Torquemeter (Turboprop Engines) Fuel-Flow Indicator $^{ }$Tachometer  Engine Oil Pressure Indicator Engine Oil Temperature Indicator 10-56 A turbofan engine has only one power control lever.  Adjusting the power lever, or throttle lever, sets up a thrust  condition for which the fuel control meters fuel to the engine.  Engines equipped with thrust reversers go into reverse thrust  Temperature is an engine operating limit and is used to  monitor the mechanical integrity of the turbines, as well as to  check engine operating conditions. Actually, the temperature  of the gases entering the first stage turbine inlet guide vanes  Exhaust gas temperature (EGT), turbine inlet temperature,  (TIT), turbine gas temperature (TGT), interstage turbine  temperature (ITT), and turbine outlet temperature (TOT) are  all relative temperatures used to monitor the temperature of  the exhaust gases entering the first stage turbine inlet guide  vanes. Even though these temperatures are taken at different  locations on the engine (each engine having one location),  they are all relative to the temperature of the gases entering  the first stage turbine inlet guide vanes.  Exhaust Gas Temperature Indicator (EGT) The engine operating procedures presented here apply  generally to turbofan, turboprop, turboshaft, and auxiliary  power units (APU). The procedures, pressures, temperatures,  and rpm that follow are intended primarily to serve as a  guide. It should be understood that they do not have general  application. The manufacturer’s operating instructions  should be consulted before attempting to start and operate  any turbine engine. Turbine Engine Operation The ability of the engine oil to lubricate and cool depends  on the temperature of the oil, as well as the amount of  oil supplied to the critical areas. An oil inlet temperature  indicator frequently is provided to show the temperature  of the oil as it enters the oil pressure pump. Oil inlet  temperature is also an indication of proper operation of the  engine oil cooler. To guard against engine failure resulting from inadequate  lubrication and cooling of the various engine parts, the  oil supply to critical areas must be monitored. The oil  pressure indicator usually shows the engine oil pump  discharge pressure. Gas turbine engine speeds are measured by the engines  rpm, which are also the compressor/turbine combination  rpm of each rotating spool. Most turbofan engines have  two or more spools, compressor, and turbine sections that  turn independently at different speeds. Tachometers are  usually calibrated in percent rpm so that various types of  engines can be operated on the same basis of comparison.  [Figure 10-73]  Also, turbine speeds are generally very high,  and the large numbers of rpm would make it very confusing.  Turbofan engines with two spools or separate shafts, high  pressure and low pressure spools, are generally referred to as  N1 and N2, with each having their own indicator. The main  purpose of the tachometer is to be able to monitor rpm under  normal conditions, during an engine start, and to indicate an  overspeed condition, if one occurs.  Fuel-flow instruments indicate the fuel flow in pounds per  hour (lb/hr) from the engine fuel control. Fuel flow in turbine  aircraft is measured in lb/hr instead of gallons, because  the fuel weight is a major factor in the aerodynamics of  large turbine aircraft. Fuel flow is of interest in monitoring  fuel consumption and checking engine performance.  [Figure 10-73] is the important consideration, since it is the most critical  of all the engine variables. However, it is impractical to  measure turbine inlet temperature in most engines, especially  large engines. Consequently, temperature thermocouples  are inserted at the turbine discharge, where the temperature  provides a relative indication of that at the inlet. Although  the temperature at this point is much lower than at the inlet,  it provides surveillance over the engine’s internal operating  conditions. Several thermocouples are usually used, that  are spaced at intervals around the perimeter of the engine  exhaust duct near the turbine exit. The EGT indicator in the  flight deck shows the average temperature measured by the  individual thermocouples.  [Figure 10-73] Only 10 to 15 percent of the thrust produced by a turboprop  engine is from propulsive force derived from the jet thrust  exiting the exhaust. Engine pressure ratio is not used as an  indicator of the power produced by a turboprop engine.  Turboprops are usually fitted with a torquemeter that  measures torque applied to a shaft turned by the gas generator  and power turbines of the turbine engine. The torquemeter can  be operated by engine oil pressure metered through a valve  that is controlled by a helical ring gear that moves in response  to the applied torque.  [Figure 10-73]  This gear moves against  a piston that controls the opening of a valve, which controls  the oil pressure flow. This action makes the oil pressure  proportional to torque being applied at the propeller shaft.  Generally, transducer is used to transfer the oil pressure into  an electrical signal to be read by the flight deck instrument.  The read out in the flight deck is normally in lb/ft of torque,  or percent horsepower. The torquemeter is very important  as it is used to set power settings. This instrument must be  calibrated at intervals to assure its accuracy. 