Patent GB-750010-A (GB)
Title: Improvements in or relating to apparatus for simulating the operation of turbo-jet engines
IPC: G09B9/18
Filed: 1953-05-27
Abstract: 750,010. Flight training apparatus. CURTISS-WRIGHT CORPORATION. May 27, 1953 [June 2, 1952], No. 14754/53. Class 4. [Also in Group XXXVI] Apparatus for simulating the operation of a high-speed aircraft turbo jet engine for use in training aircrew comprises a simulated throttle control producing a control signal means responsive to simulated altitude, Mach number, sea level temperature and true airspeed derived from preset adjustments and from flight simulating apparatus of the kind described in Specification 748,557 for producing corresponding control signals, and a complex analogue computer comprising multiple interacting self-balancing and variable potentiometer actuating servosystems which determines and displays the simulated fuel flow rate, turbo jet rotational speed in r.p.m., fuel quantity remaining, outside air temperature, and the turbo-jet tailpipe temperature corresponding 'to the prevailing simulated flying conditions. In Fig. 1 an integrating servo-system, comprising a summation amplifier 1 energizing control winding 6 of a biphase motor 2 coupled to a biphase generator 3 having an output winding 9 and a reference winding 8 energized together with the motor reference winding 7 from an A.C. source phase shifted 90 degrees from a master control voltage, receives a number of alternating control voltages from simulating apparatus described in the said Specification which represent components of dh vertical airspeed representing - together with dt a velocity feedback voltage from the generator output winding and is geared to drive linear ganged potentiometers 11, 12 together with simulated altitude indicator 13 in dependence on the magnitude and phase sense of the resultant input signal, so that the angular rotation of the potentiometer and indicator system represents simulated altitude h. Potentiometer 12 is energized with a reference alternating voltage E at its lower end and earthed at its upper end over a resistance determined by the rate of decrease of ambient temperature with increasing altitude so that the slider derives a voltage which is applied to the input of a similar servo-system 17, 5 driving ganged potentiometers 18, 19, 20 of which 19 and 20 are linear and 18 follows a square root law. The input also receives a velocity feedback voltage from the generator output, a voltage representing sea level temperature from external potentiometer 21 (centre tapped to earth and supplied with oppositely phased alternating voltages E at each end) and a balancing voltage from the slider of potentiometer 20 energized from a reference alternating voltage E. The servomotor operates until the resultant input voltage is reduced to zero at which the angular rotation potentiometers and the indicator 23 represent the outside air temperature OAT. A similar servo-system 27, 5 energized by signals from the Mach number simulating system described in the said Specification angularly rotates linear potentiometers 25, 26, 28 through an angle representing the simulated Mach number. Potentiometer 18 energized by a reference voltage E at its upper end in series with a resistance to earth at its lower end develops a voltage dependent on ##, where # is a function of OAT at its slider, which energizes potentiometer 25 in series with an earthed resistance at its lower end to develop a slider voltage, dependent on ## 2 , where # 2 =adiabatic temperature ratio =Tam/Tsl (γ-1)/2 (M<SP>2</SP> - 1) and Tam = ambient temperature, Tsl=sea level temperature, M=Mach No., γ=specific heat ratio, which is reversed in phase by amplifier 29 and transformer 30 to energize the lower end of altitude potentiometer 11 in series with an earthed resistance at its upper end to develop a slider voltage representing ### 2 . This voltage energizes the upper end of potentiometer 28 in series with an earthed resistance at its lower end to develop a slider voltage # 2 , ## 2  which is reversed in phase by amplifier 34 and transformer 35, where # 2  is the relative pressure ratio P input/P sea level=Pam+kp VT<SP>2</SP>/2 and p=air density, Pam = ambient pressure, VT = true airspeed. Potentiometer 26 is energized at its upper end in series with an earthed resistance at its lower end by the slider voltage (representing - #) from potentiometer 19 energized from reference voltage source E at its upper end in series with an earthed resistance at its lower end to develop a slider voltage representing # 2  at terminal 38a after reversal in phase by amplifier 37 and transformer 38 for application to potentiometer 97 (Fig. 3). In Fig. 2 a simulated throttle control 40 operates a linear potentiometer 59 energized by an alternating voltage E in series with an earthed resistance at its lower end to develop a slider voltage proportional to the throttle opening and simulated R.P.M.