Design optimization framework for tiltrotor composite wings considering whirl flutter stability

Abstract

This paper constructs the design optimization framework for the composite wing of a tiltrotor aircraft based on the Korea Aerospace Research Institute (KARI) Smart Unmanned Aerial Vehicle (SUAV) TRS4 model. The present optimal design attempts to find the cross-section layout that minimizes the structural weight of a composite wing, while satisfying a series of design constraints. The framework consists of various analysis and design tools that include a 2-D beam cross-section analysis, a whirl flutter analysis, and a 3-D strain/stress analysis under the worst wing-loading case. The variation of wing sectional properties of tiltrotor aircrafts in the course of design optimization greatly affects the whirl flutter stability and shows considerable influence on the structural integrity of the wing. In the design framework, the whirl flutter stability is analysed by the nonlinear flexible multibody analysis code DYMORE and the structural integrity is investigated using a MATLAB-based 3-D strain analysis module along with the previous load analysis result. The MATLAB is used to conduct the optimization with a gradient-based optimizer and integrate all of the design and analysis tools. The nonlinear constraints associated with the aeroelastic stability and the structural integrity are also considered. For optimal design examples using the developed framework, a simplified cross-section model based on the KARI SUAV TRS4 composite wing is considered as an initial model. Design optimization examples are investigated to show the validity of the proposed framework and to illustrate the reduction of the structural weight of the composite wing. It is observed that weight reductions of wing structures by 26% and 40% are achieved, while maintaining the whirl flutter stability margins.