Aeroplane construction

by Sydney Camm

Plan Alignment of Machine.

Fig. 125.—Showing points to check for correct alignment on plan.

In the plan view, [Fig. 125], the distances AB and AC must be equal, the same applying to CD and BD. With modern machines external drift wiring is obsolete, so that discrepancies in these measurements must be rectified by alterations in the wiring of the fuselage, as it is inaccuracy at some point in the latter component to which the trouble may be ascribed. It is at this point that one realizes the need for precision in the construction of the fuselage. In [Fig. 126] is shown a plan view in which the main plane is very obviously out of square with the centre line of the body, the amount is not likely to occur in actual practice, but it has been exaggerated in the drawing. The cause of this trouble can be traced to the short wing spars in the fuselage, to which the lower plane is attached, or in other cases to the fittings, to which the lower plane is anchored, being out of centre, possibly only an insignificant amount. The lengths of the fuselage wing spars are also possible causes of trouble. Assuming that the rear spar is the correct length, and the front spar is over the length, this would result, when the outer sections were attached, in the latter sloping backwards, which again emphasizes the need for accurate part production.

Fig. 126.

With regard to the tail plane, measurements taken from the extremities of the back spar to some fixed point forward on the fuselage, to the strut sockets on the planes, or to the rear wing spar anchorage, as in [Fig. 125], should be equal.

The primary consideration with regard to the rudder and fin is that, viewed from the rear, they should be perpendicular, which can be verified by a plumb-line dropped from the top of the rudder-post. In plan view the fixed fin should correspond with the centre line of the fuselage although there are exceptions to this rule, notably where the fin is set over, to neutralize propeller torque, and in this case the measurements given in the general drawings must be adhered to.