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Aviation History
1971
1971 - 0060.PDF
FLIGHT International, 14 January 1971 he transferred in 1952 to RAE Farn- borough. There he was concerned with the problems of supersonic and hyper sonic flight, constituting much of the original British work on the supersonic transport. He later became head of Projects Division, which was involved with the assessment of future aircraft designs. In 1965 he was appointed projects director, Jaguar and Anglo- French Variable-Geometry Aircraft, and became DG Concorde in 1966. V IH By T. M. B. WRIGHT ONE OF THE MOST important achieve ments of British avionics in the post-war years has been the develop ment of blind-landing techniques, and the advances made, particularly on the Trident and VC10, have had an inter national impact. The current blind- landing system is, however, based on conventional ILS, which has some fundamental, and in certain circum stances very severe, limitations which arise largely from siting difficulties. Although these do not present any crucial restrictions on deployment at most major airports, since movement rates in thick fog will initially be very low, all-weather operation implies the maintenance of clear-weather move ment rates under all conditions. In the long term it is necessary to look towards the achievement of this goal at all levels of airfield sophistication. An important step in this direction is being taken by the Royal Aircraft Establishment, Farnborough, which is developing, in conjunction with Plessey Radar and Dynamco, a technique known as Correlation Protected ILS (CPILS). This is the subject of a patent granted to G. F. Clarke and J. Benja min, of the RAE, which S. S. D. Jones, head of RAE's Radio, Navigation and Guidance Division, has summarised in the following words: " 'Correlation'—in the context in which the term is used in CPILS—is a mathematical concept. Its dictionary definition provides the basis for an explanation of the technique. The Oxford Dictionary defines correlation as 'the relation of correlates', and the noun correlate as 'either of two things necessarily implying each other'. "In CPILS the 'things' are wave forms, which modulate microwave carriers transmitted from pairs of beacons. The protection is achieved by imposition of the necessary con dition that a signal must be received from both the sources within a very PEOPLE AND POSTS Mr Richard (Dickie) Blyth, from 1953 to 1965 military aircraft sales manager of de Havilland, who specialised in after-sales service to foreign air forces, died on December 26 at the age of 56. Mr Adam Hogg has joined H. R. Smith (Technical Developments) Ltd, of Thame, Oxfordshire, as chief elec tronics designer. short time-interval. A signal received from a displaced source—for example, by way of reflection from an aircraft on the circuit—will fail to satisfy the correlation criterion, and will there fore be suppressed. "In this application the conventional ILS localiser is replaced, or aug mented, by a pair of microwave trans mitters which straddle the runway. The first transmitter radiates a train of very short pulses, the carrier fre quency being about 5GHz. The second transmitter radiates a synchronised train of pulses, but with a carrier fre quency that differs from that of the first by, say, 110MHz. "This difference-frequency (Fig 1) corresponds to one of the channels allocated to VHF ILS. The first half of the pulse transmitted by the second transmitter is time-advanced and modulated at 90Hz. The second half is time-delayed and modulated at 150Hz. These modulation frequencies are familiar to those versed in ILS; they are the frequencies with which the two halves of the split beam are 55 Mr C. L. G. Worn has been ap pointed director and general manager of Dowty Servos Ltd at Tewkesbury, Glos. Mr David McConnell has been appointed to the board of Scottish Aviation Ltd as commercial director. Mr W. T. Gill retired from the board of Rolls-Royce Ltd last month after 31 years' service with the company, including 24 years as a director. modulated to indicate magnitude and direction of displacement. "The glidepath facility (Fig 2) is identical in principle with the localiser. Its aerials are displaced vertically, however; the displacement is much smaller (about 10m) so the bandwidth is correspondingly greater, and it is convenient to use broad-band noise rather than pulses as the basis of the correlation technique. "The two C-band frequencies allo cated to each glidepath channel differ by an amount equal to the UHF glide- path frequency, which is 'paired' with the corresponding localiser channel. Consequently the same coupled chan nel switching can be used as when the VHF system is in use." The use of the correlation principle greatly reduces operational problems arising from aerial lobing (due to spurious signals arising from reflec tions of the ILS beam from large objects in the vicinity of the runway), and it is compatible with and easily incorporated in conventional ILS equipment. Fig I Localiser pattern LINES OF CONSTANT TIMEDIFFERENCEx TX I SE COURSE LINE A' ' ' La 3 1 i i FT • TX2 Fig 2 Glidepath pattern LINES OF CONSTANT &'\: I TIME DIFFERENCE "X 111 THRESHOLD
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