A340 question for those who fly them

[rumpletumbler]

I was on an A340 and during taxi, etc, the ailerons were fully deflected. During the takeoff roll ditto. I'm watching and wondering if we are going to do an unannounced roll on departure. I dismiss this idea as we are loaded for about an 8 hour flight and say goodbye to my wife, etc. The instant the aircraft started to rotate however they "snapped" into a neutral position. While being gratefull that they did I was still curious as to the why of it all and if it was computer or pilot controlled. By the way and the speed at which they moved I would guess computer.

RT

 

[Vik]

I've flown 3-4 times on a Virgin Atlantic A340 in the past 2 yrs and I've never seen that.

Very strange.

Maybe it was for a strong crosswind? Thats how we deal with it in the bugsmashers I fly anyway. Not sure about heavys.

 

[EagleRJ]

Like most large aircraft, it probably has servo tabs on the ailerons. The aileron itself is actually unpowered, and floats freely up and down. The tab on the trailing edge of the aileron is moved hydraulically when the pilot makes a roll input, which "flies" the aileron up or down and rolls the airplane. The plane was probably parked with a quartering tailwind, which forced the aileron up or down. As it started the takeoff roll, the slipstream caused the aileron to neutralize and fair with the wing. Some large aircraft use a combination of inboard and outboard ailerons, and spoilers for roll control, and the surfaces that are active may change depending on if the plane is in low speed or high speed flight.

 

[rumpletumbler]

But it didn't move from full deflection until rotation.

RT

 

[profile]

Not sure of the A-340 systems, perhaps it has deflected ailerons for additional lift on takeoff. That would be my guess, as some other types do have that feature.

As to what Eagle said, no, most large aircraft do NOT have servo tabs. Some of the smaller transport jets, B-727, etc, have that as a backup if hydraulics fail, and some others in that class have servo tabs with no hydraulics at all, but the larger widebodies are totally hydraulic (no backup to hydraulic control), and in the case of the A-340, the hydraulic actuators are controlled by digital FBW inputs. The A-380 will have a somewhat unique system of electric hydraulic controlled servos for backup, but most just have more hydraulic systems instead of a different system.

 

[Homer J simpson]

Hi

as a 330 driver I would like to give my 2 cents worth,
the 330 has NO trimdevices on the wing, all trimming is done
in the computer.
when no hydraulics present both ailerons are hanging down.
during taxi both sidesticks have to be checked for proper function.
full up/down and full left right. there is one full deflection.

also the ailerons droop when flaps are selected also done by the comp, pilots have no influence in this.

Question, did you also see the other aileron position?

also, airbus advises not to put in any aileron for T/O as done on many other aircraft.
the reason, sidestick deflection demand roll rate. which in plain terms means.if you have a small deflection of the stick, the aircraft will keep on rolling with the rate of roll which equals the stick deflection. to the max roll limit.

there is an advantage to this , but not for the TO roll, but for Xwind landings. in de landing when you put in rudder to decrab the wings stay level, no need to roll bank.

as to the ailerons snapping back to neutral, i have no answer to that. the only thing I can think of is that the computers went into another phase.
ie. there are multiple phases, in which the flightcontrol laws change in priorities.

I have never paid attention to the wing when sitting in the back.

if you have more questions let me know.

Homer...........mmmmmmmmm........donuts

 

[rumpletumbler]

No I didn't see the other wing.

RT

 

[Homer J simpson]

reason i asked is
if the were both down, it would be as part of the flap selection.

if the were opposite of each other the only thing I can come up with is input from the flightdeck.

I searched in the books and I could not find anything about it.

There is a small posibility that it only applies to the 340, I am only familiar with the 330

H.

 

[bigsky]

It has been awhile but in Feb I was also on a turkish airline a340 out of Istanbul. dont remember the particulars but on T.O. roll I too was thinking"What the Fxxx" as ailerons were doing things I had never seen.. that and after t.o. I have never seen a wing flex so much!

 

[Homer J simpson]

hello again,

on the subject of wingbending,
the FBW also has MLA=maneuver load alleviation.
the ailerons+ some spoilers will counter the bending moment

this can t be the answer for your question, because it works anly above 250kts and flaps at 0

H.

 

[checkessential]

On the ground the FBW computers will allow a linear deflection of the ailerons and elevators according to the pilot input. Assuming the pilots used a crosswind correction technique to keep the wings level, this would explain the deflection on the takeoff roll. Once the aircraft became airborne, the FBW system goes into C* or the airbus equivalent of normal law. This is why the ailerons "snapped" back to a more correct deflection for the commanded roll rate, which was significantly less than the linear sidestick deflection vs. aileron position. In addition, the sidestick input was probably decreased by the pilot as the airspeed increased, and near zero at rotation. As is the technique on any other plain-jane aircraft.

