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Aviation History
1953
1953 - 1651.PDF
FLIGHT, 18 December 1953 805 ALL-WEATHER LANDINGS Air and Ground Research by the Blind Landing Experimental Unit By W. MAKINSON, M.Sc, A.M.I.E.E. TOO often, and sometimes tragically, one is reminded of the dangers of all-weather flying, especially during the critical period of approach and landing. In civil airline operations, where the safety and comfort of passengers is all- important, the acceptable weather minima thus determined set standards which in this country have involved the Corporations in financial loss. In particular, fog, by day or night, frequently disorganizes scheduled flying and, as demonstrated last winter, may suspend air traffic for long indefinite periods. In war no such option may be available. As in this atomic age the British Isles become increasingly vulnerable to devastating air attack, it is obvious that military air movements can accept no arbitrary cancellations. Means must be found of operating air craft under all possible weather conditions. This briefly gives the background to the basic problem facing the Blind Landing Experimental Unit, formed by the Royal Air craft Establishment in 1945 with the terms of reference implicit in its title. At that time contemporary advances in radio naviga tional aids and automatic pilots encouraged an all-out attack, aimed at making the process entirely automatic. By 1949 this ideal appeared to be at least in sight. Approximately five hun dred landings had been made at Woodbridge in a specially equipped aircraft during which, from the start of the approach to the completion of the landing run, only such functions as the operation of throttles, flaps, brakes, etc., had been left to the human pilot. The system was not perfect; but the practicability of automatic landing had been proved and a useful guide obtained as to the penalty likely to be exacted, in weight and complexity, by equipment incorporating the necessary refinements. Whilst these experiments were in progress, other workers— notably E. S. Calvert at Farnborough—were making a flanking Capable of being quickly raised and lowered by a powerful winch, this small balloon permits instrument-recording of air-to-ground visi bility measurements without the need for sending up an aeroplane. Crown Copyright Clear-weather interlude at B.L.E.U.: Approach-path data being recorded by a ground observer with the aid of a Viking. THOUGH the existence of the R.A.E.'s Blind Landing Experimental Unit is well known, little is ordinarily heard about its work. In this article, its superintendent describes current investigations being made at the Armament and Instrument Experimental Unit, Martlesham Heath, Suffolk. The research involves flying in the worst of weather and, as the author states, one of the pilots has been awarded an A.F.C. in recognition of his work. Mr. Makinson points out that the views expressed are his own, and do not necessarily reflect those of the Air Ministry or M.o.S., who have given permission for their publication. attack on the same problem by introducing radical improvements to the airfield lighting systems, leading to the now familiar centre line and cross-bar pattern of approach lights. In conjunction with high-intensity runway lighting, this system is believed to provide the essential elements of visual guidance required in both horizontal and vertical planes for manual landing, provided that the visibility is such that a sufficiently large extent of the pattern can be seen from the air during the manoeuvre. As this method requires no additional airborne equipment it is attractive economically. But, as the spread of the ground lighting pattern must obviously be limited, it is essential that, during operation in low visibilities, means should be provided whereby a blind-flown aircraft can be brought accurately and without difficulty within the effective visual range of the lighting pattern, and in an acceptable configuration relative to the runway in use. At present a proportion of the scientific effort is being devoted to this more limited objective and to a study of the factors which will then decide the overall operational value of such a composite method—i.e., the determination, for any class of aircraft, of the limiting weather conditions in which safe landings will still be possible. On the results of this investigation the strength of the case for a truly blind landmg system must depend. Approach Methods.—The basic radio approach aid is the instrument landing system, the specification of which is subject through I.C.A.O. to international agreement. For military use, certain simplifications and improvements have been introduced as a direct result of the Unit's work in this field, notably the introduction of a narrow beam localizer aerial system to minimize siting effects, with the option of "offsetting" the beam where territorial considerations preclude the use of the normal centre line installation. The^I.L.S. facility provides, in both horizontal and vertical planes^ overlapping beams of coded radio-frequency energy from which radio receivers in the aircraft derive currents proportional to the angular position-errors subtended at the localizer and glide-path origins respectively. These error currents may be pre sented to the pilot on a single instrument indicating the displace ment of his aircraft from the ideal approach path in the two planes, enabling him to take corrective action. Provided he can achieve and maintain this path sufficiently closely he should be brought into a position from which a successful landing can then be completed visually. The difficulty of "flying the needles," which provide displace ment information only, will be fully appreciated by anyone who has driven a car in fog when only the near-side kerb immedi ately 'adjacent to the vehicle is visible. To prevent the pilot making an oscillatory approach, some anticipation (or an appre ciation of the rate of closing the beam) is required. This rate term, given a perfect beam, could be inferred from trie velocity of movement of the I.L.S. needle but, in azimuth, radio beam dis tortion (beam bends) caused by siting effects will introduce short-
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