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Aviation History
1959
1959 - 0548.PDF
FLIGHT, 20 February 1959 FLYI NG AIDS . . . 271 The Kelvin Hughes Flight Data System panel, incorporating a tape indicator for speeds, dial instruments for height and ver- tical rate, roller-blind horizon with slip ball, and compass/ navigation display here set for I.L.S. The steering-command ring and the symbol indicating vertical upward flight on the attitude indicator are not in realistic relationship I N STRU M EN TS Improved Displays Involve Weight and Complexity SEVERAL years ago it was said that dial instruments withrotating pointers belonged to the "clock age" and werehopelessly out of date even for aircraft of the immediate future. The theory was that a circular scale was not the rightpresentation for a quantity which was, from the pilot's point of view, linear. The background to this new approach was thedevelopment of tape indicators for height, rate of change of height, speed and Mach number. Height could be shown on a tapesystem set vertically to provide an almost pictorial indication. Speed values, similarly, were to be shown on horizontal tapes.The roller blind, in itself an extension of the tape, provided at once the ability to follow a looping manoeuvre on a continuousindicating surface and the possibility of printing several displays on one length of blind and thereby rapidly replacing one type ofinformation with another in a single dial. In attitude and naviga- tion displays, the roller-blind assembly could be convenientlyrotated to present roll and heading indications respectively. Since the conventional capsule and gyro movements could nolonger provide the extent of displacement and the power needed for this type of display, remote sensing elements were introducedin the form of air data computers and master reference gyros. The integrated blind-flying panel which resulted was evaluatedin a Meteor and, by all accounts, provided a full and effective reference for controlled aerobatics in cloud. The original require-ment had been for an all-attitude instrument system which would make it possible for a pilot to fly a prolonged vertical climb andthen level out on a given heading by pulling over into the inverted attitude and rolling level. Both in Britain and America, development of tape instrumentshas continued and such aircraft as the Convair F-106 are to be Below right, the three instruments of the Smiths Flight System with an A.S.I. The altimeter and V.S.I, would be positioned to the right. Below left, the two instruments of the Lear Integrated Flight Equipment (LIFE). The aircraft silhouette on the attitude indicator moves in relation to a fixed horizon reference. The small diamonds like tip-tanks . . are the pitch-command symbols fitted with the American system in the near future. In Britain,the master reference gyro, made by S. G. Brown Ltd., has been introduced into all the latest high-performance aircraft and theKelvin Hughes panel probably accompanies it in many installa- tions. But some of the inherent difficulties have led to the replace-ment in this panel of tape indicators for height and rate of change of height by conventional dial instruments. It is difficult to pro-vide accurate indications on a tape which is not excessively long. On a manageable length of tape, the smallest units cover too shorta distance to be accurately discerned by the pilot. A moving pointer traversing a short scale will equally give only coarseindications. In airliners, the tape instruments have not been adopted, ifonly because of the basic alterations required in the whole panel layout and particularly because of the additional equipment neededto support the system. The Services learnt the bitter lesson of the shortcomings of dial altimeters many years ago, and now civiloperators have been caught out in their turn and have the same lesson to learn. A number of recent accidents to airliners whichconsistently cruise at over 10,000ft have been tentatively attri- buted to a misreading of the conventional altimeter. Severalpalliatives can be incorporated in conventional capsule-driven instruments in the form of warning flags and additional indica-tor segments, but none of these seems to offer a completely effective solution to the problem. The veeder counter instru-ment may be unequivocal in its indication, but it requires servo operation and is hardly more pictorial than the dial. It seemsinevitable that the additional complexity, cost and weight of the remote-indicating systems with their additional power for long-scale drives will have to be accepted fairly soon. The six-dial panel which became standard during and afterWorld War 2 is recognized as containing much information of a basic kind which requires correlation and interpretation bythe pilot. The introduction of the Sperry Zero Reader and then the combination of this type of director display with attitude andheading information in integrated systems has produced a marked improvement in the information which can be directly derivedfrom the blind-flying panel. These newer instrument groups, examples of which are currently produced by Smiths in Britainand Sperry, Bendix, Lear and Collins in America, have become an important feature of airliner cockpits. Automatic approacheswith autopilot couplers are now a routine and important feature of airliner operations. But the more complicated the presentation,the harder it is to detect malfunctioning, and redundant indicators may remain in view when the director elements are not in use. Nevertheless, the flight director systems do provide an excel- lent means of monitoring the performance of an autopilot coupled to V.O.R. or I.L.S. It has long been traditional to indicate attitude on the artificialhorizon by means of a horizon bar moving in relation to a fixed aircraft symbol. The mechanical linkages in this type of presenta-tion are relatively simple and the method was universally accepted. Further studies carried out during recent years seem to indicatethat the opposite method was, in fact, better and that a moving aircraft symbol should be portrayed in relation to a fixed horizondefined either by a white reference line or a straight border between two zones of different colours, white for sky, black forground or blue for sky and green or brown for ground. A com- promise between these two methods was suggested by a Convairengineer and incorporated in an integrated display called Kinalog, described in Flight for November 28, 1958. Both horizon and
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