Hybrid Structure Solution for the A400M Wing Attachment Frames

The mainframes in the centre fuselage of the A400M have the vital function of introducing the wing loads into the fuselage. The lift distribution among the wing causing a torque and the frame curvature causing a bending moment, result in high running stress and limit loads in the frames below the rear wing attachment. These frames are made of 7000 series aluminium alloy and are primarily dimensioned by fatigue reasons, especially crack growth. Consequently, three different options for the A400M mainframes have been investigated. The first option is to reinforce the frames integrally. The second and third options are a titanium or GLARE® strap. In this paper, a trade off between the different options is made with respect to fatigue, maintenance, and weight targets.