Fuel Injection - Piper AZTEC D PA-23-250 Owner's Handbook Manual

SECTION II THE PIPER AZTEC "D"
produces sufficient force to control propeller rpm, within normal
operating range, provided airspeed is reduced and power is applied
slowly. The propellers are controlled by the levers in the center of the
control quadrant. Feathering of the propellers, which takes
approximately three to ten seconds, is accomplished by moving the
controls fully aft through the low RPM <Jetent into the feathering
position. A propeller
is
unfeathered by moving the prop control ahead
and engaging the starter. (See Section III, for complete feathering and
unfeathering instructions.)
FUEL INJECTION
The Bendix RSA-5 Type Fuel Injection System installed in
the Aztec is based on the principle of measuring airflow and
using the airflow signals to operate a servo valve. The accu-
rately regulated fuel pressure established by the servo valve,
when applied across a fuel control Getting system), makes fuel
flow proportional to airflow.
Fuel pressure regulation, by means of a servo valve, neces-
sitates only a minimum fuel pressure drop through the entire
metering system. This makes it possible to maintain metering
pressure above vapor forming conditions, and at the same time
does not require a high inlet fuel pressure. An inherent feature
of the Servo System is self-purging, which eliminates any possi-
bility of vapor lock and the associated problem of difficult
starting.
The Airflow Sensing System, which is incorporated in the
Servo Regulator, consists of the throttle body containing the
throttle valve and venturi. The differential pressure between the
entrance and the throat of the venturi is a measurement of air
entering the engine. These pressures are applied to an air
diaphragm in the Servo Regulator to create a force across the
diaphragm. A change in power will change the airflow to the en-
gine which in turn will change the force across the air diaphragm
in the Servo Regulator.
The air diaphragm in the Servo Regulator converts the
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