Patent GB-792676-A (GB)
Title: Improvements in and relating to flight computing systems
IPC: G09B9/20
Filed: 1955-06-06
Abstract: 792,676. Aircraft trainers. CURTISS WRIGHT CORPORATION. June 6, 1955 [June 14, 1954], No. 16198/55. Class 4. Apparatus for computing simulated true air speed in an aircraft trainer comprises means responsive to the controls for deriving signals representing the effect of thrust, gravity, profile drag, and induced drag on true airspeed, and an integrating device responsive to these signals for deriving a signal representing true airspeed. The apparatus comprises a series of interconnected motor generator servos, of which the true air speed (Vt) system 1 is typical, and comprises a summing amplifier 2 summing a plurality of A.C. input signals and energizing one winding 9 of a bi-phase motor 3, the other winding 10 of which is energized from a source e, de-phased 90 degrees from the input signals, so that the speed of motor 3 is governed in magnitude and sense by the magnitude and reference polarity of the resultant of the amplifier output. The motor 3 drives a generator 4 the winding 11 of which is energized from a de-phased source e2,the second winding 12 providing a degenerative rate feed back signal e fb . The motor rotates until the sum of the inputs to amplifier 2 is zero, when the position of its shaft represents the time integral of the amplifier inputs apart from the feed back signal. The motor shaft also drives, through reduction gearing 8 and a mechanical drive 16, the sliders 13, 14 and 15 of potentiometers 5, 6 and 7. True airspeed (V t ) system (Fig. 1). The inputs to the summing amplifier 2 are the negatives of the accelerations due to thrust 4, -T/m, gravity, +g sin #-g sin α, profile drag, Dp/m, and induced drag Di/m, where T is the thrust, m the aircraft mass, g the acceleration due to gravity, # the angle of pitch, α the angle of attack, D p  the profile drag and Di the induced drag. These inputs are derived from the other computing systems as described later. The slider 15 of a linear potentiometer 7 fed with a supply voltage -E is controlled by the motor 3, to derive a signal proportional to true air speed, which is applied to an amplifier 166 and transformer 168, the secondary 169 of which supplies a signal of Œ v t ,. The input -T/m is derived from a signal -T from a transformer 19, which is fed to the slider 22 of potentiometer 23, one end of which is earthed through a resistance 24, and connected by line 25 to the amplifier 2. The slider 22 is adjusted by a dial 18<SP>1</SP> set by an instructor according to the all up weight of the simulated aircraft. The line 25 thus receives a signal -T Im. Rate of pitch (W y ) and pitch (#) systems (Fig. 1). The rate of pitch system 33 has a pitching moment signal M p  input derived from a potentiometer 35 fed with a voltage Œ v i 2 derived as described later, and the slider 34 is positioned by the elevator control. The slider 37 of the associated potentiometer 36 is fed with a voltage Œ v t , and the derived signal 0 is fed to the pitch summing amplifier 40 of the pitch system 31. The slider 41 of the associated contoured potentiometer 42 fed with a supply voltage Œ E, derives a signal g sin # fed to the summing amplifier 2 by lines 43 and 44. Angle of attack and lift computers (Figs. 1 and 3). A potentiometer 96 in the V i <SP>2</SP> system, v i  being the indicated airspeed, is connected to a supply voltage +C2 representing the lift coefficient, derived as described later. The slider 97 derives a signal C 2  V i <SP>2</SP> which is fed to the slider 28 of a potentiometer 30 earthed through a resistance at one end which is also connected to the lift summing amplifier 102. The slider 28 is positioned by the dial 18<SP>1</SP> so that the line 100 carries a signal C 2Vi <SP>2</SP>/m. Further inputs as shown in Fig. 3. The pitch system 31 positions four sliders 104-107 of a potentiometer 103, which is connected to voltages +E at its ends. -E at its centre, and earthed at intermediate points. The potentiometer is contoured so that the sliders pick off voltages +sin #,- cos #, + as # respectively. The voltage + cos # is applied to the ends of a potentiometer 115 in the roll (0) system 116, and the voltage -cos 0 to the centre, the potentiometer being earthed at intermediate points, and contoured so that the slider 117 derives a signal -cos # cos # fed to amplifier 102. The voltages Œ sin # are applied through a resistance 109, across a potentiometer 110 earthed as shown, in the angle of attack system 32, so that the slider 112 derives a signal - sin # sin a fed to amplifier 102, the output of which is applied to a transformer 119, the secondary of which provides a signal representing the net lift, (W-L)/m, where W is the aircraft weight. This signal, Fig. 1, is fed to the slider 13 of a potentiometer 5 in the v t  system, earthed at one end through a resistor 122 and connected to supply a signal (W-L)/ Mv t  to the angle of attack summing amplifier 