B777 rudder trim
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B777 rudder trim
Hi All....
Feel a little embarrassed asking this question but the answer cannot be found in any of our company manuals.
My question is how does the B777 rudder trim work? Is it hydraulic or electric? Does it move the whole surface or just the tab? If you hit the "reset" button on the ramp without hydraulics powered, the indicator moves. Does anything actually move on the tail? Does the operation change as control laws change?
All our books tell us is how to turn the knob and push the button.
Feel a little embarrassed asking this question but the answer cannot be found in any of our company manuals.
My question is how does the B777 rudder trim work? Is it hydraulic or electric? Does it move the whole surface or just the tab? If you hit the "reset" button on the ramp without hydraulics powered, the indicator moves. Does anything actually move on the tail? Does the operation change as control laws change?
All our books tell us is how to turn the knob and push the button.
In direct mode the the manual rudder trim cancel switch is inoperative.
Below are extracts from the 777 Familiarisation manual
A rudder trim selector, on the aisle
stand, supplies trim signals to the
ACEs. The rudder trim actuator
moves the rudder pedals when
commanded by the ACEs. Two
rudder trim rates are available. A
rudder trim indicator, also on the
aisle stand, shows the rudder trim
position.
A manual trim cancel switch, on the
aisle stand, sends a signal to the
ACEs to command the trim to zero.
A switch on the P5 overhead panel
permits the pilots to disable the thrust
asymmetry compensation function.
A rudder tab hinges on the rudder.
The tab moves mechanically with the
rudder to increase its effect.
Below are extracts from the 777 Familiarisation manual
A rudder trim selector, on the aisle
stand, supplies trim signals to the
ACEs. The rudder trim actuator
moves the rudder pedals when
commanded by the ACEs. Two
rudder trim rates are available. A
rudder trim indicator, also on the
aisle stand, shows the rudder trim
position.
A manual trim cancel switch, on the
aisle stand, sends a signal to the
ACEs to command the trim to zero.
A switch on the P5 overhead panel
permits the pilots to disable the thrust
asymmetry compensation function.
A rudder tab hinges on the rudder.
The tab moves mechanically with the
rudder to increase its effect.
The rudder is electronically controlled and hydraulically actuated. No hydraulics, no movement.
The 'tab' is mechanically linked and increases contol effectiveness.
DC-10 had a similar rudder arrangement due to it being quite short, big engine in the fin.
The 'tab' is mechanically linked and increases contol effectiveness.
DC-10 had a similar rudder arrangement due to it being quite short, big engine in the fin.
One quirk of the system. When a trim input is made, the centre point of the nose wheel sterring is lso changed. The clue is that the ACEs move the rudder pedals. There is no need to centre the rudder trim before landing.
There is a requirement to centre the rudder trim during the cockpit setup.
If you ever taxi single engine there will be a large rudder rudder pedal input required. It is possible to trim this out, but beware it needs to be cancelled during the cockpit setup. The practice of trimming for a single engine taxi is NOT recommended.
There is a requirement to centre the rudder trim during the cockpit setup.
If you ever taxi single engine there will be a large rudder rudder pedal input required. It is possible to trim this out, but beware it needs to be cancelled during the cockpit setup. The practice of trimming for a single engine taxi is NOT recommended.
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The Rudder Trim Actuator is electrically powered and repositions the Feel and centering unit to a new 'null' position. It is located under the flightdeck floor and anchors the bus rods that tie both sets of rudder pedals together. When you input some trim from the switch in the flight deck the trim actuator either extends or retracts and repositions the feel and centering unit - this moves the Rudder through the normal controls system to a new neutral point.
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The rudder trim switch works through the ACE and PFCs to move the trim actuator. The actuator is an electric motor located under the cockpit floor and moves the rudder pedals through mechanical linkages. Trim is accomplished by this movement, which, just like manual rudder inputs, move the rudder pedal transducers, which in turn command the rudder PCUs through the ACE and PFC units.
The trim cancel switch sends its signal to both ACEs and PFCs which return the trim to center unless the asymmetric thrust input is active. The PFCs communicate with the AIMS cabinets, which in turn send signals to the trim indicator on the center pedestal.
Your observance of the trim indicator behavior on reset is due to the fact that the trim indicator position is based upon the trim actuator movement (via pedal linkages) and not the actual rudder position.
Rudder operation is electro-hydraulic. Electric signals control solenoids and valves in the rudder PCUs, which in turn route hydraulic pilot pressure to control valves that move the rudders. The rudder tab is linked directly to the lower rudder, and moves according to rudder position.
The trim cancel switch sends its signal to both ACEs and PFCs which return the trim to center unless the asymmetric thrust input is active. The PFCs communicate with the AIMS cabinets, which in turn send signals to the trim indicator on the center pedestal.
Your observance of the trim indicator behavior on reset is due to the fact that the trim indicator position is based upon the trim actuator movement (via pedal linkages) and not the actual rudder position.
Rudder operation is electro-hydraulic. Electric signals control solenoids and valves in the rudder PCUs, which in turn route hydraulic pilot pressure to control valves that move the rudders. The rudder tab is linked directly to the lower rudder, and moves according to rudder position.
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Thank you all for the most insightful and helpful replies. This has been most useful.
What started this question was that we once had a total flight control pitch and roll jam while attempting to perform the pre-take off flight control check. This got me thinking about what alternate means of controlling the airplane might be available.
In trolling around the internet, I found and nice but more detailed overview than in our manuals of the flight control architecture. I can't post the URL here because I am a new poster, but if you Google search "B777 ACES" it comes up.
What started this question was that we once had a total flight control pitch and roll jam while attempting to perform the pre-take off flight control check. This got me thinking about what alternate means of controlling the airplane might be available.
In trolling around the internet, I found and nice but more detailed overview than in our manuals of the flight control architecture. I can't post the URL here because I am a new poster, but if you Google search "B777 ACES" it comes up.
