With the aim to validate the strength of one of the most critical areas of the utilitarian aircraft Stela M1, this work shows a structural analysis of the firewall with inner stepped reinforces “Doublers”, which it is subjected to maximum static loads from typical flight manoeuvres suggested by the standard FAR 23, specifically for assessing the interlaminar effects of the stepped reinforces. The piece, including the stepped reinforces, is made totally with laminated composite materials carbon fibre/epoxy and protected with a thin aluminium plate. It was simulated with a finite element model and validated with experimental data from a representative specimen subjected to the same operational conditions. From the results, it was observed, throughout the cross-section of the piece, that the first layers and the plate have a significant effect on the X and Y stresses, whereas the effect of the stepped reinforces at the layers near to the mid-plane were more evident for the XY shear stresses. Complementary, the highest Tsai-Wu index were located around the screw hole C and at the first carbon fibre layers and suggest a security factor of around 7, validating the piece. This study also shows that the stress concentrations around the stepped reinforces barely have a deleterious effect on the firewall. Moreover, the reinforces are suitable to significantly increase the structure strength and to keep the maximum stresses concentrated at the firewall reinforced areas.
