Patent GB-775469-A (GB)
Title: Improvements relating to aerial spraying
IPC: G05D27/02
Filed: 1953-09-08
Abstract: 775,469. Selective signalling systems. RIPPER, W. E. Sept. 8, 1954 [Sept. 8, 1953], No. 24841/53. Class 40 (1). [Also in Groups XXIX, XXXIII and XXXV] A pilotless helicopter or fixed wing aircraft for aerial spraying is remotely controlled by radio. The aircraft is controlled to cover an area F, Fig. 1, in any desired pattern, e.g. by flying along a series of parallel paths C in succession. Over these parallel paths C the aircraft may be kept on course automatically, e.g. by a hyperbolic navigational aid (see Group XXXV), manual control by an operator at the transmitter V overriding the automatic course control when the aircraft has to turn as at T1 or T2 at the end of each parallel path. The switch over may be effected manually as the craft crosses the edge of area F along which a truck TR and a trailer housing the transmitter V are moved as the craft progresses from one path C to the next, and a radar MIT set may sense crossing of the craft across the remote edge of area F, and signal this crossing to the operator at V. Alternatively, a further operator may be stationed at a second control point P or R and the radar set dispensed with. The necessary control signals are transmitted from V or P to the aircraft by a pulse multiplex system using pulse amplitude modulation. The aircraft may also be maintained automatically at a fixed height above the ground (see Group XXXV). Transmitter, Figs. 7, 8, 10. An eight-channel multiplex system is shown, the channel pulse generators CG1 . . . CG8 being triggered successively under the control of a synchronizing pulse generator SPG which is itself triggered by CG8, to produce pulses timed as shown in Fig. 7, the synchronizing pulses being distinguished by having a greater amplitude. The individual channel generator output pulses are fed to respective gates G1 . . . G8 each controlled by a pulse amplitude control means PA1-PA8, the gate outputs being fed together with the synchronizing pulses to a modulating amplifier MOD for transmission over dipole DI1. The generator SPG, Fig. 10, is a blocking oscillator and the identical channel generators CG1 . . . CG8 are " one-shot " multivibrators in which TR4 is normally conductive. The trailing edge of the SPG output triggers the channel generator CG1 to block TR4 and render TR5 conducting for a predetermined time, during which an output positive pulse is fed to the gate G1 and to the channel generator CG2 which is triggered by the trailing edge of the pulse and so on for the succeeding channel generators of the train. The gate circuits G1-G8 each comprise a tetrode TET. 1-TET. 8. Where a simple on-off control is required, e.g. for switching the aerial spray on or off, the corresponding channel modulator PA. 1 may comprise a key K, operation or non-operation of which results in an output pulse of maximum or zero amplitude, respectively, during the gating period. Alternatively, if the output pulse is required to have varying depths of modulation a multi-position switch CD may be operated to short-circuit varying amounts of the resistor R20. The channel modulator G8 e.g. may alternatively comprise a free-running low-frequency multivibrator in which the ratio of the conducting times of the tubes TR6, TR7 and hence the " mark " to " space " ratio of the rectangular switching wave applied to the tetrode TET. 8 is varied by differentially operated resistors R25-R26. Amplitude control is thus obtained in that during the gating pulses, pulses are passed by TET. 8 at maximum amplitude or zero amplitude, the relative timings of the periods of these two conditions and hence the average amplitude modulation varying according to the mark space ratio. The various controls PA1 . . . PA8 are manually controlled by the operator at V, Fig. 1. Receiver, Figs. 9, 11, 12. The wave received at DI2 is amplified at RF, heterodyned at FC and the I.F. fed to detectors DET1, DET2 in parallel. DET1 passes only the synchronizing pulses to trigger channel generators CG11 . . . CG18 identical with and operating in a manner similar to the transmitter channel generators. These generators supply gating pulses to their respective gates G11 . . . G18 so that the information pulses, passed by DET1 to all the gates in parallel are separated and the signals in the channels CH1 . . . CH8 passed by the gates to their respective output circuits O11 . . . 018. Fig. 11 shows one output circuit, O11, e.g. in which the output pulses from gate G11 are connected via a rectifier D6 to a triode TR9. In the case of a simple on/off control, closure of a key such as K, Fig. 10, causes a steady stream of constant amplitude pulses in the associated channel, resulting in a steady potential being applied to the grid of TR9 to actuate a relay REL. For change-over control the multi-point control CD, Fig. 10, is used to send, selectively, one of three different signal amplitudes. The relay REL, Fig. 11, is polarized in this case and actuated to its neutral position or to its upper or lower operative position according to the signal transmitted. In either operative position one of the field coils F1, F2 of a series motor ARM may be operated to drive the motor, e.g. the steering motor, in a corresponding sense. If the amplitude modulator PA8, Fig. 10, is used, the mark/space ratio is made either small or large so that a non-polarized relay REL is caused to hold in one position for a greater time than the other. The motor will then run in a direction corresponding to the field F1, F2 which is energized for the longer periods. In another form of output circuit, Fig. 12, the gate circuit output is transformer fed to a triode TR10 to energize a polarized relay RE5 which, as described above, drives a motor ARM in one sense or the other. In this case the motor runs-assuming a constant input signal-until a potentiometer MC has been adjusted by the motor to back off the signal voltage and bring the relay to its neutral position. Actuators. The received signals may actuate the various aircraft controls (see Group XXXIII) through electro-mechanical operated racks, Figs. 13-16 (not shown), to produce both linear and angular controls.