Multidisciplinary optimization for high speed, high efficiency tiltrotors with wing extensions

In this paper, we study multi-objective optimization methodologies for tiltrotor aircraft with wing extensions. The objective is to maximize aircraft cruise performance while minimizing wing weight, subject to whirl flutter and wing loading constraints. A wing structural model for strength and wing weight predictions, an aerodynamic model for performance predictions, and an aeroelastic model for whirl flutter predictions are developed for the optimization. Parametric studies on whirl flutter speed, cruise efficiency (L/D), and wing weight are conducted, and the parameters include key variables such as wing thickness, extension span, and wing sweep. The parametric studies predict that thin wings (15% t/c) are softer in bending and torsion compared to thick wings (23% t/c), resulting in an lower stability boundary for the thin wing. The total drag, on the other hand, of tiltrotor having a thick wing is only 1% more than that of a tiltrotor with a thin wing. The parametric studies also predict that a 4.5 ft. extension on a 16.6 ft. wing (27% increase in span) can increase the aspect ratio by 48%, reducing the induced drag by 33%, and total drag by 10%. The parametric study is followed by the optimization study and the analysis shows that adding an extension span can increase L/D by 12% for only a weight penalty of (1.5%).