Electrical System - Piper PA-24-250 COMANCHE Pilot Operating Handbook

Xlrcran Public:il~ons
P~pcr Comanche 251) (Early Modcl)
Section
-
7
Systems Description
Fuel cells should be kept full when the aircraft is not
in
use to prevent accumulation of moisture
through condensation and to keep the rubber from deteriorating by drying out.
Fuel cells are vented individually by vent tubes located beneath the wing. Fuel from each cell
passes through a selector-shutoff valve to a sediment bowl in the lowest part of the fuel system
where it is filtered, and any water or foreign particles are trapped. From there the fuel is drawn to
the carburetor by an engine-driven pump. In the event of failure of the engine-driven pump, an
electric auxiliary fuel pump is provided. In addition to the back-up function, this pump is normally
operated when switching fuel tanks and during starting, takeoff and landing.
On the early model 250 the "gasculator" fuel-strainer unit is located under the right forward
section of the fuselage and is accessible from outside the aircraft. Daily draining of the sediment
bowl is accomplished by opening the hinged access door and operating the quick-drain valve for
approximately five seconds with the &el-selector valve on one cell. Change the fuel selector to the
next cell and repeat the procedure. Allow enough fuel to flow to clear the lines as well as the
sediment-bowl strainer. Fuel quantity is indicated by two electric gauges located in the engine
instrument cluster.
An engine-priming system is provided to facilitate starting. The manually operated primer pump is
located on the lower right side of the instrument panel. Be certain that the primer pump is in and
locked after use.
ELECTRICAL SYSTEM
Electrical power for the Comanche is supplied by a 12-volt, direct-current, negative-ground
system. The primary electrical power source is a 12-volt, 35-ampere (50-ampere optional)
generator controlled by a voltage and current regulator. Beginning with serial number 2202, the
50 ampere generator became standard equipment. The electrical systems of many airplanes have
been modified to operate on a 12-volt, 70-ampere alternator. Secondary power is provided by a
12-volt, 35 ampere-hour battery which supplies power for starting, and is a reserve power source
in the event of generator failure.
The battery is mounted in a stainless-steel box immediately aft of the baggage compartment. The
regulator is mounted in the engine compartment on the firewall. The ammeter, located in the
engine gauge cluster, indicates battery discharge.
Electrical switches are located on the lower left side of the instrument panel. The master switch is
positioned on the far left of these switches. Circuit breakers are mounted in a cluster below the
switches.
Standard lighting on the Comanche includes navigation lights, landing lights, cabin and instrument
lights. Optional equipment includes a rotating beacon and strobe lights. A combination on-off
rheostat switch controls the navigation lights and the instrument and radio lights.
Copyright: 1993
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