The integral twist design incorporates active fiber composites within the composite spar of the rotor blade. The active fiber plies are oriented at +45 degrees and -45 degrees in both the upper and lower spar surfaces, running over most of the span. The anisotropic actuation of the active fiber composites induces shear stresses in the spar, resulting in a linear twist along the length of the spar.
A single cell, Rehfield beam model is being used to evaluate designs for the spar lay-up. The model predictions have been validated in a demonstration model blade. A 1/16th Froude scale blade was fabricated using fiberglass and foam, with a single active layer of piezoelectric fiber composites embedded beneath the upper and lower skins.