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Aviation History
1970
1970 - 0370.PDF
implication of a joint airport-seaport plan for Foulness. The overall costing results are distilled in the table reproduced on the previous page in slightly modified form. The effects of discounting can. perhaps, best be seen in the costs of actual conctruction. Those for the four sites, each developed up to a four-runway standard and assuming that all costs were to be paid today at 1968 prices, would be £543 million for Cublington. £579 million for Foulness. £532 million for Nuthampstead and £510 million for Thurleigh. When the costs—incurred possibly over a 20 year period from 1975— are discounted to the base year of 1975 they range, as can be seen, from £166 million for Thurleigh to £184 million for Cublington. The discounted sums include not only capital costs but also the continuing costs, such as those of surface access, incurred through the life of the airport—which is assumed to be 30 years from the start of operations in. say, 1982. Obviously some of the capital costs will be incurred before and some after this year. As already explained, these costs and benefits are discounted according to the date of their incidence and expressed as though they were incurred in a common base AIRPORTS ALL AT SEA? THE construction of off-shore airports is technically feasible, and they have many advantages over land-based sites, according to the Ministry of Public Building and Works. A report by the Ministry's airfields branch, just published*, summarises their research into the possibilities of such airports. It describes the various types of off-shore construction and includes information about such airfields already built in the United States, Hong Kong and other locations. The Ministry is now undertaking further research into the "gasholder" type of construction—a floating platform supported by a cushion of air—-which is believed to offer the greatest advantages for future development. The report points out that growing world population and the large built-up areas of cities, combined with rapidly increasing air traffic, will make it more and more difficult to find satisfactory land sites for new airfields, both civil and military. Since a high proportion of the world's major cities are sited close to the sea, they could be effectively served by off-shore airports. These would have the advantages of reducing aircraft noise over populated areas, relieving air-traffic congestion close to large cities, and reducing the problems of acquiring land and gaining planning approval. Airports might consist of purely floating platforms, or of platforms supported by piles or caissons founded on the seabed, or be constructed on land reclaimed by the building of dikes or causeways. Fully floating airports could be various types: 'Floating Aerodromes; available from MPBW, Lambeth Bridge House) London SE1. 328 FLIGHT International, 5 March 1970 Three more Fokker-VFW F.27 Series SQOs have been ordered by the 2 French Ministere des Postes et Telecommunications for its night-mail services, operated by Air France. Below, one of the 12 such aircraft at , present in use, and, left, an interior view year—in this case 1975. The choice of base year, however, makes no difference to the ranking of the sites in terms of cost. * But, as the report explains, the use, as a base year, of 1982. when the bulk of the recurrent costs start, provides a "more k meaningful measure" of the actual costs and benefits involved. The last two lines in the second section of the table show » these 1982-based discounted costs. Among elements in the table which need explanation is that j relating to Luton Airport which, it is assumed, would be closed if any of the three inland sites were to be chosen—or 1 extended if Foulness were to be selected. The recorded credit of £1.3 million represents the residual value of the present * Luton site. The additional noise costs for Luton given under the Foulness heading assume the future extension and develop- ' ment of the airport. The costs of "airspace movement" are those for the flying and passenger time in an enlarged London 1 terminal area and take account of the need for any more circuitous routeings. The passenger-user costs for Foulness are expectedly greater than for the other airports—but would presumably be higher still were the site not assumed to generate the smallest amount of total traffic. Under "residential conditions (noise, off-site)" the costs include those for families leaving, and of the "dis-benefits" suffered by those remaining 3 in the area. H.A.T. a platform supported on pontoons or large floats or one 1 constructed of hollow concrete box sections filled with j expanded polystyrene, tensioned by wires to form a continuous structure. Other types studied include a large, continuous steel- 1 box type of construction or the "gasholder" type—a platform * with deep side walls all round, which can be raised above 4 sea level by maintaining a cushion of air at a controlled pressure underneath. *( The "gasholder" type has two important advantages, accord ing to the report: the platform can be raised to a convenient "• and controlled height above sea level, the magnitude of the j stresses on the structure due to waves and swell is reduced, and the stresses are more readily calculable. Expanded poly- 4 styrene would be incorporated in the structure to provide buoyancy in the event of gas pressure being lost and to ^ facilitate construction and maintenance work. The Ministry is therefore continuing its researches into this type of construe- * tion. A model will be built to enable its behaviour under load and wave conditions to be studied, and the problems of j anchorage and mooring will be investigated. Subsequently, large-scale model work will be undertaken with the aim. of collecting sufficient reliable data to allow the building of a "floating aerodrome" within two to three years at any appro priate deep water location. One of the conclusions that the i Ministry has reached is that stresses imposed on floating structures by aircraft are moderate compared with those I imposed by wave action—a 992,0001b, 450,000kg aircraft can j theoretically be carried by a floating hollow concrete structure about 2m deep. '
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