On the Effect of Geometric Nonlinearities on Static Load Alleviation

This paper investigates the importance of nonlinear aeroelastic static analysis in the structural design of high aspect ratio wings. As an indicator of the importance of static nonlinearity, the root bending moment is used. A relatively accurate prediction of the bending moment of a flexible wing is important in early design stages, since it largely determines the wing box weight. A linear Timoshenko beam element in a corotational framework is used as a nonlinear structural model. For the aerodynamics, Weissinger’s method is used. The nonlinearly coupled structural and aerodynamical equations are solved using the Newton-Raphson method. The load distribution is obtained for the aircraft trimmed at a range of load factors. Results for root bending moment, trimmed angle-of-attack, and wing tip deformation are presented for a high aspect ratio composite wing of a high performance open class sail plane. It is shown that the root bending moment obtained using nonlinear analysis differs significantly from the results of a linear analysis at high load factors. The reasons for the difference are found to be (i) end shortening, (ii) stiffening of the wing, (iii) change in trimmed angle-of-attack, and (iv) load redistribution. Therefore, it is concluded that nonlinear static aeroelastic effects are significant for the structural design of flexible high aspect ratio wings and ought to be included in the preliminary design stage. I