S
ECTION
7: A
IRPLANE
AND
S
YSTEMS
C
IRRUS
D
ESIGN
E
NGINE
SR20
7-32
P/N 11934-005
Engine Controls
Engine controls are easily accessible to the pilot on a center console. They
consist of a single-lever power (throttle) control and a mixture control
lever. A friction control wheel, labeled FRICTION, on the right side of the
console is used to adjust control lever resistance to rotation for feel and
control setting stability.
Power (Throttle) Lever
The single-lever throttle control, labeled MAX-POWER-IDLE, on the
console adjusts the engine throttle setting in addition to automatically
adjusting propeller speed. The lever is mechanically linked by cables to the
air throttle body on the fuel servo and to the propeller governor. Moving
the lever towards MAX opens the air throttle butterfly and increases the
pressure differential across the air diaphragm. This change in position of
the diaphragm opens the servo valve increasing the volume of fuel deliv-
ered to the engine. A separate cable to the propeller governor adjusts the
governor oil pressure to increase propeller pitch to maintain engine RPM.
The system is set to command 2500 RPM from idle through the cruise
power setting range and 2700 RPM at full power.
Mixture Control
The mixture control lever, labeled RICH MIXTURE CUTOFF, on the
console allows the pilot to manually lean the mixture for a specific power
setting or fuel consumption. The mixture control lever is mechanically
linked to a sliding valve inside the fuel servo. The pressure regulator within
the servo functions to maintain a differential pressure across the fuel
metering jet in proportion to the volume of airflow. The mixture control
allows the pilot to effectively change the size of the metering jet. Moving the
lever forward (toward RICH) allows the servo to meter the greatest amount
of fuel based on the volume of airflow. Moving the lever aft (toward
CUTOFF) reduces the size of the metering valve, leaning the fuel-to-air
mixture. The full aft position (CUTOFF) closes this valve, which drops the
fuel pressure in the flow divider to zero, causing it to close and shut down
the engine.
Alternate Air Control
An Alternate Induction Air Control knob, labeled ALT AIR – PULL, is
installed on the left console near the pilot’s right knee. To operate the
control, depress the center lock button, pull the knob to the open position,
and then release the lock button. Pulling the knob opens the alternate air
induction door on the engine induction air manifold, bypasses the air filter,
and allows warm unfiltered air to enter the engine. Alternate induction air
should be used if blocking of the normal air source is suspected. Operation
using alternate induction air should be minimized and the cause of filter
blocking corrected as soon as practical.
Reissue A