FAC Data on the Speed Scale of the PFD (Sheet 1/2) Figure 002
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FAC Data on the Speed Scale of the PFD (Sheet 2/2) Figure 003
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-------------------------------------------------------------------------------| SPEED | DEFINITION | PRESENTATION | PRESENTATION ON PFD | |--------|---------------------|------------------|---------------------------| | | to buffeting | VMAX OPP<VM0 | | |--------|---------------------|------------------|---------------------------| | | Predictive VFE at | Z<20,000 ft. | Two amber strips | | VFEN | next flap/slat | Not presented in | | | | position | full position | | -------------------------------------------------------------------------------
The signification of the different speed data is given below:
-VSW : stall warning speed
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VALPHA PROT : speed corresponding to angle-of-attack reached when ELAC Alpha Protection is triggered.
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VALPHA LIM : minimum speed which can be reached in ELAC Alpha Protection
-VLS : lower selectable speed for a given configuration
-VMAN (Green dot) : maneuvering speed: This speed represents the drift down speed which corresponds to the optimum speed (max. lift-to-drag ratio) in the event of engine failure.
-V3 and V4 : minimum flap and slat retraction speed V3(F) = minimum flap RETRACTION speed V4(S) = minimum slat RETRACTION speed
-VMAX : maximum allowable speed It determines a maximum value not to be exceeded. It represents, depending on the configuration, the smallest value of the following: VFE = maximum flap and slat extended speed VLE = maximum landing gear extended speed in clean configuration VM0/MM0 = maximum operating limit speed
-VMAXOP : maximum selectable speed
-VC TREND : airspeed tendency. It corresponds to the speed increment in 10s with the actual acceleration of the aircraft
-VFEN : in landing phase, it corresponds to the VFE at next flap/slat position.
3. Operation
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A. Speed Computation Principle (Ref. Fig. 004) The computation principle is based on the fact that most of the presented speed data are function of the weight. As the weight changes slowly, this parameter is frozen upon modification of the configuration (e.g. : speedbrakes or control surfaces extended, deceleration, turn) to avoid transients on the speed presentation.
Speed Computations - General Architecture
Figure 004
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On the ground, weight and XG initializations are made through the FMS. In cruise phase (Zp >15,000 ft and Vc >250 kts), updating computations are performed by engine consumption laws approximated in the FAC.
R **ON A/C 001-049, 051-099, 101-105, 151-199, 201-299,
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.
The FAC uses the FM weight and CG to compute characteristic speeds (VLS,
green dot, S, F).
(Ref. Fig. 005)
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
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