Aircraft Systems

Inlet Duct fan Fuel injector Turbine Hot gases Primary air stream Secondary air stream Compressor Combustion chamber Nozzle Figure 7-25. Turbofan engine. Inlet Compressor Combustion chamber Exhaust Power shaft Compressor turbine Free (power) turbine Figure 7-26. Turboshaft engine. turboshaft engine, most of the energy produced by the EPR system design automatically compensates for the effects expanding gases is used to drive a turbine rather than produce of airspeed and altitude. Changes in ambient temperature thrust. Many helicopters use a turboshaft gas turbine engine. require a correction be applied to EPR indications to provide In addition, turboshaft engines are widely used as auxiliary accurate engine power settings. power units on large aircraft. Exhaust Gas Temperature (EGT) Turbine Engine Instruments A limiting factor in a gas turbine engine is the temperature Engine instruments that indicate oil pressure, oil temperature, of the turbine section. The temperature of a turbine section engine speed, exhaust gas temperature, and fuel flow are must be monitored closely to prevent overheating the turbine common to both turbine and reciprocating engines. However, blades and other exhaust section components. One common there are some instruments that are unique to turbine engines. way of monitoring the temperature of a turbine section is These instruments provide indications of engine pressure with an EGT gauge. EGT is an engine operating limit used ratio, turbine discharge pressure, and torque. In addition, to monitor overall engine operating conditions. most gas turbine engines have multiple temperature-sensing instruments, called thermocouples, which provide pilots with Variations of EGT systems bear different names based on temperature readings in and around the turbine section. the location of the temperature sensors. Common turbine temperature sensing gauges include the turbine inlet Engine Pressure Ratio (EPR) temperature (TIT) gauge, turbine outlet temperature (TOT) An engine pressure ratio (EPR) gauge is used to indicate the gauge, interstage turbine temperature (ITT) gauge, and power output of a turbojet/turbofan engine. EPR is the ratio turbine gas temperature (TGT) gauge. of turbine discharge to compressor inlet pressure. Pressure measurements are recorded by probes installed in the engine Torquemeter inlet and at the exhaust. Once collected, the data is sent to Turboprop/turboshaft engine power output is measured a differential pressure transducer, which is indicated on a by the torquemeter. Torque is a twisting force applied to a flight deck EPR gauge. shaft. The torquemeter measures power applied to the shaft. 7-22