Re: Yaw Damping was: An-124 and wing dihedral

Date:         26 Jun 98 02:37:36 
From: (Ron Parsons)
References:   1 2 3
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In article <airliners.1998.942@ohare.Chicago.COM>, Chuck
<> wrote:

>Jim Wolper wrote:
>> Pete Mellor wrote:
>> > [...] Dutch roll is
>> > a vice of any delta-winged aircraft. Presumably, automatic
>> > yaw-damping was achieved in pre-FBW days by a simple
>> > analogue system (possibly part of the autopilot)?
>> >
>> > I'm guessing. Does anyone have any definite information?
>> Yaw damping can be achieved using analogue output
>> feedback and is usually included as part of an autopilot
>> installation.  It is useful in straight-wing aircraft as well,
>> especially those that fly at higher altitudes where the thin
>> air may reduce the effectiveness of the vertical tail in
>> damping yaw.
>I would add to Jim's comment that while yaw damp is concidered part of
>the autopilot system it works independantly of the autopilot.  The A/P
>does not have to be engaged for yaw damp to work.
>Also when the Y/D system moves the rudder there is no feedback to the
>rudder pedals in the cockpit.

I suspect the top writer meant to say that Dutch roll was part of a
swept-winged aircraft rather than delta.

The 727-100 had a divergent Dutch roll that could quickly get out of hand
and therefor had two yaw dampers. On the other hand, the longer geometry
of the 727-200 reduced the Dutch roll to a simple annoyance.

Back in the dark ages of the early '60s, the KC-135's with the old manual
rudder had a pretty strong Dutch roll and since each of the three axis of
the autopilot could be engaged separately, the rudder axis was used solo
as a yaw damper while hand flying. With the conversion to the powered
rudder, the KC-135 Dutch roll dropped to a small fraction of what it had
been before. None the less, crews were still required once a quarter to
complete a celestial navigation leg above 40,000 ft. with all autopilot
off. Biggest challenge in that was for the Boomer to not fall off the
stool trying to get his shot.