Page 26 - March19

Your Source for King Air Landing Gear
• Inspect • Overhaul • Exchange • Install
• Complete Ship Sets • King Air Aircraft Maintenance
601-936-3599 • www.traceaviation.com
24 •
­ KING AIR MAGAZINE Has the light bulb illuminated? Has your brain grasped
why the autopilot is not flying wings level? It is doing so
in order to fly the heading it wants while compensating
for an incorrectly-adjusted rudder. Keep in mind that
although the autopilot may be in GPSS, Nav or Approach
mode, not Heading mode, it still must find and hold an
exact heading to track the course. Sure, that heading may
be changing often as conditions – especially crosswind
components – change, but at any given time the autopilot
has a heading target when holding a heading or tracking
a course.
It is common to see a pilot attempt to raise the wing
that the autopilot is keeping low by turning the aileron
trim wheel. If the bank angle changes due to this action
then no longer will the target heading be held, so the AP
will not let that wing come up. Oh sure, there is a reaction
time so the wing will probably rise before it returns to
the position it needs. Eventually, enough aileron trim
will likely overpower the strength of the roll servo and
the wing will indeed come up … and keep coming!
Thus, it is incorrect and fruitless to adjust aileron trim
to correct the wing-low condition. Instead, just adjust
rudder trim to add rudder force on the low-wing side.
Back to our training scenario: If we are now banking
two degrees left-wing-down to compensate for the right
rudder force our instructor sneaked in, we could take
the rudder trim wheel – assuming our trainer has one
– and turn it left, toward the low wing. Eventually, the
rudder trim would create just the right amount of left-
rudder force to balance the right-rudder force that the
instructor was applying and we would have the wings
level again as we held the assigned 270 heading.
“Patience is a virtue.” I am sure you’ve heard that
adage. If we move the rudder trim wheel in our King
Air rapidly, the nose will of course momentarily swing
in the direction of the rudder force that has now been
applied. The Yaw Damper, obediently doing its job, will
apply opposite rudder to dampen that yaw. Go slow with
the trim and then stop to give the airplane and autopilot
time to stabilize. Truly, in a King Air, the initial motion
of the rudder trim wheel toward the low wing may be no
more than one-fourth of one index division on the trim
indicator. Expressed another way, the geared knurled
knob that you are moving with your hand probably
rotated only 30 degrees or less. Wait 30 seconds or so and
inspect the wings. Better, but not level? Turn the trim
wheel another small amount and wait again. Eventually
you’ll have it nailed in level flight. Doing this perfectly
throughout an entire flight (without an engine failure!) I
will state that the rudder trim index is never more than
one unit from center. Be patient; go slow.
Rarely do two different airplanes fly identically and
hence what is right for one may not apply to others,
even others of the exact same model. But let me tell you,
readers, every King Air needs rudder trim adjustment
throughout a flight! Why it drives me nuts when I ride
MARCH 2019