Page 23 - Dec 23

Before continuing, let me remind you that Webster’s dictionary includes at least three definitions of damp: (1) a noun, meaning “a slight wetness”; (2) an adjective, meaning “somewhat moist or wet”; (3) a transitive verb, meaning “to check or reduce.” It’s that last one that applies to the device that checks or reduces rotation around the airplane’s vertical axis. Further, Webster does not even include the word dampner. Instead, dampener is a noun for something that makes things moist whereas damper can be “anything that deadens or depresses.” Many King Airs are equipped with yaw dampers, but I have yet to see a King Air option for a yaw dampner, something that ... what? ... sprays water on the tail?
While we are reviewing definitions, yaw means “to turn from the desired heading” and, specifically as applied to aviation, “rotation around the vertical axis.” Notice the word “rotation”? Yaw occurs when rotation is taking place, not before or after. In other words, press a rudder pedal while using the ailerons to keep the wings level. Of course, the nose moves, yaws, in the direction of the pedal you push. But if you were to keep pedal pressure applied and maintain wings level, there is no longer yaw. A slip? Sure. Uncoordinated flight? Of course. But the yaw stopped once the nose, or longitudinal axis, stabilized at whatever position it reached relative to the plane’s direction of travel.
Vice versa, release that pedal pressure while keeping the wings level and the airplane should yaw back toward trimmed, coordinated, flight in which the longitudinal axis is pointed exactly in the direction of travel.
It is obvious that yaw action is uncomfortable and hence is something we pilots need to do our best to reduce or eliminate so as to avoid inflicting this discomfort on our passengers. The old-time pilot who could provide a reasonably yaw-free flight through turbulence in a late-‘40s or early-‘50s Bonanza (I almost wrote “V-tail Bonanza” but back then there weren’t any other kinds) was rare to find and was putting his feet and legs through a good workout!
Thank goodness for the advent of electronic yaw dampers! With these, the autopilot’s rudder control – the autopilot’s third axis of operation, the one that takes a back seat to aileron (roll) and elevator (pitch) control – could be used for reducing yaw. Not all yaw damp systems are designed the same, but usually all have an accelerometer of some type that measures lateral acceleration in the tail. Some also receive input from a heading gyro. The autopilot computer, based on these inputs, then commands the rudder to move to resist the acceleration. Simply, and obviously, when the nose yaws to the right, the left rudder is applied and when the nose goes left, the right rudder input is made.
DECEMBER 2023
KING AIR MAGAZINE • 21