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Aviation History
1928
1928 - 1104.PDF
SOTPLEMEKT TO FLIGHT 88 NOVKMBEK 29, 1928 THE AIRCRAFT ENGINEER FRAME LONGITUDINAL MAIN LONGITUDINAL INNER RIDGE GIRDERS INTERMEDIATE RADIAL STRUTS MAIN RADIAL STRUTS OUTER RIDGE GIRDERS Fig. 1. Sketch showing, diagramatically, the main structure members of R. 101. produced, from the initial stage of soft flat strip to the finished girder section ready for transport to Cardington^there to be rigid airships it has been customary to use transverse frames which were not in themselves stable structurally and had to be braced by wires or cables. The " rings " of R.lOl are self-sufficient structures in that they have been so designed that no radial wires are required in the plane of the " rings " and running to a single point in the centre of the polygon formed by a transverse section through the airship. To obtain the necessary structural stability without using cable bracing it was necessary to make the "rings" or frames very sub- stantial, and ultimately a type was evolved composed of triangular section girders in which there are two girder members on the outside, known as the " outer ridge girders," and one member on the inside., called the " inner ridge girder." These ridge girders (outer and inner) were then connected by members known as radial struts (main and intermediate), and the whole braced by cable so as to preserve the shape. The arrangement may be followed by referring to the accompanying diagram (Fig. 1). To the outside of the frames thus formed were attached the longitudinals which give the airship its streamline form, and which carry the outer fabric covering or envelope. This fundamental" scheme " having been decided upon, the next problem was to decide upon a method of joining to each other and to the longitudinals the ridge girders forming the sides of the polygon. In the Zeppelin airships, apart from the difference in the details of the various girder members, the fore and aft girders are riveted to the " rings " or frames, forming a structure which is statically indeterminate because the end conditions are not known with any degree of certainty. This it was decided to avoid, and in any case the tubular Fig. 2. Outline of R. 101, showing members made by Boulton & Paul. raised into position on the airship and bolted in place, without any fitting being done in situ. As the whole subject is so obviously one of aircraft engi- neering, and quite exceptional aircraft engineering at that, it has been decided that the notes which follow will not be likely to appeal to general readers of FLIGHT, being neces- sarily of much too technical a nature. Consequently we have decided to place this outline of the building of the main structure of R.lOl in the pages of THE AIRCRAFT ENGINEER, which has been greatly enlarged this month in order to enable us to place on record an appreciation of the very wonderful piece of engineering achievement which the building of this remarkable structure represents. Before going into detail concerning the various types of girder, &c. of which the main structure of R.lOl is composed, it may be helpful to give a very brief outline of the general principles adopted in designing this airship, as in that way it will be easier for readers to realise the problems involved and to appreciate the ingenious ways in which they were tackled by Boulton & Paul, Ltd. Keynote of the Design It is difficult, in dealing with a relatively complex struc- ture such as that of a large rigid airship, to point to any one feature and to say that this forms the basis of the whole design. In the R.lOl, however, although this airship incor- porates a large number of unusual features, it is probably permissible to regard as the keynote of the design the employ- ment of rigid transverse " rings " or frames. In previous booms used so extensively in R.lOl could not well be joined by riveting, even had it been desired to do so. In view of the rSOt EXTENSION (InchaQ EXTENSION (Irvcnee) Fig. 3. On left, stress-strain diagram of bracing cable, and on right, stress-strain diagram of stainless steel strip. 1020/
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