A380 Ailerons

[212man]

I've been fortunate enough to have had several flights in the A380 as a passenger, but this last one a few days ago was the first where I've been overlooking the wing. I was struck, during the approach and landing, by the fact that the aileron is split into 3-4 sections and - more to the point - they appear to act in opposition. Why would the system command simultaneous large up and down movements, as opposed to a single small movement?

Hope that makes sense!

[no-hoper]

This kind of movement is related to the
Load Alleviation Function mainly.
The Aileron Droop Function and
Lift Dumping and Phased Lift Dumping Functions are involved as well.

Load Alleviation Function:
The aim of the Load Alleviation Function (LAF) is to alleviate the
fatigue and static loads on the wings by reduction of the wing bending
moment.
The LAF is composed of:
- The Passive Turbulence Alleviation (PTA) and,
- The Active Turbulence Alleviation (ATA).
The Passive Turbulence Alleviation alleviates the static loads in
turbulence and during maneuvers. The activation is based on the
vertical load factor given by normal law. Once the PTA is activated,
it progressively decreases 5 seconds after the triggering condition
disappeared. The computed orders are sent to the ailerons and spoilers
6 to 8.
The pitch compensation linked to the deflections is sent to the inner
elevators.
The Active Turbulence Alleviation alleviates the fatigue and static
loads.
The activation is based on the measurement of the vertical load factor
on the wings given by the accelerometer units installed on the outer
pylons.
The ATA uses the inner and mid ailerons. It can only be activated if:
- The PTA is activated and,
- At a speed above 240 knots.
The ATA orders are added to the PTA orders, and can be added to
the roll orders.
There is no pitch compensation for the ATA.
The LAF is activated above a given speed and vertical acceleration
thresholds but is inhibited when slats and flaps are in full
configuration.

Aileron Droop Function:
The aileron droop function is computed by the lateral law.
When the pilot puts the slat/flap control lever in the position "1" or
more, the Slat Flap control computers send to the PRIMs a "flap out"
signal through ARINC 429.
The PRIMs send deflection orders to the ailerons.
The ailerons droop downward to increase the wing curve.
The ailerons continue to fulfill the roll function

Lift Dumping and Phased Lift Dumping Functions:
The lift dumping and phased lift dumping functions are used to:
- stick the aircraft on ground by suppressing the lift,
- reduce bound risks,
- decelerate the aircraft and,
- give acceptable level of passenger comfort at touch down.
All available spoilers are used for these functions.
Moreover, ailerons contribute to the lift dumping function. The ailerons
move upward.

Rgds

[atakacs]

The aim of the Load Alleviation Function (LAF) is to alleviate the
fatigue and static loads on the wings by reduction of the wing bending
moment.

Interesting.

What's the goal ? Increasing the airframe life expectancy or weight gain in the structure ?

Is this system present in other passenger aircraft ?

[PEOPLESX]

yes, the LAF or MLA (on A340/A330, but more or less a similar system) should reduce the lift of the wings (mainly outer section) to keep the g-loads an the in the design limits and reducing the load at the wing root section.
your absolutely correct, this systems helps to reduce structure weight and increase lifetime.

AFAIK it's installed in all "modern" Airbus and the L1011-500 was/is equipped with a very similar system (not really based on FBW, but both ailerons can deflect upwards). Maybe there some more types i don't know .

[411A]

Is this system present in other passenger aircraft ?
Yes, absolutely....on the L1011-500 types.
Lockheed...far ahead of most others.
No surprise, there.:E

[212man]

Thnaks, but I'm not sure that is what I was looking at. What has been described above is a relationship between the ailerons and the inner elevators (sic) to reduce wing bending moments. What I was describing was the outboard ailerons themselves being split into sections and then operating in opposition. So two neighbouring aileron surfaces would be operating in opposite senses simultaneously - why not simply move one surface by a smaller amount?

[PEOPLESX]

hmm, i've no A380 in my license, so i can't contribute with facts, sorry. There are some possibility's i think of, why the F/CTL-system act in this way, but that are just speculations of mine.
At least on the A330/A340 there is a function which supports the rudder during "low speed" situations and high "rudder demand" by splitting the ailerons and deploying Spoiler No6.

I'm waiting for the experts :8

[no-hoper]

"the outboard ailerons themselves being split into sections and then operating in opposition"

This is impossible.There are 3 Ailerons installed,each connected to
two actuators.But you can split them only once.

[dream747]

I noticed the movements of the ailerons as well on my recent flight on the A380. No-hoper, your post mentioned that the ATA activates when the PTA is active and above 240 knots. However, I noticed the split aileron movements just after lift-off to about 1000AGL. Any reason for this?

[no-hoper]

Sorry,don't know.Could be the PTA.My typcourse was nearly 2 month in the classroom,but sometimes i think it was not sufficient.
The guy who developed the software for the 6 computers(splitted in A&B off course) might know the answer...

