Yaw Damper

[Jakemaster]

Another one of these "I should know but I dont".  What exactly does yaw damper do?  In the PMDG Manual for my beloved Beech, it says to activate yaw damper at 500 ft then leave it on until final.

[commoner]

Hi Jake...well I suppose you could say in simple terms that it helps to steady the ship............have a look at this for a more detailed explanation.It's on the 727...commoner  ;)

 http://www.boeing-727.com/Data/systems/infoyawdampers.html

[Nexus]

Yaq dampers have two major functions

1) To prevent dutch rolls
2) coordinate turns

A yaw damper is a actually a gyro-system which is extremely sensitive to changes in yaw, and then feeds a signal into the rudder which applies opposite rudder to counter the yaw before the roll occurs and thereby prevents dutch rolls.

Older yaw damper systems actually moved the rudder pedals (this is called "parallell operation), but this is not the case in todays airliners

[Jakemaster]

Okay, one question: What's Dutch Roll?  IM really a newbie at the more complex "airliners", since ive just started flying the 1900.

Thanks

[Saitek]

If you use it the plane will fly straight and won't get wiggled.

[Midnight_LS1]

[quote]Okay, one question: What's Dutch Roll?

[Nexus]

The cause of dutch rolls are the aircraft's swept wing. The roll occurs when yaw is induced either by natural disturbance or commanded (or uncommanded) yaw input.

This causes the outer wing to travel faster and to become more "straight on" to the relative airflow (decreasing the sweep angle, but increasing aspect ratio) Both of those phenomenas will create greater lift - ON THE OUTER WING

However, at the same time, the inner wing will travel more slowly (remember the aircraft is yawing) and in effect the sweep angle will increase, which reduces the lift of the wing.

This will cause a marked bank up to the point when the outer upward going wing stalls and loses all lift: therefore the wing drops, causing a yaw to the stalled wing...thus leading to the sequence being repeated in the opposite direction. This sequence will continue and produce the oscillatory instability around the longitudinal axis...known as the Dutch roll  8)

Dutch Rolls are worse at high altitudes and at low speeds, btw  :)

[Jakemaster]

If its cause of a swept wing why do I care? The 1900 has a straight wing.

[Nexus]

If its cause of a swept wing why do I care? The 1900 has a straight wing.

Because the B1900's yaw damper has the ability to cancel out the adverse yaw created by an engine that is about to go bonkers?

Also, as you can note here (http://www.airliners.net/open.file/0989171/M/ ), the Beech1900 has indeed a small swept back angle, and that is enough to start the oscillations  :)

[beaky]

If its cause of a swept wing why do I care? The 1900 has a straight wing.

Because it's not due to sweep; a perfectly straight wing will produce adverse yaw. More/less airspeed equals more/less lift; more/less lift equals more/less drag. One wing swings forward because the rudder's not holding the plane straight in straight flight or a banked turn, it's now going faster as the other wing moves back and thus slows down; the faster wing produces more lift than the other; lift always produces induced drag;drag slows up the advancing wing;  advancing wing now slows down to a greater extent than the wing moving back; plane starts to go the other way(or that wing drops; depends).
The other source of induced yaw is ailerons. Most airplanes have ailerons that are deflected into the airflow over a wing more when they are down than when they are up. They create a lot of  drag (not induced drag; think "hand-out-the-car-window" drag), so if you're banking left, that left aileron's producing less drag than the "outside" aileron, so the "outside" wing slows up, sometimes to the point where the plane "heads" the wrong way and a slip develops.
Bottom line about yaw dampers is that they do what the pilot ordinarily does: compensate, with rudder inputs, for the fact that most planes are designed "wrong". That's it.
It's been pointed out that a properly designed airplane will need no rudder, or even a vertical stabilizer...  many very successful designs do fine without either.

[Hussein Patwa]

Hi just my two pence worth.

From the B744 flight manual:
The yaw dampers are engaged whilst still on the ground, before taxi and during engine startup and pre-flight configuration.  As said above, they help to steady the aircraft during turns, and prevent the passengers from hurling during flight.

Cheers.

[expat]

If its cause of a swept wing why do I care? The 1900 has a straight wing.

With the amount of strakes on the B1900 it is a wonder that it requires a yaw damper. It would appear to have a third wing transplanted all over it

Matt