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What is damping mode in A320?

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What is damping mode in A320?

Old 12th May 2022, 16:31
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Question What is damping mode in A320?

I'm going for my type rating soon and I'm working through as many CBTs as I can and I would appreciate if anybody could help me out on this concept.
I've tried researching this everywhere but I can't seem to find a reasonable answer that would satisfy my curiosity

So in the Flight Controls CBT, it's mentioned that ELAC 1 and ELAC 2 help control the elevators, THS and ailerons. ELAC 1 is in active mode for ailerons and damping mode for elevators. Similarly ELAC 2 is in active mode for elevators and damping mode for ailerons.

What is this damping mode? All I get is that in the active mode the jack is electronically controlled and in damping mode it follows surface movements?

Am I correct in assuming that active mode is the normal law and damping mode is either alternate or direct law, wherein side stick movement is directly proportional to surface movements?

Thanks in advance!

Sincerely,
A thoroughly confused soul
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Old 12th May 2022, 19:40
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That’s not my understanding of it. Active and damping modes have nothing to do with flight control laws.
The CBT you have looked at is a little misleading, because active and damping mode refers to the hydraulic jacks in the flight control surface itself.
So, in normal flight, ELAC 2 controls the elevators through the green and yellow hydraulic systems. This means the hydraulic jacks in the elevator that are doing the actual pushing and pulling are the green and yellow ones, these are the “active” ones. The damped Jacks are controlled by the blue hydraulic system and act as a damping force or drag on the active jacks. This serves to smooth out the control surface movement much like the dampers in your car.
Only if ELAC 2 fails, would the blue jacks take over, because ELAC 1 is now controlling the elevators, and the green and yellow jacks becoming the damping force. A single ELAC failure would not result in a flight control law downgrade, and you would remain in normal law (had to look that up!).

That’s my understanding of the system, and am happy to be corrected if I'm wrong.

My advice to you would be to avoid CBTs at this stage and get a copy of the FCOMS instead.
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Old 12th May 2022, 20:10
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Agreed. If the overload of study is actually required by the TR school or national CAA, it's a great pity.

There's a lot of stuff that actually will need learning and filling the brain storage with minutiae like this will definitely cause more harm than good. Not the OP's fault, at this stage he absolutely cannot recognize the importance of different bits of information.

With much good success, get a copy of the latest (new SOP) edition FCTM and print it. No, the iPad won't do because that's where the FCOM is and QRH ;-). Pre-studying that will not do harm and will lead you to the important parts of the FCOM.

Another nice book to get oriented is here https://www.smartcockpit.com/aircraf...or_Pilots.html, a bit aged but the scope is perfect before the course actually starts. Enjoy!



Last edited by FlightDetent; 12th May 2022 at 20:21.
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Old 12th May 2022, 22:24
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The number of the ELAC or SEC below the control surface; the hydraulic jack colour and the arrow shows the chain of control.

So for example: normally the left aileron is controlled by ELAC 1 using only the Blue Hyd jack. If ELAC 1 or Blue Hyd fails, control passes to ELAC 2 using only the Green Hyd jack.

The left elevator is normally controlled by ELAC 2 using the Green Hyd jack. If ELAC 2 or Green Hyd fails, control passes to ELAC 1 using the Blue Hyd jack. Or, if ELAC 1 and 2 have failed, control passes to SEC 2 using the Green Hyd jack, etc.

On each surface, the jack not in use performs a damping function - its hydraulic fluid is put into a closed loop which damps the control surface; preventing flutter etc.



Last edited by Uplinker; 13th May 2022 at 09:44.
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Old 12th May 2022, 23:31
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Originally Posted by Jonty View Post
The damped Jacks are controlled by the blue hydraulic system and act as a damping force or drag on the active jacks. This serves to smooth out the control surface movement much like the dampers in your car.

My advice to you would be to avoid CBTs at this stage and get a copy of the FCOMS instead.
Thank you! This perfectly clears up the damping terminology used so far! I think I assumed a bit too much with my lack of understanding the whole relationship between the hydraulics and the normal/alternate laws.

With respect to the FCOMs, I have the latest one with me, but I found the FCOMs to be a bit dense at the moment. I thought once I start my type rating, I'll finally start reading up on it. Wrong approach?
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Old 12th May 2022, 23:38
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Originally Posted by FlightDetent View Post
With much good success, get a copy of the latest (new SOP) edition FCTM and print it.
Any idea where I can get the latest edition of the FCTM?
I'm also just figuring out the ins and outs of the MCDU on the x plane sim just to get a general idea. You think that's a good idea or should I just wait for the type rating to start?

Originally Posted by FlightDetent View Post
Another nice book to get oriented is here, a bit aged but the scope is perfect before the course actually starts. Enjoy!
Thanks for this! I'll be sure to go through it!
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Old 12th May 2022, 23:46
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Originally Posted by Uplinker View Post
The number of the ELAC or SEC below the control surface; the hydraulic jack colour and the arrow shows the chain of control.

