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Aviation History
1951
1951 - 2252.PDF
f LIGHT, 9 November 1951 601 ANSWER to the PILOT'S PRAYER? Trying-out the Decca Flight Log npHERE can surely be few pilots who, at some point during J- the sweating penance which remorseless Link instructors innocuously term "S.B.A. practice," have not wished to be miraculously provided with some cockpit-borne indication of the path pursued by the Link trainer's "crab"—that misconceived invention which has such an infallible knack of turning the wrong way on to the beam, and such a propensity for leaving its unfor- tunate pilot to flounder in an interminable "twilight" zone. The Decca Flight Log, it seems, may well be the means of their deliverance. Much has been written in the pages of Flight about the merits of the British Decca hyperbolic fixing system and a comparison made with the American-sponsored V.O.R. associated with D.M.E. International acceptance of either aid as standard equipment is still, unfortunately, the subject of international con- troversy. In this country, however, after a protracted period of professed scepticism, the M.C.A. eventually agreed to conduct extensive trials of the Decca system; and, having done so, it is now quite convinced that the latest Decca development, the automatic Flight Log, is in fact the answer to many of our existing traffic control and navigation problems. Versions of the Flight Log have been installed in various aircraft and subjected to intensive experiment. Last week I had the opportunity of trying out for myself the latest version of the Log, the "or" unit fitted in R.M.A. Rob Roy, prototype of B.E.A.'s Clansman-class aircraft (Mara- thons). Associated with a Mk VII receiver, the equipment weighs 120 lb. I found the Flight Log conveniently mounted in the central position above the pilots' instrument panel. The three Decometers are located beside it for checking purposes and the lane-identification meter is found on the left-hand side of the cockpit. The latter unit has been developed to avoid any possibility of lane ambiguity and is also, I found, remarkably ingenious in the way in which it presents its information. The Log itself is 12J inches wide and contains up to 20ft of route charts, specially drawn to incorporate full information on ranges, marker beacons and airfields, but devoid of the normal topographical data. The aircraft track is recorded by a Perspex stylus which traverses a viewing aperture measuring 10 by 4 in. Charts of differing scale can be made up into rolls and stored in the display head itself. Should the aircraft cross the boundary of one chart on to another of different scale, a push button brings the new scale into operation. The charts now being used have been modified from those in use previously and are now almost on a conventional projection. The decometers themselves are set from the lane identification meter and the stylus can be set up on its correct starting point by positioning it at a lattice intersection shown by the Decometer readings (the lattice being printed on the 1 (Below) R.M.A. "Rob Roy," the Clansman-class prototype H.P. Marathon with which the M.C.A. is now conducting evaluation trials on the Decca Flight Log. (Above) Located well within the normal field of vision of both pilots, the Flight Log and its three Decometers form a compact unit. Tha control box is positioned on the roof. I In; lone-identification meter is mounted at the captain's left side. reverse of the chart comes into view at the touch of a light-switch). Selection of the appropriate zone and scale settings for the chart in use are made on the control panel, on which there is also a single knob by which, for setting-up purposes, the speed and direction of the stylus is controlled. In the air I found the stylus followed the aircraft's track with almost uncanny accuracy. Follow- ing a flight plan which involved the use of four-course ranges and 75 Mc/s marker beacons, it was literally possible to navigate the aircraft by steering the stylus, and although there is an initial tendency to overshoot when turning on to a new range course, a little practice will soon smooth such inaccuracies on the part of the pilot. One particularly useful gadget is the "time inject" switch; with it the flying of holding procedures is rendered easy by the fact that the stylus will, on selection of a desired interval, auto- matically record rime marks. During a G.C.A. approach to London airport, also, it was possible to check with the Log our actual distance from the end of the runway with that given by the talk-down controller. This flight, unfortunately, could only be a short one, and therefore only served to make me keen to try out the Log at greater length. To me it was nevertheless convincing proof that Decca and the automatic Flight Log must be carefully considered for the role of the major navaid on any but the long over-sea services. E.A.G.R.
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