Patent GB-684314-A (GB)
Title: Improvements in blind landing radio systems for aircraft
IPC: G01S5/12
Filed: 1948-09-20
Abstract: 684,314. Radio - navigation. OFFICE NATIONAL D'ETUDES ET DE RECHERCHES AERONAUTIQUES. Sept. 20, 1948 [Sept. 23, 1947; Feb. 19, 1948; Feb. 19, 1948; Feb. 19, 1948], Nos. 24554/48, 24555/48, 24556/48 and 24557/48. Class 40 (vii). A radio-navigation system comprises means for displaying on a cathode-ray tube correlated information concerning the altitude, distance from a desired landing point and deviation in azimuth from a prescribed course-line of an aircraft so that a desired glide-path may be followed by the craft. In the display illustrated in Fig. 3, the spacing apart of the luminous points 18 is inversely proportional to the distance from a beacon, their lateral deflection is proportional to the azimuthal deviation of the craft and they are displaced vertically a distance proportional to the altitude of the craft. The correct glide-path is followed when the spots 18 lie on the hyperbolic lines 19 drawn on the screen of the tube, touch-down being achieved when horizontal line 20 is reached. The ground apparatus comprises a continuously rotating narrow-beam beacon, situated at one end of the landing runway. Fig. 2 shows the apparatus on the aircraft. Signals received on aerials 4, 4<SP>1</SP>, spaced apart on opposite wing-tips, as the beam sweeps past them are applied through amplifying and shaping circuits to a mixer 8 whence they are applied to the grid of a cathoderay tube 9. A further omni-directional signal, radiated by the beacon when the directional beam reaches a predetermined point in its rotation, is picked up by aerial 13 and is used to trigger time-base circuit 15 providing a horizontal sweep upon the cathode-ray tube. The tube beam is normally suppressed, but is switched on by the signal from the mixer 8 whereby luminous points 18 are produced. These points are deflected vertically in accordance with the output of a radio-altimeter 16 which is connected to the vertical-deflecting plates of the tube. In a modification of this embodiment utilizing a double-beam cathoderay tube, a display as shown in Fig. 5 is produced. In this arrangement the pulse output from mixer 8 actuates an Eccles-Jordan circuit, the output therefrom being integrated to obtain a steady potential corresponding to the distance from a desired landing point. This is applied to the vertical-deflecting plates of the second cathode-ray tube structure to produce a spot 45, which, when the craft is following the desired glide-path, lies mid-way along the horizontal line joining the two spots 18. This arrangement may be modified by interchanging the connections to the cathode-ray tube, so that the vertical deflection of the points 18 is proportional to the distance to touch-down, while the vertical deflection of point 45 is proportional to altitude. The display may be modified to indicate bank of the craft either by tilting the line 20 representating the ground or by tilting the line joining the points 18. The latter arrangement may be achieved, Fig. 8 (not shown), by coupling an artificial horizon to the slider of a potentiometer energized from the horizontally-deflecting sawtooth waveform, the slider being connected to vertically-deflecting plates. Furthermore, Fig. 9 (not shown), the radio-altimeter may be connected to the vertically-deflecting plates by means of an amplifier whose gain is controlled in accordance with windspeed so that the angle of descent of the craft is modified appropriately. In an alternative arrangement for carrying the invention into effect, Fig. 10, the apparatus on the craft comprises means 101 for delivering an output U proportional to the deviation of the craft in azimuth from a prescribed courseline, means 102 for delivering an output V proportional to the distance to a desired landing point and means 103 for delivering an output W corresponding to deviation in elevation from the prescribed glide-path. Potential V is applied to a circuit 107 which gives an output V<SP>1</SP> inversely proportional to the input, this potential V<SP>1</SP> being combined additively and subtractively with potential U in units 108 and 109 respectively, the outputs from which are applied to units 110 and 111 respectively. A sweep voltage from circuit 104, which is applied to the horizontal-deflecting plates 105, 106 of the cathode-ray tube is also applied to units 110, 111 which each deliver a pulse when their two inputs are equal, the pulses being applied to the intensity-control grid 112 of the cathoderay tube. By this means two horizontallyspaced luminous points, as shown in Fig. 3, are produced on the screen of the cathode-ray tube. To obtain a potential proportional to altitude, the potentials V and W are suitably combined in unit 113, the output therefrom being applied to the plate 115 of the cathode-ray tube to produce the vertical-deflection of the display proportional to altitude. In a modification, Fig. 11 (not shown), a display produced as in Fig. 10 is rapidly alternated to one wherein a luminous point is produced vertically displaced in accordance with the potential V, whereby as display of the type shown in Fig. 5 is produced. Specification 684,313 is referred to.