Why the A380 wiggles rudder so much on landing

[bomarc]

I offer this theory, regarding the amazing amount of rudder movement during photographed landings of the A380...I do hope an A380 pilot will weigh in.

AGAIN, ONLY A THEORY:

I don't think it is anything to do with crosswinds. I think when the throttles are idled the engines don't come down at the same rate...perhaps the angle of the pilots hand not quite pulling throttles back.

anyway, the throttles and engines not coming back at the same instant (whether mechanical, electronic, or by hand) the plane wanders due to the assymetric thrust...then the pilot has to do a dance on the rudder pedals to keep the nose straight.

no proof, just a guess...I've seen pilots in other planes not retard engines/throttles and have to use rudder subconsciously to keep her going straight.

[Intruder]

More likely it's an artifact of the fly-by-wire implementation. Maybe the yaw damper has to work hard to keep the airplane from moving.

Watch videos of an F-18 or F-16 in flight, and you'll see a LOT of control surface movement, even though the pilot is not moving the stick at all.

[bomarc]

intruder:

but isn't the rudder the only non fly by wire control on the airbus? not sure on the A380, but on the 320 that seems to be the case

[Rainboe]

Bomarc- I don't think you are a pilot. Your theory is totally wrong. Large aeroplanes like this are very stable. If the thrust levers don't retard thrust evenly from a medium approach level to idle and cause the aeroplane to yaw like you suggest, then this baby is going to be grounded a long time! It doesn't happen like that!

I've watched 2 You Tube videos of the arrival- I see nothing unusual- nice stable approach, smooth landing. What's wrong with it?

[bomarc]

rainboe, I am a pilot. (and yes, rainboe is toxic...couldn't stand seeing the bottles/cylinders in the cockpit. hated it when some jerkoff used rainboe on a dry windshield.)

granted i am not an A380 pilot. are you?

but I have seen pilots fly jet transports and sometimes they don't move the throttles at the same time (as one)...I see them subconsciously correct with rudder.

Indeed, assymetric use of thrust has been used on many occasions...myself included during X winds. also in rudder hardover emergenices (simulator only of course)...the dc10 at sioux city too.

certainly, if you haven't seen this, perhaps you are not a pilot? but I think you are a pilot. have you ever seen this?



let us not get into a shouting match about who is or isn't a pilot...not unless you have a certain and sure way of proving such. and if you do, please do so.

proving someone is or isn't a pilot is beyond the capability of this forum.

try keeping a p&w jt8d 15 intermixed with jt8d 17 in perfect matched thrust on landing...

and the CVR circuit breaker on a DC9 is at Delta 5. And you can break the circuit breakers by letting loose on your shoulder harness too fast and having it snap back hitting the panel.

there are lots of things you can fake by using a book...but I don't know anyone who has published that.

[jfill]

:confused: The KLAX arrival looked like near full left rudder at touchdown and some very big excursions of a very big rudder. The KJFK landing was very smooth.

Nothing but great respect (and envy) for the pilots but all in fun it did kind of remind me of my first solo landing 35 years ago. I told my instructor I didn't know who pushed the rudder pedal!:)

[Rainboe]

OK- take it back- there are a lot of people who pretend here, and they like getting involved way out of their depth.
The BIG fan engines are fairly slow responding. In the flare, they are not giving much thrust. Even on a 747, you don't have to worry about lining the thrust levers up- it's not at all critical, and you never feel yaw due to thrust asymmetry, particularly during the flare and landing. This aeroplane is fairly stubby, hence the outrageously large fin. I would guess it needs slightly more apparent rudder due to the moment arm of the rudder in relation to the mass and size of the aeroplane. But minor differences in thrust level will be completely undetectable, just as they are on the 747.

[bomarc]

ok rainboe, I accept your "take it back".

the A380 is a new plane and needs some getting used to by pilots. I don't know which video I saw on TV, but I saw quite a bit of rudder movement and that the nosewheel was not quite on the stripe.

certainly there is a learning curve involved...getting the sight picture and all that.

who knows, maybe the rudder is so tall it is in a different wind world than the wing?

I remind all pilots, that if you takeoff, switch on the autopilot for 8 hours and then approach and turn off the autopilot at 500'...you perhaps have 6 minutes of flying time, while logging 8 hours+.

If I recall, the rudder is the only NON fly by wire thing on the plane...let me know if I am wrong.

[Huck]

Search Youtube for the LAX landing - looks like the #2 reverser was late in coming out. And they were deployed before the nose was all the way down (may be restricted to idle until NW touches - some planes do that).

