I've had some really good progress on the fly-by-wire and the Airbus Flight Control Laws. I've used data from
http://www.airbusdriver.net to work out the flight modes, and different laws. Here's a basic idea of what happens, when it happens and how it happens. (I'll keep this as a small doc to the flight control system)
-------------------------------------- Airbus Flight Control System ---------------------------------------The Airbus Flight Control System uses a "fly-by-wire" to transmit side-stick input into the aircraft's control surfaces' servos. These inputs are modified using certain system algorithms and then converted to control surface position.
Airbus divides the Flight Control system algorithms into several flight laws-
1. NORMAL LAWSummary: The Normal Law is active during normal flight conditions. A single system failure would still mean the aircraft flies according to the normal law. While using this law, the fly-by-wire has 3-axis control, provides flight envelope and load limit protection. It has 3 modes according to phases of flight.
a. Ground Mode> Active when aircraft is on ground to about 250 ft AGL after take-off
> Side-stick Input --> Control Surface Position
b. Flight Mode> Active when aircraft passes 250 AGL after take-off
> Side-stick Input --> Load Factor (G-Force) --> Control Surface Position
> With Side-stick neutral, aircraft maintains 1g pitch load and 0 deg/s roll
> Pitch-trim is not required, aircraft stabilizes with elevators
> Side-stick Pitch Deflection commands g-force (-0.75 at full forward and 2.75 at fully pulled back)
> Side-stick Roll Deflection commands roll-rate (30 deg/s at full deflection)
> Load Factor and Roll-rate are independant of airspeed
c. Flare Mode> Transition occurs at 50 ft AGL and changes to Ground mode after touch down
> At 50 ft, system memorizes pitch and progressively changes according to throttle input to give a smooth touchdown
> In case of a go-around, transition to flight mode occurs at 50 ft AGL.
- Normal Law Protectionsa. Load Factor Limitation> Prevents aircraft from overstressing even if side-stick is fully deflected
b. Attitude Protections> Pitch Limits to 30 degrees up and 15 degrees down
> With side-stick deflected all the way (roll-axis), roll limits to 67 degrees
> If side-stick is NOT deflected all hte way, roll limits to 33 degrees
2. ALTERNATE LAWSummary: The alternate law is active if multiple system failures occur. In case of alternate law, ECAM displays 'ALTN LAW: PROT LOST'. This law too is active in different ways during different flight phases-
a. Ground Mode> Performs similar to NORMAL LAW
b. Flight Mode> Performs simular to NORMAL LAW when landing gears are retracted.
> Pitch control shifts to DIRECT LAW when landing gears are lowered for landing.
c. Flare ModeThis mode does NOT exist- pitch control uses DIRECT LAW for manual flare.
- Alternate Law Protections
a. Load Factor Limitation> Similar to that under NORMAL LAW
b. Attitude Protection> Attitude protection is lost under ALTERNATE LAW
> In case of extreme low speeds, aircraft reduces pitch but CAN BE OVERRIDDEN
3. ABNORMAL ALTERNATE LAWSummary: This law is active when the aircrafte enters an unusual attitude (includes roll-over, over 60 degrees pitch up or over 30 degrees pitch down).
> Pitch Control shifts to ALTERNATE LAW
> Roll Control shifts to DIRECT LAW
> Returns to NORMAL/ALTERNATE LAW when out of unusual attitude.
4. DIRECT LAWSummary: This law is the lowest level of flight control systems and is used only in the case of major multiple system failures.
> Side-stick Input is transmitted unmodified to control surfaces
> 'USE MAN PITCH TRIM' appears on PFD
> No protections provided
5. MECHANICAL BACKUP Summary: The mechanical backup system is used in case of completed electrical or hydraulic system failure.
> Side-stick does NOT control anything
> Rudder Pedals must be used to control YAW
> Elevator Trim wheels must be used to control PITCH
> ROLL cannot be controlled while using the mechanical backup