Page 147 - The Jet Engine

Controls and instrumentation

Engine thrust the minimum thrust output can be checked under all
10. The thrust of an engine is shown on a thrust- operating conditions.
meter, which will be one of two basic types; the first
measures turbine discharge or jet pipe pressure, and 12. Suitably positioned pilot tubes sense the
the second, known as an engine pressure ratio pressure or pressures appropriate to the type of
(E.P.R.) gauge, measures the ratio of two or three indication being taken from the engine. The pilot
parameters. When E.P.R. is measured, the ratio is tubes are either directly connected to the indicator or
usually that of jet pipe pressure to compressor inlet to a pressure transmitter that is electrically
pressure. However, on a fan engine the ratio may be connected to the indicator.
that of integrated turbine discharge and fan outlet
pressures to compressor inlet pressure. 13. An indicator that shows only the turbine
discharge pressure is basically a gauge, the dial of
11. In each instance, an indication of thrust output is which may be marked in pounds per square inch
given, although when only the turbine discharge (p.s.i.), inches of mercury (in. Hg.), or a percentage
pressure is measured, correction is necessary for of the maximum thrust.
variation of inlet pressure; however, both types may
require correction for variation of ambient air 14. E.P.R. can be indicated by either electro-
temperature. To compensate for ambient mechanical or electronic transmitters. In both cases
atmospheric conditions, it is possible to set a the inputs to the transmitter are engine inlet pressure
correction figure to a sub-scale on the gauge; thus, (P1) and an integrated pressure (PINT) comprised of

Fig. 12-4 A simple torquemeter system.

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