Patent GB-356970-A (GB)
Title: Improvements relating to navigational guide systems
IPC: G01S1/02
Filed: 1930-10-17
Abstract: 356,970. Directional wireless signalling ; television. HAMMOND, J. H., Hesperus Avenue, Gloucester, Massachusetts, U.S.A. Oct. 17, 1930, No. 31120. Convention date, Nov. 2, 1929. Addition to 356,906. [Classes 40 (iii) and 40 (v).] The system described in the parent Specification, for transmitting to an aviator in foggy weather a visual indication of his actual position relative to the landing field, is modified by adapting the ground television apparatus to transmit only a view of that part of the terrain in the direct line of flight of the machine. The angular movements of the ground loop aerials are transmitted to the corresponding lamps 127, 128, 129, Fig. 1, and the point of intersection of the light rays 131, 132, 133 is followed by an eyepiece 241 as it moves over a map of the aerodrome and its surroundings. This is accomplished by rotating the handle 276 which moves the slider eyepiece 241 to and fro over a threaded shaft 237, and by another handle which rotates the disc 234 and the map about a shaft 102. The movements of the slider are transmitted by repeater gears to the television transmitter, Fig. 4, so as to maintain the distance between two shafts 341, 355 equal to the distance between the point of intersection of the light rays in Fig. 1 and the centre of the map disc 234. The rotation imparted to the map disc 234 is simultaneously transmitted by repeater gear to the shaft 355 carrying a plate 359, Fig. 4, on which is mounted a contour map of the local topography. The television transmitter comprises two lenses 332, 336, mounted on opposite sides of a rotating scanning disc 326, and a photo-electric cell 331. It is necessary that the axis 379 of the optical system shall impinge at a point on the contour map 359 which corresponds to the particular part of the landing field in the direct line of flight of the aeroplane, at any given moment. To ensure this result, the slider eyepiece 241, Figs. 1 and 3, is fitted with a " caster wheel " 256 which rotates on ball bearings 253 so as always to lag behind the direction of movement of the eyepiece 241. The corresponding angular movements of the caster wheel are made to control a reversing motor (not shown), through contact strips 251, 252, and 261, 262, Fig. 3, which, in turn, rotate a square shaft 238, Figs. 1 and 3, and thereby cause a gear wheel 244 to " follow up " the angular motion of the roller 256. The rotation of the gear 244 (which corresponds to the line of travel of the aircraft) is then transmitted by a repeater to worm gearing 344, 345 which through a rack 348 swings the disc 359 carrying the contour map about the shaft 341, so that the axis 379 of the television optical system always makes the same angle with the disc 359 as the roller 256, Fig. 1, makes with the disc 234. In this way the part of the contour map televized to the distant aviator corresponds with that part of the landing field towards which the aircraft is heading at any moment. The altitude of the craft is determined by any known method and is transmitted to a repeater 317, which moves the frame carrying the map disc 359 so that the distance of the scanning lens 336 away from the map represents the actual height of the machine above ground on the scale of the model. Automatic means are also provided for maintaining the correct focal distance between the lens 336 and scanning disc 326 as the aircraft comes gradually to ground. The televized picture is transmitted by known apparatus 310 and is projected on to a viewing screen on the instrument board of the approaching craft.