Design the measurements of the assembly

The effect of the deviations when the After Frame is positioned on the Hoist Mount and the Box Support is positioned on the After Frame cause a change in the position of the Box Support as regards the nominal one. Therefore, the axis of the engine of the winch arm, that is positioned at the centre of the hole of the Box Support, may deviate from the nominal position and this deviation may invalidate the right working of the engine. The evaluation of the deviation of the axis of the engine from the nominal position is the first measurement of the assembly. It has been evaluated on the plane of the coupling of the engine with the Box Support along the two axes of the Datum Reference Frame of the Box Support (see Fig. 11).

Design the measurements of the assembly

The effect of the deviations, when the After Frame is positioned on the Hoist Mount and the After Cowling is positioned on the After Frame, cause a change in the orientation of the After Cowling as regards the nominal one. The aerodynamic drag of the After Cowling depends by the angle of incidence the air rush on the Cowling itself. Therefore, the deviation in the orientation of the After Cowling may invalidate the right working of the winch arm. The evaluation of the deviation of the orientation of the After Cowling from the nominal is the second measurement of the assembly. It has been evaluated as the two translational motions of the centre of the ellipse along the two axis of the Datum Reference Frame of the After Cowling and the three rotations of the axis of the Cowling as regards the nominal position measured in the Datum Reference Frame of the After Cowling.

The same reasoning may be repeated for the Forward Cowling.

Design the measurements of the assembly

Fig. 12. Features and Datum Reference Frame of the After Cowling