The Effect of Aspect Ratio Variation on the Preliminary Aeroelastic Assessment of a Mid-Range Transport Aircraft

The wing aspect ratio (AR) is one of the main planform parameters to estimate the aerodynamic efficiency of a wing. A higher AR relates to a reduction in induced drag and consequently to an improved fuel economy. Since wings on civil transport aircraft are complex geometrical components with kinks, varying sweep, twist and dihedral angles over the span, mostly equipped with a heavy engine, the simplified assumptions made within the analytical formulations for wings conceptual design might be untrustworthy for modern aircraft with high AR wings. This paper evaluates the impact of the aspect ratio on the aeroelastic design of a medium-range transport aircraft using physics-based simulation at preliminary design stage. The research is conducted using the DLR-F25 configuration, developed in the German Aviation Research Program (LuFo-Project VirEnfREI). It features a baseline aspect ratio of 15.6. Since the AR of a wing is the ratio of the square of its span divided by its wing area, the AR can be varied in different ways. Within this paper, three different approaches to alter the AR are analyzed. All concepts utilize the same approach in which the center portion of the wing is kept constant until the kink. In this way, the wing-fuselage mount and the engine-wing integration is unaffected. Moreover, the leading-edge sweep angle has been kept unchanged to have comparable performance of the resulting aircraft. The baseline twist distribution at the corresponding sections of the wing is kept unchanged for the variants resulting in different lift distributions throughout the variations. Compared to other publications on the field of AR variations, where an increase of AR leads to an over-proportional ascending of wing-box mass, two variation approaches investigated in this paper show a passive load alleviation effect for higher AR leading to an even lower wing mass compared to the baseline wing. This effect is evoked by the bell-shaped spanwise lift distribution. These two variation methods result in a reduction in taper ratio with growing AR, accompanied in a reduction in wing mass. The third variation, on the other hand, increases in mass with respect to the AR, as the taper ratio is kept constant.