Instrument Panel; Vacuum System; Pitot-Static System; Heating And Ventilating System - Piper PA-24-250 COMANCHE Pilot Operating Handbook

Alrcrafl Publicmons
P~pcr Comnnchc 250 (Early Modcl)
Section
-
7
Systcms Description
INSTRUMENT PANEL
The instrument panel is designed to accommodate the customary advanced flight instruments, the
normally required engine instmments, and avionics for VFR and IFR flight. The artificial horizon
and directional gyro are vacuum operated. The turn-indicator gyro is electrically operated and
serves as a standby for the vacuum gyros in the event of a vacuum system failure.
Radios are located outboard of the control yokes on the early model Comanche. The avionics
master switch (if installed) is located with the other electrical switches to the right of the master
switch.
VACUUM SYSTEM
The vacuum system provides the suction necessary to operate the attitude indicator and the
directional gyro. The engine-driven system consists of a vacuum pump, a vacuum relief valve with
filter, a system inlet-air filter, and a suction gauge.
The vacuum pump is either a wet or dry-type pump. A shear drive in the pump assembly protects
the engine from damage. If the vacuum pump is the dry type pump, caution should be exercised to
insure that the propeller is never pulled through backward, as doing so will damage the rotary
vanes in the vacuum pump and render the gyros inoperative.
The vacuum regulator is adjustable to a normal reading of 5.0 inch Hg plus .1 or minus .2 inch
Hg. Proper adjustment is important because higher settings will damage the gyros, and the
instruments will be unreliable with a low setting.
PITOT-STATIC SYSTEM
The pitot-static system provides ram-air pressure to the airspeed indicator and static pressure to
the airspeed indicator, vertical-speed indicator, and altimeter. The system is composed of a heated
(optional) pitot tube mounted on the lower surface of the left wing, a pair of static ports located on
either side of the hselage aft of the baggage compartment, and the associated piping necessary to
connect the instruments to the sources.
A n
alternate static source is available as an option. Airspeed and altitude instruments can be
expected to read higher than normal when operating from the alternate air source.
HEATING AND VENTILATING SYSTEM
There are four individual controls located on the lower right side of the instrument panel which
regulate the flow of heating, defrosting and ventilating air.
Heat for the cabin interior is provided by a hot-air exchanger installed on the exhaust muffler.
Heated air for the defroster system is provided by the same heater muff, but has an individual
control. Caution should be used when operating the defroster on the ground as prolonged
application of heat may cause damage to the Plexiglas windshield.
Fresh air is supplied to the cabin by two adjustable ventilators located beside each seat and two
large ventilators located under the instrument panel.
Copyright:
1993
Page 7-6