Patent GB-1028329-A (GB)
Title: Jet engine analyzer
IPC: G06G7/64
Filed: 1964-02-18
Abstract: 1,028,329. Electric analogue calculating. UNITED AIRCRAFT CORPORATION. Feb. 18, 1964 [Feb. 19, 1963], No. 6672/64. Heading G4G. An arrangement for analysing the performance of a jet engine to ensure that it is functioning properly includes apparatus for providing a first signal in accord with the ratio of two engine pressures, one of which is at the outlet of the intake diffuser of the engine and the other is downstream of the outlet, and an arrangement which responds to this first signal to provide a second signal corresponding to the nominal value of an engine parameter (such as fuel flow, exhaust gas temperature or a rotational velocity) which varies as a function of the said pressure ratio for an engine in normal condition operating with a standard temperature at the outlet of the intake diffuser. A third signal corresponding to the real value of the parameter is also derived and corrected by reference to the actual temperature at the outlet of the intake diffuser to the standard temperature to provide a fourth signal. The second and fourth signals are then compared to determine any deviation in the parameter. An arrangement according to the invention is shown in Fig. 1, where the intake diffuser outlet pressure (P2) and temperature (T2) are measured at 32 and 36. Direct measurements of fuel flow (W), temperature at the inlet of the exhaust nozzle (T,), and the speeds of the low and high pressure sections of the twin spool engine (N1 and N2) are measured by the units 11-14. The pressure ratio between the intake diffuser outlet pressure and the inlet to the exhaust nozzle is determined at 39. The nominal values W(PR), T7(PR), N2(PR) and N1(PR) for the given pressure ratio at a standard temperature are derived in the function generators 20-23 respectively. In the units 33 and 37 the ratios #2 = T2/T0 and D2 = P2/P0, where T0 and P0 are a standard temperature and pressure, are evaluated. The apparatus shown determines the differences between the observed values, corrected to standard temperature and pressure, of W, T7, N2 and N1 and the nominal values calculated from the proper relation between them and the pressure ratio PR = P7/P2, by means of the equations The procedure adopted is to evaluate the logarithms of the quantities involved, in the function generators 16-19, 24-27, 34, 35 and 38, and add them (with the appropriate signs) in the units 28-31, wherein also antilogarithms are taken, to yield the required outputs. The various functions generated in the units 20-23, and the logarithms and antilogarithms functions derived throughout the apparatus are obtained by piece-wise linear synthesis, using circuits incorporating diodes biased from potentiometer chains. A logarithmic function is typically generated by the circuit of Fig. 2 (not shown), unit 53 being an output amplifier, resistors 48-51 being voltage dividing, break point determining resistors, and resistors 45-47 being slope determining resistors. The circuits 33 and 34 may be combined in the circuit shown in Fig. 3a, where T2 and a negative reference - T0 are added across the resistors 56a, 56b, to give T2 - T0=T0(T2/T0 - 1). A change of scale eliminates the factor T0, and it is desirable to use the value T2/T0 - 1 as an input to the logarithm generator including the diodes 64-66 and amplifier 76 so as to transpose the origin. When #2(T2/T0) is greater than unity, the generator including the diodes 64-66 is operative. When #2 is less than unity a linear positive output is initially obtained from the amplifier 76, but the variable feedback around this amplifier due to the circuit incorporating the diodes 78-80 ensures that the amplifier delivers the required output. The circuits 37 and 38 of Fig. 1 may be provided by a similar arrangement. The function generating circuits 20, 24 may be combined in the arrangement of Fig. 6 (not shown). The output P7/P2 from the unit 39 is fed to the amplifier 130 which has a feedback connection incorporating the diodes 132-134, arranged so that the function - W(PR) is generated. This is fed directly to the part of the circuit incorporating the diodes 145-147 to generate the required logarithm. The circuits 21-23, 25-27 may be provided using similar diode circuits (Figs. 7 and 8, not shown). The various logarithms are added (with suitable sign) at the input of a feedback amplifier 225 (Fig. 9a (not shown), which illustrates the circuit of unit 28, Fig. 1). The amplifier output is thus -1n(1+#W) which is approximately -#W. Components 227-245 serve as an antilogarithm generator, with allowance for unity shift, so that #W is obtained as the output of the amplifier 236. #T7, #W, and #N2 are obtained using similar circuits with the appropriate inputs as shown in Fig. 1 (Figs. 10 and 11 not shown). The magnitudes of these difference signals indicate whether or not the jet is functioning properly.