Patent GB-865009-A (GB)
Title: Improvements in or relating to apparatus for simulating the operating characteristics of turbo-jet aircraft engines
IPC: G09B9/18
Filed: 1957-05-07
Abstract: 865,009. Aircrew training apparatus. CURTISS-WRIGHT CORPORATION. May 7, 1957 [May 15, 1956No. 14548/57. Class 4. Apparatus for simulating steady-state and dynamic characteristics of a turbo-jet aircraft engine comprises a system including a simulated throttle control for producing a first signal representing requested turbine r.p.m., a system for producing a second signal representing instant turbine r.p.m., means for comparing said signals and producing a third error signal representing the difference between the instant turbine r.p.m., and the requested turbine r.p.m., means for producing a fourth signal representing a function of air pressure ratio and adiabatic temperature ratio and a computing system responsive to said error and function signals for computing actual and steady state engine fuel flow, said computing system also producing a signal for controlling the operation of said instant r.p.m. system. A simulated throttle control member 1 derives a voltage N2R representing requested engine speed at slider contact 2 of a potentiometer 3 which is energised by an alternating voltage f(T2) derived from line 126 of Fig. 3 to represent a function of simulated compressor inlet temperature. Voltage N2R is fed over line 5 to a comparing system 6 which compares it with another voltage N2, representing actual turbine speed derived from an engine speed servo 7, Fig. 1 (to be described). Card 55 of servo 6 is centre tapped and energised at its upper and lower ends by oppositely phased voltages representing respectively available acceleration fuel (Wfa) derived from card 31 of a servo 14 (to be described) and deceleration fuel (Wfd) derived from a summing amplifier  59 as the difference between a constant idle fuel " signal Ei and the answer signal Wf from a servo 10 (to be described). The difference signal N2 (requested change in engine speed) from card 55 is fed by line 8 to terminal 9 of the servo system 10. Actual engine fuel flow Wf is derived from servo 10 to which the inputs, other than that at terminal 9, are a feed-back signal Efb at terminal 11; a signal Wfss at terminal 12 representing steady-state ' fuel flow derived from a servo 14 that is 'slaved' to servo 10 during dynamic phases of fuel flow, and a system 'answer' signal Wf at terminal 13. The output from amplifier 15 drives an M-G set 16, 17 which through gearbox M drives slider 18<SP>1</SP> of potentiometer 18 and an indicator 25 to provide respectively a signal and visual indication of fuel flow. Servos 10 and 14, as stated, are coupled and in the steady-state engine operating condition both servos are balanced to represent computed fuel flow Wf. Under dynamic operating conditions however, the servo 10, which has relatively fast response receives first a " requested change in engine speed signal from system 6 and immediately moves out of step with servo 14 which has a slower response. If the throttle setting is not changed, slave servo 14 is pulled by servo 10 into step to represent a new steady-state fuel condition, the time lag corresponding to the characteristic inertia lag of the simulated turbine. Steady-state fuel flow computation primarily takes place in "slave" system 14 which comprises amplifier 26 energised by a plurality of input signals to operate through mechanism 27 a plurality of function potentiometers 28, 29, 30, 31 and 32. The inputs are feed-back signals at 33 and 34 over lines 155 and switch 156 and line 157 respectively for rate control from the generator (Switch 156 is operated by a " flame-- out relay 73 operated by an instructors switch 135, Fig. 3) ; a signal representing corrected rotor speed at 35 derived through card 18 of servo 10 and line 36b from card 63 of a servo 7 (to be described), line 36c, switch 94 and line 36d ; a signal representing rotor windmilling RPM at 37 fed over line 38, switch 158 and line 109 from a cam switch 108 Fig. 3 (to be described) ; a signal at 39 derived at card 29 through an engine " start " switch 41 ; and an answer signal at 42 from card 28 which provides also over line 44 the signal at terminal 12 of servo 10 as previously described. Actual engine speed is determined at servo 7, wherein amplifier 52 is energised at 51 by one signal, representing computed turbine r.p.m. fed over line 50 from card 32 of servo 14, which card is energised by a signal representing square root of adiabatic temperature ratio generated as described in Specification 750,010 ; and an answer signal at 54 from card 49, which signal is also fed over line 48 to amplifier 45 of servo 6 as previously described. The output from amplifier 52 is used to operate an r.p.m. indicator 62 and wipers 491 and 631 of cards 49 and 63, energised respectively by a voltage -E and a fuel flow signal from card 18 of servo 10, and the output signal from card 63 is fed to terminal 35 of servo 14 as previously described. Engine