Patent GB-736200-A (GB)
Title: Improvements in or relating to aiming systems for missile-despatching apparatus
IPC: F41G9/00
Filed: 1944-05-16
Abstract: 736,200. Automatic steering systems. SPERRY GYROSCOPE CO., Inc. May 16, 1944 [Feb. 8, 1943], No. 9412/44. Class 38 (4). [Also in Groups XXI, XXXVI and XL (c)] An aiming system for the guns fixedly mounted on a vehicle or aircraft comprises a sighting means which observes the misalignment between the line of sight and the axis of the craft and guns; a computer which derives from range and rate-of-turning data the necessary lead angles for effective fire; and means for comparing the angular misalignments and computed lead angles, the differences between which should be zero in order that the craft should be correctly oriented for effective fire. The sighting means for a fixed-gun fighter preferably comprises a pulse radar apparatus for defining a line of sight to a target in which a directive radiator scans a solid conical angle about a fixed axis and in which signal voltages proportional to the angular position of the line of sight with respect to the fixed axis are derived from the modulation of the reflected signals and are fed into a computer. The radar apparatus is first arranged to perform a searching operation in range during which in formation as to the range, azimuth and elevation of all targets within the field of the apparatus may be displayed. The apparatus is then caused to track a selected target in range and supplies the present position of target data to the input of a computer which determines the instantaneous lead angles in azimuth and elevation. The pilot is caused to fly the aircraft by the indication on a cathoderay tube so that the instantaneous azimuth and elevation of the target with respect to the axis of the craft (the gun axis) are equal and opposite to the corresponding lead angles computed and the craft and guns are correctly oriented for effective fire. An automatic pilot system may also be incorporated whereby the aircraft may be flown automatically in such a manner that it is correctly oriented to secure a hit. Radio apparatus, Fig. 1A.-This is similar to that described in Specification 621,485. Pulse transmitter 3 is modulated by pulses B, Fig. 6, under the control of triggering pulses B produced by pulse generator 2 from the sinusoidal output A of the control oscillator 1. The scanning radiator, a simplified version of that described in Specification 616,522, [Group XL (c)], comprises a parabolic reflector 6 mounted on a supporting column 7 adapted to be rotated about a spin axis 8 by motor 9 and gearing 10, 11. The reflector has its axis 12 offset from the spin axis and is energized with pulses C from the transmitter through wave-guides 4, 18 and 21, a rotating joint 20 being provided. A deflecting plate 19 is provided and a fan-shaped beam of radiation is thus radiated into a solid conical angle of space due to the reflector spin. The axis 8 is normally the fore-and-aft axis of the craft and coincides with the gun axis, although this is not essential. Energy reflected from targets is received by reflector 6 and passes through wave-guides 21, 18 and 4<SP>1</SP> to the receiver 23, a limiter 22 comprising a resonant gas-filled chamber being inserted in wave-guide 4<SP>1</SP> at such a position that when it is ionized by each transmitted pulse it protects the receiver from the transmitted pulse, a high impedance being presented by wave-guide 4<SP>1</SP> at its junction with waveguide 4. The receiver is also blocked during transmission by a pulse fed from the pulse generator 2. The signal output from the receiver, consisting of noise and received reflected pulses such as 24, 25, 26 shown in Fig. 6 (D), is fed to a range gating system which selects a particular signal and feeds it to the control grid of the cathode-ray tube indicator 62 to remove the blackout. The reflected pulse from a particular target will vary in amplitude at the spin frequency, the amplitude and phase of the variation depending upon the amount and direction of the angular deviation of the line of sight to the target with respect to the spin axis. Search operation, Fig. 1A.-With switch 32 in the search (S) position a constant D.C. voltage is fed to the servo system 34 to cause rotation of the contact 37 of a range potentiometer 38, a saw-tooth voltage wave L, Fig. 6, being fed over leads 44, 45 to a delay multivibrator 46 which is also fed with the trigger pulses B from pulse generator 2. The delay multivibrator produces on lead 47 a square wave as shown in Fig. 6 (E), which is initiated by the trigger pulse and has a duration proportional to the instantaneous magnitude of the saw-tooth wave. The square wave is fed to the " early gate pulse" generator 48 which produces in its output leads 49, 50 a voltage pulse as indicated in Fig. 6 (F), which is initiated at the end of the square wave from the multivibrator. The " late gate pulse" generator 55 produces on lead 51 a pulse, Fig. 6 (G), equal in duration to but