P/N 11934-002
8
Cirrus Design
Section 9
SR20
Supplements
Section 7 - Systems Description
The airplane is equipped with an S-Tec System Twenty single-axis
Automatic Flight Control System (Autopilot). The autopilot is a pure
rate autopilot that uses an inclined gyro in the turn coordinator case as
the primary turn and roll rate sensor. In addition to the turn coordinator
instrument and rate gyro, the case encloses an autopilot pick-off, a
gyro RPM detector, an instrument power monitor, and the autopilot
computer/amplifier. Roll axis steering is accomplished by autopilot
steering commands to the aileron trim motor and spring cartridge. Low
electrical power will cause the Turn Coordinator to flag and low RPM
will cause the autopilot to disconnect. 28 VDC for autopilot operation is
supplied through the 5-amp AUTOPILOT circuit breaker on the Main
Bus 1. Turn Coordinator instrument dimming is controlled through the
INST light dimmer on the bolster switch panel.
• Note •
The altitude hold mode discussed in the following paragraphs
and shown in Figure 1 is not available with the System Twenty
Autopilot. This feature is available on the System Thirty
Autopilot. Altitude hold is shown in this supplement only
because both the System Twenty and Thirty Autopilots use the
same Turn Coordinator.
Altitude hold is not selectable and the associated annunciators
will not illuminate.
All Autopilot mode selection and annunciation is performed with the
Turn Coordinator/Autopilot Controller.
Refer to Figure 1
for an
illustration of the following listed modes and controls:
RDY (Ready) Light
– Illuminates green when autopilot is ready for
engagement. When the airplane’s Battery Master switch is turned on
and the rate gyro RPM is correct, the green RDY light will come on
indicating the autopilot is ready for the functional check and operation.
The autopilot cannot be engaged unless the RDY light is illuminated.
Mode Select / Disconnect Switch
– Each momentary push of the
knob will select an autopilot mode, left to right, beginning with ST
(Stabilizer) mode and ending with TRK HI (Track) mode. Holding the
knob in for more than 2 seconds will disengage the autopilot.
Revision 1: 12-07-04
Summary of Contents for SR20
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