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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.
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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 |
Originally Posted by XPMorten
(Post 2877010)
Correct me if I'm wrong, but doesn't the the FBW enter direct law below 50' (or so) AGL?
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)
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Sometime since I flew the 'bus but as I recall on landing, you land with pitch in direct law and roll in normal law.
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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 ;) |
Originally Posted by Dan Winterland
(Post 2878462)
In all cases, the aircraft is in direct law on the ground.
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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 ???.
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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: |
Airbus say :
weight saving is considerable, the system is cheaper, safer (!) and allows the handling characteristics of all types (A319-A340/A380) to be closely matched to allow common type ratings and MFF. |
Tinstaafl, thanks for the info, much appreciated.
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Not aware of 'Take off law' or 'Landing law' - not in any Airbus documents I have.
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club. Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy. Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly! |
I understand that FBW is lighter, cheaper to maintain, "safer" etc. buut why this method of controlling. As I said, the 777 is FBW but totally conventionally controlled. What drove Airbus down the path they went on? I suppose the commonality point is a good one, but couldn't you engineer any FBW system to give pre-programmed feedback to the pilot?
Flapsone - Good point, I suppose most things in flying are a heck of a lot easier to do than to describe! |
Perhaps for take-off and landing I should have used 'mode' instead of 'law'?
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Originally Posted by FlapsOne
(Post 2886822)
Not aware of 'Take off law' or 'Landing law' - not in any Airbus documents I have.
There is NORMAL LAW - which has Ground mode, Flight mode and Flare mode; ALTERNATE LAW - which is a slightly degraded form of normal law offering certain reduced protections and DIRECT LAW - which is the same law 'used' by everything at your local flying club. Don't know why Airbus chose this route but it's nowhere near as complicated as certain explanations try to make it sound. Having said that, it's harder to write down (type) than to explain verbally or actually operate. It takes approx 10 mins to get used to and 15 mins to totally enjoy. Bottom line, the aircraft fly very well indeed and have to suffer several (big) failures before they end up in DIRECT LAW - which is where we all all learnt to fly! |
This must be the thread with most correct answers ever. :D :D :D
http://img247.imageshack.us/img247/9...20p1cl9.th.gif Apart from the "normal law" the FBW provides for some "reconfiguration laws". These are:
All are correctly described in the post above. Perhaps except for the mechanical back-up that enables the pilot to control the aircraft during temporary complete loss of electrical power. Pitch is controlled manually by setting the trimmable horizontal stabiliser and lateral control is provided conventionally via rudder and pedals. Airbus claims that aircraft were succesfully landed in mech. backup, however such manuoevre is not part of the training curriculum. FD (the un-real) |
MECH BACKUP i.e. only ths and rudder is encountered only at ridculously high level of multiple failure eg : all comp failure-
SEC 1+2+3+ELAC1+2+FAC1+2 phew!!.:eek: once in a while we try it on the sims freeplay.( sim is set up calm cavok ). fool around on the down wind to come to grips with the trim (tremendous amount of control lag) use rudder sparingly, wait for the secondary effect of yaw:* well after a while :O we actually landed it |
after a long long while and after many approach resets:\ :uhoh: :p
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Just to ad up another law no one talked about: ABNORMAL law!
Let's say we are flying into extreme weather, aircraft flips over due to very strong turbulences, it will leave the protected envellop, normal laws will be exceeded and abnormal law becomes active. This is a safety feature to ensure that the flight control computers will never prevent the pilots from recovering from abnormal attitude. I may be wrong: got my type rating last december , sent 50 resumes, was invited to one single interview...and still on the ground... |
Yesss. That's all if them.
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So much for user-friendly
i fly the 330. that what i get paid to do. given the choice, Boeing ANYTIME.
anybody remember KISS ? just look at the disaster airbus has gone and done on the 380. some:ugh: guys sound like nerd geeks, not pilots. |
So what happens when the RAT deploys ?
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Originally Posted by yachtno1
(Post 2897150)
So what happens when the RAT deploys ?
Well, He gets off the wheel and puts his little parachute on and..... Just kidding. it deploys automaticly in an serious electrical failure or is deployed manually for a hydraulic failure or various combinations thereof. Depending on which failure the sim guy is throwing at you. You'll follow the ECAM procedure and ftfp. Okay? Have at it techno geeks! RDG |
I must add respect to the test pilot who managed to land the thing in mechanical back up! Tried it in the sim when I was doing my initial A330 endorsement and the results were "none to pleasing"......................and that is being generous from the sim instructor!
Go Airbus!!!!!:D |
Originally Posted by qwertyuiop
(Post 2886591)
GLAD I FLY BOEINGS!!!!!!!!!!!!!!!!!!!
Ask 10 bus pilots a tech question and you will end up with 10 different answers. |
Originally Posted by reelydune
(Post 2905230)
I wonder if the PF ( RIP ) on AA 587 an Airbus A300-600 (A NON FBW airbus from1984 re-design of earlier A300 ) which crashed at Belle Harbour in 2001 wished he had FBW protection against his excessive aggressive rudder movement which snapped off the Vert Stab according to NTSB?
Anyone? palgia |
I found this on www.airbusdrivers.net, I am not claiming that I wrote it, and the name of the author is not published on the website.
