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Aviation History
1918
1918 - 1160.PDF
OCTOBER 17, 1918. THE FORKER BIPLANE, TYPE D VII. (Concluded from page 1144.) As already mentioned the wings of the Fokker biplane formone of the most interesting features of the design, both aerodynamically and structurally. In Fig. 11 are shownfour typical sections, taken at various points in the planes. The top section in the illustration is taken in the centresection of the top plane. Underneath this is a section taken on the top plane rib occurring a short distance inside theattachment of the inter-plane struts. These two sections give a good idea of the manner in which the planes of theFokker biplane taper in camber towards the tips. It will be seen that both upper and lower surfaces of the section areflattened out towards the tip. The other two sections shown in Fig. 11 represent the lower plane rib at the root and inside together and to the web by horizontal tacks driven throughand riveted over. The wing spars are of the box type of construction, as indi-cated in Fig. 12, which shows the sections of all four spars in the centre, i.e., where the maximum dimensions are found. Theflanges, it will be noticed, are not solid, but are built up of two laminations each. The top flanges of all four spars areso shaped as to form an approximately rectangular space between them and the bottom flanges. At the points ofattachment of the spars, such as to body or to inter-plane struts, this space is filled with a distance-piece in the form ofa piece of wood. The distance-piece does not, however, touch the flanges direct, a piece of wood tapering towards TOP PLANE SECTION IN CENTRE. we "— 130 TOP PLANE SECTION INSIOC STRUT ATTACHMENT . 150 ISO — . 150 • 150- — - - 150 • —- LOWER PLANE SECTION, AT SIDE FUSELAGE 1200 LOWER PLANE SECTION, INSIDE. ATTACHMENT OF /NTER-PLANE STRUTS Fig. 11.—Fouritypical sections of the wings of the Fokker biplane. the attachment of the inter-plane struts respectively. Here,it will be seen, there is no flattening out of the bottom camber, in fact it appears that the maximum bottom camber ofthe thinner section is glightly greater than that of the section at the root... In both upper and lower plane sections it willbe observed that the distance from centre line of front spar to leading edge diminishes slightly as the tip is approached.This accounts for the sweep back referred to in a previous instalment of this article.j». Constructionally the ribs are built up of solid webs of thin three-ply wood. The flanges of the ribs are attached in asomewhat unusual manner to the webs. Instead of having the flanges in one piece and grooved for the web, the flangesin the Fokker biplane are in two halves, the three-ply web passing between the two halves of the flanges and extendingthe full thickness of the section. The flanges are tacked the ends, which are forked, being interposed between thedistance-piece or packing block and the flanges. The object of this arrangement appears to be connected with shearstresses on the spars, which are disposed of gradually instead of suddenly in this manner. The rib flanges are made ofpine, and are connected by thin webs of three-ply, about 1.5 mm. thick, which are glued to the flanges. The tops andbottoms of the spars are afterwards covered with a strip of fabric, which extends over the sides of the spar to past theedge of the flanges, thus acting ••as a protection for the glued joints. The leading edge, as in the Fokker triplane, is in theform of very thin three-ply wood, which extends back to the front spar, where it finishes off in a serrated edge having itspoints tacked to the spar. This feature is shown in Fig. 13. This sketch also shows the vertical triangufar-section piecesof wood which reinforce the rib webs, as well as the manner G 2
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