Patent GB-857671-A (GB)
Title: Improvements in or relating to approach aids for aircraft
IPC: G01S1/02
Filed: 1957-06-27
Abstract: 857,671. Aircraft landing approach aids. COMMONWEALTH OF AUSTRALIA. June 27, 1957 [July 4, 1956], No. 20383/57. Class 4. An airborne aircraft landing approach aid comprises means superimposing on the external scene, in the pilot's normal field of vision, a visual display comprising indicia providing the pilot with a direct indication of the position of the aircraft relative to the horizon. Fig. 5 shows the optical system, wherein the light from a graticule 21 illuminated by a lamp 42, is incident in turn on a prism 43, a Dove prism 27 rotated in accordance with the angle of bank as detected by a gyro vertical, a mirror 28 deflecting the light in accordance with the yaw detected by a directional gyro or gyro compass, a mirror 26 deflecting the light in accordance with the angle of pitch detected by the gyro vertical, a prism 44, a collimating lens 45, and the windscreen or other glass plate 46 set at 45 degrees to the vertical, so that the image of the graticule appears to the pilot to be in front of him, and is stabilized in pitch, roll, and yaw. The pilot can disable the stabilization in yaw. The image is shown in Fig. 2 as a horizontal row of dots 24, and a vertical row 25, the interval between dots subtending an angle of 1 degree at the pilot's eye. Alternate dots are larger and smaller, and the dots of 5 degrees from the image centre are marked accordingly. The light from a second graticule 23, Fig. 5, is deflected by a mirror 48 tiltable about two axes at right angles in accordance with signals received from localizer and glide path beams. The deflected light is then fed through the same optical path as that from graticule 21. The displacement of the image of graticule 23 (shown in Fig. 4) from that of graticule 21 thus indicates the deviation of the aircraft from the radio beam path. The light from graticule 22 is deflected by mirrors 32 and 33 tilted in accordance with the outputs of a computer having as inputs the wind speed and direction and the aircraft weight, all set by the pilot, and the airspeed, rate of climb, and angle of incidence. The corresponding " aiming point " image is shown in Fig. 3. Under visual flying conditions, while in the horizontal part of the approach, the pilot " flies " the miaing point image on to the centre of the image of Fig. 1. When the desired touch down point on the runway appears at an angle of depression, as measured by the dots 25, equal to the desired glide path angle, the pilot " flies " the aming point image onto the desired touch down point. Under instrument flying conditions, the horizontal part of the approach path is flown from a conventional I.L.S. instrument display. For the final approach, the pilot " sets " the desired glide path angle, say 2¢ degrees, the image of Fig. 4 moving down to the corresponding position on dots 25. The pilot then " flies " the image of Fig. 3 onto the image of Fig. 4, which results in an asymptotic approach to the desired glide path. A further image, e.g. a triangle circumscribing the aiming point image, may appear during the last few hundred feet of descent. Air speed information may be provided by a visual display by the variation of aural tones, or by arranging an airspeed instrument to operate disc or tape recordings to " say " the airspeed at set intervals of time.