Truing of Main Planes.
The planes or sections of a machine of the straight-wing type, as distinct from a machine possessing arrow-shaped or retreating wings, should, when erected on the fuselage, form a straight line from tip to tip. This feature is dependent upon (1) the trueness of the planes, and (2) the alignment of the attachments on the fuselage, the latter being considered under the fuselage heading. To ensure that the plane is quite square, it should be checked previous to covering by diagonal measurements on the wing spars, these being taken from accurate set positions such as are provided by the wing-root attachments and the interplane strut fittings. Should a difference in the diagonals exist, this can easily be rectified by a slight adjustment of the turnbuckles incorporated in the internal plane wiring. As the ribs of the plane are built up beforehand, and checked for correct contour by pattern, little variation should occur in the camber. A point where differences may occur is between the front spar and the leading edge, as the nose formers are generally inserted during the assembling of the plane. For the detection of faults in this direction the template illustrated by [Fig. 34] in Chapter IV. is of great utility.