There is one view from a helicopter that is quite scary - imagine the sideloads felt in the cockpit:

LAX landing. (http://www.latimes.com/news/local/la-me-airbus20mar20,0,7798733.story?coll=la-home-local)

[Intruder]

bomarc:

I don't know the A380's flight control system. However, if the rudder control system is anything like the 747-400's, the autopilot controls the rudder when coupled to the ILS. Also, the yaw damper acts as a turn coordinator as well at low speeds, so it may respond to stick inputs as well.
I haven't seen any close-ups of the A380 on approach, so I can't do any more than take a reasonable guess.


rainboe:

The 747-400 has automatic N1 synchronization, so there is no need to line up the thrust levers, as long as they're within a half knob of each other.

The 747 Classic is a whole 'nother story, though! You can get significant yaw if the N1s are not matched! If the thrust levers are not rigged correctly, there can be several inches between them when N1s match.

[wobble2plank]

Also take a look at the plan area of the tail fin, it's huge! As Rainboe has already said it's a stubby beast with a massive fin, add in a x-wind and you're going to need a pretty hefty rudder swing to counter act the sideways wind forces from the fin.

I was behind the beasty into LHR last year and watched the video later, that was a blustery day when we were all stirring to controls a bit and the landing look perfectly normal to me.

The rudder in the 320 is the only control that is directly linked to the cockpit (cables), however in normal flight laws it is still actuated by the flight control computers it only reverts to manual if there is a serious fly by wire failure.

[Conan The Barber]

Speculation? DC9? Déjà Vu?

Change and stay the same. No?

[Rainboe]

but I saw quite a bit of rudder movement and that the nosewheel was not quite on the stripe.

If I get the darn thing within 5 yards of the stripe without breaking anything, I'm pleased!

I've been watching several of these videos, and I have to say I can't see much wrong. If you see a telephoto shot taken mostly fore/aft, any rudder movement will look quite exaggerated. There is slightly more rapid rudder movement than I would expect- I would be very surprised if this was a pilot technique. I think there may be a bit of excess yaw damper movement at low speed- this would be corrected during development flying. I would remind you the 777 was known to have similar problems that needed software correction to stop people feeling sick during flight.

[bomarc]

conan speculation on deja/vu...right of course, but consider this:

conan speculation on deja/vu...right of course, but consider this:

conan speculation on deja/vu...right of course, but consider this:

an airbus with rapid rudder movements in the vicinity of JFK...do we wonder about the A300 repeating itself on a massive scale?

hmmmmmm

[Conan The Barber]

an airbus with rapid rudder movements in the vicinity of JFK...do we wonder about the A300 repeating itself on a massive scale?No we don't. Obviously you do.

Unfounded speculation should be kept for CNN. Jon.

[forget]

It doesn't seem too bothered with this cross wind landing -

http://www.youtube.com/watch?v=d8DW7fVIiB8&mode=related&search=

[bomarc]

don't know what you are talking about...I watch Fox

[Conan The Barber]

Of course you do, Jon.

Leopard, spots, too obvious.

[fireflybob]

Maybe the pilot was "pedalling" the rudders a bit, something we all have a tendency to do from time to time! Question is though if you pedal the rudders does this set up an oscillation which the yaw damper takes a while to damp out?

By the way, when I talk about pedalling the rudders I dont mean putting huge bootfuls in and then rapidly reversing same but small inputs. Maybe good pilots (like test pilots hehe!) are better at detecting and correcting small amounts of yaw?

[ARINC]

Having seen a few of these land at Finkenwerder To my eye the LAX touchdown looked like the right gear touched first and maybe failed to castor enough. causing the departure to the right. In any event It was definately not a standard touchdown.

[Rainboe]

Look Bomarc, this is getting farcical!
an airbus with rapid rudder movements in the vicinity of JFK...do we wonder about the A300 repeating itself on a massive scale?
The problem there was not the Airbus, it was the person applying vastly excessive bootfuls of rudder to the extent the structure broke. The Airbus fin has never been any more of a problem, in fact less, than 737 rudder hardovers! And aren't we all still concerned about that little problem?

The chief problem of the A380 is NIH (Not Invented Here). It's a great aeroplane, and it's going to sell well, because it has the capacity, so let's stop nitpicking and admire it for what it is- the next step up. Boeing's baby, the 787, will sell well, but it's a medium capacity machine only. Let's not denigrate this fine piece of engineering with petty finger pointing Any minor faults will be cleared up just as the 747s were- maybe you don't remember, but that was a total disaster to begin with. The BOAC ones were not used for the first 18 months because of a pilot ban on them for industrial reasons. It gave BOAC the chance to make a fortune lending the engines to other operators who all had 747s grounded due to Pratt & Whitney JT9 engines failing all over the world. Can we remember DC10s grounded all over the world because of dangerous LE flap design? So the rudder waggles more than you would like? So it was flared 'sharply'? So it had crab on touchdown? I do sometimes! Yes....but isn't it great?

