2.25. ENGINE INSTRUMENTATION
Engine performance is monitored by instruments mounted on the instrument panel in the cockpit.
- Tachometer system. The tachometer gives the pilot a continuous indication of engine rpm. A variety of systems or a combination of systems may be used on gas turbine engines. Gas producer or gas generator tachometers, turbine and rotor tachometers, and N1 and N2 tachometers are some of the tachometer systems used. The system may consist of dual indicators, registering rpm for multiengine aircraft, registering engine and rotor rpm for rotary-wing aircraft, or engine and propeller rpm for fixed-wing aircraft. A typical tachometer indicator is driven by a tachometer-generator. The generator supplies power at a frequency proportional to the driven speed which drives the synchronous motors in the indicator.
- Torquemeter indicating system. Sometimes called a torque pressure indicating system, the typical torquemeter indicating system is a pressure indicator for continuous readings of engine output-shaft torque. It is powered by an electrical transmitter mounted on the engine inlet section.
- Engine oil pressure indicating system. A typical engine oil pressure indicating system gives continuous readings of engine oil pump pressure in psi to the indicator, by means of an electrical transmitter mounted on the engine inlet section. The transmitter is connected to the 28-volt ac electrical system, and by a hose to a pressure tap on the engine oil filter housing.
- Engine oil temperature indicating system. In a typical engine oil temperature indicating system, the indicator is electrically connected to the 28-volt dc system. An electrical resistance type thermobulb installed in the engine oil pump housing measures temperatures of the oil entering that unit. The temperature readings are transmitted to the indicator in degrees centigrade.
- Exhaust gas temperature indicating system. The indicator in a typical exhaust gas temperature indicating system operates on electrical potential from an engine thermocouple harness with probes mounted in the aft section of the engine exhaust diffuser. The thermocouple is a device which converts heat into electricity. The exhaust gas temperature indicator (thermocouple thermometer indicator) is actually a sensitive millivoltmeter, calibrated in degrees centigrade. Its D'Arsonval movement is activated by an electrical force generated by its related thermocouple. The indicator circuit is entirely independent of any other electrical power source, and includes a coil resistor which provides a means of systems calibration.
- Fuel pressure indicating system. A typical fuel pressure indicating system gives continuous readings of fuel pressure(psi) in the main fuel supply line from the boost pumps in the tanks, by means of an electrical transmitter. The transmitter is connected to a tap on the valve manifold where all the fuel supply lines join to deliver fuel to the engine through the fuel control inlet hose. Electricity is supplied to the transmitter by the 28-volt ac system.