Page 29 - June24

away the wheel will move back to where the AP wants it. If you find your KFC-400 flying with one wing low, an avionics technician with experience in that system will be required. (This does not apply to the much-more- common KFC-300 system.)
All other autopilot systems available in King Airs have four, not five, autopilot servomotors, more commonly called servos. One servo controls roll by moving the ailerons, one controls pitch by moving the elevators, one controls yaw by moving the rudder, and one adjusts the elevator trim to lighten the load on the elevator servo. Only the KFC-400 has the fifth one that adjusts the rudder trim.
A single-axis autopilot controls only roll. A two-axis autopilot controls both roll and pitch. A three-axis autopilot (yes, you guessed it!) controls all three: roll, pitch and yaw. To the best of my knowledge all King Air autopilots are and always have been the three-axis type.
As you know, the only trim control that routinely gets much use is pitch trim. Change airspeed? Trim. Change configuration? Trim. Aileron trim hardly ever gets touched unless a large fuel imbalance exists. Rudder trim? Many pilots must believe it is akin to aileron trim ... hardly ever used (except for single-engine work). Yes, a normal flight can be successfully completed without
a tweak of the rudder trim wheel. Is that the way to go? No! Did you hear me? NO!
The rudder (yaw) servo is there for only one purpose ... to dampen yaw. It helps in keeping the nose from swinging side-to-side. Cruising in perfectly smooth air with no change in power, the rudder servo would never be needed and would never activate. But since air is rarely that smooth, imagine keeping your feet on the floor while flying manually. What? You say you’ve ridden with pilots who do that? Yes, I have too ... and it drives me nuts! Now every little bump usually leads to some nose-swinging. Even in perfectly smooth air, lack of rudder awareness and proper usage leads to what this article is all about ... correcting a wing-low situation.
Imagine this scenario, which is a very good one for instructors to teach/demonstrate to their flying students. In level flight, tell the student to keep both feet on the floor, away from the rudder pedals. Now assign a heading – let’s use an example of 270 degrees –and observe the student doing the proper job, on the control wheel only, to maintain altitude and heading. Now suppose the instructor slowly put some force on the right rudder pedal. The airplane will respond by swinging the nose slightly to the right, making the heading change to, say, 275 degrees. The student, following the assignment
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JUNE 2024
KING AIR MAGAZINE • 27