Why does Alternate becomes Direct law whenever landing gear down on Airbus?
Direct Law is the simplest and most instinctive
For example, in Airbus normal law, you apply a control force, the aircraft will ALWAYS pitch at the same rate irrespective of speed, when you release the control force, it will hold the attitude. How simple is that
In a Boeing, pitch rate with control force depends on airspeed, and then you must TRIM to hold any new attitude that you have set. This does not seem to be simple and instinctive to me
Join Date: Feb 1998
Location: Formerly of Nam
Posts: 1,595
Likes: 0
Received 0 Likes
on
0 Posts
Maybe simplest to understand but not simplest to fly
Horrors! One might have to reach down and move the stab trim wheel!
Elevator pitch deflection is proportional to stick deflection
Bad news indeed - your back in a normal airplane!(almost)
And if you want to push the envelope :
No load factor protection )
No angle of attack protection )
No angle of bank protection ) actual hands-on piloting required
No pitch attitude protectionc )
No high speed protection )
I dont think youd enjoy flying my little PA18 unless I shoehorned an ELAC into it eh JR!
Simple = easy to use, as per Dictionary.com | Find the Meanings and Definitions of Words at Dictionary.com
I did not ever mention horrors, bad news, dangerous or pilot inability/skill level.
The discussion was purely about what is more simple.
What is more simpler (easier) :
1- adjust pitch attitude with only ONE control movement
or
2 - adjust pitch attitude with a control movement (primary control - elevator though the control column) THEN adjust another secondary control (pitch/stabilator trim) AS WELL
What is easier ?
1 or 2 control movemente/adjustments ? Its not that hard to work out
I did not ever mention horrors, bad news, dangerous or pilot inability/skill level.
The discussion was purely about what is more simple.
What is more simpler (easier) :
1- adjust pitch attitude with only ONE control movement
or
2 - adjust pitch attitude with a control movement (primary control - elevator though the control column) THEN adjust another secondary control (pitch/stabilator trim) AS WELL
What is easier ?
1 or 2 control movemente/adjustments ? Its not that hard to work out
Join Date: Jun 2005
Location: AUSTRALIA
Posts: 58
Likes: 0
Received 0 Likes
on
0 Posts
Mr Citizen
John,
Didnt realise you know the AIRBUS systems that well. Whats your thoughts on the Phenom 300? I thought it was crap to be honest. Just the quality of the build. Soon Learjet will be bringing down a 45XR more speed, more range and bigger cabin.. Only slightly more on price! Cheaper to run also and they hold their value better. Didnt realise your boss was American.
Didnt realise you know the AIRBUS systems that well. Whats your thoughts on the Phenom 300? I thought it was crap to be honest. Just the quality of the build. Soon Learjet will be bringing down a 45XR more speed, more range and bigger cabin.. Only slightly more on price! Cheaper to run also and they hold their value better. Didnt realise your boss was American.
Join Date: May 2000
Location: Glorious West Sussex
Age: 76
Posts: 1,020
Likes: 0
Received 0 Likes
on
0 Posts
JC
To be picky, with sidestick neutral the FBW trys to maintain 1.0g and zero roll rate - it will not return to the previous attitude after atmospheric disturbance, although the effect is very close.
Pedant's hat back in cupboard.
when you release the control force, it will hold the attitude. How simple is that 
Pedant's hat back in cupboard.
Join Date: Mar 2000
Location: Sunrise Senior Living
Posts: 1,338
Likes: 0
Received 0 Likes
on
0 Posts
Had a go at Alt Law landing in the box by way of Abnormal Attitude Law. It's different!
From the FCTM:-
'Takeoff and landing maneuvers are naturally achieved. For example, a flare requires the PF to apply permanent aft pressure on the sidestick, in order to achieve a progressive flare.'
- hence the need for the nose down pitch introduced by flare law at 50'. In Alt Law this does not happen so a permanent 'aft pressure on the sidestick' will send you flying again - and alpha floor is inhibited below 100'RA. So you need to arrest the ROD with small backwards movements of the stick - releasing between them. You'd think they might mention that somewhere!
Cheers
mcdhu
From the FCTM:-
'Takeoff and landing maneuvers are naturally achieved. For example, a flare requires the PF to apply permanent aft pressure on the sidestick, in order to achieve a progressive flare.'
- hence the need for the nose down pitch introduced by flare law at 50'. In Alt Law this does not happen so a permanent 'aft pressure on the sidestick' will send you flying again - and alpha floor is inhibited below 100'RA. So you need to arrest the ROD with small backwards movements of the stick - releasing between them. You'd think they might mention that somewhere!
Cheers
mcdhu
Join Date: Aug 2007
Location: Middle East
Posts: 93
Likes: 0
Received 0 Likes
on
0 Posts
To land the sim in ALTN law:
1. Fail Both RAs.
2. Extend flaps to posn 3 (Landing flaps) then fail both SFCCs.
3. Fail Both LGCIUs then lower gears by gravity.
4. Fail both FACs.
The landing can be done now in ALTN Law and it does not differ much than Normal law with flare mode.
Thanx
1. Fail Both RAs.
2. Extend flaps to posn 3 (Landing flaps) then fail both SFCCs.
3. Fail Both LGCIUs then lower gears by gravity.
4. Fail both FACs.
The landing can be done now in ALTN Law and it does not differ much than Normal law with flare mode.
Thanx
The biggest problem with a direct law landing is the lack of feel through the side stick, and a tendency of most people to over correct (control) with the trim wheel. This can lead to the approach becoming destabilised in the latter stages, and the pilot has a natural tendency to not want to go-arround in direct law.
