Simviation Forums

after many post asking about the real function of this,wich I have many many technical asnwers wich seems like they where tooken from a book of aeronautic,i found out that seems in a few words is that when i activate Yaw D. it block the tail rudder to let use only the front wheel on the ground,AM I wrong?

Yaw Damper is to counteract 'Dutch Roll'.  It limits the movement of the rudder when you manually try to turn it.

An example of Dutch Roll is the JAL Flight #123 which a 747 rear pressure bulkhead failed due to improper repair following a hard landing recently before flight #123.
The pressure released from the cabin blew off the rudder, in this case all the hyd lines were cut (later hyd fuses were installed for updates) and they had no control except the engines.  
The aircraft did a dutch roll (more like banking to the left and to the right slowly in harmoney while the aircraft is veering to the left and right at the same time)

As like this:

This oscillatory motion consists mainly of a combination of roll and yaw - supposedly resembling the staggering behaviour of a Dutch sailor, hence the name. The effects are quite unpleasant for the aircraft's occupants so is not tolerated in the majority of aircraft designs. This usually results in a trade-off with the spiral divergence behaviour discussed above, particularly regarding the wing dihedral angle of the design. Typically, the motion has a period of 5 seconds or so. It tends to be more of a problem for swept-wing aircraft than straight-wing aircraft.

for the first time i understand what that damm buttom realy does thanks Midnight_LS1 its an emergency buttom as you said that limit the movement so wont be a mess in case of emergency,but not the front wheel,roll and yaw movements due when activate yaw damper,instead free rudder wich would produce a spin and crash in case of specific failiures(hidraulic),with the pilot skills to control the plane by some sort of banking by using the limited rudder(yaw damper),also I see why the standard procedures of when taking off,saids to set it on,thats one of the most risk moment of a flight,i got the idea,once again thanks pal

Hi Alrot
You are still not quite there. A yaw damper, as Midnight says is to limit Dutch Roll as indicated in his diagram. In most aircraft it is an automatic action, no pilot input is required, or he would be pumping the rudder pedals from lift off to landing to counteract this problem. A large aircraft, for example a 737, 747 does not naturally fly straight, but will have this very gentle roll motion. As the aircraft starts to Dutch Roll, the rudder is automatically deflected in the opposite direction to counteract this roll motion. It is a very small deflection, a couple of degrees only.
It is not in an emergency a button to limit the rudder movement. In an emergency, you may want all deflection that you can have. I think that you are also confusing a yaw damper with a rudder travel limiter. So here it is condensed.

Yaw damper.....automatic deflection of the rudder by a couple of degrees in the opposite direction of the Dutch Roll.

Rudder travel limiter..... Limits the amount of rudder deflection in connection with the aircrafts speed, that is, low speed allows a larger rudder movement. At high speed limits the movement, so that the pilot cannot give full deflection above a speed decided by the aircraft designer. Thus preventing stress on the aircraft and loss of control.

As for your button, if the system is not functioning correctly, the crew have the option to turn it off.
Hope this helps a little.
Matt

ALROT,

Start up FS and load the aircraft that has the yaw damper option.  Then go to spot view and zoom in on the rudder, enough to notice an difference from a locked rudder.

Now move to full left and right with the yaw damper off, see you can obtain full left and right movement.

Turn the yaw damper on and go back to spot view, notice it doesn't allow you to full left or right movement? it's only limited to little left or right until the system is turned off.

We do seem to have a little confussion between a yaw damper and a rudder travel limiter in this thread!

Matt