Effect of compressive force on strut-braced wing response

Our investigations of a strut-braced wing aircraft, show that at high positive load factors, a large tensile force in the strut leads to a considerable compressive axial force in the inner wing, resulting in a reduced bending stiffness and even buckling of the wing. Studying the influence of this compressive force on the structural response of the strut-braced wing is thus of paramount importance. To perform such a study in a Multidisciplinary Design Optimization (MDO) environment requires an approach that is both accurate and computationally efficient. To that end, we have developed a non-prismatic beam finite element that takes into account the effect of compressive forces on the aeroelastic response of the inner wing. Both the elastic and the geometric stiffness matrices along with the mass matrix are derived. The buckling load of the wing can be obtained using either an eigenvalue analysis or specifying a constraint on the wing deflection. The influence of the compressive force on the aerodynamic load distribution due to the wing flexibility is also studied, as is the sensitivity of the wing response to the strut position. As expected, the effect of compressive forces on the response can be reduced by placing the strut closer to the wing tip. The proposed procedure is validated by comparing results with those given by NASTRAN.