Hey Everyone,

I'm hoping someone can clarify as to why the 777 and 74 both have a split rudder but not the 330 or 340's?

Furthermore with regards to the split rudder, what sort of authority does the lower rudder have over the upper half. Does the yaw damper in the cruise control the lower section of the spit rudder to preserve tail life?

The 777 doesn't have a split rudder.

747: Because it can?

I guess having four hydraulic systems allows the 747/744 to control each rudder with different pairs of hydraulic systems (redundancy). The upper and lower rudders move in unison, however (under normal circumstances).

The 744 Rudder Ratio System reduces the movement of both rudders at higher speeds (by the same amount) for a given manual pedal input. The Yaw Damper System (acting independently) would factor in airspeed and things like the number of IRUs and ADCs available.

Rgds
NSEU

Because Boeing wanted it that way and Airbus didn't.

The 727 also has upper and lower rudders. Both the 727 and 747 have yaw dampers on both. On the 727 the lower rudder has more throw when the flaps are not up. On the 747 the rudder ratio control varys the throw of both rudders as the speed changs.

Ok I can see where my mistake went with the 777. Thanks, you saved my ar$e there.


Photos: Boeing 777-206/ER Aircraft Pictures | Airliners.net (http://www.airliners.net/photo/KLM---Royal/Boeing-777-206-ER/0742885/&sid=e3a902466a2220fbdfaa49845771a946)


Excuse if the question sounds a bit pathetic, but would the 74's lower and upper rudder sizes have something to do with the moment arm?

Size!

747s and A380s have split rudders anything smaller is single. (Unless it's simply archaic)

"... hoping ... clarify as to why ... 74 ... a split rudder ...?"

TBC design history may reflect their lessons from "discrepant rudder" fatal mishaps.

B307 Stratoliner had a fatal upset on 18Mar39 (single Rudder).

B707 had two fatal discrepant rudder upsets (Single Rudder). [Crew trainer 19Oct59 B707 N7071, & AA Flt One / 1Mar62.] Much later: WAL366, a B720, at ONT of 31Mar71, failed Rudder Control System (fractured Support Fitting for the Rudder Hydraulic Actuator; due to high tensile loading and stress-corrosion cracking). The "artificial feel" mechanism (included in the rudder control system) masked this failure from the crew during their yaw/roll upset.

Recall that Bill Cook invented Boeing's "Yaw Damper" for the XB-47 project (see _Road to the 707_, pg181+).

TBC seemed to forget lessons learnt from the XB-47 project, the initial B707 lacked both Rudder boost and the (artificial S&C) Yaw-SAS. As always, the new engineered-safety-feature (Yaw Damper) introduced new failure-modes: that fatal rudder-Y/D-softover aboard AA Flt One 1Mar62.

So, after early S&C mistakes on the B707 model, the B727 was introduced (FF=9Feb63) with an Upper and Lower Rudder, and a separated "Yaw Damper" for each Rudder [B727-100 was undamped and divergent above FL260 without that artificial S&C addition].

B747 FF = 9Feb69, and B747 had two Rudders:
http://www.pprune.org/tech-log/392015-yaw-damper-747-400-a.html [some mishaps cited and some history on split-rudder].
Woooo!!--> There's a whole TV show on B747 discrepant Rudder:
http://www.youtube.com/watch?v=KiSFe7sMcL8&feature=player_embedded

Later, around 1982 during testing on the B767, even the short body B767-200 was much less prone to "dutch roll" at very high altitudes (a surprise test condition at FL450 convinced me that B767 had much better "natural" damping and B767 was a big improvement over B727's "undamped & divergent").

DC-10 and MD-11 have split rudder and the Vickers VC-10 has three rudders.

*"... would the 74's lower and upper rudder sizes have something to do with the moment arm?"

Looks like the 'SP has double-hinged Rudders (like the 727) Upper and Lower.
http://www.747sp.com/images/D45Ykukuexeqfotr.jpg
Re' the Moment Arm (Tail Volume) & Fin-Rudder SIZE:
B747SP - - Vertical tail Area = 885.5 Sq Ft
B747-200 - Vertical tail Area = 830 Sq Ft

In the TV-show discussing NW85 B747 discrepant Rudder
flygc.info – Northwest Flight 85 – Boeing 747/400 Rudder Jam « flygc Air Crash Investigation (http://flygc-aircrashinvestigation.com/2012/02/23/flygc-info-northwest-flight-85-boeing-747400-rudder-jam/)
the narrator mentions an Air France B747 Rudder mishap, that happened years later (maybe 2006 or 2007??):

?? -- Anyone have a lead on that case, location, date, investigating authority??
[I didn't see anything about it on BEA's website.]