C17 Steering Question
12-16-2010, 12:25 PM
#1
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Joined APC: Dec 2009
Position: 127.0.0.1
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C17 Steering Question
This is guy is turning left to take the active, but the rudder shows right. You might not be able to see it, but the nose wheel is in a left turn.
Thanks for any insight. For all I know, he could have been straightening out from left to right on centerline.
Thanks for any insight. For all I know, he could have been straightening out from left to right on centerline.
12-16-2010, 01:17 PM
#3
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Joined APC: Dec 2007
Position: ATL717A
Posts: 890
That would be my guess too. On my Douglas jet, I can, and do, use full rudder authority regardless of the positioning of the tiller whenever I do a flight control check.
12-16-2010, 04:44 PM
#10
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Joined APC: Dec 2007
Position: ATL717A
Posts: 890
Here. Now we both can sleep. I can't believe this actually bothered me enough to research it.
The C17 nose wheel steering is controlled by both the rudder pedals and the steering tillers. Full rudder pedal movement permits a maximum of twelve degrees of nosewheel steering either side and the tiller provides about 70 degrees either side. If the steering tiller and rudder pedal commands are in disagreement the rudder command will be overidden.
On takeoff the tiller is not used and the rudder movement and nosewheel steering work in the correct sense. That is until you lose an engine and abort, when it will automatically give you the opposite rudder for yaw compensation.
The rudder is split into two, and with the full electronic flight control system on, as it should be for taxi both the top and bottom rudders should operate essentially as one. In the backup emergency mode only the lower half will be powered and move. A failed rudder will float.
The movement you saw is due to the fly by wire computer systems stability augmentation rather than anything mechanical. When the flaps are up the system is in normal mode for both taxi and flight after takeoff. Therefore, it may be giving yaw dampening correcions during taxi. This is normally performed by the lower rudder only, so if that is the one that moved then we have solved it. The aircraft will use both rudders for stability augmentation at high AOA and lower rudder saturation situations.
The C17 nose wheel steering is controlled by both the rudder pedals and the steering tillers. Full rudder pedal movement permits a maximum of twelve degrees of nosewheel steering either side and the tiller provides about 70 degrees either side. If the steering tiller and rudder pedal commands are in disagreement the rudder command will be overidden.
On takeoff the tiller is not used and the rudder movement and nosewheel steering work in the correct sense. That is until you lose an engine and abort, when it will automatically give you the opposite rudder for yaw compensation.
The rudder is split into two, and with the full electronic flight control system on, as it should be for taxi both the top and bottom rudders should operate essentially as one. In the backup emergency mode only the lower half will be powered and move. A failed rudder will float.
The movement you saw is due to the fly by wire computer systems stability augmentation rather than anything mechanical. When the flaps are up the system is in normal mode for both taxi and flight after takeoff. Therefore, it may be giving yaw dampening correcions during taxi. This is normally performed by the lower rudder only, so if that is the one that moved then we have solved it. The aircraft will use both rudders for stability augmentation at high AOA and lower rudder saturation situations.
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