Originally Posted by
Dani
Or you could get into a heavy windshear (say 100kts within a second or so), so that the aircrafts authority to pitch down wouldn't be enough, but split seconds before stall you would lose valid speed information and crash in alternate law, too.
Huh? Would you be kind enough to elaborate?
Perhaps you were implying an airspeed < 160kts, before the windshear. Why not. But with an airspeed > 160kts, why/how would you "lose valid speed information"?
Originally Posted by
FCeng84
A related question is what percentage of maximum aerodynamic lift capability does the Airbus normal law allow the pilot to command? It is my understanding that alpha-max as chosen by the control law designers to be the maximum commandable AOA is actually lower than the AOA corresponding to Cl-max. Seems to me that this system leaves some lift capability on the table and does not allow the pilot to command max lift. Anyone who knows the details care to comment?
As per the tests (FAA) on CFIT avoidance:
Yes, the maximum commandable AOA is lower than the AOA corresponding to Cl-max. The difference being the "safety margin" included to let "time" to the flight controls protection to kick in, approaching stall.
IIRC FAA also validated the Airbus "theory" when facing pilots who were "annoyed" that they cannot reach Cl-max ("what if I just need a few feets more to pass that mountain?") :
- with Airbus AoA protection, you can (very easily)
maintain alpha-max for as long as needed
- without protection you could reach Cl-max, but also stall, then unload under Cl-max, then pull, then stall... etc. (and that all depends on piloting skills, average may not be sufficient to do it correctly)
That's from memory, but the FAA report is online if you care to more details.