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Aviation History
1949
1949 - 1022.PDF
June znd, 1949 653 fretnCKW Coptam ffsi OH'Cw Strom* Officer Dtpartvrt forecast Ftiqhi Am,at CM 1:. Nav>qator C. M t Oumtion DECCA FLIGHT LOG. To AlCHo Datt Takt off Data Nanfotifn Ofhctr CrauWtifM Radio OfUctr ... .. futl Ftlfht enoineer Wind 'T. r<r*» Off Q.MK On Count.. CM.T. • EXA. .. Timt in Air Captain Tr+ No-rOO fali Sn ktt DrKSJIy Altitudt c.M.r f ktt officially adopted by the Royal Da*nish, Swedish and Dutch Navies. Knowing how monstrously heavy normal maritime components are by comparison with their airborne counterparts, it should at once be made clear that the Decca aircraft equipment is designed to standard S.B.A.C. rack sizes, and that a complete installation, including cabling, weighs but 52 lb. As for coverage, there exists at the moment the original English chain, plus the Danish chain, but these are to be supplemented by the end of this year by two further British chains, one in the north- west and one in the "south-west. This position, and the limits of operational scope, are defined by one of the accompanying maps. Up to a range of 300 miles from the centre of each chain a position-fix accuracy of a minimum of a quarter-mile is given; up to a range of 500 miles on-route navigation is possible; and up to a range of 1,000 miles the system provides satisfactory tracking information. The adjacent map shows what the coverage would be if six further chains were to be built, four in Europe and two in North Africa. It is at once apparent that an aircraft could be flown from Crete to Caithness, from Biskra to Bergen or fronrfirest to Belgrade with the pilot given the ability to plot its position instantaneously, accurately and at any moment. Futher, suppose that in flying from Brest to Belgrade the track lies virtually parallel to one of the signal hyperbolae; all the pilot need do is to home along that lane by keeping th'e appropriate Decometer registering the appropriate value. Where the track /lane, relationship is such that homing is not possible, at worst, fixes can be taken, say, every ten minutes and the adherence to or deviation from track plotted and, if necessary, corrected. The foregoing dilation upon the basic Decca system will serve to emphasize that, even as it now stands, it offers to aviation a navigational aid unmatched in accuracy and coverage and unapproached in simplicity by any other system in the world. How far, then, it outstrips everything else by the advent of the Flight Log may be judged by our own experience. We were given a demonstration of continuous position-recording whilst travelling in a car along a stretch of the Kingston By-pass road, to the south-west of London. The road is, perhaps, 50ft wide. The actual record of the journey is reproduced here; the incredible performance of the Decca Flight Log is manifest. - • . The device is a Perspex drum, at present i6in long x 7 Jin diameter, around the surface of which is fitted the map. This is, in fact, distorted as the signal hyperbolae are used as co-ordinates for the map projection: nevertheless, the position-fixes given are absolutely accurate relative to all the conventional physical features of terrain shown. The signals translated by the normal Decca Mk VI receiver to actuate the ordinary Decometers are, with the Flight Log, given to a torque amplifier and drive unit. This is used to rotate the map drum and to traverse a stylus cursor. Thus, as the journey is made the stylus traces the progress directly on" to the map in the form of track made good. >• During our journey along the road we passed bus stops, crossed intersections, and went under foot-bridges and over railway and river bridges; and on every occasion the stylus was showing our position—undeniably, remorselessly and with incon- trovertible accuracy. It was a most profound experience. Perhaps at this stage one should state that the Flight Log equipment weighs 30 lb, so that the total Decca Facsimile of Flight Log tracking obtained on a two-way demonstration run along the Kingston by-pass, London. The divergence above the Ewell cross-roads was due to trolley-bus wires and the divergences by and above Coombe Lone HOCSMIU RIVCR are one minute time-base marks. It will be noticed that at no other points does BRIDQE the recorded track diverge outside the SOft.-width of this ordinary arterial road. ' roorMfoce. ROBIN HOOD CATC ROUNDABOUTBUS STOP- BUS STOP noam ROBIN HOOD LANC BUS STOP- KCSWKtC AV€MJt- BUS STOP rOOTPHTH TV NORBITON couece DOAD ROUNDABOUT eweu. no AD CROSSROADS HINCHiet WOOD CA0SSA0AOS
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