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Why don't they have yaw dampers if they are always "suffering" from adverse yaw?

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    $\begingroup$ You mean aside from the extra cost, complexity, and maintenance required? Yaw damper systems are pretty complicated, a touch of rudder or rudder trim is pretty cheap and easy for a GA pilot to deal with. Small aircraft don't have much of a dutch roll tendency, and passenger ride isn't a concern, so the need for such a complicated and expensive system isn't there. $\endgroup$ – Ron Beyer Feb 29 '16 at 18:58
  • $\begingroup$ I think the fact that most GA aircraft are not swept wing is another factor. $\endgroup$ – J Walters Feb 29 '16 at 21:39
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    $\begingroup$ A yaw damper is mostly aimed to prevent Dutch roll on long fuselage aircraft. $\endgroup$ – mins Feb 29 '16 at 22:38
  • $\begingroup$ Because the pilot's leg muscles need exercising. $\endgroup$ – quiet flyer Aug 14 '19 at 14:25
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A yaw damper means added cost, weight, complexity, and one more system that has to be maintained. That's the downside. The upside, for most GA aircraft is that they relieve the pilot of having to make a "coordinated" turn. In other words, having to apply appropriate rudder input along with aileron input. Is that convenience worth the downside when the pilot has internalized doing that without having to think about it? That's a matter of opinion. For myself, a yaw damper in any of the, say, single engine Cessnas would be a waste.

There are some GA aircraft that could benefit from a yaw damper in other than banking into a turn or leveling from a turn. For example, in level flight the old V-tail Bonanza would yaw around the vertical axis in turbulence to an objectionable degree in my opinion. Very uncomfortable, especially to passengers in the back seat. It would have been great to have had a yaw damper.

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    $\begingroup$ Its worth noting that some GA aircraft do have a pseudo yaw-damper: An aileron/rudder interconnect that applies some rudder when the ailerons are deflected (usually a spring or bungee). I believe some models of the Beechcraft Bonanza have such an interconnect, though I'm not sure if it's on the V-tails. $\endgroup$ – voretaq7 Feb 29 '16 at 20:10
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    $\begingroup$ @voretaq7 The Erco Aircoupe was famous for its linked rudder and aileron controls. The linked controls were sold as a safety feature to prevent spins. $\endgroup$ – Wayne Conrad Jun 26 '16 at 0:27
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    $\begingroup$ @WayneConrad The Ercoupe is an extreme example, but an interesting one: As originally built it had no rudder pedals, and the interconnect between the rudder and the ailerons produced inherently coordinated turns. That plus its limited elevator travel makes it one of the few aircraft certificated as "characteristically incapable of spinning" (because you can't hold it in a stall long enough to develop into a spin). $\endgroup$ – voretaq7 Jun 26 '16 at 4:55
  • $\begingroup$ And some like the SR-22 have a full on yaw damper... $\endgroup$ – Dave Aug 14 '19 at 18:50
  • $\begingroup$ @voretaq7: Hope no Ercoupe pilot ever had to perform a crosswind landing... $\endgroup$ – Sean Sep 16 '19 at 3:26
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Adverse yaw is the yawing moment that occurs due to aileron deflection.

  • Yawing moment from aileron deflection: upon a left turn the right aileron deflects downwards and the left one upwards. The downwards deflecting aileron creates more drag friction, pulling the nose of the aeroplane to the right.
  • Yawing moment from roll velocity. The wing rolling up has a different Angle of Attack than the wing rolling down: the downwards going wing has the lift vector tilted forwards (like in a glider) and vice versa, which creates a yawing moment pulling the aeroplane nose to the right.

So adverse yaw pulls the nose into the opposite direction of where we want to turn, and the effect scales with wing span. One way to counteract this is to couple the rudder to the aileron, and give automatic nose left rudder deflection upon left aileron roll. Some of the Learjets and I'm sure some other aeroplanes have this, a way to automatically fly coordinated turns.

Yaw dampers on smaller planes do not coordinate turns but damp out Dutch rolling: the rudder deflects to counteract yaw velocity. Only airliners have yaw dampers that also coordinate turns.

The thing is that GA aircraft are mostly manually flown, control surfaces are manually deflected. For a yaw damper you need an actuator, so will need to install a powered rudder system. A major cost driver.

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  • $\begingroup$ "A yaw damper does not coordinate turns but damps out Dutch rolling": That may have been the original intention and the source of the name yaw damper, but every yaw damper system on a modern airliner is performing turn coordination. $\endgroup$ – Bianfable Aug 14 '19 at 14:08
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    $\begingroup$ @Bianfable noted and included. OP asks about GA aircraft though. $\endgroup$ – Koyovis Aug 14 '19 at 14:15
  • $\begingroup$ For what I know, the situation is rather the opposite. Larger airplanes (airliners) are typically underdampened in yaw and prone to dutch roll, esp. at higher speeds. They also have higher demands due to passenger comfort issues. So they require (or 'desire') a yaw damper per se. Turn coordination is a bonus. GA airplanes are typically well dampened naturally (except some, partricularly with V-tail) and have much smaller speed range, and for them turn coordination is the main driver. $\endgroup$ – Zeus Aug 15 '19 at 1:18

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