initiated at the termination of the " early gate pulse" received on lead 50. The gate pulses are fed to coincidence circuits 27, 28 which are also fed with the receiver output and produce on their output leads 52, 53 pulses corresponding to those portions of a receiver signal which coincide with the gate pulses. With the range gating system instantaneously set as shown in Fig. 6 (F) and (G), voltages pulses as indicated at Fig. 6 (H) and (I) will be produced on leads 52 and 53 and the output of the summation circuit 30 consists of a pulse, Fig. 6 (K), which is fed to the grid of the cathode-ray indicator tube 62 to remove the blackout. An indication is thus visible on this cathode-ray tube only when the rangegate setting allows a reflected signal to pass. A two-phase generator 15, driven by gearing 13 from the spinning reflector, produces on leads 16, 17 two 90 degree phase-displaced reference voltages corresponding to the azimuthal and elevational components of the angle made by the reflector axis with the spin axis. These voltages are fed to the deflector plates of the cathode-ray tube through modulators 64, 65, which are also fed with the voltage from the range potentiometer 38 over lead 66, switch 67 being in the search (S) position. The electron beam is thus caused to trace out a circle of radius corresponding to the setting of the range gate, a visible indication consisting of a circle or portion of a circle being produced during the interval when the setting of the range gate substantially corresponds with the range of a target as shown at 73, 74 and 75, Fig. 3, which shows indications from three targets as they would appear successively. The radius of the indication corresponds to the range of the target which may be measured on a scale 77. Variation of intensity of the trace results from the spin frequency variations in received signal pulses and provides an indication of the amount and direction in azimuth and elevation of angular deviation of the line of sight to the target with respect to the spin axis. An incomplete circular trace indicates that the target is outside the fan-shaped radiated beam during a portion of the spin cycle, while an equi-intensity trace such as 74, Fig. 3, indicates a target lead ahead. Whenever a target is encountered during the range searching operation the system is automatically switched to the tracking condition, the pulses on lead 54 being rectified at 78 and fed via lead 79 and normallyclosed switch 80 to energize solenoids 81, 82 and so pull switches 67 and 32 to the track (T) position against the tension of springs 83, 84. The searching operation may be retained by holding switch 80 in its open position, the apparatus being caused to track a selected target by releasing switch 80 just prior to the time when that target indication is due to appear on the cathode-ray tube screen. Tracking operation.-If the range gate provided by the output of the delay multivibrator, Fig. 6 (E<SP>1</SP>), and the two gate pulses, Fig. 6 (Fl and G<SP>1</SP>) is not completely coincident with the signal pulse, such as 24<SP>1</SP>, Fig. 6 (D<SP>1</SP>), the outputs from the coincidence circuits 27, 28 will not be equal, one output pulse being shorter than the other as shown at Fig. 6 (H<SP>1</SP> and I<SP>1</SP>). These pulses are fed over leads 87, 88 to the rectifier 86 which produces on leads 89, 90, D.C. voltages corresponding to the rectified outputs from the coincidence circuits. These voltages are fed to a subtraction circuit 91, the output from which, Fig. 6 (J<SP>1</SP>), comprires a direct voltage of magnitude and polarity dependent upon the outputs from the coincidence circuits, and which is zero when the setting of the range gate is correct. This output voltage is fed over lead 92 to provide the input control voltage for the servo system 34 and thus by controlling the rotation of the range potentiometer 38 causes the range gate always to be correctly positioned to track the target in range. During the tracking operation the voltage appearing on leads 44 and 66 is proportional to the present range Do of the target. The received pulses on lead 54 are conducted over lead 56 to a detector and filter 133, Fig. 1B, where the spin-frequency sinusoidal variation in amplitude is extracted and fed over lead 93 to phase-sensitive amplifiers 94, 95. These amplifiers have fed to them also the azimuth and elevation voltages on leads 16 and 17 from the two-phase generator 15, and produce on their output leads 97, 96 direct voltages and magnitude and polarity corresponding to the components Ao, Eo of the voltage on lead 93 which are in phase with the azimuth and elevation reference voltages. Computing system.-In order to compute the future position of the target for a hit, the time of flight to is first determined as the product of three functions of present range (Do), height (H) and indicated air speed (I.A.S.) respectively. The logarithm of the function of H is first introduced as a rotation of ring 102, Fig. 1A, by knob H and gear 104