Trio Pro Pilot Manual 4.1
71
Chapter 17
Trim and Auto-Trim
Autopilots love a well trimmed aircraft. If an airplane is out of trim, the autopilot servo must constantly
fight the controls to keep the plane in a proper attitude. If the out of trim condition is severe, autopilot
performance may deteriorate significantly.
This is especially true for the elevator control. In the Altitude Hold (
ALT HLD
) mode, improper trim may
cause the aircraft to “hunt” vertically (i.e. experience small repetitive vertical excursions). If the autopilot
is commanding a climb or descent (
AS/VS
mode), improper trim may prevent it from achieving the proper
climb or descent rate.
The Pro Pilot will issue trim alerts to the pilot. If the elevator servo is equipped with the Auto-Trim option
it will automatically operate the existing aircraft electric trim to remove trim errors.
No trim messages are provided for aileron trim.
Manual Elevator Trim
Aircraft are generally equipped with a manual trim that requires the pilot to adjust a mechanical trim
control to change the trim of the aircraft. Some airplanes employ an electric motor or “trim servo” to
allow the pilot to adjust trim by means of an electrical switch that might be positioned on the control stick
or instrument panel.
Trim Messages
With the autopilot active, when the elevator is out of trim a
small flashing arrow will appear in the bottom R/H corner of
the display to indicate that the pilot should adjust the aircraft
pitch trim. The direction of the arrow will indicate if the trim adjustment should be up or down.
If this subtle trim message is ignored, after a short interval the
message “
TRIM UP REQD
” or “
TRIM DN REQD
” will be
displayed.
In either case, the pilot should adjust the trim until the trim alert no longer appears. This may be done in
two ways:
Leave the autopilot engaged and adjust the trim in small increments. Make minor
adjustments and wait 5 to 10 seconds before making further adjustments. This will allow the
system to recognize that the adjustment has been made. Continue to adjust until the
message no longer appears.
Momentarily press the
V NAV
button to disconnect the vertical servo and observe if the
aircraft tends to climb or descend. Trim the elevator until level flight is achieved. Press the
V NAV
button to re-engage the pitch servo.
Automatic Elevator Trim
The automatic trim is an optional feature that allows the altitude hold system to automatically adjust the
aircraft electric trim motor to keep the elevator forces balanced. The pilot may then change engine
power settings and command climbs and descents without the necessity to manually re-trim the aircraft.