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Aviation History
1957
1957 - 0492.PDF
494FLIGHT, 12 April 1957 Reading clockwise: Kelvin Hughes altimeter with warning flag, Smiths motorized 100,000ft altimeter, Kelvin Hughes combined A.S.I./Machmeter, and Kelvin Hughes roller-blind horizon showing almost-level flight and vertical climb "aimed" at the special marker. The Changing Instrument Picture strumentation, the Sperry Zero Reader Flight Director is men-tioned in our review of radio-aid instruments (see page 498); and the Sperry, Smiths, Collins and Bendix instrument systems aredescribed in the same section, which deals with the various naviga- tion instruments developed as pilot aids for V.O.R. and I.L.S.flying. All of them are noted where they are intended for use as integral components of the Smiths Flight System, Bendix PB-20,Sperry SP-30 and Collins AP-101 automatic flight-control systems. But these instruments generally conform to the traditional styleand presentations; and their performance is still related to the behaviour of airliners and similar aircraft.An entirely new requirement has arisen for instrumentation for the new intercepters which will be able to sustain a vertical climband supersonic speed on the level. To meet it an entirely new instrument panel is being developed; Kelvin Hughes, who are pre-paring it, have been able to release no general view, but the Americans have published details of various possible arrange-ments. One of them is shown on page 493. Instrument-mounted gyros cannot maintain indications duringsustained vertical flight or the pull-out into horizontal flight, and Kelvin Hughes have therefore developed the roller-blind horizonusing attitude information supplied by a remotely mounted stable platform, the main example of which is the S. G. Brown, Ltd.,Master Reference Gyro described on page 484. The new horizon is based on a servo-operated roller-blind mechanism, half the blindof which is painted white to represent sky and the other half black to represent ground. Vertical references are in the form oftarget shapes in the middle of the black and white sections. The whole blind assembly is revolved to give indications of roll. The roller blind/Master Gyro combination will allow con- tinuous instrument indications throughout aerobatic flight. Duringa vertical climb the pilot would "aim" at the vertical marker in the white zone of the blind. A difficulty arises when he has topull over on to his back and roll upright onto an accurate compass heading; unless he can do this the ability to climb vertically hasno operational usefulness. Kelvin Hughes are therefore develop- ing a compass which will indicate during the vertical climb thecourse which the aircraft would assume if it were pulled straight over on to its back. This instrument, too, takes heading-gyrosignals from the Master Reference Gyro. A method has also been found of rapidly orienting the horizon to have the correct verticalsetting as soon as the aircraft deviates significantly from a true vertical climb in any direction. This facility is built into theMaster Reference Gyro and noted in the description of that equipment. Another basic instrument requirement for this type of perform-ance is something to replace the conventional dial presentation. Introducing the roller-blind horizon last year, Sir John Booth-man, sales director of Kelvin Hughes, said "We have got to get away from dials and revolving hands. Imagine watching an alti-meter in an aircraft climbing at 50,000ft/min. It would be like looking into an airscrew. It is quite certain that we shall be goingover to a linear type of presentation." The American panel, which conforms very closely to ideasoriginated by Kelvin Hughes, has this presentation. Moving-tape indicators replace dials and each instantaneous value is shownagainst a continuous lubber line across the panel. Mach, airspeed and angle of attack are on the left, the little-used lower end of theMach scale being marked to show maximum speeds for extending wheels, flaps and drag chute. The horizon instrument includesindicator and director functions for radio coupling and is arranged as a "forward look" display. The "downward look" element forcourse control is the compass system on a sloped panel below the horizon. The layout in this case closely resembles the Smithsbeam compass, but includes V.O.R. radial selector window and D.M.E. or Tacan range window. Subsidiary arrows and marks on the tape indicators show the"command" settings selected by the pilot for specific flight pro- cedures. Ground elevation is set on the altitude tape as a stripedblind covering all altitude indications below ground level—in this case 4,900ft. This type of panel is much easier to read than any other hithertodevised. Development of such displays and the new equipment required to make them work is continuing apace on both sidesof the Atlantic. Weather Radar A LMOST certain to become a standard item of transport air-A\ craft equipment, weather radar is already widely used in •*• -*- both military and civil aircraft. It has proved invaluableas a guide to airline crews in picking a smooth and safe path through storm areas and in map-reading through cloud. Themain advantages claimed for it are that it allows the pilot to avoid areas of severe turbulence which may cause discomfort and alarmto passengers and not infrequently result in structural damage to the aircraft; pilot fatigue is reduced when negotiating such stormareas; delays resulting from detours round storms through which safe paths can be found by radar are eliminated; and weatherradar's map-painting ability is a most useful adjunct to navigation. Weather radar as such was developed when possibilities in thisdirection were realized during military airborne radar research programmes soon after World War 2. It was found that waterparticles suspended in cloud or in the form of raindrops reflect a radar beam in proportion to their concentration or the density ofmoisture. Though rain is not in itself dangerous to aircraft, its extent and density give an accurate indication of local turbulenceintensity. A dish scanner mounted in the nose of the aircraft is generallyarranged to scan a wide arc ahead with a narrow beam. The scan- ning plane can be tilted up or down as required and the aerial is gyro-stabilized to maintain a steady tilt angle relative to thehorizon. It is also stabilized in the aircraft's roll axis to avoid lateral inclination of the scanning plane during turns. Associatedreceiver/transmitter, amplifier, synchronizer and power supply are usually packaged in two rack-mounted units. A control paneland single or duplicated P.P.I, displays are mounted within easy reach of the pilots. Viewing hoods are used during strong ambientlight conditions, but bright display tubes are being prepared for many indicators. The radar C- or X-bands (5,000 Mc/s or 10,000Mc/s) are used, the former offering rather better penetration of rain areas, though the X-band has other advantages which haveled to its being more widely adopted. In order to show up storm cores, iso-echo contour control isgenerally provided to cut out radar returns on the P.P.I, which exceed a preselected intensity. The storm cores then appear asblack patches within the rain return. Sensitivity time control is also provided to even out responses from varying ranges. Avariety of range settings and tube-face range markers is general, and some weather radars can interrogate and display Racon groundradar beacons. For map-painting the aerial is tilted downwards to the requireddegree. Cosec2 scan is often provided to deepen the arc searched by the radar beam when used for map-painting. Coastlines, rivers,
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