FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506bracket and a transmitter unit. The transmitter unitcontains a multicell, diaphram-actuated computer; geartrain; two-phase motor; and transmitting synchros. Theindicators are graduated from 1.0 to 2.5 EPR units with0.1 EPR markings and a vernier dial graduated in 0.01EPR markings. An adjustable pointer on the face of theindicator is set to the maximum EPR for the ambienttemperature to indicate possible engine overspeed. Themaximum EPR for given temperatures is listed on theinstrument panel. The AC Power system supplies electricalpower through the EPR circuit breaker.TURBINE DISCHARGE PRESSUREINDICATORThis instrument indicates the internal engine pressureupstream of the jet nozzle, immediately aft of the laststage of the turbine (Pt5 to Pt7). It indicates pressureavailable across the nozzle to generate thrust. Turbinedischarge pressure must be used in conjunction with T12and P12.ENGINE PRESSURE RATIO INDICATORThis instrument (Figure 9-15) indicates the enginepressure ratio as a measure of thrust developed by theengine. This is the ratio of the turbine discharge totalpressure to the equivalent of the compressor inlet totalpressure (Pt5/Pt2 or Pt7/Pt2). Values for Pt2 must becorrected for inlet duct loss on the engine pressure ratiocurves or charts by the aircraft manufacturer. Therefore,both for static (takeoff) and flight use, the actual value forPt2 will vary among different aircraft types and modelsbecause of installation effects. However, the relation ofPt2 at the engine face to Pam plus Pr is equivalent to totalpressure at or near the compressor inlet when airborne.It is not advisable to instrument the compressor inletwhen airborne. It is not advisable to instrument thecompressor inlet directly for Pt2. The Pt2 sensor for thepressure ratio indicator may be placed at some otherlocation on the aircraft, preferably as near the engine airinlet as possible. After appropriate corrections are madeto the in-flight charts in the flight of operation manual,any rated thrust or percent of rated thrust may be set withthe aircraft throttle (as a function of the TAT or Tt2).Pressure ratio between the pressure at the engine airinlet and the discharge pressure at the jet nozzle indicatesthrust developed by the engine. Turbine discharge pressurealone is not an accurate indication of engine output.Compressor inlet pressure (Pt2) must be taken into accounton curves or charts when only turbine dischargepressure is instrumented.For static engine operation, this is usually accomplishedby showing barometric pressure (correctedfor inlet duct loss) rather than Pt2 values on the curves orcharts. In flight, curves or tables usually show airspeedand altitude. This eliminates the need for actually9-11