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Aviation History
1951
1951 - 1274.PDF
FLIGHT, 6 July 1951 CONCERNING FLYING-BOATS . . • lightness and ease of maintenance, was jhe basic design require- ment for the electrical power system. The advantages obtainable from permanently paralleled sources of supply led to the adoption of a D.C. distribution system at 120 volts, in conjunction with a 24-volt D.C. system. The use of A.C. alternators for generation, with rectification of either part or all of their output, was fully investigated, but eventually the close speed range of the Proteus free-running airscrew turbine made the use of D.C. generators possible, eliminating the complications of an A.C./D.C. supply system. After describing the electrical system and powered flying controls at some length, Mr. Knowler turned to air-conditioning and de-icing. At the time the design was commenced, he said, no air-conditioning plant suitable for an altitude of 40,000ft, and capable of delivering the air requirements for over a hundred passengers plus the crew, was available. In order to meet Saunders- Roe's needs, and in view, also, of the Brabazon Mk II development, the Bristol Aeroplane Company's Engine Division was asked to develop equipment. This resulted in the development of two-stage centrifugal compressors delivering 60 lb of air per minute when operating at 40,000ft. The maximum cabin altitude under these conditions was 8,000ft. In parallel with this development was that of an expansion turbine refrigerator capable of dealing with the total air delivered. Two of these units were installed in the leading edge and were driven by shafting from the inner coupled engines. The installation also included humidifying units of vapourizing type, silencers, water extractors, etc. The supply would be automatically controlled for pressure, temperature and humidity. Air circulation in the cabins included re-circulation of filtered air, II the latter being mixed with the warmed fresh-air supply before passing through the wall linings. The system was duplicated. The icing conditions which the Princess had been designed to meet were minus 25 deg C. at 20,000ft, the icing being continuous, and a water concentration of £ gram/cubic meter being assumed. These conditions were met mainly by thermal means. A hot-air sandwich was provided over the whole length of the leading edge of the wings to 10 per cent chord, the supply being taken from muffs surrounding the jet-pipes of three power units on each side of the aircraft. The heat supplied to the leading edge was estimated to be 1,200 B.Th.U./sq ft/min as a mean, with a maximum in the stagnation area of about 4,000 B.Th.U. Hot air for tail de-icing was supplied by combustion heaters, each supplying 400,000 B.Th.U./hr. The air supply was from a forward-facing entry in the leading edge of the fin, the entry itself being de-iced by exhaust heat from the heaters. The fuel supply for these heaters was taken from the main fuel tanks. The air intakes to the engines were heated by hot-air muffs supplied with combustion gases by a bleed from a position on each power unit between stages of the turbines. Hot gas from this source was also supplied to radiators, surrounding the entries for cooling air for the generators, jet-pipe shrouds, etc. The airscrews were fitted with electrically heated over-shoes which were supplied via cyclic timers from the main electrical power supply. The power available for this operation was 30 kW, the current being cycled to the blades of two airscrew discs at one time. Provision was made for varying the period of the cycle. To de-ice windscreens, it was proposed initially to use variable alcohol-jets and windscreen wipers, but, eventually, the wind- screens were to be fitted with Nesa glass. Dry-air sandwiches were applied to all windows for demisting purposes and, in addi- tion, warm air was ducted to the inside. LATERAL STABILIZATION DURING excursions through the Saunders-Roe assembly shopsvisitors had often commented on the particular float arrange- ments adopted for the Princess and the S.R./A.i, and comments and questions had suggested to Mr. Dowden that a review of some developments and ideas associated with the lateral stabiliza- tion of flying-boats on the water would be of interest. When discussing flying-boats, said Mr. Dowden, the term "float" was used to describe a particular form of auxiliary flotation which, due to weight and wind upsetting-forces, must be provided in order to obtain lateral stability on the water under static and low-speed conditions. It would be realized that hydrodynamic considerations being the reason for its presence, the size and form of the auxiliary flotation would be primarily dictated by these factors. Having satisfactorily fulfilled the hydrodynamic or water- borne conditions, the designer was left (like the landplane designer and his undercarriage) with an appendage which was not required when the aircraft was airborne. Throughout the years of flying-boat design, the float had been the more common method of supplying the necessary auxiliary flotation; however, designers had sometimes departed from this more general formula in their efforts to achieve greater overall efficiency in their aircraft, or from necessity when other factors of greater importance had dictated. In its early days the flying-boat had been invariably of the biplane type, with the lower wing close to the water. The auxiliary flotation equipment required for static stability had then to be placed within the restricted height between wing and water, and, consequently, the float had been attached directly to the under- surface of the wing. As the size of aircraft increased and the lower wing/water clearance had become greater, there had arrived a requirement for suspending the float some distance below the wing. Thus the float chassis had come into being. The trend to the monoplane arrangement with its increased speed possibilities, and high wing-position dictated by airscrew Fig 1 Fig 3
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