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Martinlest
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Yaw Damper: On or Off?

Sat Dec 03, 2022 5:52 pm

Hi - another little question which Mr. Google hasn't really managed to answer properly for me! Can anyone here kindly help?

What I understand in regard to the Yaw Damper is this:

1. In some aircraft, the pilots switch on the YD before takeoff and turn it off after landing. I have read that some modern a/c do not engage the YD, even though it is switched on on the OH panel, until a certain altitude is reached, and it is automatically turned off again on descent at a certain altitude, even though the YD switch is still in the 'on' position.
2. Otherwise, the YD is only engaged along with the Autopilot and disengaged by the pilots as the AP is turned off. This makes sense (to me!), as I imagine that having the YD active when hand flying the plane is hardly helpful!
3. In some planes (e.g. the Dash8) the YD acts as the third axis of the autopilot. Not sure how that works in practice but must mean the pilots don't have a lot of manual control over the rudder?

What would be most useful to know is, assuming statements 1 & 2 are broadly true, to which type of aircraft each case applies.... in which a/c types do pilots manually engage/disengage the YD at the same time as the AP, and in which is it turned on before TO and left on until taxiing to the gate?

Any info (not too 'techie' please!) appreciated.

Thanks, as ever.
 
GalaxyFlyer
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Re: Yaw Damper: On or Off?

Sat Dec 03, 2022 6:30 pm

On the jets I’ve flown, the YD is on all the time, unless selected off for a procedural reason—failure. It didn’t inhibit pilot inputs, it just responds to transient yaw such as turbulence or a slip or skid during banking and turns. Mostly invisible unless it’s inop and the design is susceptible to Dutch roll.

Loads of planes have them from a Cirrus to a 747, so lots of variations in application and use.
 
N1120A
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Re: Yaw Damper: On or Off?

Sat Dec 03, 2022 6:41 pm

In smaller airplanes, the yaw damper is off for taxi, takeoff and landing. Even in many business jets, you depart without it on, but put it on at V2 or whatever. Many autopilots will leave yaw damp on if you turn off the autopilot with the trim interrupt and only the red button will turn it off.
 
GalaxyFlyer
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Re: Yaw Damper: On or Off?

Sat Dec 03, 2022 7:44 pm

Been a long time, but the original Citation damper was like that—off until airborne, off for landing.
 
Flow2706
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Re: Yaw Damper: On or Off?

Sat Dec 03, 2022 10:50 pm

In most jet the yaw damper would be on whenever it is not failed. On the A320, the Yaw Damper function is integrated into/is a function of the Flight Augmentation Computer (FAC), therefore it is "always" on whenever it or the FAC is not failed. As both FACs are able to provide the yaw damping function, the yaw damping function will still be available through the other FAC in case of a single failure (one yaw damper/one FAC). The complete loss of yaw damper function (i.e. when both are failed) on the A320 results in the loss of both Autopilots and a degradation of the flight controls to alternate law. The Yaw Damper ist actually quite helpful in case of an engine failure as the yaw damper will provide an initial rudder input, which is not fully sufficient to counter the engine failure (further rudder input, either manually or through an engaged autopilot will still be necessary), but results in a stable flight path (in case of no pilot input during an engine failure after takeoff the airplane will slowly climb with a side slip, but it will not enter a dangerous attitude).
 
Martinlest
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Re: Yaw Damper: On or Off?

Sat Dec 03, 2022 11:14 pm

Thank you.

In smaller airplanes, the yaw damper is off for taxi, takeoff and landing. Even in many business jets, you depart without it on, but put it on at V2 or whatever


So as a rule of thumb (even if it is a generalisation), Boeings, Airbuses, Embraer jets and the like will have the YD on from (say) taxi out to taxi in. I would have to make a judgment as to what constitutes a 'smaller plane': I suppose, ATRs, Dash8, Emb110, Cessna Citation and so forth.
 
ArcticFlyer
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Re: Yaw Damper: On or Off?

Sun Dec 04, 2022 6:36 am

In my experience, jet airliners always fly with the YD on and failure in flight is considered a non-normal procedure. For smaller airplanes like business jets and turboprops YD use runs the gamut; some use it all the time, some have limitations and in others it is completely optional.

