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Aviation History
1947
1947 - 0431.PDF
MARCH 27TH, 1947 FLIGHT 263 non-stop), they considered the bomber design study andfound that, broadly, •with sundry necessary modifications, it would fill the bill. On M.A.P. suggestion the BristolAeroplane Co., Ltd., then started to review the design as a civil aircraft to conform to the Brabazon Committee'srequirements. From that point development of the aircraft went ahead—albeit very slowly, since every priority wasof necessity, and very properly, given to the company's war commitments. Thus was the Bristol 167 born; andalthough there is every possibility that the finished aircraft will be accorded some resounding and appropriate name,it is almost inevitable that in most people's minds it will always be known by the title '' Brabazon I." In this article we are attempting no more than anappraisal of the structure of the 167. So mammoth an aircraft as this cannot possibly be accorded the attention Wing centre-section and fuselage juncture, showing fuselageframes, stringers, longerons, and raised* floor structure, together with spar frames and essentialstructure of centre-section. air range requirement to a figure exceeding 5,500 miles.Such range requirements, when related to some sort of effective payload and performance, make an aircraft ofBrabazon I size almost inevitable. Having settled on an aircraft of the 300,000 lb category, the weight of the struc-ture and that of the fuel is likely to be approximately four times as much as the payload; it is thus even more impor-tant than usual to achieve the greatest possible efficiency. Obviously a light and safe structure cannot be designedwithout an accurate knowledge of external applied forces and the resulting internal loads in the structure. It is extremely difficult to obtain this knowledge for alarge aircraft by virtue of the great importance of dynamic effects arising from vibrations.- The standard way of deter-mining theyfaodes and frequencies of vibration is ts resonanceytfet the finished aircraft, but in the case of an it warrants in a single review. We have already dealt withthe power installation of the prototype (Flight, December 26th, 1946), and other elements of the aircraft will formthe subjects of later articles. In very broad outline the design considerations whichfinally resulted in the 167 can be summarized as follows. The aircraft is needed for the North Atlantic non-stopservice, the Great Circle route between London and New York being roughly 3,450 statute miles. When allowanceis made for minor navigational errors and the use of an alternative airport if need be, the total range requirementapproximates to 3,750 miles. However, if an aircraft is intended to fly this route non-stop with 100 per cent regu-larity, the design must cater for prevailing headwinds of up to 100 miles an hour at 35,000 feet. The natural effectof this is to increase the required still-air cruising range to the order of 5,000 statute miles. On top of this, allowancesfor take-off, climb, and circuits in stand-off periods, together with allowances for engine and aircraft deprecia-tion in efficiency, can easily boost up the equivalent still- aircraft such as the 167 this method was obviously unten-able, and a theoretical method had to be devised for pro- viding the information, the aircraft being idealized for thispurpose as an elastic body with 42 degrees of freedom. These calculations were checked by making a one-twentiethscale vibration model, designed to represent the elastic and inertial characteristics of the aircraft, and in point of factgood agreement was obtained with the theoretical results. Designing to Close Limits It may thus be seen that in the composition of such amachine as the Brabazon 1 not only did the operational requirements regulate the aircraft design to limits verymuch closer than is usual, but the structural make-up of the aircraft is also very closely defined by the dynamicparameters. The fuselage profile gives one of the most graceful body shapes yet designed; a circular sectionobtains over almost the total length, this basic form being modified only at the nose, where the windscreen causesdisruption, and at the extreme tail where the section
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