Applied aeronautics; the airplane - Beeldbibliotheek

54 APPLIED AERONAUTICSNearly all wood used in wing construction is spruce, with the exceptionof the nose covering which is made of birch or gum wood, theweb ribs, which are made of laminated wood, and small quantities of pineor other woods in the sidewalk and other unimportant places.The sidewalk is a boxed-in or wood-covered portion of the inner endof the lower wing. It furnishes a solid footing for the pilot or observerwhen entering or leaving the cockpit and for mechanics working aroundthe engine, guns, instruments, control mechanism, etc.Steel hinge pieces are bolted to the inner ends of the wing sparsand serve as a means of connecting the lower wings to the fuselage andthe upper wings to the center wing panel.Interplane struts are vertical or inclined wooden struts of streamlinesection used to transfer compression stresses from the lower wingsto the upper wings when the machine is in flight. These struts are usedin conjunction with diagonal stay wires which serve to transfer the loadtowards the center of the machine when in flight.The stay wires are divided into two general groups, those which takethe drift load or fore-and-aft stresses due to the forward motion of theairplane, and those which take the lift load or vertical load due to theweight of the machine itself and the vertical resistance when in theair. The lift wires are again divided into those which take the load whenthe machine is flying and those which take it when on the ground. Thewires which take the lift load when the nuichine is in the air are calledthe flying wires, and those which take the load when on the ground arecalled ground or landing wires.Drift and Anti-Drift WiresThe set of wires in the wings which carry the drift load when flyingarecalled the flying drift wires, or drift wires for short. There is noreversal of load in these wires when the machine is on the ground, butopposition wires are necessary to maintain structural symmetry. Theselatter are called the anti-drift wires.When the wing frames are covered it is of course impossible to inspectthe internal stay wires of the wings, hence every precaution mustbe taken to guard against corrosion. The wire used at this point is tincoated before assembling, the steel parts of the turnbuckles and otherfittings are copper plated and when completely assembled, all the metalparts are given a coat of enamel paint.All screws, tacks and brads areof brass or copper.Wings are covered with a closely woven fabric. At present unbleachedlinen seems to give the best satisfaction. Owing to its scarcity,ho^^ever, a satisfactory substitute is being sought for. A cloth made oflong fibre sea island cotton is used to some extent and makes a fairlysatisfactory substitute.Linen fabric weighs 3^ to 4f oz. per sq. yd. and has a strengthof GO to 100 lbs. per in. of width. Its strength is increased 25 to 30