pressure ratio (ratio of turbine outlet pressure to compressor inlet pressure) is simulated by servo 65 wherein amplifier 66 receives at 67 one input from card 30 of servo 14 representing engine pressure ratio and an answer voltage at 69 from card 68, to drive a motor operating an engine pressure ratio indicator 64 and also the wipers of cards 70 and 71. Card 70. is energised by a signal T2 representing compressor inlet temperature derived over line 127 from a T2 servo, Fig. 3, and its output is fed over line 77 to the terminal 82 of the amplifier 80 of a servo 78 which operates a steady-state and dynamic turbine outlet temperature indicator 79. Card 71 is energised by a signal f(VT) representing corrected thrust derived over line 117 from an airspeed servo 103, Fig. 3, and its output is fed under normal conditions through a " flameout " switch 72 to a flight computer 74. When the flame-out switch 72 is de-energised to indicate a " no-flame " condition, the switch engages a contact 76 which is energised by a negative drag signal ¢pv<SP>2</SP> derived from airspeed servo 103. Turbine outlet temperature as stated above is determined in servo 78. Inputs to the amplifier 80 other than that on terminal 82 are an answer signal at terminal 83 derived from answer card 81 ; a velocity feed back signal from the M-G set at terminal 85 and a " dynamic " temperature signal Tdyn at terminal 84. Signal Tdyn is derived according to the difference between the answer signals from actual fuel flow computer 10 and steadystate fuel flow computer 14 obtained respectively from card 18 over line 86 and card 28 over line 87 to energise a comparing amplifier 88, the output of which is fed over line 89 ; through switch 100 controlled by " flameout" relay 73 ; line 89a ; switch 90 (camoperated by servo 6 over mechanical connection 61) and line 89b. The input Nw through switch 158 to terminal 37 of amplifier 26 of servo 14 representing rotor windmilling r.p.m.; the input f(VT) representing corrected thrust to card 71 of servo 65 and the input ¢ Pv<SP>2</SP> to contact 76 of switch 72 are derived at airspeed servo 103 and the input T2 to card 70, servo 65 and the input f(T2) to throttle card 3 are derived by the joint operation of systems M2 (Mach number) and o.a.t. (outside air temperature), all shown in Fig. 3. The windmilling r.p.m. signal Nw is obtained by energising card 98 of airspeed (h) servo 95 on its lower terminal by a voltage on line 104 from card 105 of M<SP>2</SP> servo system 106. Card 105 is energised at its lower terminal by constant signal E and is grounded through a resistance at its upper terminal so that the derived signal at slider 1051 represents a reverse function of M<SP>2</SP>. The h card 98 energised by this signal derives a signal at slider 98<SP>1</SP> that is fed to a summing amplifier 100 which is also fed by a constant voltage -E. The resultant voltage representing NW is fed by line 107 through a cam operated switch 108 forming part of the true airpseed (VT) servo to the line 109 by which it is fed to servo 14 when the airspeed exceeds 30 m.p.h. The corrected thrust signal f(VT) is derived according to the combined operation of the h, M<SP>2</SP> and VT servos. The voltage slider 971 of h card 97 is also fed by line 113 to M2 card 114 from which a signal at slider 114<SP>1</SP> is fed by line 115 to the VT card 116 from whence a signal at slider 116<SP>1</SP> representing f(VT) is fed to servo 65. The drag factor ¢ PV<SP>2</SP> is derived by taking a signal from card 97 of the h servo, as a function of air density, and feeding it over line 101 to card 102 of the VT servo 103 so that the signal derived at 102<SP>1</SP> is fed to switch 72 to represent a drag factor ¢ PV<SP>2</SP>. The signals representing T2 and f(T2) are obtained by feeding the output of the OAT amplifier 118 by lines 119 and 120 to the T2 amplifier 121 and the M<SP>2</SP> card 122 respectively. Card 122 derives at slider 122<SP>1</SP> a signal representing a combined function of OAT and M2 that is fed by line 123 back to T2 amplifier 121. The amplifier output signal, which corresponds to T2, operates the servo motor and cards 124 and 125. Card 124 is energised at its upper terminal by a constant voltage for producing at slider 1241 a signal on line 126 representing f(T2) for energising throttle card 3, Fig. 1. Card 125, also energised by a constant voltage produces at slider 125<SP>1</SP> a signal T2 fed by line 127 to card 70 of servo 65, and also by line 128 to the " relight " thyratron 133. Simulation of engine relight conditions is achieved by energising thyratron 133 with a plurality of signals which " fire" the thyratron to energise a relay 136 for opening a relight switch 131 to be described. The signals are a compressor inlet temperature signal T2 referred to above ; an altitude signal h from card 99 of h servo 95 and an airspeed signal VT from card 139 of airspeed servo 103. Simulation of engine "flame " or "flameout " conditions is obtained through the operation of a plurality of switches which a