32<SP>1</SP>. A further input # is derived from the rate of pitch computer. The associated potentiometer 126 is connected to supply voltages ŒE through resistor 127 and is earthed as shown, and contoured so that the slider 125 derives a signal-g sin a which is fed to the v t  summing amplifier 2. Profile drag, indicated airspeed, and height systems (Figs. 1 and 4). The height summing amplifier 172 receives inputs g sin e and -g sin α on lines 178 and 177 from potentiometers 42 and 126, being the same signals as are used for amplifier 2. The feed back signal -h from the generator winding 175 is fed to the slider 14 of potentiometer 6 in the v t  system, one end of this being earthed through resistor 173, and connected to provide a modified feedback signal -h/v t  for amplifier 172. The associated potentiometer 179 and a resistor 180 are connected across a +v t  voltage, and the slider 182 derives an indicated air speed signal v i . This siganl operates an i.a.s. instrument 170 through a rectifier 183, and also provides an input to the amplifier 185 of the  Vi <SP>2</SP> system 45. This system includes a potentiometer 187 contoured to derive a square root function, whereby the -v i  feed back signal is obtained when the angular position of the motor shaft represents V i <SP>2</SP>. The profile drag coefficient summing amplifier 134, Fig. 4, sums input signals representing components of drag due to angle of sideslip #, rudder deflection #r, wing ice and angle of attack, WI, a, and wing flap angle oiii. The first component is derived by slider 132 from a potentiometer 131 earthed as shown and forming part of the side slip angle system 130. The second component is derived from the slider 137 of a potentiometer 138 supplied and earthed as shown, the slider being operated by the rudder pedal 135. An instructors' wing ice dial 74 adjusts the slider 142 of a potentiometer 143 connected across voltages -E, -2E, and derives a signal supplied in the manner shown to a potentiometer 145 in the angle of attack system 32, the slider 146 deriving the third component of profile drag. The fourth component is derived by a slider 149 of a potentiometer 150, adjustable by the trainee's wing flap dial 83. The output of amplifier 134 representing the profile drag coefficient C op  is applied to a transformer 136, which energizes a potentiometer 150, Fig. 1, in the vi<SP>2</SP> system, the slider 151 deriving a signal C op v i <SP>2</SP> which is the profile drag Dp. This signal is fed to the slider 27 of a potentiometer 29, earthed at one end through a resistor and connected by line 153 to the amplifier 2. The slider is operated by dial 18<SP>1</SP>, so that line 153 carries a signal D p /m. Induced drag, lift coefficient, and normal acceleration systems (Figs. 1 and 2). In the lift coefficient computer, Fig. 2, a signal -T from the thrust system 19 is fed to the slider 47 of a potentiometer 48 in the V i <SP>2</SP> systems 45, an intermediate point of the potentiometer being earthed through a resistor 49 and connected to an amplifier 51, so that the amplifier output represents -Tvi<SP>2</SP> which is the thrust coefficient Tc<SP>1</SP>. A transformer 53 supplies signals ŒT c 1. The signal--T c <SP>1</SP> is applied to an intermediate point of a potentiometer 55 in the angle of attack system 32 which is earthed near one end. The signal derived by slider 63 is applied to a potentiometer 78, the slider 80 of which is positioned by the trainee's wing flap dial 83, and derives a component C 2 (T c <SP>1</SP>, α, #fu) of the lift coefficient fed to amplifier 86. The signals ŒT c 1 are applied by line 54 and resistors 58i, 61 to a potentiometer 56 in the angle of attack system, which is earthed as shown, so that slider 64 derives a component C 1 (T c <SP>1</SP>, α). A potentiometer 65 in the angle of attack system is energized and earthed as shown, and the signal derived by the slider 76 is applied to a potentiometer 79, the slider 81 of which is positioned by the wing flap dial to derive a component C 1 )(α, # fw ). The instructor's wing ice dial 74 positions the slider 70 of a potentiometer 69 connected across supply voltages -E, -2E, and the derived signal is fed by line 73 and resistor 72 to a potentiometer 66 in the angle of attack system which is energized and earthed as shown. The slider 77 derives a component C 1 (WI, α). The four components are summed in a C, amplifier 86, connected to a transformer 92, Fig. 1, with outputs - Ci which are connected across a potentiometer 159 which forms part of the normal acceleration - (n) system 154. The amplifier 155 has an input Ci vii /m, L /m where L is the lift, being the same signal as is fed to the lift system amplifier 102. An answer feed back signal -n is derived from the potentiometer 158, so that the shaft position is dependent on the value of n. The shaft also adjusts the slider 162 of the potentiometer 159, which accordingly derives a signal which is a function of C 1  and n, and is taken as the induced drag