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Engine thrust
10. The thrust of an engine is shown on a thrust- meter, which will be one of two basic types; the first measures turbine discharge or jet pipe pressure, and the second, known as an engine pressure ratio (E.P.R.) gauge, measures the ratio of two or three parameters. When E.P.R. is measured, the ratio is usually that of jet pipe pressure to compressor inlet pressure. However, on a fan engine the ratio may be that of integrated turbine discharge and fan outlet pressures to compressor inlet pressure.
11. In each instance, an indication of thrust
output is given, although when only the turbine discharge pressure is
measured, correction is necessary for variation of inlet pressure;
however, both types may require correction for variation of ambient
air temperature. To compensate for ambient atmospheric
conditions, it is possible to set a correction figure to a
sub-scale on the gauge; thus, the minimum thrust output can be checked
under all operating conditions.
12. Suitably positioned pilot tubes sense the pressure or pressures appropriate to the type of indication being taken from the engine. The pilot tubes are either directly connected to the indicator or to a pressure transmitter that is electrically connected to the indicator.
13. An indicator that shows only the turbine discharge pressure is basically a gauge, the dial of which may be marked in pounds per square inch (p.s.i.), inches of mercury (in. Hg.), or a percentage of the maximum thrust.
14. E.P.R. can be indicated by either electro- mechanical or electronic transmitters. In both cases the inputs to the transmitter are engine inlet pressure (P1) and an integrated pressure (PINT) comprised of fan outlet and turbine exhaust pressures. In some cases either fan outlet pressure or turbine exhaust pressure are used alone in place of PINT.
15. The electro-mechanical system indicates a change in pressure by using transducer capsules (fig. 12-3)
to deflect the centre shaft of the pressure transducer causing the yoke to pivot about the axis A.A. This movement is sensed by the linear variable differential transformer (L.V.D.T.) and converted to an a.c. electrical signal which is amplified and applied to the control winding of the servo motor.
16. The servo motor, through the gears, alters the potentiometer output voltage signal to the E.P.R. indicator and simultaneously drives the gimbal in the same direction as the initial yoke movement until the L.V.D.T. signal to the motor is cancelled and the system stabilizes at the new setting.
17. The electronic E.P.R. system utilizes two vibrating cylinder pressure transducers which sense the engine air pressures and vibrate at frequencies relative to these pressures. From these vibration frequencies electrical signals of E.P.R. are computed and are supplied to the E.P.R. gauge and electronic engine control system (Part 10).
Engine thrust
10. The thrust of an engine is shown on a thrust- meter, which will be one of two basic types; the first measures turbine discharge or jet pipe pressure, and the second, known as an engine pressure ratio (E.P.R.) gauge, measures the ratio of two or three parameters. When E.P.R. is measured, the ratio is usually that of jet pipe pressure to compressor inlet pressure. However, on a fan engine the ratio may be that of integrated turbine discharge and fan outlet pressures to compressor inlet pressure.
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| Fig. 12-3 Electro-mechanical E.P.R. transmitter. |
12. Suitably positioned pilot tubes sense the pressure or pressures appropriate to the type of indication being taken from the engine. The pilot tubes are either directly connected to the indicator or to a pressure transmitter that is electrically connected to the indicator.
13. An indicator that shows only the turbine discharge pressure is basically a gauge, the dial of which may be marked in pounds per square inch (p.s.i.), inches of mercury (in. Hg.), or a percentage of the maximum thrust.
14. E.P.R. can be indicated by either electro- mechanical or electronic transmitters. In both cases the inputs to the transmitter are engine inlet pressure (P1) and an integrated pressure (PINT) comprised of fan outlet and turbine exhaust pressures. In some cases either fan outlet pressure or turbine exhaust pressure are used alone in place of PINT.
15. The electro-mechanical system indicates a change in pressure by using transducer capsules (fig. 12-3)
to deflect the centre shaft of the pressure transducer causing the yoke to pivot about the axis A.A. This movement is sensed by the linear variable differential transformer (L.V.D.T.) and converted to an a.c. electrical signal which is amplified and applied to the control winding of the servo motor.
16. The servo motor, through the gears, alters the potentiometer output voltage signal to the E.P.R. indicator and simultaneously drives the gimbal in the same direction as the initial yoke movement until the L.V.D.T. signal to the motor is cancelled and the system stabilizes at the new setting.
17. The electronic E.P.R. system utilizes two vibrating cylinder pressure transducers which sense the engine air pressures and vibrate at frequencies relative to these pressures. From these vibration frequencies electrical signals of E.P.R. are computed and are supplied to the E.P.R. gauge and electronic engine control system (Part 10).
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