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Aviation History
1961
1961 - 1585.PDF
FLIGHT, 2 November 1961 689 SYSTEM SURVEY Elements of a future ATC system,which would include the DeccajC.S.F.ITelefunken Harco, described here Harco and Eurocontrol MOMENTOUS developments for the whole field of civil air-craft navigation were announced last week by the DeccaNavigator Co. As briefly reported on pages 648-660 last week, a consortium composed of Decca Navigator in Britain,C.S.F. in France and Telefunken in Germany are developing a new navigation system based on Decca Navigator and called Harco(Hyperbolic ARea COverage). Thus not only the design and sales, but also the name of equipment based on Decca, is now inter-national. Most important of all, Eurocontrol is to evaluate Harco as a standard navaid to supersede VOR/DMET. During 1959 the technical group of Eurocontrol consideredavailable navaids to meet the ATC requirement for the upper air- space. They rejected the NDBs and decided that VOR/DME wasinadequate; and they drew up a specification which was distri- buted in April 1961 to the electronic industries of the Europeancountries. The provisional target was for an aid which could be provided by 1965. The French Radio Mailles and developed CossorGee were submitted and rejected. Very recently S.T.C., L.M.T. and Lorenz submitted a VOR/DMET scheme and an Americancompany suggested MOPTAR. Assessment of these two systems was left to the FA A. Inevitably, Eurocontrol findings on Harcowill be closely examined by the FAA and by ICAO. The Eurocontrol operational specification mainly requiresmaximum coverage, including sea areas, at minimum cost; high diversity of use among all categories of aircraft; area coverage topermit any desired route structure and to facilitate changes without costly re-deployment of ground stations; simplicity of interpreta-tion and use of airborne equipment; integration with automatic techniques into the ATC system by automatic data links withoutloss of basic accuracy; great reliability; compatibility with the long-range navigation systems; high accuracy, particularly forterminal area; low-altitude cover for helicopters and light aircraft. The specification also called for a 95 per cent probability of a track-keeping accuracy of ± 2 n.m. with a position accuracy of not less than ± 1.5 n.m. Coverage was to extend from ground level to80,000ft. Pictorial presentation was to be provided in the cockpit to facilitate ATC procedures in terminal areas and position infor-mation was to be continuous. DATA LINK « 1 RAOAR DMA I VISUAL DISPLAY VOICE COMMUNICATIONS The New International Aid Harco, based on Decca principles, will effectively cover thisspecification. Chains already located in the Eurocontrol countries, with the addition of three new chains in France and one in WestGermany, will provide an accuracy not worse than 0.25 n.m. by day and 1.5 n.m. by night along the worst direction of the errorelipse. For Harco, all the chains will have to be slightly modified by the provision of a central synchronous clock, but this will notaffect the operation of existing airborne Decca. On the airborne side, computers and display systems range from a relatively simpleand unsophisticated display for light and slow aircraft to an auto- matic, self-setting presentation with push-button operation andutilizing conformal charting. Full Harco capability is based on a revolutionary new miniaturization of the Decca receiver now beingdeveloped by C.S.F. in France. The red, purple and green receivers are reported to measure about 9in by lin by lin each. They arefully transistorized and are being designed for a mean time to failure of l,000hr. Telefunken are working on the presentationand on the two-way data link described below. Decca are contri- buting patent rights for their existing equipment and have nowcompleted trials of the Self-setting Flight Log and Omnitrac com- puter. The full Harco equipment now presents itself as follows.Decometers and associated manipulation are entirely eliminated and the three small C.S.F. receivers feed Decca signals directly intothe Omnitrac computer. This will contain a small core memory which will control the sequence of 19 multiplications, 14 additions,one division and one square root, plus the retention of seven intermediate results required in the process of converting Deccahyperbolic co-ordinates to Cartesian co-ordinates once every 0.6 sec. The resultant stream of newly calculated positions would befed directly to the photo-electric sensers which will position the pen on the chart by means of the black-and-white digital tracksalong one edge of the chart and an equivalent mechanism behind the pen. The pen itself now consists of a mechanical pecker stippling a track on the reverse side of the chart through a type-writer ribbon. The chart itself is no longer held in a cassette but simply wound on a spool much like a film in a camera. Almost40ft of chart can be carried. Additional digital tracks between the various charts on a strip will automatically programme the computerto the appropriate scale and the divergence of the chart axis from axis of the Cartesian grid, which is aligned with True North. Opera-tion of Harco therefore requires the pilot only to switch the system on and, by pressing appropriate buttons, align the computer-setting digital tracks of the appropriate chart beneath the photo- electric element. Harco, incidentally, involves no loss of accuracyrelative to Decca Mark 8 and avoids manual setting errors. Decca envisage a duplicate Harco installation in which the firstpilot would have a receiver, Omnitrac and Self-setting Flight Log, while the second pilot would have a plain Flight Log backed by aMk 10 receiver. Another part of the basic Harco navigational system is a "Ghost Buoy" facility based on the Cartesian grid ofOmnitrac. The crew will be able to select range and bearing to any geographical point up to 256 miles distant. In their Valetta on Monday of last week Decca demonstratedthe Self-setting Flight Log Mk 3 and Omnitrac computer with range-and-bearing facility. Omnitrac was the original prototype,occupying about 1 ATR case size and containing a memory drum turning at 12,000 r.p.m. No exotic electronic techniques have beenemployed and components are in all cases of-the-shelf items. The Self-setting Flight Log can be arranged in many ways and Deccahave suggested a version which is mounted flat in the glare shield and can be tilted vertical when in use. Half-million scale chartingwas being used, showing some 40 n.m. either side of the track without any distortion. The flight from Gatwick led overMayneld,down and up the Amber airways across the south coast and back via Mayfield. Range and bearing to successive reporting points werecontinuously shown—an eerie sensation, because the information was not being derived from any beacon. Two chart-changesinvolved only 12sec interval each and the pen moved itself to the new position. Way points for range and bearing signals wouldnormally be selected by turret switch or punched card. The proto- type Omnitrac has run for 1,200hr with only two faults. As important as the basic navigating function of Harco will bethe additional capacity inherent in the system for ATC purposes. Omnitrac will, for instance, be able to operate from air data,Doppler or inertial systems to provide navigation information with or without Decca. Automatic chart-changing may be provided.Optical sensers in conjunction with the pictorial display could allow autopilot coupling for following curved as well as straight tracks.Finally, the digital output could be fed into a two-way VHF data link transmitting position, height and identity to an ATC com-puter without loss of basic navigational accuracy. The scanning rate of the data link would be of the order of ten aircraft persecond per channel and the sequence of automatic interrogation could be varied by the controller as required. Required positionor track could be fed back to the aircraft from the ground and the autopilot coupling might eventually be actuated by such instruc-tions. It might also be possible to combine the position informa- tion with height, so defining a three-dimensional track either as anotification from the aircraft or as an instruction from the ground. Ultimately, the information derived from the data link could beused to feed synthetic radar displays. Eurocontrol evaluation will involve flying by French aircraftand possibly the co-operation of A. and A.E.E. Boscombe Down. The distribution of sales at present envisaged is that C.S.F. will sellthe receiver and Telefunken the presentation and data link within the Common Market. Decca would produce and sell the equip-ment elsewhere and would also receive the licence royalties. But Decca intend to allow manufacture virtually anywhere in theworld; they have already secured the co-operation of Teleregister Corporation, a major American company specializing in on-linedata processing and systems design. Bendix, Decca's present US representatives, will concentrate on military applications.
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