View Full Version : B747 Yaw Damper

YHZ Pilot
22nd Feb 2008, 15:03
Hi Everyone,

I just want to confirm the type of yaw damper on the 747 (paralle or series). I know that newer aircraft usually have series type yaw dampers.

Thanks for the help!

YHZ Pilot

Chris Scott
22nd Feb 2008, 16:26
Quote from ASFKAP:
Don't most modern A/C have parallel type YDs, ie the pedals don't move when the yaw damper actuator actuates the rudder.......
Or is my memory failing me?

I fear it is the latter...:{ ; I know the feeling!

To illustrate the point, will have to resort to 707s, I'm afraid. In the 1970s and early '80s, my company operated a medium-sized fleet of B707-320Cs. All bar one of them were 'Advanced' versions, with a single SERIES-type yaw damper on the rudder [The VC10 had 3 - one per rudder!].

As you meant to say, series yaw damper-generated rudder movements do not feed back to the rudder pedals; parallel ones do.

One of our 707s, however, had an old-fashioned PARALLEL-type yaw-damper. I was once unfortunate enough to position as passenger LGW-NBO, and it rolled gently from side to side all the way...

Never did the 747, sorry to say. But as they dated from 1969 (?), early ones MIGHT have had parallel dampers.

22nd Feb 2008, 20:57
Older airplanes - PARALLEL Y/D (Letter P is first on the alphabet) -
Newer airplanes - SERIES Y/D (Letter S later than letter P in alphabet) -
747s all have 2 SERIES Y/D, and had them since day one..
A 747 flies perfectly well with both Y/D failed... NO RESTRICTIONS.
Older Boeings -
The old 707s had PARALLEL Y/D. The switch on the pedestal had 3 positions, which were OFF, Y/D and A/P. Takeoff and landing was flown without Y/D engaged. Flying the 707 without Y/D engaged was a guarantee to have airsick passengers in the tail... Later 707s got one SERIES Y/D... I threw my old 707 manuals away, sorry, cannot recall more details.
For the 727, both 100/200s, all have SERIES Y/D, 2 of them. In case of Y/D failure, 727 is very unstable plane. Altitude limitations (cannot recall) are some FL 270 with failed Y/D.
Happy contrails

Chris Scott
22nd Feb 2008, 22:10
Quote from Buenos Aires:
I threw my old 707 manuals away, sorry, cannot recall more details.

Tsk, Tsk! := [Mine are somewhere in the garage...] Your memory is in line with mine, though. The 707 Dutch-rolled at the drop of a hat on the approach, as you say, if the Y/D was switched off. But not seriously.

The VC10, if all 3 Y/Ds switched off, was still fine on the approach. But at high altitude it could be quite vicious. One of the items on the conversion was to allow it to build up to about 40 degrees of bank from side-to-side, and then recover manually... [In case anyone wonders, manual recovery is by aileron.]

YHZ Pilot
23rd Feb 2008, 00:08
Thanks BelArgUSA!