(N) and also operates a cam 47 to open switch 43 when the throttle is closed and vice versa. Switch 44 is operated by relay 48 and switch 49 when the fuel valve (not shown) is opened, and switch 45 is closed after a time delay when the throttle is opened, whereby the automatic firing of the engine on throttle opening is simulated. Closure of the above switches energizes relay 41 to close contacts 52, 52a to the " fired " position and develop R.P.M. voltage from potentiometer 53, energized by the reference voltage and operated by the R.P.M. servo-system 55, 5 (Fig. 3). When the engine is unfired relay 41 is deenergized, and contacts 52, 52b are closed, whereby a voltage is derived through switch 56, 56a (closed by relay 57 when air door opening simulation switch 58 is operated) direct from the throttle opening potentiometer. When switch 58 is inoperative, switch 56 is earthed through contact 56b. Servo-system 54, 5 driving linear potentiometers 61, 62 thus receives an input voltage representing R.P.M. prevailing in either the fired or unfired condition of the jet engine, providing the air doors are open, and also receives a velocity feedback voltage from the generator together with a voltage from potentiometer 61 which is energized by a voltage representing - ## 2  from transmitter 30 (Fig. 1), so that the servosystem operates to reduce the resultant input voltage to zero and rotate potentiometers 61, 62 through an angle proportional to the equivalent R.P.M. value defined as N/## 2 . Potentiometer 62 is energized from the slider of linear potentiometer 63 driven by the Mach number servosystem 27 and energized in turn from linear potentiometer 64 driven from the altitude servo-system 1 while fed with a voltage proportional to +# 2 ## 2  from transformer 35 (Fig. 1), so that the slider voltage of potentiometer 62 represents total fuel flow Wf as a function of equivalent R.P.M., N/## 2  altitude, and Mach number and is supplied to amplifier 67 in phase opposition to a reference alternating voltage representing the idling fuel flow Wi, so that the antiphase output voltages of transformer 68 represent the fuel flow increment (Wf - Wi). An integrating retroactive servosystem 69 is supplied with this voltage, and the reference idling fuel flow voltage drives a linear potentiometer 69b energized by a reference voltage to derive a voltage energizing a simulated fuel gauge 69c. In Fig. 3 the simulated throttle control 40 operates potentiometer 70 energized by an alternating reference voltage to derive a signal corresponding to simulated R.P.M. (N.) as a function of throttle opening, and is supplied to the input of amplifier 72 together with a fuel flow increment signal (Wf - Wi) from transformer 68 (Fig. 2) and a balancing R.P.M. signal N from potentiometer 81 of the simulated R.P.M. servo - system hereinafter described. When the engine is accelerating normally, relay 74 is operated by thyratron 73 energized by the amplifier output so that contacts 75a, 75 and 77a, 77 are closed, while when the engine is idling the thyratron and relay are inoperative so that contacts 75, 75b and 77, 77b are closed. When the engine is fired, relay 41 is operative to close contacts 76, 76a and 78, 78a while when it is unfired, the relay is inoperative and contacts 76, 76b and 78, 78b are closed. Thus in the normal fired condition of the engine the simulated R.P.M. servo-system is controlled by the signal from potentiometer 70 and by a rebalancing signal from potentiometer 81 driven by the servosystem through an angle proportional to the simulated R.P.M. determined by the throttle setting while when the engine is idling but fired the sole input to the servo-system is the signal (Wf - Wi) derived from transformer 68 (Fig. 2), which determines the rotational angle of the servo-system as a function of the fuel flow increment. When the engine is unfired and the simulated air doors are open, the simulated R.P.M. servo-system 55, 5 is supplied with a voltage representing true airspeed from transformer 88 energized by amplifier 87 in simulating apparatus described in the said Specification, together with a rebalancing voltage from potentiometer 81 so that the angular rotation of the simulated R.P.M. servo-system is a function of the true simulated airspeed T T . With the air doors closed, relay 57 is released, and contact 79 is grounded so that the input to the R.P.M. servo-system is zero for zero indication. The simulated engine speed is registered by indicator 85 driven by the R.P.M. servosystem and a corresponding signal voltage is derived on line 94 from the linear potentiometer 86 driven thereby. Fig. 3 also shows a system for simulating the turbine outlet temperature (TOT) as a function of Mach number, turbine R.P.M. and ambient temperature, wherein a # 2  signal from transformer 38 (Fig. 1) energizes a linear potentiometer 97 driven by the Mach number computing servo-system to develop a signal energizing a linear potentiometer 98 driven by the N/## 2  equivalent R.P.M. servosystem (Fig. 1) to develop a signal representing the TOT temperature. When the