Lower Rudder question

[Guest henkb]

Hi -took a while before I found out it's actually called the "lower rudder", but that's a whole different story ;-)I was wondering what the added functionality of such a lower rudder is. Is it always moving or is it kicking in at certain speeds e.g.Does it operate independently from the main rudder.Anyhow, with the 747 coming up, perhaps there's a 747 jocky (real or sim) who can shed some light on this.I found plenty sites which talk about the lower rudder and almost all of them were sites about aircraft crashes, so I guess the lower rudder is somewhat important......thanks & have a great 2005!HenkNetherlands

[Qavion 19]

Henk....The Upper and Lower Rudder on the 747 operate together at all speeds (assuming the applicable hydraulic systems are powered.... The Upper Rudder uses Sys 1&3 and the Lower Rudder uses 2&4 systems on the 747-400).However, there is a Rudder Ratio system which varies the deflection of both rudders, automatically/electronically, depending on speed. At low speeds, the rudders move a maximum of 31~32 degrees from centre. At high speeds, 4~5 degrees.Hope this helps?Cheers.Ian.P.S. Aircraft like 737's and 767's only have one rudder, but, like the 747, several hydraulic actuators.