TruTrak Digiflight II Instal Manual - Manual (Page 9)

TruTrak Flight System 7 DigiFlight II Series Auto Pilot Installation Manual
December 2009 8300-008 Rev D
Next, the LAT TORQUE field is adjusted. Again, it is best that this be done in light to moderate turbulence. The reason is that
more torque is required of the autopilot in turbulence than is the case in still air, because the velocity of the servo is greater as
turbulence requires more rapid servo movement. This means that when activity is set to the high end of the acceptable range, a
higher torque setting will be required.
The reason for setting LAT TORQUE to a setting less than its maximum (12) is to reduce the current draw of the servo and to
make it easier to override the autopilot should the need arise. Manual override is not normally required, as using the control-
wheel switch or holding the knob for three seconds, then releasing it, will disengage the autopilot, but it is best to have a setting
of torque which can be comfortably overridden if necessary.
Once the desired LAT TORQUE level is established, press the ALT button to move to the next setup screen.
The BAUD RATE setting has already been done before this flight. Press the ALT button to move to the next setup screen.
The BANK ANGLE setting can be adjusted to suit the pilot. This setting controls how much bank the autopilot will command
when in a turn. The possible settings are low, medium, and high. Press the ALT button to move to the next setup screen.
The MICRO ACTIVITY setting in most aircraft will be left at zero (0). Micro activity is used only in aircraft in which a slow
wing rock has been observed in very still air. Sometimes there will be a small amount of lost motion in an aircrafts control
system, and the micro activity setting is a way to compensate for the lost motion. Press the ALT button to move to the next
setup screen.
The GPS GAIN setting is used to increase the bank angle that the autopilot will fly in GPS Steering mode. Increase the value
to increase the maximum allowable bank angle. Press the ALT button to move to the next setup screen.
The YAW DAMPER setting is only adjusted if a yaw damper is present. Set to Y if a yaw damper is installed. Press the ALT
button to move to the next setup screen.
Press and hold the ALT button until the screen displays PITCH AXIS (DII VS). To turn the pitch axis off, select OFF. The
default of ON will always be selected after a power cycle. This screen is not there on DII units. Press the ALT button to move
to the next setup screen.
The next setup screen will show VRT ACTIVITY along with an underlined value. In the same manner as was done for the roll
axis, use the knob to find a setting which results in the appropriate response. Again, too high a value will be jittery or
oscillatory and too low a setting will be sluggish and unresponsive. Having found the desired VRT ACTIVITY setting, press
the ALT button to move to the next setup screen.
In a manner similar to the lateral axis, rotate the knob to choose a torque setting sufficient to fly the aircraft in light to moderate
turbulence without slipping the servo, yet not so high as to be difficult to override manually. Having selected this value, press
the ALT button to move to the next setup screen.
The MIN AIRSPD setting has already been done before this flight. Press the ALT button to move to the next setup screen.
The MAX AIRSPD setting has already been done before this flight. Press the ALT button to move to the next setup screen
The next screen is the STATIC LAG field. It is set to 0 at the factory but can vary between 0 and 2 to suit a particular static
system. The value 0 assumes a static system with very little “lag”; the value 2 assumes a fairly large amount of lag. To
diagnose the lag of a particular system, it is necessary to be in the altitude hold mode of the autopilot, in very still air, in
straight-and-level flight. If these conditions cannot be found during the first flight, leave STATIC LAG set to zero, press
ENTER to exit and restore the main flight screen to the display, and perform the operation on a later flight.
To determine the correct setting for STATIC LAG, fly in still air in straight and level flight, in altitude hold mode. Observe
whether the altitude appears to oscillate, or “hunt” up and down. If this is the case, it may be caused by several factors, one of
which is the amount of lag in the static system. Increasing the STATIC LAG value to a 1 or a 2 may cure the problem; however
this should be set to the smallest value that satisfactorily flies the aircraft in the pitch axis, as the larger the value the less
responsive the autopilot will be to vertical commands or altitude error. Other possible causes of hunting in altitude hold are
“lost motion” in the servo or control linkages or too low a level of vertical activity setting. If there is hunting in altitude, but the
lag setting does not seem to make any difference, leave it set at zero. Excessive lag in the static system itself can be caused by
undersized static ports, improperly placed ports, long static lines, or especially by attached equipment with large static
reservoirs. The autopilot can be adapted to cover a wide range of static systems, but in truly extreme cases it may be necessary
to provide a separate static line for the autopilot so that other equipment attached to the port does not degrade the autopilot’s
performance.
The MICRO ACTIVITY setting in most aircraft will be left at zero (0). Micro activity is used only in aircraft in which a slow
wing rock has been observed in very still air. Sometimes there will be a small amount of lost motion in an aircrafts control