Fig. 1 shows the internal structure of the wing of an all-aluminum alloy aircraft. It consists of a front, middle and rear spar with spanwise stringers. You may assume the leading edge cell ahead of the front spar and the structure behind the rear spar are ineffective in carrying stresses.

Figs. 2 and 3 show scaled drawings of the wing, viewed from the top and the cross-section at the wing root, respectively. Fig. 4 provides information on the dimensions of the flanges or stringers, which are riveted to the skin and spars. The skin is 1.25 mm thick throughout.

A vertical load P is applied to the wing at the mid-spar, indicated by the red arrow in Figs. 1 and 2.

Determine the maximum bending stress and shear stress at the wing root. State all assumptions and provide sample calculations.