Effect of ribs and stringer spacings on the weight of aircraft composite structures

Low cost and less weight are the two primary objectives of any Aircraft structure. Efficient design of Aircraft components is therefore required to reduce cost and weight. For components with compressive loading, ribs and stringer spacing and stringer cross-section play a major role for weight efficient design. The main objective of the present work is aimed at establishing optimum stringer and rib spacing and stringer cross-section for minimum weight of buckling design driven components using FEA. The problem is formulated with flat ‘skin-stringer’ and ‘skin-stringer- rib’ panels with different stringer cross sections viz. blade, hat, I and J. Parametric studies are executed with different stringer spacings, rib spacings and stringer cross sections to study the effect of these parameters on the weight of the structure using Composite (T800class+epoxy system) material through linear buckling analysis of the FE model. Simply supported boundary conditions are used on all four edges of the plate with compressive loading. The software tools used are Hypermesh as pre and post processor and Radioss as solver. Initially for all the stringer cross sections considered, stringer spacing is varied from 600mm to 50mm. It is found that the spacing below 120mm is stabilizing the weight. Too small a spacing will increase the number of stringers with issues in fabrication without much benefit in terms of weight. With this view point, two stringer spacing configurations viz. 150mm and 120mm are considered for further study on the rib spacing for each of the stringer cross sections stated earlier. Optimum stringer spacing, rib spacing and stringer cross sections are established quantitatively