Aeroelastic tailoring using the spars and stringers planform geometry

The aeroelastic performance of a wing, including static aeroelastic shape, flutter/divergence speed and gust load response, has a significant influence on aircraft design. The tailoring of aeroelastic responses therefore offers potential weight savings. In this paper, the spars and stringers planform geometry (i.e. shape and root/tip chord wise location) on a representative wind tunnel model aircraft wing are used to modify the wing aeroelastic performance. Several optimisations are performed to illustrate the ability of the spars and stringers planform geometrical features to change the wing vibrational mode natural frequencies, deformation under a static tip load and aerodynamic load, gust response and aeroelastic instability speed. Changing the stringers planform geometry is shown to offer minor variation in the wing deformation and loads. Changing the spars planform geometry is shown to enable a reduction in root bending moment under static aerodynamic loading greater than 10%, a reduction in maximum root bending moment encounter during a worst case scenario gust event greater than 10% and a 25% increase in flutter speed. The improvements due to a change in the spar planform geometry are compared to the effect of changing the wing sweep angle. A framework to characterise Euler-Bernoulli beam properties on wings with geometric coupling is then developed and validated to relate the stiffness and bend/twist coupling parameter to the full 3D FE models.