Patent GB-985974-A (GB)
Abstract: 985,974. Aircraft instruments. MINISTER OF NATIONAL DEFENCE OF H.M. CANADIAN GOVERNMENT. Feb. 8, 1961 [Feb. 15, 1960], No. 4701/61. Heading B7W. [Also in Division G1] In a ground position indicator for an aircraft, an optical projector comprises a point source of light, a light transmitting graticule beneath the light source and provided with a representation of the aircraft, means responsive to an input analogue of aircraft track bearing to orientate the graticule and representation, and means for moving the light source relatively to the graticule in a plane parallel thereto in response to input analogues of the co-ordinates of change of aircraft ground position, whereby a pictorial representation of aircraft position and track bearing may be projected on a chart. The upper part of the projector seen in plan in Fig. 9 comprises a housing 93 having a rack 95 and guideway 92. A frame 90 has a roller 91 engaging guideway 92, and rack 95 passes through the frame and is engaged by a pinion 96 on the frame driven by a servomotor (not shown) by one aircraft Cartesian co-ordinate analogue signal. Movement of the frame by the servomotor drives a wiper on the frame along a potentiometer winding on the housing, to derive a feedback signal fed to the servomotor so that the position of the frame is dependent on the analogue input signal. The frame comprises a rack 82 and guideway 88, and the rack passes through a housing 80 having a roller 87 engaging guideway 88. The housing contains the point source of light, and a servomotor driving a pinion 84 engaging rack 82. The housing 80 is positioned along the frame 90 in the same way that the frame is positioned along rack 95, but in response to a second aircraft Cartesian co-ordinate analogue signal. Electrical connection between relatively moving parts is effected by flexible printed circuits. Below the point source of light are positioned two graticules 26, 27, shown in Fig. 6, which occupy horizontal planes. One graticule, Fig. 8, is opaque at an area between an annular part 30 and a representation 31 of an aircraft. The second graticule, Fig. 7, is opaque except at a central area 51 which extends over the areas 30, 31, and a radial slit 50. The image projected on to the chart is thus a bright ring containing representation 31, and a radial ray formed by slit 50. Each graticule has a toothed periphery 32, 53, and a recessed rim, so that it can be mounted in rollers 34, 35, or 46, 47 and a third roller (not shown) for each graticule which is urged to engage the graticule by a leaf spring. The periphery 32 of graticule 26, Fig. 8, is driven by a servomotor having an aircraft track bearing analogue input signal, and drives a transducer generating a feedback signal, so that the projected representation on the chart shows the track heading by its orientation. The position of the representation is governed by the Cartesian co-ordinate analogue signals controlling the position of the light source relatively to housing 90, and the sensitivity of the servomotors effecting this is selected to suit the scale of the chart used. The graticule 27, Fig. 7, is orientated by a servomotor under manual control, to show, by the ray of light transmitted by slit 50, the bearing of a target or destination. The setting of this manual control may be indicated on navigator's, pilot's and radar operator's instruments, and the control may be set by the navigator or radar operator. A switch may be operated to substitute the destination co-ordinates for the aircraft coordinates, the former being derived by resolution of destination range and bearing information set in manually. The range value may be indicated, and reduced to zero automatically as the destination is approached, and this information is repeated at the pilot's station. The Cartesian co-ordinates may be in terms of miles, or Mercator co-ordinates. Specifications 985,975 and 988,976 are referred to.