AIRBUS FLIGHT CONTROL LAWS NORMAL LAWNormal operating configuration of the system. Failure of any single computer does not affect normal law. Covers 3-axis control, flight envelope protection, and load alleviation. Has 3 modes according to phase of flight. Ground Mode • Active when aircraft is on the ground. • Direct proportional relationship between the sidestick deflection and deflection of the flight controls. • Is active until shortly after liftoff. • After touchdown, ground mode is reactivated and resets the stabilizer trim to zero. Flight Mode • Becomes active shortly after takeoff and remains active until shortly before touchdown. • Sidestick deflection and load factor imposed on the aircraft are directly proportional, regardless of airspeed. • With sidestick neutral and wings level, system maintains a 1 g load in pitch. • No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees. • At full aft/fwd sidestick deflection system maintains maximum load factor for flap position. • Sidestick roll input commands a roll rate request. • Roll rate is independent of airspeed. • A given sidestick deflection always results in the same roll rate response. • Turn coordination and yaw damping are computed by the ELACs and transmitted to the FACs. • No rudder pedal feedback for the yaw damping and turn coordination functions. Flare Mode • Transition to flare mode occurs at 50' RA during landing. • System memorizes pitch attitude at 50' and begins to progressively reduce pitch, forcing pilot to flare the aircraft • In the event of a go-around, transition to flight mode occurs again at 50' RA. Protections Load factor Limitation • Prevents pilot from overstressing the aircraft even if full sidestick deflections are applied. Attitude Protection • Pitch limited to 30 deg up, 15 deg down, and 67 deg of bank. • These limits are indicated by green = signs on the PFD. • Bank angles in excess of 33 deg require constant sidestick input. • If input is released the aircraft returns to and maintains 33 deg of bank. High Angle of Attack Protection (alpha): • When alpha exceeds alpha prot, elevator control switches to alpha protection mode in which angle of attack is proportional to sidestick deflection. • Alpha max will not be exceeded even if the pilot applies full aft deflection High Speed Protection: • Prevents exceeding VMO or MMO by introducing a pitch up load factor demand. • The pilot can NOT override the pitch up command. Low Energy Warning: • Available in CONF 2,3, or FULL between 100' and 2,000' RA when TOGA not selected. • Produces aural "SPEED SPEED SPEED" when change in flight path alone is insufficient to regain a positive flight path (Thrust must be increased). ALTERNATE LAW If Multiple Failures of Redundant Systems occur, the flight controls revert to Alternate Law. The ECAM displays the message: ALTN LAW: PROT LOST Ground Mode The ground mode is identical to Normal Law. Flight Mode • In pitch alternate law the flight mode is a load factor demand law similar to the Normal Law flight mode, with reduced protections. • Pitch alternate law degrades to pitch direct law when the landing gear is extended to provide feel for flare and landing, since there is no flare mode when pitch normal law is lost. • Automatic pitch trim and yaw damping (with limited authority) is available. • Turn coordination is lost. • When pitch law degrades from normal law, roll degrades to Direct Law - roll rate depends on airspeed. Protections • All protections except for load factor maneuvering protection are lost. • The load factor limitation is similar to to that under Normal Law. • Amber XX's replace the green = attitude limits on the PFD. • A low speed stability function replaces the normal angle-of-attack protection o System introduces a progressive nose down command which attempts to prevent the speed from decaying further. o This command CAN be overridden by sidestick input. o The airplane CAN be stalled in Alternate Law. o An audio stall warning consisting of "crickets" and a "STALL" aural message is activated. o The Alpha Floor function is inoperative. • The PFD airspeed scale is modified: o VLS remains displayed o VALPHA PROT and VALPHA MAX are removed o They are replaced by a red and black barber pole, the top indicating the stall warning speed VSW • A nose up command is introduced any time the airplane exceeds VMO/MMO to keep the speed from increasing further, which CAN be overridden by the sidestick. • Bank angle protection is lost. • Certain failures cause the system to revert to Alternate Law without speed stability. • Yaw damping is lost if the fault is a triple ADR failure. ABNORMAL ALTERNATE LAW Abnormal Alternate Law is activated if the airplane enters an unusual attitude, allowing recovery from the unusual attitude. • Pitch law becomes Alternate (without autotrim or protection other than Load Factor protection). • Roll law becomes Direct law with mechanical yaw control. • After recovery from the unusual attitude, the following laws are active for the remainder of the flight: o Pitch: Alternate law without protections and with autotrim. o Roll: Direct law o Yaw: Alternate law • There is no reversion to Direct law when the landing gear is extended. DIRECT LAW Direct law is the lowest level of computer flight control and occurs with certain multiple failures. • Pilot control inputs are transmitted unmodified to the control surfaces, providing a direct relationship between sidestick and control surface. • Control sensitivity depends on airspeed and NO autotrimming is available. • An amber message USE MAN PITCH TRIM appears on the PFD. • If the flight controls degrade to Alternate Law, Direct Law automatically becomes active when the landing gear is extended if no autopilots are engaged. If an autopilot is engaged, the airplane will remain in Alternate Law until the autopilot is disconnected. • There are no protections provided in Direct Law, however overspeed and stall aural warnings are provided. • The PFD airspeed scale remains the same as in Alternate Law. MECHANICAL BACKUP In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode. • Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel. • Lateral control is accomplished using the rudder pedals. • Both controls require hydraulic power. • A red MAN PITCH TRIM ONLY warning appears on the PFD. |
Airbus tech discussion is a lot like Mornington Crescent. Must be a euro thing. :D :D
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it kind of spread after the shunnel;)
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