Re: Ground handling

Date:         22 Feb 99 03:30:43 
From:         "John Weiss" <jrweiss@seanet*NOSPAM*.com>
Organization: Seanet Online Services, Seattle WA
References:   1
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Bill Urban wrote in message ...
>I have some questions about ground handling of large a/c.
>I know that the nosewheel tiller, the rudder, and the brakes may all be
>used to control direction on the ground at various speeds.  But I still
>wonder about some of the particulars:
>* Does the nosewheel caster, so that the tiller returns to center when
>released?  Does it lock on center so you don't have to worry about the
>tiller being off-center when you land?

(All answers based on 747-400)

Nosewheel does not caster.  Nosewheel steering is always active on the
ground (using a strut extension sensor), controlled by the rudder pedals and
overridden by the tiller when used.  It doesn't "lock" on center, but the
rudder is essentially centered when rolling down the runway.  The tiller is
not used on takeoff roll.

>* On rollout, what combination of rudder and asymmetric braking is used
>to steer, and when does nosewheel steering take over?

Rudder pedals are used, which control rudder and nosewheel steering.  Rudder
is effective down to 80 knots or so.  Tiller is not used on the landing roll
until at taxi speed (<10 knots, normally).  Asymmetric braking is not
normally used.

>* Finally, what is the physical arrangement that (I think) lets you use
>the same pedals to control the rudder and the two sides' brakes? It seems
>at least that the sense is correct on this user interface, i.e. left
>rudder pedal -> left turn and asymmetric left brake -> left turn as well.

When the bottom of either rudder pedal is pressed, the rudder and nosewheel
steering are moved toward that side.  The pedal is hinged at the bottom so
that brakes are applied on one side of the airplane when the top of the
rudder pedal on that side is pressed.
John R. Weiss
Seattle, WA
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