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Second, the rate feedback signal is integrated to obtain
position feedback, gain adjusted and summed with the
steering command. When these signals are equal, the
elevator is in the proper position to satisfy the vertical
command. As the aircraft responds, the flight director
command diminishes and the position feedback signal drives
the elevator servo back to its original position.
Should there be a mismatch between vertical command and
elevator servo position, a flightpath standoff could occur.
To prevent this standoff, any command at the output of the
second pitch limiter is routed through a command rate taker
and limiter.
The signal is changed to rate, and summed with tach
generator rate feedback. The summing of these two signals
is then integrated to obtain position data and summed with
the vertical command.
3.
B.
(8)
(i) ~
Autopilot Pitch Attitude Hold (See Figure 260, sheet 1.)
Pitch attitude hold is the basic vertical autopilot mode.
It is automatically active if the autopilot is engaged and
no vertical flight director mode has been selected. Prior
to autopilot engagement, pitch attitude is routed through a
summing point-d
through the normally closed PITCH HOLD +
(AP ENGAGE
TCS
NO VERTICAL FD MODE SELECTED) switch to a
synchronizer. The output of the synchronizer is inverted
and summed with pitch attitude to give a zero output from
the summing point.
If the autopilot is engaged and no
vertical flight director mode is selected, the synchronizer
switch opens, clamping the synchronizer with the reference
pitch attitude at the time of autopilot engagement. Should
the aircraft deviate from the desired reference attitude,
the difference from the summing point is limited and routed
to Figure 260, sheet 7, as a pitch hold command signal and
is processed as discussed in paragraph 3.B.(8)(i)~. The
reference pitch attitude can be changed through the use of
the pitch wheel on the PC-880 Turn Pitch Controller, with
the autopilot engaged. Moving the pitch wheel will cause a
rate generator output. The direction of pitch wheel motion
will determine the polarity of the output, while the speed
of pitch wheel motion will determine the amplitude of the
signal. The pitch wheel signal is then TAS gain programmed
to more accurately adjust the signal as a function of
aircraft speed and barometric altitude. The pitch wheel
signal then changes the pitch attitude reference, and the
output from the summing point is identical to what was
previously discussed.
22-14-00
Page
298.123
Aug 15/91
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