Experimental validation of inertial twist concept for rotor blade application

The present study performs a set of static tests to demonstrate a novel passive morphing concept. The concept introduces a bend–twist coupled composite spar to rotor blades, allowing for twist morphing to be achieved by imposing a lagwise bending moment using centrifugal forces produced by a movable mass at the blade tip. First, three composite spars are fabricated using a symmetric layup configuration with varied ply orientations. A set of static tests are designed to replicate the effect of the centrifugal forces during rotation, where the detailed distribution of twist, deflection and strain are measured on each spar with varied loading conditions. The experimental results suggest that the blade twist can be well controlled by the position of the tip mass and rotational speed. It was also found the distribution of the twist is linear when the spar deflection is small, whereas a quadratic twist distribution was observed for a large tip deflection due to the induced lateral restoring forces. Furthermore, the influence of the ply angle upon the coupled twist is demonstrated from the experimental and numerical results.