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Speed Computation - Use of FM Weight/CG
Figure 005
m(t) = Weight as a function of time (consumption law) iH = THS position PS = Static pressure R **ON A/C 106-149, 301-399, 401-499,
The sequence of the computations (which lead to generation of characteristic speed data) and the parameters is shown in the figure. The computation is initiated from the curves Cz max and from the conditions of equilibrium of the aircraft with thrust and balance correction. This permits to obtain the stall warning speed Vs 1g. From Vs 1g, the FAC computes the aircraft weight taking into account:
-
The equilibrium incidence
-
The equilibrium speed
-
The thrust
-
The center of gravity
-
The altitude.
Beyond the computation range, the computation of the weight is frozen.
The weight is re-aligned through a correcting fuel-used term previously
defined in the FAC.
The following is deduced from the weight computation:
-Computation of the center of gravity according to the stability plane,
altitude, configuration and speed. In order to harmonize the FAC and FMS characteristic speeds displayed on the PFDs and on the MCDUs (basic or optional), the FAC uses the FM weight and CG to compute characteristic speeds (VLS, green dot, S, F). (Ref. Fig. 005A)
List of Abbrevations: Az1 = Vertical acceleration with respect to aircraft centerline AOA = Voted angle-of-attack Vc = Corrected airspeed N1R and N1L = Left or right engine thrust Phi = Bank angle with respect to aircraft centerline Teta = Pitch attitude Z.. = Vertical acceleration with respect to reference VZBI = Baro inertial vertical speed M = Mach number S/F = Slat/flap position XG = Center of gravity Z = altitude AB = Speedbrakes mFMS = Weight given by FMS t(s) = Time MLGS = Landing gear shock absorber compressed Delta N1 = Delta between N1 command and N1 actual m(t) = Weight as a function of time (consumption law) iH = THS position PS = Static pressure
Speed Computation - Use of FM Weight/CG
Figure 005A
**ON A/C ALL
B. Computation of Aerodynamic Flight-Path Angle (Gamma-a) and Potential Flight-Path Angle (Gamma-T) (Ref. Fig. 006) These data which are necessary for the FMGC control laws are calculated and duplicated in the FAC.
C. Computation of Alpha Floor Protection (Ref. Fig. 007, 008) The alpha floor protection is calculated in the FAC but not duplicated. This function permits:
-
To protect the aircraft against excessive angle-of-attack. To do this, a comparison is made between the aircraft angle-of-attack and predetermined thresholds function of configuration. Beyond the thresholds, the FAC transmits a command signal to the autothrust which will apply full thrust.
-
To protect the aircraft against longitudinal wind variations in approach by determining a wind acceleration (deduced from the difference between ground acceleration and air acceleration).
At the second detected or undetected failure of the ADIRS, the alpha-floor signal is no longer available. The ELAC direct computation of the alpha floor protection is taken into account directly as soon as the first detection is made either by the FAC or by the ELAC.
R **ON A/C 001-049, 051-099, 101-105, 151-199, 201-299,
D. Rudder Trim Position (Ref. Fig. 009) The actual position of the rudder trim (rudder position) is sent to:
-
The rudder trim indicator
-
The ECAM system
-On the label 313.
This position is validated by:
-
The status matrix which turns to:
. NCD if the RUD TRIM function is not available
. F/W in the event of a computer failure.
-
The FAC HEALTHY hard-wired discrete.
A flag appears if the signal is not available.
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FAC - Computation of Aerodynamic Flight-Path Angle (Gamma-a)
and Potential Flight-Path Angle (Gamma-T)
Figure 006
Alpha Floor _ Computation and Interface R Figure 007
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FAC - Alpha Floor Figure 008
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ECAM - Rudder Trim Position
Figure 009
R **ON A/C 106-149, 301-399, 401-499,
D. Rudder Trim Position and Rudder Travel Limiter
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