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Rudder question

Old 14th Oct 2012, 02:07
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Rudder question

I have observed on many occasions that on idle aircraft the rudder moves about.Sometimes it's the wind but at other times there is no wind and no pilot in the front so why and how does the rudder move on it's own.Also I have notized that the 777 or A380 flap their rudder alot more than a 767 or E-195.The E-Jets never seem move their rudder when idle.The A320 and 737 does it alot,wonder why some jets do it more than others.
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Old 14th Oct 2012, 05:27
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Rudder authority has mostly to do with the compensation of an engine out scenario, given the amount of thrust lost on one side of the aircraft and it's ability to fly straight on one engine.
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Old 15th Oct 2012, 00:31
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Anne do you mean that the aircraft is idle ie parked nothing running or the engines idling?
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Old 15th Oct 2012, 01:36
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It is difficult to say as I'm always behind glass or fences so always have restricted view.But I would say,in most cases,the engines are idling.
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Old 15th Oct 2012, 04:03
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[quote]Sometimes it's the wind but at other times there is no wind and no pilot in the front so why and how does the rudder move on it's own.
It is difficult to say as I'm always behind glass or fences so always have restricted view.But I would say,in most cases,the engines are idling.
So the pilots must be inside if the engines are idling...and hydr pump will be ON,so the rudder wont be moving by its own..

Last edited by de facto; 15th Oct 2012 at 04:07.
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Old 15th Oct 2012, 10:16
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Like I said,it is difficult to see and I'm no expert,that is why I'm asking here
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Old 15th Oct 2012, 11:02
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anne - a lot of people do not realise that the engines sometimes appear to be 'idling' but it is just the wind turning the blades.

Regarding the rudder, depending on the way a (powered) rudder assembly is controlled, there is normally a 'hydraulic lock' inside the rudder actuator so that the rudder control cannot move even when hydraulic pump pressure is removed. Some a/c may not have this in their design OR the 'lock' may dissipate with time through seepage of fluid .
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Old 15th Oct 2012, 16:36
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That makes sense,thanks BOAC.I have seen tails with dirty black markings near the rudder which indicates some sort of seepage.
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Old 16th Oct 2012, 01:00
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Anne many flight controls will flop around randomly in a breeze with no hydraulics on. Being in a 737 cockpit for example can be a hazard when windy as the controls can move rapidly without warning. On windy days we often leave a pump(s) powered for crew safety. Once hyd power is on the control wont normally move without pilot input.
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Old 16th Oct 2012, 02:11
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717 & BAe146 had the rudder "dampened" when there was no hydraulic power to the aircraft. In other words, when the wind/breeze blew on the rudder, the rudder was free to apparently flap in the breeze, and damage was avoided by the dampening action of the hydraulic fluid moving the actuators, as opposed to the actuators moving the rudder under a powered situation.
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Old 11th Sep 2015, 03:26
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Apologies for digging up an old thread, but I have a question regarding the rudder on the A380 and, upon searching, this was the closest thread topic.

A day or two ago I was bussed from a remote stand at Dubai past more A380s than you could shake a stick at, and noticed that when parked, they all have one part of the split rudder in the same offset position - is this a default position for safety or something to do with the hydraulics?

As a supplementary question, how many gazillion dollars worth of Emirates aircraft are on the ground at DXB on any given morning??
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