Influence of flexibility on the steady aeroelastic behavior of a swept wing in transonic flow

Abstract The development in the last decades generally shows that large aircraft wings have become more light and flexible, thus the investigation of the effects of elasticity is suggested. If for example the flexible wing is also backward swept, then the situation becomes even more complex — the kinematic coupling between bending and torsion leads to a structural washout effect. In order to investigate the influence of flexibility, in the project “Aerostabil” an aeroelastically scaled half-model was tested compared to its rigid equivalent. The flexible model was equipped with pressure transducers in three wing sections and accelerometers, while the rigid model had a reduced number of sensors. The experiments were performed in the adaptive test section of a transonic wind tunnel. Steady and unsteady pressure-, and force measurements were conducted for fixed and oscillating wings. Already Dietz et al. (2003) have reported about the special features of the wing models, their structural properties and preliminary results. The present paper is focused on the analysis of the global forces and pressure distributions for the range 0.5 ≤ M a ≤ 0.88. The angle of attack was varied from −4° to 4° and also the quasistatic aeroelastic derivatives for lift and moment were obtained. When the model is rigid in the transonic regime and at moderate angles of incidence the pressure distribution exhibits a single shock system, in contrast for the flexible wing there is a double shock system. For the flexible wing up to about M a = 0 . 82 the curves of global lift, moment and their derivatives are rather smooth and are remaining on nearly the same level. Beyond there are moderate deviations up to the end of the transonic regime. However examining the corresponding curves of the rigid wing the changes are drastic, particularly in the transonic range. Obviously the structural wash-out, particularly of the outer wing leads to an attenuation of the transonic effects.