Patent GB-626084-A (GB)
Title: Means of presentation of blind approach information to the pilot of an aircraft preparing to land
IPC: G01S1/02
Filed: 1946-11-11
Abstract: 626,084. Kinematograph apparatus ; kine. matograph picture films. PARKES, G. H. Nov. 11, 1946, Nos. 33389/46 and 1196/47. [Classes 97 (i) and 98 (ii)] [Also in Groups XXVI, XXXV and XL (c)] In a kinematograph system for providing the pilot of an aircraft with a coloured stereoscopic picture of the view seen from the aircraft in conditions of good visibility, means are provided for controlling the speed of the film by means of radio signals radiated from a beacon on the ground. Means are also provided for blanking out the edges of the projected image in accordance with the deviation of the craft from a landing-path defined by the radio beacon, for rotating the image in accordance with the banking of the aircraft, and for automatic threading of the film after the insertion of a fresh spool. Images of certain of the pilots instruments are formed in a space below, and the view through the wind-screen is presented above, the image of the film. Control of display in accordance with deviations of the craft from the landing beam.-Light from the source 33, Fig. 9, is split into two beams by the double prism 113 and is projected on to the translucent screen 116 immediately behind the two pictures 42a, 42b of the stereoscopic pair. A colour, filter 115 may be provided. if desired. Light from the pictures 42a, 42b is passed to the eye-pieces 29a, 29b respectively, along optical paths containing the prisms 128a, 128b. These prisms are controlled by a gyroscope or a pendulum so that thev rotate when the craft banks and the picture seen by the pilot rotates accordingly. A diaphragm 117, shown in greater detail in Fig. 13, is arranged in the light-path, so that an image thereof is formed upon the screen 116. The diaphragm 117 comprises two plates 145a, 145b, which form the pointers of two moving- coil galvanometers controlled by the signals received from the landing beam. The plates are deflected in accordance with deviations of the craft from the beam so that the edges of the picture are darkened as shown in Fig. 13a (which indicates that the craft is above and to the left of the beam). Radio control of projector speed.-The film which is prepared by an aircraft flying along the landing beam in conditions of good visibility, incorporates a sound-track 42c, Fig. 13a, of the beacon signals received by the aircraft. The sound-track signals are compared differentially with signals received by the aircraft making the blind landing and any difference in amplitude is used to control the setting of a vane governor (see Groups XXVI and XXXV) which so controls the projector speed that the difference in amplitude between the signals is eventually reduced to zero. The film view then seen corresponds to the actual position of the aircraft. Further adjustment is provided by a periodic checking of the position of the film. The film has a plurality of slots along its length and corresponding to these there is a plurality of radio beacons 155, 156, 157, Fig. 15, along the landing path 154, each radiating signals upwards in a narrow beam. A roller 158, Fig. 16, presses against the film 42 and when it comes to a slot it passes through into a recess 168 and causes contact 164 to open, thereby stopping the projector motor. When a signal is. received from the corresponding beacon, the electromagnet 162 is energized, contact 164 is closed and the motor commences running again. The slots, corresponding to the separate beacons, have different transverse spacings across the film and corresponding to each there is a re-setting mechanism, as described, actuated by its respective beacon. The motor speed is arranged to be very slightly fast so the re-setting operation is performed correctly as each beacon is passed. Film threading mechanism, Fig. 6.-A length of flexible steel strip 76 is permanently threaded in position upon the receiving reel. Its free end which has a small hook 77 is magnetized so that it is attracted and held by permanent magnet 78. The film upon spool 36 has a steel tongue 80 attached to its free end. The spool is rotated by an external knob until the tongue 80, which is also attracted by the magnet 78, engages with the hook 77. Further movement is prevented by a stop on the end of the magnet 78. When the motor is started, the leader 76 draws the film with it on to the receiving spool. Details of optical system.-Means are provided for adjusting the spacing of the eyepieces 29a, 29b. The rectangular prisms 121a, 121b, Figs. 9 and 14 are coupled by linkages 127a, 127b to the eye-pieces so that on rotating the head 123, the prisms are rotated and the beams are displaced to keep their axes centralised within the eye-pieces. Means are also provided for producing, in the focal plane of the eye-pieces, images of the altimeter dial and airspeed indicator so that the pilot may observe these dials while looking at the kinematograph picture. According to the first Provisional Specification, the apparatus for indicating deviation of the craft from the landing beam comprises a frame driven by a clockwork motor controlled by the beacon signals received. Also mounted within this frame is a gyro-controlled sub-frame upon which the kinematograph projector is mounted. In this arrangement there is no continuous control of the film-speed ; instead the interval between the instant that the film is stopped by the pawl falling into the slot in the film and the instant that it is re-started by the beacon signals is measured and used to adjust the governor setting. In the system described in the second Provisional Specification a warning indicator, such as a lamp, is provided to show when the film has started. Also cross wires controlled gyroscopically for roll and projected on the picture seen by the pilot co-operate with fixed cross-wires in the eye-pieces of the viewing arrangement.