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input and control surface position.
Aircraft response depending on aircraft dynamics and
flight envelope area coverage.
Airworthiness and aircraft performance requirements
leading to increasingly complex system :
- variable artificial feel to modulate pilot forces with
flight conditions (efforts / g),
- hydraulically powered servocontrols, servoed
autopilots, control wheel steering,
- stall protection devices (stick shaker, stick pusher),
- stability augmentation systems (Mach trim, speed
trim, angle-of-attack trim, roll and yaw damping).
Fly-by-wire controls
No directly proportional relationship between pilot stick
input and control surface position.
Computers’ response to stick input modulating
servocontrolled jacks to satisfy :
- normal, alternate or direct laws (pitch, roll and yaw
axes),
- optimised flight control characteristics (easy
handling, good stability),
- improved safety :overspeed, stall, windshear,
manoeuvre and attitude protections.
STL 945.7136/97
A319/A320/A321 C* law description
5.10
Control surface autotrim
function
Autotrim function
Ground or Z < 100 ft*
* Before landing
Ground
Electric trim
GAIN
GAIN
GAIN
Z < 100 ft*
Elevator
THS
NZ
(θ and Ø compensated)
Z < 100 ft*
θ
STL 945.7136/97
A319/A320/A321 normal law – pitch axis
5.11
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 : ΔNz = n Nz = n + 1g
stick neutral : ΔNz = O Nz = 1g
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.
Automatic pitch trim eliminating need to correct for
speed or configuration changes :
- electric autotrim function holding elevator position
for constant flight path,
- control surface autotrim function returning elevators
to the THS trail.
Automatic elevator for bank angle compensation up to
33°.
STL 945.7136/97
A319/A320/A321 normal law – pitch axis
5.12
Adaptation of basic control law objectives to :
- Ground phase : ground mode
Direct relationship between stick and elevator
available before lift-off and after touch-down
- Take-off phase : take-off mode
For smooth transition, blend of ground phase law
and Nz command law over 5 seconds after lift off.
- Landing phase : landing mode
At 50ft the attitude is memorized as reference pitch
attitude.
At 30ft this value is progressively reduced to 2°
nose down to induce gentle positive pilot action for
a conventional flare.
STL 945.7136/97
A319/A320/A321 normal law – roll and yaw axes
5.13
Roll rate demand (15° / Sec max.) as basic flight
mode :
Coordinated roll and yaw surfaces deflections :
- to achieve and maintain bank angle up to 33°, stick
released
Bank angle protection above 33° :
- positive spiral stability restored up to 67° inside
normal flight envelope
- limit of 67° bank angle
Lateral control laws providing handling quality features
such as :
- bank angle resistance to disturbance, stick free,
- precise piloting
- good turn coordination,
- dutch roll damping,
- sideslip minimization.
Sidestick free with pedal deflection results in stabilized
sideslip and bank angle facilitating “de-crabbing” in
crosswind landings.
Engine failure or aircraft asymmetry compensation
consisting of :
- If no pilot action :
stabilized sideslip and bank angle followed by,
automatic rudder trimming to compensate
asymmetric thrust
slowly diverging heading.
- Recommanded action :
zero sideslip target with pedals (take-offf, goaround),
heading stabilization with stick input,
steady flight stick free / no pedal forces (rudder
trim).
Adaptation of basic control law objectives to :
- Ground phase : ground mode
Direct relationship between stick and roll control
surfaces
Rudder : mechanical control from pedals + yaw
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A319/A320/A321飞行员驾驶舱和系统简介(6)
