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Aviation History
1928
1928 - 1105.PDF
NOVEMBER 29, 1928 89 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT fact that the actual construction was to be done at the Boulton & Paul works at Norwich, the Royal Airship Works at Cardington to do erection only (as regards the main struc- ture), a form of bolted joint was chosen, of such a type that . a complete ridge girder could be assembled at Norwich and sent to Cardington. The main longitudinals obviously had to be built in sections, being much too long to be transported as a whole, even if they could have been so manufactured. The logical thing seemed to be to divide the longitudinals at the " rings " or frames, and this was actually done. Over the outside of each frame corner is placed a relatively short length of fore-and-aft girder known as the frame longitudinal. This member is to be regarded as a part of the transverse frame, and to its ends are bolted (during the erecting process) the ends of the main longitu- dinals. The diagrammatic sketch, Fig. 1, will probably make the arrangement clear. & Paul, experimental sections of the airship were constructed for the purpose of proving the methods df detailed construc- tion, and also the type of stiff transverse frames evolved by Cardington. The various structural members developed by Boulton & Paul gave good results on test, and the complete test bay was erected at the Royal Airship Works and tested with entirely satisfactory results. Then, and not until then, the contract for the complete hull, fins and rudders of the airship was entrusted to Boulton & Paul, who built the following special classes of members : Main longitudinals, frame longitudinals, ridge girders, radial struts, shear wires, floor bearers, and all the necessary joints for connecting these members together. Types of Girder Used Generally speaking, two main types of girders have been used in the structure framework of R.101, both developed by Boulton & Paul, Ltd., and made possible by the long Fig. 4. View of the four drawbenches in the Boulton & Paul Works, Division of the Design Work Having thus completed, as it were, the single-line diagram of the main structure of the airship (shown in Fig. 2), the designing office of the Royal Airship Works at Cardington carried out the stress calculations, supplying the loads in various members to the Boulton & Paul designing office, which used the geometry and loads thus made available to convert the line diagram into an actual structure. The very closest co-operation between the Royal Airship Works and the Boulton & Paul works was obviously necessary, and Mr. J. D. North, chief engineer and designer of Boulton & Paul, was appointed to act as consultant in metal construc- tion to the Director of Airship Development. The detailed geometry of the design had to be calculated to fifteen signifi- cant figures, and the difference of the spacing of the strut joints on the inner and outer longitudinal booms, as well as the overall lengths of these booms, were calculated by using arcs of circles for each main and frame longitudinal, the main longitudinals being between 1° and 2° of an arc having a curvature of the order of a quarter of a mile radius. Before the actual manufacture was commenced, and in fact before the order for the structure was placed with Boulton previous experience of the firm in the design and construction of all-metal aircraft of the heavier-than-air type. These two types of girder are used in the main longitudinals and frames, respectively. Variations of the two have been employed in certain cases, as dictated by local considerations, but in the main the two types may be said to be characteristic of the structure. The " rings," or transverse frames, are composed of compression members stabilised by cables, the compression members being, generally speaking, built up of " bulb-section" steel booms with Duralumin webs. The radial struts are of similar design, but as the loads in them are considerably smaller, the booms as well as the webs are made of Duralumin. The fore-and-aft members of the structure, arranged as are the frame members to form triangular girders, are com- posed of tubular booms and struts, braced by cable, but the booms are of a different type, owing to the absence of the Duralumin webs used in the girders of the frames. These booms have been developed by Boulton & Paul after con- siderable research, and are used extensively by them as longerons in the fuselages of Boulton & Paul aeroplanes. They have become known as " closed-joint" tubes, and are 1020g
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