Why does Alternate becomes Direct law whenever landing gear down on Airbus?
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Why does Alternate becomes Direct law whenever landing gear down on Airbus?
In many failures cases on Airbus when u put the landing gear down the flight control law becomes direct law. I didnīt find anything written about it and i donīt understand why whould they do it, because no one wants to fly a plane in a worst condition.
There must be a logical explanation but i canīt find it. Any insights?
There must be a logical explanation but i canīt find it. Any insights?
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The bus always lands in direct law and it uses the radio alt to alert the prims that you are about to land. In the failure cases you mentioned, the radio alt is not available and the only way the plane knows you are going to land is by gear extention.
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It has to be stated, and it has been before, that there is no alternate law, there is only normal law in pitch and direct law in roll, which is called then alternate law.
If you have certain failures your roll falls into direct, but your pitch not yet. It only does when you lower the gear. That's when your Airbussy is in direct law. It had to because the flight control computers are not able to do a normal landing anymore.
I'm sure they could have sorted it out differently, but that's how they designed it - and it's not bad.
Dani
If you have certain failures your roll falls into direct, but your pitch not yet. It only does when you lower the gear. That's when your Airbussy is in direct law. It had to because the flight control computers are not able to do a normal landing anymore.
I'm sure they could have sorted it out differently, but that's how they designed it - and it's not bad.
Dani
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The bus always lands in direct law
A normal landing is in the flare mode of normal law. There is no flare mode in alternate law, hence the reversion to direct law at gear down.
Normal law and alternate law both have the same characteristics in pitch, i.e. adjusting the sidestick adjusts the flight path of the aircraft. Without flare mode, an attempt to land in normal/alternate law would result in the aircrafts flight path shallowing as you pulled back the stick to flare and a resultant float until you ran out of speed.
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The way I understood it:
As the airplane approaches the runway in normal law, at a specific RA height it (50 feet IIRC) starts rolling in fwd trim, which the pilot overrides, by pulling back on the stick, much like a normal airplane. I suppose one could actually call it artificial feel.
With certain failures, the fwd trim input will not happen, since the airplane doesn't know it's height, so as a back up, it goes into direct law with the gear down. In direct law, the pilot has to trim the airplane, or I suppose one could accept much higher stick forces, however, this manual trimming gives the pilot a, dare I say it, a direct feel for the airplane.
Basically the point is, while it would be possible to land with the a/c in alternate law, due to the way pitch forces on the stick would would feel to the pilot, there is a much bigger chance of over controlling, since there is no real feel.
As the airplane approaches the runway in normal law, at a specific RA height it (50 feet IIRC) starts rolling in fwd trim, which the pilot overrides, by pulling back on the stick, much like a normal airplane. I suppose one could actually call it artificial feel.
With certain failures, the fwd trim input will not happen, since the airplane doesn't know it's height, so as a back up, it goes into direct law with the gear down. In direct law, the pilot has to trim the airplane, or I suppose one could accept much higher stick forces, however, this manual trimming gives the pilot a, dare I say it, a direct feel for the airplane.
Basically the point is, while it would be possible to land with the a/c in alternate law, due to the way pitch forces on the stick would would feel to the pilot, there is a much bigger chance of over controlling, since there is no real feel.
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Hi,
Direct Law is the simplest and most instinctive - ask any Boeing Pilot or even Wilbur Wright.
the flight control law becomes direct law......no one wants to fly a plane in a worst condition
Last edited by rudderrudderrat; 12th Sep 2010 at 12:31.
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MCDHU simple - leave the gear up and ignore warns to
simulate what the flare is like and just do a wheels
up if you want to go that far. In the early sims the panel
could insert a failure of changeover to Direct with gear
down (mainley for EMERG CONFIG change with G/D at
1,000ft) but not any more since Airboos now regard it as
l'imposible.
Correct. I fly the frigging thing much better in Direct. In
certain hyd sim situations I'll drop the gear earlyer after I
got me flap 3. NPAs are then spot on (dispite the damn
sidestick!)
simulate what the flare is like and just do a wheels
up if you want to go that far. In the early sims the panel
could insert a failure of changeover to Direct with gear
down (mainley for EMERG CONFIG change with G/D at
1,000ft) but not any more since Airboos now regard it as
l'imposible.
Direct Law is the simplest and most instinctive -
ask any Boeing Pilot or even Wilbur Wright.
ask any Boeing Pilot or even Wilbur Wright.
certain hyd sim situations I'll drop the gear earlyer after I
got me flap 3. NPAs are then spot on (dispite the damn
sidestick!)
Direct Law is the simplest
No auto pitch trim
Elevator pitch deflection is proportional to stick deflection
And if you want to push the envelope :
No load factor protection
No angle of attack protection
No angle of bank protection
No pitch attitude protectionc
No high speed protection