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Aviation History
1918
1918 - 1312.PDF
NOVEMBER 21, 1918 og ^ FROM A RIGGER'S NOTE-BOOK. By •< PLUMB-LINE." [From the amount of correspondence that reaches us it is quite evident that the subject of rigging has been badly neglected in aero- nautical literature, and that, in consequence, the man mho wishes to post himself on this subject—in so far as is possible by book study—finds that very little has been written on the subject. Some of the text-books published contain chapters dealing with rigging, and then there is the excellent little booklet issued by the Avro firm dealing with the erection and rigging of the Avro biplanes, but beyond that there is Httle of value to the student who wishes to become familiar with the rigger's art. The reason for this scarcity is, perhaps, not far to seek, for rigging is eminently a practical man's task, and can, it goes without saying, only be mastered after long practical experience. There are, however, fundamental principles governing the procedure, and these, at any rate, may be indicate^, by written instructions. This is precisely what " Plumb-line " has done in the present brief notes, which are, as a matter of facCtaken from the note-book of a practical rigger, and which will, we feel sure, be found useful by many of our readers. We apologise for having picked on the notes dealing with such an ancient machine as the B.E.zc, but to publish methods dealing with a modern machine might convey information likely to be of use to the enemy, which, in these days, one must avoid at all costs. We trust, however, that it will be found that, generally speaking, much of what is said regarding the B.E.zc will apply with no or with only slight modification to other types of two- seater tractors. At any rate sufficient will have been indicated of the general procedure to form a basis on which to determine the best way to " go about it " also in the case of other machines differing in many details from the B.E.zc.—ED.] Rigging a B.E. 2c Trueing up the Fuselage. FIRST place the fuselage on trestles and start by trammelling the inner cross-bracing wires, tightening them up to a fair tension and making sure that the diagonal distances are equal in each pair. The next step is to fit on the rudder post and to hang a plumb-line from the top of it as shown in Fig. 1. Then bisect all side struts in fuselage except the steel strut aft of the pilot's seat, which should be marked off J in. above its centre. Trammel the side bracing wires of the first two bays, and when this has been done clamp a piece of wood laterally through the fuselage on the front struts in such a position that its upper edge is level with the centres previously marked on the struts. Similarly a piece is clamped on the rear struts, projecting about six inches on each side. A piece of line is then stretched tightly between front and rear transverse pieces and secured in place. If the line is only just allowed to clear the side struts it will form a convenient datum line for trueing up the side bracing. The side bracing is now adjusted, starting in front and working towards the stern, until the under side of the line is level with the centres marked on the side struts. An exception is, as already mentioned, the steel strut .which should intersect the line £ in. above its centre. Both sides must be equally tensioned, and to ascertain that this is being done the plumb-line must be watched constantly. It must hang perfectly true with the rudder post. This operation is somewhat difficult at first, and requires a good deal of experience. The bracing wires must not be too slack, or the machine will be soft and flabby. Neither must they be too taut, as this puts unnecessary strain on struts and^ longerons. The tension should be just sufficient to keep the** fuselage rigid. Anything more than this spoils the rigging by putting various parts into undue compression, by pulling the metal fittings into the wood, and will ultimately distort the whole machine. Only experience will teach the right tension to employ and the knack of making all wires of equal tension. When all is trued up lock all wires by tighten- ing the lock nuts, taking care not to alter th3 adjustment previously obtained. Flying Position Having trued up the fuselage, the next job is to put rt*up in flying position on trestles. The trestles should be a sufficient height to ensure that when the chassis is put into place it will just clear the ground. Place a spirit level on the forward portion of the bottom longeron and pack up the stern securely until the spirit level shows perfectly true. This gives the longitudinal level. To get the lateral level place a parallel straightedge across the engine bearer tubes, and on this straightedge place the spirit level. Pack up the fuselage on the trestles until it is quite level. This levelling-up is very important, and the greatest care should •>* taken to see that it is correct, as the adjustments of wings, undercarriage, tail plane and engine depend upon its correct adjustment. Now go over the fuselage again and check for truth. Centre Section and Undercarriage Erect the centre section on its struts and temporarily connect all wires. Now trammel the front and rear cross bracing wires, adjusting them to a fair tension. Drop plumb- lines on both sides of machine from centres of front spar plates 310
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