[SMOC]

Here you go, all three right side ailerons acting independently.

JetPhotos.Net Photo » F-HPJC (CN: 43) Air France Airbus A380-861 by Rui Alves - Madeira Spotters (http://jetphotos.net/viewphoto.php?id=6937055)

And video

YouTube - SQ A380 001.avi (http://www.youtube.com/watch?v=YqLyKwx8KNE&feature=youtube_gdata_player)

[212man]

This is impossible.There are 3 Ailerons installed,each connected to

Just looked at a photo I took in the cruise and yes there are 3 sections - you call it 3 ailerons, I called one aileron split into 3 sections. I think we mean the same thing :ok:

At least on the A330/A340 there is a function which supports the rudder during "low speed" situations and high "rudder demand" by splitting the ailerons and deploying Spoiler No6.

That had occurred to me - there seems to be unnecessary drag being produced for any given roll demand. Proverse yaw? But surely the FBW will take care of any artificial stability requirements?

[PEOPLESX]

the video of the SQ A380 is pretty cool, looks like the wing is "alive" and every aileron does his own thing.
Maybe its a mixture of all functions.

[dream747]

Whatever the reason it was really interesting to observe. Really something new.

[OATNetjets]

I understand this was done on purpose in order not to excite the flexible modes of the wing, for comfort reasons. The surfaces are not deflected independantly, but follow a certain relationship.

[Machinbird]

Likely the aileron deflection is a form of bias to prevent aileron limit cycle oscillation (LCO).
By deflecting aileron segments on a wing oppositely there is no net roll input, but each aileron is pressed firmly against its actuator's rod end and thus cannot flutter.
The flight control system can set the appropriate bias as necessary for the current flight conditions, thus minimizing drag.
The A320 series, for example, apparently have a significant LCO induced maintence problem.

[stilton]

Amazing Aileron action.



Is the Aircraft really that quiet ?

[Volume]

Is the Aircraft really that quiet ? Yes it is. You can even hear babies crying at the other end of the airplane or on the other deck...

[Brian Abraham]

212man, if you still have my email address send a note and I can give you a Airbus PDF document which I think may explain all to your satisfaction.

[CabinMaster]

My guess: Droop aileron combined with roll command.
Did this kind of "differential aileron" ever happen in clean configuration?

[Brian Abraham]

I came across this old thread A380 outboard aileron segmenting [Archive] - PPRuNe Forums (http://www.pprune.org/archive/index.php/t-362242.html) wherein Spanner Turner posted

A380 TECHNICAL TRAINING MANUAL

PRIMARY F/CTL: FLY BY WIRE DESC. (3)
Auxiliary Functions (continued)
Load Alleviation Function

The aim of the Load Alleviation Function (LAF) is to alleviate the fatigue and static loads on the wings by reduction of the wing bending moment.

The LAF is composed of:
- the passive turbulence alleviation and,
- the active turbulence alleviation.

The passive turbulence alleviation alleviates the static loads in turbulence and during maneuvers. The activation is based on the vertical load factor given by normal law. The computed orders are sent to the ailerons and spoilers 6 to 8.

The pitch compensation linked to the deflections is sent to the inner elevators.

The active turbulence alleviation alleviates the fatigue and static loads.
The activation is based on the measurement of the vertical load factor on the wings given by the accelerometer units installed on the pylons. The computed orders are superimposed (added) to the computed orders of the passive turbulence alleviation. They are sent to the ailerons. Compensation orders are sent to the inner elevators.

The LAF is activated above a given speed and, vertical acceleration thresholds but are inhibited when slats and flaps are in full configuration.

I see also the PDF I mentioned earlier is available at IFAC-PapersOnLine: A380 roll kinematics design (IFAC-PapersOnLine: A380 roll kinematics design (http://www.ifac-papersonline.net/Detailed/38622.html))

[Volume]

Did this kind of "differential aileron" ever happen in clean configuration? It did. MSN 007 (The first one for Singapore) in December 2007 cruising over Australia, about 1 hour to destination (low fuel load).

http://i31.photobucket.com/albums/c370/NixusMinimax/IMG_6674.jpg

[jimjim1]

It's just playing air guitar.

More seriously I think the software designers put in the aileron wiggle for some kind of bet:)

[Trent 972]

There are 3 ailerons assisted by the 6 outer spoilers, for roll control, on each wing
The outer ailerons:
Are not deflected down above ​240 kt .
Are not deflected up above ​300 kt (except for the Load Alleviation Function).

The maximum aileron deflection is ​20 ° down and ​30 ° up.
Each aileron has two electrically-controlled actuators (conventional or EHA):
One actuator is active (it commands the position of the surface)
The other actuator is in damping mode (it follows the movement of the surface).

