Hi HazelNuts39,
Sorry to come back to C*,
the speeds which keep my interest are
V and
Vco, as I readed these two documents, in post #1 Thread8 AF447
Thank you for your help... Perhaps I misunderstand something, but were ? what ? why? ...
Originally Posted by a) Alpa FBW Primer
C Star
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).
C*U ("U" represents forward velocity in flight equations) is a modified C* control law used in the B-777 to provide apparent speed stability. The trim switches set a reference speed that is summed with the actual speed in the feedback loop in such a way that the pilot feels conventional control force cues as speed changes. You "trim a speed," not the stabilizer (weight off wheels). Because the max trim reference speed is 330 knots, you would have to push on the control wheel to further increase speed toward Vmo. This provides a tactile high-speed cue.
Fly-by-wire allows designers to optimize the effective dynamics for different flight tasks--for example, an approach mode or a flare mode. This is called task tailoring and produces a multi-mode FCS.
In both the A320 and the B-777, the control laws are not fully active during takeoff until after liftoff because the sensors used for feedback would sense a lot of vibration and "noise" during the ground roll. Landing requires other transitions. Accident investigators should thoroughly understand mode transition points and effects
.
Originally Posted by b) Cranfield, report n°9303
The application of a C* flight controllaw to large civil transport aircraft
c*= Knz.nz + Kq.q (2)
q= (nz.g.Ttheta2/V) (s+1/Ttheta2) (3)
qSS=nz.g/V (4)
Kq=Vco/g (6)