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Aviation History
1951
1951 - 0804.PDF
27 April 1951 501 large components as test wings, the early development of tooling and i^he elimination of snags had proved a great asset to the department. The glass-cloth moulding was a development by the production department, and to enable this to be done before designs were available, typical designs were used to make the experiments and to develop the technique. The Redux process on the wing skin and fuselage had already been partially developed and was in full production on the Dove. Taking a retrospective view, it was now obvious that the technique used on the Dove was only in its infancy by comparison with the requirements of Redux on the Comet. As an exercise, and to enable the production department to develop its technique and tooling, a typical design of wing and fuselage skin was used. The production of these skinsnecessitated the design and manufacture of suitable presses, and these were designed by the company's engineeringdepartment and made by the tool section. As soon as the technique had been developed to a reasonable standard, theproduction department proceeded to produce a complete wing and a 24ft-long portion of the fuselage for physical test.By this time the" production of tools and development had gone entirely to plan and was working out extremely satis-factorily. Under heading (ii), "production of tools at a reasonable cost for a small batch of aircraft," Mr. Povey stated that, throughout, the policy had been adopted of using plaster models for the development of drop-hammer, stretcher-press and Hufford tools on all major components. The method of producing these large plaster models was to obtain from the loft department accurate information and loft plates. Loft plates printed on sheet metal were then cut out and assembled into three-dimensional structures, which were thereafter filled with plaster and so provided accurate, solid models from which the majority of the tooling was made. As Reduxing was one of the most advanced techniques on the Comet, the production of stringer-to-skin Redux tools used for the production of double-curvature panels was worthy of brief description. The fuselage-nose plaster model was accurate to within a tolerance of i/32in, and contained a complete replica of the position and shape of all stringers and panels. The stringers were represented by grooves which were formed in the plaster. In side elevation, the centre-line of the fuselage- nose structure was a curve, and this fact necessitated the production of separate left- and right-hand tools for each stringer. The total number of tools produced from this model for Redux purposes was no fewer than 64 pairs. The mating surfaces of the top and bottom tools had to be a 100 per cent perfect fit, as it was essential that every part of the surface for which adhesion was required had to have equal pressure. Models of "surface-table" building floor showing (above) the build-up of the complete fuselage from basic sub-assemblies, and (left) the track circuit for the process of assembling complete stub-wings to fuselages. The method of making the main fuselage rings was believed to be unique: it was the first time that such a tech- nique had been used in Great Britain. Straight sections were produced in a set of standard rolls, and the sections were then formed by stretching and bending the fuselage rings of varying radii on the A. 10 HufTord machine. Economy was exercised by producing one basic tool which, by adding different radii segments, adjusted the tool to all ring diameters. The rings were bent round the tool while under tension, by which means the webs of these 20-gauge, 10ft 3m diameter rings were perfectly flat. The method of attaching window frames to the fuselage skin was somewhat novel, in that the window frames, which were deep-drawn drop-hammer pressings, were Reduxed to the fuselage skin in situ while the skin was being assembled in the fuselage side jig. The equipment used for this opera- tion consisted of two castings: one was located accurately in the side jig and determined the position of the window frames, whilst the mating casting was hollow and formed a steam box; this was drawn into position by two standard 4in Mosquito hydraulic flap-jacks, which applied the necessary pressure. The steam which supplied the heat was obtained from a pipe located over the top of the jig; the exhaust passed out through steam traps at the base of the jig. Fluid pressure to the jacks was supplied by an obsolete type of Mosquito hand-pump, and the whole of the apparatus was mounted on a trolley which could be wheeled into position at any station required on the jig. The operation for fixing a window complete was approximately 25 minutes. One of the company's great aims had been to keep the external part of the fuselage free from jig structure, so that the operatives had ready access to their work. The whole of the fuselage-building floor area was regarded effectively as a surface table. The accuracy of the floor itself, or the rails which were mounted on the floor and formed the track, was not critical, in that the accuracy and flatness of this large area actually depended on the alignment of a number of vee blocks and small flat-surface stools. It was considered that the horizontal plane of the area was accurate to within ±i/32in. The jigs used on this floor to locate the various elements of the fuselage had been designed so that they could be used as mobile trolleys and could be transported, complete with components, between stations on the track lines. Once the jig trolleys had received from the initial static building jigs, the components such as keels, noses and centre sections, they could be readily transported to any station on the track for the purpose of completing the opera- tions which eventually built up the whole of the fuselage. These jig trolleys were each fitted with vee blocks and sur- face pads which corresponded with, and could be mated to, any of the vee blocks and surface-plate stools on the line. By this means, a simple series of fuselage-building jigs had been produced economically which, by adding four track wheels each, became substantial trolleys that could handle the large and heavy components. The wing-building track was constructed on similar lines to the fuselage track. The stub-wing building jigs were
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