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Aviation History
1951
1951 - 0067.PDF
January 1951 45 INTERNATIONA! NAVIGATION-AIDS ... Before assessing the refinement implicit in the Flight Log, let us review what the basic realities of the Decca Navigator system are. That a master station and three slave stations, together comprising a "chain," emit continuous wave signals in hyperbolic patterns is widely known. The effec- tive range of these signals is 300 miles, measured in any direction from the master station, i.e., the centre of the chain. Thus, on a linear range basis alone, Decca has, at the very least, six times the coverage of V.O.R| whilst the area coverage is 36 times as great; at the same "time Decca possesses inherently greater accuracy than V.O.R. over all ranges. Again, and in complete contrast to V.O.R., Decca provides fixes and distance measuring as intrinsic functions. So much for the " capacity " of the aid. As to cost, we have mentioned that V.O.R. alone may cost between £12,000 and £30,000 per ground station. Ground stations are required at 100-mile intervals, and because of the uni-directional limitation, they must be duplicated, one for incoming and one for outgoing traffic, along an air corri- dor. If D.M.E. is used as well—and it is necessary if fixes are to be obtained—then the cost per aircraft will be in the region of £l,5O0-£2,OO0. Against this, the cost Of a Decca chain is estimated at £140,000,* to which must be added a small sum for the Decca equipment in each aircraft. The figure would be the subject of an agreement between the operators and the company building the equipment; to give an example, the cost of shipping, on a hire basis, is £350 per ship per annum. The great number of V.O.R. stations required to provide a given coverage vis-a-vis Decca not only has its effect in prime cost, but also affects running costs as well. These are, of course, chiefly concerned with maintenance, and whilst a V.O.R. installation might not require any greater maintenance than Decca, the maintenance factor is in- creased by the power of the numerical difference in ground stations required. There is, too, the not incon- siderable point that, in so far as the financial commitments of a Government are concerned, a Decca installation is equally as applicable to maritime use as to aviation, and in this regard it is worthy of note that the siting of *he proposed chain in Spain has been considered primarily from the maritime aspect. It is also worthy of consideration that the only extraneous costs to be borne by foreign Governments by the adoption of the system are * This sum will, naturally, varyaccording to rates of exchange, labour rates, costs of materials, trans-port and many other items subject to variation as between one countryand anothtt- The Decca Company, in any case, consider £140,000 to beon the liberal side, and suggest that "somewhere between £100,000 and£140,000" is likely to be more realistic. This map shows the siting of the proposed Decca chain in Germany, together with the (dark-tone) existingor projected control areas and air- corridors. The black-line boundary defines the limit at which better than one mile (day) and five mile (night) accuracy is given. The harlequin squares are V.O.R. sites, and it is of Point to note that within the area covered by one Decca chain, « V.O.R. stations are required. those of the licences to manufacture, and those of the drive and phase locking units for the slave and master stations. These units the company reserve to themselves the right to supply. The whole of the rest of the chain would be financially a subject of internal arrangement in die country concerned. Finally, if a navaid system can, without exten- sion, be used by ships as well as aircraft—as this system can—then the specific cost in terms of total-cost/user-units is very considerably reduced: an attractive picture to Treasury eyes. To revert to the Flight Log, however, we have stated that it is a compact form of pictorial presentation which the pilot can use broadly or acutely, according to the requirements of the moment. Many visitors to the S.B.A.G show at Farnborough in September were able to see for themselves how the Flight Log worked in the Airspeed Ambassador. The Flight Log was installed in the aircraft, in addition to the standard Decometers, just before the S.B.A.C. dis- play, and track records were obtained not only of the flights from Christchurch to Farnborough and back, but also of the demonstration circuits and landing approaches made on each day during the show week. The accuracy of the records on the maps was quite remarkable. In one case, the trace even shows a mild "jink" made during the approach on one day when the Ambassador was found to be closing-up on the aircraft preceding it; the lengthening of the flight-path is faithfully recorded. The difference between the radii of the demonstration and approach cir- cuits in this follow-my-leader performance was also closely indicated on each day. From the navigational point of view the results obtained during the Ambassador's flight to Farnborough from Christ- church on the Monday preceding the opening of the Exhibition were probably of more interest than any other. The weather conditions on that day were ideal for an initial check, with a deep layer of continuous cloud covering the whole route, but breaking, conveniently enough, within a two-mile'radius of Farnborough. The aircraft entered cloud at Bournemouth, where the
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