ELECTRICAL CONTROL
Only one flight control computer per aileron is active. The others are in stand-by.
When all systems are operative:
PRIM 1 controls the inboard ailerons
PRIM 2 controls the outboard ailerons
PRIM 3 controls the mid ailerons.
If a PRIM or a hydraulic system fails, another flight control computer and power source will take over, to ensure maximum aileron availability.
For example: for the outboard ailerons, if PRIM 2 or the green hydraulic system fails, PRIM 3 and the yellow hydraulic system will takeover.
The inboard ailerons remain available in backup control.

[212man]

I've just read the latest Airbus flight safety magazine - 'Safety First' - and I see that it has a fascinating article on just thsi topic, written in a very readable style:
(sorry about the formatting - the two column copy from a pdf didn't transfer well!)

The Lateral Flight Control Laws

On July 27th 2005, in Toulouse we had a strong wind from the south, called “vent d’Autan”, giving rise to a lot of turbulence. It was flight 51 of the f irst A380. We performed several landings and it became apparent that the lateral flight control laws would have to be tuned again: the pilots
were very active on the stick, the ailerons were moving a lot and created unpleasant lateral accelerations, mainly at the back of the aircraft. The flight
test engineers had several possibilities to adjust the control laws: gains, damping…, but none of them could solve the issue. This typical development
flaw had to be corrected, but it was not an easy task. Mid October, new PRIM
flight controls computers were delivered with a new control law for the ailerons that the engineers of the design office called “VDA” or “Valse Des Ailerons” (ailerons waltz). As an example, when moving the stick to the
left, on the left wing, the internal aileron started to move up immediately. The outer aileron was doing the same, but with a different deflection. Finally,
the centre aileron was either initially going down, in opposition to the two others, then taking an upward position, or going up after a very short delay in a neutral position. Several adjustments were available for the flight engineers, for example, the ratio between the deflection of inner and outer ailerons and the logic of the centre aileron. The target of this strange
kinematic was to “break” some wing oscillations as two of them had very close frequencies and, in certain circumstances, they had the possibility to couple together. Looking at the page dedicated to the flight controls
on the screen at the disposal of the crew, it was easy to understand
why this strange motion of the ailerons received this nickname of “VDA”. A similar differential deflection was also implemented on the two rudders
and was called “VDR” or “Valse Des Rudders” (rudders waltz), a typical Airbus “British – French” acronym, as rudder is not a French word! The
improvement on comfort was spectacular. However, some tuning was still needed. In January 2006, we installed a new standard of the computers,
with some improvements on the VDA laws. The main one was a reduction in the activity of the ailerons. The adjustments were again performed in flight. The final tuning is such that, for speeds below 300 kts, the deflection
of the inner aileron is 2.5 times the value of the outer one. The centre aileron follows the inner, but with a time delay of 350 milliseconds. Some more
modifications were needed at high altitude due to the Mach effect.
But we had another issue: the tuning of the spoilers. At the beginning,
they were deflected as soon as there was a command in roll and this created some buffet. Mid February 2006, new settings were proposed by the
design office in order to reduce these vibrations, with a limitation of the deflection to 3° as long as there was not a strong demand from the pilot. Without this trick, one of our British test pilots told us that he had the
impression of being “punished” by this buffet when entering a standard turn! On top, in the final tuning, when more manoeuvrability was needed, there was a higher deflection of the outer spoilers than of the inner ones, because they were creating less buffet. For all these flights where it was
important to get an idea on the comfort, a qualitative judgement at various locations in the plane was needed. In the cockpit, the pilots gave their impressions, both on the ease of flying and on the comfort in the forward
part of the aircraft. The flight test engineers, seating close to the centre of gravity, gave their sensations based on their feelings and the available traces. At the back, close to the most rear door of the main deck, we
installed a seat equipped with an intercom connected to the other crew members. A young flight test engineer was sat there, to give his opinion about his perception of comfort. Taking into account the number of roll manoeuvres we were performing on each flight, we had to hope that he would not become sick! It is true that a choice could have been made based on an analysis of the traces of several parameters of the motion at the
various positions in the plane, but we considered that the opinion of a potential “passenger” was fundamental in order to make the final decision. Obviously, all the records of these parameters were used by the design office to make progress in the tuning of the flight controls laws. It is to be noted that, at the beginning of the program, we were concerned by a possible
difference of comfort between the two decks. The f irst flights demonstrated that this was not an issue. At the opportunity of your next flight on an A380, if you travel in business or economy class, I recommend that you book a “window seat”, close to the wing or at the back of the plane in order to see how the ailerons are working (in first class you will not have this chance as you will be too far forward!). The effect is best observed just after take-off and during the early climb manoeuvres with the ailerons moving around their neutral position. You will see that when entering into a simple turn
or for a unique roll correction, taking as a base the inner aileron, the one closest to you, the outer aileron will move simultaneously but with a smaller deflection. Then with a small time delay, the centre will join the inner. If several corrections are made by the pilot, in one direction then in another, taking into account the different deflections and the time delay, you will see
the ailerons in totally different positions, up and down. The nickname “Valse Des Ailerons” is really well chosen and it is effective