Structural Design of an Instrumented Double-Swept Wind Tunnel Model

The design of a highly instrumented, double-swept CFRP wind tunnel model and its experimental setup are presented. A forced sinusoidal pitching motion is applied to the one-sided clamped helicopter rotor blade tip. Challenges of the structural design and the manufacturing process are addressed. A mold with inserts to check the leak-tightness of the pressure transducers and retain the half shells in the mold is presented. Insights in the finite element analysis (FEA) of the blade tip model are given. The strength analysis reveals peak stresses in the adhesive and the spar. The finite element model is validated with an experimental modal analysis. The experimental and numerical mode shapes and eigenfrequencies show an excellent agreement. The design goal of a very stiff lightweight model is met with the first eigenfrequency at 70 Hz. The results of the fluid-structure interaction simulation at Ma=0.4 show no significant differences for the global forces compared to the simulations with the rigid contour. However, the maximum tip deformation is up to 20 mm and a slight excitation of the first bending mode can be observed.