A319/320 description Nz Law
Manoeuvre demand law as basic flight mode
- neutral speed stability with full flight envelope protection
-Vertical load factor control proportional to stick deflection : C* law
- independent of speed, weight, center of gravity ;
stick displacement : Nz = n Nz = n + 1g
stick neutral : Nz = O Nz = 1g
C* = q + K_C* x delta_Nz
q = pitch rate
delta_Nz = incremental load factor
K_C* = C* crossover gain - chosen to balance q and delta_Nz contributions
Flight path stability instead of speed stability
- control inputs are made to alter the flight path, not to hold it.
Medium-term flight path stability :
- maintenance of parallel trajectory 1g in pitch even after atmosphere disturbance.
C* (pronounced "C Star") is the popular name for a control law in which Nz (g) and pitch-rate feedback are blended. (In the late 60s and early 70s, Nz feedback was called the C law. NASA space shuttle approach studies added pitch-rate feedback, which was called C*.) At low speed in a C* airplane, pitch rate is primary; at higher speeds, g is primary. The changeover is transparent and occurs at about 210 knots in the A320 ("Fly-By-Wire for Commercial Aircraft: The Airbus Experience," C. Favre, 1991).
4.3.4. Longitudinal static stability. The A320's C* pitch control law is a manoeuvre demand law: the pilot's control inputs are interpreted as a demand for a given level of manoeuvre rate and the control system provides the surface deflection needed to generate this rate. Releasing the side-stick commands flight path stability.
. C* (pronounced ‘‘C-Star”) is a term that is used to describe the blending of the airplane pitch rate and the load factor (the amount of acceleration felt by an occupant of the airplane during a maneuver). At low airspeeds, the pitch rate is the controlling factor. That is, a specific push or pull of the column by the pilot will result in some given pitch rate of the airplane. The harder the pilot pushes or pulls on the column, the faster the airplane will pitch nose up or nose down. At high airspeeds, the load factor dominates. This means that, at high airspeeds, a specific push or pull of the column by the pilot will result in some given load factor.
And who likes to dig deeper and compare it to the 777, can read
here.
Going back to my armchair again
franzl