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Aviation History
1921
1921 - 0214.PDF
MAJRCH 24, 1921 Photo. No. 1.—F boat, showing wrong method of holding moulds together. Photo. No. 2.—N4, showing web frames and longitudinals. such a committee was considered necessary for ships, a similar committee of naval architects should be appointed to deal with flying boat bulkheads. Before touching upon the detail of construction, I think a few words on the" laying ofi " would not be out of place here. To illustrate the importance of the loft work, I should like to point out that it was owing to the bad laying off that many flying boats at the sea stations required individual trolleys for themselves •which had to be specially shaped at the station to take one particular boat. If all these boats had been laid off by a naval architect who appreciates the fineness of the scrieve board lines, then the correct offsets supplied to each builder who would not have required to do any fairing in or out, and if the moulds had been properly held by ribands, all the boats would have been very close in shape. I am aware that many engineers and aircraft builders do not realise to what fine limits naval architects have to work when scrieving out the lines. I have often heard it stated that anything from J in. to J in. in or out did not matter, hence the reason for so many unfair boats. If a yacht-builder worked to these lines, I am afraid many of his racing yachts would be outclassed if she drew J in. more than her designed draft; and soon the builder would have to construct flying boats for the agents who consider that such fine lines are not necesary. Aircraft manufacturers who have not had any experience in power boat building will find it essential to lay a mould loft floor if they intend building flying boat hulls, and when the floor is properly laid and painted, fair lines will be much more easily scrieved. In the, first place, the sheer plan must be delineated on the floor, then the half breadth, and finally the body plan. When these have been scrieved and the thickness of plank removed, then the moulds for frames can be lifted direct, also the various moulds showing the shape of different parts of the hull, battens and templates giving precise information as to the sizes and disposition of the structural parts can then be lifted. These lines are very useful as they often dispense with the necessity of fitting a mock-up in the shops. When the moulds are made, the stocks have to be set to take same, and here many of the builders of flying boats placed these about one foot above the floor to find that when the boat was ready for riveting they had to lift the whole hull and raise the stocks to a convenient height to allow the men to work under. The moulds now set in place on the stocks have to be kept in position by ribands, each riband running the whole length of the boat; here again many builders erred by fastening each pair of moulds together by small battens, as will be seen in photograph No. 1, and then they wondered why the boat was not fair when she was planked up. A good example of this was seen in the F. 5 boats, where many metal fittings were made to a jig by one firm to obtain good production, but this object was defeated as many of the fittings did not coincide with their structural part, therefore the various builders had then to make their own fittings to suit their particular lines. The principal feature in many hulls is the skin; all the other structural parts are more or less subsidiary, their function being to support and stiffen it. The skin is stiffened by framework disposed transversely and longitudinally, and further the sides are united by beams to support same against collapse. The same total strengthening can be effected by heavy frames spaced at wide intervals or by numerous small frames spaced very closely, but these systems cannot, for practical reasons, be exceeded, as in the former, if the frames were widely spaced and proportionately heavy, they might preserve the form of the hull as a whole, but they would not give sufficient local stiffness to the skin in order that it would not buckle between the frames. If the latter was carried to excess the ultimate result would be equivalent to a mere thickening of the skin. If made sufficiently thick it would be self-supporting, but owing to the excessive thickness it would be too heavy and useless for flying boats. Before setting the scantlings of a hull, the most efficient disposition of material should be considered in conjunction with the duties the boat has to perform. The cost of con- struction should also be taken into account, and this is de- pendent to a certain extent on the quantity of material used and on the method of construction. If the hull is built of few and heavy parts, it would involve less skilled labour, therefore would be much cheaper, but the hull built of more numerous parts, smaller, but efficiently formed, and disposed Photo. No. 3—N4 Atalanta. Skeleton view showing longitudinal system. 214
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