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Aviation History
1953
1953 - 0070.PDF
68 FLIGHT, 16 January 1953 Terms used to describe take-off performance are visually defined by this diagram, which shows how a pilot can make use of the stopway (or, alternatively, both the stopway and clear way) if an engine fails at critical speed. If he decides to occe/erote-stof), the aircraft comes to rest within the "take-off area" (AX), also referred to as the acce/erate-stop distance; on the other hand, he may continue the take-off to clear the "screen" at Z by a specified margin (the aircraft is also required to clear subsequent obstacles by an increasing margin. AZ is known as the take-off distance. For purposes of clarity, the aircraft is assumed to use all available space; thus, the take-off run (AY) is equal to the take-off surface. 50»t SCREEN-; STOPWAYS AND CLEARWAYS . . . It was finally recommended that stopways and clearways should be provided when "various economic considerations" indicated that operational requirements could best be met by their use. Some further recommendations were made as to the physical characteristics of stopways and clearways. Certain minimum widths (varying between 100 and 200ft) are specified for runways, and it is further required that these widths be augmented by strips on either side of the runway. (The distance between the runway centre-line and the outside edge of the strip varies between 250 and 500ft according to the classification of the runway.) The stopway must have the same width as the runway it augments and the clearway should be as wide as the corresponding strip. Maximum values for slope angle were also decided. The question of defining the required strength of a stopway provoked considerable discussion between delegates; their recom mendation was finally phrased as follows : "The stopway should be so prepared or constructed to enable aircraft which the runway is intended to serve to run over it in exceptional cases and without hazard at the operating speeds that might be expected in this area after the interrupted take-off." As clearways and stopways are liable to be used as approach paths, it was agreed that approach light fittings could be installed in either, provided that such fittings were breakable and unlikely to cause serious damage to aircraft. Since I.C.A.O.'s performance requirements for aircraft are still in the development stage, recommendations made during the A.G.A. session were intended only as guidance to airport designers during the interim period. The new concept of a three-part run way must be considered not only in relation to standard aircraft performances, but in relation to the effects of high temperature and elevation. It would be pointless, for example, to build a clearway catering for an aircraft's engine-out take-off performance if, under high-temperature conditions, the rate of climb were insufficient for it to clear obstacles upwind of the take-off area. These simple rules were therefore framed to allow for the effects of elevation and temperature in deciding on runway dimensions : the basic length should be increased at the rate of 7 per cent per 1,000ft elevation above mean sea level; this corrected length is further increased at the rate of 1 per cent for every 1 deg C. that the aerodrome "reference temperature" exceeds the temperature in the standard atmosphere for that elevation. A specific study of local conditions is required when corrections by this method exceed 35 per cent. At present the relationships between performance requirements and aerodrome lengths are complicated and often far from satis factory, but the I.C.A.O.'s work in evolving systems of standards is bringing continuous improvement. Meanwhile, progress will depend largely on co-operation between the airport authorities and the airlines. As the concept of the three-part runway takes effect, operators will find it necessary to keep close watch on changes in aerodrome characteristics if the potential advantages of stopways and clearways are to be fully realized. * Copies of an I.C.A.O. document which discusses the subject in greater detail ("Aerodromes, Air Routes and Ground Aids Division: Report of the Fifth Session**) may be obtained at 5s. 2d. from Her Majesty's Stationery Office, P.O. Box 569, London, S.E.I THE VALUES OF PROTOTYPES THE impressive sums of money for which various British *- prototypes were insured while flying at Farnborough, were revealed at a recent meeting, in London, of the Insurance Institute. Members had assembled for a talk on aviation insurance by Capt. A. G. Lamplugh, underwriter and principal surveyor of the British Aviation Insurance Co., Ltd. His talk was followed by a showing of the Shell film of last year's Farnborough display; and, as a supplement to the sound track commentary, the audience were quoted values for several of the aircraft depicted. The machines and the amounts men tioned were as follows : Hawker Hunter, £140,000; Vickers- Supermarine Swift, £135,000; Vickers Valiant, £750,000; Vickers-Supermarine Type 508, £230,000; Fairey Gannet, £100,000; Short S.A.4, £500,000; Gloster Javelin, £250,000; Avro 707B, £160,000; Avro 707A, £180,000; Avro Vulcan, £700,000; Bristol 173, £100,000; Bristol 171, £38,000; Westland S-5i> £22,000; Saro Skeeter Mk. 4, £11,500; Bristol Britannia, £500,000; D.H. Comet (Mk. 1 prototype), £500,000; Vickers- Armstrongs Viscount, £250,000. The Saunders-Roe Princess flying-boat, the audience were told, was not fully insured while flying, but was covered against acci dents "on the ground" to the extent of £1,500,000. No sum was quoted for the D.H.110, which was destroyed during the display. It can be misleading to express the value of a prototype in precise terms of £ s. d. The true value of such an aircraft varies according to the amount of useful knowledge and experience which it yields. In some cases, the sums quoted seem to be based solely on the manufacturing costs involved; production Britannias, for example, will cost more than the sum for which the prototype is insured. On a £/lb basis, the most highly insured machines are the Avro delta-wing research types, followed by the fighters and the twin-engined helicopter prototype. Values quoted for the bombers appear to be higher, in proportion to weight, than those for the airliners. In his lecture, Capt. Lamplugh traced the earliest beginnings of aviation insurance, remarking that he still possessed a proposal issued in 1910. An interesting reflection on the increased safety of airline travel was provided by the fact that in 1918 insurance was the second or third item in the cost of commercial air transport; today, it was only seventh or eighth. In 1919, however, the total premium market in this country was only £50,000, and the amount which might have been paid out was obviously much greater. Discussing the handling of claims, he observed that it was an unwise practice to re-insure with foreign companies inexperienced in aviation. As an example of the changing values encountered in air-transport insurance, Capt. Lamplugh pointed to the DC-4, originally sold for £50,000 and now in some cases insured for up to £250,000. There were virtually no spares for these aircraft (the fact that manufacturers retained the copyright of aircraft repair schemes was one of the important differences between aviation and marine insurance), and every one was a potential total loss. The lecturer showed slides illustrating the impressive increase in values with increased all-up weight and wing loading.Cost of repairs was also rising as a direct result of increased complexity. The quality of surveyors was most important, not only to individual companies but to the market as a whole. The speaker felt there was much to recommend an independent technical pool of resources under the control of a suitable committee capable of advising on the more technical questions. To support his belief that official accident investigators are prone to overlook evidence and draw wrong conclusions, Capt. Lamplugh quoted the case of a Canadian airliner which dis integrated in the air. The official conclusion was that no explana tion could be found, but the company bought the entire area and erected a building over the scene of the crash. After months of research the cause was traced to a bomb explosion and the man responsible was finally brought to trial and executed. It was unfortunate, said Capt. Lamplugh, that the power of the Accident Investigation Branch had been strengthened under new regulations. In conclusion, the lecturer outlined some of the more important problems which would confront the insurance market in the near future. These included the question of insuring aircraft leased to independent operators for trooping; of tourist services operated by high-density aircraft; and of helicopters, which must still be regarded as potentially dangerous.
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