Design of Flutter Characteristics of Composite Wings Using Frequency Constraint Optimization

This paper is concerned with designing an optimum composite flexible wing structure to enhance flutter speed by imposing modal frequency distribution constraints and comparing it with an optimum design obtained with the flutter velocity constraint. The composite wing is subjected to three flight conditions to satisfy stress constraints in addition to modal frequency distribution or flutter constraints. The multidisciplinary optimization system ASTROS was used for this study. This study indicates that flutter velocity of a wing structure can be enhanced with less increase in the weight of the structure by using frequency distribution constraints than flutter velocity constraint. In the case of a design with modal frequency constraints, the distribution of the ±45° and 90° fiber layers provided required stiffness distribution in order to produce an acceptable solution with less increase in weight than the design obtained with flutter velocity constraint. It is speculated that the required stiffness change in order to achieve necessary modal frequency separation can be achieved to prevent flutter by providing a system of "smart" actuating elements distributed within the internal substructure of a wing.