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Aviation History
1918
1918 - 0569.PDF
MAY 23, X91S. THE, rORRER TRIPLANE. Continued from page 536.) ~l~-.'. >* -.. '"/ • "J-." r ' ;• WE now come to deal with the most interesting part Briefly speaking, the principle of the Fokker triplane of the Fokker triplane, the wing structure. It has spar is the following : There are two spars as in the already been pointed out that the machine is of the majority of other wings, but placed absurdly close " wireless " type, inasmuch as there are no lift wires together. Each spar is of the box type inasmuch or landing wires, the only wires employed in the the diagonal cross bracingwing structure being between the centre struts sloping upwards and out- wards from the body to the top wing. Aerodynami- cally this is advantageous from the point of view of low resistance, but structurally it is open to criticism on the score that it is difficult to provide adequate strength in such a structure, and that the only possibility of doing so is to employ a very deep wing section which will allow of using spars of such a section and depth that its moment of inertia is large without its area being excessive. This is precisely what the designer of the Fokker triplane has done. The wing section is one of far greater depth than one is accustomed to find on a modern fast machine, and inside this deep section he has built up a compo- site spar of somewhat unusual construction. Hitherto the vast majority of aeroplanes of any nationality have had wing spars which were either of the I or of the box section. In the Fokker spar we have neither strictly speaking, since it is certainly not an I section and only a box spar after making certain allowances. as it consists of spruce flanges top and bottom, with a web of three-ply on each side. The top and bottom faces of these two spars are then united by a sheet of three-ply covering, them up so as to form in effect two boxes within a box. In this manner there is no need—or at any rate the designer appears to be of that opinion—for any internal wing bracing, this being provided by the top and bottom three- ply covering. In Fig. 11 are shown some of the constructional details of the Fokker wings. The sketch at the top of the illustration shows the upper starboard wing in general arrangement. The construction is similar in all wings as regards fundamental principles, and only differs in minor details where this is necessi- tated by local requirements. The outward appearance of the wing spar is shown in the top sketch, and also the manner of attaching the ribs, which are pre- vented from sliding along the spar by little tri- angular section blocks of wood tacked to the spars The sketch in the centre shows the construction of the spar, and one of the longitudinal partition. Ffg. 11 Some of the wing details of the Fokker triplane. 567
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