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Aviation History
1964
1964 - 2714.PDF
FLIGHT international, 22 October 1964 709 Head-up Over the Hills Flying the Hunter Mk 12 with Head-up Display BY MARK LAMBERT THE need to approach a target beneath enemy radar cover hasproduced many technical advances, and not the leastvaluable of these has been the head-up display, which allows the pilot simultaneously to follow a flight director and to observe the external scene. The story began eight years ago, with an MoA specification, which was answered by the Sperry head-up Zero Reader, the Smiths Para-visual Director and an electronic system, at one time called PEEP. Originated at RAE Farnborough's Instrument and Electrical Engineering Department under Dr J. M. Naish, the equipment was engineered first by Rank Cintel and subsequently by Specto Avionics. Primary objectives of the head-up display at the moment are the TSR.2, the Belfast and the Buccaneer, but development is continuing apace. While the main application is based on viewing on part-silvered glass and through an optical system flight director symbols generated in a cathode-ray tube, there is now the obvious extension of using a larger tube mounted in the main instrument panel to form a primary head-down flight instrument system. By this means, the flexibility and natural appearance of electronically generated displays can be used to replace conventional dial instru- ments which require varying degrees of interpretation. When the system was first suggested, its use as a primary flight director must have appeared fairly risky, in view of the complexity and probable reliability of the electronics involved. Since then, remote indicating instruments and advanced miniaturization permitting the inclusion of redundant channels within acceptable limits of size have greatly improved the prospects. Early limitations in the optical system are also being progressively overcome to allow greater freedom of viewing. Independent evaluations have been made by Boeing and the US Navy and considerable interest was aroused following a presentation at the IATA technical conference in Lucerne last year. Flexible and Adaptable Display Although a major function of the head-up display in the Belfast must be to monitor the automatic landing system, the principal development effort has been directed towards the terrain-following operation of the TSR.2. Displays in the three aircraft mentioned above are manufactured by Rank Cintel, but the I.E.E. Flight at RAE Farnborough has for some time been operating the special Hunter Mk 12 with a dual Specto display and manually-controlled inputs. This system is miniaturized, meets Service climatic specifi- cations and has been flown without major fault for more than lOOhr. It was in this aircraft that I was able to make a 90min sortie in order to gain first-hand experience of this type of flight director. During previous sessions in various forms of simulator, I had formed a rather unfavourable impression of the head-up display's potentialities. The limitations of the optics were such that per- missible lateral head-movement was of the order of ±2in and the display seemed seriously in danger of becoming over-cluttered or actually confusing. In practice, however, the essential benefits became abundantly clear. Calibrated experiments have shown that the mean time to acquire visual stimuli in the external field is even faster when using a head-up display than when simply scanning through the normal windscreen—and it is, of course, infinitely faster than when dividing the scan between conventional head-down instruments and the external scene. The display can be raised or lowered so that the axis of viewing is elevated or depressed relative to the aircraft flight Path so that the background scenery can be selected to a certain extent. Another advantage is that, during an approach, the pilot obtains considerable warning of the external scene he is hoping to see and acquires it commensurately more quickly. There is an obvious temptation to add more and more infor- mation to the basic tracking and attitude display, to the point where Ac pilot's perception becomes overloaded and the value of the display is lost. To a great extent, this danger can be avoided by appropriate shaping of the symbols, and also by a judicious com- Specto's proposal for a c.r.t. director display for head-down instrument flying. Central pattern is the aiming ring, horizon bar and pyramid- shaped director pattern. The dotted lines marked "20" are 20° climb and dive markers. Round them are, clockwise from "9 o'clock," a barometric height read-out of 15,400ft; digital read-out of an instantan- eous or datum Mach number of 1.85 with an error scale and indicator mark; vertical speed scale and indicator; compass display indicating a heading of 245°; and a slip indicator. This display is therefore equivalent to six or seven conventional dials and combines alpha-numeric with symbolic information -©- DEMAND SATISFIED DEMAND TO CLIMB DEMAND TO DESCEND -o _: TURN TO STARBOARD The basic director element of thi display is the dot at the head of the pyramid of horizontal lines. The base lint remains fixed and the pyramid stretches, contracts or leans sideways in the various demands. The pilot simply "flies" the ring to overlap the dot bination of alpha-numeric and symbolic information. The flexibility of the wave-form generator and c.r.t. make it possible to write virtually any shape and the total length of line which can be generated is well beyond the useful capacity of the system. RAE estimate that a pilot can without difficulty follow seven or eight symbols. Beyond this number, special training becomes necessary. The basic tracking pattern is, in fact, very simple and consists of a "winged" ring representing the aircraft bore sight, which re- mains fixed in the centre of the display. Moving relative to it is a broken horizon line giving conventional attitude indication in pitch and roll. To this may be added further horizon lines represent- ing given angles of climb and dive, as well as zenith and nadir crosses representing vertical upward and downward attitudes. The director element is a tapered pattern of three parallel lines and a dot. The tracking task is simply to fly the fixed ring on to the dot. The diagrams above indicate the deformation of the tracking pattern during turn and climb or dive demands. Around this main tracking display, it is possible to add various forms of symbol indicating course, speed, vertical rate, height,
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