TruTrak Digiflight Install Manual - Manual (Page 15)

TruTrak Flight Systems DigiFlight Autopilot Installation Manual
13 March 2002 Printing
Magnetic Calibration
The DigiFlight autopilot contains a built-in magnetometer which is used to maintain gyro centering and slaving for the built-in
Electronic DG of the autopilot in case of GPS loss. This magnetometer is icalibrated at the factory in a disturbance-free
environment, but once installed in the aircraft it may be necessary to account for any magnetic disturbances in the aircraft
itself.
For best results, this operation should be done on a day when the winds are relatively calm, so that air is still and heading and
ground track are approximately the same in all directions. The operation should be deferred until such flight conditions exist.
For this operation the autopilot will fly four legs of approximately half a minute each, first north, then east, then south, then
west. Prior to the calibration sequence, fly the aircraft to an area where this can suitably be done. Verify that the autopilot is
receiving GPS properly (note the flashing “*” in the display). Engage the autopilot in its normal tracking (TRK) mode. If the
unit is a DigiFlight 200 or 200 VS, engage the altitude hold at an appropriate altitude; if the unit is a DigiFlight 100, the entire
calibration sequence needs to be hand-flown in pitch by carefully holding attitude constant during the straight segments of the
process.
Once the autopilot is engaged, press and hold MODE until the setup screen appears. Press ENTER to cycle through the activity
and baud rate setup screens until MAG CALIBRATE? Appears on the screen. Rotate the knob to select Y (yes) and press
ENTER. The autopilot screen will announce “CALIBRATING… TURNING NORTH”. It will fly to a ground track of 000
degrees, then say “HOLDING NORTH”. For approximately twenty seconds, the unit will obtain data from the magnetometer
for this heading. It will then announce “TURNING EAST”, then “HOLDING EAST” and so on, until it has flown a twenty-
second leg in all four directions, ending up flying towards the west. Having completed this operation, the display will change to
“CALIBRATION COMPLETE” “PRESS ENTER”. Confirm the calibration sequence by pressing ENTER. At this point, the
autopilot will revert back to its normal flight mode with a direction selector, but the upper-left display will show MAG rather
than TRK, indicating that the autopilot is in its magnetic backup mode. This allows the mode to be confirmed in flight. Rotate
the knob to select various headings and observe the flight of the autopilot in the magnetic backup mode. If problems or
innacuracies occur with various headings, it is possible that these problems are due to excessive turbulence or winds on this
particular flight, and it may be necessary to repeat the operation at a different time. Once the check-out of the backup mode is
finished, disengage and then re-engage the autopilot to return to normal Track (TRK) mode.
This concludes the in-flight setup of the DigiFlight 100 / 200 / 200VS autopilot.