Patent GB-849568-A (GB)
Title: Improvements in or relating to visual position-indicating arrangements
Inventor: FERGUSON HAROLD MATTHEW
IPC: B64F1/20
Filed: 1957-12-20
Abstract: 849,568. Optical projection systems; lenses. GENERAL ELECTRIC CO. Ltd. Dec. 5, 1958 [Dec. 20, 1957], No. 39763/57. Addition to 793,868. Class 97(1) [Also in Group XXXVIII] An arrangement for providing the pilot of an aircraft approaching the deck of an aircraft carrier with an indication of his angular position with respect to an approach plane for the aircraft comprises a plurality of light sources extending on both sides of the approach plane along a line transverse thereto and a visual marker fixed relative to the line of light sources, the light sources being so, arranged as to project towards the observer light beams which are of narrow width in a direction perpendicular to the approach plane with the direction of the central axes of successive beams changing progressively from one beam to the next and the angular widths of the beam being such that each beam overlaps at least half, but not the whole, of the beam width of the immediate neighbours so that an observer within the angular range of the arrangement sees at least two adjacent light sources (except at the extremities of the working range) the position of which relative to the marker, which is arranged to be visible over the entire working range giving an indication of his angular position with respect to the approach plane. The light sources are mounted within a common housing and comprise each a lamp 11, a condenser reflector 8, a slit 4 and a projection lens 5. The slits 4 are formed in an opaque screen 3 which may be moved vertically by an electric motor 9 in response to an automatic stabiliser 10 so as to maintain the directions of the light beams fixed in space despite pitching of the aircraft carrier. The widths of the slits, their spacing from the lenses and the diameters of the lenses are all so chosen in relation to the focal lengths that the overall width of each beam is 30 feet while the optical axes of successive optical systems are displaced with respect to each other by 8 feet. As a result a pilot approaching the aircraft carrier within the angular range of the arrangement sees portions of virtual images of three or four adjacent slits, covering in all an area equivalent to about two and a half times that of a single lens. Fig. 3 shows the arrangement as seen by an approaching pilot, the mean positions of the lenses appearing illuminated with respect to the marker 15 indicating the position of the aircraft with respect to the desired glide plane. The lenses 5 are preferably provided with amber filters while the marker 15 is preferably constituted by a row of lamps provided with green filters, though, since. the marker need not be directional it may instead be constituted by an arrangement which is not self-luminous. The arrangement is preferably mounted as indicated in Fig. 8 with respect to the deck of the carrier and provides a luminous intensity between the extreme directions 20, 21 in azimuth as indicated in Fig. 9. It will be seen that the arrangement behaves as a high intensity source to aircraft which are distant from the carrier and approaching it along the line 19 but that the intensity falls to a comparitively low value as the aircraft nears the carrier thus avoiding possible dazzling of the pilot at night. To achieve - this distribution a cylindrical spreader lens having a section as shown in Fig. 10 is arranged in front of each of the lenses 5.