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Aviation History
1955
1955 - 1039.PDF
FLIGHT, 29 July 1955 151 CITY HELICOPTER TRAFFIC Some Thoughts on Airstops and Traffic Control By J. MACDONALD IN November last year the foundation stone of the futureParis airstop was laid. Construction is to cost li millionpounds, and it is estimated that when it is ready there will be a helicopter service between London and Paris every 20 minutes. This year Belgian Airlines plan to extend existing Continental schedules to include regular flights between Brussels and London. Let us look at London and see where, should it arise, all this traffic is likely to terminate, and examine possible arrangements which might be made in preparation. The South Bank airstop (Fig. 1) introduced a little over a year ago, is essentially an interim arrangement. This site, the life of which is limited by building-development plans, offers at the moment a patch of concrete measuring some 300ft X 100ft. Any facilities which are provided have to be brought in when required, and withdrawn in entirety when flying has ceased, since the alighting area then reverts to the category of public gardens. A maximum of three aircraft of size equivalent to the S-55 can be accommodated in the space available. The dimensions of the Piasecki helicopter, 134ft overall and standing 25ft high, gives us some idea of the size of alighting areas which must be considered in the future. Allowing for terminating and international services, a total area of something like 500ft x 700ft is likely to be required (shown by the dotted area in Fig. 1). There are four attractions in the roof-top site: (1) Since the building which supports it may be used for other purposes, it puts highly valuable land to more economic use. (2) Accom- modation in the building may be let and thus help to defray a substantial part of the total cost. (3) Operationally it will be more satisfactory, since there will be few obstacles in the approach path. (4) Alighting on ground sites between large buildings will undoubtedly be difficult, and ground sites in large cities may for this reason have to be larger in area than roof-top sites. In most cases it would be impracticable to adapt or strengthen existing roofs and it is therefore inevitable that heavy capital expenditure will be required, and there will be town-planning problems. An official survey some four years ago estimated that a five-storey building giving a roof area of 300ft x 150ft in each of two directions would cost around £1,200,000. The building or buildings which form the base should, generally speaking, be as tall as possible so that the expense of roof strengthening would be but a small proportion of the cost of the main structure. It should not be necessary to think of Fig. 1. The South Bank site and its sur- roundings. Latterly the grass area has been used as well as the concrete (shown in black). Dotted lines mark the 500ft x700ft "ideal" area. HUNGERFORD BRIDGE: Fig. 2. Arrangement of the proposed Paris airstop, on the roof of a ten-storey build- i anything higher than the proposed Paris airstop, which will reach to approximately ten storeys (Fig. 2). It is likely that helicopter traffic will make use of a system on the lines of the Decca Navigator. One authority has specified a course indication sufficient to enable the pilot to remain ± 300ft horizontally and ± 150ft vertically from the centre of his prescribed track up to a distance of 75 miles. Since heli- copters will be largely confined to the airspace between 500ft and 1,500ft any navigational system must be capable of providing satisfactory information from ground level upwards and must be free of atmospheric effects, fading and line-of-sight limitations. A recent forecast indicates that the ultimate navigational system will be by means of airborne radar, with ground reflectors provided where required. The helicopter must offer at least the same schedule reliability as surface transport, and therefore a let-down aid must ultimately be available to provide a means of alighting at the landing area in zero conditions, from any direction, and at relatively steep approach angles, depending on terrain, winds and obstructions if any. There is a future here for G.C.A. controllers—given the right equipment. In ten years' time, it has been calculated, New York City will have 300 helicopter movements per day. In the U.K. we can expect a somewhat lower frequency, but we can depend on more inclement weather conditions. We must therefore be ready with a collision-avoidance system which will allow for considerable traffic expansion later. Airways specifically for rotating-wing aircraft must be estab- lished on the same principle as those provided under the National Airways scheme. Their dimensions will be, perhaps, half-a-mile either side of the prescribed track and vertically between 500ft and 2,000ft above terrain. Control zones of three miles' radius and 2,000ft high may be necessary at certain junctions and terminals (Fig. 3). Contd. overleaf Fig 3. Control zone for helicopters using the South Bank site. HUNGERFORI BRIDGE ^^~I/7c'•
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