Yaw dampers make flying more comfortable for passengers and easier for pilots. Here’s how they work…
Accelerometers Detect Yaw Rate
You can think of a yaw damper as an automated pair of feet on the rudder pedals. “The yaw damper is a servo that moves the rudder in response to inputs from a gyroscope or accelerometer that detects yaw rate” (FAA AFH 12-7). Pilots flying airplanes equipped with yaw dampers can often enter and exit turns with their feet flat on the floor, while the slid/skid ball remains centered.
A series of accelerometers or rate sensors (gyros) in the tail constantly communicate yaw trends with the rudder servo system to provide adequate damping information. The rudder is smoothly adjusted in either direction to maintain smooth, coordinated flight.
Simply put, when the yaw damper is on, you keep your feet off the rudder pedals. The yaw servo motor does all the work, keeping you in coordinated flight.
On Swept-Wing Jets, Yaw Dampers Counter Dutch Roll
Dutch roll is a series of out-of-phase turns, when the aircraft rolls in one direction and yaws in the other. In a typical swept-wing aircraft, yaw stability isn’t as strong as the roll stability caused by the sweepback. While the tail’s still trying to line up the nose, the aircraft has over-banked to the left, causing a left sideslip. Now the sweepback starts to raise the left wing, rolling your 737 right. The drag from the left wing starts to pull the nose to the left.
Most modern swept-wing aircraft have yaw dampers that automatically correct for Dutch roll by quickly adjusting the rudder. If your yaw damper’s inoperative, stopping the roll can be more tricky. Many modern swept-wing jets will fly themselves out of Dutch roll if you stop adding control inputs. However, some of the older jets, like the 727, can be difficult to recover.
Automatic Yaw Dampers
In some new piston aircraft equipped with autopilots, like the Cirrus SR22, the yaw damper turns on automatically at 200 feet above the ground during climb, and is disengaged at 200 feet above the ground before landing.
The system operates whether or not the autopilot is engaged, however, you can disengage the yaw damper at any time by pressing down and holding the autopilot disconnect button.
Restrictions On Yaw Damper Use
While the yaw damper can be engaged separately of the autopilot, in most airplanes the yaw damper is prohibited from being engaged during takeoff or landing. In strong crosswind situations, you may find yourself fighting the yaw damper as you try to make corrections. If it’s not disengaged automatically, many pilots have mistakenly landed with the yaw damper on. Generally speaking, it’s not going to cause an accident by itself and you’ll usually notice the mistake by the feeling on the rudder pedals before you touch down.
Remember the “dead foot, dead engine” concept for engine failures? In multi-engine airplanes, if one engine were to fail, the yaw damper might try to automatically correct for a sudden yawing motion. This can make it hard to quickly identify which engine has failed.
What Do You Think?
Have you flown aircraft with a yaw damper? How do you use the system? Tell us in the comments below.
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