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Aviation History
1961
1961 - 0090.PDF
ft**** SYSTEM 90 FLIGHT, 20 January 196 SURVEY Visual Flight Simulator A FTER several years of concentrated development, General /^ Precision Systems Ltd, of Aylesbury, Bucks, have com-•L -»- pleted the first model of an effective visual simulator system which can be added to almost any existing aircraft simulatoror group of simulators. A similar objective has been achieved before, but only with rigid models of very considerable sizescanned by closed-circuit television cameras mounted on moving gantries; one such model is no less than 95ft long. GPS havesucceeded in mounting a realistic, three-dimensional model at 1 : 2,000 scale, covering a ground area equivalent to 12 n.m. by3.3 n.m., on a continuous moving belt. The scene is scanned by closed-circuit television slaved to aircraft movement and eitherprojected ahead of the simulator or displayed close to the wind- screen on a television tube. The cost of the Visual Flight Attachment, as it is called, is alittle under £40,000 and deliveries could be made in nine months. The device meets both civil and military specifications in Britainand America and considerable interest has already been shown. A Flight representative handled a simplified, typical turbopropairliner and proceeded to demonstrate the simulator, making a number of take-offs and ILS approaches in a variety of ceilingand visibility conditions and in lighting from broad daylight to full night. The realism of both scenery and motion, with accompanyingengine noise and wheel rumble, was most impressive. Nosewheel steering and brakes could be used on the ground and the "air-craft" bounced most realistically if roughly landed. In training, the psychological effect of having to carry an instrument approachright through to a full stop on the runway must be very con- siderable, quite apart from the ability to practice actual minimum-visibility landings. In addition, the visual attachment makes it possible to gain some familiarity with the handling characteristicsof a new type of aircraft before first flying it; and co-pilots can practise the technique of telling the captain when to go visual. In developing this system GPS have solved numerous problems.The model is based on a continuous belt of fabric on which the ground features are plotted either from an aerial photograph orfrom a large-scale outline map. In the case of the London Airport model, some 75,000 miniature houses and 250,000 treeswere mounted on the belt, ground texture being carefully repro- duced by rough and very smooth finishes and colouring in variousshades of grey and dark blue (models of representative airfields can also be used). Forward movement is accurately reproducedbv driving the belt over two rollers of 2ft 6in diameter. The scene is viewed by a Marconi image orthicon, closed-circuit television camera mounted normal to the belt, its line of sight being turned through 90° by a mirror. The aperture is stopped right down and the field of view set at 60° to provide thebest definition. Lateral displacement of the aircraft is reproduce d by movement of the whole camera mounting across the face >fthe model; and height by camera movement normal to the modi 1, Roll, yaw and pitch movement of the aircraft are fed in byappropriate movement of the camera lens-system. Aircraft move- ment is derived from the computer of the aircraft simulator.Cloud-base is regulated by the insertion of a card in the k is assembly; and a second card is introduced to restrict visual ran,:eand introduce mist or fog effects. The cards are electrica:iy positioned according to values preselected at the controller'smonitor position, where the picture can also be adjusted. Cloud- base from 1,000ft to zero and visibilities from 4.5 n.m. to 300ftcan be selected. If the aircraft turns more than 30° from tae model axis it automatically becomes IFR. If the viewing mirrordescends to less than the equivalent of 60ft from the model outside the airfield area it is automatically retracted to 100ft; and if thisproves ineffective, the mirror is displaced by striking the model, when microswitches and a precompressed spring automaticallycause the camera to move sharply back. The face of the model is illuminated by fluorescent strip lightingand inclined flood-lamps to give both daylight and shadow effect. The light can be dimmed to produce the effect of dusk or completedarkness. Runway and approach lighting of appropriate bright- ness is produced by strip lights behind the model, reflected by thebevelled edges of plastic inserts in the canvas. Street lighting near the airport is simulated by highly reflective points which pick upeven the dim overall surface lighting applied for full night. The whole model and camera assembly is 20ft high; but if, asseems likely, some operators require a maximum cloud-base of only 500ft, the height of the model assembly could be halved,Alternatively, the scale of the model could be increased to 1 : 1,000 with better definition. Camera focus is automatically adjusted. To create the scene ahead of each pilot, either a projector ormonitor screen may be used, two of one kind or one of each, according to requirements. Each pilot must have a presentationcorrect for his viewpoint, but the projector can be freely located and adjusted to avoid distortion. With a moving-base simulator,projector and screen are mounted on the cockpit assembly. To keep their edges out of sight, the displays are viewed throughclear windscreen-wiper segments in the frosted windscreen panels; and this has proved comfortable and effective in thedemonstration installation. The projector screen measures 6ft X 8ft and is positioned lO^ft ahead of the pilot's eyes. It isintended that 625-line television with 27in tubes should be employed. Further refinements, such as colour television, may beaccommodated when they become available. Left, reading anti-clockwise: Lon- don's 28L runway seen on the monitor screen at 400ft in 4]A n.m. visibility; at 150ft in 700yd visibility; and over the threshold at 100ft in 4Vi n.m. visibility at dusk Right, the 1 :2,000-scale model on its endless belt aligned vertically in its 20ft-high frame with strip- and flood-lighting in front of it. The camera, which moves vertically and sideways, is at the foot of the frame
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