to the "technical" stuff
- First of all, and to A33Z, what's the document you are using for elevator deflection per "g"? And for the c.g. versus elevator moment arm? etc.
About 95% of the military FBW jets have the all-moving HS, and no "elevator". This is extremely important once past the mach, if not essential ( ask Yeager about his X-1 missions). So your document must be pointed at subsonic designs and heavies. And by the way, several subsonic designs have the all-moving HS/elevator.
As far as aircraft movement about the c.g......... where's the center of aero forces, the mean aero chord (MAC)? There are very good reasons to have the elevator at certain distances from both the c,g, and the MAC. Too close and the plane is 'twitchy", and too far makes the beast sluggish, and so forth.
I also question a minimum of 1 deg of elevator per gee. That seems very sensitive, and unless the control surface movement is biased by dynamic pressure, you can get into trouble real fast. I would prefer a surface deflection related to maximum movement AND maximum gee AND dynamic pressure, as we had in the Viper ( probably Shuttle, but have to ask some friends).
- Secondly. I'll beat the dead horse once again. Why doesn't the system have a "standby gains" to be used by HAL when the pitot system fails or is deemed unreliable. Our primitive FBW system had such, and it worked in just the situation AF447 encountered, and a prominent caution light came on.
"Standby gains" prevent the potential problem another poster has questioned - "what does HAL use for control surface "laws" when airspeed is unreliable or missing? maybe A33Z can answer that?
- Finally, I disagree that the plane was unrecoverable without using a horrendous 30 degree nose down attitude, or more. The 'bus appears to have excellent, if not oustanding directional capabilities, whether in a rudder "law" or basically good aero design. Our little jet took rudder away from us once AoA was above 29 -30 degrees to help avoid a spin. Hence, our deep stall was relatively free of yaw and had little uncommanded roll excursions.
Our problem was the pitch moment with the full nose down stabilizer, yet nose up capability was still there. Sound familiar?
The swept wing beasts don't have the sharp stall break that straight wing planes have. The usual problem at extreme AoA is that drag exceeds available thrust if you maintain the "back" stick pressure Concorde, all the delta designs, Vulcan, Shuttle, and the beat goes on. On all of those, you could get flying again without lowering the nose to a horrendous nose down attitude, while using all available power. I speak from personal experience from my hours in the Deuce long ago.
It seems that AF447 came close to "breaking the stall", i.e. getting thrust greater than drag. Using the full movement of the THS could have been the key.