Checking of Fuselage.
To check the fuselage for alignment it should be placed on a pair of trestles, one underneath the forward undercarriage strut fixing and the other under a vertical strut a short distance from the stern post. The body should then be levelled up longitudinally by a straightedge placed on two short straightedges of exactly similar widths, one being placed at the front and the other towards the tail. It should then be packed up on the trestles until the top longerons are dead level across. At this point, if the body is in correct alignment, the engine-bearers would be level both longitudinally and transversely, the incidence of the main spar attachments should be correct and the stern post perfectly vertical in all directions. Other tests should include the placing of a straightedge at the nose, and another placed at the points where struts occur, should, when sighted across the top edges, be “out of wind,” that is in agreement. A point which should be carefully levelled is that portion of the fuselage towards the stern post to which is attached the fixed tail plane. Any inaccuracy here will result in the tail being twisted in relation to the main planes. Each fitting or attachment should also be equidistant from the stern post, and the effect of variation here will be evidenced by the tail plane being out of square with the centre line of the fuselage. Where the type of machine is such that the engine is supported on bearers of wood, it is usual to drill the holes for the accommodation of the holding-down bolts to jig before the bearer is built in the structure. In this case care should be taken to ensure that the corresponding bolt holes in each bearer are square with the centre line. Any deviation will result in the axis of the engine forming an angle with the centre line.