GulfstreamGuy From United States of America, joined Jul 1999, 647 posts, RR: 1 Posted (11 years 4 months 4 weeks ago) and read 32767 times:
Saturday, our NW flt 5807 (CRJ) LIT-DTW was canceled because a "yaw damper would not engage", thus the plane had to be ferried to MEM for maintenance. I am a little fuzzy on the understanding of what it exactly does.
B747skipper From , joined Dec 1969, posts, RR:
Reply 1, posted (11 years 4 months 3 weeks 6 days 23 hours ago) and read 32767 times:
Yaw damper is a gyro system which acts on the rudder(s), this for aircraft stability.
Have you ever heard about Dutch roll ??? (nothing against our friends from NL !)
Some (swept wing) airplanes are unstable on the yaw axis.
This because if they yaw to the left, the RH (swept) wing will present itself as a straight wing.
Straight wings create more lift, and more drag...
More lift = that RH wing will go up - More drag = RH wing is pulled aft (around yaw axis)...
Result, now, the RH wing being further aft, the LH wing will do that game...
LH wing will get more lift, more drag... result is the aircraft will yaw L and R.
Result could be a loss of control = Dutch roll.
So the yaw damper prevents Dutch roll.
Generally, the yaw damper is the "3rd axis" of the autopilot.
Modern airplanes generally have a full time "series" yaw damper, engaged at all times.
Some airplanes being unstable, their yaw damper is a "NO GO item" on the MEL.
Some other airplanes may be limited in speed and altitude if yaw damper is INOP.
The 747s have 2 yaw dampers... But the airplane flies perfectly without them. Not a NO GO item for 747s.
Hope this helps you...
Airplay From , joined Dec 1969, posts, RR:
Reply 3, posted (11 years 4 months 3 weeks 6 days 19 hours ago) and read 32767 times:
The yaw damper system isn't exclusively based on "gyro" systems. It also receives yaw acceleration information, often from an internal liquid base yaw acceleration sensor.
The yaw damper offsets the rudder in proportion to the roll angle. It also "kicks" the rudder pedal in response to yaw acceleration to provide a smooth flight and offset the effects of dutch roll as mentioned.
In some aircraft, typically the smaller ones, the yaw damper is required equipment. If it is unservicable, the aircraft may be subject to operating restrictions in speed and/or altitude. This is primarily due to the descision to use a smaller (low drag) vertical stabilizer that just isn't efficient at high altitudes without some help from the yaw damper. Of course the 747 could never be accused of having a small tail....
According to the CRJ MMEL, only the -700 and -900 variants require an operational (1 out of 2) yaw damper for dispatch. The 100/200 doesn't.
AC_A340 From Canada, joined Sep 1999, 2251 posts, RR: 1
Reply 4, posted (11 years 3 months 2 weeks 9 hours ago) and read 32767 times:
Though the CRJ may not require operational yaw dampners, some airlines do opt to include it in the MEL. I have heard that the CRJ is really hard to fly without this system. I know for sure that one of the systems needs to be operational in order to engage the autopilot. The Citation 10 has 3 of the systems because the aircraft is so susceptible to Dutch Roll.