So my understanding is that for example: normally the left aileron is controlled by ELAC 1 using only the Blue Hyd jack. If ELAC 1 or Blue Hyd fails, control passes to ELAC 2 using only the Green Hyd jack.

The left elevator is normally controlled by ELAC 2 using the Green Hyd jack. If ELAC 2 or Green Hyd fails, control passes to ELAC 1 using the Blue Hyd jack. Or, if ELAC 1 and 2 have failed, control passes to SEC 2 using the Green Hyd jack, etc.

On each surface, the jack not in use performs a damping function - its hydraulic fluid is put into a closed loop which damps the control surface; preventing flutter etc.
Thanks for the reply! Just one question
If ELAC 1 (and by extension the blue hydraulics) responsible for the left aileron fails, then ELAC 2 would end up controlling the right aileron using the blue hydraulic jack. Correct?
If that's the case then how is this possible? Since the blue hydraulics already failed when ELAC 1 failed. Or do the blue hydraulics for both the left and right aileron act independently of each other?
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Old 13th May 2022, 09:43
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I would read and understand the section on flight controls and auto-thrust. It is really important to understand how they work and the logic involved. Airbus FBW flies just like a conventional jet, you just have to understand how the design engineers have made your life easier by the way you control it.

Also the speed tape; Green Dot, VLS, Alpha Prot, Alpha Max etc - very important to understand these and how the aircraft and auto-thrust will interact with them.

Understand how Ground speed mini operates on approach. Instead of referencing IAS; Ground speed mini ADDs thrust if the head wind increases and REDUCES thrust if the headwind reduces - within certain limits. So it locks the ground speed on approach, not the air speed, and is why the engines can thrust up and down a lot on a turbulent approach. This is opposite to conventional systems but it keeps the aircraft energy constant with changing head winds.

Nobody I have ever been taught by could teach the side-stick. Hold it properly like a pistol. If you need to make a correction move the stick until the aircraft attitude is where you want it, then return the stick to neutral. Airbus FBW will hold that attitude you have set - within reason and certain limits. (The FBW has surface and aircraft feedbacks to enable it to adjust the flight controls in the background to hold your selected attitude). Make small side-stick corrections and always return to neutral between each input. There is a large arm rest on the outboard side of your seat. Adjust this this to rest your forearm along when you hold the side-stick. It will make your manual control much smoother.

The Airbus FBW auto-thrust is brilliant. It is a very logical system, and works very well. The auto-thrust will move the thrust between IDLE and CLB or MCT, depending which detent the thrust levers are in. If you click the levers out of a detent, the thrust will rapidly change to match whichever angle the levers are at, and then you have manual thrust - push forwards for more thrust, pull back for less. At any time, from any position or detent; pushing forwards will give you more thrust, just like any jet. The levers don't move by themselves so it simply means that you look at the engine N1 or EPR gauges to see any thrust changes instead of looking at the thrust levers themselves. You are looking at the instruments anyway, so you can see exactly what is happening.

On the FCP; if you pull SPD, HDG, ALT, V/S out towards you, you are telling the Airbus "do what I select". If you push them in you are telling the Airbus "you control it according to what I have programmed in the FMGS", e.g. Managed Nav.

A reasonable understanding of how to use the MCDU to enter basic flight data, waypoints and and routes will be a great help in setting up the SIM.

Airbus FBW is a fantastic machine. Enjoy !
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Old 13th May 2022, 09:49
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Originally Posted by mahendru1992 View Post
Thanks for the reply! Just one question
If ELAC 1 (and by extension the blue hydraulics) responsible for the left aileron fails, then ELAC 2 would end up controlling the right aileron using the blue hydraulic jack. Correct?
If that's the case then how is this possible? Since the blue hydraulics already failed when ELAC 1 failed. Or do the blue hydraulics for both the left and right aileron act independently of each other?
How many failures are you talking about? Do you have only ELAC1 failure or BOTH ELAC1 AND Blue HS failure? Or just Blue HS failure?

- In the first case (ELAC1 failed), ELAC2 will control left aileron using Green HS and right ailerone using Blue HS.
- In the second case (ELAC1 and Blue HS failed), ELAC2 will control left ailerone using Green HS and right ailerone will switch to damping mode (that means that ailerone will be slowly moved by aerodynamic forces and jack will follows surface movement)
- in the 3rd case (Blue HS failed), left ailerone will switch to damping mode and ELAC1 will control right ailerone using Green HS.
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Old 13th May 2022, 09:59
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Originally Posted by Uplinker View Post
No, look again at the diag I posted and the coloured circles I drew on: ELAC 1 controls only the Blue jack in the left aileron. If ELAC 1 or Blue hydraulics fail, control will be passed to ELAC 2, which only controls the Green jack in the left aileron - that is what the diagram is showing you, but it is a bit subtle.
Are you sure that ELAC2 will take control over ailerones in case of Blue HS failure?
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Old 13th May 2022, 10:03
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Originally Posted by mahendru1992 View Post
Thanks for the reply! Just one question
If ELAC 1 (and by extension the blue hydraulics) responsible for the left aileron fails, then ELAC 2 would end up controlling the right aileron using the blue hydraulic jack. Correct?
If that's the case then how is this possible? Since the blue hydraulics already failed when ELAC 1 failed. Or do the blue hydraulics for both the left and right aileron act independently of each other?

