A yaw damper is a system fitted to inhibit movement around the aircraft's vertical axis, damping the repetitive rolling and yawing motion pilots call Dutch roll. Acting as an automated pair of feet, it senses yaw rate through gyros or accelerometers and moves the rudder in direct opposition to unwanted yaw, providing automatic rudder displacement proportional to the disturbance. By smoothing out all the aircraft's gyrations, the device increases the damping of the Dutch roll and thus establishes smoother, coordinated turns. During asymmetric thrust like an engine failure, the same mechanism can assist the pilot by detecting the yaw toward the failed engine and correcting for it, preventing the airplane from yawing out of control.
What is a yaw damper on an aircraft?
A yaw damper is a system that reduces undesirable tendencies of an aircraft to oscillate in a repetitive rolling and yawing motion. The yaw damper system consists of accelerometers and sensors that monitor the aircraft rate of yaw. Yaw dampers quickly adjust the rudder to automatically correct for Dutch roll.
A yaw damper is an autopilot for yaw. It is an automated pair of feet on the rudder pedals: a gyroscope detects yaw rate, accelerometers measure lateral acceleration in the tail, and these sensors are electronically connected to a flight computer that processes their signals and automatically controls actuators connected to the rudder. The servo then moves the rudder in response to those inputs, opposing the aircraft's tendency to oscillate.
What is the function of a yaw damper in an aircraft?
The purpose of yaw damper is to make an aircraft easier to fly by smoothing out aircraft gyrations and reducing pilot workload. It detects yaw rate and provides automatic rudder displacement proportional to the yaw experienced, quickly adjusting the rudder to counteract unintended motion. Using yaw rate sensors, accelerometers and gyroscopes, the device sends inputs to a flight computer that computes the required yaw order. The computer then drives three independent hydraulic servo-jacks to move the rudder appropriately.
Which airplane behavior is corrected by a yaw damper?
The airplane behavior corrected by a yaw damper is the Dutch roll. Yaw dampers automatically correct for Dutch roll, the left-right fishtailing of the vertical stabilizer that appears whenever sideslip disturbs the aircraft. Because Dutch roll couples roll with yaw, attempts to restore wings-level by aileron alone make things worse. The drag from the descending wing pulls the nose farther sideways, increasing roll-yaw coupling and prolonging the motion. Instead, sensors nudge the rudder to cancel sideslip before it grows, so the airplane corrects itself without pilot pedal inputs. On large jets, yaw damper employed from takeoff onward therefore guards against sudden yawing motions and adverse yaw from power or configuration changes, keeping the fin centered and the flight path steady.
What is a yaw damper issue on a plane?
A yaw damper issue is the failure or inoperation of the small, automatic rudder that keeps the tail from fishtailing. When the accelerometers or rate sensors in the tail detect the first hint of Dutch roll, they normally communicate yaw trends with the rudder servo system. If that link is lost, the airplane enters a grossly uncoordinated condition and the wing motion induces a series of oscillating overcorrections that take nearly a minute to die out. Because the servo has only limited authority - 1/4 to 1/3 of the available rudder travel - its absence is felt immediately. Without yaw damper the pilot has to step on the pedal when rolling the airplane and stopping the roll becomes more tricky.
On some types, an inoperative yaw damper is listed in the minimum equipment list as a no-go item, or it limits the aircraft to a lower altitude. A 727-100, for example, demands an immediate descent to FL 260 after a single failure, while on other models, failure of both yaw dampers above FL 350 results in an irrecoverable loss of control. A total electrical failure silences the system, and an active yaw damper during the takeoff run masks serious issues like engine failure by hiding the first tell-tale yaw.
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
