Weight Saving on Composite Stiffened Panels by New Design Philosophy

The common design approach applied by the civil aircraft manufacturers to satisfy the current certification requirements of composite structure (EASA AMC 20-29), is based on the application of a very conservative design philosophy that leads to oversized structures. A new design methodology is under evaluation based on the incorporation of SHM (structural health monitoring) systems into composite structures aiming at supporting a new design philosophy exploiting the full potential of composite materials. This work proposes the preliminary design of two aircraft wing box composite stiffened panels: one at the wing root and the other one at the wing tip. These panels have been designed according to the current conservative industrial design approach. Then they have been re-designed releasing some of the conservative design criteria, because they were considered resolved by SHM systems: no BVID knockdown factor, no notch material design allowables (only bonded joints and bonded repair are considered) have been applied and post-buckling regime between limit and ultimate load has been allowed. The new design has shown the greatest weight reduction achievable, the design parameters and panel subparts to which the panel weight is more sensitive. This work aims at providing useful indications on the weight saving expected by applying a new design philosophy based on the information coming from a reliable SHM system and which parameters needs to be monitored and where.