Aeroelastic Design Optimization of a Two-Spar Flexible Wind-Tunnel Model

Aeroelastic wind-tunnel models are usually designed to represent the aeroelastic behavior of full-scale structures. The behavior of the model is then related to that of the full-scale structure by certain scaling rules. The scaling procedure is simple, although a difficult and highly constrained model design problem often results. This is not a concern in the present case, where the requirements are specified for the wind-tunnel model itself. In this paper, the feasibility of one possible concept for the model structural design is investigated by solving an optimization problem in which the structural weight is minimized subject to the aeroelastic constraints. The optimization formulation of minimizing structural weight was successfully applied to the present aeroelastic design problem, and a feasible design was obtained using numerical optimization. However, the design process was not without flaws. Whereas the low torsional stiffness of the two-spar design enabled a low flutter speed and frequency, the wing was also very prone to divergence. Taking wing sweep into account revealed that no significant improvement was to be expected for moderate sweep. Instead, the optimization resolved this obstacle by tapering the front spar only, which increased the divergence speed through bending/torsion coupling. (CSA)