Wednesday, July 11, 2012

Cessna 152 Instrument System

                         INSTRUMENT PANEL. The instrument panel assembly consists of a stationary panel and shock mounted panel. The stationary panel contains fuel and engine instruments which are NOT sensitive to vibration. The shock-mounted panel contains major flight instruments such as horizontal and directional gyros which ARE affected by vibration. Most of the instruments are screw-mounted on the panel backs..
                                     ENGINE INDICATORS.
TACHOMETER. The tachometer is a mechanical indicator driven at half crankshaft speed by a flexible shaft Most tachometer difficulties will be found in the drive-shaft To function properly, the shaft housing must be free of kinks, dents and sharp bends. There should be no bend on a radius shorter than si inches and no bend within three inches of either terminal. If a tachometer is noisy or pointer oscillates, check cable housing for kinks, sharp bends and damage. Disconnect cable at tachometer and pull it out of housing. Check cable for worn spots, breaks and kinks.
 OIL PRESSURE GAGE. On some airplanes, a Bourbon tube-type oil pressure gage is installed. This is a direct-reading instrument, operated by a pressure pickup line connected to the engine main oil gallery. The oil pressure line from the instrument to the engine should be filled with kerosene, especially during cold weather operation, to obtain immediate oil indication. Electrically actuated gages are installed on some airplanes which utilize a pressure sending bulb
OIL TEMPERATURE GAGE. The oil temperature gage is an electrically operated indicator mounted in the instrument cluster with the oil pressure gage. One electrical lead is routed from the indicator to the sending unit installed in the engine. The other lead supplies power from the bus bar to the indicator.
ECONOMY MIXTURE INDICATOR  The economy mixture indicator is an exhaust gas temperature (EGT) sensing device which is used to aid the pilot in selecting the most desirable fuel-air mixture for cruising flight at less than 75% power. Exhaust gas temperature (EGT) varies with ratio of fuel-to-air mixture entering the engine cylinders. Refer to the Pilot's Operating Handbook for operating procedure of the system.
 CALIBRATION. A potentiometer adjustment screw is provided behind the plastic cap at the back of the instrument for calibration. This adjustment is used to position the pointer over the reference increment line (4/5 of scale) at peak EGT. Establish level flight below 10000 ft. altitude with the throttle control advanced to 75% of full throttle, then carefully lean the mixture to peak EGT. After the pointer has peaked using the adjustment screw. Position pointer over reference increment line (4/5 scale).
Turning the screw clockwise increases the meter reading and counterclockwise decreases the meter reading. There is a stop in each direction and damage can occur if too much torque is applied against stops. Approximately 600°F total adjustment is provided. The adjustable pointer on the face of the instrument is a reference pointer only
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