The Dash 8 was interesting - if our takeoff weight was below 31,750 lbs (I'm amazed I remember that years later) or if we were using flaps 15 (required for tailwinds over 10 kts) the YD had to be off for takeoff. This was due to the fact that the YD reduced rudder effectiveness to the point that, at such a low VR, VR would be less than VMC. With the YD off VMC was reduced several knots and this was no longer a problem. I will say from experience that the airplane was squirrely as heck with the YD off, particulaly in strong tailwinds, and that limitation was often "forgotten" by crews.
 
Martinlest
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Re: Yaw Damper: On or Off?

Sun Dec 04, 2022 3:15 pm

Right, thanks. I think I have had my question answered. Since this is obviously for flightsim use, I am tending towards a rough generalisation of when to have the YD engaged in any particular aircraft type, some of which of course have this feature better modelled than others (the Dash8 (payware addon) in X-Plane is a bit of a gem, in fact!).
 
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CarlosSi
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Re: Yaw Damper: On or Off?

Sun Dec 04, 2022 11:20 pm

Would it be on for a crosswind landing? Does yaw damper only dampen external yawing and not pilot induced?
 
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Starlionblue
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Re: Yaw Damper: On or Off?

Sun Dec 04, 2022 11:41 pm

CarlosSi wrote:
Would it be on for a crosswind landing? Does yaw damper only dampen external yawing and not pilot induced?


I can only speak for Airbus but we can't actually turn the yaw damper off as it is an integral part of the flight control system. Large swept wing jets tend to require a yaw damper on at all times due to the aerodynamic characteristics of the designs. We never touch the rudder except on the ground, on landing, and with an engine out.

Yes, it is on for a crosswind landing. Yaw damping dampens "external yawing", e.g. Dutch Roll, and also coordinates turns, that is inputs rudder in a turn so the tail doesn't "drag".

In a crosswind landing we purposefully uncoordinate the turn, so to speak. Hence why we need to add rudder input in order to straighten out the aircraft.
 
Martinlest
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 2:08 am

So as a rule of thumb (even if it is a generalisation), Boeings, Airbuses, Embraer jets and the like will have the YD on from (say) taxi out to taxi in


Yes, when I wrote that, I should not of course have included Airbus in the list :-)
 
Max Q
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 4:03 am

727 / MD80, 757 and 767 yaw dampers were always on and operation was automatic, no pilot action required


There were significant altitude and speed restrictions for the 727 with the failure of one of the two yaw dampers or dispatching with one inoperative


Without any yaw dampers at altitude the 727 would experience a severe Dutch roll that was not easy to suppress with control inputs


You had to carefully time your aileron movements to make very positive opposite inputs as these uncommanded rolls happened


If you didn’t do it properly it was easy to end up inverted, this was only practiced in the simulator



Best remedy was full speed brake (which helped to alleviate the problem) and an immediate descent to lower altitude where it wasn’t a significant issue


So glad to see no one call it a yaw ‘dampener’
 
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seat55a
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 4:18 am

For the usage in smaller jets refer to some well known YouTube channels. One of the pilots really struggles with 'dampener'. He obviously knows it's wrong but still says it about half the time. It's a checklist item.
 
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Starlionblue
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 4:36 am

Martinlest wrote:
So as a rule of thumb (even if it is a generalisation), Boeings, Airbuses, Embraer jets and the like will have the YD on from (say) taxi out to taxi in


Yes, when I wrote that, I should not of course have included Airbus in the list :-)


Why not? Airbus has definitely has yaw damping. It just isn't a discrete logic unit. However, the older A330s have a dedicated yaw damper servo, whilst the newer A330s and the A350 do not.

I doubt it is a discrete logic unit on modern Boeings either! :)
 
N1120A
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 4:49 am

seat55a wrote:
For the usage in smaller jets refer to some well known YouTube channels. One of the pilots really struggles with 'dampener'. He obviously knows it's wrong but still says it about half the time. It's a checklist item.


Steve definitely uses that term a lot. You can fly a TBM without putting on the yaw damper, which is off for takeoff and landing, but your right leg would be getting a major workout with 850 HP spinning the prop.
 
Max Q
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Re: Yaw Damper: On or Off?

