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Aviation History
1946
1946 - 1883.PDF
SEPTEMBER IOTH, 1946 FLIGHT 315 AIR TRAFFIC CONTROL the runway. The navigator measures the distance as beforeon the Rebecca set, but ascertains the position of the aircraft relative to the correct approach path by comparing the ampli-tude ratio of short- to long-duration pulses received. THE ORBIT METERThis is an attachment to Rebecca which enables aircraft to circle a Eureka beacon at selected radii. The pilot selectsthe radius of the orbit which he intends to fly and the dash- board instrument indicates whether the aircraft is inside oroutside that selected orbit. The instrument also shows the distance in miles from the Eureka beacon.The remaining radar and radio equipment on exhibition consisted of the following :— G.C.A. Ground Controlled Approach is a runway approach systemin which all the radar equipment is positioned on the ground and the aircraft requires nothing more than good two-wayR/T. The ground equipment is mobile and contains two radar instruments and a wide choice of R/T channels. The firstradar is called the "search" system, and displays on two cathode-rav tubes the radar location of all aircraft within25 miles' horizontal distance. The second is the precision radar system and displays on cathode ray tubes the instan-taneous plan and elevation position of a single aircraft approaching the runway concerned. Sub-controllers watchthe tubes and a traffic director marshals the aircraft by telling each pilot the courses to fly to position the aircraft for theapproach to the runway in use. The approach controller uses the information provided by the sub-controllers to guide theaircraft on to the correct approach and to watch for any departure from that approach. Several aircraft may be con-trolled simultaneously by the traffic director, but only one aircraft can be handled at one time by the approach controller. This system was described in detail in Flight of July nth this year. CONSOL Consol provides long-distance- navigational aid for aircraft,using automatic transmitting beacons on the ground and a standard M.F. receiver in the aircraft. The range is about1,500 miles over the sea and 1,000 miles over land. The system radiates dot and dash signals and a position-line canbe determined by making a count of the dot and characters heard during the transmission cycle. The complete cycle ofoperation takes one minute. During the -first twenty-eight seconds an omni-directional characteristic transmission takesplace. After a break of ij sees the keying cycle of 60 dot and dash characters commences. The cycle takes 30 sees,which is followed by a break in transmission for half a second, after which the cycle restarts. The total operation involvestuning the receiver to the ground beacon, identifying the station code, taking a bearing with D/'F loop, if necessarymaking dot and dash counts, and then referring to the chart. The observer can establish his position by reference to twoindependently operated Consol beacons, and the advantages are that a position-fixing service is always available withoutthe need for carrying special equipment in the aircraft. THE AUTOMATIC RADIO COMPASSThe function of a radio compass is to present a continuous indication of the bearing of a known transmitting station withrespect to the heading of an aircraft. By linking the indicator with the D/R compass it is possible to obtain the true bearingof the transmitter from the aircraft; thus, by taking bearings of two or more stations it is possible to obtain a fix. Theequipment consist of, a normal medium-frequency loop and receiver, together with a device which automatically pointsthe loop towards any transmitter to which the receiver is tuned. Continuous-wave beacons are provided for homing purposesat most airfields, and specially placed beacons, usually of higher power, than those for airfield homing, are used fornavigational purposes. . - . Fir in"-Track Control New Development of Decca Navigator System : Flight Control Up to Landing Approach IT has long been realized that the future traffic densitieson air routes—particularly those of short and medramdistance in highly populated areas—are likely to be such that a saturation point will quickly be reached where traffic control of the aircraft using the routes cannot cope with a greater number of aircraft movements whilst main- taining the minimum requirements cf safety. Particularly is this position aggravated in the. vicinity of terminal and major junction airports where poor weather conditions might necessitate arriving aircraft being told to orbit until they can be called in to land. Such a state of affairs already exists in America, where traffic densities are higher than ours at present. Alternative airports where.clear conditions exist is not a tenable answer. It affords an escape in extreme conditions, but it is an answer that nobody wants to accept since it ruptures all possibility of schedule-keeping and negatives passenger con- venience. This is but one of the many problems which face air transport authorities and planning commissions, but it is the one which particularly interests us here in giving an appraisal of the Decca Navigator Track Control Unit. . The Decca Navigator System was described in the September 13th, 1945, issue of Flight and, as many of our readers will be aware, is a navigational aid whereby in- stantaneous and accurate position-fixing is made possible -by the constant emission of long-wave radio signals along ^hyperbolic lanes from established ground stations. ^Throughout a flight, readings given on special indicators *give the fix of position when referred to an appropriate chart. This permits navigation to be carried out in such •k way that the aircraft is free to follow any desired track intended to bring it to its required destination. Whilst this technique permits the lateral dispersion of aircraft, and so reduces the chance of saturating any area, it involves the determination of position by reading certain instru- ments, of plotting this position on a chart and maintaining a proper air plot. In examining this problem the Decca Navigator Company reached the conclusion that while the hyperbolic systems, of which Decca is one example, provide a very useful flexibility and freedom of lateral dispersion, they fall short of meeting the fundamental requirements for future air- route operation. The new Decca Track Control Unit removes these limitations and opens up an entirely new field. It is the invention of Mr. R. Calvert, technical director of the Wayne-Kerr Laboratories, New Maiden, who are undertaking its development on behalf of the Decca Navigatoi Company. The Decca Navigator normally displays the co-ordinates Pilot's panel for Track Control Unit. Selectors for orbitingand landing approach tracks are at left, and meters for distance and destination, ground speed, and schedule keepingat right. The central indicator is for maintaining the track flight path. Q
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