Airbus Flight control laws
 

Have any of you ever fly the plane in Direct law ?
is part of your interest to understand the difference /if any in handling the A/C in different flight control laws.

I have flown the A320 in direct law during testing...confirming to a large extent that an airplane is an airplane is an airplane. You lose, of course, your full flight envelope protection, however the handling qualities of the aircraft are far from objectionable.

Correct me if I'm wrong, but doesn't the the FBW enter direct
law below 50' (or so) AGL?

Cheers,

M

"Correct me if I'm wrong, but doesn't the the FBW enter direct
law below 50' (or so) AGL?"

Eh no. The airbus will at flare start to automatically lower the nose a couple of degrees to give you some kind of artificial feel when you start pulling back on the stick.

If you due to some system redundancies are in alternate law the moment your gear is selected down you will then be in direct law.
TFCM

Not exactly. You are looking for the take-off phase.

FD
(the un-real)

It amazes me the amount of pilots in my compnay with 1000's of Airbus hours that still think the aircraft goes into direct law for landing!

TFS

This is how the A320 works.

On the take off roll, the aircraft is in ground law - which is direct law. Normal laws are blended in from lift off, being fully introduced by 50' agl.

On landing, from 50', flare law is blended in and at touchdown you should be in full flare law. The attitude at 50' is remembered and at 30' the law introduces a 2 degree pitch down progressively over 8 seconds. This is similar to direct law inasmuch that sidestick movements have direct authority over control surface movement.

Some landing malfuntions (such as double rad alt fail) will pt the aircraft into direct law when the gear is extended. This is because the aircraft systems relying on the rad alts won't know how high you are so they assume landing from gear selection.

In all cases, the aircraft is in direct law on the ground.

Direct Law
 

if the flight controls degrade to alternate law , Direct law automatically become active when the landing gear is extended (if no autopilots are engaged)

Sometime since I flew the 'bus but as I recall on landing, you land with pitch in direct law and roll in normal law.

flare mode is a sub-mode of normal law. the pitch is not in direct law, it is in flare mode which is normal law with an added pitch-down input which artificially creates an environment where the pilot has to flare. Ask yourself this, 'if the aircraft was in direct law for landing, why would it need the pitch-down added?'. Obviously it wouldn't, the pitch down is added to allow the pilot to apply a 'conventional' flare in normal law.

TFS ;)

Strictly speaking on the ground it is in Normal Law - Ground Mode, which behaves like Direct law. There will still be little green ticks on the PFD.

Ground mode is active when the aircraft is on the ground. It is a direct relationship between sidestick deflection and elevator deflection, without auto trim.
It automatically sets the trimmable horizontal stabilizer (THS) at 0° (inside the green band). A setting that the pilot enters manually to adjust for CG has priority for takeoff.
When the aircraft reaches 70 knots during the takeoff roll, the system reduces the maximum up elevator deflection from 30° to 20°, and the aircraft performs the rotation maneuver in direct law.
As soon as the aircraft becomes airborne, the system blends in the flight mode.(when a/c's RA> 50' for more than 5sec or pitch>8up+airborne)

When the aircraft is on the ground (in "on ground" mode), the sidestick commands the aileron and roll spoiler surface deflection. The amount of control surface deflection that results from a given amount of sidestick deflection depends upon aircraft speed. The pedals control rudder deflection through a direct mechanical linkage.

outlaws!!!!!!!!
 

At ground speeds below 70 knots, the sidesticks have full authority over the controls in pitch and roll to permit control checks.
At ground speeds above 70 knots, the authority in pitch is reduced from 30° up to 20° up. In this ground mode, movements of the control surfaces in pitch and roll correspond directly to the stick inputs.;)

No idea.

Have heard pilots describe the difficulties of some landings, because the A-319/320 seems to have no 'crosswind law'.

In our much older 60's era jets, WE are the law, as in the sci-fi. movie "Judge Dread".
We must remember, among many other things in "steam-gauge" planes, the 'flare lower than it looks at night law'.:O


GearPins: Is the direct pedal linkage (on the ground) to the rudder hydraulic actuators?

Ignition Override - I know that some people are trying to "invent" flying again when it comes to landing the airbus (319 for me). Only thing I can say is that during my course I was told 15 different ways of doing it and none seemed to work very well for me.. During my base training I had x-wind and after one (not so nice try) I decided to land the damn thing as I would land every other airplane I had flown before... Result? Very nice...So, land the thing like you where tought during ppl training - Keep the crab until you start the flare, then put some rudder in, line up the plane and "dip" the wing a bit to stay lined up....simple as that!
Happy landings!
/CP

Ignition Override:
thats right my friend:)

excuse my ignorance, but what is meant by "ground/takeoff/landing laws ???.

GLAD I FLY BOEINGS!!!!!!!!!!!!!!!!!!!

Ask 10 bus pilots a tech question and you will end up with 10 different answers.

Blueskiesup

Airbus a/c are 'fly-by-wire' (FBW) designs. This means that a computer sits between the pilot's controls and the various control surfaces/devices.

In a non-FBW a/c there is some direct connection between the levers & knobs that the pilot uses and the surfaces/devices that cause the a/c to move. It could be wire cables, pushrods, hydraulic actuators or electrical actuators or whatever. The pilot has to determine what combination of inputs are needed to cause the a/c to respond in a desired manner. It's possible for the pilot to choose to use too much, too little or even incorrect inputs to try to achieve the desired response from the aircraft.o

FBW a/c have a computer that determines what combination of a/c surfaces/devices must be moved to cause the a/c to respond in a desired manner. The pilot knows what response is desired from the a/c & uses the various control devices to tell the computer what s/he wants the a/c to do. The computer reads those inputs and, using the data inputs & surfaces at its disposal and in accordance with pre-programmed sets of rules, makes a decision about what surfaces must be moved, by how much and how fast. For safety there are multiple computers acting in parallel doing the job and not just one.

Those pre-programmed sets of rules, in Airbus language, are the 'laws'. There are groups of rules for various stages of flight to allow for unique requirements or more desirable behaviour. Some laws provide greater protections against undesirable use of the controls whilst others provide fewer protections but need fewer data sources to do their job.

'Normal law' is - as it implies - the normally operating set of rules the computer abides by. It's not always appropriate for the stage of flight or the mechanical condition of the a/c.

If the a/c loses certain resources then the computer can't provide reliable solutions to provide the a/c response the pilot wants. In this case it falls back to a less protective (but somewhat more directly responsive) 'Alternate law'.

If providing even that level of reliability is doubtful then the system falls back to 'Direct law'. Direct law provides direct control from the pilot's inputs to the controls - much like a non-FBW a/c.

Ground law has its own variant of what the computer does for the pilot vs. what the pilot can directly control.

Take-off law is optimised for that phase of flight & allows for an orderly transition from the more direct law control mode used during the take-off to the normal law mode used in-flight.

Landing law is likewise optimised for that phase. It causes the a/c to pitch nose down slightly because pilots almost invariably will pull on the control column/sidestick during landing to counter (a non-FBW) a/c's pitch down when power is reduced to land.


Any mistakes in the above are the result of my own misunderstandings....

A bit off topic, but can anyone tell me why Airbus chose this method of controlling their aircraft?

The 777 is FBW but without the hassle of laws and whatever. It flies like any other aircraft. Why did Airbus decide so make something relatively simple so complicated?:confused: