C-17 flight controls/nose wheel steering

[jettison valve]

Good morning everybody,

watching C-17s recently, it seemed as if steering the nose wheel to the left/right falls together with rudder movement right/left (yep, this orientation: NWS left, rudder right for instance).

Coincidence? Yaw damper influence? Or a mechnical connection between tiller/pedals/etc...?

Cheers,
J.V.

[eng1170]

Yeh probably mech. connection, on the 737's I work with the rudder pedals control whats known as rudder/fine steering, and when the pedals are moved at low taxi speed it gives I think 7 deg's of nosewheel steering as well as rudder movement (don't quote me on that figure!) for more than that the tiller is moved to give up to 78 deg's left and right nosewheel steering.

Don't know about C-17 but given it is also a Boeing product there's a good chance the system is similar.

Damn nice machine the C-17!!! Would give an arm and a leg to fly/work on those.

Eng ;)

[HectorusRex]

From memory Eng 1170's description of Boeing nose wheel steering systems is correct.
If I read Jettison Valve's statement correctly, then he is suggesting that the rudder and nose wheel movements are opposite, which would be most unlikely:confused:

[Man-on-the-fence]

To throw a fly in the ointment. Wasn't the C-17 designed by McDonnell Douglas? So comparisons to a Boeing design by default are somewhat wide of the mark.

Unless Boeing redesigned it of course.

[smack]

Actually JV is correct, the lower half of the rudder only does move and it is in opposition to the direction you would expect if it was simply a mech link to the NWS. Yaw damping is the most likely explanation imho.

[SirPeterHardingsLovechild]

Maybe the Captain had forgotten to de-select the 'Supersonic Config' switch.

I'll get my coat...

[SALAD DODGER]

I think smack has the right idea.

Sorry some rather dry facts!

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 Take-Off the tiller is not used and I can assure you that the rudder movement and nosewheel steering work in the correct sense. That is until you loose 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 (most of the time!). In the backup emergency mode only the lower half will be powered and move. a failed rudder will float.

I think 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 poor thing is trying to keep you in ballance even during taxi!

The aircraft will use both rudders for stability augmentation at high AOA and lower rudder saturation situations. But I cant see it doing this on the ground. So if both moved I am stumped!

However those McDonnell Douglas and Boeing guys have built one clever jet, it might have just been bored and decided to start playing with us.

:zzz: