Cessna 152 - Page 131

CESSNA
MODEL 152
SECTION7
AIRPLANE & SYSTEMS DESCRIPTIONS
The heated pitot system consists of a heating element in the pitot tube,
a
rocker-type switch labeled PITOT HT on the left switch and control panel,
a 15-amp circuit breaker under the engine controls on the instrument
panel, and associated wiring. When the pitot heat switch is turned on, the
element in the pitot tube is heated electrically to maintain proper opera-
tion in possible icing conditions. Pitot heat should be used only as
required.
AIRSPEED INDICATOR
The airspeed indicator is calibrated in knots and miles per hour.
Limitation and range markings (in KIAS) include the white arc (35 to 85
knots), green arc (40 to 111 knots), yellow arc (111 to 149 knots), and a red
line (149 knots}.
If a true airspeed indicator is installed, it is equipped with a rota.table
ring which works in conjunction with the airspeed indicator dial in a
manner similar to the operation of a flight computer. To operate the
indicator, first rotate the ring until pressure altitude is aligned with
outside air temperature in degrees Fahrenheit. Pressure altitude should
not be confused with indicated altitude. To obtain pressure altitude,
momentarily set the barometric scale on the altimeter to 29.92 and read
pressure altitude on the altimeter. Be sure to return the altimeter baromet-
ric scale to the original barometric setting after pressure altitude has been
obtained. Having set the ring to correct for altitude and temperature, read
the true airspeed shown on the rotatable ring by the indicator pointer. For
best accuracy. the indicated airspeed should be corrected to calibrated
airspeed by referring to the Airspeed Calibration chart in Section 5.
Knowing the calibrated airspeed, read true airspeed on the ring opposite
the calibrated airspeed.
RATE-OF-CLIMB INDICATOR
The rate-of-climb indicator depicts airplane rate of climb or descent in
feet per minute. The pointer is actuated by atmospheric pressure changes
resulting from changes of altitude as supplied by the static source.
ALTIMETER
Airplane altitude is depicted by a barometric type altimeter. A knob
near the lower left portion of the indicator provides adjustment of the
instrument's barometric scale to the current altimeter setting.
VACUUM SYSTEM AND INSTRUMENTS
An engine-driven vacuum system (see figure 7-9) is available and
1 July 1978 7-29