Mon Dec 05, 2022 10:24 am

seat55a wrote:
For the usage in smaller jets refer to some well known YouTube channels. One of the pilots really struggles with 'dampener'. He obviously knows it's wrong but still says it about half the time. It's a checklist item.


Just another example of our language being mangled !
 
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tb727
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Re: Yaw Damper: On or Off?

Fri Dec 09, 2022 2:44 am

Max Q wrote:
727 / MD80, 757 and 767 yaw dampers were always on and operation was automatic, no pilot action required


There were significant altitude and speed restrictions for the 727 with the failure of one of the two yaw dampers or dispatching with one inoperative


Without any yaw dampers at altitude the 727 would experience a severe Dutch roll that was not easy to suppress with control inputs


You had to carefully time your aileron movements to make very positive opposite inputs as these uncommanded rolls happened


If you didn’t do it properly it was easy to end up inverted, this was only practiced in the simulator



Best remedy was full speed brake (which helped to alleviate the problem) and an immediate descent to lower altitude where it wasn’t a significant issue


So glad to see no one call it a yaw ‘dampener’


I almost broke the sim getting the plane to Dutch Roll for my sim partner once lol

Learjet 20/30 series it was off for takeoff and landing. It was hard to use the rudder pedals swiftly if it was on.
 
BoeingGuy
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Re: Yaw Damper: On or Off?

Mon Dec 12, 2022 3:02 am

Starlionblue wrote:
Martinlest wrote:
So as a rule of thumb (even if it is a generalisation), Boeings, Airbuses, Embraer jets and the like will have the YD on from (say) taxi out to taxi in


Yes, when I wrote that, I should not of course have included Airbus in the list :-)


Why not? Airbus has definitely has yaw damping. It just isn't a discrete logic unit. However, the older A330s have a dedicated yaw damper servo, whilst the newer A330s and the A350 do not.

I doubt it is a discrete logic unit on modern Boeings either! :)


The 737 Max has a Yaw Damper/Stabilizer Module. It is a discrete unit on the 767, IIRC. Yaw Damping functionality is part of the Primary Flight Computers on the 777 and 787.
 
Unclekoru
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Re: Yaw Damper: On or Off?

Sat Dec 17, 2022 1:00 am

ArcticFlyer wrote:
In my experience, jet airliners always fly with the YD on and failure in flight is considered a non-normal procedure. For smaller airplanes like business jets and turboprops YD use runs the gamut; some use it all the time, some have limitations and in others it is completely optional.

The Dash 8 was interesting - if our takeoff weight was below 31,750 lbs (I'm amazed I remember that years later) or if we were using flaps 15 (required for tailwinds over 10 kts) the YD had to be off for takeoff. This was due to the fact that the YD reduced rudder effectiveness to the point that, at such a low VR, VR would be less than VMC. With the YD off VMC was reduced several knots and this was no longer a problem. I will say from experience that the airplane was squirrely as heck with the YD off, particulaly in strong tailwinds, and that limitation was often "forgotten" by crews.


Was that on the Dash 8-100? I don't remember that limitation from my time on the Q300.
 
ArcticFlyer
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Re: Yaw Damper: On or Off?

Sat Dec 17, 2022 3:14 am

Unclekoru wrote:
Was that on the Dash 8-100? I don't remember that limitation from my time on the Q300.

Yes that was on the -100 which is the only variant I have experience on.
 
Unclekoru
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Re: Yaw Damper: On or Off?

Sat Dec 17, 2022 8:49 pm

ArcticFlyer wrote:
Unclekoru wrote:
Was that on the Dash 8-100? I don't remember that limitation from my time on the Q300.

Yes that was on the -100 which is the only variant I have experience on.


The -100 always looked like it'd be a great aircraft to fly.

And yes, I remember the Q300 being unpleasant to fly without the yaw damper, very "squirrely". Also meant we didn't have an autopilot available.
 
ArcticFlyer
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Re: Yaw Damper: On or Off?

Sun Dec 18, 2022 1:27 am

Unclekoru wrote:
The -100 always looked like it'd be a great aircraft to fly.

It was the most fun I've ever had in a "big" airplane. Flew like a giant 182.

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