 

[Tref]

What's the difference between a new Airbus pilot and an old Airbus pilot?

A new Airbus pilot says "what's it doing now?" And an old Airbus pilot says "oh $hit! It's doing that again!"

 

[rumpletumbler]

checkessential,

If you will read my original post you will see that they didn't move from full deflection until the point of rotation, I further clarifed this during yet another post when someone else had missed it. After saying this twice I didn't think I needed to disclaim it but let me go ahead. Excuse me this is making me so sleepy. The ailerons were at full deflection from taxi through takeoff until the point of rotation. At the point of rotation they snapped into a neutral position. There was no gradual decrease, there was nothing gradual about it. Does snapped sound gradual to you?

PS: Just in case anyone has missed the above point that has now been stated on 3 different occasions I'd just like to clarify once again the ailerons were at full deflection from taxi through takeoff until the point of rotation. At the point of rotation they snapped into a neutral position.

PSS: The ailerons were at full deflection from taxi through takeoff until the point of rotation. At the point of rotation they snapped into a neutral position.

If your reading this post and haven't bothered to read the others I'd like to say the ailerons were at full deflection from taxi through takeoff until the point of rotation. At the point of rotation they snapped into a neutral position.

Please take a break before you respond to this post. Then re-read it 100 times. Then re-read all the other posts in the thread. Then write the following on a piece of paper:

The ailerons were at full deflection from taxi through takeoff until the point of rotation. At the point of rotation they snapped into a neutral position.

Thanks.

Now, you may respond to the post.

Yet another disclaimer follows. Someone will be smart enough to go back and say that they saw that I didn't see the other aileron and see that I'm using ailerons in my sentences and will point that out. "Holding up a fish for you and making a barking seal noise" the reason I say this since the one on my side was deflected up I would assume the other to be deflected down as this would indicate to me that it wasn't being used as a lift device.

RT

 

[Vik]

Hey RT,

Don't get your panties in a bunch. You seem to be getting way to excited over a small issue.

 

[rumpletumbler]

Vik,

I don't wear panties. I'm not excited, however, I do get irritated with having to state the same thing over and over and over because what was there already wasn't read. Speaking of accuracy in assesing a situation be it a post, an emergency, determing the gender of a poster, etc. What was it that made you think I wore panties? I mean Vik could be short for Victoria or Vikie or maybe Victor ,however, I don't even after looking at your profile have a clue as to your gender. Perhaps you meant that I might be a man or woman wearing panties. Remember for the purpose of accuracy I can't relate to or understand what your saying unless I have actually worn panties and they have gotten in a wad while I was wearing them. Of course the chances of this happening would be far greater if I were female which I am not. What does all this mean? It means the same thing that the post you are commenting on means. Accuracy and being informed is important in replying to a post. Now don't think I'm sitting here stoneface serious typing this cause I am.

RT

 

[checkessential]

What is the problem? Are you sure that it was the ailerons you were looking at? Were the roll spoilers deployed? Could you see both wings? Please excuse my inattention to particular detail which you yourself forgot to include. I didn't realize this was so serious......

 

[rumpletumbler]

At 08-01-2002 09:19 I posted the following in this thread:

No I didn't see the other wing.

At 08-02-2002 13:15 I posted the following in this thread:

Someone will be smart enough to go back and say that they saw that I didn't see the other aileron.

This what I mean by having to repeat things. I'm not trying to offend you and am not angry etc. It would be my preference though that someone actually read a thread before responding to it. It isn't that serious. Remember it can be hard to know someones frame of mind from reading e-mail, posts, etc. Especially with me. I should be more carefull.

As for them being ailerons if they were spoilers they were the largest spoilers I've ever seen by a big stretch. It was a large control surface and in the same position you would expect it to be for an aileron.

RT

 

[checkessential]

You pose a good question. Most likely the ailerons were acting in tandem to provide a load alleviation function, or the aileron computers calculate a minimum drag position for the takeoff based on CG and weight. I don't really know jack about the a340, so I'll look for the answer too....

 

[Vik]

RT,

I dont take this message board that seriously. It was a joke. You just seemed to be on the verge of having a stroke so I figured a little humor might be in order.

 

[bigD]

rt - I'm just trying to get a sense of what happened here...so the ailerons gradually moved back into a neautral position as the plane was taking the runway, right? And you said you saw the aileron on the other wing deflected the other way too? I'd guess the PF just had some correction in for the taxi. What exactly is the problem, and why are you so worked up?





And yes, I'm laughing as I write this!