Finite Element Beam/Plate Model for Modal Analysis of Light Aircraft Structures

In the present work, the finite element method is adopted for modal analysis of a reduced model of light aircraft structures using Beam/Plate Model. The Aircraft structure is modeled by spatial beam and plate elements, where the fuselage is a long beam of isotropic constant section, wing and empennage (horizontal and vertical tails) are modeled by trapezoidal plate elements. The Lagrange principle is adopted to determine the mass matrix and stiffness matrix of both beams and plates. After assembling the elements in global mass and global stiffness matrices of the whole structure (fuselage, wings and empennage) followed by the introduction of the boundary conditions, a numerical method to determine the natural frequencies and associated modes is used. The obtained results are compared with those obtained by SAP 2000 "Structural Software for Analysis and design".