Why the A380 wiggles rudder so much on landing
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Why the A380 wiggles rudder so much on landing
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.
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.
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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.
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.
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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?
I've watched 2 You Tube videos of the arrival- I see nothing unusual- nice stable approach, smooth landing. What's wrong with it?
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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.
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.
Last edited by bomarc; 19th Mar 2007 at 23:43. Reason: spelling of "TO vs. TOO"
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Are We All Talking About the Same Thing?
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!
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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.
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.
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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.
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.
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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.
There is one view from a helicopter that is quite scary - imagine the sideloads felt in the cockpit:
LAX landing.
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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.
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.
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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.
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.
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but I saw quite a bit of rudder movement and that the nosewheel was not quite on the stripe.
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.
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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 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
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Originally Posted by bomarc
an airbus with rapid rudder movements in the vicinity of JFK...do we wonder about the A300 repeating itself on a massive scale?
Unfounded speculation should be kept for CNN. Jon.
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It doesn't seem too bothered with this cross wind landing -
http://www.youtube.com/watch?v=d8DW7...elated&search=
http://www.youtube.com/watch?v=d8DW7...elated&search=
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?
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?
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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.