Applied aeronautics; the airplane - Beeldbibliotheek

:ALIGNMENT 61In general the procedni'e in aligning a fuselage will lie about as follows:A horizontal reference plane is nsnally specified by the makers inconnection with the fuselage. Sometiuies the top longerons are takenas this reference plane, in which case they are to be aligned horizontally,laterally, and longitudinally from a specified station to the tail post.Sometimes horizontal lines are drawn on the vertical fuselage struts, andthe fuselage is so aligned that these lines all fall in the same horizontalplane.Alignment of LongeronsIn the first case, after the fuselage has been placed in a flying position,the top longerons are aligned for straightness, using a straight edgeand a spirit level to aid in finally placing them laterally and longitudinallyin a liorizontal plane.The longerons are next aligned symmetrically with respect to theimaginai'y vertical plane of symmetry through the fore-and-aft axis ofthe fuselage. There are two general methods of doing this, as followsFirst Method—The center points are mai'ked on all horizontalfuselage struts. A small, stout cord is stretched from the center of thefuselage nose to the tail post and the horizontal bracing wires adjusteduntil the centers of the horizontal struts fall beneath this line. A smallsurveyor's plumb bob is held at different points so that the suspendingcord just touches the fore-and-aft aligning cord. The centers of thebottom horizontal struts should fall directly below the bob.Second Method—A plumb line is dropped from the center of thepropeller and from the tail post and a string is stretched on the groundor floor between these two points. Plumb bobs dropped from the centersof the horizontal struts must point to this line.The whole fuselage alignment is checked to make sure that it agreeswith the specifications. If the airplane has a nou-liftiug tail, it wouldbe advisable as the next step to support the fuselage in such a way thatthe rear part (about two-thirds of the total fuselage length) remains unsupported,and then re-check tlie fuselage alignment once more.All turnbuckles should then be securely locked and the fuselagecarefully inspected.Horizontal and VerticalStabilizersThe vertical stabilizer is examined to see that tlie bolts holding it inplace are properly drilled and cotter-pinned, also to see that it is setparallel or dead on to the direction of motion. It is trued up verticallyby the turnbuckles on the tie wires or brace wires connected to it. Theseturnbuckles are then properly safetied.The horizontal stabilizer usually is braced with tie wires fitted withturnbuckles. By means of these its trailing edge should be made straightand at right angles to the horizontal center line of the fuselage. Allbolts fastening the horizontal stabilizer to the fuselage should be inspectedto make sure they are properly drilled and cotter-pinned. Allturnbuckles should be safetied, as shown iu Fig. 41.