Patent GB-895562-A (GB)
Title: Improvements in or relating to electric analogue computers
Inventor: JOHN PHILIP BOWEN
IPC: G09B9/18
Filed: 1958-08-11
Abstract: 895,562. Electric analogue computers. COMMUNICATIONS PATENTS Ltd. Aug. 11, 1958, No. 25772/58. Class 37. The computer calculates the performance of a simulated aircraft turbine and comprises a " Mach number servo " 40 controlled by the Mach number of aircraft simulated speed, said servo comprising pairs of input and output points 1-10 which are respectively interconnected by controlling devices which modify the associated input by a predetermined function of Mach number (MN). Data signals representing P1, T1 and #T1 (where P1 and T1 represent ram pressure and temperature) are obtained from outputs 1, 7, 2 of the servo, the corresponding inputs being supplied with signals representing Palpha, Talpha and #Talpha, respectively (where Palpha, Talpha are ambient pressure and temperature) and the corresponding controlling devices represent MN<2> <3.5> Mach number functions [#(MN)], (1+#) -) 5 #MN<2> #MN<2> (1 + -), # 1 + - respectively (where #= 5 #5 intake efficiency), the said ram data signals being then used to derive other values defining engine performance. Inputs corresponding to Mach number MN, Palpha, #/Talpha and Talpha are supplied at terminals 1a, 1b and 1c. The " controlling devices " referred to above are potentiometers contoured to provide the desired function of MN. The outputs from servo 40 all in terms of P1 and/or T1 are provided as inputs to the three sections 43, 44, 45 (Figs. 2 and 3) of a highpressure compressor r.p.m. servo controlled by engine normalized R.P.M. Ne. An analogue of this speed is derived from servo amplifier 35 controlled by switching amplifiers 32, 33, 34 which operate in dependence on fuel flow and compressor speeds, so that the output of amplifier 35 is a correct analogue of Ne for all conditions of flight. The inputs and outputs of servo sections 43, 44, 45 are connected by potentiometers profiled to give predetermined functions of Ne. The following equations are derived:- Steady state conditions. Engine fuel flow.-Information on this is provided at outputs 1, 2 of ram pressure servo 41 at amplifiers 24, 25, F1 representing idling flow and #F1 the difference between maximum flow and idling flow. Actual fuel requirement F = P1 #T1f1(Ne) - P1 #T11f4(MN)f2(Ne), The first term represents the actual fuel requirement and is derived from the first output of servo 45. The second term represents a change in fuel requirement due to changes in Mach number and is derived at the second output of servo 45. F1 - #F (see above) also represents the fuel flow but in some circumstances not as accurately, and either expression can be switched alternatively to fuel flow indicator 661. Turbine discharge pressure P8 is shown to be P1f6(Ne) - P1f3(MN)f7(Ne) the first and second terms being obtained at the fourth and fifth outputs of servo section 43. Jet pipe temperature T4 = T1Te (where Te= normalized jet pipe temperature). T4 is shown to be T1 f8(Ne) - T1f6(MN)f9(Ne) the first and second terms being obtained at the outputs of servo section 44, the voltage output representing jet pipe temperature decay from unit 48 and a bias signal from terminal 8 representing the conversion from degrees absolute to degrees centigrade also providing inputs to amplifier 29 which is coupled to an indicator 63. High pressure compressor speed NHP = #T1NE #T1 is applied to the third input of servo section 45, the third output then giving the required output, which is connected to an r.p.m. indicator 64. Low pressure compressor speed NLP = #T1f10(Ne) + #T1f5(MN)f11(Ne). The two terms are given by the fourth and fifth outputs, respectively, of servo section 45, and connected to an r.p.m. indicator 64. Transient conditions. An acceleration control unit is provided to limit the quantity of fuel supplied to the engine under conditions and the computer is required to show the correct compressor speed and fuel flow response times. The value for instantaneous fuel flow from amplifier 30 is compared with a bias value F max. in a switching unit 32 which operates when the fuel demand exceeds F max. to remove the normal drive signal to servo amplifier 35 to substitute therefor a fixed integrating signal equivalent to a fixed flow which is answered by a tacho control signal derived from a potentiometer cord on the servo 43, 44, 45 to give the correct acceleration response rate. Fuel flow data.-The throttle signal is removed from the fuel flow servo 49 by switching unit 32 and substitutes the actual fuel consumption rate signals at the third and fourth inputs of amplifier 31 from the servo section 45 so that fuel flow and high-pressure compressor speed move in step. High-pressure compressor overspeed governor is simulated by the switching unit 34 and takes control from the acceleration control unit at a high-pressure compressor speed value of 8,000 r.p.m. when the engine can absorb full throttle fuel and accelerate to its maximum speed. The governor holds back the fuel supplied to maintain a steady speed of 10,000 r.p.m. and unit 34 is held in its normal inoperative state by a bias signal corresponding to a speed of 9,980 r.p.m. When this speed is exceeded unit 34 operates to remove the normal drive to amplifier 35 and substitute input signals from unit 34 to bring speed of servo 46 to 10,000 r.p.m., a signal on fuel difference amplifier 30 at the second input of unit 34 assists the bias thereof to bring it into inoperative state. Low-pressure compressor overspeed governor system 33 is similar to system 37. Idler governor characteristic is provided for in the provision of the idle fuel barostat curve. Engine flameout condition, i.e. when the burners are not alight, provides windmilling data represented by two formulµ giving High pressure and Low pressure compressor speeds NHp=K4###MN##T1 and NLP=K6Ne ##T1 where K7, K6 are constants. Fuel flow data can be disconnected from fuel difference system 30 under true conditions and the required speeds read on lines 194, 195/196, respectively. Net engine thrust XN=XG (gross thrust)+XD (intake momentum drag) and is derived as the following equation:- K1P1f3(Ne) - K1P1f1(MN)f4(Ne) - K1Palpha - K3P1f2MNf5(Ne) where K1 is a constant for a particular engine. The first and second terms are derived from the first and second outputs of servo 43, the third term from terminal 55 and the fourth term from the third servo output, all the terms being combined by an amplifier 26.