The Aeroplane Speaks. Fifth Edition

If a mistake is made and the measurement taken along the wrong line, it may result in a difference of perhaps 1/4 inch or more to the stagger, with the certain result that the aeroplane will, in flight, be nose-heavy or tail-heavy. After the adjustments of the angles of incidence, dihedral, and stagger have been secured, it is as well to confirm all of them, as, in making the last adjustment, the first one may have been spoiled. OVER-ALL ADJUSTMENTS.--The following over-all check measurements should now be taken. The straight lines AC and BC should be equal to within 1/8 inch. The point C is the centre of the propeller, or, in the case of a "pusher" aeroplane, the centre of the nacelle. The points A and B are marked on the main spar, and must in each case be the same distance from the butt of the spar. The rigger should not attempt to make A and B merely the sockets of the outer struts, as they may not have been placed quite accurately by the manufacturer. The lines AC and BC must be taken from both top and bottom spars--two measurements on each side of the aeroplane. The two measurements FD and FE should be equal to within 1/8 inch. F is the centre of the fuselage or rudder-post. D and E are points marked on both top and bottom rear spars, and each must be the same fixed distance from the butt of the spar. Two measurements on each side of the aeroplane.