Alignment of Machine in Side Elevation.
Considering the side elevation, [Fig. 123], alignment here is concerned with the incidence of the main planes, the distance forward of the top plane from the lower plane or stagger, and the level of the engine bearers in relation to the top longerons of the fuselage.
Fig. 122.—Showing use of dihedral board and spirit-level.
Fig. 123.—Checking of main-plane incidence and stagger.
Fig. 124.—Template for checking incidence.
The fuselage should be levelled longitudinally by placing the level on the engine bearers, assuming the engine is not in place. When the bearers are level, the top longeron should also be level, in any case the incidence of the plane should only be adjusted in relation to the engine bearers. To check the stagger, a plumb line should be dropped from the leading edge of the centre plane, and adjustments made with the incidence wires from the fuselage to the centre-plane struts, until the required distance forward from the leading edge of the lower plane is obtained. The incidence can be tested by a straightedge placed under the plane and a clinometer, as in [Fig. 123], and another device sometimes used is shown by [Fig. 124]. This is made of dry wood, the lengths of the legs to the tops of the spars being obtained from a drawing of the wing section, and its incidence.