[XPMorten]

The A380 has huge longitudal stability due to the fuselage design.
Probaby more than the 747.
This requires a big rudder/big deflections.

Anyone got a link to the LAX landing?

EDIT: http://www.youtube.com/watch?v=ho8pMRHf0HQ

M

[chornedsnorkack]

If I get the darn thing within 5 yards of the stripe without breaking anything, I'm pleased!

How many inches wiggleroom does a 747 have in Rand airport?

A380, with a few feet wider main landing gear, probably should not operate from Rand...

[KATLPAX]

http://www.youtube.com/watch?v=8fZK_mPM6tw

If you do a search on youtube, a few videos show the landing at LAX from a high vantage point. The touchdown seems does have a bit of a crab and slide, and the need for a large rudder input to keep her pointing true. Does not seem unusual for such a large aircraft. The video link above shows it in slow motion which is interesting...(excuse the title of the video please, not my doing)

[Rainboe]

That's it? That's what all this rabbit has been about? Utter nonsense these theories of thrust mismatch- it was touchdown! They were all at idle. The large rudder displacement to the left was quite correctly applied to counter a pronounced yaw to the right after touchdown. It corrected for it, the fin did not fall off, it was not a rudder hardover, the engines did not get excessively close to the ground, and the wing did not excessively bend. I don't know what caused the yaw, really quite minor- maybe a gust, maybe vortex from the preceding 747. It does not mean the program will fail!

[KATLPAX]

Not a big deal, agreed... a question was asked about the observed landing at LAX..and a few theories proposed...and finally the actual video which should put much of this to bed...I hardly think it amounts to a criticism at all, let alone a prediction/desire of a program failure for the A380...

[Intruder]

The rudder appeared to be neutral when the nose moved right. It is possible a brake grabbed, or the pilot's foot slipped on the brake pedal. The left rudder correction was of a speed and magnitude to suggest manual input.

[vapilot2004]

Landed 24R, which is about 250 degrees magnetic. Winds at the time of touchdown were light. (5 kts WNW)

To my eye the LAX touchdown looked like the right gear touched first and maybe failed to castor enough. causing the departure to the right. In any event It was definately not a standard touchdown.

Had it been a passenger flight, those folks in the back would have surely felt that swinging about. Must have been fun up in the pointy end as well.
Big bird safely on the ground nonetheless.

Now that the meet and greet is complete, LAX only needs to complete improvements for the super jumbo. :rolleyes:

[EGBM]

Is it just me or is there an overt fascination on pPrune from some quarters in wanting the A380 to fail, and fail catastrophically? Even comparing it with the tragic events of the A300 over New York, fer chrissakes!

Ask yourselves how many hours in development and test this aircraft has done, and will do, before entry into service and take a look at the history of other new types before fleet introduction. Honestly.:bored:

I thought this site was more than the aviation equivalent of a tabloid newspaper website where arguments and discussions are reduced to the level of what manufacturer's badge is stuck on the side. Ridiculous.

Come on people, get a grip! :ugh:

[Rainboe]

Well said! I can't believe the level of comment here. A 'firm' landing seems to mean 'the program has severe problems'. We've had critical comment of engine ground clearance, the wing bending on touchdown (incidently, the graphic of the 787 in the latest Flight Intnl really shows a marked degree of wing bending), rudder waggling, yaw on touchdown. All I want to know is 'what was the electrical problem?', and how, having built something like the A340-600, was this allowed to impact the program to that degree.
Large wing bending is a factor in these new high-aspect ratio wings. I've noticed it in diagrams of the new 787, 380 and A350, and 747-800, where the wingtips will easily be able to say hello to each other in normal 1g flight. I think it will incite a lot of passenger comment when these things are common!

[EGBM]

I believe the wiring issue was something to do with a disparity in the versions of wiring design toolsets the teams in France and Germany were using - I'm sure someone will know better, I'm only going off (at least) second hand information. I'm sure the issue is well understood in Airbus and has been or is being dealt with - I'm also confident they'll know why it caused such a delay to the programme but I don't personally and I'm not in a position to speculate.

No doubt it'll all come out in the wash.