The right aileron is normally controlled by ELAC 1 using only the Green jack, so if Blue Hyd and ELAC 1 failed, you would be left with left aileron only, controlled by ELAC 2 using the Green jack. (You would also have most of your roll spoilers)

Yes, all the controls work independently, to give redundancy. Certain hydraulic and FBW failure combinations will leave you with a single aileron or elevator.
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Old 13th May 2022, 10:07
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To my previous question.
I always thought that only one ELAC can be in control of ailerones. So you cannot use ELAC1 for your right ailerone and ELAC2 for your left ailerone at the same time.
Am I correct? Or not?
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Old 13th May 2022, 10:13
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The arrows on the hydraulic architecture diagram tell you which FBW computer normally controls which flight surface and which computer takes over from it. All the ELACs, SEC and FACs are used all the time - that is how they monitor each other and take over or assist when required.
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Old 13th May 2022, 10:20
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Originally Posted by Uplinker View Post
The arrows on the hydraulic architecture diagram tell you which FBW computer normally controls which flight surface and which computer takes over from it. All the ELACs, SEC and FACs are used all the time - that is how they monitor each other and take over or assist when required.
Hmm, let me check it later on the sim...
Thanks anyway! Always nice to refresh knowledge.
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Old 13th May 2022, 10:49
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Yes, let us know I can't think how to confirm one way or the other?
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Old 13th May 2022, 10:58
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Originally Posted by Samten View Post
To my previous question.
I always thought that only one ELAC can be in control of ailerones. So you cannot use ELAC1 for your right ailerone and ELAC2 for your left ailerone at the same time.
Am I correct? Or not?
Incorrect.

If you lose Blue Hyds, then the only surface you lose is spoiler 3.
Therefore the Left Aileron must be controlled by ELAC 2 with Green Hyds and Right Aileron must be controlled by ELAC 1 with Green Hyds.
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Old 13th May 2022, 11:51
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No, actually, I think I was partly wrong. I have just re-read DSC-27-10-20 "Roll control" which states, (from Airbus FCOM):

ELECTRIC CONTROL
  • The ELAC 1 normally controls the ailerons.

    If ELAC1 fails, the system automatically transfers aileron control to ELAC2.

    If both ELACs fail, the ailerons revert to the damping mode.
  • ..........
    Normally on a schematic or an electrical diagram, if two separate components in different parts of the diagram operate together, there would be a dashed line drawn between the two components to indicate this. But they probably left those out to de-clutter the diag.

    Also, while I am in the FCOM:

    AILERONS

    Each aileron has two electrically controlled hydraulic servojacks.

    One of these servojacks per aileron operates at a time.

    Each servojack has two control modes :
    The system automatically selects damping mode, if both ELACs fail or in the event of blue and green hydraulic low pressure.

    Active :Jack position is controlled electrically

    Damping :Jack follows surface movement.
    The bottom line though is that us pilots don't need to know the exact ins and outs really; the system has multiple redundancy layers. In the event of a failure the ECAM page and STATUS page will tell us what is what and what we need to do.
    .

    Last edited by Uplinker; 13th May 2022 at 12:12.
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    Old 13th May 2022, 12:09
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    And here is the full Hyd architecture diag to make our cross referencing easier ! From Airbus A320 FCOM :



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    Old 13th May 2022, 15:24
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    I asked my friend to check it in the sim (haven't seen it by my eyes, so I'm not 100% sure).

    Switched off Blue HS. Both ailerons operable (from Green HS). So my previous post was wrong. Thanks guys!

    Now the interesting part:
    Next ELAC2 was switched off (with Blue HS already offline). One aileron stopped operation!

    Bottom line:
    In case of HS failure BOTH ELACs can operate simultaneously - each moving one aileron. But, in fact, each ELAC is hard-wired to only one jack per aileron. So in case of Blue HS failure, ELAC1 cannot simply switch to Green jack on the left aileron and needs help from ELAC2.
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    Old 13th May 2022, 18:30
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    Originally Posted by Samten View Post
    I asked my friend to check it in the sim (haven't seen it by my eyes, so I'm not 100% sure).

    Switched off Blue HS. Both ailerons operable (from Green HS). So my previous post was wrong. Thanks guys!

    Now the interesting part:
    Next ELAC2 was switched off (with Blue HS already offline). One aileron stopped operation!

    Bottom line:
    In case of HS failure BOTH ELACs can operate simultaneously - each moving one aileron. But, in fact, each ELAC is hard-wired to only one jack per aileron. So in case of Blue HS failure, ELAC1 cannot simply switch to Green jack on the left aileron and needs help from ELAC2.
    For the same reason with dual engine flame out you loose right Aileron because it requires ELAC2 to operate it with Blue system and ELAC2 is lost till at least APU comes on line.
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