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Yaw Damper  
User currently offlineSKYSERVICE_330 From Canada, joined Sep 2000, 1467 posts, RR: 5
Posted (15 years 8 months 1 week 5 days 18 hours ago) and read 1625 times:

What exactly is the Yaw Damper on the autopilot and what does it do?

7 replies: All unread, jump to last
User currently offlineIainhol From , joined Dec 1969, posts, RR:
Reply 1, posted (15 years 8 months 1 week 5 days 17 hours ago) and read 1442 times:

My understanding is it stops the plane from doing dutch rolls.

User currently offlineB737 From Italy, joined Aug 2000, 41 posts, RR: 0
Reply 2, posted (15 years 8 months 1 week 5 days 17 hours ago) and read 1443 times:

Check out this website after you have run through it I
think you will know the working of an airplane like your Toaster.
Good luck

User currently offlineEWR757 From United States of America, joined Apr 2000, 360 posts, RR: 8
Reply 3, posted (15 years 8 months 1 week 5 days 2 hours ago) and read 1391 times:

It minimizes movement about the yaw axis of the aircraft which is more prevelant in swept wing aircraft.

It also will not prevent dutch roll, but helps a great deal.

User currently offlineCricri From France, joined Oct 1999, 581 posts, RR: 6
Reply 4, posted (15 years 8 months 2 days 3 hours ago) and read 1299 times:

Simply said, it helps passengers from the rear not to be sick!  

User currently offlineMinuteman From United States of America, joined Aug 2000, 271 posts, RR: 0
Reply 5, posted (15 years 7 months 3 weeks 4 days ago) and read 1264 times:

The lower rudder on the 747 is actually used to damp a structural oscillation...Without the rudder actively damping an approx. 1 Hz lateral "wag" of the fuselage, passengers would tend to get kinda sick at the back of the plane.

I'm told Boeing did this to gain some flutter margin for the 747's certification?

User currently offlineZartan From , joined Dec 1969, posts, RR:
Reply 6, posted (15 years 7 months 3 weeks 3 days 8 hours ago) and read 1245 times:

I'd love to hear more about this... Particularly in terms of how it affects turbulence, etc...

User currently offlineAaron atp From United States of America, joined Mar 2000, 533 posts, RR: 2
Reply 7, posted (15 years 7 months 3 weeks 2 days 20 hours ago) and read 1248 times:

A dutch roll is a yawing motion produced by an aircraft with greater lateral stability relative to directional stability.

If an aircraft makes an uncommanded bank in flight (turbulence), the aircraft will enter a small sideslip in the direction of the lower wing. If factors influencing lateral stability (dihedral) correct the bank before the factors resulting in directional stability (vertical fin size) correct the yaw, the aircraft will enter a sideslip in the opposite direction because the aircraft has yawed away from the direction of bank. The strength of the oscillation will usually decrease over time, but since it may occur over a long time span, it becomes very uncomfortable (it wouldn't have such an opportunity to stabilize in continuing turbulent conditions). The oscillations usually occur faster than the pilots reaction time, so pilot inputs will most often aggravate the motions causing "pilot induced oscillations." For these reasons, aircraft displaying properties of dutch roll must be fitted with yaw dampers (see below). Without yaw dampers, the quickest way for a pilot to stop the oscillations is to use full opposite control deflections, just long enough to stop the motions. [V-tail Bonanza owners make yearly sacrifices to their add-on yaw dampers because it improves handling and comfort 100%]

14 CFR 25 Airworthiness Standards: Transport Category Airplanes
Sec. 25.181 Dynamic stability.

(a) Any short period oscillation, not including combined lateral-directional oscillations, occurring between 1.2 VS and maximum allowable speed appropriate to the configuration of the airplane must be heavily damped with the primary controls--
(1) Free; and
(2) In a fixed position.
(b) Any combined lateral-directional oscillations ("Dutch roll") occurring between 1.2 VS and maximum allowable speed appropriate to the configuration of the airplane must be positively damped with controls free, and must be controllable with normal use of the primary controls without requiring exceptional pilot skill.

The yaw damper for older aircraft is a stand-alone unit with an accelerometer and servos, while newer a/c incorporate it into the basic control system.

Spiral Instability is the opposite of dutch roll; when directional stability is greater than lateral stability. After the wing drops, the aircraft yaws into the new relative wind before the wings level out. The accelerated movement of the higher wing produces more lift, increasing the angle of the bank and tightening the spiral. Since the spiral is easy to correct with intuitive control inputs, a/c are not required to have preventative measures installed (as is the case of the yaw damper for dutch rolls).


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